This session aims to advance our knowledge on the role of root exudation across all terrestrial ecosystems. We invite contributions that study root exudation from a molecular to an ecosystem level. Among others, we especially welcome studies covering the following topics: novel methods in sampling and analyzing root exudation; deciphering how much carbon is exuded in diverse ecosystems from grasslands, agricultural systems to savannas or forests; environmental influences on root exudation amount and composition including nutrient and water availability or soil and air temperature; the role of exudates in mitigating biotic and abiotic stressors; the functional role of exudates in nutrient uptake; how do root exudates shape the soil microbiome; can exudates change soil physical properties; how stable are root exudates in the soil and how long do they persist in the soil environment; is there a tradeoff between root growth and root exudation; how do we model root exudation across spatial and temporal scales.
We encourage researchers across multiple disciplines and backgrounds to contribute to this session, including experimental manipulations, field observations and modelling from molecular to global scales. Collectively, insights from this session will help to improve our understanding of the role of root exudation in the global carbon cycle and their function in rhizosphere processes. This knowledge will help in improving predictions on soil carbon storage and plant responses to environmental stress which is crucial for developing effective strategies in sustainable land management and land conservation.
Orals: Fri, 8 May, 10:45–12:30 | Room 2.95
The input of soluble carbon from living plant roots (i.e., root exudation) into soil has received increasing attention over recent decades, as root exudates are recognized as key drivers of plant–soil–microbe interactions. However, obtaining ecologically meaningful root exudate samples remains challenging. In this presentation, I will highlight insights into often overlooked aspects of existing exudate sampling schemes, including the effects of sampling solution volume, sampling matrix, and microbial activity. Furthermore, I will introduce a new experimental scheme that integrates established approaches for root exudate collection with rhizosphere microbiota characterization into a single, unified protocol. Fine-tuning our exudate sampling techniques is essential for advancing our understanding of the identity, fate, and function of plant metabolites released into soil and their impact on (soil) ecosystem processes.
How to cite: Oburger, E., Oxtanorena-Ieregi, U., Santangeli, M., Spiridon, A., Schwalm, H., Browne, E., Brown, M., Brown, L., Roberts, D., Duffe, A., Morris, J., Hedely, P., Abbot, J., Thorpe, P., Brennan, F., Bulgarelli, D., George, T., and Escuerdo-Martinez, C.: Sampling Root Exudates – Mission Impossible II: Small Details Matter, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22130, https://doi.org/10.5194/egusphere-egu26-22130, 2026.
Glucose is frequently used as a surrogate for root exudates in priming studies because it plays a central role in plant metabolism. Glucose-induced priming can accelerate the decomposition of organic matter via co-metabolism, thereby enhancing the release of greenhouse gases such as CO₂, N2O, and CH₄. However, despite Glucose’s widespread use as a proxy, actual root exudates are far more complex and further include organic acids, phenolic compounds, and nitrogen-containing molecules. Many studies fail to capture this complexity, particularly functions related to mineral dissolution, nutrient acquisition, and microbial interactions.
We hypothesized that glucose, compared to plant-derived exudates, leads to disproportionately high soil respiration and methanogenesis, thereby overestimating carbon decomposition and associated biogeochemical processes. To test this hypothesis, we collected thawed permafrost mineral soil from Abisko, Sweden. Permafrost soils store nearly twice as much carbon as is currently present in the atmosphere, thus, they represent a critical component of the global carbon cycle. The soil was incubated in anoxic microcosms and amended with four different exudate mixtures at environmentally realistic concentrations: glucose; a more complex carbon mixture composed of sugars and organic acids without nitrogen; the same complex carbon mixture with nitrogen-containing glycine; and exudates derived from graminoid plants obtained from thawed permafrost soil in Abisko. Within days of amendment, plant-derived and nitrogen-containing exudates resulted in lower CO₂ emissions than glucose and the nitrogen-free mixture, highlighting a key role of nitrogen in diversifying microbial metabolism. The effects on CH₄ emissions were even more pronounced than those on CO₂: glucose and the nitrogen-free mixture produced significantly higher CH₄ emissions compared to plant-derived and nitrogen-containing exudates.
Together, our results suggest that artificial mixtures of sugars, organic acids, and nitrogen-containing compounds should be preferentially used in priming studies to better reflect the complexity of root exudation.
How to cite: Muehe, E. M., Mollenkopf, M., Keldenich, S., and Kappler, A.: Glucose as a surrogate for root exudates overestimates greenhouse gas emissions from anoxic soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8110, https://doi.org/10.5194/egusphere-egu26-8110, 2026.
Measuring root abundance, root exudation, and exudation chemistry requires destructive and cumbersome measurement protocols. Respiratory CO2 and O2 fluxes are simpler to measure and are related to these processes: 1) greater root abundance and exudation of labile compounds are expected to increase respiratory fluxes; 2) the apparent respiratory quotient (ARQ, the CO2/O2 fluxes ratio) is primarily derived from the nominal oxidation state of carbon (NOSC) of the respiratory substrate, with high expected ARQ in roots and rhizosphere (fed by exudates) and low ARQ in bulk soil. To test the control of root abundance and exudation on respiration fluxes, we conducted a pot experiment in a greenhouse with three crops (Brassica napus, Helianthus annuus and Panicum miliaceum). We measured CO2 and O2 fluxes from soil chambers and from jar incubations of excised roots and soil samples. Additionally, we measured root abundance and exudation rates and characterized exudate composition using untargeted direct-infusion Orbitrap mass spectrometry. Molecular formulas were assigned to derive NOSC and stoichiometric indices (H/C, O/C, N/C and P/C). We found that the species differed in their CO2 and O2 fluxes, reflecting their distinct root traits. Higher respiration fluxes were associated with greater root abundance and exudation rates, but a higher exudate N/C ratio was the strongest predictor. While the effect of species on ARQ was insignificant, small and consistent interspecific differences in ARQ were observed. Brassica napus exhibited comparatively high ARQ values, coinciding with exudates with high N/C ratio and NOSC, fast root respiration, and high root abundance. Overall, our results indicate promising links between root exudation and respiratory fluxes, with exudate N/C emerging as a significant factor in flux variability.
How to cite: Lengert, A., Lange, D. F., Gleixner, G., Zhang, Q., and Hilman, B.: Linking root abundance and exudation with soil CO2/O2 fluxes ratio in three crops, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7075, https://doi.org/10.5194/egusphere-egu26-7075, 2026.
Tree root exudates and rhizosphere microbe interactions are a key pathway influencing tree health in the forest. However, the chemical mechanisms mediating these belowground interactions, particularly under climate driven drought stress, remain poorly understood. Mediterranean forests experience recurrent seasonal drought, providing a natural system to examine how water limitation alters root derived carbon inputs and associated microbial responses. We conducted a two-year field experiment in a mixed Mediterranean forest comprising mature trees of Pinus halepensis, Quercus calliprinos, and Pistacia lentiscus. Across four seasons, we simultaneously quantified root exudation rates and metabolite composition and characterized soil and root associated microbiomes using 16S rRNA gene sequencing at species level resolution. This integrative approach allowed us to directly link drought-induced changes in root chemistry with microbial community structure and interaction patterns. Root exudation rates increased on average 2.7-fold during the dry compared to the wet season, reaching up to 21.7 μg C cm⁻² day⁻¹ across all three tree species. Metabolomic analyses identified 89 drought responsive compounds, dominated by amino acids (24), phenolics (22), carbohydrates (11), and terpenoids (8). While metabolite profiles varied strongly with both tree species and season, eight metabolites consistently responded to drought across all species, suggesting conserved metabolic responses to water stress. In contrast to the pronounced chemical shifts, rhizosphere microbial community composition remained largely stable across seasons, although it differed among host tree species. Despite this taxonomic stability, correlation analyses revealed multiple bacterial taxa that were positively or negatively associated with drought responsive metabolites. Notably, 19 actinobacterial species correlated with compounds such as the terpenoid glaucocalyxin A, deoxyribose, and a C5 sugar alcohol, highlighting diverse microbial strategies for exploiting drought altered root exudates. Together, our results demonstrate that seasonal drought reshapes belowground interactions primarily through changes in root exudate chemistry rather than large scale microbial turnover. We propose that drought-induced shifts in root derived metabolites act as finely tuned metabolic signals that selectively modulate microbial interactions while preserving the overall structural stability of the rhizosphere community in Mediterranean forests.
How to cite: Oppenheimer-Shaanan, Y., Obersteiner, S., Yalin, D., Sade, D., Zavaro, V., Reich, Z., and Klein, T.: Seasonal Drought Reshapes Root Exudate Chemistry and Microbial Associations in a Mixed Mediterranean Forests, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7727, https://doi.org/10.5194/egusphere-egu26-7727, 2026.
Forest ecosystems are particularly relevant for global root exudation rates as they cover about 31% of Earth’s land area and store ~861 Pg C as live biomass, dead wood, litter, and soils—making them one of the largest terrestrial carbon reservoirs. Root exudation represents a dynamic carbon flux pathway linking plant allocation to soil microbial activity, potentially accounting for 7–14% of global gross primary productivity. However, current global estimates often aggregate diverse biomes (forests, grasslands, croplands) or rely on seedling experiments, leaving the specific environmental and biological drivers of root exudation in established forest ecosystems poorly quantified. This study presents the first meta-analysis of in-situ root exudation rates focusing specifically on forest trees, aiming to evaluate how biotic and abiotic factors jointly influence belowground carbon flux. We conducted a meta-analysis to compile a curated database of in-situ root exudation measurements. To ensure ecological relevance, we excluded greenhouse and seedling experiments, restricting the analysis to established forest stands during the growing season (April–November). The final dataset includes 248 monthly observations from 33 studies across 76 tree species. Time-series observations allow for an in-depth analysis of seasonal root exudation patterns. These observations were integrated with global databases (GRooT, FungalRoot, WorldClim, Harmonized World Soil Database) to test drivers of root exudation rates including climatic variables, soil types, mycorrhizal type and Root Economic Spectrum (RES) traits. Preliminary results from 189 growing-season observations indicate that exudation rates were low in tree species associated with ectomycorrhizas (that were potentially forming a sheath around root tips and reducing exudates transferred into soil). Evergreens had greater exudation rates than deciduous species, but climate was purely linked to exudation. Furthermore, exudation rates were only weakly aligned with the main axes of the RES (e.g., specific root length and root tissue density), suggesting that exudation rates vary largely independently of morphological conservation-acquisition trade-offs. Furthermore, our analyses highlight a critical lack of data outside the growing season, particularly in winter and early spring. In conclusion, ectomycorrhizas are major C sinks, with little carbon from exudates reaching soil in colonised roots. Root traits are overall poor predictors of exudation and we postulate that root tips should be measured preferentially, as tips are the site of exudation in tree roots. This synthesis provides a more robust framework for understanding rhizosphere carbon dynamics, which is vital for improving the representation of root-soil processes in global carbon models.
How to cite: Aydogdu, A., Stokes, A., Rossi, L., Zhang, G., Trueba, S., Viennois, G., Mohamed, A., and Mao, Z.: Drivers of Tree Root Exudation in Forest Ecosystems: A Global Synthesis , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21404, https://doi.org/10.5194/egusphere-egu26-21404, 2026.
Micronutrient (MN) deficiencies, particularly iron (Fe), zinc (Zn), and copper (Cu), severely limit crop productivity and frequently coincide with regions of human micronutrient malnutrition ("hidden hunger"), a problem exacerbated by high‑pH, calcareous soils that restrict metal availability through the formation of insoluble metal pools. In these challenging environments, grasses (Poaceae) rely on root exudates, most notably phytosiderophores (PS), to mobilize micronutrients such as Fe through the release of specialized ligands that promote metal dissolution and uptake.
However, the ecological complexity surrounding PS-driven micronutrient acquisition remains largely understudied, primarily due to limited availability of these compounds. Our previous work showed that grass species exhibit distinct PS exudation patterns, varying in both quantity and quality, with exudation decreasing in the order Fe > Zn > Cu deficiency. Building on these findings, we conducted detailed PS–soil interaction studies using naturally Zn- and Fe-deficient soils to examine whether specific PS types differ in their micronutrient mobilizing efficiency. Our results show that metal mobilization is soil-specific and largely dependent on the inherent availability of the metals themselves, following trends similar to the DTPA-extractable metal pool, i.e., the more available the metal, the more effectively it can be mobilized by PS. While soil properties primarily dictated overall mobilization patterns, differences among PS themselves also emerged. Despite their structural similarities, the eight PS displayed distinct mobilization efficiencies that changed with time and PS concentration.
Mobilization occurred rapidly within the first few hours but plateaued after approximately six hours, consistent with rapid PS depletion in an active rhizosphere. Notably, only a small fraction of the applied PS contributed to metal mobilization; most remained inaccessible, likely due to strong sorption to soil particles even under sterile conditions. When real root exudates were supplied together with PS, mobilization increased synergistically, enhancing the release of several metals, including Zn and Mn, beyond the capacity of PS alone.
These results highlight that MN acquisition is not a one-dimensional process but relies on multiple, complex rhizosphere interactions. Understanding these dynamics brings us closer to optimizing crop breeding and management practices that harness root exudation and soil potential for improved micronutrient uptake.
How to cite: Spiridon, A., Causon, T., Hann, S., Kratena, N., Stanetty, C., and Oburger, E.: Wanted: Micronutrients – Exploring the efficiency of phytosiderophores and grass root exudates in mobilizing metals in soils. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9461, https://doi.org/10.5194/egusphere-egu26-9461, 2026.
The rhizosphere is a hotspot of biological activity, representing a zone of interaction between plants and microbial communities. Root exudates are a key factor shaping this unique environment by significantly influencing belowground processes, such as carbon (C) and nutrient cycling. Despite this importance, main drivers of root exudation are still unknown. In this study, we investigated how the composition of root exudation in temperate forests relates to nitrogen (N) concentrations and δ13C isotopic signatures in different tree tissues. Enriched δ13C values can hereby serve as an indicator for drought stress.
Root exudates were sampled at four temperate forest sites in Germany in sycamore maple (Acer pseudoplatanus), European beech (Fagus sylvatica) and Norway spruce (Picea abies). We used an in-situ approach, where cleaned roots were incubated in cuvettes with glass beads and a diluted nutrient solution for 24h. Compound-specific root exudation rates from four sampling events in late spring and late summer of two consecutive years (2023 & 2024) were analysed by gas chromatography-mass spectrometry.
Tree tissues were sampled in late summer 2023 and in late spring 2024, including roots, branch bark, branch wood and leaves from the sun-lit tree crowns and analysed by isotope ratio mass spectrometry to determine C and N concentrations and the isotopic signature δ13C.
In maple, a higher N status in leaves, bark and wood went along with an elevated exudation of hydrocarbons, including fatty acids and sugars. In contrast, the exudation of N-containing compounds, namely amino acids, was reduced under higher tree N concentrations. Therefore, the exudation of hydrocarbons could be a mechanism to scavenge for N, while the loss of N through exudation is reduced. A reduced water availability indicated by more enriched δ13C values led to compound-specific reactions in the exudates of maple. While the exudation of hydrocarbons was reduced under more enriched δ13C values in leaves, bark and wood, N-containing compounds were exuded in higher rates, even though not significantly higher. This suggests a targeted exudation of specific compounds under reduced water availability.
In spruce, we observed significant tissue dependent correlations between tree N status and exudation. In contrast to maple, higher tree N concentrations in needles, bark and roots generally went along with reduced exudation. Also contrasting maple, spruce tended to decrease N exudation and increase the exudation of other compounds, when tree tissues were more enriched in 13C. This effect was especially strong and significant for roots, indicating an elevated investment into roots and root exudates under drier conditions.
In beech, no significant correlations between N concentration or δ13C and exudation could be observed.
Our results indicate that the interaction of N and water status in tree tissues with root exudation strongly depends on the tree species, which could partially explain contrasting results reported in literature. While differing abiotic conditions are often held responsible for inconsistencies, our results suggest species identity as an important factor.
How to cite: Wannenmacher, M., Haberstroh, S., Kreuzwieser, J., and Werner, C.: Relationship of compound-specific root exudation with nitrogen and water status of temperate tree species, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6765, https://doi.org/10.5194/egusphere-egu26-6765, 2026.
Differences in root exudate and litter quality are known to regulate microbial activity and net soil carbon (C) accumulation. For example, legume root exudates are known to have high amino acid content, and their root litters are characterized by low lignin and high C/N ratio. Therefore, root-derived C from legumes can potentially enhance microbial activity and turnover rates, and facilitate microbial necromass production – the precursor for mineral-associated organic matter (MAOM) in soils.
Stable isotope probing has been widely applied to trace C fluxes into microbial respiration and soil C pools such as particulate organic matter (POM) and MAOM. However, most existing studies rely on artificial substrates or single compounds as proxies for root exudates, thereby neglecting the chemical complexity of root exudates and potential interactions between root exudates and litters on microbial C processing.
Here, we address this gap by isolating ¹³C-labelled species-specific root exudates and litter derived from three grassland species (L. perenne, P. lanceolata, and T.pratense) with contrasting root traits for an incubation experiment. Matured plants were pulse-labelled with ¹³CO₂ for three days, after which ¹³C-labelled root exudates and litter were collected and amended to bare soil either individually or in combined in a 75-day incubation experiment. We expect high quality root exudate and litter from T.pratense to induce higher microbial respiration and priming effect, and overtime, elevated necromass production and C stabilization in MAOM.
Root exudates and litter derived from P. lanceolata, and T. pratense induced higher cumulative priming effects than those from L. perenne. Thereafter, microbial respiration rates declined over time. By the end of the incubation, the highest microbial turnover rate was observed in the T. pratense litter treatment, suggesting rapid microbial mortality and substantial necromass production over the incubation period.
Consistent with this pattern, mean residence times of P. lanceolata, and T. pratense root exudates in MAOM (1973 and 1754 yrs) were higher than those of L. perenne root exudates (493 yrs). In addition, T. pratense root litter exhibited the longest mean residence time in POM (149 yrs). Together, these results suggest that legumes can increase soil C accumulation through the positive impacts of their root exudate and litter on microbial turnover.
How to cite: Shi, C., Morriën, E., Jansen, B., Wanek, W., and de Vries, F.: Root exudate and litter impacts on microbial turnover and soil carbon stabilization are species specific, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21438, https://doi.org/10.5194/egusphere-egu26-21438, 2026.
Plant roots release a great diversity of root exudates into soil, creating hotspots of biochemical activity. Species-level differences in root exudate chemistry may modulate these dynamics, with consequences for soil biogeochemical cycles at larger spatial scales. Therefore, the aim of this research was to investigate the link between species variation in root exudates and soil microbial respiration in temperate grasslands. We hypothesized that sugars would stimulate and phenolics would suppress soil microbial respiration across species. Second, we hypothesized that species variation in sugars and phenolics would be oppositely associated with root traits indicating fast vs. slow growth and their degree of collaboration with mycorrhizal fungi, allowing for these results to be generalized across grassland species.
To test these hypotheses, we conducted a greenhouse study with 53 plant species (grasses, forbs, legumes) common to managed and semi-natural grasslands on sandy soil in the Netherlands. We collected root exudates during peak vegetative growth using a hybrid soil-hydroponic collection method. Root exudates were analysed for total organic carbon, phenolic and sugar content, as well as individual metabolites using untargeted LC-MS analyses. Collected root exudates were freeze-dried and applied at the same carbon concentration to soil using an incubation setup in order to test their effects on soil microbial respiration. Root morphological traits and mycorrhizal colonization of plant species were also measured and aboveground growth was monitored during the study. Preliminary results suggest that species variation in root exudate chemical classes does not relate to core root traits representing nutrient use and acquisition strategies. Results on more detailed metabolite analysis and species-specific root exudate effects on soil microbial respiration will be presented at the conference.
How to cite: Zwetsloot, M. J., Zetterlind, B., Hoffland, E., Mommer, L., and Tamminga, D.: A plant’s deepest secret: translating root exudate profiles into their effects on soil microbial respiration in grasslands , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7131, https://doi.org/10.5194/egusphere-egu26-7131, 2026.
Root exudation is a substantial carbon (C) flux from plants to soils and a key pathway by which vegetation influences soil respiration. Especially in phosphorus (P) limited ecosystems, enhanced nutrient availability as a consequence of root exudation links plant C allocation to microbial activity and soil respiration. However, we have limited knowledge of how root exudation and soil microbial activity modulate soil respiration when P limitation is alleviated through fertilization. Previous studies have showed that the response of soil respiration to P fertilization is ambiguous and dependent on the ecosystem but the underlying causes often remain unidentified.
Here we used the microbial-explicit terrestrial biosphere model QUINCY-JSM, including an implementation of dynamic root exudation based on plant carbon surplus and nutrient deficiency, to investigate the role of plant-soil interactions in the response of soil respiration to P fertilization. The root exudation implementation was previously tuned and tested for the Eucalyptus Free Air Carbon Enrichment (EucFACE) experiment, where the role of increased root exudation under CO2 fertilization on soil organic matter cycling and soil respiration in a P-limited forest was evaluated. This experiment has now been fertilized with P, and here we take advantage of this modification to the experiment by simulating the EucFACE experiment under P fertilization. We investigate how microbial stoichiometry and P availability influenced simulated responses. In agreement with measurements, our model reproduced a decrease in soil respiration on P addition. Our simulations reveal root exudation as a key driver in this response: P fertilization alleviated plant P limitation, leading to a decrease in root exudation by up to 40 %. Consequently, the reduced C supply to the rhizosphere decreased microbial respiration up to 10 % and soil respiration up to 5 %. However, in simulations with high microbial P demand, microbes out-competed plants for the additionally available P and therefore suppressed the feedback to root exudation.
Our results highlight the role of root exudation in modulating soil respiration response to nutrient addition and the influence of soil microbial stoichiometry and baseline soil P availability. We make recommendations for further research by identifying critical variables for future modeling and observational studies.
How to cite: Schufft, K., Fleischer, K., Zhao, M., Medlyn, B. E., Yu, L., Rammig, A., and Zaehle, S.: Modeling the role of root exudation and plant-microbe interactions in the response of soil respiration to P fertilization, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12590, https://doi.org/10.5194/egusphere-egu26-12590, 2026.
Transitioning from monocultures to mixed-species plantations is a key strategy for enhancing soil organic carbon (SOC) sequestration. However, the specific mechanisms by which tree species interactions, particularly through root exudation and morphological traits, shape rhizosphere SOC stability remain poorly understood. This study investigated the effects of introducing broad-leaf species into coniferous plantations on rhizosphere SOC dynamics.
We examined a near-mature Pinus massoniana monoculture and two paired plantations interplanted with Erythrophleum fordii (a nitrogen-fixing species) and Castanopsis hystrix. We quantified root exudation rates, root morphological traits, microbial biomass carbon, and rhizosphere physicochemical properties to identify the controlling factors of SOC stability.
Our results revealed divergent stabilization pathways depending on the companion species. Interplanting with C. hystrix significantly stimulated the root exudation of P. massoniana. This increase in exudates was positively correlated with the mass proportion and carbon content of both large and small macro-aggregates, suggesting that exudate-mediated physical protection is the primary driver of SOC stability in this mixture. Conversely, interplanting with the N-fixing E. fordii did not significantly alter root exudation rates or their relationship with aggregation. Instead, SOC stability in the P. massoniana rhizosphere was primarily attributed to increased nitrogen availability.
Our findings highlight that root exudates play a conditional role in SOC stabilization, heavily dependent on the identity of neighbor species. We conclude that selecting appropriate companion species is critical for managing specific SOC sequestration pathways in mixed-species plantations.
How to cite: Xia, Q.: Divergent pathways of rhizosphere SOC stabilization in mixed-species plantations: The role of root exudates versus nitrogen availability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2909, https://doi.org/10.5194/egusphere-egu26-2909, 2026.
Plant roots exhibit coordinated suites of functional traits that reflect different strategies for nutrient acquisition, commonly described along the root economics space (RES). In phosphorus (P)-limited systems, plants may rely on contrasting pathways for P acquisition, including fine-root proliferation, root exudation, and mycorrhizal symbioses. However, how these strategies are coordinated across genotypes within a single tree genus remains poorly understood.
Here, we investigate root economic traits, mycorrhizal colonization, and root-associated metabolites in twelve eucalypt species grown under controlled low-P conditions. We quantify key root morphological traits (e.g. root diameter, specific root length), mycorrhizal (AM and ECM) colonization, extraradical hyphal development, and the composition of root exudates, with a particular focus on organic acids and phenolic compounds.
Preliminary analyses indicate pronounced interspecific variation in root traits and associated P-acquisition strategies across eucalypt species. Trait coordination patterns suggest potential trade-offs between root morphological investment, symbiotic associations, and metabolic pathways involved in P mobilization. In particular, variation in root diameter appears to be associated with shifts in the relative reliance on root-based versus mycorrhiza-mediated strategies for P acquisition, although the strength and consistency of these relationships are still being evaluated.
Overall, this study aims to provide a trait-based framework for understanding how woody plant species coordinate alternative P-acquisition pathways under nutrient limitation. By integrating root economics, symbiotic interactions, and root metabolic traits, our work contributes to a more mechanistic understanding of belowground resource foraging strategies in forest ecosystems.
How to cite: Zhang, Z., Ranathunge, K., Migliorini, D., Albornoz, F., and Lambers, H.: Beyond the Root: Linking Economics Space, Symbiosis and Exudation in Phosphorus-Stressed Eucalyptus Species, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4498, https://doi.org/10.5194/egusphere-egu26-4498, 2026.
It is estimated that about half of the cultivated soils are deficient in zinc (Zn), contributing substantially to human Zn deficiency. As cereals constitute a major component of the human diet, improving their Zn content by breeding is a crucial agricultural goal to mitigate human Zn deficiency. However, breeding nutrient-rich cereals requires the identification of the plant traits that most strongly contribute to efficient Zn acquisition under deficient soil.
Plants can enhance Zn acquisition through multiple, potentially interacting mechanisms. They can enhance the uptake by adapting their root morphology or by increasing the expression of Zn cell-membrane transporters. Beyond the physical root system, roots secrete a chemically diverse blend of high- and low-molecular weight compounds that mobilise Zn from the soil. Cereals employ a strategy based on phytosiderophores (PS), metal-chelating agents released by roots into the soil. Root-associated microorganisms can also impact the plant's micronutrient status either by directly mobilising micronutrients or enhancing general plant health. While the mechanistic importance of individual traits has been demonstrated, their relative contributions have rarely been evaluated within a single integrative framework.
Using barley (Hordeum vulgare L.) as a model crop, sixteen genotypes representing the northern European germplasm were grown in a Zn-deficient soil. A diverse array of root and rhizosphere phenotypes was screened. We quantified and characterised the root exudate metabolome, placing a special focus on phytosiderophores. Root morphological traits such as root length and surface area were characterised. The expression levels of genes involved in Zn uptake were also assessed. Amplicon sequencing of the 16S rRNA gene and the ITS2 region was conducted to explore the root-associated microbiome.
Zn uptake efficiency varied substantially among barley genotypes. Barley genotypes that efficiently acquired Zn, exuded higher amounts of phytosiderophores and exhibited a distinct exudate metabolome profile, suggesting that exudates may play a key role in plant Zn nutrition. Specific root length also emerged as a possible key phenotype. While root-associated microorganisms were influenced by the plant’s Zn status and genotype, we found only subtle microbial differences between Zn-efficient and less efficient genotypes, providing little indication of their role in Zn uptake. This study establishes an integrative framework for root and rhizosphere phenotyping with the aim of identifying key traits for producing nutrient-rich crops.
How to cite: Otxandorena-Ieregi, U., Spiridon, A., Aleksza, D., Santangeli, M., Escudero-Martinez, C., Woebken, D., George, T. S., Russell, J., Causon, T., Hann, S., Stanetty, C., Kratena, N., and Oburger, E.: Identifying key root and rhizosphere traits for efficient zinc uptake in barley, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9532, https://doi.org/10.5194/egusphere-egu26-9532, 2026.
Estuarine alluvial forests, which are characterized by short, intense flooding events, are recognized as global carbon (C) hotspots. However, predicted increases in flooding intensity and prolonged summer droughts due to climate change may alter the timing, quantity and quality of C transfer from alluvial trees to soil, with potential consequences for the C sink strength of alluvial forests. The surplus C hypothesis suggests that trees assimilate a surplus of photosynthates at the onset of resource limitation (Prescott et al. 2020) and that, consequently, frequent shifts from hypoxia to water drainage (or even summer drought) may result in particular high levels of surplus C in alluvial trees, which can be released by alternative root respiration or by root exudation into the rhizosphere. To test this hypothesis for alluvial trees, we conducted an outdoor mesocosm study with young pedunculate oak (Quercus robur L.) trees exposed to different climate change scenarios and examined the consequences for the release of surplus C by alternative root respiration and root exudation. Specifically, we simulated flooding events and increases in average temperature in a full factorial experiment. Over the course of one growing season aboveground performance of trees was monitored, fine roots were sampled to measure alternative root respiration, determined from the isotopic discrimination against 18O in O2, and root exudates were repeatedly collected with the culture-based cuvette method, quantified as TOC and later analyzed by LC-MS. We observed that flooding reduced the C sink strengths of aboveground and belowground growth and biomass by up to 40%, independent from temperature. In my presentation I will focus on C release dynamics via root exudation and root respiration and discuss the potential role of flooding and temperature rise on surplus C in alluvial forest trees, and potential consequences for root-microbiome interactions. Our findings will contribute to a broader understanding of the C sink strength of estuarine alluvial forests under climate change.
Prescott CE, Grayston SJ, Helmisaari H-S, Kaštovská E, Körner C, Lambers H, Meier IC, Millard P, Ostonen (2020) Surplus carbon drives allocation and plant–soil interactions. Trends in Ecology & Evolution 35: 1110-1118.
How to cite: Bergmann, M., Mohamed, A., Dyckmans, J., Jensen, K., and Meier, I. C.: A mesocosm study: Carbon release dynamics in young alluvial oak trees affected by flooding stress and elevated temperature , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10999, https://doi.org/10.5194/egusphere-egu26-10999, 2026.
Root exudates can significantly modify soil hydraulic properties by affecting water surface tension. When released into the rhizosphere, exudates from certain plant species can act as natural surfactants, notably influencing water movement and retention in the soil.
This study analyzes how root exudates affect water infiltration and redistribution in soils composed of wet and dry layers. Transparent soil microcosms were constructed using Nafion particles in glass chambers, with a wet top layer, a dry intermediate barrier, and a wet bottom layer. Exudates extracted from winter wheat roots, along with a dye tracer, were added to the wet top layer in half of the chambers, while the controls contained only water with the tracer. Time-lapse image analysis was used to quantify the movement of the wetting front and assess the effect of the exudates on soil permeability.
The results show that the presence of exudates promotes water infiltration through the dry barrier and improves hydraulic connectivity between different soil layers. These results demonstrate that the natural surfactant activity in root exudates can facilitate water movement, highlighting it as an important mechanism in the interaction between root systems and soil water dynamics.
How to cite: Gómez Peral, E., Mair, A., Martín Sánchez, I., Ptashnyk, M., and Dupuy, L.: Root exudates help to rewet dry soil and may improve root water uptake performance in certain environmental conditions., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18987, https://doi.org/10.5194/egusphere-egu26-18987, 2026.
Roots release soluble organic compounds, known as root exudates, into the soil that influence carbon and nutrient cycling. Understanding the quantity, quality and spatial dynamics of root exudates is crucial to gain deeper insights into plant-soil-microbe interactions. Despite advances, knowledge gaps remain regarding exudate dynamics and composition in soil systems, as many studies mainly relied on hydroponic methods, which may not accurately replicate natural conditions of soil. This study investigated the spatial variability and composition of root exudates by assessing the difference between localized root segment sampling and whole root system (WRS) sampling as well as the contribution of root hairs to exudation. Two genotypes of Zea mays, wildtype B73 (WT) and root-hairless mutant (rth3), were grown in soil-filled rhizoboxes under controlled conditions in a growth chamber. Root exudates were collected by custom-designed exudation traps targeting different positions along the root axis and root tissue types, and were compared to WRS exudation rates obtained with a soil-hydroponic-hybrid approach. Exudates were analysed spectrophotometrically for total dissolved organic carbon, soluble carbohydrates, phenolic compounds, and amino acids. Results revealed significant spatial variability in exudation along the root axis, with young root tissue exhibiting higher exudation rates than older segments, and double those of WRS. Root hairs and genotypic differences showed less influence than anticipated, with position along the root axis being the dominant factor. Extrapolating exudation rates of individual segments to WRS consistently overestimated whole root system exudation, emphasizing the need for careful interpretation of exudation hotspots and WRS rates. This study highlights the importance of soil-based approaches and ecologically relevant root exudate sampling for spatially resolved insights into carbon input via plant roots into the soil.
How to cite: Brumen, F., Oburger, E., and Santangeli, M.: A novel design for sampling root exudates: Does root exudation differ depending on root tissue type and along the root axis?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19687, https://doi.org/10.5194/egusphere-egu26-19687, 2026.
Root exudation is a significant pathway for belowground carbon (C) allocation in forest ecosystems, with profound implications for soil processes, nutrient cycling, and overall ecosystem functioning. Despite its importance, quantifying root exudation from mature trees in situ remains technically challenging, and methodological inconsistencies among studies hinder the synthesis and upscaling of findings. Here, we evaluated how variations in commonly used exudate collection protocols influence measured C fluxes. Specifically, we tested the effects of root resting, trap moisture, and trap solution composition on exudation rates in two contrasting ecosystems: a temperate forest in Germany and a Mediterranean forest in Israel. By incorporating both inter- and intraspecific root combinations, we also accounted for potential species-interaction effects.
Our results highlight several methodological sensitivities. Omitting root resting can streamline sampling. Moisture conditions within cuvettes strongly affect flux estimates, with saturated traps yielding higher values than moist traps. Exudation responses were further influenced by soil phosphorus availability in the trap solutions, with elevated root C exudation under P-deficiency.
Together, these findings emphasize that methodological variation can substantially alter root exudation C flux rates. We conclude that while some streamlining of protocols is feasible, careful attention to incubation procedures and the use of second flush samples yield more reliable results. Standardized approaches- or, at a minimum, transparent and detailed reporting - are essential to improve comparability across studies. Addressing these methodological challenges will allow more accurate quantification of root exudation, strengthen its integration into terrestrial C models, and ultimately refine our understanding of belowground C allocation under global change.
How to cite: Brunn, M., Obersteiner, S., and Klein, T.: Technical note: Methodological choices influence root carbon exudation measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2096, https://doi.org/10.5194/egusphere-egu26-2096, 2026.
Root-derived carbon (C) inputs via root exudates are a key pathway linking crops to soil C and nutrient cycling. Yet, it remains insufficiently understood how programmed cell death (PCD) processes such as root cortical senescence or aerenchyma formation control root exudation. In cereals, PCD processes can lower the metabolic costs of soil exploration and reshape radial transport and rhizosphere interactions. These anatomical strategies may therefore influence both the magnitude and composition of rhizodeposition. Here, we assessed whether genotypic contrasts in cortical cell death are reflected in root exudation patterns in two cereal species.
We compared five barley (Hordeum vulgare) and six maize (Zea mays) genotypes obtained from the IPK genebank in Gatersleben and from University of Bonn selected for contrasting root anatomical properties. Plants were grown in pots for one month in a common garden experiment. Root morphology was quantified via root scanning (e.g., total root length and root surface area), and root biomass was determined. Root exudates were collected using a semi-hydroponic hybrid system and analysed for dissolved organic carbon (DOC), soluble sugars, and phenolic compounds (CGA equivalents); amino acid analyses are ongoing. After root exudation sampling, two cm long root sections were sampled from each node. Samples were taken 5-8 cm behind the root tip. Root anatomy was imaged and root cortical senescence and aerenchyma formation were quantified and are currently analysed.
Across barley genotypes, exudate DOC, sugars and phenolics showed limited differentiation during. In contrast, maize exhibited pronounced genotypic variation in root system size (root surface area, total root length) and biomass, accompanied by genotype-specific exudation profiles. Total C exudation per root surface area were lowest in Zea141 and highest in Zea90 and Zea3426, while sugar exudation was reduced in Ky228, Zea141 and Zea294 relative to other genotypes.
Overall, our results reveal strong genotype dependence of rhizodeposition in maize but comparatively conservative early patterns in barley under the tested conditions. Ongoing analyses of root cortical senescence and aerenchyma will directly test whether genotypes exhibiting greater PCD show altered root exudation pattern providing a mechanistic basis for trait-based selection of cereal genotypes to enhance root-derived C inputs to soils.
How to cite: Holz, M., Pusch, V., Visconti, A., Yu, P., and Schneider, H.: Programmed cortical cell death as a driver of root exudation in barley and maize genotypes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11151, https://doi.org/10.5194/egusphere-egu26-11151, 2026.
Root exudation constitutes a major pathway by which plants exchange carbon and nitrogen with the soil, yet its temporal dynamics remain poorly understood under field conditions. In particular, it is unclear to what extent short-term variations in exudation reflect diurnal carbon assimilation patterns or are driven by transport-related processes within the plant.
We investigated diurnal patterns of root carbon exudation and nitrogen uptake and release in two temperate tree species, European beech (Fagus sylvatica) and Norway spruce (Picea abies), at high-resolution (4-hour) sampling intervals over three full diel cycles. For each species, we studied both mature canopy trees and juvenile understory individuals to assess the dependency of exudation dynamics on light availability and plant internal storage capacity. In addition, we quantified non-structural carbohydrate (NSC) pools in fine roots.
Across species and tree age, root carbon exudation exhibited a pronounced bimodal diurnal pattern, with one peak occurring during midday and a second peak during the evening. These peaks were separated by two distinct minima in the early morning and afternoon. Nitrogen was released during the day with a peak during midday, similar to the time of carbon release. In turn we found that nitrogen uptake by fine roots happened during the night, while carbon exudation was still detectable. Nighttime carbon release and nitrogen uptake was higher in mature than in understory trees.
Our results demonstrate that root exudation in forest trees follows diurnal dynamics that cannot be explained by instantaneous carbon assimilation alone. We propose that transport-related processes and internal carbon storage play an important role in regulating belowground carbon release. (Net) nitrogen uptake occurred exclusively at night, possibly to support nighttime tree growth or regeneration. These diurnal carbon and nitrogen dynamics have important implications for associated soil biogeochemical processes.
How to cite: Hafner, B. D., Friedl, C., Scharfetter, J. B., Bauerle, T. L., and Zare, M.: Bimodal diurnal patterns of belowground carbon exudation and nitrogen uptake and release in beech and spruce suggest source and sink driven controls, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19613, https://doi.org/10.5194/egusphere-egu26-19613, 2026.
Root exudates are key regulators of rhizosphere processes, which control nitrogen (N) and carbon (C) cycling in the rhizosphere that underpin forest ecosystem functioning. However, how species and season-specific exudate quantity and quality influence these processes remain poorly understood. We compared exudates quantity and quality from an N₂-fixing alder (Alnus glutinosa), with a non-N₂-fixing oak (Quercus robur) tree across the growing season and its implications for N and C dynamics in the rhizosphere of a young forest (c.5 years old). We also scanned and recorded root traits of relevance to nutrient acquisition. We investigated how tree species and seasonality affect root exudate composition, soil N transformation, and mineralization potential of soil organic matter (SOM) among fast- and slow-cycling SOM pools. To isolate exudate effects, we complemented field observations with controlled additions of artificial exudates cocktails to soils mimicking natural concentrations and C:N ratios.
Root exudates were collected in situ as in Philip et al. (2008). Exudate quantity and composition differed markedly between species and varied seasonally. Oak exudates exhibited substantially greater exudation rates, including 57.0% higher carbon (p = 0.005) and 64.5% higher nitrogen exudation (p< 0.001). In contrast, alder exudates had a 15.9% higher C:N ratio than oak across the growing season, indicating lower organic C quality and reduced lability. Furthermore, oak exhibited a more acquisitive root strategy than alder, with higher specific root length (+125.8%, p = 0.016) and root tissue density (+86.8%, p = 0.186). Root exudation peaked in summer and declined in autumn, tracking seasonal photosynthetic activity. Exudates metabolomic analyses showed dominance of secondary metabolite biosynthesis pathways, followed by amino acid metabolism, which was more pronounced in alder, whereas oak exudates were characterized by enhanced aromatic compound degradation, likely reflecting stronger microbial processing in the oak rhizosphere.
Artificial root exudate addition showed that oak exudates, characterized by lower C:N ratios and higher carbon (C) inputs, stimulated stronger microbial nutrient cycling responses than alder exudates, increasing soil respiration by up to 1.74-fold, microbial biomass C by 1.62-fold, microbial biomass N by 11-fold, and gross N mineralization by fourfold. N Mineralization rates increased with exudate concentration and incubation time, with the strongest responses under oak exudates. However, net nitrification declined at high exudate inputs, likely due to microbial immobilization of N and gaseous N losses.
Carbon fractionation revealed that mineral-associated organic carbon (MAOC) dominated soil C and N stocks (>90%), whereas particulate organic carbon (POC) varied seasonally and between species (alder > oak; autumn maximum). Despite its smaller pool size given that this restored forest stand was 5 years old at the time of sampling, POC mineralized over 25 times faster per unit C than MOAC overall.
Overall, root exudate quantity and quality regulate microbial activity, nutrient retention, and C–N coupling in young forest soils, with consequences for productivity, carbon sequestration, and ecosystem–climate feedbacks.
How to cite: Kusumarini, N., Cox, L., Lynch, I., and Ullah, S.: Species-specific root exudation drives Carbon and Nitrogen Dynamics in Young Reforested Alder and Oak Forests , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21644, https://doi.org/10.5194/egusphere-egu26-21644, 2026.
Invasive plant species often alter soil chemistry through root exudates, including phenolic compounds, which can inhibit native plant growth. Understanding how these compounds influence soil-plant interactions is crucial for predicting the ecological impacts of invasive species. This study focuses on the effects of phenolic compounds, particularly coumaric acid, a widely occurring phenol in invasive plant species, on biomass production, nitrogen cycling, and exudation dynamics of a native plant grown in soil affected by contrasting water regimes (regularly flooded and non-flooded). To test the hypothesis that phenols affect nitrogen cycling and impact plant growth, initial experiments evaluated the effects of four phenols in inhibiting nitrification. Subsequent experiments focused on coumaric acid, as it was the phenol with the strongest reduction of nitrification rates in soil, measuring its influence on biomass production of the native plant Persicaria lapathifolia as well as their exudation patterns under flooded and non-flooded soil conditions. Preliminary findings suggest that phenolic compounds reduce biomass production, primarily above ground, supporting the hypothesis of growth inhibition. Exudation patterns showed high variability, with phenols disrupting established exudation trends. In flooded soil conditions, plants exposed to phenols exhibited increased nitrogen uptake, potentially as an adaptive response to altered nutrient dynamics. These findings highlight the complex interactions between phenols, root exudation, and nitrogen dynamics in riparian soil that underwent varying flooding patterns. The results suggest that invasive species may leverage phenolic compounds to inhibit native plant growth and alter nutrient cycling, providing insight into invasion strategies and their potential implications under climate change.
How to cite: Grange, S., Khatiwada, P., Mendoza-Lera, C., Jungkunst, H., and Brunn, M.: Phenol-Driven Changes in Root Exudation and Nutrient Cycling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16653, https://doi.org/10.5194/egusphere-egu26-16653, 2026.
Root exudate is comprised of complex compounds which have multiple function for plant performance and plant-soil interactions. Although the carbon fluxes of root exudates is considered as an important trait towards the fast-slow growing axis in the multidimensional root economics space, the complexity of the metabolome in root exudates is not well evaluated. Here, we present a community-weighted PCA for species chemospace. Compounds are aggregated to species with two weightings: presence (detection proportion) and relative (softmax of logabundance). Isomer candidates are pooled using Dirichlet priors (A1 symmetric; A2 similarityweighted). Dimensions are selected by Horn's parallel analysis, and robustness is assessed with leave-one-out principal angles. Of 22 descriptors, nine were near-constant or missing and were excluded. Variance concentrated in two components: presence 55.7% and 28.4%; relative 75.8% and 15.5%; both PCs exceeded the 95th percentile noise envelope. The PC1 and PC2 subspace was stable (mean cosine 0.993 to 0.994; largest deletion about 22 degrees), and A1 and A2 produced nearly identical subspaces. PC1 reflected hydrophobicity versus polarity and hydrogen bonding (higher LogP/LogD, lower H-bond acceptors/donors and polar surface area). PC2 captured adsorption and bioconcentration together with molecular flexibility and optical proxies (higher KOC and BCF, more freely rotating bonds, higher refractive index). Relative weighting is recommended as primary; presence serves as a concordant robustness check.
How to cite: Sun, L., Wang, J., Wang, X., Zeng, F., Xia, S., and Yang, X.: A robust CWM-PCA for evaluating chemospace of metabolome of root exudates across 9 tropical species, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1410, https://doi.org/10.5194/egusphere-egu26-1410, 2026.
The ability of plants to distinguish between self and non-self roots significantly influences competitive dynamics and resource allocation. However, the mechanisms underlying these discriminatory responses remain largely elusive. This study investigated the responses of cherry tomato (Solanum lycopersicum L.) and bell pepper (Capsicum annuum L.) grown as self by using a polypropylene separator for the roots (C, B) and in non-self-pairings, without a separator (CC, BB and CB) in a semi-commercial greenhouse experiment. Root respiration increased in non-self-pairings and awas highest in low degrees of relatedness pairings (L-DOR). Cherry tomato exhibited enhanced morphology, physiology, fruit quality, and quantity, and root thickening when paired with bell pepper, whereas bell pepper showed reductions in these parameters. Root exudate carbon and nitrogen concentrations were highest in non-self-combinations and highest in CB pairings. Distinct metabolic profiles were observed in root exudates and root tissues depending on the existence and identity of the neighbor. Upregulation of TCA cycle intermediates, specifically citric acid, was associated with enhanced root respiration in L-DOR pairing, suggesting a metabolic cost associated with neighbor recognition. Auxin analogue indole-3-lactic acid was significantly upregulated in cherry tomato when paired with bell pepper, coinciding with improved morphological traits, while being downregulated in bell pepper under the same conditions. Amino acid profiles further differed between species in L-DOR pairings, reflecting species-specific metabolic regulation. These findings suggest that exudate composition may serve as a specific communication language between individuals that can change in response to the existence and identity of a neighbor.
How to cite: Rachmilevitch, S. and Nyein Ko, A.: Root-root communication within Solanaceae and its effects on root exudate composition, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2616, https://doi.org/10.5194/egusphere-egu26-2616, 2026.
Root exudates play a central role in rhizosphere processes, many of which support plant growth. While increased exudation under abiotic stresses has been frequently linked to enhanced plant resilience, crop- and genotype- and soil-specific exudation patterns under non-stress conditions remain poorly understood. This study aimed to assess how soil type and genotype influence quantity and quality of root exudation in major and emerging European crops and to explore how root morphology and plant growth are related to exudation.
Four genotypes each of barley (Hordeum vulgare), faba bean (Vicia faba), potato (Solanum tuberosum), and sweet potato (Ipomoea batatas (L.) Lam.) were grown in three distinct European soils under non-stress conditions. Exudates were collected using a soil–hydroponic hybrid approach and analysed for dissolved organic carbon and nitrogen, total carbohydrates, amino acids, and phenolic compounds. In addition, broader exudation patterns were explored using non-targeted analytical approaches. Shoot and root samples were collected for the analysis of biomass and root morphology to examine correlations with exudation patterns.
Results showed that soil type and genotype affected exudation patterns, but their influence varied by crop. Plant growth was negatively correlated with exudation rates across most crops, likely reflecting a trade-off in carbon and nitrogen allocation between biomass accumulation and rhizodeposition. Root morphological traits partly correlated with root exudation rates, but no universal relationships were detected across crops.
Our results provide novel insights into belowground resource partitioning and broaden the understanding of soil and genotype-specific exudation patterns to previously underexplored crops, thereby improving our knowledge of mechanisms driving exudation dynamics.
How to cite: Schwalm, H., Escudero-Martinez, C., Brown, M., Brown, L., Roberts, D., Mitchell, S. M., Lozano, I. R., Bodenhausen, N., Bulgarelli, D., Houston, K., George, T. S., and Oburger, E.: Soil and genotype-driven root exudation patterns in barley, faba bean, potato, and sweet potato, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3516, https://doi.org/10.5194/egusphere-egu26-3516, 2026.
Understanding plant–soil–microbe interactions is key to increasing nutrient use efficiency and soil carbon (C) storage. Root exudates play a central role in nutrient acquisition, structure microbial communities and influence organo-mineral association. Yet, how soil development stage and resulting soil chemical properties regulate root exudation and the fate of C in the rhizosphere remain poorly understood.
We used a soil–plant–microbe–mineral approach to assess how soil development stage influences plant stoichiometry, rhizosphere C release, microbial activity, and organo-mineral associations. In a growth chamber, we grew Lupinus albus, a model species for phosphorus (P) acquisition, for 30 days under three P levels (5, 15, and 40 mg P kg⁻¹) in three podzolic horizons representing contrasting soil development stages: an organic matter- and quartz-rich Ae, an iron (Fe) and aluminum (Al) oxide-rich Bh, and a primary silicate-dominated BC. Plant-derived C transfer to the rhizosphere, microbes, and reactive iron oxides was traced using a 13C-CO₂ pulse-labeling experiment, with Fe-oxide mesh bags used to assess newly stabilized organo-mineral C. We measured plant biomass, shoot stoichiometry, rhizosphere metabolites, microbial biomass, and enzyme activities.
Soil development stage strongly influenced shoot response to P supply and the fate of root-derived C. Shoot biomass was highest and insensitive to P supply in the primary mineral-rich BC, while it was lowest and responding to P supply in the Bh horizon, due to P sorption onto Fe and Al oxides. While dissolved rhizosphere organic C was similar, the metabolomic profile of rhizosphere solutions and microbial parameters varied markedly among soil horizons. 13C recovery in the rhizosphere varied strongly between soil horizons and P levels, reflecting interactions between mineral sorption capacity, metabolomic profiles and microbial activity. In the Ae horizon, high microbial biomass likely enhanced microbial processing of root-derived ¹³C, whereas in the Bh horizon, lower microbial biomass combined with high Fe and Al oxide content likely favored greater adsorption of 13C onto reactive minerals. Iron oxides in mesh bags showed pronounced, horizon-specific capacity to stabilize C, peaking in Bh, followed by Ae and BC.
Overall, soil development stage and resulting chemical and mineralogical properties tightly control plant P responses and the fate of C in the rhizosphere. These results highlight the tight coupling of plants, microbes, and minerals, and underscore the importance of soil genesis and integrative approaches for tracing the fate of photosynthates in soil–plant systems. Extending these findings to agroecosystems will require further validation though field trials.
How to cite: Pollet, S., Cornelis, J.-T., Wang, C., Knipfer, T., Prescott, C., Ahkami, A., Balasubramanian, V. K., Lehmann, S., Winkler, T., Varga, T., Kim, Y.-M., Tate, K., and Lobet, G.: Soil development stage shapes shoot-to-soil carbon flow and organo-mineral association under variable phosphorus supply, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9447, https://doi.org/10.5194/egusphere-egu26-9447, 2026.
A major challenge in root exudation research is obtaining exudate samples that accurately reflect exudation processes under natural soil growth conditions, as both the growth environment and the experimental setup can significantly influence root exudation dynamics. This study investigated the effects of different experimental systems and growth conditions on carbon (C) exudation in maize (Zea mays L.) roots, and whether these factors affect the ability to resolve genotypic differences between the wild type (B73) and its root hairless mutant (rth3).
Plants were cultivated under various experimental conditions, including soil-based and hydroponic systems, and root exudates were collected using a combination of traditional and innovative sampling approaches. Carbon exudation rates were compared across systems and genotypes, and laboratory results were additionally evaluated against data from a separate field experiment.
Carbon exudation rates varied greatly with experimental design and environmental context, whereas the contribution of root hairs to total C exudation was minor in comparison. Notably, exudation rates measured in soil-based laboratory systems were consistent with those obtained in the field when growth temperatures were similar, indicating that soil-based laboratory experiments can provide ecologically relevant estimates of C exudation when designed to match field-relevant conditions. However, large differences in root biomass introduced systematic bias into exudation measurements, especially when the root-to-sampling volume ratio (RSVR) differed substantially among systems or genotypes. These findings demonstrate how experimental setup and environmental conditions influence measured exudation rates and can potentially outweigh genotypic effects.
Overall, these results provide methodological guidance for reliably quantifying root carbon exudation in maize. Specifically, soil-based laboratory systems that closely replicate field conditions, particularly temperature, together with maintaining a consistent RSVR, can provide comparable estimates of maize root carbon exudation for field experiments.
How to cite: Santangeli, M., Heindl, A., Stein, L., Tognacchini, A., and Oburger, E.: Comparative assessment of root exudation in maize: Influence of experimental setup, growth conditions and root hairs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10998, https://doi.org/10.5194/egusphere-egu26-10998, 2026.
Crop diversification as an agricultural practice has been proposed for increasing carbon (C) storage in agricultural soils. Plants allocate C belowground differently depending on biotic and abiotic factors, which can be observed through variations in root architecture and root economics space. Root exudates are an important source of organic matter inputs to soils, and their composition is an important driver of plant-soil interactions in the rhizosphere. However, little is known about whether varieties of the same species differ in terms of organic matter inputs and thus their potential influence on soil functioning (e.g., C sequestration potential), and whether there is a relationship between root architecture and the composition of exudates. In a growth chamber experiment, we investigated root exudate compositions of commonly used cereal species and varieties, and their architectures were determined. Cereals were grown in rhizoboxes (40.2 x 26.1 x 3cm) for 21 days with 12-h light, 24°C and 19°C during the day and night respectively with a relative humidity of 60%, and included: 3 oat (Avena sativa L., varieties Galant, Fatima, and Ferry), 2 wheat (Triticum aestivum L., varieties Informer, and Julius), and 2 barley (Hordeum vulgare L., varieties Anneli, and SW Judit). Root system development and architecture were quantified from pictures taken regularly during the growth period, while exudate composition, collected via the soil-hydroponic-hybrid approach, were determined by 1H Nuclear Magnetic Resonance. Root system architecture varied significantly across species, while within species variation was only significant for barley and wheat. This coincided with patterns of significant variations in exudate profiles across and within species. Furthermore, our results show both how root systems and organic matter inputs can vary depending on choice of genotype within commonly grown cereals. In this presentation, we will discuss the possible link between C input and root architecture, as well as the use of intraspecific diversity in cereals to increase C storage in agricultural soils.
How to cite: Sparkes, B., Maaroufi, N., Nunan, N., Moazzami, A., Colombi, T., and Herrmann, A.: Intraspecific diversity of cereals – root architecture and quantification of root carbon inputs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12112, https://doi.org/10.5194/egusphere-egu26-12112, 2026.
Root exudates are a primary pathway through which plants can recruit and interact with microbial communities surrounding their roots. Yet little is known about how crop species differing in root exudate quantity and quality influence the microbial mineralization of organic nitrogen in the rhizosphere. This is a particularly urgent question considering the need for effective novel organic fertilizers, such as insect-based fertilizer from black soldier fly (flytilizer), without compromising crop yields. Therefore, the aim of this study was to examine root exudation across 20 crop species, then link this to root traits indicative of fast vs. slow-growing strategies, mineralization of nitrogen in the rhizosphere, and plant nitrogen uptake. Additionally, we wanted to examine how these patterns changed when flytilizer was added. We expected that the total organic carbon (TOC) of root exudation would be positively correlated to rhizosphere microbial nitrogen cycling enzyme activity and plant N content. We also expected higher TOC and sugar to phenolic ratio to be positively correlated to strategies where plants grow quickly. Finally, we expected that when flytilizer is added, the relationship between TOC of root exudates and rhizosphere microbial nitrogen cycling activity to be weakened. To fill this gap, we conducted a greenhouse experiment with 20 crop species from 10 families grown in sandy field soil without and with flytilizer. We ensured the plants were nitrogen limited by applying mineral fertilizer containing all essential elements for plant growth apart from nitrogen. We measured relative growth rate and, after 7 weeks, we measured a variety of root traits, root exudation, as well as microbial biomass and the activity of five nutrient-cycling enzymes in the rhizosphere. Plant productivity and plant nitrogen (N) content were also quantified and for each crop species.
How to cite: Harris, F., De Deyn, G., Knoester, I., Glashier, H., Kandeler, E., Poll, C., and Zwetsloot, M.: An exudate extravaganza – how changes in root traits and exudation in response to insect-based fertilizer could elucidate differences in crop species nitrogen uptake strategy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20338, https://doi.org/10.5194/egusphere-egu26-20338, 2026.
Roots regulate a variety of carbon cycle processes in ecosystems. I will discuss the scope of inferring rhizosphere function from broad spatial scale analyses of root traits and carbon cycle state factors. In the first example, fine root carbon (FRC) in soils is typically hypothesized to be positively related to soil organic carbon (SOC). However, FRC inputs can also enhance SOC loss through priming. We tested the broad-scale relationships between SOC and FRC at 43 sites across the US National Ecological Observatory Network (Malhotra et al. 2025). We found that SOC and FRC stocks were positively related with an across-ecosystem slope of 7 ± 3 kg SOC m−2 per kg FRC m−2, but this relationship was driven by grasslands. Grasslands had double the slope compared to the across-ecosystem slope while forest FRC and SOC were unrelated. Furthermore, deep grassland soils primarily showed net SOC accrual relative to FRC input. Conversely, forests had high variability in whether FRC inputs were related to net SOC priming or accrual. We conclude that while FRC increases could lead to increased SOC in grasslands, especially at depth, the FRC-SOC relationship remains difficult to characterize in forests; suggesting a disproportionate role of priming in shaping forest SOC. In addition to regulating SOC, roots influence trace gas production in ecosystems. I will also discuss examples relating root form to methane function in wetlands (Määttä and Malhotra 2024), highlighting the elusive role of root exudation in methanogenesis.
Citations:
Malhotra A, JAM Moore, S Weintraub-Leff, K Georgiou, AA Berhe, SA Billings, M-A de Graaff, JM Fraterrigo, AS Grandy, E Kyker-Snowman, M Lu, C Meier, D Pierson, SJ Tumber-Dávila, K Lajtha, WR Wieder & RB Jackson. Fine root and soil carbon stocks are positively related in grasslands but not in forests. Communication Earth & Environment 6, 497 (2025). https://doi.org/10.1038/s43247-025-02486-9
Määttä T and A Malhotra, The hidden roots of wetland methane emissions (2024). Global Change Biology. 30, e17127
How to cite: Malhotra, A.: Fine root and carbon cycle relationships across broad scales: what can we infer about rhizosphere function?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22018, https://doi.org/10.5194/egusphere-egu26-22018, 2026.
Although many temperate agricultural soils contain substantial P, most of this P is unavailable to plants, and its mobility is further restricted by drought. Root exudation contributes to drought tolerance and P mobilization and is considered to play a major role in soil resource acquisition strategies in crops. Its position, however, within the root economics space (RES) remains contradictory. We assessed differences between maize landraces and modern cultivars in root economic strategies, plasticity under combined water and phosphorus deficiency, and the consequences for plant performance. We investigated root and rhizosphere responses of six maize varieties (three landraces, three modern hybrids) grown in a controlled pot experiment under combined water and P limitation. Pots were assigned four treatments: well-watered (20% Water content (WC)) and water-stressed (8% WC) condition, combined with high (47.97 mg P kg-1) or low (23.3 mg P kg-1) P. After four weeks of growth, water-stressed plants underwent a two-week drought period, adjusting to 8% WC after one week, while well-watered plants continued to grow under optimally watered conditions. Root traits were assessed through root scanning and dry biomass measurements. Root exudates were collected using a soil-hydroponic hybrid method and analysed for dissolved organic carbon, sugars, organic acids, carboxylates and phenolics. Soil DNA was analysed for its bacterial and fungal composition. We found that landraces followed a “do-it-yourself” RES strategy, whereas modern varieties adopted an “outsourcing” strategy that was associated with increased root exudation. Water availability drove rapid plastic responses in root exudation, with the strongest response under combined deficiency. In contrast, morphological root traits were driven by P, rather than water. Under combined deficiency, landraces maintained higher P use efficiency while moderns exhibited greater P acquisition efficiency. These findings demonstrate that contrasting root economic strategies of different maize varieties shaped the performance under combined P and water stress.
How to cite: Visconti, A., Yang, S., Pausch, J., Wild, A. J., Kolb, S., Pusch, V., Chibesa, M. C., Hajirezaei, M.-R., and Holz, M.: Contrasting belowground strategies of maize varieties under combined water and phosphorus deficiency: the role of root exudation. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6538, https://doi.org/10.5194/egusphere-egu26-6538, 2026.
Plants actively modify their rhizosphere by releasing carbon-rich exudates that alter the physical and hydraulic properties of the surrounding soil. High-molecular-weight compounds such as mucilage are known to enhance rhizosphere water retention and increase liquid-phase viscosity. However, it remains poorly understood whether maize strategically modulates mucilage exudation in response to contrasting soil textures and water availability. Soil hydraulic properties differ strongly between textures, particularly under drying conditions, where non-linear relationships between matric potential and hydraulic conductivity may constrain root water uptake. We hypothesized that maize enhances mucilage exudation in soils with reduced soil–root contact and low hydraulic conductivity in order to maintain water uptake.
We grew maize plants in rhizoboxes filled with two contrasting soil textures (sand and loam) under well-watered and water-limited conditions. Rhizosphere extension around newly emerged roots was quantified using neutron radiography. In a second experiment, soil water was labeled with deuterated water to quantify root water uptake dynamics using time-resolved neutron radiography combined with a diffusion–convection model.
Rhizosphere extension was significantly larger in sand than in loam, indicating an adaptive modification of rhizosphere properties in response to reduced soil–root hydraulic connectivity. This pattern is consistent with enhanced mucilage exudation, which increases soil–root contact and maintains liquid-phase continuity under hydraulically limiting conditions. For the first time, in situ water retention curves of the maize rhizosphere were quantified for both sandy and loamy soils. Root water uptake rates of individual roots were similar across soil textures and moisture regimes; however, individual roots in sandy soils contributed more strongly to total plant transpiration than those in loamy soils. Notably, single roots maintained water uptake under water-limited conditions, demonstrating the capacity of maize to sustain water acquisition even as soil moisture declined.
These results demonstrate a high degree of adaptive plasticity in maize, highlighting its ability to engineer rhizosphere hydraulic properties to optimize water uptake under contrasting soil textures and moisture regimes.
How to cite: Adamczewski, R., Holz, M., Pausch, J., Kaestner, A., and Zare, M.: Shaping rhizosphere properties enables better root water uptake performance in contrasting soil conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11011, https://doi.org/10.5194/egusphere-egu26-11011, 2026.
