This interdisciplinary session invites contributions to the study of P from all disciplines, and aims to foster collaborations between researchers working on different aspects of the P cycle. We target a balanced session giving equal weight across the continuum of environments in the P cycle, from agriculture, forests, soils and groundwater, through lakes, rivers and estuaries, to oceans, marine sediments and geological P deposits. We welcome both empirical studies furthering process-level understanding of P cycling and modeling studies leveraging that knowledge to larger spatial scales.
Phosphorus (P) availability has regulated terrestrial productivity over geological time, leaving a persistent imprint on ecosystem structure, biodiversity, and function. In tropical forests, strong soil P gradients are overcome by fine-tuned P use and acquisition strategies, enabling forests to maintain high productivity despite large differences in soil P supply. Rising atmospheric CO₂ increases biological P demand, making P constraints a central factor for tropical forest carbon sink capacity and a major source of uncertainty in future model projections. Climate change and human disturbances further disrupt plant–soil–microbial interactions and reconfigure P losses and recycling, raising questions about forest functioning and vulnerability.
I synthesize current understanding of tropical forest functioning across soil P gradients, focusing on the co-evolution of soil P pools, vegetation P acquisition strategies, and consequences for the forest carbon (C) cycle. Evidence on P acquisition spans “foraging” strategies in relatively P-rich systems to “mining” of less accessible P forms in highly weathered soils.
Building on this framework, I present model results showing that internal recycling of organic P pools plays a critical role in shaping carbon sink capacity and vulnerability under rising CO₂. Simulations with a terrestrial biosphere model across the Amazon reveal that CO₂ fertilization effects depend not only on background soil P, but also on the capacity of forest ecosystems to enhance enzyme-driven acquisition of rapidly recycled organic P, intensifying internal P recycling. This strategy occupies an intermediate position between foraging and mining, relying on carbon investment to increase turnover of actively cycling P. Such recycling may support short-term forest functioning while increasing sensitivity to P disruption and loss under global change.
Finally, I highlight how an upcoming CO₂ enrichment experiment in the Amazon will provide a unique opportunity to directly test these mechanisms and provide empirical constraints on how internal phosphorus recycling shapes tropical forest carbon sink capacity and vulnerability under global change.
How to cite: Fleischer, K.: Tropical Forests on a Phosphorus Loop: Internal Recycling Regulates Carbon Sink Capacity and Vulnerability under Global Change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12109, https://doi.org/10.5194/egusphere-egu26-12109, 2026.
Phosphorus (P) is essential for plant growth, but excessive accumulation in soils can pose environmental risks, particularly through losses into water bodies. However, despite large spatial variability in P concentration and availability, no nationwide map of soil P exists for Switzerland. Moreover, knowledge of the relative importance of management-related factors compared to soil chemical and pedoclimatic drivers on the distribution of total and available P remains limited.
This study aims to predict and explain the distribution of total and available P pools in Swiss topsoils. For this purpose, we combined machine-learning approaches (ML) using Random Forests with model interpretation based on Shapley values to identify the main drivers controlling the P distribution. As model input, we used total P data measured at 960 sites of the Geochemical Soil Atlas of Switzerland in combination with predictor variables representing land use, soil properties, as well as environmental and geological conditions. To further investigate P dynamics in agricultural soils, we integrated a dataset from the Swiss Proof of Ecological Performance (PEP) subsidy scheme, which comprises 14 years of soil analyses since 2010. Available P pools were operationally defined using CO₂ saturated water extraction as a proxy for immediately plant available P, and ammonium acetate - EDTA extraction (AAE10) representing a larger pool of exchangeable soil P. This dataset includes approximately 150’000 observations, allowing differentiation between arable land and grassland.
As expected, total P concentrations are significantly higher in arable land and in pastures/grasslands compared with forests and alpine areas. Accordingly, interpretable ML measures, including Shapley values, indicate that land use is the most important predictor, followed by the presence of nutrients such as nitrogen (N), potassium (K), and sulfur (S). In contrast, soil chemical properties (e.g. pH, soil organic carbon) and proxies for pedoclimatic conditions, such as temperature or lithology, are less important for the prediction on a national scale.
Across Switzerland, the lowest available P concentrations are observed in north-western and southern regions, whereas the highest concentrations were measured along the Swiss Plateau and in central and north-eastern Switzerland. While P concentrations extracted with CO₂ saturated water are similar between arable crops and grassland, arable soils exhibit systematically higher AAE10 extractable P. Further work will focus on identifying the main drivers of available P pools and their temporal changes across Switzerland, including data from remote sensing and other monitoring programmes.
By combining spatially resolved geochemical data, interpretable machine learning approaches, and long-term agricultural monitoring data, this study provides a framework for identifying key drivers of the distribution of P pools in Swiss soils, thereby supporting targeted and sustainable nutrient management strategies.
How to cite: Reusser, J. E., Gilgen, A., Schneuwly, J., Baumgartner, S., Aasen, H., Bürge, D., and Hirte, J.: Disentangling the drivers of total and available phosphorus distributions in Swiss soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9236, https://doi.org/10.5194/egusphere-egu26-9236, 2026.
The pedogenic minerals in volcanic soils are predominantly composed of short-range order (SRO) aluminosilicates (e.g. allophane, imogolite) and Fe-hydr(oxides) (e.g. ferrihydrite), which influence the geochemical cycling of phosphorus (P). SRO minerals are metastable and can transform into more stable crystalline phases, a process influenced by environmental conditions like temperature and soil moisture. The present study aimed to analyze the variation in Fe and Al contents associated with SRO and their reactivity toward P across two soil toposequences with different soil moisture conditions on the Irazú Volcano, Costa Rica. Soil samples were collected from various horizons along an East-South (ES) toposequence (1734–2853 m.a.s.l.) with a consistently humid udic regime, and a West-South (WS) toposequence (1724–3178 m.a.s.l.) that transitions from a udic to a drier ustic regime when altitude decreases. Pedogenic forms of Fe, Al, and Si were operationally defined using ammonium oxalate (AO), dithionite-citrate (DC) and sodium pyrophosphate (Py) extractions. Phosphorus pools (P-Olsen, AO-extractable P (Pox), total P) were also quantified. Phosphorus adsorption was evaluated using batch experiments, and data were interpreted using the Langmuir equation and the mechanistic Charge Distribution (CD) model to estimate P adsorption capacity (Qmax) and reactive surface area (RSA) of the soils. In the humid ES toposequence, AO-extractable Al (Alox) and (Feox), Qmax and RSA, increased as altitude decreased. Those trends were attributed to the stable moisture along the altitudinal gradient and the increasing temperatures with decreasing altitude, favoring the formation and persistence of SRO minerals. In contrast, the WS toposequence showed no consistent trend with altitude, probably because the transition to ustic regime at lower altitudes promoted the transformation of SRO minerals into more crystalline phases. The P-Olsen/Pox ratio was low (<10%) across all samples and significantly lower in the ES toposequence, suggesting that the persistence of SRO minerals under humid conditions severely constrains P availability. An independent dataset of samples (n = 88) from the same study region corroborated the above findings. The udic soils showed a strong negative correlation between altitude and Alox (r = -0.80), Feox (r = -0.77), Pox (r = -0.53), and total C (r = -0.64). In ustic soils, the relationships were not evident and only Feox correlated with altitude (r = -0.63). The results show that soil moisture regime is a key factor regulating the persistence of highly reactive SRO minerals along altitudinal gradients. Thus, in humid regimes, persistent SRO minerals increase the capacity of soils to retain P and stabilize organic C, resulting in direct implications for P availability and cycling in these tropical volcanic landscapes.
How to cite: Mendez, J. C., Solano-Solano, C., Camacho-Umaña, M. E., Solano-Arguedas, A. F., and Kaune, A.: Moisture-driven controls on the stability of short-range order minerals and phosphorus cycling in tropical volcanic soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-204, https://doi.org/10.5194/egusphere-egu26-204, 2026.
Phosphorus is considered a limiting nutrient in many ecosystems, and is therefore likely to constrain global carbon sinks. A thorough understanding of organic P composition in soils is vital across fields, from agriculture to ecology. Organic phosphorus (P) is a large fraction of soil P, but its speciation is still poorly understood.
NMR spectroscopy gives important insights into the speciation of soil P, because each P species gives rise a specific signal, and information on molecular weight can also be obtained from NMR spectra. Here we present new methodology to define soil P speciation, results concerning identification of P monoesters in soils, and on P speciation in tropical ecosystems.
Orthophosphate monoesters, with are intrinsically linked to P biochemistry, make up a central region in 31P NMR spectra. This region often contains resolved signals overlaid on a background. The resolved signals have been identified, but the background hampers their quantification. More important, the background can represent a large fraction of soil P, but its P biogeochemistry is completely enigmatic.
We have previously reported that the background is not composed of macromolecular P species. Instead, measurements of the true linewidths of the signals revealed that the background is composed of hundreds of small-molecule P species (Haddad et al., 2024). Here we show that the background contains a large number of P monoesters, and we present data on their identity based on a combination of MS-metabolomics and new NMR experiments, to understand the origin and ecological significance of this large unexplored P pool.
Highly weathered soils in the tropics often contain low P levels. In two tropical forests in French Guiana, the effect of P fertilization in these ecosystems has been studied (Lugli et al., 2023). Here we present NMR data on the P speciation in the two forests which differ in nutrient status, and on the effect of P fertilization on P speciation.
Haddad, L.; Vincent, A. G.; Giesler, R.; Schleucher, J. Small Molecules Dominate Organic Phosphorus in NaOH-EDTA Extracts of Soils as Determined by 31P NMR. Sci. Total Environ. 2024, 931, 172496.
Lugli LF., Fuchslueger L et al. Contrasting responses of fine root biomass and traits to large-scale nitrogen and phosphorus addition in tropical forests in the Guiana shield. Oikos 2024:e10412
How to cite: Schleucher, J., Ruda, A., Fuchslueger, L., and Giesler, R.: Insights into soil phosphorus biogeochemistry using new NMR techniques and P fertilization experiments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20853, https://doi.org/10.5194/egusphere-egu26-20853, 2026.
Long-term phosphorus (P) fertilization has resulted in substantial P accumulation in Taiwanese rice paddy soils, with concentrations reaching several thousand mg kg⁻¹. To assess the phytoavailability of this legacy P to rice, soil P speciation was characterized using X-ray absorption near-edge structure (XANES) spectroscopy and a sequential extraction procedure, and quantified P accumulation in rice as soil-to-plant translocation. Despite lower total and extractable P, acidic soils showed greater soil-to-root P translocation, whereas alkaline soils contained larger soil P pools but exhibited more constrained P translocation. Sequential extraction and XANES consistently indicated the coexistence of Ca-bound P (Ca–P) and Fe-bound P (Fe–P) across the pH range, including species not predicted to dominate from thermodynamic considerations. In acidic soils, the persistence of Ca–P suggests a potentially available pool that may supply P through gradual dissolution. In alkaline soils, abundant Fe–P implies retention within mineral phases that could remain chemically labile over long timescales. Overall, these findings highlight the need to account for soil P speciation when evaluating legacy P use and guiding fertilizer management, and the information is essential for developing strategies to sustain rice growth while reducing or eliminating P inputs.
How to cite: Huang, Z.-L. and Wang, S.-L.: Decoupling Phosphorus Pools and Plant Uptake: Chemical Speciation and Phytoavailability of Legacy P in Taiwanese Rice Paddies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6111, https://doi.org/10.5194/egusphere-egu26-6111, 2026.
The concentration of soil available P is influenced by multiple processes, including the input, loss, and transformation of available P. Phosphorus limitation in terrestrial ecosystems is considered a major issue that needs to be urgently addressed for ecosystem management and restoration. Microorganisms exert important effects on soil P cycling and regulate its availability. Alkaline phosphatase (ALP), primarily derived from soil microbes, is a key enzyme responsible for hydrolyzing organic phosphorurs.
In this study, we analyzed soil samples from uncultivated land to investigate the relationships among ALP gene abundance, enzyme activity, and soil chemical properties, including total carbon, phosphorus, and nitrogen. Quantitative PCR (qPCR) was used to quantify ALP-related genes, while 16S rRNA gene sequencing was employed to characterize microbial community structure. Species richness, Shannon diversity index, and available phosphorus levels were also measured to provide ecological context.
Our findings reveal complex interactions between microbial community composition, functional gene abundance, and phosphorus availability. Notably, ALP activity did not always correspond to gene abundance—particularly phoD—suggesting the influence of regulatory mechanisms, community diversity, or environmental constraints. Furthermore, correlations between microbial diversity and ALP activity varied, underscoring the nuanced role of community structure in functional gene expression.
This integrative approach highlights the importance of combining molecular, biochemical, and ecological data to enhance our understanding of phosphorus cycling in uncultivated soils and provides valuable insight into the microbial ecology of low-disturbance terrestrial ecosystems.
How to cite: Dawas, A., Ghose, A., and Kolton, M.: Linking phosphorus-solubilizing bacterial activity in uncultivated soils with soil chemical properties and key gene abundance, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14119, https://doi.org/10.5194/egusphere-egu26-14119, 2026.
Phosphorus (P) dynamics at the sediment-water interface of aquatic ecosystems are receiving increasing attention due to their implications for water quality. P uptake by microbial biofilms can serve as a mechanism to control and mitigate the risk of eutrophication. Microbial biofilms capture P both intracellularly and extracellularly. While the significance of extracellular P entrapment in biofilms in engineered systems has recently been established, little is known about its dynamics in aquatic ecosystems. Current research on eutrophication control predominantly emphasizes nitrogen, phosphorus, or nitrogen-phosphorus ratio-based approaches, often overlooking the potential indirect influence of bioavailable dissolved organic carbon (DOC) on P uptake by heterotrophic microorganisms.
In this study, we tested the effect of bioavailable DOC on P entrapment patterns in biofilms and in biofilm P-regulation mechanisms such as polyphosphate accumulation and alkaline phosphatase activity in semi-natural flow-through experimental flumes. Our results show that intracellular P entrapment, is limited by bioavailable DOC, while extracellular P entrapment is independent of bioavailable DOC and potential to offset intracellular P saturation.
We further demonstrate that DOC bioavailability influences benthic P cycling and that its implications may extend into critical areas of ecosystem functioning such as river self-purification, competitive resource utilization and organic P cycling.
How to cite: Perujo, N., Graeber, D., Fink, P., Neuert, L., Sunjidmaa, N., and Weitere, M.: Bioavailable dissolved organic carbon serves as a key regulator of phosphorus dynamics in stream biofilms , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19734, https://doi.org/10.5194/egusphere-egu26-19734, 2026.
River–floodplain systems are multifunctional and hydrologically dynamic systems that provide key ecosystem services, including water storage and nutrient retention. Albeit reduced phosphorus (P) inputs to freshwater systems, eutrophication remains widespread. In shallow systems such as floodplains, sediment P released through microbial mineralisation can sustain high nutrient concentrations in water. Lateral hydrological connectivity further shapes sediment nutrient fluxes and microbial processes by changing biogeochemical conditions. However, the mechanistic pathways linking hydrological dynamics to sediment P release remain insufficiently understood.
Here, we synthesise findings from three complementary studies combining field campaigns along a hydrological river-floodplain gradient with experimental drought–rewetting incubations. We propose a framework in which hydrological connectivity functions as the ultimate driver, regulating microbial activity and organic matter quality, which in turn act as proximate drivers of sediment P release.
Across a hydrological gradient in a floodplain of the German Elbe River, we find that hydrological connectivity between floodplain water bodies and the main river consistently mediates sediment P release. Field measurements during floodplain connection and retraction phases revealed spatially distinct dynamics, with P release increasing progressively along the hydrological gradient during retraction. This pattern coincided with enhanced sediment phosphatase enzyme activity and organic matter concentrations. An experimental drought-rewetting incubation further showed that short-term drought modifies microbial controls on sediment P release but exerts weaker effects than long-term hydrological connectivity. Moreover, we observed P release under oxic conditions, which was linked to heterotrophic microbial carbon use and humic-like dissolved organic matter.
Our findings collectively suggest that P fluxes are shaped by hydrologically mediated shifts in microbial organic matter decomposition, with hydrological connectivity possibly defining the boundary conditions under which microbial processes operate. Ultimately, hydrological connectivity should be integrated into river–floodplain research for its simultaneous effects on phosphorus transport and turnover.
How to cite: Meyer, M., Koschorreck, M., Weitere, M., Graeber, D., Kneis, D., and Perujo, N.: How hydrological connectivity controls sediment phosphorus release in a river–floodplain system, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17437, https://doi.org/10.5194/egusphere-egu26-17437, 2026.
Phosphorus (P) is essential for marine life, but fungal roles in the marine P cycle remain unclear despite the increasing recognition on marine fungal biomass. Using size-fractionated (0.8-5, 5-20, 20-180, 180-2000 µm) metagenomes and metatranscriptomes from the global epipelagic ocean, we reveal size-dependent fungal P metabolism dominated by Ascomycota . Pyrimidine metabolism dominates in the 20–180 µm fraction, whereas functions diversify in other sizes. Fungi on the largest particles (180-2000 µm) exhibit pronounced P uptake via transporters but limited extracellular alkaline phosphatase expression relative to smaller fractions. Signal peptide analysis indicates alkaline phosphotase (APase) as the main extracellular APase on large particles, yet overall AP expression remains modest and size-dependent. Linking P metabolism with carbohydrate and protein pathways shows coupling of P metabolism and carbohydrate/protein metabolism, suggesting acquisition of bioavailable P during particle degradation. Considering the notable biomass of marine fungi, these patterns imply an overlooked P sink and a particle-associated transfer route for P to fungal cells.
How to cite: Guo, K. and Zhao, Z.: Ubiquitos and dynamic phosphorus cycle mediated by marine fungi, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6497, https://doi.org/10.5194/egusphere-egu26-6497, 2026.
Phosphorus is transported laterally within river catchments due to weathering and erosion processes, but may also be retained on floodplains and in lake sediments. The balance between lateral transport and retention on the catchment scale is important in determining downstream impacts of phosphorus loading on water quality. In low-relief boreal environments with positive water balance, river catchments typically consist of complex lake chains connected by short lotic sections. The density of lakes enhances the potential for retention of phosphorus mobilized in upstream areas and thus protection of downstream water quality. However, the morphometry of individual lakes may impact upon retention capacity, through regulating sedimentation and redox conditions and thus also phosphorus regeneration. Here we studied phosphorus retention in lake sediments in the Siuntionjoki river catchment in southern Finland. The 487 km2 catchment includes 65 lakes of at least one hectare in surface area, draining into the Gulf of Finland to the west of Helsinki. We monitored sedimentary phosphorus accumulation and release in 10 primary lakes along the axis of the main Siuntionjoki river during one annual cycle. In this contribution, we present first results of the project and discuss these in the context of known water quality variability in the catchment.
How to cite: Jilbert, T., Zhao, S., Vesterinen, J., and Tammeorg, O.: Regeneration and burial of phosphorus along a lake chain in a complex boreal catchment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18787, https://doi.org/10.5194/egusphere-egu26-18787, 2026.
In reduced soils, phosphorus (P) biogeochemistry is strongly governed by iron (Fe) oxides, particularly poorly crystalline ferrihydrite due to its large surface area. Ferrihydrite is metastable and naturally transforms into more stable phases such as lepidocrocite and goethite. Under reducing conditions, under reducing conditions, adsorption of Fe(II) on the Fe(III) oxyhydroxide surface catalyzes this transformation via iron atom exchange (IAE). Structural impurities, including retained anions and organic ligands, influence transformation kinetics and products. Stable 57Fe isotope tracer experiments showed that neither P nor organic ligands prevent initial IAE, but P strongly suppresses lepidocrocite and goethite recrystallization, whereas organic ligands were less effective.
P speciation in natural environments is complex and includes inorganic (Pin) and organic (Porg) forms. Porg, especially inositol phosphates, often dominates total soil P and acts as a long‑term sink when retained by poorly crystalline Fe oxides. Different P compounds interact differently with ferrihydrite surfaces, thereby potentially influencing its transformation products in various ways. However, to the best of our knowledge, the influence of P speciation on Fe(II)-catalyzed ferrihydrite transformation remains unexplored.
In this study, NAFe ferrihydrite (⁵⁴Fe: ~5.84%; ⁵⁶Fe: ~91.76%; ⁵⁷Fe: ~2.12%; ⁵⁸Fe: ~0.28%) co‑precipitated with inorganic P (Pin‑Fh) and/or organic P (inositol phosphate; Porg‑Fh) suspensions were spiked with a ⁵⁷Fe(II) stock solution (⁵⁷Fe = 97.3%) to reach a Fe(II):Fe(III) ratio of 0.14 mol/mol. Suspensions were incubated for 4 weeks at pH 6.0 (40 mM MES buffer). Variations in aqueous P and Fe(II) concentrations, as well as the Fe isotopic composition of the solution, used to track atom exchange between solid NAFe(III) and aqueous ⁵⁷Fe(II), were measured by inductively coupled plasma mass spectrometry (QQQ‑ICP‑MS). The mineral composition of the solid phase was determined by X‑ray diffraction (XRD), Fe extended X‑ray absorption fine structure (EXAFS) spectroscopy, and ⁵⁷Fe Mössbauer spectroscopy.
The obtained results demonstrate that neither inorganic nor organic P fully prevented IAE; however, Porg‑Fh showed a faster and overall greater exchange compared to Pin‑Fh. After 4 weeks of incubation, Porg‑Fh resulted in nearly complete atom exchange, while only 60% of the atoms were exchanged in Pin‑Fh. This effect can be attributed to the pronounced decrease in ferrihydrite surface charge induced by Porg co‑precipitation, which may have promoted aqueous Fe(II), especially at pH < 7.
After 2 weeks of incubation, XRD showed that Porg‑Fh progressively started to transform into lepidocrocite, while no changes were detected for Pin‑Fh. Fe‑EXAFS showed that initial Porg‑Fh transformed into 40% lepidocrocite, and high‑resolution Mössbauer temperature profiles further confirmed the presence of <10% goethite fractions. Pin‑Fh was nearly unchanged in Fe‑EXAFS, while Mössbauer showed a slight increase in blocking temperature, likely associated with increased mineral structural ordering.
The release of P into solution was <1% of the P initially retained in the solid and was entirely attributed to Pin. No Porg release was detected. Overall, our results indicate that ferrihydrite is an effective sink for P during Fe(II)‑catalyzed transformation. Porg is much more strongly retained than Pin, which likely limits its availability for biological degradation processes and favors accumulation over time.
How to cite: Martinengo, S., Grigg, A. R. C., Voegelin, A., and Kretzschmar, R.: The divergent role of inorganic versus organic P during the Fe(II)-catalyzed transformation of ferrihydrite, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16317, https://doi.org/10.5194/egusphere-egu26-16317, 2026.
Organic phosphorus (Po) plays a critical role in soil phosphorus (P) cycling, yet the behavior and fate of specific Po species remain poorly understood. In this study, ion chromatography coupled with inductively coupled plasma mass spectrometry (IC-ICP-MS) was employed to characterize NaOH-extractable Po species in two soil types, with a focus on their temporal dynamics and responses to soil degradation. Nine distinct phosphorus peaks were identified in soil extracts, of which four remain unidentified. Based on their occurrence patterns and sensitivity to environmental change, these Po species were classified into three groups: unstable species, detected only in fresh plant or algal materials; stable species, consistently present across all samples with minimal variation; and indicator species, exhibiting moderate sensitivity to environmental conditions. Notably, the indicator species α-glycerophosphate (α-gly) and an unidentified compound (P150) showed pronounced declines during degradation. Along a grassland degradation gradient, P150 concentrations decreased by 66% in highly degraded soils compared with non-degraded soils, while α-gly declined by 27%. In addition, IC-ICP-MS revealed a tenfold discrepancy between conventional colorimetric and direct Po measurements, indicating the dominance of recalcitrant macromolecular Po fractions in soils. These results provide new insights into the molecular-level dynamics of soil Po and highlight the importance of small-molecular Po species in sustaining soil fertility and ecosystem resilience.
How to cite: Wang, Y. and Chen, Z.: Characterization and Dynamics of NaOH-Extractable Organic Phosphorus Species in Soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10267, https://doi.org/10.5194/egusphere-egu26-10267, 2026.
Phosphorus (P) bioavailability is crucial for the productivity of natural and agricultural ecosystems, and soil P speciation plays a major role therein. Better understanding of P forms present in soil is thus essential to predict bioavailability. However, P speciation studies are only as powerful as the reference spectra used to interpret them, and most studies rely on a limited set of reference spectra. Most studies on soil P forms differentiate between Ca-bound P (e.g. apatite), organic P, Fe-bound P, and Al-bound P. In our analysis of a Ca, Al, and P rich soil from the Kohala region of Hawaii, we identified the mineral crandallite, CaAl3(PO4)2(OH)5∙H2O, a mineral previously not considered to play a significant role in soils. Crandallite was first identified with powder X-ray diffraction. Subsequently reference spectra were collected, and the presence of crandallite was confirmed using micro-focused P K-edge X-ray absorption near edge structure (XANES) spectroscopy, micro-infrared spectroscopy, and solid-state 31P nuclear magnetic resonance (NMR) spectroscopy. Crandallite XANES spectra were distinct from other common XANES spectra due to the presence of features in the post-edge region of the spectrum. Linear combination fitting of bulk P K-edge XANES spectra allowed the determination of the proportion of crandallite to the total P content, indicating that crandallite comprises up to half, possibly even more of the soil P in the samples. Crandallite is therefore an important and potentially overlooked component of soil P, which pedogenically forms in soils with high P, Al, and Ca contents, where it could play an important role in P bioavailability.
How to cite: Vogel, C., Helfenstein, J., Massay, M., Kretzschmar, R., Schade, U., Verel, R., Chadwick, O., and Frossard, E.: Spectroscopic analysis shows crandallite can be a major component of soil phosphorus, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5410, https://doi.org/10.5194/egusphere-egu26-5410, 2026.
Legacy phosphorus (P) from long-term fertilization persists in farmland soils due to strong soil P fixation. Because P mobility and accumulation are linked to reactions with other elements, excessive soil P accumulation may alter nutrient translocation across the soil-rhizosphere-plant continuum, potentially disrupting crop nutrient homeostasis. To investigate these effects, this study collected samples from 77 rice paddies across Taiwan, which spanned a wide range of soil P levels. Element concentrations in soils and in rice (Oryza sativa L.) roots, shoots, and grains were analyzed using ICP-OES and ICP-MS after microwave digestion. Accumulation factors and translocation factors were subsequently calculated and compared with data from previous studies. The results showed that increasing soil P led to a significant increase in P concentration only in roots, but no corresponding increase in P concentrations in shoots or grains, indicating strong retention of excess P in roots. Magnesium (Mg) and zinc (Zn) concentrations in rice grains were lower than literature benchmarks, with Mg ranging from 865.0 to 1344.4 mg·kg⁻¹ (≈1400 mg·kg⁻¹ in previous studies) and Zn averaging 23.3 mg·kg⁻¹ (36.1 mg·kg⁻¹ in previous studies). As root P concentrations increased, the root-to-shoot translocation of both Mg and Zn decreased, suggesting that phosphate-driven binding and/or precipitation within the root system. Selenium (Se) concentrations in rice grains also showed a declining trend (averaging 0.01 mg·kg⁻¹) relative to previous soil-based studies (≈0.07 mg·kg⁻¹). Furthermore, Se accumulation in roots decreased with increasing soil phosphorus levels, suggesting competition between selenite (SeO₃²⁻) and phosphate (PO₄³⁻) during plant uptake and translocation. Manganese (Mn) in shoots averaged 303.6 mg·kg⁻¹, lower than the 560 mg·kg⁻¹ reported previously, and root Mn concentrations decreased with increasing soil P concentrations, suggesting that elevated P may reduce Mn availability through precipitation or adsorption processes under high P conditions. Overall, these results suggest that soil legacy P can alter the uptake and internal partitioning of multiple micronutrients in rice, and may reduce some micronutrients in grains. Mechanistic confirmation (e.g., root-phase speciation and transporter-level evidence) is needed to resolve the processes underlying these patterns.
How to cite: Chang, Y.-C. and Wang, S.-L.: Soil Legacy Phosphorus Reshapes the Soil–Plant Nutrient Continuum: Evidence from 77 Taiwanese Rice Paddies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15957, https://doi.org/10.5194/egusphere-egu26-15957, 2026.
Soil organic matter (SOM) dynamics involve interactions between carbon (C) and phosphorus (P) cycling; while organic phosphorus (OP) constitutes only a small fraction of total SOM, its long-term turnover remains poorly constrained and may strongly influence nutrient availability and long-term biogeochemical cycling. While organic carbon (OC) turnover has been extensively studied using radiocarbon (14C), OP dynamics are commonly assumed to mirror those of OC, despite evidence that phosphorylated compounds interact more strongly with soil minerals and may persist longer than non-phosphorylated compounds. Here, we use bomb-derived 14C as a tracer to investigate multi-decadal OP turnover in agricultural soils based on a technique that allows us to isolate soil OP to measure its isotopic signature [1].
We analysed archived topsoil samples (0–20 cm) collected between 1957 and 2019 from a long-term field experiment, replicated at three sites in southern Sweden. This time series spans the period of atmospheric bomb 14C enrichment caused by thermonuclear weapons testing in the late 1950s, and subsequent decline, enabling thus direct comparison of C incorporation into OC and OP pools over more than five decades. Using a recently developed extraction–precipitation approach [1], we isolated soil organic phosphorus (TPOP) and measured its Δ14C signature alongside the Δ14C signature of soil total OC.
At the beginning of the observation period, the Δ14C values of bulk soil organic carbon (TOC) were consistently lower than those of the total precipitated organic phosphorus (TPOP) fraction across all sites. Over time, Δ14C of bulk TOC increased, reflecting incorporation of bomb-derived radiocarbon, and subsequently declined following the decrease in atmospheric Δ14C. In contrast, Δ14C values of TPOP showed a slower, attenuated response compared to bulk TOC across the study period. This pattern indicates a slower incorporation of recently fixed carbon into the OP-associated pool relative to bulk soil organic carbon.
The attenuated Δ14C response of TPOP therefore suggests that OP-associated organic matter is preferentially stabilized within mineral-associated pools [2,3], leading to longer persistance compared to bulk soil organic carbon. Although TPOP accounted for only a small proportion of soil TOC (≤ 14%), its older radiocarbon signature indicates a distinct contribution to long-term SOM persistence.
Our results provide the first long-term, radiocarbon-based evidence that soil OP turns over more slowly than TOC, likely due to stronger mineral associations and reduced microbial accessibility. These findings support the view that carbon and phosphorus cycling in soils are partially decoupled at multi-decadal timescales, with OP turnover constrained not by pool size but by stabilization mechanisms.
References:
[1] Tian, Y., & Spohn, M. (2025). A method to isolate soil organic phosphorus from other soil organic matter to determine its carbon isotope ratio. Soil Biology and Biochemistry, 210, 109911.
[2] Kögel‐Knabner, I., Guggenberger, G., Kleber, M., Kandeler, E., Kalbitz, K., Scheu, S., Eusterhues, K., & Leinweber, P. (2008). Organo‐mineral associations in temperate soils: Integrating biology, mineralogy, and organic matter chemistry. Journal of Plant Nutrition and Soil Science, 171(1), 61-82.
[3] Spohn, M. (2020). Phosphorus and carbon in soil particle size fractions: A synthesis. Biogeochemistry, 147(3), 225-242.
Acknowledgement:
This research was funded by the European Research Council (ERC) (grant number 101043387).
How to cite: San Emeterio, L. M., Sierra, C. A., and Spohn, M.: Long-term soil organic phosphorus dynamics: evidence from 14C time series, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7661, https://doi.org/10.5194/egusphere-egu26-7661, 2026.
To promote sustainable crop production, the use of synthetic mineral fertilisers must be reduced. Bio-based fertilisers (BBF) offer a sustainable alternative, but their adoption is hindered by a lack of understanding of their fertilising value and behaviour in soil. This is particularly crucial for phosphorus (P), a finite, non-renewable resource that limits crop productivity in 67% of soils worldwide and is subject to potential supplier monopolies.
The addition of BBF to soil introduces significant amounts of carbon (C) and nitrogen (N), which can greatly influence nutrient cycling driven by soil microorganisms. These microorganisms are key drivers of the P cycle, and their activity is often limited by the availability of C and N. Another source of C in soil is plant root activity, which continuously supplies a small amount of labile C during plant growth. Microbial communities may respond differently to this continuous C supply depending on previous C and N availability.
The overarching goal of the PRIME-P project is to achieve a mechanistic and dynamic understanding of soil P cycling mediated by microorganisms in relation to different forms of C and N introduced by BBF and plant roots. I propose using state-of-the-art approaches to evaluate the effects of BBF and root exudates on microbial P mobilisation. This will allow to address the following specific objectives:
- Identify how regulating soil nutrient balance can positively affect microbial-P processing for plants
- Determine how different BBF additions affect soil OM over time and influence microbial P mobilisation
- Assess whether rhizosphere P priming occurs in soils that have received BBF
- Enhance modelling capabilities for P derived from BBF
These objectives are fundamental for identifying more sustainable agricultural practices that promote nutrient circularity. They will address critical challenges in soil-plant-microorganism interactions, paving the way for scalable, bio-based solutions to sustainable soil fertility and beyond.
How to cite: Raymond, N. S.: Can microbial phosphorus mobilization be primed? Organic fertilisereffect on biological soil phosphorus cycling (PRIME-P), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22251, https://doi.org/10.5194/egusphere-egu26-22251, 2026.
Phosphorus (P) is essential for crop production, yet inefficient management contributes to nutrient losses, water pollution, and eutrophication. Phosphorus use efficiency (PUE) is a key metric for balancing agronomic productivity with environmental sustainability. However, within-field spatial variability of PUE remains poorly understood. This study presents a spatially explicit framework integrating proximal sensing, field measurements, and machine learning to assess and map PUE in corn (Zea mays L.) systems from Central Texas, USA. Grain yield was measured with an Ag Leader yield monitor, while grain protein, oil, and starch were assessed using a CropScan grain quality sensor mounted to the combine. Apparent soil electrical conductivity (ECa) was mapped using a Veris platform to characterize soil spatial variability. Grain and soil P contents were determined from strategically selected locations using conditioned Latin hypercube sampling and scaled across fields through regression with CropScan measurements. PUE was calculated as the ratio of grain P removal to residual soil P plus applied fertilizer P. A Random Forest (RF) model was trained using ECa and terrain attributes to predict spatial patterns of PUE. The proximal sensing approach effectively captured P dynamics, with CropScan-based grain P predictions achieving R² up to 0.97. The RF model predicted PUE with high accuracy (R² = 0.78; RMSE = 0.01). ECa, elevation, and wetness index were the dominant drivers of PUE variability, with predicted values ranging from 0.02 to 0.25. Fields with higher residual soil P exhibited lower PUE, while P-limited fields showed greater efficiency. This framework enables high-resolution assessment of within-field PUE and supports precision P management to enhance productivity while reducing environmental impacts.
How to cite: Adhikari, K., Smith, D., and Hajda, C.: A geospatial framework to model within-field phosphorus efficiency via proximal sensing and machine learning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14673, https://doi.org/10.5194/egusphere-egu26-14673, 2026.
Soil organic phosphorus (SOP) can represent a large fraction of the total soil phosphorus pool, and its mineralization plays a key role in plant P supply. Phosphorylated organic compounds generally exhibit stronger adsorption to soil minerals than non-phosphorylated organic carbon, suggesting that SOP may cycle more slowly than bulk soil organic carbon (SOC). However, direct comparisons of SOP and SOC turnover times remain largely unknown due to methodological limitations.
Here, we investigated SOP turnover using soils from a 56-year chronosequence documenting the conversion of C₄ pasture to C₃ oil palm, thereby exploiting the natural δ¹³C contrast between vegetation types as an in situ tracer of carbon turnover. To specifically assess SOP dynamics, we applied a recently developed method to isolate SOP compounds from other soil organic compounds and quantified the δ¹³C signature of this SOP pool (Tian and Spohn, 2025). Turnover times of isolated SOP were then compared with those of bulk SOC across the chronosequence.
This study provides empirical data on SOP dynamics that are currently poorly represented in soil biogeochemical assessments and offers a transferable approach for disentangling phosphorus and carbon turnover in soils across ecosystems.
Reference
Tian, Y., & Spohn, M. (2025). A method to isolate soil organic phosphorus from other soil organic matter to determine its carbon isotope ratio. Soil Biology and Biochemistry, 210, 109911.
Acknowledgement
This research was funded by the European Research Council (ERC) (grant number 101043387).
How to cite: Tian, Y., Quezada, J. C., and Spohn, M.: Comparing turnover of soil organic phosphorus and bulk soil organic carbon in a 56-year oil palm chronosequence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7061, https://doi.org/10.5194/egusphere-egu26-7061, 2026.
Forests play a fundamental role in supporting global biodiversity, supplying key resources such as timber, paper, and energy, and acting as one of the largest terrestrial carbon sinks. Forest productivity, however, is constrained by several environmental factors, including the availability of carbon dioxide (CO2) and essential nutrients such as nitrogen (N), phosphorus (P), and potassium (K). Over the past decades, an increasing number of terrestrial ecosystem models (TEMs) have incorporated representations of nutrient cycles, most frequently considering N (Zaehle et al. 2009, Vuichard et al. 2019) more rarely P (Goll et al. 2012, 2017, Jiang et al. 2024) and K (CASTANEA model, see Cornut et al. 2022a, b).
Our study contributes to that effort by focusing on to the quantification and modelling of phosphorus (P) cycles, based on data and model simulations from Eucalyptus plantations in Brazil. As a starting point, we studied the fluxes of P between the soil (i.e., soil organic and inorganic P stocks) and the trees (i.e., aboveground biomass and P stocks). To do so, we used data from a P fertilization experiment conducted at the Itatinga experimental station (University of Sao Paulo) with various forms of P fertilizers. Using allometric relations and concentration measurements, we quantified the mass of phosphorus in each compartment of the trees (leaves, branches, trunk wood, bark and roots) during the entire rotation and compared it to the variation of P stock in the soil, measured in different chemical forms.
Results showed that, compared to control conditions (no fertilizer added), phosphorus fertilization increased the tree biomass production, the amount of P accumulated in plant tissues, as well as increasing the soil P stocks. However, the magnitude of these effects depended on the type of fertilizer used. Complexed humic phosphate, designed to enhance phosphorus bioavailability, produced the highest tree biomass and phosphorus mineralomass. In contrast, rock phosphate was most effective at increasing total soil phosphorus stocks. This outcome aligns with previous findings, as rock phosphate is less readily absorbed by plants than more soluble forms. Accounting for the spatial heterogeneity in soil P concentrations proved essential when computing the ecosystem P. In 5 out of 6 treatments we observed apparent P losses (i.e. unclosed P balance), which may reflect underestimation of deep root biomass and P pools in deeper soil layers. By contrast, in rock phosphate treatment, apparent P gains probably stemmed from overestimations of soil P related to uncertainties in the estimation of soil P spatial variability.
Given limitations in the data, we are currently considering incorporating a simplified representation of soil P in the CASTANEA model, representing only a small number of phosphorus compartments (organic vs. mineral form and availability to trees).
How to cite: Dubertrand, P., le Maire, G., da Cruz Rodrigues, A., de Moraes Gonçalves, J. L., Cornut, I., and Delpierre, N.: Analysis of phosphorus stock variation in soil and biomass during an Eucalyptus rotation: a step towards modelling the phosphorus cycle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6796, https://doi.org/10.5194/egusphere-egu26-6796, 2026.
