Phosphorus availability may shape plantmicroorganism-soil interactions in forest ecosystems. Our aim was to quantify the interactions between soil P availability and P nutrition strategies of European beech (Fagus sylvatica) forests. We assumed that plants and microorganisms of P-rich forests carry over mineral-bound P into the biogeochemical P cycle (acquiring strategy). In contrast, P-poor ecosystems establish tight P cycles to sustain their P demand (recycling strategy). We tested if this conceptual model on supply-controlled P nutrition strategies was consistent with data from five European beech forest ecosystems with different parent materials (geosequence), covering a wide range of total soil P stocks (160-900 g P m -2 ; \1 m depth). We analyzed numerous soil chemical and biological properties. Especially P-rich beech ecosystems accumulated P in topsoil horizons in moderately labile forms. Forest floor turnover rates decreased with decreasing total P stocks (from 1/5 to 1/40 per year) while ratios between organic carbon and organic phosphorus (C:P org ) increased from 110 to 984 (A horizons). High proportions of fine-root biomass in forest floors seemed to favor tight P recycling. Phosphorus in fine-root biomass increased relative to microbial P with decreasing P stocks. Concomitantly, phosphodiesterase activity decreased, which might explain increasing proportions of diester-P remaining in the soil organic matter. With decreasing P supply indicator values for P acquisition decreased and those for recycling increased, implying adjustment of plantmicroorganism-soil feedbacks to soil P availability. Intense recycling improves the P use efficiency of beech forests.

Phosphorus is one of the major limiting factors of primary productivity in terrestrial ecosystems and, thus, the P demand of plants might be among the most important drivers of soil and ecosystem development. The P cycling in forest ecosystems seems an ideal example to illustrate the concept of ecosystem nutrition. Ecosystem nutrition combines and extents the traditional concepts of nutrient cycling and ecosystem ecology. The major extension is to consider also the loading and unloading of nutrient cycles and the impact of nutrient acquiring and recycling processes on overall ecosystem properties. Ecosystem nutrition aims to integrate nutrient related aspects at different scales and in different ecosystem compartments including all processes, interactions and feedbacks associated with the nutrition of an ecosystem. We review numerous previous studies dealing with P nutrition from this ecosystem nutrition perspective. The available information contributes to the description of basic ecosystem characteristics such as emergence, hierarchy, and robustness. In result, we were able to refine Odum's hypothesis on P nutrition strategies along ecosystem succession to substrate related ecosystem nutrition and development. We hypothesize that at sites rich in mineral-bound P, plant and microbial communities tend to introduce P from primary minerals into the biogeochemical P cycle (acquiring systems), and hence the tightness of the P cycle is of minor relevance for ecosystem functioning. In contrast, tight P recycling is a crucial emergent property of forest ecosystems established at sites poor in mineral bound P (recycling systems). We conclude that the integration of knowledge on nutrient cycling, soil science, and ecosystem ecology into holistic ecosystem nutrition will provide an entirely new view on soil-plant-microbe interactions.

Defined, quartz-diluted mixtures of sulfur (S) compounds with different oxidation state (OS) were analyzed by K-edge XANES spectroscopy using linear combination fitting (LCF) and spectrum deconvolution by fitting several Gaussian and arctangent functions (GCF). Additionally, for different soils the S speciation as calculated by both methods was compared with results of a wet-chemical S speciation. For mixtures of FeS, L-cysteine, and Na2SO4, the S speciation was recovered with satisfactory accuracy and precision by both methods at the 2 and 0.2 mg S g(-1) level. For GCF, white-line peaks must be normalized with respect to their OS-specific absorption cross-section. LCF must be conducted with dilute reference compounds to avoid self-absorption effects. For mixtures of FeS, FeS2, S°, and L-cysteine, both procedures showed poor accuracy. For the soils, similar percentages of reduced inorganic S, organic S, and sulfate were calculated by LCF, GCF, and wet chemical S speciation. GCF allows a fair estimation of S species groups with different OS (inorganic reduced S, organic reduced S, organic intermediate S, oxidized S) in soils without standards. If dilute standards of all S compounds assumed to be present in a sample are available, LCF is more objective and allows a more detailed S speciation.

Phosphorus availability in terrestrial ecosystems is strongly dependent on soil P speciation. Here we present information on the P speciation of 10 forest soils in Germany developed from different parent materials as assessed by combined wet‐chemical P fractionation and synchrotron‐based X‐ray absorption near‐edge structure (XANES) spectroscopy. Soil P speciation showed clear differences among different parent materials and changed systematically with soil depth. In soils formed from silicate bedrock or loess, Fe‐bound P species (FePO4, organic and inorganic phosphate adsorbed to Fe oxyhydroxides) and Al‐bound P species (AlPO4, organic and inorganic phosphate adsorbed to Al oxyhydroxides, Al‐saturated clay minerals and Al‐saturated soil organic matter) were most dominant. In contrast, the P speciation of soils formed from calcareous bedrock was dominated (40–70% of total P) by Ca‐bound organic P, which most likely primarily is inositol hexakisphosphate (IHP) precipitated as Ca3‐IHP. The second largest portion of total P in all calcareous soils was organic P not bound to Ca, Al, or Fe. The relevance of this P form decreased with soil depth. Additionally, apatite (relevance increasing with depth) and Al‐bound P were present. The most relevant soil properties governing the P speciation of the investigated soils were soil stocks of Fe oxyhydroxides, organic matter, and carbonate. Different types of P speciation in soils on silicate and calcareous parent material suggest different ecosystem P nutrition strategies and biogeochemical P cycling patterns in the respective ecosystems. Our study demonstrates that combined wet‐chemical soil P fractionation and synchrotron‐based XANES spectroscopy provides substantial novel information on the P speciation of forest soils.

Summary Current wet chemical methods for the speciation of sulphur (S) in soils are inaccurate and do not allow one to assess the S speciation of individual soil particles and colloids. X‐ray microscopy and Near Edge X‐ray Absorption Fine structure Spectroscopy (NEXAFS) can be used to study individual species of S at the K‐adsorption edge. We have used these techniques to identify and quantify S species in bulk soil, soil particles and colloids from Oh and Bh horizons of two forested Podzols. The partitioning of soil sulphur as determined on bulk samples of the Oh horizons by X‐ray spectromicroscopy agreed fairly well with the results of a conventional S speciation for the soil at Schluchsee, and reasonably well for that at Rotherdbach. The NEXAFS analyses on individual soil particles revealed that they are richer in reduced organic sulphur than the bulk soil for the Schluchsee Oh and richer in sulphate for Rotherdbach Oh. The techniques can be used reliably to separate and quantify sulphur species with different oxidation states in the soil. The combination of X‐ray transmission and sulphur fluorescence images with unfocused and focused NEXAFS spectra at the K‐adsorption edge of sulphur at specific microsites allowed us to compare the distribution of S species in bulk soil with that of distinct soil particles and soil colloids. Moreover, we can use it to assess the spatial distribution of different S species on soil particles on a scale of a few hundred nanometres.

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Minerals with large specific surface areas promote the stabilization of soil organic matter (SOM). We analysed three acidic soils (dystric, skeletic Leptic Cambisol; dystric, laxic Leptic Cambisol; skeletic Leptic Entic Podzol) under Norway spruce (Picea abies) forest with different mineral compositions to determine the effects of soil type on carbon (C) stabilization in soil. The relationship between the amount and chemical composition of soil organic matter (SOM), clay content, oxalate-extractable Fe and Al (Fe o ; Al o ), and dithionite-extractable Fe (Fe d ) before and after treatment with 10% hydrofluoric acid (HF) in topsoil and subsoil horizons was analysed. Radiocarbon age, 13 C CPMAS NMR spectra, lignin phenol content and neutral sugar content in the soils before and after HF-treatment were determined and compared for bulk soil samples and particle size separates. Changes in the chemical composition of SOM after HF-treatment were small for the A-horizons. In contrast, for B-horizons, HF-soluble (mineralassociated) and HF-resistant (non-mineral-associated) SOM showed systematic differences in functional C groups. The non-mineral associated SOM in the B-horizons was significantly depleted in microbiallyderived sugars, and the contribution of O/N-alkyl C to total organic C was less after HF-treatment. The radiocarbon age of the mineral-associated SOM was younger than that of the HF-resistant SOM in subsoil horizons with small amounts of oxalate-extractable Al and Fe. However, in horizons with large amounts of oxalate-extractable Al and Fe the HF-soluble SOM was considerably older than the HF-resistant SOM. In acid subsoils a specific fraction of the organic C pool (O/N-alkyl C; microbiallyderived sugars) is preferentially stabilized by association with Fe and Al minerals. Stabilization of SOM with the mineral matrix in soils with large amounts of oxalate-extractable Al o and Fe o results in a particularly stable and relatively old C pool, which is potentially stable for thousands of years.

Iron speciation in soils is still poorly understood. We have investigated inorganic and organic standard substances, diluted mixtures of common Fe minerals in soils (pyrite, ferrihydrite, goethite), soils in a forested watershed which constitute a toposequence with a hydrological gradient (Dystric Cambisol, Dystric Planosol, Rheic Histosol), and microsites of a dissected soil aggregate by X-ray Absorption Near Edge Spectroscopy (XANES) at the iron K-edge (7112 eV) to identify different Fe(II) and Fe(III) components. We calculated the pre-edge peak centroid energy of all spectra and quantified the contribution of different organic and inorganic Fe-bearing compounds by Linear Combination Fitting (LCF) conducted on the entire spectrum (E ¼ 7085-7240 eV) and on the pre-edge peak. Fe-XANES conducted on organic and inorganic standards and on synthetic mixtures of pyrite, ferrihydrite and goethite showed that by calculating the pre-edge peak centroid energy, the Fe(II)/Fe(III) ratio of different Febearing minerals (Fe sulphides, Fe oxyhydroxides) in mineral mixtures and soils can be quantified with reasonable accuracy. A more accurate quantification of the Fe(II)/Fe(III) ratio was possible with LCF conducted on the entire XANES spectrum. For the soil toposequence, an increased groundwater influence from the Cambisol to the Histosol was reflected in a larger contribution of Fe(II) compounds (Fe(II) silicate, Fe monosulphide, pyrite) and a smaller contribution of Fe(III) oxyhydroxides (ferrihydrite, goethite) to total iron both in the topsoil and the subsoil. In the organic topsoils, organically bonded Fe (33-45% of total Fe) was 100% Fe(III). For different microsites in the dissected aggregate, spatial resolution of m-XANES revealed different proportions of Fe(II) and Fe(III) compounds. Fe Kedge XANES and m-XANES allows an approximate quantification of Fe(II) and Fe(III) and different Fe compounds in soils and (sub)micron regions of soil sections, such as mottles, concretions, and rhizosphere regions, thus opening new perspectives in soil research.