MOVED TO WED, COS 78-4, 2:30 PM // Arbuscular mycorrhizal fungal P provision to plants not dependent on fungal sensitivity to soil P

Background/Question/Methods -

Phosphorus (P) is an important potentially limiting nutrient for plant growth, and associations with arbuscular mycorrhizal fungi (AMF) often enhance its uptake by plants. The fraction of soil P thought to be available for uptake by plants and AMF is that which is frequently extracted by NaHCO₃. We tested this assumption and also explored relationships between AMF community composition, soil P pools, and plant P storage. We visited 58 temperate agricultural grasslands in Germany and collected data on AMF diversity, P storage in aboveground biomass, and soil P availability in five fractions (NaHCO₃-P_i, NaHCO₃-P_o, NaOH-P_i, NaOH-P_o, and HCl-P) using the Hedley sequential extraction procedure. This is the first analysis of how AMF communities are structured by P availability to use such a comprehensive P profile. We performed redundancy analysis (RDA) corrected for spatial autocorrelation with principal coordinates of neighborhood matrices to test for effects of P availability on AMF community composition. We then ran path models to further clarify how AMF community composition was related to soil P pools and plant P storage.

Results/Conclusions

The contrast between labile (NaHCO₃-P_i, NaHCO₃-P_o, and NaOH-P_i) and recalcitrant (NaOH-P_o and HCl-P) P fractions was important for structuring AMF communities, but not the contrast between inorganic and organic forms of P. Our data suggest that AMF interactions with soil P pools and AMF contribution to plant P storage are regulated by independent processes. This therefore suggests taxonomic decoupling of two important AMF functions: P uptake from soil and P delivery to plants.