Plant-microbe strategies for utilization of mineral-associated P sources

During the first project phase we obtained evidence that P compounds adsorbed to secondary minerals like Fe and Al oxyhydroxides are a quantitatively relevant fraction of soil P in both acquiring and recycling ecosystems. Laboratory experiments suggested that P bound to minerals can be mobilized and utilized by microorganism to some extent but seemingly more under P-limited conditions where other P sources are rare. In order to investigate more detailed into plant-microbe strategies for utilization of mineral-associated P, our research during phase 2 involves experiments in mesocosms and in natural ecosystems. Therefore, mineral−P associations were prepared by loading goethite each with organic P (phytate) and inorganic P (phosphate) and were offered to plants and their microbial communities (mycorrhiza and bacteria). Field experiments are conducted at three forest sites along a P availability gradient (Bad Brückenau, Mitterfels, and Lüss). Mineral−P associations filled in fine mesh bags are exposed to the soils for one year. Afterwards, microbial colonization and net P mobilization will be quantified. In the mesocosm experiment, saplings of Fagus sylvatica were grown in pots filled with mixtures of P-poor Lüss soil and each one mineral−P association for two vegetation periods. Short before harvest, a 13C pulse labelling experiment was conducted in order to quantify photosynthate production and translocation. Additionally, plant P uptake and shifts in different soil P fractions will be quantified.