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

易获取的磷灰石资源枯竭以及无机和有机磷对次生矿物的吸附是老风化森林生态系统磷限制的主要方面。尽管有迹象表明，磷的吸收不是不可逆的，而且生命群落能够循环利用与矿物有关的磷，但其潜在的过程和控制因素仍然知之甚少。在这个项目中，我们将验证一个假设，即特别是在磷限制的生态系统中，植物微生物群落可以利用矿物结合的磷。我们假设，与磷单酯相比，次生矿物（尤其是吸收的正磷酸盐）对磷的利用效率更高，这是由于光合产物对具有风化活性的菌根和细菌的投资增加了。这种策略既适用于外生菌根化植物，也适用于与丛枝真菌共生的植物。因此，在不同磷供应的土壤中进行中生态试验，并添加额外的磷源，即吸附正磷酸盐和单磷酯的水合铁，将在森林Fagus sylvatica（外生菌根）和pseudoplatanus Acer（丛枝菌根）下进行。13CO2同位素标记和磷脂脂肪酸和低分子量有机酸的物质特异性13C分析以及酶活性测量将告知植物对微生物群落的投资以及风化剂作为土壤P有效性和P类型的函数。此外，磷酸盐的180 - o标记结合NanoSIMS应用将用于直接揭示矿物结合磷的利用。在野外暴露实验中，磷吸附配合物将被掩埋并孵育一年以验证中观结果。磷损失将通过x射线荧光和光电子能谱进行评估，所涉及的微生物群落将基于实时荧光定量PCR和454焦磷酸测序进行描述。所获得的数据将澄清从二次矿物中回收P是否是一个相关的过程，以及实现了哪些生命策略。

Depleted resources in easy accessible apatite as well as the sorption of inorganic and organic phosphorus (P) to secondary minerals are the main proposed aspects for P limitation of old weathered forest ecosystems. In spite of that indications exist that sorption of P is not irreversible and that life communities are capable to recycle mineral-associated P. But the underlying processes and controlling factors are still poorly known. In this project we will test the hypothesis that particularly in P-limited ecosystems plant-microbe communities can utilize mineral-bound P. We assume that a higher P use efficiency from secondary minerals, especially of sorbed orthophosphate in comparison to P monoesters, is due to an enhanced investment of photosynthates into weathering-active mycorrhiza and bacteria, with such a strategy being realized for both ectomycorrhized plants as well as for plants living in symbiosis with arbuscular fungi. Therefore, mesocosm experiments with soils varying in P supply and amended with additional P sources, i.e. ferrihydrite with adsorbed orthophosphate and P-monoesters, will be run under Fagus sylvatica (ectomycorrhiza) und Acer pseudoplatanus (arbuscular mycorrhiza). 13CO2 isotope labeling and substance-specific 13C analysis in phospholipid fatty acids and low-molecular weight organic acids as well as enzyme activity measurements will inform about the investment of plants into microbial communites as well as weathering agents as a function of soil P availability and P types present. Further, 18O-labeling of phosphate in combination with NanoSIMS application will be used to directly reveal the utilization of mineral-bound P. In a field exposure experiment, P adsorption complexes will be buried and incubated for one year to verify the mesocosms results. Phosphorus losses will be assessed by X-ray fluorescence and photoelectron spectroscopy and the involved microbial communities will be described based on quantitative real-time PCR and 454 pyrosequencing. The obtained data will clarify whether the recycling of P from secondary minerals is a relevant process and which strategies of life are realized.