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

易获取的磷灰石资源的枯竭以及无机磷和有机磷对次生矿物的吸附是风化老森林生态系统限制磷的主要方面。尽管有迹象表明，磷的吸收不是不可逆转的，生命群落能够循环利用与矿物相关的磷，但其潜在的过程和控制因素仍然知之甚少。在这个项目中，我们将检验这一假设，特别是在磷有限的生态系统中，植物-微生物群落可以利用矿物质结合的磷。我们假设次生矿物，特别是吸附的正磷酸盐的磷利用效率比P单酯高，这是因为光合作用增加了对具有风化活性的菌根和细菌的投资，这一策略在外生菌皮化植物和与丛枝真菌共生的植物中都实现了。因此，对不同磷供应并添加额外磷源(即吸附了正磷酸盐和P-单酯的亚铁水合物)的土壤进行的中观试验将在野油茶(外生菌根)和枫树(丛枝菌根)下进行。磷脂脂肪酸和低分子有机酸中的13CO2同位素标记和特定物质的13C分析以及酶活性的测量将根据土壤磷的有效性和存在的磷类型来了解植物对微生物群落和风化剂的投资。此外，~(18)O标记磷酸盐结合NanoSIMS的应用将被用来直接揭示矿物结合磷的利用。在野外暴露实验中，磷吸附复合体将被埋藏并孵化一年以验证介孔结果。磷的损失将通过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定量聚合酶链式反应和454焦磷酸测序进行描述。所获得的数据将澄清从次生矿物中回收磷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.