Soil microbial necromass as an essential phosphorus reservoir in forest nutrition

森林生态系统通过利用最低限度可获得的无机和有机磷形式并将磷保留在生态系统内，成功地应对了低磷供应的挑战。微生物有效地动员植物难以获得的P，但也与植物竞争P。虽然微生物生物和necromass可以占土壤总P的10%以上，他们很少被认为是主要的P贡献者森林P营养。该建议旨在解开的相关性微生物生物和necromass作为P池山毛榉P营养的特征的空间异质性的P分布在森林生态系统和对比P循环在收购与回收森林生态系统。根据森林土壤中磷的有效性和形态分析了单个微生物类群在磷（im）动员、减少磷流失和微生物坏死体磷（Pnecro）再动员中的作用。通过用KH 233 PO 4标记土壤和植物，通过灯芯法在围隔生态系统中定量分析了微生物生物量中根沉积磷和土壤溶液磷的固定。在模拟降雨事件后，溶解有机磷和胶体排放将被量化和表征。微生物磷保留和微生物组占磷固定将确定氯仿熏蒸提取（33 P-CFE）和33 P磷脂脂肪酸（33 P-PLFA）分析。为了确定Pnecro的来源，将在随后的孵育实验中用33 P-CFE和33 P-PLFA分析来靶向来自低可用P源（33 P磷灰石、Fe-33 P-磷酸盐和33 P植物残留物）的微生物P形成。微生物稀释将揭示微生物群落内的功能冗余和专业化。Pnecro源识别后，其功能作为一个中间的磷水库森林营养将评估应用33 P标记的微生物necromass。季节性收获的根际实验与非均匀分布的Pnecro将使P再动员在山毛榉根际33 P成像和磷酸酶酶谱可视化。T形围隔将允许定量测定Pnecro的贡献山毛榉营养与茎的距离增加，特别是考虑外生菌根作为替代Pnecro吸收途径。在中央P x N施用实验中，在离茎的距离增加的情况下分析PLFA、CFE和磷酸酶活性将允许将这些关于Pnecro作用的结果转移到田间尺度的单树影响圈。微生物坏死团作为中间磷库的功能及其在森林磷营养中的作用将在拟议的项目中进行评估，考虑到不同磷有效性的地点，物种形成了解森林土壤中微生物坏死体磷的空间和季节动态将从根本上提高我们对森林生态系统面对低磷供应能力的认识。

Forest ecosystems successfully meet the challenge of low phosphorous (P) supply by exploiting minimally accessible inorganic and organic P forms and retaining P within ecosystems. Microorganisms efficiently mobilize plant inaccessible P but also compete with plants for P. Although microbial bio- and necromass can account for greater than 10% of total soil P, they rarely were considered as primary P contributors to forest P nutrition. This proposal seeks to unravel the relevance of microbial bio- and necromass as P pools for beech P nutrition by characterizing the spatial heterogeneity of P distribution in forest ecosystems and contrasting P cycling in acquiring versus recycling forest ecosystems. The role of individual microbial groups in P (im)mobilization, reduction of P losses via leaching and re-mobilization of microbial necromass P (Pnecro) will be analyzed depending on P availability and speciation in forest soils.Immobilization of rhizodeposit P and soil solution phosphate in microbial biomass will be quantified in mesocosms by labeling of soils with KH233PO4 and plants via the wick method. After simulating rainfall events, dissolved organic P and colloidal discharge will be quantified and characterized. Microbial P retention and microbial groups accounting for P immobilization will be determined by chloroform fumigation extraction (33P-CFE) and 33P phospholipid fatty acid (33P-PLFA) analysis. To determine sources of Pnecro, microbial P formation from low available P sources (33P apatite, Fe-33P-phosphate and 33P plant residues) will be targeted in a subsequent incubation experiment with 33P-CFE and 33P-PLFA analysis. Microbial dilution will reveal functional redundancy and specialization within microbial communities. Following identification of Pnecro sources, their functions as an intermediate P reservoir for forest nutrition will be assessed by application of 33P-labelled microbial necromass. A seasonally harvested rhizotron experiment with heterogeneously distributed Pnecro will enable visualization of P re-mobilization in beech rhizosphere by 33P imaging and phosphatase zymography. T-shaped mesocosms will allow quantitative determination of Pnecro contribution to beech nutrition with increasing distance to the stem, especially considering ectomycorrhiza as an alternative Pnecro uptake pathway. Within the central P x N application experiment, PLFA, CFE and phosphatase activity analyzed at increasing distance to the stem will allow transferring these results on the role of Pnecro to single tree influence circles at the field scale.Consequently, functions of microbial necromass as an intermediate P reservoir and its role in forest P nutrition will be assessed within the proposed project considering sites of contrasting P availability and speciation. Understanding spatial and seasonal dynamics of microbial necromass P in forest soils will fundamentally enhance our understanding of forest ecosystems capability to face low P supply.