Bioaccessibility of phosphorus in the subsoil (SubsoilP)

植物需要量的10% ~ 80%来自地下土壤，但目前尚不清楚作物序列管理对地下土壤磷的形态和可及性的影响。本项目旨在(i)量化具有不同生物孔系统的中央田间试验（CeFiT）不同底土区室（CeFiT）的P储量和结合形式，（ii）阐明蚯蚓洞对底土层P吸收的贡献，以及（iii）测试土壤和植物磷酸盐δ18O特征作为追踪其来源和停留时间的新工具的可行性。样品取自根际、散装土壤、蚯蚓洞衬里和原根通道，分别来自中央大田试验（CeFiT）和中央微观试验（CeMiX）。通过顺序P提取程序、高分辨率元素映射和31P-NMR光谱来表征P的形式和浓度。使用33P和18O标记的磷酸盐进行同位素吸收和交换研究，以评估生物孔对P的吸收速率和土壤中磷酸盐的停留时间。

Plants may take up between 10 and 80 % of their P demand from subsoils, but the forms and accessibility of subsoil P as affected by crop sequence management are currently hardly understood. This project aims at (i) quantifying the P stocks and binding forms in different subsoil compartments of the central field trial (CeFiT) with varying biopore systems, (ii) elucidating the contribution of earthworm burrows to P uptake from subsoil horizons, and (iii) testing the feasibility of the δ18O signature of soil and plant phosphates as a novel tool for tracing back their origin and residence time. Samples are taken from rhizosphere, bulk soil, earthworm burrow linings and former root channels both from the central field trial (CeFiT) and central microcosm experiment (CeMiX). The P forms and concentrations are characterized by sequential P extraction procedures, high-resolution element mapping, and 31P-NMR spectroscopy. Isotope uptake and exchange studies using 33P and 18O labelled phosphate are used to evaluate P uptake rates from biopores and phosphate residence time in soil.