Bioaccessibility and bioavailability of subsoil P

在我们目前的研究中，我们发现磷在底土生物孔系统中富集，但在大块底土中不具有生物可及性。后一结论的证据来自于缺少土壤中磷酸盐和土壤水之间的同位素平衡。该项目的设计目的不是为了验证以下假设：(i)磷酸盐的δ ta18o特征表明生物孔壁中磷的生物可及性高于普通土壤；（ii）地下土壤根系可能很容易从矿物质中获取磷；（iii）植物磷酸盐至少部分反映了土壤磷酸盐的δ ta18o特征；（iv）当表层土壤缺乏养分和水分时，地下土壤磷的吸收程度会增加。(v)在R-SWMS中可以实现热点地区更高的磷可达性，从而可以更精确地估计从底土中吸收的磷。为了实现这些目标，我们将在土壤磷酸盐和水之间进行18O同位素交换实验，用土壤和三标记磷灰石（44Ca, 33P, 18O）进行放射性和稳定同位素示踪实验，以及根系养分获取的数值模拟。

In our current studies we found that P is enriched in subsoil biopore systems but not bioaccessible in the bulk subsoil. Evidence for the latter conclusions was derived by missing isotope equilibria between subsoil phosphates and soil water. This project was no designed to test the hypotheses that (i) the delta18O signature of phosphates indicate higher bioaccessibility of P in biopore walls than in the bulk soil, (ii) subsoil roots may readily acquire P from minerals, (iii) plant phosphates reflect at least partly the delta18O signature of soil phosphates, (iv) the degree of subsoil P uptake increases when the surface soil is deficient in nutrients and water, and that (v) higher P-accessibility in hotspots can be implemented in R-SWMS, allowing for estimating P uptake from the subsoil more precisely. To achieve these goals we will apply 18O isotope exchange experiments between soil phosphates and water, perform radioactive and stable isotope tracing experiments with soil and triple-labeled apatite (44Ca, 33P, 18O) as well as a numerical modeling of nutrient acquisition by the roots.