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矿体系统中是富含的，但在大部分底土中是不可生物获取的。后一结论的证据来自于底土磷酸盐和土壤水之间缺失的同位素平衡。这个项目不是为了测试假设：(I)磷酸盐的delta18O特征表明生物矿壁中磷的生物可获得性高于土壤，(Ii)地下根系可以很容易地从矿物中获取磷，(Iii)植物磷酸盐至少部分反映了土壤磷酸盐的delta18O特征，(Iv)当表层土壤缺乏养分和水分时，底层土壤的磷吸收程度增加，以及(V)R-SWMS可以实现热点地区更高的磷可及性，从而能够更准确地估计底层土壤的磷吸收。为了实现这些目标，我们将应用土壤磷酸盐和水之间的18O同位素交换实验，对土壤和三标记磷灰石(44Ca，33P，18O)进行放射性和稳定的同位素示踪实验，以及根部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.