Phosphorus (P) is usually stratified in the topsoil layer under pasture, due to the broadcast application of fertiliser, excreta and leaf-litter deposition on the soil surface, and minimal soil disturbance. The objective of this study was to investigate root proliferation and P acquisition in response to P stratification by comparing two Trifolium subterraneum cultivars with contrasting root morphologies. Clover micro-swards were grown with deficient, constrained and sufficient P supplied in a topsoil layer overlying a P-deficient subsoil that mimicked the stratification of P that occurs under pasture. Phosphorus labelled with 33P- and 32P-radioisotope tracer was mixed throughout the topsoil and subsoil layers, respectively. The shoot yield and total plant P uptake of the cultivars increased in response to increased topsoil P supply. The length of roots produced by the cultivars was equivalent in each of the P treatments, although the specific root length achieved by the cultivars was substantially different. In the P-constrained and P-sufficient treatments, ~91% and ~ 99% of total plant P was acquired by topsoil roots, respectively. In contrast, subsoil roots acquired 60–74% of total plant P in the P-deficient treatment. Topsoil roots were most important for P acquisition when P was highly stratified, whereas subsoil roots contributed to P acquisition when P was uniformly distributed throughout the P-deficient soil profile. Selection for prolific nutrient-foraging roots, in conjunction with plasticity for subsoil exploration, may improve the P-acquisition efficiency of T. subterraneum genotypes and confer adaptability across a range of soil-P environments.

中文翻译：

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两种不同的三叶草地下栽培品种对土壤磷分层响应的根系增殖和磷获取

磷（P）通常在牧场下的表土层中分层，这是由于施肥、排泄物和凋落物沉积在土壤表面，以及最小的土壤干扰。本研究的目的是通过比较两种具有对比根形态的三叶草栽培品种，研究响应磷分层的根增殖和磷获取。三叶草微型草丛在表土层中供应不足、受限和充足的磷，覆盖在缺磷底土上，模拟了牧场下发生的磷分层。用 33P- 和 32P- 放射性同位素示踪剂标记的磷分别混合在整个表土和底土层中。随着表土磷供应的增加，栽培品种的芽产量和植物总磷吸收增加。在每个 P 处理中，由栽培品种产生的根长是相等的，尽管由栽培品种获得的特定根长有显着差异。在磷限制和磷充足的处理中，表土根系分别获得了植物总磷的~91% 和~99%。相比之下，在缺磷处理中，底土根获得了植物总磷的 60-74%。当磷高度分层时，表土根对磷的获取最重要，而当磷在整个缺磷土壤剖面中均匀分布时，底土根对磷的获取有贡献。选择多产的营养觅食根，结合底土勘探的可塑性，可以提高 T. subterraneum 基因型的磷获取效率，并赋予对一系列土壤磷环境的适应性。