Department of Plant Science, The Pennsylvania State University, Tyson Building, University Park, PA, USA.
IBG2, Forschungszentrum Jülich, Jülich, Germany.
Ann Bot. 2018 Aug 27;122(3):485-499. doi: 10.1093/aob/mcy092.
Root architecture is a primary determinant of soil resource acquisition. We hypothesized that root architectural phenes will display both positive and negative interactions with each other for soil resource capture because of competition for internal resources and functional trade-offs in soil exploration.
We employed the functional-structural plant model SimRoot to explore how interactions among architectural phenes in common bean determine the acquisition of phosphate and nitrate, two key soil resources contrasting in mobility. We evaluated the utility of basal root whorl number (BRWN) when basal root growth angle, hypocotyl-borne roots and lateral root branching density (LRBD) were varied, under varying availability of phosphate and nitrate.
Three basal root whorls were optimal in most phenotypes. This optimum shifted towards greater values when LRBD decreased and to smaller numbers when LRBD increased. The maximum biomass accumulated for a given BRWN phenotype in a given limiting nutrient scenario depended upon root growth angle. Under phosphorus stress shallow phenotypes grew best, whereas under nitrate stress fanned phenotypes grew best. The effect of increased hypocotyl-borne roots depended upon BRWN as well as the limiting nutrient. Greater production of axial roots due to BRWN or hypocotyl-borne roots reduced rooting depth, leading to reduced biomass under nitrate-limiting conditions. Increased BRWN as well as greater LRBD increased root carbon consumption, resulting in reduced shoot biomass.
We conclude that the utility of a root architectural phenotype is determined by whether the constituent phenes are synergistic or antagonistic. Competition for internal resources and trade-offs for external resources result in multiple phenotypes being optimal under a given nutrient regime. We also find that no single phenotype is optimal across contrasting environments. These results have implications for understanding plant evolution and also for the breeding of more stress-tolerant crop phenotypes.
根系结构是获取土壤资源的主要决定因素。我们假设，由于内部资源竞争和土壤探测功能权衡，根系结构表型之间将表现出相互促进和相互抑制的作用，以获取土壤资源。
我们采用功能结构植物模型 SimRoot 来探讨普通豆科植物中结构表型之间的相互作用如何决定对两种关键土壤资源（磷和硝酸盐）的获取，这两种资源在流动性上存在差异。我们评估了在不同磷和硝酸盐供应条件下，当基本根轮数（BRWN）、胚轴根和侧根分支密度（LRBD）变化时，BRWN 的效用。
在大多数表型中，三个基本根轮数是最佳的。当 LRBD 减少时，最佳值向更大的方向移动，而当 LRBD 增加时，最佳值向更小的方向移动。在给定的限制养分情景下，给定 BRWN 表型下积累的最大生物量取决于根生长角度。在磷胁迫下，浅表型生长最好，而在硝酸盐胁迫下，扇形表型生长最好。增加胚轴根的效果取决于 BRWN 以及限制养分。由于 BRWN 或胚轴根的增加导致轴向根的产生增加，从而导致在硝酸盐限制条件下根系深度降低，生物量减少。BRWN 以及 LRBD 的增加增加了根的碳消耗，导致在氮限制条件下地上生物量减少。
我们得出的结论是，根系结构表型的效用取决于组成表型是协同的还是拮抗的。内部资源的竞争和外部资源的权衡导致在给定的养分条件下，多个表型是最佳的。我们还发现，没有单一的表型在对比环境下是最佳的。这些结果对于理解植物进化具有重要意义，也对培育更能耐受胁迫的作物表型具有重要意义。
