Zhu Jinming, Kaeppler Shawn M, Lynch Jonathan P
Department of Horticulture, Pennsylvania State University, University Park, PA 16802, USA.
Department of Agronomy, University of Wisconsin, Madison, WI 53706, USA.
Funct Plant Biol. 2005 Sep;32(8):749-762. doi: 10.1071/FP05005.
In soybean and common bean, enhanced topsoil foraging permitted by shallow root architectures is advantageous for phosphorus acquisition from stratified soils. The importance of this phenomenon in graminaceous crops, which have different root architecture and morphology from legumes, is unclear. In this study we evaluated the importance of shallow roots for phosphorus acquisition in maize (Zea mays L.). In a field study, maize genotypes with shallower roots had greater growth in low phosphorus soil than deep-rooted genotypes. For physiological analysis, four maize genotypes differing in root shallowness in the field were grown in solid media with stratified phosphorus availability in a controlled environment. Of the four genotypes, one shallow and one deep genotype were also inoculated with arbuscular mycorrhiza (AM). Shallower genotypes had significantly greater growth and phosphorus accumulation compared with deeper genotypes at low phosphorus availability. Mycorrhizal colonisation altered root shallowness under low phosphorus conditions, increasing shallowness substantially in a deep-rooted genotype but slightly decreasing shallowness in a shallow-rooted genotype. Mycorrhizal colonisation increased phosphorus acquisition under low phosphorus availability. Respiration costs of roots and shoots of phosphorus-efficient genotypes were significantly lower under low phosphorus conditions compared with inefficient genotypes. The physiological efficiency of phosphorus acquisition, expressed as root respiration per unit of phosphorus acquisition, was greater in shallow rooted genotypes. Our results demonstrate that genetic variation for root shallowness exists in maize, that phosphorus and AM can modulate root shallowness independently, and that a shallower root system is beneficial for plant performance in maize at low phosphorus availability. We propose that root architectural traits that enhance topsoil foraging are important traits for improved phosphorus acquisition efficiency of annual grain crops such as maize in addition to legumes.
在大豆和菜豆中，浅根系所允许的更强的表土觅食能力有利于从分层土壤中获取磷。这种现象在禾本科作物中的重要性尚不清楚，因为禾本科作物的根系结构和形态与豆科植物不同。在本研究中，我们评估了浅根对玉米（Zea mays L.）获取磷的重要性。在一项田间研究中，浅根玉米基因型在低磷土壤中的生长比深根基因型更好。为了进行生理分析，在可控环境下，将在田间根系深度不同的四种玉米基因型种植在具有分层磷有效性的固体培养基中。在这四种基因型中，一种浅根基因型和一种深根基因型还接种了丛枝菌根（AM）。在低磷有效性条件下，浅根基因型的生长和磷积累显著高于深根基因型。菌根定殖在低磷条件下改变了根系深度，使深根基因型的根系深度大幅增加，而浅根基因型的根系深度略有降低。菌根定殖在低磷有效性条件下增加了磷的获取。与低效基因型相比，磷高效基因型的根和地上部分在低磷条件下的呼吸成本显著更低。以单位磷获取量的根系呼吸表示的磷获取生理效率，在浅根基因型中更高。我们的结果表明，玉米中存在根系深度的遗传变异，磷和AM可以独立调节根系深度，并且较浅的根系系统有利于玉米在低磷有效性条件下的生长表现。我们提出，除了豆科植物外，增强表土觅食的根系结构性状对于提高一年生谷类作物如玉米的磷获取效率是重要性状。
