水分和磷对苗期玉米根系形态和磷吸收的耦合效应

摘要

Although water deficit and soil phosphorus (P) deficiency are key limiting factors of maize production, it still remains unclear how water and P regulate maize root morphology and P uptake. In this study, a pot experiment was carried out to explore the coupled effects of water and P on maize root growth and P uptake under four water gradients [35% (W1), 55% (W2), 75% (W3), 100% (W4) of field capacity] and two P treatments [high P of 205 mg(P)kg1(soil) and low P of 11 mg(P)kg1(soil)]. The results showed that irrespective of P supply, shoot dry weight (SDW), root dry weight (RDW), total root length (TRL) and root surface area (RSA) initially increased and then decreased with increasing water supply. This trend was similar to trend in soil available P content. Root mass ratio (RMR) and average root diameter (ARD) declined, while shoot P content and accumulation steadily increased with increasing water supply. There were both adverse effects of water deficit and excess water supply on root growth and dry matter accumulation of maize. While soil P acquisition was inhibited by water deficit (W1), it was greatly improved by excess water supply (W4). Slight water stress (W2) increased maize root growth and dry matter accumulation, but decrease excess soil P uptake. Adequate water supply (W3) simultaneously improved maize root growth, dry matter accumulation and soil P uptake. P application obviously increased SDW, RDW (except for in W4 treatment), TRL, RSA, P content (except for in W4) and total P accumulation in plant, but decreased RMR. Two-way analysis of variance showed that the relative contribution of water to SDW, RDW, RMR, TRL, RSA, ARD, shoot P content, shoot P accumulation and soil available P content were 45.94%, 36.71%, 67.95%, 59.63%, 58.34%, 81.86%, 24.75%, 35.66% and 3.00%, respectively. The relative contributions of P to the above parameters were 34.78%, 21.19%, 14.84%, 9.22%, 9.21%, 1.56%, 35.54%, 49.75% and 94.40%, respectively. It was clear that water was more important for the regulation of maize root morphology and dry matter accumulation, and P was more important for the regulation of P absorption in maize aerial parts and soil available P content. In all, the acquisition of soil P by maize root was connected with root morphology-oriented adaptations under low P, but was connected with root physiology-oriented adaptations under high P. An appropriate coupling of water and P improved root growth and dry matter accumulation, and decreased excess soil P uptake by maize root.%水分亏缺和土壤缺磷已经成为玉米(Zea mays L.)生产的主要限制性因素，但水分和磷如何调节玉米根系形态和磷吸收尚不完全清楚。本研究采用盆栽土培试验，设置4个水分梯度[田间持水量的35%(W1)、55%(W2)、75%(W3)和100%(W4)]和2个磷处理[高磷：205 mg(P)·kg1；低磷：11 mg(P)·kg1]，探究水分和磷对苗期玉米根系生长和磷吸收的耦合效应。结果表明：(1)不管土壤磷供应如何，玉米苗干重、根干重、总根长和根表面积随水分供应强度的增加呈现先增加后降低的趋势，土壤有效磷含量也表现出相似的变化趋势，根质量比和平均根直径随水分供应强度的增加呈现下降的趋势，植株磷含量和磷累积量随水分供应强度的增加呈现稳定增加的趋势；(2)水分亏缺(W1)和过量供应(W4)均不利于玉米根系生长和干物质累积，水分亏缺(W1)抑制玉米对土壤磷素的获取，水分过量供应(W4)引起土壤磷素的奢侈吸收(W4)，轻度的水分胁迫(W2)能够促进玉米根系的生长和干物质累积，减少对土壤磷的奢侈吸收，充足的水分供应(W3)能够促进玉米根系的生长、干物质累积和土壤磷素的吸收；(3)磷供应显著增加了玉米苗干重、根干重(W4除外)、总根长、根表面积、植株磷含量(W4除外)和磷累积量，但降低了玉米的根质量比。(4)两因素方差分析结果表明，水分对苗干重、根干重、根质量比、总根长、根表面积、平均根直径、植株磷含量、植株磷累积量和土壤有效磷含量的相对贡献分别为45.94%、36.71%、67.95%、59.63%、58.34%、81.86%、24.75%、35.66%和3.00%，磷对这些参数的相对贡献分别为34.78%、21.19%、14.84%、9.22%、9.21%、1.56%、35.54%、49.75%和94.40%，可见水分是控制玉米根系形态和干物质累积的关键因子，磷是控制玉米地上磷吸收和土壤有效磷含量的关键因子。总体来说，低磷条件下玉米根系对土壤磷的获取偏向于以根形态为主导的适应策略，高磷条件下玉米根系对土壤磷的获取偏向于以根生理吸收为主导的适应策略。水分和磷之间较好的耦合能够促进玉米根系生长、干物质累积，减少对土壤磷素的奢侈吸收。