适度局部水分胁迫提高玉米根系吸水能力

局部根区灌溉可以刺激灌水区根系吸水的补偿效应。为了揭示局部灌溉条件下玉米根系补偿效应的动态变化及其影响因素,以聚乙二醇6000(polyethylene glycol 6000,PEG-6000)营养液的渗透势模拟水分胁迫,采用分根技术,通过水培试验模拟局部根区水分胁迫,设置3个水分胁迫程度处理(-0.2、-0.4、-0.6 MPa)和1个对照处理(无营养液),于处理后0、0.25、0.5、1、3、5、7、9 d连续动态监测各根区根系的生长及导水率。结果表明,局部根区受中度及其以下(≥-0.6 MPa)经水分胁迫0.25 d内,所有处理胁迫区根系总导水率和单位根长导水率均与非胁迫区和对照无显著差异(P0.05)。胁迫持续时间超过0.25 d,胁迫区根系总导水率和单位根长导水率均显著小于非胁迫区(P0.05),降低程度随水分胁迫程度而增大,各处理间胁迫区根系总导水率的差异随胁迫持续时间延长也逐渐增大。对于非胁迫区,轻度胁迫(-0.2 MPa)持续0.5 d,单位根长导水率较对照高10.11%(P0.05),1~9 d与对照持平;-0.4 MPa胁迫持续9 d,单位根长导水率为25.08×10-11 m2/(MPa·s),显著高于对照(P0.05);中度胁迫(-0.6 MPa)持续0.5~3 d单位根长导水率显著小于对照(P0.05),较对照低19.05%~40.11%,5 d后与对照持平。说明局部根区水分胁迫能有效刺激非胁迫区根系吸水的补偿效应,这种补偿作用在局部水分胁迫0.5 d时就已发生,受到局部水分胁迫程度和持续时间的影响,且根系吸水补偿效应的临界胁迫程度为≥-0.4 MPa。该研究可为更好的发挥局部灌溉在农业节水中的作用提供理论依据。

Appropriate partial water stress improving maize root absorbing capacity

Abstract: Partial root-zone irrigation can stimulate the compensation effect of root water uptake at the irrigated zone. Plants can compensate for water stress in one part of the root zone by taking up water from other parts of the root zone where water is available. This study aimed to identify the dynamics and influencing factors of the compensation effect of maize roots (Zea mays L. hybrid cv. Aoyu No. 3007) under partial root zone irrigation. With the split-root technology, we conducted a hydroponic experiment to analyze the root zone water stress that was simulated by the osmotic potential of a nutrient solution (PEG-6000). There were 3 water stress levels, -0.2 (mild water stress), -0.4, -0.6 MPa (moderate water stress), and a control treatment (control, both sides of the root zone supplied with sufficient water). The root growth and hydraulic conductance of each root zone were measured at 0, 0.25, 0.5, 1, 3, 5, 7 and 9 d after the experiment started. Within 0.25 d after the experiment start, the total hydraulic conductance and the hydraulic conductance per root length between the two root zones in all three treatments and control were not significantly different (P>0.05) if the water stress was less than -0.6 MPa. When the partial water stress lasted more than 0.25 d, the total hydraulic conductance and the hydraulic conductance per root length in stressed root zone were lower (P<0.05) than that in the non-stressed root zone. Compared with non-stressed root zone, the reduction rate of root hydraulic conductance in the stressed root zone was significantly (P<0.05) increased with the increase in partial water stress degree and duration. At five days, compared to the root hydraulic conductance per root length in the non-stressed root zone, the corresponding value in the stressed root zone for the treatments -0.2, -0.4 and -0.6 MPa decreased by 32.70%, 49.90% and 50.97%, respectively. Within 0.25 d after the experiment start, for the treatment -0.4 and -0.6 MPa, the total hydraulic conductance in the stressed root zone reduced by 20% and 30% compare with the treatment -0.2 MPa. Twelve hours after the experiment start, the hydraulic conductance per root length in the non-stressed root zone for the treatment -0.2 MPa increased by 10.11% compared to control, and recovered to control level after 1 d. On the ninth day, the hydraulic conductance per root length in the non-stress root zone for the treatment -0.4 MPa (25.08×10-11 m2/(MPa·s)) was significantly greater (P<0.05) than that for control, indicating this treatment had an obvious compensation effect on root water uptake. However, the corresponding value for the treatment -0.6 MPa reduced by 19.05%-40.11% after 0.5 d, which recovered to the level of control after 5 d. The results indicated that the compensation effect of root water uptake in the non-stress zone can be effectively stimulated. The compensation effect started to occur at 0.5 d after the experiment start and was affected by the degree and duration of the water stress. -0.4 MPa was the threshold of partial root zone water stress for effectively stimulating compensatory effect of root water absorption in non-stressed root zone.