局部恢复供水对苗期玉米生长、根系吸收能力及解剖结构的影响

Effect of Partial Water Resupply at Seedling Stage on Maize Growth, Water Absorption Capacity and Anatomical Structure

【目的】作物对局部灌溉的响应研究已受到广泛关注,能否采用局部灌溉还需考虑局部灌溉前的土壤水分状况。研究水分亏缺后局部恢复供水下玉米生长、水分吸收的动态变化以及补偿效应的生理机制有重要意义。【方法】以聚乙二醇6000(polyethylene glycol 6000,PEG-6000)调控营养液的渗透势模拟水分亏缺,采用分根技术,通过水培试验模拟前期水分亏缺后局部根区恢复供水,设置3个水分亏缺程度(-0.2、-0.4、-0.6 MPa)和1个对照(无PEG),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和导水率状况,玉米干物质累积以及叶水势。并在此基础上,于处理后0、1、5、9 d连续动态测定对照和-0.2 MPa两个处理各根区根系解剖结构特征。【结果】水分亏缺6 d后局部恢复供水,恢复供水区根干重和导水率平均增长速率显著大于持续胁迫区(P<0.05);-0.2 MPa亏缺后局部恢复供水下,0—0.25 d时,恢复供水区根干重平均增长速率较对照明显增大(P<0.05),且持续到局部恢复供水后5 d,表现出根系生长的补偿效应;-0.4和-0.6 MPa亏缺后局部恢复供水处理分别于0.25—0.5 d和0.5—1 d时恢复供水区根干重平均增长速率较对照明显增大(P<0.05),产生根系生长的补偿效应,可见,根系生长的补偿效应发生随水分亏缺程度增大而延迟;-0.2 MPa亏缺后局部恢复供水5 d时,恢复供水区根系导水率平均增加速率恢复到对照水平,产生根系吸水的补偿效应,继续增大亏缺程度或延长恢复供水时间,补偿效应均消失,说明局部恢复供水有效刺激恢复供水区根系吸水补偿效应的临界水分亏缺程度为≥-0.2 MPa。此外,-0.2 MPa亏缺后局部恢复供水5 d,恢复供水区根系直径与导管直径显著小于1 d(P<0.05),但仍维持或超过对照水平,皮层厚度占根系直径的比例与对照无显著差异(P>0.05),9 d时,根系直径与导管直径明显减小(P<0.05),较对照减小19%,皮层厚度占根系直径的比例仍显著大于对照(P<0.05),与根系吸水补偿效应的产生与消失同步,从根系解剖结构特征方面揭示了恢复供水区根系吸水补偿效应的生理机制。【结论】局部恢复供水可有效刺激恢复供水区根系生长和吸水的补偿效应,但与局部恢复供水前水分亏缺程度和局部恢复供水时间有关,恢复供水区根系解剖结构的变化是补偿效应产生或消失的一个生理机制。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。

[Objective] Response of crops to partial water resupply has attracted more attention. It is necessary to investigate soil moisture condition previous partial root-zone irrigation when the technology of partial root-zone irrigation is applied. This study was aimed to identify the dynamics of maize growth and water absorption capacity under partial water resupply and the physiological mechanism of compensation effect. [Method] With the split-root technology, a hydroponic experiment was conducted to analyze non-stressed and stressed sub-root under partial water resupply, where the water stress was simulated by the osmotic potential of a nutrient solution （PEG-6000）. There were three water stress levels, i.e., -0.2 Mpa, -0.4 Mpa, -0.6 Mpa and a control treatment （no PEG）. The maize growth, root hydraulic conductance and leaf water potential were measured on the 0, 0.25, 0.5, 1, 3, 5, 7 and 9 day after partial water resupply （DAT）. [Result] Root growth rate and hydraulic conductance in non-stressed sub-root were higher than that in stressed sub-root under partial water resupply. Compared to control treatment, root dry weight growth rate in non-stressed sub-root was significantly enhanced during 0-5 DAT, 0.25-0.5 DAT and 0.5-1 DAT in -0.2, -0.4 and -0.6 Mpa treatments, respectively. Average increase rate of root hydraulic conductance in non-stressed had no significant difference at 5 DAT in -0.2 Mpa treatment if compared to control treatment, whereas it was significantly reduced in the whole treatment period in -0.4 and -0.6 Mpa treatments, indicating that the threshold of water stress previous partial water resupply for the compensatory effect of water uptake in non-stressed sub-root system was ≥-0.2 Mpa. Moreover, root diameter and vessel diameter in non-stressed sub-root was significantly reduced at 5 DAT compared with that of 1 DAT in -0.2 Mpa treatment, but it was maintained or higher than the level of control treatment. There was no significant difference in root cortex thickness/diameter ratio in non-stressed sub-root at 5 DAT between -0.2 Mpa and control treatments. At 9 DAT, compared to control treatment, root diameter and vessel diameter in non-stressed sub-root was significantly decreased by 19%, but cortex thickness/diameter ratio showed a reverse trend. [Conclusion]The compensatory effects of root growth and water uptake in non-stressed sub-root under partial water resupply were closely related to water stress severity and water resupply duration, which depended on root anatomical structure in non-stressed sub-root. Thus, the above conclusion provides theoretical support for regulating the interaction between plants and soil environment and making use of the potential plant response to soil water stress.