水分亏缺下紫花苜蓿和高粱根系水力学导度 与水分利用效率的关系

利用聚乙二醇(PEG-6000)模拟水分亏缺条件(胁迫水势-0.2MPa,胁迫48h),研究了变水条件下紫花苜蓿(品种:阿尔冈金和陇东)和高粱(品种:抗四)根系水力学导度(Lp_r)、根系活力、根叶相对含水量、水分利用效率等参数的动态变化,以期进一步明确植物水分吸收及散失过程调控的生理生态学基础。结果表明:水分亏缺限制了紫花苜蓿和高粱根系吸水,表现在Lp_r的下降和根系活力的降低;继而调控了其地上部反应,引起气孔导度、光合速率、叶片相对含水量和蒸腾速率等的下降,但限制性的提高了其水分利用效率,尤其在胁迫初期。恢复到正常供水条件后,Lp_r、根系活性、气孔导度等水分利用参数逐渐部分或完全恢复到了胁迫前水平,但恢复程度存在种间和品种间差异,并且根系吸水能力的恢复对于是植株地上部生长状态的恢复至关重要,尤其是水分恢复初期。紫花苜蓿根系中检测到水通道蛋白(AQPs)的存在,水分亏缺对紫花苜蓿Lp_r的影响认为主要是通过影响AQPs的活性实现的。比较紫花苜蓿和高粱水分吸收与利用状况在变水条件下的动态变化,认为紫花苜蓿幼苗对干旱逆境的适应能力相对弱于高粱,品种间陇东适应能力更强。

The root system hydraulic conductivity and water use efficiency of alfalfa and sorghum under water deficit

How to absorb more water and consume less water for plant has become increasingly more important because of water shortage. Root system is essential to uptake water from soil and stomata are important tissues to dismiss water for plant growth. However, one of great challenges in agricultural production is how to balance water absorption by roots and water use by shoots, especially under water deficit. In this paper we are focus on the regulating mechanism between roots water absorption and shoots water consumption, to clarify eco-physiological basis of drought resistance and understand the adaptive traits to drought stress. In drought-stressed plants, roots system hydraulic conductivity (Lp_r), roots vigor, relative water content of leave and roots, water use efficiency and some parameters dedicated water use characteristics, such as stomatal conductivity, net photosynthetic rate, intercellular CO₂ concentration and transpiration rate, etc. of alfalfa (Medicago sativa L cultivars: Algonquin and Long-Dong) and sorghum (Sorghum bicolor L. cultivars: Kang-Si) were studied. Under variable water conditions of mimicked by PEG-6000, when tested plants undergo for 48 h stress (-0.2MPa water potential) and subsequent water recovery of 48 h, the experimental results indicated that roots water absorption (Lp_r) affected vitally water use and photosynthesis of shoots, especially at primary of water deficit and water recovery. Water absorption of alfalfa and sorghum was inhibited firstly by water deficit companying with decrease of Lp_r and root vigor and then, decline of stomatal conductivity. Net photosynthetic rate, relative water content of leave and transpiration rate etc. were induced. On the other hand, a limited increased in water use efficiency not in sorghum but in alfalfa are observed. It also shows that water deficit affect alfalfa stronger than that of sorghum. After rewatering from stress, Lp_r, root vigor, other parameters related to water characteristics (stomatal conductivity, net photosynthetic rate, relative water content of leave and transpiration rate and so on) and water use efficiency recovered gradually to the level of control treatment partly in alfalfa and completely in sorghum. These changes show that variable water conditions induced some significant differences, such as roots water absorption and shoots water consumption between two specie as well as two cultures. In this experiment, we also checked the role of aquaporins (AQPs) in alfalfa roots, results indicate that water deficit decrease Lp_r of alfalfa through inhibiting activity of AQPs. Comparing to the change extents of alfalfa and sorghum in Lp_r and other water parameters under variable water conditions, alfalfa is more sensitive to water stress than sorghum, and Algonquin is more sensitive than Long-Dong. All these data could increase our better understanding on the adaptive mechanism to drought and control role of root water absorption in water balance of alfalfa and sorghum.