根环境供氧状况对盐胁迫下棉花幼苗光合及离子吸收的影响

摘要

以溶液培养的棉花(Cossypium hirsutum L.)幼苗为材料,测定了不同盐胁迫程度和不同根环境供氧状况条件下棉花幼苗的叶片气体交换参数、叶绿素荧光参数和植株的Na+、K+离子含量等的变化,以探索根环境供氧状况对盐胁迫下棉花光合作用和离子吸收的影响.结果表明,盐胁迫和根环境供氧不足均导致净光合速率下降.在处理后的前期,盐胁迫对棉花叶片光合作用的不利影响大于供氧不足(不通气)的影响,而后期根环境供氧不足的不利影响快速增大,并逐渐超过盐胁迫的影响.在低浓度盐胁迫和根环境不通气处理的初期,棉花叶片光合速率下降的主要原因是气孔因素(气孔关闭或部分关闭引起的CO2供应不足);随着盐胁迫程度的增大和胁迫持续时间的延长,光合速率下降的原因逐渐转变为非气孔因素(光合系统损伤引起的光合能力下降).相同程度盐胁迫下,根环境通气处理的棉花叶片的净光合速率和PSⅡ最大光化学效率等均显著高于根环境不通气处理的,说明根环境供氧不足加重了盐胁迫对光合作用的不利影响.对棉花植株各器官离子积累量的测定、分析发现,盐胁迫导致了棉花根系拒Na+、吸K+的能力和选择性运输K+的能力降低,使棉花根系和叶片的Na+含量增多、K+含量减少、[Na+]/[K+]比值升高;而根环境通气则可显著提高盐胁迫下根系的拒Na+、吸K+能力和根系向叶片选择性运输K+的能力,降低根系和叶片的[Na+]/[K+]比值.试验还发现,根系K+、Na+含量受盐胁迫的影响较大,而叶片K+、Na+含量受根环境通气状况的影响更大一些.综合分析可见,盐胁迫和根环境供氧不足均可导致棉花叶片光合速率下降、光合机构损伤以及离子平衡失调,而根环境通气可以缓解盐胁迫对棉花叶片光合作用的不利影响、增加根系和叶片对K+的选择吸收和积累、降低[Na+]/[K+]比值,从而增强棉花植株对盐胁迫的适应性和抵抗力.%In this study,the effects of rhizosphere aeration on leaf photosynthesis and root ion absorption in hydroponically cultivated cotton seedlings under salt stress were investigated in terms of the changes in the leaf gas exchange parameters,chlorophyll fluorescence parameters,and Na+ and K+ contents.The results showed that net photosynthetic rates decreased under salt stress and hypoxia.In the early stages of stresses,salt stress caused a more severe effect on leaf photosynthesis than oxygen deficiency.In contrast,insufficient oxygen negatively affected leaf photosynthesis in the late stages of stress than salt stress.Under mild salt stress,the additional hypoxia stress resulted in a decrease in the net photosynthetic rate,mainly due to the stomatal factor (insufficient carbon dioxide resulting from stomata closure or contraction) rather than the effect of the photosynthetic apparatus.Non-stomatal factors (injury to the photosynthetic system) gradually lowered the net photosynthetic rate with intensified salt and prolonged hypoxia stresses.The net photosynthetic rates and maximum quantum efficiency of photosystem Ⅱ in cotton leaves under rhizosphere aeration were significantly higher than those in cotton leaves without rhizosphere aeration under the same salt stress.It was suggested that oxygen deficiency in the root environment worsened the adverse effect of salt stress on photosynthesis.Ion accumulation in different organs of cotton seedlings indicated that salt stress reduced the capability of K+ absorption,Na+ exclusion,and the selective transportation of K+,thus decreasing K+ content and increasing Na+ content and the [Na+] / [K+] ratio both in roots and leaves.However,rhizosphere aeration could significantly improve the above conditions induced by salt stress,and reduce the [Na+]/[K+] ratio.Moreover,K+ and Na+ contents in roots were more influenced by salt stress,whereas K+ and Na+ contents in leaves were more affected by rhizosphere aeration.In conclusion,salt stress and oxygen deficiency around roots can lead to the decline in the net photosynthetic rate,injury of photosynthetic apparatus,and a disorder in the ion balance in cotton seedlings.On the other hand,rhizosphere aeration could alleviate the adverse effects of salt stresses on photosynthesis,increase the selective absorption and accumulation of K+ in roots and leaves,thereby reducing the ratio of [Na+] / [K+],and improving the adaptability and resistance of cotton seedling to salt stress.