水盐胁迫下棉花叶片光合的气孔与非气孔限制

Reduction in Photosynthesis of Cotton Seedling under Water and Salinity Stresses is Induced by both Stomatal and Non-stomatal Limitations

【目的】明确水盐胁迫下植物叶片光合过程受抑制的因素。【方法】在人工气候室内,设置无胁迫(T1)、水分胁迫处理(T2)、盐分胁迫处理(T3)和水盐胁迫处理(T4),研究了不同胁迫处理对棉花叶片气孔特征与色素量、叶片光合速率以及荧光参数的影响。【结果】与T1处理相比,T2处理并没有显著降低棉花叶片气孔的长度和宽度,但却显著降低了气孔密度;而T3处理和T4处理则显著降低了棉花叶片的气孔特征(密度、宽度和长度),T3处理和T4处理间差异并不显著。不同胁迫处理均较T1处理显著降低了棉花叶片的色素量(叶绿素a、叶绿素b和类胡萝卜素),但T3处理和T4处理只在类胡萝卜素量存在显著差异。不同胁迫处理均显著降低了棉花叶片的光合速率,T2—T4处理的气孔限制和叶肉限制的平均值分别为0.38和0.35,表明水盐胁迫条件下,棉花叶片光合速率降低主要受气孔和叶肉限制。当棉花叶片光合性能受到抑制时,植株主要通过热耗散途径来消除过剩能量。【结论】在水分和盐分胁迫条件下,棉花叶片光合性能受气孔限制和非气孔限制的共同影响。

【Background】 Drought and salinity are two common abiotic stresses facing agricultural production in arid and semi-arid regions and salt-affected regions.An elevated soil salt content is lethal to plant growth, which reduce plant productivity of irrigated agriculture worldwide by about 20%.NaCl-induced soil salinity has attracted increased concern for its impact on non-halophytic plants as it alters plant metabolism due to its ion toxicity and the increased osmotic potential.Cotton, as the largest fiber source for textile, is a crop with moderate salt-tolerance, but salinity exceeding a certain level could still impede its growth and development dramatically, especially for salinity occurring at seedling stage, by inhibiting the photosynthesis.Reduction in photosynthesis is the most important response of cotton to water and salinity stresses, but the mechanisms underlying the relative significance of stomatal restriction and non-stomatal restriction in this reduction remains obscure despite its importance in sustaining cotton production.【Objective】This paper aims to experimentally investigate the response of photosynthesis of cotton seedlings to water and salinity stresses in both isolation and combination.【Method】Pot experiments were conducted in a phytotron to examine the effects of different water and salinity stresses on stomatal characteristics, pigment content, photosynthetic rate and chlorophyll fluorescence of cotton seedling.We compared four treatments: water stress only(T2), salinity stress only(T3), combining water and salinity stress(T4), with the absence of any stresses taken as the control(CK).【Result】Compared to CK, T1 did not reduce the length and width of the stomata at significant level, but reduced the stomatal density markedly.In contrast, T3 and T4 reduced the length, width and density of the stomata at significant level despite the difference between T3 and T4 being insignificant.In addition to reducing photosynthetic rate, all treatments also reduced the contents of chlorophyll a and b, as well as the carotenoid in the leaves at significant level.The difference in carotenoid content between T3 and T4 was significant.The photosynthesis in CK was reduced mainly by biochemical characteristics;the average stomatal and mesophyll limitations in photosynthesis under T2—T4 was 0.38 and 0.35 respectively, indicating that the decline in photosynthesis was primarily due to the stomatal and mesophyll limitation.When photosynthesis was inhibited, the cotton seedlings dissipated excessive energy via heat dissipation.【Conclusion】Under water and salinity stresses, the photosynthesis of cotton seedling was inhibited by stomatal and mesophyll limitation.