水淹导致皇冠草光合机构发生变化并加剧其出水后光抑制

通过气体交换和叶绿素荧光等方法研究了水淹及胁迫解除后皇冠草不同功能叶的光合特性及光抑制的变化.结果表明:与对照相比,气生叶(全淹组淹水前形成的功能叶)在水淹条件下叶片大小和气孔没有明显变化,但沉水叶(全淹组淹水后新生的功能叶)的叶面积增加,气孔变小,上表皮气孔密度增加.水淹导致气生叶碳同化能力、光化学效率和叶绿素含量下降.沉水叶在发育过程中碳同化能力、光化学效率和叶绿素逐渐升高.气生叶和沉水叶出水后其活体叶片在强光下的相对含水量急剧下降,发生明显的光抑制;而弱光下无明显光抑制发生.出水后离体叶片强光照射下6h后两种功能叶均发生严重光抑制,且弱光下不能恢复.因此,可以认为淹水条件下,沉水叶上表皮气孔密度的增加使其蒸腾速率提高;沉水叶较强的碳同化能力和增加的叶面积是确保其植株水下生存的重要因素;强光使气生叶和沉水叶出水后均发生严重光抑制,导度和蒸腾速率提高导致的叶片失水则加剧了这一过程,两者共同作用导致自然条件下两种功能叶的出水死亡.

Effects of submergence and subsequent re-emergence on photosynthetic characteristics and photoinhibition in Echinodorus amazonicus seedlings

Gas exchange and chlorophyll a fluorescence kinetics were used to explore photosynthetic characteristics during complete submergence and photoinhibition after subsequent re-emergence in Echinodorus amazonicus seedlings. After submergence, leaf area and stomata size of the leaves developed before submergence (referred to as "aerial leaves") showed no difference in comparison with that of control. But "submerged leaves" developed during submergence were enlarged and its stomata size was smaller than normal plants. However, the total number of stomata in submerged leaves was almost the same as that in control. In the submerged leaves, most stomata were distributed on the upper epidermis, thus the stomata conductance and transpiration rate increased gradually. During the submergence, carbon assimilation capacity, photochemistry efficiency and chlorophyll content decreased sharply in aerial leaves but increased gradually in submerged leaves with the development and maturation. After re-emergence, the relative water content (RWC) and the maximum photochemistry efficiency of photosystem Ⅱ (Fv/Fm) dropped sharply caused by strong irradiance both in aerial and submerged leaves;but all these parameters showed little changes under the weak light. In vitro, with sufficient water supply, serious photoinhibition still occurred both in aerial and submerged leaves when exposure to strong irradiance for 6 hours and this photoinhibition was not fully recovered even in the weak light. Based on above results, we suggested that keeping relative high carbon assimilation capacity and large leaf area in submerged leaves were the key causes to survive under submergence for Echinodorus amazonicus seedlings. For aerial and submerged leaves, strong light resulted in serious photoinhibition;excessive water loss result from increased stomata conductance and transpiration rate aggravated photoinhibition under high light. The combination of the two causes lead to the death of aerial and submerged leaves after re-emergence under natural conditions.