大田遮阴对夏玉米光合特性和叶黄素循环的影响

Effects of Shading on Photosynthetic Characteristics and Xanthophyll Cycle of Summer Maize in the Field

以郑单958和振杰2号为试验材料,大田条件下设置花粒期遮阴(S1)、穗期遮阴(S2)、全生育期遮阴(S3)3个处理,遮光度为60%,以自然光照为对照,研究遮阴对夏玉米光合特性和叶黄素循环的影响。结果表明,遮阴后夏玉米产量显著降低,且遮阴时期对产量的影响表现为S3>S1>S2,郑单958和振杰2号的S3分别减产96.87%和90.78%。遮阴后叶片的光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、叶绿体色素含量显著降低,胞间CO2浓度(Ci)较同期对照先降低后升高,即叶片光合作用的降低受到气孔与非气孔因素双重影响,2个供试品种变化一致。遮阴期间光合电子传递量子效率(ФPSⅡ)降低,原初光能转换效率(Fv/Fm)和非光化学猝灭(NPQ)显著升高,叶黄素循环库(A+Z+V)和脱环化状态(A+Z)/(A+Z+V)升高,即在长期遮阴条件下叶片捕获的光能分配发生了变化,光合电子传递的能量占吸收光能的比例降低,叶黄素循环的启动辅助过剩光能的热耗散。遮阴结束初期(A+Z)/(A+Z+V)和NPQ迅速升高,说明光恢复初期叶片对弱光适应后的自然光照比较敏感,叶黄素循环增强抑制强光对光合机构的破坏。

A field experiment was conducted to study the effects of shading on photosynthetic characteristic and xanthophyll cycle of summer maize. One non-shading treatment was used as control and three shading treatments with a shading degree of 60% were designed in growing period ranging from tasseling to maturity （S 1）, from jointing to tasseling stage （S2） and whole growing period （S3）, respectively. Two cultivars Zhengdan 958 and Zhenjie 2 were used as experimental materials. Results showed that grain yield decreased significantly under shading condition. Effects of different shading treatments on grain yield showed $3 〉 S 1 〉 S2, and there was a yield reduction of 96.87% and 90.78% for Zhengdan 958 and Zhenjie 2 in S3. Compared with CK, photo- synthetic rate （Pn）, transpiration rate （Tr）, stomatal conductance （Gs）, chlorophyll content decreased and the intercellular CO2 con- centration （Ci） increased at first and then decreased, with the rame tendency for two maize cultivars. The stomatal factor and the non-stomata factor had double impacts decreasing photosynthesis. The actual photo-chemical efficiency （ФPSII）, the xanthophyll cycle pool （A＋Z＋V） and the de-epoxidation extent of xanthophyll cycle （A＋Z）/（A＋Z＋V） increased, and the maximal photo- chemical efficiency （Fv/Fm） and non-photochemical quenching （NPQ） increased. In other words, in a long time shading, the dis- tribution of sunlight captured by leaves changed and the start of the xanthophyll cycle promoted the heat dissipation of excess light energy. Meanwhile, the ratio of the energy of photosynthetic electron transport to the absorbed light reduced. Finally, the （A＋Z）/（A＋Z＋V） and NPQ increased rapidly in early days after ceasing shading, showing that leaves adapted shading are sensitive to normal illumination in initial stage of light recovery and the enhancement of xanthophyll cycle restrains the damage of photo- synthetic structure by sunlight.