漓江上游毛竹生理生态特征对不同土壤水分的响应

漓江上游毛竹林面积大,是我国毛竹最南端产区。该研究针对当地季节性干旱问题,通过模拟降水使土壤水分变化,共设立了5个毛竹水分处理小区(CK.对照;A.无降水+覆膜;B.降水5 mm+覆膜;C.降水10mm+覆膜;D.降水20 mm+覆膜),并与HM(木荷Schima superba)(自然状态)进行对比。结果表明:土壤水分变化影响了毛竹叶片水势和叶绿素的变化,叶片白天水势下降,傍晚均可恢复到凌晨水势。C处理的毛竹午间水势下降值最小,叶绿素含量也最高。本研究区位于最南端产区,毛竹的光合生产力也属偏低水平。适当的土壤水分亏缺,毛竹表现出相对的高净光合速率(P_(n))、高蒸腾速率(Tr)、低水分利用效率(WUE)的特点;过多或过少土壤水分,则为低P_(n)和Tr,但高WUE。毛竹叶片的P_(n)与气孔导度Gs呈极显著的正相关关系,说明毛竹的光合速率受气孔调节明显;Tr与午时叶水势呈负相关(符合二项式函数)关系,土壤水分问题造成的叶片水分不足同时也影响了毛竹的Tr。水分亏缺,P_(n)主要由气孔调节,但水分过多导致P_(n)的下降应该是由气孔导度的下降和叶肉细胞光合能力的下降共同作用的结果。水分过少或过多均对毛竹生理生态过程产生负效应。相对于木荷,毛竹的P_(n)较高,但同时也消耗更多的水分。

Effects of soil moisture on the ecophysiology of moso bamboo (Phyllostachys edulis)in upper reaches of Lijiang River

There is a large area of moso bamboo plantation in upper reaches of Lijiang River, where it is the most southern moso bamboo plantation area in China. Seasonal drought occurs frequently in this area which may influence on ecophysiological strategy of moso bamboo. In this paper, we simulated rainfalls which might lead to soil moisture change, thereby to investigate the response of gas exchange of moso bamboo. We made five water treatments: CK. no rainfall and no plastic cover(PC); A. no rainfall but with PC; B. 5 mm rainfall with PC; C. 10 mm rainfall with PC; D. 20 mm rainfall with PC)in bamboo community, and one treatment(natural condition)with native plant Schima superba for comparison. The results showed that simulated rainfall causing soil moisture increase, which resulted in moso bamboo leaf water potential and chlorophyll change. Water potential of the sampled moso bamboo leaves decreased during day time, and could increase again to the level of predawn by the evening. Comparing to other treatments, in Treatment C, water potential decreasing value from predawn to noon was the least, while chlorophyll concentration was the highest. In this most southern area, photosynthetic productivity of our moso bamboo was low compared to other references. Under small water deficiency, moso bamboo leaf might present a high net photosynthesis rate(P_n), high transpiration(Tr)and low water use efficiency(WUE), while under saturated and prolong soil water and low soil water condition, it presented a low P_n and low Tr, but high WUE. P_n and stomatal conductance(Gs)of moso bamboo presented a closely positive correlation indicating P_n was regulated evidently by stomatal. Meanwhile, Tr and water potential at noon presented a negative correlation(binomial function)demonstrating that soil water influencing on moso bamboo leaf water concentration and transpiration. When water deficiency, P_n was regulated mainly by stomatal, but when water saturated and prolong, decreasing of P_n might be due to mutual influence by Gs decreasing and the decline of photosynthetic capacity of mesophyll cells. Therefore, sever water deficiency and over water may result in a negative effect on ecophysiology of moso bamboo. Comparing to native broad evergreen leaf species S. superba, moso bamboo has a higher P_n, and consumes much more water at the same time.