不同土壤水分下黄土高原侧柏生理生态特点分析

Study on Physio-Ecological Characteristics of Platycladus Orientalis under Different Soil Water Condition on Loess Plateau

采用人工控制土壤水分,形成单株幼龄侧柏的不同水分梯度环境。在自然环境下利用Li- 16 0 0稳态气孔仪和Li- 6 2 0 0光合仪对山西省方山县试验基地内侧柏的蒸腾速率、净光合速率、气孔阻力及其环境因子进行了观测,并辅以盆栽苗木水分胁迫条件下的林木生理指标观测,对生理指标和土壤含水量的关系进行了研究。结果表明:侧柏蒸腾日进程为双峰曲线,水分状况较差时蒸腾日进程曲线到达波谷的时间比水分状况较好时大大提前,干旱条件下蒸腾速率较低;净光合速率的日进程为双峰曲线,水分状况较差时日进程变为单峰曲线,侧柏叶片光合作用午前以气孔限制为主,而午后以非气孔因素限制为主。维持蒸腾速率所适宜的土壤含水量为19.90 % ;净光合作用的最佳土壤含水量为15 75 % ;维持叶片水分利用效率的最佳土壤含水量为10 6 5 % ,选取维持最佳叶片水分利用效率的土壤含水量临界值作为林木密度调控的土壤水分阈值,侧柏为9 5 %～11%。

Soil moisture graduations of signal Platycladus orientalis on Loess Plateau were established through artificial control of water amount.The transpiration rate,net photosynthesis rate,stomatal resistance and environmental factors were measured by portable steady porometer(Li-1600) and portable photosynthesis system(Li-6200) under natural conditions in Fangshan Country,Shanxi Province.The effects of soil water on physio-ecological characteristics were studied by pot experiment.The results show that the diurnal changes of transpiration displays a double-peak curve.When the water situation is in worse condition,the time of reaching trough is much earlier than that of in better condition and the transpiration rate is lower.The diurnal changes of net photosynthetic rate displays a double-peak curve and displays a signal-peak curve in worse water condition.The predominant limiting factor of photosynthesis are stomatal conductance of stomatal limitation in the morning and low carboxylation capacity of the leafmesophyll in the afternoon.Optimum soil water content keeping better transpiration rate,net photosynthesis rate and water use efficiency is 19.90%,15.75% and 10.65% respectively.The soil water content maintaining the best water use efficiency can be chosen a critical value for tree density control and be shown as 9.5%～11% for Platycladus orientalis.