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20 0 1年 4— 10月 ,通过林内标准地观测的方式 ,对北京西山地区一块 3 1年生的油松栓皮栎混交林的水势 (用压力室测定 )日变化、净光合速率和蒸腾速率 (用Licor 640 0测定 )日变化过程进行测定 .结果表明 ,在土壤 植物 大气连续体 (SPAC)系统中 ,生长季内水势的波动幅度按从大到小的顺序是大气 >植物 >土壤 ,其中大气水势的绝对值要比植物和土壤水势高 1～ 3个数量级 .土壤、植物和大气水势的日变化规律类似 ,并表现出明显的季节差异 .在生长季不同标准日内 ,油松和栓皮栎的净光合速率和蒸腾变化规律差异较大 .通常 ,栓皮栎的净光合速率和蒸腾速率明显高于油松 ,但在水分胁迫时 ,二者的差异会减小 .在生长季中的绝大部分时段 ,树木由于环境因子特别是土壤水分的限制作用不能达到其潜在的光合和蒸腾能力
From April to October in 2001, the diurnal variation, net photosynthetic rate and transpiration rate (measured by pressure chamber) of a 31 year old Pinus tabulaeformis and Quercus variabilis mixed oak forest in Xishan, Beijing, (Licor 640 0) was used to determine the diurnal variation of water potential. The results showed that the order of fluctuation of water potential during the growing season was Atmosphere> Plant> Soil, in which the atmosphere The absolute value of water potential is 1 ~ 3 orders of magnitude higher than plant and soil water potential.The diurnal variation of soil water, plant and atmosphere water potential are similar and show obvious seasonal differences.During different seasons of growth seasons, Pinus tabulaeformis and Quercus variabilis The net photosynthetic rate and transpiration varied widely, but the net photosynthetic rate and transpiration rate of Quercus variabilis were significantly higher than those of Pinus tabulaeformis, but the difference between them decreased under water stress.In most of the growing season During the period, trees can not reach their potential photosynthesis and transpiration due to the limiting effect of environmental factors, especially soil moisture