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采用 L I- 62 0 0型植物光合测定系统、L I- 160 0型稳态气孔计和 L NW- 5 0 A型中子水分测定仪 ,对不同土壤水分胁迫下刺槐、侧柏林木和苹果树及其盆栽苗木生长的生理、生态特征进行实地观测 ,研究了叶片净光合速率( Pn)、蒸腾速率 ( Tr)、羧化效率 ( CE)、叶片水分利用效率 ( WUEL)以及气孔导度 ( Cs)和气孔阻力 ( Rs)对土壤含水量 ( SWC)变化的响应过程。结果表明 :刺槐、侧柏和苹果净光合速率最高时的 SWC分别为 17.13 % ,15 .90 %和 16.11% ;维持其最高净光合速率 70 %以上的土壤含水量 (即气孔导度的土壤水分响应曲线转折点对应的土壤含水量 )临界值分别为 10 .5 0 % ,9.5 0 %和 9.75 % ;其蒸腾速率最高时的 SWC分别为 18.82 % ,19.70 %和16.3 3 % ;其叶片水分利用效率最高时的 SWC依次为 13 .2 3 % ,10 .66%和 12 .3 8% ;其羧化效率最高时的 SWC依次为 15 .70 % ,15 .5 0 %和 15 .83 %。根据半干旱地区林业建设以提高林木水分利用效率为核心的土壤水分管理思想 ,分别选取维持最高叶片水分利用效率的土壤含水量临界值和维持较高光合速率 (最大光合速率的 70 %以上 )的土壤含水量临界值作为林木生长适宜土壤水分环境的上、下限标准。这一标准概化为 :刺槐 10 .5 %～ 13 .5 % ,侧柏 9.5 %～ 10 .5 %
L I-62 0 0 plant photosynthesis system, L I-160 0 steady-state stomatometer and L NW-50 A neutron moisture analyzer were used to measure the photosynthesis of Robinia pseudoacacia, Platycladus orientalis and apple trees under different soil water stress (Pn), transpiration rate (Tr), carboxylation efficiency (CE), leaf water use efficiency (WUEL) and stomatal conductance Cs) and stomatal resistance (Rs) on the changes of soil water content (SWC). The results showed that SWC at the highest net photosynthetic rate of Robinia pseudoacacia, Platycladus orientalis and apple were 17.13%, 15.90% and 16.11%, respectively. The soil water content (Stomatal conductance, soil moisture The critical values of soil water content corresponding to the turning point of the response curve were 10.5%, 9.5% and 9.75%, respectively. The SWC with the highest transpiration rate was 18.82%, 19.70% and 16.33%, respectively. The leaf water use efficiency The highest SWC was 13.23%, 10.66% and 12.38%, respectively. The SWC with the highest carboxylation efficiency was 15.7%, 15.5% and 15.83%, respectively. According to the thought of soil moisture management with forestry water use efficiency as the core in the forestry construction in semi-arid region, the critical value of soil water content to maintain the highest leaf water use efficiency and maintain the high photosynthetic rate (above 70% of maximum photosynthetic rate) The critical value of soil moisture as forest growth suitable for the upper and lower soil moisture environment standards. This standard is generalized as: Locust 10 .5% ~ 13 .5%, Arborvitae 9.5% ~ 10 .5%