黄土高原半干旱区林木生长适宜土壤水分环境的研究

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 %

Fitting Soil Moisture Environment of Trees Growth on Loess Plateau in Semi-arid Region

Using portable photosynthesis system (Li-6200) and portable steady porometer (L i-1600), This paper study mainly the quantitative relation between plant physio logical parameter and soil moisture, namely the response process of the tree net photosynthesis rate(Pn),transpiration rate(Tr),carboxylation efficien cy(CE),water use efficiency of leaf(WUE L), stomatic conductivity(Cs ) and stomatic resistance(Rs)to soil water content(SWC)using three ki nds of trees of Black Locust, Oriental Arborvitae and Apple tree in semi-arid r egion on Loess Plateau (Fangshan county, Shanxi Province). The results show that the optimum SWCkeeping the highest Pnof Black Locust, Oriental Arborv itae, Apple tree is 17.13%, 15.90%, 16.11%; the critical SWCvalue of mainta ining the highest Pnupwards 70% (namely the SWCof turning point of C s~SWCcurve) is 10.50%, (9.50)%, 9.75% respectively; the best SWCto sup port the highest WUE Lis 13.23%, 10.66%, 12.38% in turn; the SWCis 15 .70%, (15.50)% and 15.83% with the highest CE; the SWCof the highest Tris 18.82%, (19.70)% and 16.33% respectively. According to the essential a im to saving water and increase effectively water use efficiency of forest by water-h arvesting afforestation, the critical value of the SWCkeeping the optimum WUE Lcan be chosen as a upper limit value for control woodland soil moistu re and stand density as wall as calculating the trees water requirement, the SWCcritica l value of maintaining the highest Pn70% upwards is chosen as the lower l imit value to control woodland soil moisture on Loess Plateau in semi-arid regi on, This range of the optimum SWCcan be generalized as Black Locust 10.5%~ 13.5%, Oriental Arborvitae 9.5%~11.0%, Apple tree (10.0)%~12.5% (equal to 50 %~64%, 45%~52%, 48%~60% of field capacity) respectively.