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本文研究了多重复干旱循环对１年生北美短叶松（ＰｉｎｕｓｂａｎｋｓｉａｎａＬａｍｂ．）和黑云杉（Ｐｉｃｅａｍａｒｉａｎａ［Ｍｉｌ］Ｂ．Ｓ．Ｄ．）苗木的气体交换速率及水分利用效率的影响。结果表面，多重干旱循环对它们的气体交换（Ｃｓ，Ｐｎ，Ｔｒ）有显著影响（Ｐ＜０．５），而对其水分利用效率（ＷＵＥ）影响不大（Ｐ＞０．１）。尽管北美短叶松的气孔对轻度干旱胁迫不如黑云杉敏感，但是它对中度及严重干旱胁迫的敏感程度却高于黑云杉。在轻度及中度干旱胁迫下，北美短叶松的光合作用主要受非气孔因素的影响，而黑云杉则主要受气孔因素的影响。解除干旱胁迫后，黑云杉的气孔敏感性、光合能力及水分利用效率的恢复都要比北美短叶松更快．我们认为，延迟脱水是北美短叶松的主要耐旱机理，而忍耐脱水则是黑云杉重要的耐旱途径。轻度的干旱胁迫锻炼可以帮助北美短叶松在更严重的干旱胁迫下保持固有而较强的耐旱能力。然而，通过多重复干旱循环锻炼后黑云杉在改善耐旱能力的强度方面则大于北美短叶松
In this paper, we studied the effects of multiple cycles of drought on the gas exchange rates and water use efficiency of Pinus tabulateiana Lamb. And Piceamariana [Mil. B.S.D.] Seedlings. As a result, the multiple drought cycles had a significant effect on their gas exchange (Cs, Pn, Tr) (P <0.5), but had little effect on their water use efficiency (WUE) (P> 0.1). Although the Pinus tabulaeformis stings are less sensitive to mild drought stress than black spruce, they are more susceptible to moderate and severe drought stress than black spruce. Under mild and moderate drought stress, the photosynthesis of Pinus thunbergii was mainly influenced by non-stomatal factors, whereas that of black spruce was mainly affected by stomatal factors. After drought stress was relieved, stomatal sensitivity, photosynthetic capacity and water use efficiency of black spruce were all recovered faster than N. nigra. In our opinion, delayed dewatering is the main mechanism of drought tolerance in N. crassipes and tolerance to dehydration is an important drought-resistance pathway in P. spruce. Mild drought stress exercises can help Pinus thunbergii maintain inherent and strong drought tolerance under more severe drought stress. However, black spruce increased the intensity of drought tolerance after multiply arid cycle exercise than that of N. americana