多重复干旱循环对苗木气体交换和水分利用效率的影响

该文研究了多重复干旱循环对１年生北美短叶松和黑云杉苗木的气体交换速率及水分利用效率的影响．结果表明，多重复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．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强劲的耐旱能力．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大于北美短叶松．

Effects of Repeated Cycles of Dehydration-rehydration on Gas Exchange and Water Use Efficiency of Seedlings

Effects of repeated cycles of dehydration\|rehydration on gas exchange and water use efficiency were studied in one\|year\|old jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana B.S.P.) seedlings subjected to five cycles of dehydrationrehydration by water withholding in root misting chamber (RMC). Jack pine had higher rate of gas exchange and water use efficiency than black spruce when seedlings were well watered. Repeated cycles of dehydrationrehydration had significant effects (P<0.05) on gas exchange (Cs, Pn and Tr), but no significant effects (P>0.1) on WUE in both species. Despite less sensitive to mild drought stress in jack pine than in black spruce, stomata was more sensitive to moderate and severe stress in jack pine than in black spruce. Photosynthesis was mainly affected by nonstomata factors in jack pine but by stomata factor in black spruce, resulting in a less decrease of Pn despite a great reduce of Cs in jack pine than in black spruce under mild and moderate drought stress. After relief of drought stress, stomata sensitivity, photosynthetic capacity and water use efficiency were more recovered in black spruce than in jack pine. Hardening of mild drought stress can help jack pine to maintain its greater inherent ability to tolerate drought under more severe drought stress. But the extents of improving ability to tolerate drought is larger in black spruce than in jack pine through hardening of repeated cycles of dehydrationrehydration.