Koch K E, Kennedy R A
Botany Department, University of Iowa, 52242, Iowa City, Iowa, USA.
Oecologia. 1980 Jan;45(3):390-395. doi: 10.1007/BF00540212.
Seasonal changes in the Crassulacean Acid Metabolism (CAM) activity and growth characteristics of Opuntia humifusa Raf. were examined under midwest climatic conditions. Twenty-four hour studies were done at monthly intervals for two years, with diurnal changes in transpiration, gas exchange, and titratable acidity monitored under natural conditions. CAM activity was observed only from April to September, but occurred regardless of changes in temperature or precipitation. The maximum rate of dark CO uptake occurred in May, while greatest acid fluctuations coincided with flowering, new growth, and high tissue water content in June. In spite of conditions favorable for CAM, acidification and rate of dark CO assimilation decreased progressively through September as stem water content dropped and shoot production ceased. No CAM was evident during sub-zero winter months and tissue water content decreased to only 65% (Ψ<-20 bars). Winter survival of plants in test plots was found to be affected by the amount of water received the preceding growing season; the driest group showing the lowest mortality rate.Although spring and autumn were considered periods likely to exhibit CAM, it was not observed during those months just prior to or immediately following winter (Oct. and March). Acid fluctuations were minimal with CO being taken up during the day and released at night, indicating some degree of flexibility in the CAM activity of Opuntia humifusa.
在中西部气候条件下，研究了平卧仙人掌（Opuntia humifusa Raf.）景天酸代谢（CAM）活性和生长特性的季节性变化。连续两年每月进行一次24小时研究，在自然条件下监测蒸腾作用、气体交换和可滴定酸度的昼夜变化。仅在4月至9月观察到CAM活性，但其发生与温度或降水量的变化无关。黑暗条件下CO吸收的最大速率出现在5月，而最大的酸波动与6月的开花、新生长和高组织含水量同时出现。尽管条件有利于CAM，但随着茎含水量下降和新梢生长停止，9月期间酸化作用和黑暗条件下CO同化速率逐渐降低。在冬季零下月份未观察到CAM，组织含水量仅降至65%（Ψ<-20巴）。发现试验地植物的冬季存活率受前一个生长季节降水量的影响；最干燥的组死亡率最低。尽管春秋两季被认为可能表现出CAM，但在冬季之前或之后的那些月份（10月和3月）未观察到。酸波动最小，白天吸收CO，夜间释放，表明平卧仙人掌的CAM活性具有一定程度的灵活性。
