Effect of moisture supply on CAM in Opuntia aurantiaca (jointed cactus)

Abstract

The patterns of gas exchange exhibited by Opuntia aurantiaca under controlled conditions (photoperiod 12 h; day/night temperature regime 30/15°C) were investigated for plants subjected to various levels of moisture stress. Unstressed plants exhibited a typical full-CAM pattern of gas exchange in which all four phases of CAM-linked CO₂ exchange were evident. Net CO₂ uptake during phase 1 contributed up to 82% of total carbon fixed per 24 h. The transpiration: photosynthesis ratio was low (night 31; day 135), within the range exhibited by many CAM plants and indicative of a high water use efficiency. Under all conditions of water stress net carbon gain was reduced with phase IV showing the greatest reduction and phase 1 the least. On watering, stressed plants recovered rapidly. Within 48 h of receiving water total CO₂ uptake per 24 h had risen from 5,8% to 76,5% of the unstressed value.