Ecophysiology of a wild platyopuntia exposed to prolonged drought

The effects of reduced annual rainfall over a 7-year period on the daily patterns of gas exchange were analyzed for a wild platyopuntia ( Opuntia robusta) growing in rocky soil. In spite of the prolonged water stress, stomata opened at night and net carbon gain was observed for eight 1-day sampling periods during 2000. Daily net CO 2 uptake increased more than five-fold from the end of the dry spring season to the middle of the summer wet season. Curtailment in the formation of both new cladodes and new roots is considered to be an avoidance strategy to water scarcity, which in combination with net CO 2 uptake responses to temperature and relative humidity at night, and perhaps association with arbuscular-mycorrhizal fungi, were the most important adaptations for O. robusta to the prolonged drought conditions that prevailed in its rocky environment. Such adaptations of O. robusta are in addition to the classical physiological and structural modifications of CAM plants to tolerate prolonged drought.