INDUCTION OF CRASSULACEAN ACID METABOLISM IN MESEMBRYANTHEMUM-CRYSTALLINUM INCREASES REPRODUCTIVE SUCCESS UNDER CONDITIONS OF DROUGHT AND SALINITY STRESS

Mesembryanthemum crystallinum L., an inducible crassulacean acid metabolism (CAM) plant, was grown for approximately 5 weeks following germination in well-watered, non-saline soil in a controlled-environment chamber. During this time, plants were characterized by C3 photosynthetic carbon metabolism. After the initial 5 weeks, CAM was induced by a combination of high soil salinity and reduced soil water content. One group of plants was allowed to engage in CAM by being continuously exposed to normal CO2-containing air (about 350-400 ppm). A second group of plants was deprived of ambient CO2 each night (12 h dark period) until completion of their life cycle, thereby minimizing potential carbon gain via dark CO2 fixation. The capacity to express CAM under conditions of drought and salinity stress markedly improved reproductive success: plants kept in normal CO2-containing air produced about 10 times more seeds than plants kept in CO2-free air during dark periods. Seeds from plants deprived of ambient CO2 overnight had more negative delta-C-13 values than seeds from plants kept in normal air.