Seasonal variation of net CO2 uptake for cactus pear (Opuntia ficus-indica) and pitayo (Stenocereus queretaroensis) in a semi-arid environment

The objective of this work was to evaluate the effects of seasonal variation in temperature, irradiation, and soil moisture content on the photosynthetic rates of Opuntia ficus-indica and Stenocereus queretaroensis. The lowest values of positive dairy net CO2 uptake were recorded during the summer rainy season and the highest values during autumn and winter. These optimum values are likely to be the result of a prolonged period of CO2 assimilation caused by decreased cloudiness, and high rates of nocturnal CO2 assimilation due to moderate day/night air temperatures. In spring, when drought was exacerbated, daily net CO2 uptake was negative for both O. finus-indica and S. queretaroensis. Stem photosynthesis allowed both O. ficus-indica and S. queretaroensis to obtain carbon during the fall and winter, when soil water was at its lowest. (C) 2000 Academic Press.