Seasonal variation of net CO2uptake 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 daily net CO2uptake 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 CO2assimilation caused by decreased cloudiness, and high rates of nocturnal COassimilation due to moderate day/night air temperatures. In spring, when drought was exacerbated, daily net CO2uptake was negative for bothO. ficus-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.