Stomatal conductance and CO2 uptake rate in sabila (Aloe vera Tourn) under drought

Sabila (Aloe vera Tourn) is an important crop for the pharmaceutical and cosmetic industries. The crassulacean acid metabolism (CAM) photosynthetic pathway is present in this plant. In Mexico, this crop grows in diverse subtropical climates. The objective of this study was to compare the sabila crop in two environments: in a warm semi-arid environment (Marin, Nuevo Leon) and in a semi-arid temperate environment (Buenavista, Coahuila). The irrigation treatment (T1) supplied water twice a week, and the drought stress treatment (T2) suspended irrigation until soil moisture reached levels between 1.3 and 8.4 %. Four cycles of water stress were evaluated for a whole year. Stomatal conductance (g(s)) and instantaneous CO2 net assimilation rate (Ai) measurements were taken at the beginning and the end of each cycle, at intervals of 1.5 to 2 h for 24 h, with a portable photosynthesis apparatus. The results showed that in T1 sabila plants showed the four classic phases of CO2 assimilation in CAM plants in the two environments. However, Ai was 25 % higher in Buenavista than in Marin, due to lower temperatures. Under drought conditions in Marin, sabila plants reduced g(s) by 41 % by 65 %. Meanwhile, in Buenavista the reductions were 44 % in g(s) and 56 % in A. Lower night temperatures in Buenavista than in Marin were associated to higher g(s) and Ai.