Gas exchange in genotypes of Nopalea cochenillifera in different seasons and evaluations times

This study aimed to evaluate the gas exchanges in genotypes of Nopalea cochenillifera Salm-Dyck in different seasons and times of the day. The experiment was conducted with the varieties Miúda and Baiana at the Experimental Station Prof. Ignacio Salcedo, belonging to the National Semi-Arid Institute (INSA), in the municipality of Campina Grande, State of Paraíba, Brazil. The treatments were distributed in a 24 × 2 factorial arrangement, corresponding to gas exchange evaluations performed every hour for 24 hours in the rainy season (June) and in the drought season (December). Analyzed were stomatal conductance, transpiration rate, CO2 uptake, and internal CO2 concentration, besides instantaneous water-use efficiency, intrinsic water-use efficiency, and instantaneous carboxylation efficiency. In both drought and rainy seasons, variety Baiana presented higher gas exchange intensity than the variety Miúda. In the rainy season, gas exchanges are potentialized in both varieties evaluated. In this period, the peak of CO2 uptake occurs from 1:00 a.m. to 3:00 a.m. for the verity Baiana, and from11:00 p.m. to 2:00 a.m. for the variety Miúda, whereas, in the drought season, it occurs from 11:00 p.m. to 2:00 a.m. for both varieties, with these constituting the ideal intervals for measuring gas exchanges in the field.