Photosynthesis and water relations of six tall genotypes of Cocos nucifera in wet and dry seasons

Abstract

Despite the larger total amount of photosynthetic photon flux density (PPFD) in dry seasons, the integrated values of stomatal conductance (Gs), photosynthesis (A) and transpiration (E) were higher during the wet season in six tall genotypes of Cocos nucifera L. Average values of A and E from all genotypes were correlated with PPFD (r2 = 0.711, p <0.001) but not with Gs (r2 = 0.301) in the wet season. Conversely, A and E were strongly correlated with Gs (r2 = 0.776, p <0.001) but not with PPFD (r2 = 0.169) in the dry season. Five genotypes showed strong reduction (between 46–86%) of the integrated values of A, E and Gs in the dry season. Contrastingly, the Brazilian tall genotype (BRT) reduced only between 12–29% of the integrated values of leaf gas exchange in the dry season, tolerating lower values of leaf water potential and showing drought tolerance behavior more clearly. The integrated intrinsic water use efficiency increased up to 126% in the dry season in five genotypes but in BRT only 12%. Hence, the dry season imposed serious restrictions to water and carbon balances during the daily course. Such balances were sharply conditioned by an ambient variable (PPFD) in the wet season but by a biological controlled variable (Gs) in the dry season.