Epiphytic orchids Stanhopea tigrina and Prosthechea cochleata are differentially affected by drought in a subtropical cloud forest

Abstract

We investigated the physiological responses of two epiphytic orchids under three light regimes of 20, 50, and 70\% of total daily radiation under drought and rewatering conditions. Stanhopea tigrina was the one more affected because it exhibited strong photoinhibition and reduction of both electron transport rate and nocturnal acidity under drought and high radiation. However, this species maintained relatively high relative water content (RWC) values and underwent osmotic adjustment during the drought period and recovered photosynthetic variables during watered period. Prosthechea cochleata maintained similar water and photosynthetic responses to light conditions during the drought period and was more tolerant than S. tigrina. Principal component analysis provided evidence that water variables, such as RWC and succulence of both leaf and pseudobulb, were the most important variables for both species. Our results suggest that S. tigrina is more sensitive to drought than P. cochleata, and could be more affected by global warming.