Metabolismo ácido das crassulaceae e absorção foliar de água: uma análise integrada de determinantes estruturais, fisiológicos e bioquímicos em plantas suculentas

Abstract

Epiphytes, including many orchids and bromeliads, have evolved morphological and physiological strategies that enhance water-use efficiency in response to water deficit. Among these strategies are the presence of succulent organs, the expression of Crassulacean Acid Metabolism (CAM), and foliar water uptake (FWU). In some cases, these traits are interconnected, such as the relationship between succulence and CAM, as well as the influence of leaf succulence and cell wall composition on FWU capacity. Therefore, the central hypothesis of this thesis is that FWU is related to the circadian cycle inherent to CAM metabolism. To address this hypothesis, the thesis is organized into three chapters. In the first chapter, we hypothesized that the accumulation of organic acids associated with CAM expression reduces leaf water potential at dawn, thereby increasing FWU rates in Vanilla phaeantha. We also expected that cell wall components associated with water retention and movement, particularly pectins, would be widely distributed throughout the leaves. In the second chapter, we hypothesized that water restriction alters leaf water balance and photosynthetic activity, increasing CAM expression (i.e., promoting greater accumulation of organic acids) and consequently maximizing FWU. To test this hypothesis, drought conditions were simulated through water restriction in Cattleya forbesii and Cattleya guttata. In the third chapter, we proposed that FWU enhances water-use efficiency, promotes photosynthetic activity, and reduces oxidative stress in Puya chilensis, a species frequently exposed to fog events. Additionally, we hypothesized that fog frequency may modulate the intensity of CAM expression and influence FWU capacity. To test this, an experiment was conducted simulating artificial fog events and water deficit conditions. Overall, our results contribute to a better understanding of the water-use strategies adopted by succulent plants, such as epiphytic orchids and bromeliads, in response to fluctuations in water availability commonly experienced in the environments where they occur.