A influência do habitat e do Metabolismo Ácido das Crassuláceas (CAM) na absorção de água em orquídeas

Abstract

The adaptive success of orchids in different habitats is due to the development of morphological and physiological strategies that promote greater efficiency in water use. Among these strategies, we can mention foliar succulence, foliar water uptake (FWU), and the expression Crassulacean Acid Metabolism (CAM). Furthermore, aerial roots can maximize the absorption of water and nutrients, processes that can be related to the presence of a canopy and the composition of its cell wall. Therefore, we hypothesized in Chapter 1 that FWU may be a strategy for water acquisition by epiphytic and rupicolous orchids due to the low water availability in these environments and that CAM metabolism would further increase the rate of water absorption by these plants. To test this hypothesis, we evaluated the capacity of FWU and verified variations between epiphytic, rupicolous, and terrestrial habitats, and between C3 and CAM metabolism in 16 orchid species. We found that foliar water uptake may be a strategy developed by orchids, and is related to the structural characteristics of leaves. The rupicolous species showed higher FWU, but this water absorption strategy was not favored by CAM metabolism. In Chapter 2, we hypothesized that the aerial and terrestrial roots of Vanilla bahiana may present cell wall characteristics that contribute to their role in each environment, as well as understand how changes in their structure occur during their development. To verify the alterations in the composition of the cell wall of the roots of V. bahiana, immunocytochemical analyzes were performed using monoclonal antibodies that mark epitopes of proteins, hemicelluloses, and pectin. We found that the cell wall composition of aerial (free and attached to the phorophyte) and terrestrial (fixed to the soil) roots of V. bahiana changes in response to the environment, which consequently reflects on the function performed by these roots. In summary, the foliar water uptake is likely related to habitat conditions and leaf morphological traits associated with water use and helps orchids cope with drought events. The aerial roots of V. bahiana showed greater complexity and presence of pectin, favoring the influx of water and nutrients. Our results provide new perspectives to understand the water use strategies presented by orchids in their vegetative organs to deal with environmental conditions.