Plasticidade ecofisiológica como mecanismo de adaptação à deficiência hídrica em plantas jovens de ipê branco Tabebuia roseoalba (Ridl). Sand. (bignoniaceae)

Abstract

Tabebuia roseoalba (white ipe) occurs naturally in biomes with very peculiar characteristics of precipitation, radiation and temperature, as it is widely distributed throughout the country, being widely used for urban afforestation due to its exuberant flowering, in addition to having a very good wood, desired by loggers. Understanding how species present in different biomes behave and resist long periods of drought in a semiarid environment, for example, is very important for restoration programs in impacted areas. This study aimed to investigate whether young plants of white Ipê are tolerant to water stress through an experiment in a greenhouse, where two treatments were imposed: control (irrigated regularly) and water deficit (which had the irrigation completely suspended) gas exchange, chlorophyll fluorescence, water potential and, at the end, the dry biomass of plant parts such as leaves, stem and root were determined. From the stomatal conductance, transpiration and net photosynthesis data, the water use efficiency and intrinsic water use efficiency were calculated. After 15 days of imposition of deficit, photosynthesis reduced about 85% in the treatment under water deficit, reaching 0, as a result of the reduction in stomatal conductance, which occurred due to the closure of the stomata. As a consequence, a reduction in transpiration was also verified, an important aspect in water deficit conditions in which the plant uses the stomata closing strategy to restrict the loss of water from the leaves. Furthermore, the Fv/Fm values at noon were lower than those found in the morning, indicating dynamic photoinhibition. Water use efficiency (USA) and intrinsic water use efficiency (EIUA) were higher in stressed treatments, indicating that when the species is subjected to water stress it tends to reduce losses and tries to adapt to the new scenario imposed by the restriction water. These are important resources that species normally use in these intense climatic conditions that are frequent in this environment. Proving that when subjected to water stress this species adapts physiologically and morphologically, which explains the wide distribution of this plant throughout the Brazilian territory, even in environments with long periods of drought and irregular rainfall.