Adaptive mechanisms and/or morphophysiological and biochemical compensations in seedlings of an endangered Atlantic Forest species exposed to water deficit and high temperatures

Climate change is intensifying water deficit in many regions, impacting tropical ecosystems. Melanoxylon brauna , a native endangered Atlantic Forest species, faces threats from biome fragmentation and exploitation, thus requiring studies of its responses to environmental stress. In this study, we evaluated the effects of water stress and increased temperature on the growth of M. brauna , focusing on morphological and physiological responses to assess its resilience. The experiment was conducted in two controlled environments: Environment 1 (maximum temperature 32°C, vapor pressure deficit 1.50 kPa) and Environment 2 (42°C, 3.27 kPa), combined with soil water availabilities of 100, 75, 50, and 25% of field capacity during 60 days. Morphological, physiological, and water-use efficiency variables were analyzed. In Environment 1, plants had higher photosynthetic rates, transpiration and stomatal conductance, with 100% water availability favoring photosynthesis and water-use efficiency. In Environment 2, plants exhibited greater root growth and antioxidant enzyme activity, indicating higher oxidative stress. Relative water-use efficiency was greater in Environment 1, while higher hydrogen peroxide and malondialdehyde levels in Environment 2 indicated increased stress. M. brauna seedlings are sensitive to thermal and moisture variations, but have adaptive mechanisms, especially under moderate stress (up to 50% water availability), associated with root development.