ECOPHYSIOLOGICAL RESPONSES OF SPONDIAS TUBEROSA TO CONTRASTING TROPICAL CLIMATES: ADAPTIVE STRATEGIES UNDER WATER STRESS

This study investigates the ecophysiological adaptations of Spondias tuberosa (umbu) trees across two contrasting ecological zones in northeastern Brazil: tropical wet and tropical arid ecosystems. We assessed their adaptive strategies to fluctuating water availability by analyzing photosynthetic efficiency, water status, chlorophyll fluorescence parameters, carbon isotope discrimination (Δ¹³C), and anti-oxidant system activity. Our findings revealed that maximal net photosynthesis was closely associated with reduced vapor pressure deficit (VPD), indicating strong environmental regulation of gas exchange processes. Elevated internal-to-ambient CO₂ ratios (Cᵢ/Cₐ), coupled with minimal changes in chlorophyll fluorescence, suggested a predominance of non-stomatal limitations under water-scarce conditions. Notably, umbu trees exhibited dynamic modulation of antioxidant activity during the dry season, mitigating oxidative stress through shifts in pigment composition, increased hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) accumulation, elevated electrolyte leakage, and enhanced antioxidant enzyme activity. A pronounced decline in Δ¹³C further corroborated improved water-use efficiency under drought. Multivariate analysis of variance (MANOVA) revealed a significant interaction between sampling period and ecological zone, emphasizing a pronounced "dry season effect" on physiological performance. Importantly, S. tuberosa individuals from humid zones exhibited greater vulnerability to drought stress compared to those from arid regions, highlighting the species' capacity for climatic adaptation. These results provide critical insights into the physiological trade-offs underlying drought resilience in woody species within seasonally dry tropical forests, advancing our understanding of their adaptive strategies in response to environmental variability.