Functional Trait Variation and Reverse Phenology in the Tropical Dry Forest Species Bonellia nervosa

Bonellia nervosa is an understory tree with reverse phenology in tropical dry forests (TDFs), where seasonal water and temperature stress typically shape plant phenology and trait expression. This species is heliophytic and phreatophytic, relying on high light availability and deep-water access during the dry season. However, the role of dry-season light variation in influencing leaf traits of species with inverted phenology remains poorly understood. We examined how plant size, reproductive stage, and canopy structure influence trait variation in B. nervosa during the dry season. We measured plant height and diameter, reproductive status, and canopy structure using hemispherical photographs to estimate canopy openness, leaf area index, and transmitted light. Leaf structural traits included specific leaf area (SLA), thickness, water content, and stomatal density, while photochemical performance was assessed via chlorophyll fluorescence and rapid light curves. Principal component analysis and linear regression were used to examine the trait-environment relationships. Photosynthetic efficiency was not affected by plant size or reproductive status. However, SLA increased significantly with canopy openness, indicating structural acclimation to light. Our results demonstrate that dry-season variation in light availability is a key driver of leaf trait expression in B. nervosa, highlighting how reverse phenology in phreatophytic species is functionally decoupled from seasonal water stress.