Tropical seedling performance under drought: a functional trait approach for species selection in restoration

Tropical rainforests experience seasonal variations in water availability, with dry periods resulting in severe soil water scarcity that critically affects seedling performance. A functional trait-based approach, focusing on morphological characteristics, provides a practical means of identifying drought-tolerant tropical woody species for restoration initiatives. This study aimed to evaluate the effects of drought stress on the early establishment of seven tropical woody seedling species and to identify the traits that contribute to seedling performance under these conditions. A greenhouse experiment was conducted to assess seedling responses to varying drought levels, measuring seedling performance (survival rate, relative growth rate, and wilting state) along with traits related to resource acquisition and allocation. The 12-week experiment revealed that drought significantly reduced soil moisture and seedling performance, with species-specific responses. Principal component analysis reveals a shift in trait importance under drought, suggesting altered resource allocation strategies. The root-to-shoot ratio and leaf mass per area emerged as critical indicators of seedling survival during drought, with larger seed and higher leaf dry matter content initially promoting growth but diminishing in effectiveness under severe drought conditions. Larger seeds exhibited greater drought tolerance, as evidenced by lower wilting rates. Although a functional trait-based approach offers valuable information, our results indicate that it may not be fully predictive of seedling performance under all drought scenarios. These findings underscore the importance of selecting species based on their sensitivity to drought stress for specific restoration strategies.