Seedling is the bottleneck stage across plant life stages, which can influence community structure at later stages. While the varied survival probability of seedling with height and environmental gradients has been recently documented, the mechanisms underlying this pattern are not clear. For example, previous studies usually suggest that functional traits may explain the increased survival for higher seedlings. We used three databases in this study to address these issues: first, we measured 11 leaf lamina and petiole traits for > 2800 seedlings of 33 species across 283 plots in a 9 ha forest dynamics plot; second, we examined the survival dynamics of seedlings using a 4-year census; third, we measured the elevations and light availability of each seedling plot. We used two multilevel mixed-effect models to examine the effects of height, elevation and light availability on leaf traits and seedling survival, respectively. Random slopes and intercepts of species were allowed for all predictors (i.e., height, elevation, and light availability) to examine the interspecific (random slope) relationships between height-related trait variation and height-related survival variation, and between environment-related trait variation and environment-related survival variation.
Results/Conclusions
We found most traits show height-related trait variation across species that higher seedlings showed increased leaf size and resource conservative strategies than smaller seedlings. With increased light availability, most species showed an increased resource conservative strategy. The probability of seedling survival increased with increased height and decreased with increased light availability. Height- and light-related trait variation (i.e., the slope of each predictor) across species could explain the height- and light-related variation of the seedling survival probability across species: species with faster-increased resource conservative with increased height also showed a slower increase of seedling survival probability with increased height; light-driven trait variation also was correlated to the light-driven survival probability. Our study suggested that intraspecific trait variation of seedlings can mediate how the survival probability of each species responds to height growth and environmental gradient. We call for the considerations of intraspecific trait variation when analyzing seedling dynamics using the trait-based method.