Neighborhood interactions and environment modulate individual-level trait correlations and divergent functional trade-offs among co-occurring trees

Individual-level neighborhood interactions and environment are predominant drivers that maintain the diversity of plant form and function within communities. However, it remains unclear whether individual-level trait correlations are consistent with broader interspecific trait correlations. Moreover, how the interplay between environmental conditions and neighborhood interactions modulates plant ecological strategies (adaptations in growth, survival, and reproduction as reflected by functional traits) among locally co-occurring individuals is still not well understood. We examined whether pair-wised relationships among plant architectural, leaf and wood traits change when using species- versus individual-level information, and how these traits respond to environmental conditions (soil fertility and moisture/acidity), neighborhood crowding, and shading within a 1 ha spatially mapped subtropical forest in Eastern China. Plant architectural, leaf and wood traits were more robustly coupled at the individual than at the species level. Plant traits responded divergently to the soil environment and neighborhood interactions at both the individual and species levels. Plant architectural, leaf and wood traits exhibited divergent responses to environmental conditions and neighborhood interactions at the individual level, whereas responses of leaf and wood traits to environmental conditions were mainly observed at the species level. Our results highlight the importance of individual-level trait variations in shaping the within-community spectrum of plant form and function. This study provides evidence that the interplay between environmental conditions and neighborhood modulates alternative functional trade-offs among locally interacting individuals, thereby promoting the diversity of plant ecological strategies within forest communities.