Linking individual and species-level leaf traits with ontogenetic development stage to explain tree performance under competition and environmental contexts

To verify how species traits and individual traits link ontogenetic size, external biotic and abiotic factors to influence tree performance. In a temperate natural forest in northeastern China, we measured dynamic performance, size, as well as competition, topography, and soil variables as biotic and abiotic variables for all 1320 trees of 17 species in 62 monitoring plots from 2010-2020. For each individual tree, we also measured five typical functional traits representing leaf size and elemental content: leaf area, specific leaf area, leaf dry matter content, leaf nitrogen content, and leaf carbon : nitrogen ratios. These traits are not only strongly associated with performance, but trade-offs between traits have previously been shown to express plant acquisitive-conservative strategy characteristics. Reconceptualized based on previous understanding of trait-based approach (Fig. 1). We first tested the direct explanatory effects of species traits and individual traits on performance in multifactorial contexts. We first tested the direct explanatory effects of species traits and individual traits on performance in multifactorial contexts. Subsequently, we analyzed the moderating and mediating effects of these two levels of traits in explaining ontogenetic size, external competition, and environmental influences on performance. The following three questions were posed in response to the results:

QI: Do species and individual traits differ in directly explaining performance in a multifactor context that includes ontogenetic size, external biotic and abiotic factors?

QII: How species and individual traits explain the effect of ontogenetic size on performance by moderating and mediating effects.

QIII: Can traits at the species and individual level influence competition- and environment-performance relationships through trait-based approaches? Does ontogenetic size work jointly with traits at different levels in this process?