Functional traits mediate seedling survival response to climate in a temperate forest.

Functional traits are increasingly used to forecast the response of plant performance to abiotic and biotic conditions. However, it remains unclear how functional traits will mediate the complex responses of plants to interactive drivers in a rapidly changing world. Here, we collected 17-year monitoring data on seedlings of 28 locally coexisting species and 8 functional traits in a temperate forest, and built multi-level regression models to evaluate (1) whether seedling survival varied among species along the acquisitive-conservative strategy gradient, and which functional trait affected seedling survival; and (2) how survival of species with different functional strategies responded to negative density dependence (NDD) and climate variation. We found that species with an acquisitive strategy had higher seedling survival. Specifically, seedling survival was positively correlated with specific root length (SRL), specific leaf area (SLA), and leaf area (LA), but inversely correlated with leaf dry mass content (LDMC). Functional strategies along the acquisitive-conservative gradient showed no significant effects on survival response to conspecific and phylogenetic negative density dependence. Negative effects of heterospecific negative density dependence on seedling survival were weaker for species with higher LDMC, but stronger for seedlings with larger SRL. In addition, species with more conservative strategies had higher resistance to drought stress and freezing damage. For example, species with lower SRL and SLA, and higher LDMC had higher survival under severer seasonal drought. Also, heavier seeds and thicker roots enhanced freezing resistance, whereas higher SRL and LA intensified the negative effects of cold weather. Our study provides strong evidence that functional traits could widely mediate the effects of local biotic interactions and climatic variation on plant performance dynamics, and help to infer community assemblages and species coexistence in the context of a changing world.