The Role of Plant Evolutionary History in Shaping the Variation in Specific Leaf Area Across China

Specific leaf area (SLA, leaf area per unit leaf dry mass) occupies a central position in both community assembly and ecosystem functioning. Although SLA has significant phylogenetic signals, how and to what extent the evolutionary history influences the variation in SLA remain poorly understood. In this study, based on a dataset containing 1264 plant species belonging to 549 genera and 141 families in gymnosperms, monocots, and eudicots across China, we analyzed the influences of climatic conditions and soil properties on SLA, calculated the phylogenetic signals of SLA, and quantified the relative contributions of evolutionary history (represented by interspecific relatedness and intraspecific variation) to the variation in SLA. The results showed that the interspecific relatedness accounts for 50.46% of the total variance in SLA, followed by the intraspecific variation (36.12%), climatic conditions (30.68%), and soil properties (24.74%). Along the phylogenetic tree, the split between angiosperms and gymnosperms had the largest contribution to the variation in SLA. Other detailed splits (e.g., the split between monocots and eudicots, the splits within Rosidae, and etc.) had significant but much smaller contributions. The relationship between SLA and environmental variables (climatic conditions and soil properties) was different between angiosperms and gymnosperms, with the climatic conditions having larger influences on SLA than the soil properties, implying interactive effects between environment and evolutionary history on SLA. Within the woody angiosperms, deciduous and evergreen species exhibited differential responses of SLA to climatic and soil factors, suggesting a non-negligible role of leaf longevity in explaining the variation in SLA. Our results highlighted a much more important role of evolutionary history in the variation in SLA than previous studies. Neglecting such a great contribution could lead to biased conclusions if the evolutionary rate does not keep pace with the rapidly changing environments in the future.