Cell sizes dictate hydraulic traits but not economics traits: implications for leaf design and evolution in woody angiosperms

Qiaoling Su, Le Li, Zeqing Ma
Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China

Understanding the relationship between different leaf cell sizes and key leaf functional traits can provide valuable insights into leaf diversity and evolution. Here, we explored the variation pattern among five key leaf cell sizes, leaf hydraulic traits and leaf economics traits in species-rich tropical-subtropical forests in China. We sampled mature leaves and measured nine traits for 85 woody angiosperm species and then employed Pearson correlation and stepwise regression analyses to explore the relationships between leaf cell sizes vs. leaf hydraulic traits, and leaf cell sizes vs. leaf economics traits. Different leaf cell sizes were negatively correlated with areal densities of leaf hydraulic structures(i.e., vein density and stomatal density), because of biophysical constraints. By contrast, different leaf cell sizes were decoupled with traditional leaf economics traits (e.g., leaf dry mass per area). Consistent with previous studies, unified changes were found among different leaf cell sizes. Our results indicate that the divergence of angiosperms was associated with smaller cell sizes of leaves, higher vein density, and higher stomatal density, driven by higher transpirational pull accompanying the radiation of angiosperms from shaded understory to open habitats. This trend may have greatly contributed to leaf evolution in the radiation of angiosperms from understory-shaded environment to open habitats.