Plant functional traits and their interrelationships are critical in shaping the evolutionary and adaptive trajectories of plant species, as well as their responses to environmental changes. Grassland ecosystems serve as a natural laboratory for exploring plant trait coordination, given their high biodiversity, environmental heterogeneity and intricate species interactions. However, the patterns of trait covariation across grasslands—the largest terrestrial ecosystems globally—and their environmental dependencies remain poorly understood.

In this study, we compiled a newly updated dataset for grassland ecosystems to analyse global patterns of leaf traits across grassland species and to identify their key climatic drivers. A global database comprising 9158 site-level observations was used. 

We found that leaf traits and their relationships varied significantly across climatic zones and plant functional types. Globally, C4 plants, forbs and annuals exhibited a resource acquisition strategy. Plants in temperate climates tended to adopt a conservative strategy, whereas those in boreal, subtropical, tropical and Mediterranean climates were more likely to employ a resource acquisition strategy. A clear conservative-acquisitive trade-off axis among functional traits was observed across global grasslands. Precipitation primarily drove the first axis of trait variation, which largely reflected a resource-acquisition strategy. In contrast, temperature predominantly influenced the second axis, which was associated with leaf nitrogen status.

Synthesis. Our findings underscore the strong global associations among plant functional traits, the pivotal role of plant functional types in mediating trait coordination and trade-offs and their dependencies on climatic zones and environmental factors. These findings provide valuable insights into the coordination and trade-offs of trait relationships at a global scale.