Root elemental composition in Chinese forests: implications for biogeochemical niche differentiation

1. Trait-based community analysis provides a new approach to integrate functional ecology with community ecology. However, our understanding of the linkages between root chemical traits and community chemical diversity and assembly is still in its infancy.
2. Environmental filtering and niche differentiation are two opposite driving forces of community assembly based on deterministic niche processes. We hypothesize that environmental filtering is a strong driver of root chemical assembly at a large spatial scale, whereas biogeochemical niche differentiation drives root chemical traits divergence among co-occurring species at site scale.
3. We analyzed the concentrations of 15 elements in the fine roots of 281 species across five forest types of China. Discriminant analysis was used to measure the degree of similarity of root chemical traits at the community level and biogeochemical niche differentiation at the species level.
4. Root chemical traits at the community level showed a systematic shift along environmental gradients. The growth rate-related dimension represented by root P and Ca was the most important niche dimension associated with community root chemical assembly, driven by large-scale environmental filters, particularly soils and climate. Biogeochemical niche differentiation of co-occurring species could be a consequence of reducing nutrient competition, especially the competition for nitrogen.
5. Root chemical traits provide a new dimension for assessing the functional niche and may help improve our understanding of the underlying mechanisms of root chemical assembly from the local to the biome scale.