Community-level economics spectrum of fine-roots driven by nutrient limitations in subalpine forests

1. Fine-root traits show remarkable variation with plant community structure and environmental shifts, but there is limited understanding of how trait covariation that exists among fine-root traits shifts among different communities, especially in forests. We explored links among the fine-root traits of forest communities to determine whether community root traits shift predictably according to an economics framework along environmental gradients.
2. Measurements of root morphology, nitrogen, phosphorus and carbon concentrations, and measures of standing root densities were collected on fine roots (diameter ≤ 2 mm) from 129 forest plots in five subalpine forests.
3. This study demonstrates an existence of a community-level fine-root economics spectrum (REScom) in the subalpine forests, in which specific root length was strongly and positively related to root nitrogen and phosphorusconcentrations, but negatively related to root diameter. Soil nutrient limitation was a major driver of the REScom as changes in soil [N], [P] and [C] contents were related to changes in SRL, root [N], root [P]. Variables related to standing fine-root length and mass were independent of the REScom and was primarily related to forest community structure, particularly in tree closure and herbaceous plant mass.
4. These results indicate two distinct functional dimensions of community fine-root trait variation: resource-use efficiency via changes in root structure and construction, and separately via changes in the standing root system. Identifying shifts in allocation to and investment in fine roots enhances our understanding of a root and whole-plant economics spectrum and community functioning.