Root traits across environmental gradients in Mediterranean woody communities: are they aligned along a single acquisition-conservation axis?

Abstract

Root traits play a critical role in plant resource-use strategies and ecosystem functioning, but there is great controversy regarding their identity and functionality in different dimensions of belowground functional variation. Here, we explored the level of covariation among a suite of key root traits as well as between them and two aboveground parameters related with plant function (leaf nutrients and growth rate). We also evaluated whether these patterns of trait covariation were consistent at different spatial scales and organisational levels. We collected fine roots traits of 534 individuals (of 80 woody species), sampled along a wide regional range of environmental conditions in southern Spain. In general, strong correlations among the root morphological traits (except root mean diameter) were found, as well as between them and the aboveground parameters, supporting the existence of a ‘root economics spectrum’. This syndrome of root trait covariation was consistent at the different spatial scales and organisational levels. Soil nutrients and water availability were the main drivers of this root trait variation. Our results indicate that root trait variation is primarily aligned along a leading dimension related to resource economics. However, the distinct pattern of root diameter may indicate a multidimensionality of belowground traits that needs to be explored in greater depth.