Root economics spectrum and construction costs in Mediterranean woody plants: the role of symbiotic associations and the environment
O_LIQuantifying the functional variation of fine root traits and their interactions with symbiotic organisms is an uprising research topic to understand the overarching trade-off between maximizing resource acquisition or conservation (root economics spectrum -RES-). The currency of root traits economy is based on the carbon required to construct them; however, we lack a clear understanding of this question. C_LIO_LIOur main aim was to quantify construction costs (CC) of fine roots (<2 mm) and their underlying components (concentration of carbon, minerals and organic nitrogen) in 60 Mediterranean woody species with contrasting symbiotic association types (ectomycorrhizas, arbuscular and ericoid mycorrhizas and N-Fixing nodules). We examined (1) if the CC depended on the symbiotic type, and if they were associated with morphological traits; (2) the relation of each component of the CC with the root structure for each symbiotic type; and (3) whether soil water and nutrient availability determined differences in CC across sites and symbiotic types. C_LIO_LIThe multivariate analysis of root traits showed a main plane of covariation accordingly to the RES expectations, with contrasting symbiotic types at both ends of the spectrum. We found a significant relationship between root CC and RES; interestingly the slopes of this relationship differed among symbiotic types, which was mainly due to the different role that each specific components of CC plays across them. In addition, independently of the symbiotic type, the CC decreased linearly with the nutrient availability and quadratic with the water availability. C_LIO_LISynthesis. Our study demonstrates that woody plants have different strategies in their root carbon investment, which depend on their position along the economics spectrum (RES) and on their main symbiotic association preference. The intrinsic components of the cost of root production varied across species with contrasting symbiotic associations, pointing to a trade-off between structural and metabolic compounds. We also found that root CC are strongly modulated by soil resource availability, following a non-linear pattern with water availability. Thus, CC shifts from high to low at the most arid sites, which points to a strong role of symbiotic associations in this shift. C_LI