Functional responses of Mediterranean plant communities to soil resource heterogeneity: a mycorrhizal trait-based approach

Questions: How are ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) traits related to other plant traits at the community level? Which abiotic factors drive the variability of these ECM and AM traits? What is the relative importance of plant species turnover and plant intraspecific differences on mycorrhizal trait variability among communities? Location: Nine Mediterranean woody communities, Sierra Morena Mountains, Cordoba, south Spain. Methods: Mycorrhizal and plant traits were weighted by the abundance of constitutive plant species to calculate community-weighted means (CWM). Maximum likelihood techniques were used to analyse how variation in these functional community traits was driven by soil abiotic factors. Results: The degree of ECM colonization was positively related to the abundance of evergreen species and to tissue drymatter content (in leaves and roots), but negatively to specific root length and specific leaf area. The best abiotic predictor of ECM colonization was soil moisture, with higher ECM colonization in drier sites. However, AM colonization was not related to any of the plant traits studied, and was positively related to soil Cu and other physico-chemical soil properties. Changes in community mycorrhization of both types were primarily due to plant species turnover (mainly species occurrence), with a remarkable importance of plant intraspecific variability in the case of AM colonization (especially in the percentage of vesicles). Conclusions: The degrees of colonization by ECM and AM at the community level exhibited different patterns, influenced by both biotic factors (plant functional structure) and abiotic conditions (soil moisture and chemical composition). The proposed mycorrhizal trait-based approach can help to better understand the role of these symbioses on plant community functioning.