Functional Plant Diversity: Traits, Evolution, Biodiversity Conservation and Ecosystem Restoration

Trait-based ecology has long relied on leaves to explain how plants influence ecosystems, yet most of the carbon, nutrient and water exchanges that sustain terrestrial ecosystem functioning take place in soil, where roots and their mycorrhizal partners operate. Over the past decade, the reconceptualisation of fine-root variation as a multidimensional root economics space, the recognition of a mycorrhizal collaboration gradient, the global mapping of mycorrhizal vegetation and the refinement of multifunctionality metrics have created an opportunity to connect aboveground traits, belowground traits and symbiotic strategies to the simultaneous provision of multiple ecosystem functions. These research streams have nevertheless developed largely in parallel. This critical narrative review examines whether current evidence supports an integrated, whole-plant explanation of ecosystem multifunctionality in terrestrial vegetation. Literature published between 1998 and mid-2026 was identified through structured searches of open multidisciplinary scholarly indexes, supplemented by backward and forward citation tracking, and appraised for design, scale, measurement standardisation and consistency. The synthesis indicates that leaf and root economic traits are only partially coordinated: nitrogen concentration and tissue density show recurrent covariation, whereas specific root length and root diameter vary largely independently of the leaf economics spectrum because many plants outsource resource acquisition to mycorrhizal fungi. Tree mycorrhizal type predicts contrasts in nitrogen cycling, litter decay and soil carbon distribution, particularly in temperate forests, but the direction of carbon storage effects depends on soil depth, climate and the pools measured. Root-derived inputs, exudation and fungal traits appear to be at least as influential as leaf litter for soil organic matter formation, although field evidence remains limited. Relationships between traits and multifunctionality are sensitive to which functions are measured, how they are aggregated, and whether dominance or diversity is considered, and most studies remain correlative, short-term and geographically concentrated. An evidence-based conceptual framework is proposed that distinguishes well-supported pathways from hypothesised ones. Priorities include standardised whole-plant trait measurement in the same individuals, experiments crossing mycorrhizal type with plant diversity, explicit treatment of function trade-offs, and long-term studies in tropical, dryland and agricultural systems. Integration is warranted, but predictive claims should remain proportional to this still-fragmented evidence base.