Belowground plant functional ecology: Towards an integrated perspective

1. In recent years, belowground plant ecology has experienced a booming interest. This has resulted in major advances towards a greater understanding of belowground plant and ecosystem functioning focused on fine roots, mycorrhizal associations and nutrient acquisition. 2. Despite this, other important functions (e.g., on-spot persistence, space occupancy, resprouting after biomass removal) exerted by different belowground plant organs (e.g., roots, rhizomes, bulbs) remain largely unexplored. 3. Here, we propose a framework providing a comprehensive perspective on the entire set of belowground plant organs and functions. We suggest a compartment-based approach. We identify two major belowground compartments, that is, acquisitive and nonacquisitive, associated with biomass allocation into these functions. Also, we recommend the nonacquisitive compartment to be divided into structural (e.g., functional roles carried out by rhizomes, such as sharing of resources, space occupancy) and nonstructural (e.g., functional roles exerted by carbohydrates reserve affecting resprouting ability, protection against climate adversity) subcompartments. We discuss methodological challenges-and their possible solutions-posed by changes in biomass allocation across growth forms and ontogenetic stages, and in relation to biomass partitioning and turnover. 4. We urge the implementation of methods and approaches considering all the belowground plant compartments. This way, we would make sure that key, yet less-studied functions would be incorporated into the belowground plant ecology research agenda. The framework has potential to advance the understanding of belowground plant and ecosystem functioning by considering relations and trade-offs between different plant functions and organs. At last, we identify four major areas where using the proposed compartment-based approach would be particularly important, namely (a) biomass scaling, (b) clonality-resource acquisition relations, (c) linkages between resprouting and changing environmental conditions and (d) carbon sequestration.