Belowground plant functional ecology: Towards an integrated perspective

Abstract

Abstract1. 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 lessstudied 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 tradeoffs 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. K E Y W O R D Sacquisitive and nonacquisitive compartments, belowground plant functions, biomass allocation and turnover, buds and carbohydrates storage, growth forms, ontogeny, rhizomes, roots

Half of the (big) picture is missing!

“…; Laliberté, ; Freschet and Roumet, ; Klimešová et al., ). Thick roots, rhizomes, bulbs, and tubers rarely play a role in absorbing water and nutrients, but they can affect resource acquisition by determining fine root placement and longevity (Klimešová et al., ). Most importantly, these coarse organs do provide other key functions including anchorage in the soil, connection and transport of resources to aboveground parts, storage of carbohydrates and of buds for resprouting, space occupancy, resource sharing, and support for fine root placement in the soil (Klimešová et al., ; Pausas et al., ).…”

“…This may reflect an unbalanced focus of ecologists on fine roots while overlooking coarse, non‐acquisitive roots and belowground stems (Fig. ; Laliberté, ; Freschet and Roumet, ; Klimešová et al., ). Thick roots, rhizomes, bulbs, and tubers rarely play a role in absorbing water and nutrients, but they can affect resource acquisition by determining fine root placement and longevity (Klimešová et al., ).…”

“…Thick roots, rhizomes, bulbs, and tubers rarely play a role in absorbing water and nutrients, but they can affect resource acquisition by determining fine root placement and longevity (Klimešová et al., ). Most importantly, these coarse organs do provide other key functions including anchorage in the soil, connection and transport of resources to aboveground parts, storage of carbohydrates and of buds for resprouting, space occupancy, resource sharing, and support for fine root placement in the soil (Klimešová et al., ; Pausas et al., ). For example, the acquisitive properties of a root system are affected by the growth direction of coarse roots; a horizontal growth direction will result in a shallow root system, while an oblique growth direction will distribute fine roots in the lower soil horizons.…”

“…In addition to their role in plant functioning, coarse belowground organs also contribute to define key ecosystem properties because they may constitute most of the belowground biomass in many ecosystems (e.g., Pausas et al., ). Examples of key ecosystem functions affected by coarse organs include protection against soil erosion (Stokes et al., ) and contributions to nutrient cycling and carbon sequestration (Freschet and Roumet, ; Klimešová et al., ). We urgently need to refine our understanding of coarse belowground organs, starting by considering them in our studies and then representing them accurately in drawings, i.e., with all their organs correctly reported and positioned and with adequate size proportions.…”

“…Ecologists can use a variety of methods to study roots in situ. However, most of these methods do not allow the observation of belowground plant organs as a whole (e.g., fine and thick roots, rhizomes; Klimešová et al., ). Solutions to these challenges are becoming available based on past fundamental work (e.g., Rauh, ; Kutschera and Lichtenegger, ; Bell, ), involving different ways of looking at plants, i.e., plants as modular organisms (Klimešová et al., ).…”