Why functional ecology should consider all plant organs: An allocation-based perspective

Abstract

Functional ecology often analyses a few selected traits and relates them either to environmental conditions or ecosystem properties. However, not the individual trait, but the whole plant with a set of coordinated traits responds to the environment or affects ecosystem properties. Here we argue that the correlation among traits of all major plant organs should be an integral part of response or effect studies. Plants allocate elements and biomass among roots, perennial clonal organs, stems, leaves and seeds to ensure growth and reproduction. Assessment of trait responses to the environment and effects on ecosystems is hardly possible without simultaneously considering all plant organs and the biological functions they perform, namely resource uptake, vegetative regeneration, support and hydraulic pathways, photosynthesis and generative reproduction. Suitable traits to indicate these functions include those of mass, density, size, volume, and element contents of the main plant organs. In principle, we do not propose to collect many traits, but those of similar significance across organs. For instance, specific leaf area should be complemented by specific root length and specific stem length. We present some thoughts on how coordinated allocation to biological functions sets boundaries to the range of trait expressions in successional series and consequently also to species responses to the environment and effects on ecosystems. Considering the coordination of traits amongst all major plant organs will improve our understanding of plant strategies ensuring survival in patterned landscapes.