COS 224-4 - CANCELLED - Root structure, leaf morphology, plant size and phenology: a whole-plant functional integration among 44 wetland herbaceous species

Abstract: The complexity of root systems and their multifunctionality present challenges in understanding the relationships between root and leaf traits and how they relate to whole-plant functioning across different species. Multivariate analysis methods, such as network analysis and structural equation modelling (SEM), provide opportunities to investigate these relationships and uncover underlying hierarchies.
This study focused on herbaceous monocots in local wetlands in Northern Ontario, which face severe selective forces and have relatively similar structures and growth forms. Using the aforementioned multivariate analyses, we examined how the traits of root system structure (rooting depth, branching density/length, and the diameter, dry-matter content, and porosity of axile and lateral roots), leaf morphology (thickness, dry matter content, specific leaf area, and porosity), plant size (shoot dry mass and height), and plant autumnal phenology (root overwintering habits and timing of leaf senescence) are integrated across 44 species. Phylogenetic dependence of trait correlations was considered in analyses.
The network analysis identified three functional modules based on inter-species trait correlations: size and form, turnover, and leaf morphology. At the module level, the size and form module represented a syndrome where species’ above-ground size matched their root system traits in depth, lateral root branching, root porosities and axile root thickness. Shared ancestry was not found to significantly shape the observed pattern. SEM results showed that root architecture (root depth and branching length) directly determined shoot biomass, and that root porosities and axile root thickness strongly correlated with shoot biomass but without direct links due to the mediating effect of root architecture. The turnover module emphasized the coordination between leaves and roots in their autumnal phenology and dry-matter content, although they were more phylogenetically conserved than traits in the size and form module. At the network level, we identified plant height as central to whole-plant functional integration. It connected with other module-level central traits from three modules, reflecting the multiple constraints that shape plant stature from both leaves and roots.
Overall, our results suggest that root traits are closely integrated with above-ground traits, all the traits forming modules of interdependent traits based on function, not on organ or plant part. We highlight the importance of root architecture as a functional mediator between single root traits and shoots, and the coordination of herbaceous root and leaf in phenology. With careful trait selections, network analysis is suggested to explore the complex relationships of functional traits at the whole-plant level.