Intraspecific Functional Trait Variation and Coordination in Schizachyrium scoparium

Plant functional traits are vital tools in ecological restoration and biodiversity conservation. While functional traits and functional diversity are increasingly being used to inform restoration efforts, challenges remain in the characterization of trait variation in many systems, including within-species. Likewise, understanding axes of trait variation describing trade-offs in plant function is important for trait-based restoration frameworks, yet the degree of coordination between above-ground functional traits and their below- ground counterparts is often unknown. Here, we investigate intraspecific trait variation among five populations of Schizachyrium scoparium (little bluestem), a species commonly used for restoration, from different habitat types across a gradient from southern Wisconsin to Northern Illinois. We asked (1) how regional populations of S. scoparium differ in their functional traits, (2) how functional trait variation in S. scoparium is structured among and within populations, and (3) how above- and below-ground functional traits of S. scoparium coordinate and describe axes of functional trade-offs. We found that populations differed in multivariate trait space, but evidence for differences in individual traits among populations was mixed. Trait relationships with habitat types were idiosyncratic and often misaligned with expectations of plant economic spectra. Variation within populations was as high, or higher, than between populations across traits. We found evidence for weak coordination in several trait pairs, including two above- and below-ground trait combinations, while others appeared to be uncoordinated. Our findings support previous research that trait differentiation can occur at multiple scales, both between and within populations. Extensive within-population trait variability could be leveraged in trait-based restoration frameworks targeting intraspecific functional diversity. The lack of strong signals of coordination between above- and below-ground functional traits suggest that sourcing decisions meant to match below-ground functional traits to recipient restored communities should rely on direct measurement of root traits associated with desired functions rather than above-ground proxies.