Root Functional Diversity of Native and Nonnative C3 and C4 Grass Species in Hawai‘i

C3 and C4 plants are often reported to differ in functional traits and resource-use strategies, whereas nonnative plants may differ from native plants in functional traits, leading to different resource-use strategies that facilitate their invasion. In this study, we compared root functional traits of native and nonnative C3 and C4 grasses with the prediction that different resource acquisition strategies would be observed among these groups. We examined five root functional traits [mean diameter, specific root length, root tissue density, fine root percentage (diameter <0.2 mm), and root length density] among natural communities of C3 and C4 grass species along an elevation gradient in Hawai‘i to classify resource-use strategies. We also examined how root functional traits were related to environmental characteristics (mean annual, seasonal, and July soil moisture; mean annual precipitation and temperature; and soil nitrogen percentage) along this elevation gradient. Root traits corresponded broadly to differences in photosynthetic pathway [C3 versus C4 (P < .05)]. However, significant variation occurred within the C3 functional group (P < .05), whereas all C4 species had similar root functional traits. Grass assemblages were associated with differences in seasonal soil moisture, but root traits did not sort consistently along any environmental gradient. Principal component and cluster analyses of root functional traits showed that nonnative C3 species tended to be resource acquisitive whereas the native C3 species was resource conservative, similar to native and nonnative C4 species. Evaluating functional traits of native versus nonnative species will provide a better understanding of invasion dynamics and suggest possible restoration and conservation strategies in grassland communities where native species still persist.