Assessment of N fixation capability of native legumes from the longleaf pine-wiregrass ecosystem

摘要

Longleaf pine (Pinus palustris) is a major ecosystem in the southeastern United States. Native legumes species are viewed as an important component of successful restoration of the longleaf pine-wiregrass (Aristida stricta) ecosystem as a result of their ability to fix atmospheric nitrogen (N). However, virtually no measurements exist on the N fixation potential of the various native legume species in this ecosystem. The objective of this study was to compare the N fixation capability under ambient and half ambient light conditions of nine native legume species: Centrosema virginianum, Clitoria mariana, Crotalaria rotundifolia, Lespedeza hirta, Mimosa quadrivalvis, Orbexillum lupinellus, Rhyncosia reniformis, Tephrosia virginiana, and Chamaecrista nictitans. Their N fixation activity was indexed using five approaches (nodule biomass, total plant N content, acetylene reduction assay, N transport and storage product analysis, tp#eN natural abundance) since no single measure by itself has proven to be a completely reliable result. Based on the results of these five approaches, a decrease in light levels by half had no impact on the N fixation potential of any of the species. At least under a relatively open longleaf pine canopy, native legumes could be important contributors to the N balance. Considering all measures, two legumes proved consistently to be superior in N fixation capability: Mimosa quadrivalvis and Centrosema virginianum.