Species of legumes are abundant and diverse in neotropical forests, where they can fix atmospheric nitrogen (N) and promote post-disturbance forest recovery. Some studies have shown that N fixation capacity can vary between different legume species. This suggests that in regions with high legume diversity (such as the Atlantic Forest of Brazil), that phylogenetic history may influence patterns of symbiotic N fixation (SNF). Determining the species responsible for the majority of SNF during secondary succession will help to improve species selection during active reforestation efforts. Here we quantify SNF across a chronosequence of regrowth in the Atlantic Forest of Bahia, Brazil. On all excavated root nodules, we quantified SNF and used DNA barcodes for four loci (rbcL, trnH-psbA, ITS, and matK) to link rates of N fixation to the responsible plant host. Plant identifications were made by comparing DNA barcodes from root samples to a curated reference library of DNA barcodes from vouchered herbarium samples of legume species found in the region.
Results/Conclusions
The DNA barcodes identified 13 legume genera (representing 18 species) that fix N during secondary succession in the Atlantic Forest. Inga was the dominant genus observed to fix N (52% of root samples were identified as Inga) and their roots were responsible for 40% of the N fixation we measured. Inga also had the greatest range of N fixation per unit of nodule biomass (or N fixation efficiency) of any genus. We were unable, however, to resolve the identity of all Inga species with DNA barcoding, even with the addition of a fourth barcoding region, ITS. These data suggest Inga plays an important role in the N cycle during secondary succession, but that current barcoding approaches (e.g. four-region approach) are not able to distinguish among the six dominant Inga species in this region of the Atlantic Forest.