No differences in community dominance of nitrogen-fixing plants across the savanna, woodland and forest biomes of Brazil: a meta-analysis

Abstract

The geographical extent of nitrogen (N)-fixing legumes is widespread in South America, but patterns in distribution of N fixers across the two largest biomes in South America (forests and savannas) are unknown. Due to the competitive ability of N-fixing plants to access nutrients, it should be expected that they thrive in areas of high disturbance and low N, such as fire-present savannas. In turn, I would expect to see a lower abundance of N fixers in the fire-absent forest biome. However, this pattern of N fixer distribution on the biome level has never been tested. Here, I utilize a meta-analysis approach to compile woody vegetation inventory data and compare (1) the relative number of N-fixing species, (2) the relative abundance of N-fixing individuals, and (3) the relative basal area of N fixers across the savanna, woodland and forest biomes of Brazil. The results show no significant effect of biome on any of these metrics of Nfixing community dominance, even with the consideration of possibly confounding climatic and soil fertility variables in the analysis. These results not only challenge the notion of fire as a selective agent for N fixing communities, but also have implications for evolutionary tradeoffs of N fixation and ecosystem dynamics in the Brazilian forestsavanna boundary.