Soil microbiomes associated with two dominant Costa Rican tree species, and implications for remediation: A case study from a Costa Rican conservation area

Abstract

It is now widely accepted that the majority of tropical landscapes are in transition from disturbance to recovery. Remediation efforts are occurring in Central and South America, attempting to recuperate the soils, often using indigenous nitrogen (N)-fixing tree species. Tree species-generated soil microbial heterogeneity might be important in facilitating regeneration of forest vegetation growth and, although some work has identified these efforts may enhance the soil carbon (C), there have been few studies conducted on how these trees are affecting the below-ground soil biological dynamics in these regions. Here, we explored how and to what extent individual plant effects of a native N-fixing and non-N-fixing plant has affected the below-ground soil C and N metrics and soil bacterial and fungal community composition. To begin to address this, we examined if there were differences in various soil abiotic factors (ToC, TN, C:N ratio, Cmic, NH4+, NO3−, pH, and % moisture) and in the soil bacterial and fungal community composition associated with soil of a native non-N-fixer, Dipteryx panamensis and a native N-fixer, Pentaclethra macroloba, and in comparison to the primary forest bulk-soil in which these tree species occur. We found that primary forest-soils had the greatest amounts of soil NH4+ and Cmic, followed by Pentaclethra-soils. Dipteryx-soils had the least amount of soil Cmic and NH4+, but the greatest amounts of soil NO3−. The PERMANOVA results indicated that the Bray-Curtis soil bacterial and fungal community compositions were significantly different between N-fixing and non-N-fixing tree-soils, and also to that of the primary forest-soils. Our results also demonstrated that soil NH4+ best explained the variation observed in the soil Cmic patterns (39.2%), and, both the soil bacterial (22.8%) and fungal community composition (18.1%). Furthermore, we provide evidence that the N-fixer Pentaclethra-soils stimulates the production of more soil Cmic than the non-N-fixer Dipteryx-soils. It is clear that these tree species are important in creating changes in the soil microbial community composition, and that NH4+ may be associated with a shift in a functional response that may have implications for CUE and remediation in this region.