Soil microbiomes and C and N dynamics associated with two dominant Costa Rican tree species, and implications for remediation: a case study from a Costa Rican conservation area. Soil 16S

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-fixing tree species. Although some work has identified these efforts may enhance the soil carbon (C), there has been few studies conducted on how these trees are affecting the below-ground soil biological dynamics in these regions. Tree species-generated soil microbial heterogeneity might be important in facilitating regeneration of forest vegetation growth. Conversely, the trees might also influence the biota in the soil ecosystems in which they occur, possibly resulting in better C-use efficiency (CUE) and C-sequestration. Here, we explored how and to what extent tree species identity (and associated functional type) has affected the below-ground soil C and N dynamics and soil bacterial and fungal community composition, and if, one of the trees, Pentaclethra macroloba, shows potential for the recuperation of soil ecosystems in the Northern Zone of Costa Rica. To begin to address this, we examined if there were differences in various soil abiotic factors (% C, % N, C:N ratio, Cmic, NH4+, NO3-, pH, and % moisture) and in the soil bacterial and fungal community composition between Dipteryx panamensis-soils and Pentaclethra macroloba- soils, and in comparison to the primary forest bulk soil in which these tree species occur. We found differences in soil NH4+, NO3-, and Cmic with primary forest-soils having the greatest amounts of soil NH4+ and Cmic, followed by P. macroloba-soils. Dipteryx panamensis-soils had the least amount of soil Cmic and NH4+, but the greatest amounts of soil NO3-. There were no differences in the %C, %N, C:N ratio, pH, and % moisture across the D. panamensis-, P. macroloba-, and primary forest-soils. The soil bacterial and fungal community composition was significantly different between tree species-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 and both the soil bacterial and fungal community composition. Furthermore, we provide evidence that P. macroloba stimulates the production of more soil Cmic than a native non-N-fixing tree species. This indicates the potential of using Pentaclethra macroloba for possible facilitation of CUE, and thus, a potential remediation strategy of secondary forest soil recuperation in this region. It is clear that these tree species are important in creating changes in the soil microbial community composition that is associated with a shift in a functional response that may have implications for CUE and remediation in this region.