Changes in soil bacterial communities, and carbon and nitrogen metrics as potential indicators of land use effects in a humid tropical forest

It is unclear how different management practices influence tropical soil ecosystems in post-logging habitats over short or long terms. In this project, we demonstrated that critical differences in soil C and N metrics, organic C use efficiency, and DNA-identified bacterial community structures occurred along a land use disturbance gradient in a humid tropical primary forest (PF) Costa Rica following deforestation and conversion of the forest into logging roads (LR), grasslands that were grazed and then abandoned (GR), and regenerating secondary forests (SF). The mean proportion of DNA sequences, their richness and diversity for total bacterial genera and those linked to N-fixation, ammonium oxidation, and degradation of complex organic C compounds were generally greater in the PF than the SF soils, followed by the GR and then the LR soils. The specific land useassociated changes in soil NO3-/NH4+, TN, TOC, and biomass C/TOC best predicted these differences in bacterial communities. The SF soil ecosystems were on a better trajectory towards similarity with the PF soils, followed by the GR soils, with the LR soils still being the most negatively influenced. This study showed that the soil biotic and abiotic factors were clearly different along the disturbance gradient, with each soil ecosystem responding differently to the forest clearing, followed by development of logging roads, abandoned grasslands, and secondary forests. This work also showed that differences in C and N metrics, and the structure of total and functional group communities of bacteria, in particular, the genera Solibacter, Burkholderia, Bradyrhizobium, Comamonas, Geobacter, Azospirillum, Nitrospira, Nitrosovibrio, Rhodoplanes and Phenylobacterium can serve as future indicators of soil damage and recovery following different types of disturbances.