The Fate of Microbial Groups in Tropical and Temperate Forest Soils

This research investigates the importance of microbial biochemistry to carbon (C) humification pathways in two climatically different forested ecosystems, Blodgett forest (BF), a temperate forest in the Sierra Nevada and Luquillo forest (LF), a tropical forest in Puerto Rico. 13C enriched tropical and temperate species from four microbial groups (fungi, actinomycetes, bacteria gram (+), and bacteria gram (-)) were separately added to soil at both sites. Substrate decomposition rates were substantially greater in LF than BF, as were overall respiration rates. After several months most new C was retained in the top 7.5cm at both sites, indicating insignificant loss due to leaching. While there were no significant differences in decomposition rates between temperate and tropical microbial additions at either site, there were treatment differences in C recovery within the microbial biomass C (MBC) pools, the dissolved organic C (DOC) pools, and recovery as CO2-C for both sites. Recovery as MBC at BF was initially greater for tropical additions than for temperate; at LF recovery as MBC was initially greater for temperate fungi and bacteria gram (+) than for tropical, and greater for tropical actinomycetes than for temperate. After several months, the trends at BF reversed, and there were little to no treatment effects at LF. Treatment recovery as DOC initially showed similar patterns to MBC-recovery at both sites, but after several months DOC-recovery drastically declined for all treatments, amounting to <0.05% of input C. Both soils respired more tropical fungi C than temperate, and more temperate actinomycetes C than tropical. These results demonstrate potentially different stabilization mechanisms associated with microbial groups and are most likely associated with differences in microbial biochemistry. The soil microbial community plays a key role in SOM dynamics, and this research provides important insight into these relationships and the biogeochemical processes governing soil carbon dynamics.