Laboratory warming and wetting drives microbial respiration, enzyme activity, and community composition in a boreal...

Soils in northern latitudes are warming, resulting in changes to soil abiotic and biotic processes. We conducted a laboratory study of boreal forest soils from Finland where we manipulated temperature and moisture while measuring respiration. The temperature and moisture reflected field data collected during the summer. Microbial respiration and potential extracellular enzyme activity (EEA) both significantly increased with warming. The nitrogen-degrading potential EEA values were significantly affected by both temperature and moisture conditions, with peak activity occurring at -10 kPa. Both bacterial and fungal community composition shifted with incubation temperature with more fungal families than bacterial families decreasing in relative abundance with increasing temperature. Overall, microbial activity increased with temperature and the changes in community composition were driven by temperature. The effect of matric potential was stronger for the fungal communities. These results suggest potential increases in the rate of microbial respiration and increased seasonal nutrient cycling as boreal forest regions experience warmer and wetter climate regimes.