Climate variation and soil microbial biomass and activity in northern hardwood forests

Background/Question/Methods

The effects of climate variation on soil moisture and temperature, and on snow and frost dynamics, are critical uncertainties about the long-term impacts of climate change on temperate forests. We used a 395 m elevation gradient at the Hubbard Brook Experimental Forest (NH, USA), which encompasses the range of climate variability that has been predicted for the northeastern U.S. over the next 50-100 years, to evaluate the effect of climate warming on soil microbial biomass and activity. Our objectives were to (1) characterize landscape scale controls on soil microbes expressed through temperature, moisture, snow and frost dynamics, and 2) use the setting as a platform for exploring how microbial biomass and activity vary with climate.

Results/Conclusions

Results show that the elevation gradient experienced a wide range of soil temperature and moisture conditions (e.g. mean soil temperature and moisture ranged from ~4.7 °C to ~8 °C, and from ~20% to ~40%, respectively, in 2011) and snow and frost depth (e.g. maximum snow and frost depth ranged from 66 cm to 96 cm, and from 4.2 cm to 9.9 cm, respectively, in 2011). This variation in abiotic conditions due to elevation resulted in a wide range of soil microbial biomass and activity, but the magnitude or even the direction of the elevation effect varied depending on the sampling season and the soil horizon. We also observed important inter-annual differences in snow and frost dynamics (e.g. maximum snow depth in February 2011 = ~ 88 cm, in February 2012 = ~33 cm; maximum frost depth in February 2011 = ~12 cm, in February 2012 = ~21 cm), likely affecting soil microbes and nutrient cycling in these forests. Further work on our results will allow us to determine and model how climate change will affect soil microbial biomass and activity through changes on abiotic drivers such as soil temperature and moisture, and snow and frost dynamics.