Rapid response of soil GHG emissions and microbial parameters to the addition of biochar and the freeze-thaw cycle

Abstract

A reduction in snow cover makes soil more exposed to freezing-thawing processes. We tested the rapid response of greenhouse gas (GHG) emissions in fertilized soil to biochar addition under the freeze-thaw cycle. The soil (at a moisture of 55% water holding capacity) was enriched with biochar at a rate of 20 t ha-1, frozen at -20°C for 12 h and thawed at 20°C. The control was soil without biochar and with biochar incubated at temperature of 20°C. Unfrozen soil was a CO2 and N2O source and a weak sink for CH4. The GHG fluxes were not significantly altered by biochar, although biochar-treated soil emitted CH4. The frozen soil emitted all the tested GHGs during the thawing period. A pulse of CO2 and CH4 emissions (and N2O in soil with biochar) occurred in the period of rapid temperature growth, while GHG fluxes reached levels similar to unfrozen soil after temperature stabilization at 20°C. In frozen soil, the addition of biochar significantly increased the CH4 and N2O peak only in the first phase of thawing with a dynamic temperature growth. Biochar changed microbial parameters, therefore we assume that both physical and biological mechanisms could be responsible for GHG emissions in frozen soils.