Fire Severity Effects On Nutrient Dynamics And Microbial Activities In A Siberian Larch Forest

High-latitude ecosystems store large amounts of carbon in soil organic matter and are among the most vulnerable to climate change. Fire severity and frequency are increasing in boreal ecosystems, and these events are likely to have direct effects on climate feedbacks via increased emissions of carbon (C) from combustion of soil organic matter and vegetation, and indirect effects on climate feedbacks via changes in vegetation composition, ground thaw, and edaphic variables. This study examines the indirect effects of fire on climate feedbacks by determining how fire affects C, nitrogen (N), and phosphorus (P) pools, soil microbial processes, and how these effects scale across severity and time since fire. In this study we created experimental burns of three severities in a larch forest in the northeastern Siberian arctic, near Cherskiy, Russia, and quantified dissolved C, nitrogen (N), and phosphorus (P), and microbial respiration and extracellular enzyme activities at 1-day, 8-days, and 1-year post-fire.
We found labile C and nutrients increased immediately post-fire, but were not statistically different from unburned controls within a week. Phosphorus alone remained elevated through 1-year post-fire. Fire severity had a linear effect on extracellular enzyme activities, and suppressed most extracellular enzyme activities 1-year post-fire. Soil respiration was reduced by half in high severity plots 1-year post-fire, while net rates of N mineralization increased by an order of magnitude. Microbial communities recovering from more severe fires have the possibility to decrease future ecosystem C losses through reduced respiration. The changing fire regime in permafrost ecosystems has the potential to alter soil microbial community dynamics, the retention of nutrients, and the stoichiometry of C, N, and P availability, and these indirect effects of fire will ultimately drive post-fire regeneration and feedbacks of fire on global climate.