Abstract: Understanding the changes in soil enzyme activities and the influencing factors after forest fire distur-bances can help assess and predict the impacts of climate warming on permafrost ecosystems. We analyzed the acti-vities of extracellular enzyme, including urease (UR), acid phosphatase (AP), acetyl-glucosidase (NAG), β-glucosidase (βG), and leucine aminopeptidase (LAP), in soils (0-60 cm depth) across unburned, lightly burned and severely burned sites within the 2015 burned area in the northern Da Xing’anling Monntains. The results showed that fire intensity, soil depth, and soil physicochemical properties significantly influenced extracellular enzyme activities. Compared to that in unburned site, the activities of UR, AP, βG, and LAP increased by 59.8%-241.7%, while NAG decreased by 35.5% at lightly burned site. The activities of all soil enzymes increased, with the magnitidues ranging from 26.0% to 206.0% at severely burned site. Soil enzyme activities gra-dually decreased with increasing soil depth. Redundancy analysis identified soil temperature (ST), total phosphorus (TP), C:P, C:N, soil depth and soil water content (SWC) as important influencing factors of soil enzyme activities, contributing 70.9%, 12.2%, 4.7%, 3.6%, 2.9%, and 1.9%, respectively. Soil enzyme activities were signifi-cantly positively correlated with ST, TP, C:P, C:N, and SWC, but significantly negatively correlated with soil depth. Forest fires and the resultant changes in soil physicochemical properties jointly affected soil extracellular enzyme activities, with the effects intensifying with increasing fire intensity.

Key words: forest fire; permafrost; Da Xing’anling Mountains; soil extracellular enzyme activity; fire intensity