Post-Pyrogenic Restoration of the Biological Activity of Soils of Artificial Forest Plantations in the Arid Zone of the Shirinskaya Steppe in the Republic of Khakassia

In the coastal zone of Lake Shira (The Republic of Khakassia), in forty-year-old artificial forest plantations of Siberian larch, Siberian elm, and Scots pine growing on loamy dark carbonate-accumulative agrozems (Chernozems), the state of soil microbial communities and the rate of restoration of their biological activity after the ground fire of 2015 were assessed. The condition of the soil under forest plantations was studied using physicochemical, microbiological, enzymological, and respirometric methods. In 2015 (after the fire), the intense input of the products of pyrogenesis into the soil resulted in the high values of microbial biomass (3458 mg C/g soil) and microbial respiration intensity (12.23 μg C–CO2/(g h). During 2017–2019, a decrease in the content of humus and biophilic elements and a slowdown in the activity of carbohydrate and phosphorus metabolism were generally observed in the soils of the studied plots. At the same time, in 2017, the highest cellulose-decomposing activity was observed because of the intensive mineralization of burnt plant residues. By 2023, a gradual increase in the humus content, the total number of microorganisms, and the microbial biomass took place against the background of a significant decrease in the values of the microbial metabolic quotient. These features indicate a tendency for the restoration of the functional activity of soil microbial cenoses. The biological activity of the soil in the postfire sites restored faster than that in the soil of completely burnt areas; the species composition of the tree stand affected the main soil parameters that differed under different stands, which was confirmed by the principal component analysis.