Changes in the Microbiological and Physico-Chemical Properties of Soils after Fires in Pine and Birch Forests of Central Regions of the Zabaikal Krai

The microbiological and some physico-chemical properties of illuvial-ferruginous soddy-podburs (Entic Rustic Podzols) soils in Scots pine forests and gray-humic typical light loamy soils (Umbrisols) in secondary birch forests of the central regions of the Zabaikal krai have been studied. Fires in soddy-podburs pine forests resulted in decrease in the total exchangeable basis, total nitrogen, mobile forms of potassium and phosphorus, and in increase in the proportion of C : N; while in birch forests, on the contrary, an increase of the mentioned indicators and a narrowing of the C : N proportion in the gray-humic typical soils were observed. The content of humus in the upper soil horizon decreases only in recently burned Scots pine forests after a high-severity fire, while in other sites it increases. A decrease in the soil acidity was observed at all burned sites. High-severity fires lead to a significant decrease in the content of microbial biomass and the intensity of basal respiration, as well as to a change in the structure of ecological and trophic groups of microorganisms in the soils up to a depth of 10 cm of the mineral horizon, while low-severity fires mainly affect the duff. The qCO₂ coefficient increased 2–5 times after fires in the duff and 1.5–2 times in the humus horizon only after high-severity fires. In recently burned Scots pine forests, the storage of microbial biomass and microbial production of carbon dioxide significantly decreased up to a depth of 10 cm of the mineral soil layer. In the steppe site formed after the impact of fires in the pine forest, and in the birch forest after a high-severity fire, in the humus horizon the carbon storage of microbial biomass decreased by 15–20%, and the microbial production of CO₂ increased by 10–20%, predetermining the predominance of mineralization processes. The considered post-fire transformation of the structural and functional parameters of soil microbiocenosis, as well as a 20–40% decrease in the total carbon storage of microbial biomass in the soils of all sites demonstrate a long recovery period of soils after fires in light coniferous and deciduous forests of the central regions of the Zabaikal krai.