ИСТИНА

Enzymatic activity, basal respiration rate and microbial biomass are the most sensitive indicators of post-agrogenic changes in soils due to their quick response to cessation of agricultural use. In this study, we examined the dynamics of microbial and enzymatic activity in post-agrogenic Phaeozems and Chernozems of Central Russia. A chronosequential study was carried out in two bioclimatic regions of European Russia: deciduous forest (Moscow region; Luvic Phaeozems) and dry steppe (Rostov region; Chernozem). Each chronosequence included a current arable soil, abandoned lands of different ages, and natural cenosis. The rate of basal soil respiration (BR), microbial carbon content (Cmic) and activity of hydrolases were determined in the mixed soil samples collected from different depths of former arable layer: 0-5, 5-10, 10-20, and 20-30 cm. The most visible changes in biological parameters were revealed in the uppermost 0-5 cm layer for both chronosequences. We observed a progressive increase in BR values (from 0.6 to 3.4 mg C kg-1 soil h-1) and Cmic content (from 342 to 636 mg C kg-1 soil) in soils during the postagrogenic evolution in the deciduous forest zone. As a rule, the younger abandoned soils were characterized by low activity of hydrolytic enzymes. In older abandoned soils (>35 years old), hydrolase activity was 3-3.5 times higher than in younger ones and was comparable to that in the forest soil. In steppe zone, a similar trend was also revealed in the upper 0-5 cm layer: a progressive increase of the BR values (from 0.7 to 1.1 mg C kg-1 soil h-1) and Cmic content (from 511 to 970 mg C kg-1 soil). There was no obvious trend in activity of enzymes during post-agrogenic restoration. The activity of hydrolases was the highest in abandoned soils of 19 years. In post-agrogenic Phaeozems, the total activity of hydrolytic enzymes of carbon cycle rised progressively. We revealed an increase of portion of enzymes with a narrow substrate specificity from 20% to 44% during the postagrogenic evolution. There were no obvious trends in the post-agrogenic Chernozems due to the immobilization of enzymes in soil matrix. The changes in the Cmic content explained 50 - 70% variability of hydrolytic enzymes activity in post-agrogenic soils. Concluding, post-agrogenic evolution of former arable soils resulted in an increase in microbial C content, rate of basal respiration, and activity of hydrolytic enzymes due to the input of fresh plant residues.