Microbial growth rates, carbon use efficiency and enzyme activities during post-agricultural soil restoration

Microorganisms are critical for litter decomposition, organic carbon (C) and nutrient transformations in soil, corresponding to the vegetation succession. The dynamics of microbial activities and ecological functions during the soil recovery after agricultural land use (post-agricultural restoration) remains unclear. We investigated the effects of vegetation and soil restoration duration on active microbial biomass, microbial growth rates, C use efficiency (CUE, analyzed by C-14 glucose utilization), and enzyme activities in three soil types of Russia: Haplic Luvisol in a deciduous forest (chronosequence from 0 to 37 years), Luvic Phaeozem in forest steppe (0-66 years), and Haplic Phaeozem in forest steppe (0-42 years). The microbial CUE (0.66-0.82) decreased during restoration and was highly dependent on soil type: the lowest in Luvisol and the highest in Haplic Phaeozem. The activities of beta-1,4-glucosidase, beta-1,4-N-acetylglucosaminidase, leucine aminopeptidase, and acid phosphatase increased during post-agricultural restoration. Microbial growth rates and the proportion of active microorganisms increased with restoration, reflecting a shift of microbial community to fast-growing decomposers (mainly r strategists) caused by large litterfall from recovered natural vegetation. The increase of the portion of active microorganisms and microbial growth rates was correlated with activities of enzymes responsible for C, N and P cycling. In conclusion, the post-agricultural restoration activates microorganisms, raises microbial growth, increases enzyme activities and accelerates microbially-mediated C and nutrient turnover.