Organic carbon accumulation and microbial activities in arable soils after abandonment: A chronosequence study

Increased plant carbon (C) input into the soils after cropland abandonment results in not only C accumulation, but also higher microbial activities and consequently faster organic matter decomposition. We investigated the link between soil C accumulation and microbial properties in a chronosequence (0–65 years) of post-agricultural self-restoration of Luvisols - the dominating soil type worldwide. Microbial biomass carbon (MBC) and enzyme activities increased in the top soil (0–20 cm) during the 37-year period of self-restoration. Accumulation of microbial biomass was faster than of soil organic C at earlier stages of self-restoration (0–22 years) because of the fast microbial growth induced by labile litter components. The response of microbial activity was more sensitive to land use changes compared to that of soil organic C. Activities of enzymes responsible for C cycle increased more than that of nitrogen (N) and phosphorus (P) cycles at least up to 37 years after abandonment, indicating microbial adaptations to high input of litter with wide C/N and C/P ratios. Similarly, β-xylosidase was the solely enzyme which reached the activity similar to secondary forest soils after 65 years, due to the accumulation of recalcitrant C in litter with cropland abandonment age. The increased C demand was caused by the higher bacterial portion in soil microbial community (based on PLFA composition), which in turn, resulted in a lower microbial biomass C/N ratio. Enzyme stoichiometry revealed that microorganisms were limited by C and N in the topsoil during the self-restoration up to 37 years. Overall, the quantity and quality of plant C inputs, which changed with post-agricultural land restoration, regulated the microbial activity and enzyme production, offering a profound comprehension of ecosystem succession.