Nitrogen and carbon losses from decomposing litter in natural and agroecosystems of two different climate regions of Brazil

Abstract

In the past four decades, Mato Grosso in Central-West Brazil has undergone rapid changes from forested area to pasture and/or cropland. Yet, little is known about how these changes affect litter turnover and nitrogen (N) and carbon (C) cycling. We carried out litter breakdown experiments with litter mesh bags and investigated the effects of five factors on the release of N and C after 20 weeks, i.e. season (rainy, dry), litter quality (local, standard), land-use (forest, pasture, cropland), soil organisms (soil fauna, micro-organisms), and region (savannah climate, Amazon climate). We found that: (1) season had an overall effect on N and C losses by influencing the activity of soil organisms; (2) N and C losses correlated negatively with the initial litter C:N and lignin:N ratio, respectively; (3) N and C losses increased with decreasing human impact on the land-use; (4) soil fauna increased N loss by 35% and C loss by 16%; (5) the effect of the soil fauna on N and C correlated negatively with the initial litter lignin:N ratio; (6) higher N and C losses were observed in South-Amazon systems (except for C losses in the dry season); and (7) soil fauna exclusion resulted in N immobilisation, particularly in the Cerrado. Although the seasonal effect was a major driver of N and C release, our findings indicate that soil organisms are the key to understanding the differences in N and C cycling at regional and land use level.