Plant species effects on soil carbon and nitrogen dynamics in a temperate steppe of northern China

Abstract

We evaluated plant species effects on soil carbon (C) and nitrogen (N) dynamics in a steppe ecosystem of northern China. In two subsequent years, we measured soil properties in the top 10 cm of the soil under replicated mono-dominant plant patches in two sites that differed in land-use history: a cultivated site (old field) and an uncultivated site (steppe). Both in the cultivated site and the uncultivated site, we selected patches of three of the dominant plant species. Contrast analyses in ANOVA showed that soil organic carbon (SOC) and total N content (g per m2) was on average lower in the cultivated site than in the uncultivated site. On average, soil respiration was also lower in the cultivated site than in the uncultivated site. However, overall differences in soil C and N dynamics between the cultivated site and the uncultivated site (if existing) were generally small compared to the effects of individual plant species. Soil respiration differed among plant species in the cultivated site, but not in the uncultivated site. In contrast, SOC content, total N, and N mineralization rate differed among plant species in the uncultivated site, but not in the cultivated site. Mineralization and nitrification rates strongly varied among the dominant plant species, particularly in the uncultivated site. Variation in both C and N pools and fluxes could be best explained by a combination of plant biomass, litter, and soil microbial and micro-climatic parameters. Cultivation can directly affect soil C and N dynamics. However, importantly, our data suggest that indirect effects through changes in plant species composition are also important, and probably strongly interact with direct effects in affecting soil C and N dynamics after land-use change. Hence, evaluation of land-use history on soil C and N dynamics requires integral analyses of changes in plant community composition.