Effects of long-term enclosing on distributions of carbon and nitrogen in semia-arid grassland of Inner Mongolia

Abstract

The effects of long-term grazing exclusion on Carbon (C) and Nitrogen (N) partitioning in the green-plant–litter–root–soil system of grassland are unknown. As such, in this study, we evaluated the C and N contents, stocks, and ecological stoichiometry in Inner Mongolian grasslands by enclosing them for 18 and 39 years inside a fence (F18 and F39, respectively), in comparison with those outside the fence (F0), an area that was under long-term grazing. In F18 and F39, C and N stocks were higher in green plants and litter (undecomposed, incompletely decomposed, and completely decomposed litter), but C and N stocks were lower in the roots and soil (P < 0.05). The N stocks in F39 in incompletely and completely decomposed litter were lower (P < 0.05) compared with those in F18. The C contents in green plants and soil were 5% higher in F39 than in F18, whereas the N contents of litter and soil were 17.13%–37.92% lower. The C/N ratio in green plants and litter substantially increased after long-term enclosure, but decreased in roots and soil. The C/N ratio in litter and soil in F39 was 6.5%–36% higher than at F18, but 1.2%–8.2% lower in green plants and roots. Finally, following long-term enclosure, C and N were primarily transported from the soil and roots to green plants and litter. After 39 years of enclosing, C primarily moved from the litter to soil, while N primarily transferred from the soil to roots, compared with 18 years of enclosing. Our results indicated that the duration of enclosure has different effects on C and N distribution in the green-plant–litter–root–soil system. In conclusion, long-term grazing exclusion is not beneficial for soil C and N sequestration in the grasslands of Inner Mongolia.