Abstract
The grazing exclusion in degraded grassland has been extensively used to prevent the loss of grassland resources and to improve grassland services. The effects of grazing exclusion on C and N balance, however, have not been well addressed but are essential for assessing grassland C sinks, the sustainable use of grassland resources and the support of grassland services. To understand the response of ecosystem C and N to grazing exclusion in semiarid grassland, we determined the C and N in litter, aboveground biomass, roots and soils from ungrazed grassland fenced at different times in northwest China. Our results showed that the aboveground biomass, root biomass and plant litter were 70–92%, 56–151% and 59–141% higher, respectively, in grazer excluded grassland than in grazed grassland. Grazing exclusion significantly increased C and N stored in plant biomass and litter and increased the concentrations and stocks of C and N in soils. Grazing exclusion thus significantly increased the C and N stored in grassland ecosystems. The increase in C and N stored in soil contributed to more than 95% and 97% of the increases in ecosystem C and N storage. The highest C and N stocks in ecosystems were observed in 17-year grazer excluded grassland. The results from this study indicate that grazing exclusion has the potential to increase C and N storage in degraded semiarid grassland and that the recovery of ecosystem C and N was mainly due to the accumulation of C and N in soils.
Highlights
Grasslands cover 20% of the terrestrial surface and account for 20% or more of total terrestrial production [1]
Grasslands store more than 10% of terrestrial biomass C and 10–30% of global soil organic carbon (OC), and they have been estimated to sequester C in soil at a rate of 0.5 Pg C yr21, accounting for about one-fourth of the potential carbon (C) sequestration in world soils [1,3]
The C and N stocks in the aboveground biomass were not affected by grazing exclusion age, but the C and N stocks in the root biomass increased with grazing exclusion age
Summary
Grasslands cover 20% of the terrestrial surface and account for 20% or more of total terrestrial production [1]. Owing to their importance in socio-economics, culture, ecology and environmental quality, grassland ecosystems have become one of the most active subjects of research by ecologists around the world [2]. Grasslands store more than 10% of terrestrial biomass C and 10–30% of global soil organic carbon (OC), and they have been estimated to sequester C in soil at a rate of 0.5 Pg C yr, accounting for about one-fourth of the potential carbon (C) sequestration in world soils [1,3]. Possible mechanisms of the loss of C and N include changes in composition of plant communities, changes in plant roots and their control of the soil microbial community [11,12], decreased input of organic material from aboveground biomass and roots due to biomass removal [13], decreased availability of soil resources in grasslands [14,15,16,17] and the disruption of soil structure resulting in losses of C and N through accelerated mineralization of soil organic matter and erosion by water and wind [9,18,19,20,21,22,23]
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