Grazing exclusion alters carbon flux of alpine meadow in the Tibetan Plateau

Abstract

• Carbon flux in grazing and enclosure grasslands is highly inconsistent. • Fencing in alpine grassland is a promising measure to carbon sequestration. • Compared to FG, Q 10 of respiration raised in GE5 but declined in GE9. • C, N, and P content of plant and soil provides a new insight for carbon flux. Grasslands contain a large global pool of soil organic carbon (C), but the carbon flux in response to grazing exclusion and the affecting factors are still under debate. In this study, a manipulative experiment was conducted in alpine meadow of the eastern Tibetan Plateau. The sites were: 9 years grazing exclusion, GE9; 5 years grazing exclusion, GE5; and free grazing, FG in degraded alpine meadow. Results showed that there had been a significant increase in soil respiration (SR) and net ecosystem exchange (NEE) with fencing duration. However, no significant difference of ecosystem respiration (ER) was found between grazing and fencing sites. Though, carbon sink occurred in all three sites during the growing season, only the site for 9 years fencing increased gross ecosystem productivity (GEP). Remarkably, temperature sensitivity (Q 10 ) of both soil and ecosystem respiration raised in GE5 but declined in GE9. These findings indicated that grazing exclusion could be a promising measure to CO 2 sequestration in alpine meadow. Of the governing factors, exponential relationships among SR, ER and soil temperature and significant relationships among NEE, GEP and plant biomass were found. Besides, our results showed that plant nitrogen (N), phosphorus (P) content exhibited significant effects on SR, NEE, respectively. While soil C and N were significant explanatory factors for ER. These results indicated that C, N, and P content of plant and soil could provide a new insight for understanding carbon flux in alpine meadow. Together, the findings are not only vital to improve understanding of C cycle in grasslands, but also to provide scientific data for assessing the ecological effect and carbon budget of grazing exclusion.