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ARS Home » Pacific West Area » Logan, Utah » Forage and Range Research » Research » Publications at this Location » Publication #302056
Title: Grazing effects on carbon fluxes in a northern China grassland

Author
item ZHU, LINGLING - Australian National University
item Johnson, Douglas
item WANG, WEIGUANG - Marshall University
item MA, LEI - China Agricultural University
item RONG, YUPING - China Agricultural University

Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2014
Publication Date: 12/1/2014
Citation: Zhu, L., Johnson, D.A., Wang, W., Ma, L., Rong, Y. 2015. Grazing effects on carbon fluxes in a northern China grassland. Journal of Arid Environments. 114:41-48.

Interpretive Summary: Grazing is a widespread use of grasslands in northern China. However, if stocking rate exceeds grassland carrying capacity, degradation and desertification can occur. Consequently, grazing management is critical and can play a critical role in driving carbon cycling in grassland ecosystems. In this study, carbon exchange patterns were evaluated in the grasslands of northern China maintained at three stocking rates: no grazing, moderate grazing, and heavy grazing. The results showed that green biomass, plant standing dead, litter mass, and carbon storage were markedly reduced in the heavy grazing treatment compared to the moderate grazing or ungrazed treatments. The greatest amount of carbon was assimilated in the moderate grazing treatment followed by the ungrazed and heavy grazing treatment. HIgh carbon assimilation was associated with high biomass, high temperature, and high soil water content. These results indicated that grazing influenced vegetation and soil charateristics, which altered the spatial and temporal patterns of carbon exchange in grasslands of northern China. Reducing stocking rates on heavily grazed grasslands of northern China to moderate grazing levels would enhance carbon assimilation, and benefit biomass and animal production.

Technical Abstract: Grazing is a widespread use of grasslands in northern China, but if stocking rate exceeds grassland carrying capacity, degradation and desertification can occur. As a result, grazing management is critical and can play a significant role in driving C sink and source activity in grassland ecosystems. In this study, CO2 exchange patterns during the growing season were evaluated in the grasslands of northern China using a closed-chamber technique on plots located at three sites maintained at three stocking rates, including (no grazing), moderate grazing (6.7 sheep/ha), and heavy grazing (9.3 sheep/ha). The results showed that heavy grazing markedly reduced green biomass, plant standing dead, and litter mass as well as reduced net ecosystem exchange (NEE). The moderate grazing site exhibited the greatest NEE with a mean growing season rate of -7.5 umol CO2 m-2 s-1 followed by the ungrazed site (-5.4 umol CO2 m-2 s-1) and the heavy grazing site (-2.4 umol CO2 m-2 s-1), which was significantly lower than the ungrazed and moderate grazing site (P<0.05). The rates of gross C assimilation (GCA) were in the order: moderate grazing > ungrazed > heavy grazing (P<0.05). Partial component analysis (PCA) indicated that spatial and temporal patterns varied in ungrazed, moderate grazing and heavy grazing sites. High NEE was associated with high biomass, high temperature, and high soil water content (SWC) with the maximum values of NEE, ecosystem respiration (Re), and soil respiration (Rs) being -10.8 umol CO2 m-2 s-1, 6.7 umol CO2 m-2 s-1, and 4.5 umol CO2 m-2 s-1, respectively. Temperature dependence of Rs (as indicated by Q10) was higher at the moderate and heavy grazing sites than the ungrazed site. In contrast, Q10 values for ecosystem respiration (Re) and canopy respiration (Re) were higher at the ungrazed than moderate and heavy grazing sites. THese results indicated that grazing influenced vegetation and soil characteristics, which altered the spatial and temporal patterns of CO2 fluxes in grasslands of northern China. Therefore, reducing stocking rates on heavily grazed grasslands of northern China to moderate grazing levels would enhance NEE, and benefit biomass and animal production.