We found that the consistently greater growing-season GEP occurring at a grazed site is mainly caused by greater photosynthetic capacity thanks to suitable environmental conditions and longer growing times per day and over the growing period. Growing-season ecosystem respiration also appears to be greater at a grazed site than a fenced one, especially in a non-severe drought season when the grass is active.

We believe that increased heterotrophic respiration may be among the primary mechanisms behind this phenomenon. Lack of increased carbon storage in un-grazed systems indicates that eliminating grazing to increase carbon sequestration is not likely to be a viable option in natural grassland systems. Higher carbon-dioxide uptake is possible in a semi-arid desert steppe if the land in this area and soil/vegetation is suitably managed.

In our study, we used so-called paired eddy-covariance systems to measure the net ecosystem exchange (NEE) and microclimate of adjacent pastures of grazed and ungrazed steppes to determine the role of grazing on carbon-dioxide fluxes in a desert steppe. Although the grazed site takes up more carbon in a normally rainy year in contrast to a dry year, the daily NEE variation for both years is lower in the fenced site, suggesting that the latter is more resistant to a changing climate. It also means that future models should take into account year-to-year differences in carbon balance because relationships between fluxes and climatic regulators change annually in different land-use-change scenarios.

Shao and colleagues reported their work in Environmental Research Letters (ERL) as part of the ERL Focus on Extreme Events and the Carbon Cycle.

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