Winter CO₂ Efflux From Sagebrush Shrublands Distributed Across the Rain‐to‐Snow Transition Zone

Abstract

The projected shifts in winter weather and snowpack conditions are expected to impact carbon storage in western U.S. rangelands. Sagebrush shrublands comprise much of the western United States, yet contribution of winter CO2 efflux to the overall carbon budget of these ecosystems remains uncertain. We explored factors controlling winter CO2 efflux measured using eddy covariance at five sagebrush‐dominated sites along an elevation/climate transect extending from 1,425 to 2,111 m. Results showed that winter CO2 efflux was modest but had important impacts on annual carbon budgets, and its impact increased in high‐elevation, snow‐dominated ecosystems compared to low, rain‐dominated ones. Observed cumulative winter CO2 efflux accounted for 8–30% of annual gross ecosystem production (GEP) and roughly approximated annual net carbon uptake. Omission of winter periods would have increased net uptake by 1.5 to 2.2 times. Within‐site variability in observed 30‐min winter CO2 efflux was related to soil temperature and moisture. Between‐site variability was attributed to available carbon stocks, including soil organic carbon and the previous year's GEP. At low elevations, lack of snow cover to insulate soil from freezing, coupled with lower carbon stocks, limited CO2 efflux. Conversely, large carbon stocks and deep snowpack that prevented soil freezing at high elevation led to increased CO2 efflux. These results show how climate and biota exert strong controls on winter ecosystem respiration and extend our understanding of how state factors influence winter CO2 efflux. Collectively, our findings suggest that an upward climatic shift in the rain‐to‐snow transition elevation may alter the carbon budget of sagebrush shrublands.

Response of Soil Respiration to Altered Snow Cover in a Typical Temperate Grassland in China

“…In spruce forests in western Sichuan, China, it was found that the average Rs rate under snow removal treatment was 0.52 µmol•m −2 •s −1 , which reduced the average winter Rs rate by 21.02% [17]. Similarly, snow removal in wetlands and tundra reduced the average Rs rate in winter [20][21][22]. But some other studies have found completely contrary results that snow removal increased the degree of soil freezing, resulting in a 27.6% increase in Rs, and the reason could be that fine root mortality increased linearly with soil freezing severity induced by colder temperature under the treatment of reduction of snow cover and it provided a substrate for heterotrophic respiration [23].…”