Winter CO2 efflux from sagebrush shrublands distributed across the rain-to-snow transition zone

Authors: Fellows, Aaron; Flerchinger, Gerald; Seyfried, Mark; Biederman, Joel; LOHSE, KATHLEEN - Idaho State University

Submitted to: Journal of Geophysical Research-Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2020
Publication Date: 2/24/2020
Citation: Fellows, A.W., Flerchinger, G.N., Seyfried, M.S., Biederman, J.A., Lohse, K. 2020. Winter CO2 efflux from sagebrush shrublands distributed across the rain-to-snow transition zone. Journal of Geophysical Research-Biogeosciences. 125(2). https://doi.org/10.1029/2019JG005325.
DOI: https://doi.org/10.1029/2019JG005325

Interpretive Summary: Climate warming and associated shifts in winter precipitation from snow to rain are expected to effect wintertime plant and soil respiration, impacting carbon cycling and storage. Sagebrush shrublands comprise much of the Western US, yet the contribution of winter CO2 emission from these ecosystems is uncertain, even under current conditions. We therefore examined winter ecosystem respiration and explored factors controlling CO2 emission from four sagebrush sites with varying elevation, snow and winter conditions. Factors controlling CO2 emission were shown to change with elevation. Limited CO2 emission was observed at low elevation sites due to lack of snow cover to insulate the soil from freezing, limited water availability, and low soil organic content. Conversely, high soil organic content and a deep snowpack that prevented soil freezing at the high elevation site led to increased winter CO2 emission that resulted from higher rates of respiration and organic decomposition. Results suggest that anticipated reductions in snow depth with climate warming may lead to colder winter soil temperatures, increased freezing and therefore reduced winter respiration and CO2 emission.

Technical Abstract: Shifts in winter conditions are expected to impact carbon cycling and storage in Western US rangelands over the coming century. Sagebrush shrublands comprise much of the western US, yet the contribution of winter CO2 efflux to the overall carbon budget of these ecosystems is uncertain, even under current conditions. We therefore examined winter CO2 efflux across the rain-to-snow transition zone in the Reynolds Creek Experimental Watershed and Critical Zone Observatory, Idaho, USA and explored the factors controlling CO2 efflux in sagebrush shrublands during winter conditions. Sites included four sagebrush-dominated sites along an elevation/climate extending from 1425 to 2111m. Results showed that winter CO2 efflux was modest but had an important impact on the annual carbon budget, and its impact increased in high elevation snow-dominated ecosystems compared to low rain-dominated ones. Observed winter CO2 efflux accounted for 7-23% of the annual Gross Ecosystem Production (GEP) lost to the atmosphere and roughly approximated the annual net carbon uptake from the sites (approximately 25-150 gC m-2 yr-1). Within-site variability in observed 30-min winter CO2 efflux was related to soil temperature and moisture, but reductions due to variations in temperature and moisture at a given site were similar to the difference in median flux between the lowest and highest elevation sites. Between-site variability was attributed to available carbon stocks, including soil organic carbon and the previous year’s gross productivity. Lack of snow cover to insulate the soil from freezing and its impact on water availability coupled with lower carbon stocks limited CO2 efflux from low elevation sites. Conversely, large carbon stocks and a deep snowpack that prevented soil freezing at the high elevation site led to increased winter CO2 efflux. These results showing that climate and biota exert strong controls on landscape carbon availability during winter extends our understanding of how state factors influence winter CO2 efflux. Potential changes in the carbon budget of sagebrush shrublands that may result in a potential upward shift in the rain-to-snow transition zone under climate warming were discussed.