Depthwise Soil CO2 Production Is Controlled by Freeze‐Thaw Processes in a Tibetan Alpine Steppe. Issue 1 (18th January 2022)

• Record Type: Journal Article
• Authors: Zhang, Jianxin; Wei, Da; Hong, Jiangtao; Wang, Xiaodan
• Is Part Of: Journal of geophysical research. Volume 127:Issue 1(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-18
• Subjects: Soil CO2 production -- freeze‐thaw processes -- Tibetan Plateau -- alpine steppe; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2021JG006678
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: Cold ecosystems in regions of high‐latitude and altitude with vast stores of soil organic carbon suffer strong freeze‐thaw cycles, which can greatly affect soil CO2 release. However, on the Tibetan Plateau, where altitude is >4, 000 m, it remains unknown how freeze‐thaw processes regulate CO2 production across the soil profile. In this study, we used the gradient method to explore impacts of freeze‐thaw processes on depthwise soil CO2 production in an alpine steppe. We found almost all soil CO2 was produced in the root‐zone layer (<30 cm), while the root‐free layer (>30 cm) frequently alternated between being a source and sink of CO2 and thus acted largely as a buffer. The surface layer (0–15 cm) and subsurface layer (15–30 cm) had a similar CO2 production rate in the thawed period. However, during the freezing‐frozen‐thawing period, the subsurface layer consistently functioned as a weak CO2 source, although parts were trapped in frozen soil, resulting in a weaker CO2 sink in the surface layer. Soil CO2 production in subsurface layer is thus more sensitive to temperature variability compared with surface layer. Furthermore, our results suggest water content plays a more important role than temperature in regulating soil CO2 production. For the first time, our data set reveals the vertical production of CO2 within the seasonally frozen soils on the Tibetan Plateau, which will benefit understanding of belowground carbon processes and modeling of soil CO2 release in the region. Plain Language Summary: Freeze‐thaw cycles occur frequently in cold regions, which can greatly affect soil CO2 release. However, it remains unknown how freeze‐thaw processes regulate soil CO2 production at multiple soil layers. Here, we report a unique data set of belowground CO2 profile in an alpine steppe on the Tibetan Plateau. Deeper root‐zone layer (15–30 cm) dominated the soil CO2 production, especially in ice season, while surface layer (0–15 cm) are more productive in the ice‐free season. By contrast, root‐free layer (30–150 cm) show none of CO2 production, where they store inorganic carbon, rather than organic carbon. Moreover, a more important role of soil water content than temperature in regulating soil CO2 production was found in this study site. Thus, information regarding the vertical distribution of soil CO2 production and its response to environmental factors is critical for a proper understanding of the belowground carbon dynamic and accurate predictions of soil CO2 emissions. Key Points: Most soil CO2 was produced in the root‐zone layer (<30 cm), while the root‐free layer (>30 cm) acted largely as a buffer of CO2 Freeze‐thaw processes impact the hotspot location of CO2 production in the soil profile Soil water content plays a more important role than temperature in regulating soil CO2 production