Diurnal Freeze-Thaw Cycles Modify Winter Soil Respiration in a Desert Shrub-Land Ecosystem

Abstract

Abstract:Winter soil respiration (R s ) is becoming a significant component of annual carbon budgets with more warming in winter than summer. However, little is known about the controlling mechanisms of winter R s in dryland. We made continuous measurements of R s in four microsites (non-crust (BS), lichen (LC), moss (MC), and a mixture of moss and lichen (ML)) in a desert shrub-land ecosystem northern China, to investigate the causes of R s dynamics in winter. The mean winter R s ranged from 0.10 to 0.17 µmol CO 2 m´2¨s´1 across microsites, with the highest value in BS. Winter Q 10 (known as the increase in respiration rate per 10˝C increase in temperature) values (2.8-19) were much higher than those from the growing season (1.5). R s and Q 10 were greatly enhanced in freeze-thaw cycles compared to frozen days. Diurnal patterns of R s between freeze-thaw and frozen days differed. Although the freeze-thaw period was relatively short, its cumulative R s contributed significantly to winter R s . The presence of biocrust might induce lower temperature, thus having fewer freeze-thaw cycles relative to bare soil, leading to the lower R s for microsites with biocrusts. In conclusion, winter R s in drylands was sensitive to soil temperature (T s ) and T s -induced freeze-thaw cycles. The temperature impact on R s varied among soil cover types. Winter R s in drylands may become more important as the climate is continuously getting warmer.

Soil respiration of alpine meadow is controlled by freeze–thaw processes of active layer in the permafrost region of the Qinghai–Tibet Plateau

“…The Qinghai-Tibet Plateau (QTP) of China has the largest extent of permafrost in the low to middle latitudes of the world and is very sensitive to global climate change (Liu and Chen, 2000;Wu et al, 2010). Soil organic carbon (SOC) pools in the permafrost regions of the QTP were estimated to be 160 ± 87 Pg, which is approximately 8.7 % of those in the northern circumpolar permafrost region (Mu et al, 2015).…”

Novel determination of effective freeze–thaw cycles as drivers of ecosystem change

“…Freeze–thaw cycles (FTCs) regulate globally important processes, including nutrient cycling, biological activity, soil aggregation, soil greenhouse gas emissions, and winter hydrology (Boswell, Balster, Bajcz, & Thompson, 2020; Liu et al., 2016; Song, Zou, Wang, & Yu, 2017; Wagner‐Riddle et al., 2017; Watanabe & Osada, 2017). Approximately 58% of the land area in the northern hemisphere is directly affected by winter FTCs (Zhang, 2005).…”

Modelling the diurnal and seasonal dynamics of soil CO<sub>2</sub> exchange in a semiarid ecosystem with high plant-interspace heterogeneity

“…Hence, models considering only autotrophic and heterotrophic respiration often fail to account for the observed F S dynamics (Austin and Vivanco, 2006). Gas-transport processes are im-portant mechanisms regulating the magnitudes and hysteretic features of soil CO 2 fluxes (Ma et al, 2013). A substantial fraction of respired CO 2 may be transported to the atmosphere via xylem and may not be measured by techniques like soil reparation chambers (Bloemen et al, 2013(Bloemen et al, , 2016.…”

“…During wet periods, soil CO 2 efflux could decrease significantly by water clogging of soil pores, which restricts the diffusion of O 2 and CO 2 gases (Šimunek and Suarez, 1993;Fang and Moncrieff, 1999). In dryland soils of high salinity/alkalinity, CO 2 transport and the water cycle are tightly coupled, as large inorganic C fluxes can be driven solely by dissolution and infiltration of CO 2 and carbonates (Buysse et al, 2013;Ma et al, 2013;Fa et al, 2014). Such inorganic processes may introduce fluctuations not only to hourly or diurnal soil CO 2 effluxes (e.g.…”