Winter soil CO2 efflux in two contrasting forest ecosystems on the eastern Tibetan Plateau, China

Abstract

Significant CO 2 fluxes from snow-covered soils occur in cold biomes. However, little is known about winter soil respiration on the eastern Tibetan Plateau of China. We therefore measured winter soil CO 2 fluxes and estimated annual soil respiration in two contrasting coniferous forest ecosystems (a Picea asperata plantation and a natural forest). Mean winter soil CO 2 effluxes were 1.08 lmol m -2 s -1 in the plantation and 1.16 lmol m -2 s -1 in the natural forest. These values are higher than most reported winter soil CO 2 efflux values for temperate or boreal forest ecosystems. Winter soil respiration rates were similar for our two forest ecosystems but mean soil CO 2 efflux over the growing season was higher in the natural forest than in the plantation. The estimated winter and annual soil effluxes for the natural forest were 176.3 and 1070.3 g m -2, respectively, based on the relationship between soil respiration and soil temperature, which were 17.2 and 9.7 % greater than their counterparts in the plantation. The contributions of winter soil respiration to annual soil efflux were 15.4 % for the plantation and 16.5 % for the natural forest and were statistically similar. Our results indicate that winter soil CO 2 efflux from frozen soils in the alpine coniferous forest ecosystems of the eastern Tibetan Plateau was considerable and was an important component of annual soil respiration. Moreover, reforestation (natural coniferous forests were deforested and reforested with P. asperata plantation) may reduce soil respiration by reducing soil carbon substrate availability and input.

Soil respiration and its environmental response varies by day/night and by growing/dormant season in a subalpine forest

“…Our results suggest that R H was the dominant component of R S , indicating a dominant control of microorganism-associated respiration on R S in the subalpine forest. In the DS, we supposed that soil microbial activity is still functioning to generate CO 2 fluxes by decomposing soil organic matters, while the root activity of plants is inhibited in winter because plants stop growing in cold temperature9, and consequently, ending up with a high proportion of R H to total R S (Table 1). Therefore, soil C fluxes in the DS must be taken into consideration when assessing the carbon sink/source patterns of the subalpine forests.…”

“…Soil CO 2 efflux in the DS plays an important role in the regional, national, and the global carbon balance78, which accounts for 3–50% of annual soil CO 2 efflux in forests8910. Annual carbon sequestration would be largely overestimated if soil CO 2 fluxes in the DS were not included10.…”

“…The changes in R S and its temperature sensitivity will have a significant influence on regional and global carbon cycle and their feedback on climate change20. Some studies on R S and heterotrophic respiration have been conducted in subalpine forest ecosystems921, but most of them were based on short term measurements in daytime and during the GS. The CO 2 fluxes in the DS and at nighttime in the subalpine forests in Eastern Tibetan Plateau have not been fully determined, and the factors controlling the temperature sensitivity of the R S are even less understood.…”

Soil respiration in a subtropical forest of southwestern China: Components, patterns and controls

“…Based on the continuous soil temperature at the 5 cm depth, monthly and annual soil CO 2 fluxes of each fraction was estimated by integrating CO 2 fluxes for the period from November 2015 to October 2017 using the observed specific response equation between soil respiration fraction and soil temperature. Monthly and annual soil CO 2 fluxes of each fraction was estimated by interpolating measured soil respiration between sampling dates for every day of the year and then computing the sum to obtain the annual or winter values [ 19 ].…”

Temporal Variability in Soil Greenhouse Gas Fluxes and Influencing Factors of a Primary Forest on the Eastern Qinghai-Tibetan Plateau

“…Notably, the roles of GHG fluxes during the dormant season are not negligible in their annual budget estimates according to previous evidence [70]. For example, the CO 2 emission [71] and the uncertainty regarding CH 4 emission or uptake [70] beneath snow cover and the N 2 O emission pulse during the freeze-thaw period [72] are important aspects determining the magnitude of annual GHG budgets in seasonally snowcovered regions. Therefore, soil GHG fluxes during winter and their response to climate change warrants further study.…”