Nongrowing Season CO2 Emissions Determine the Distinct Carbon Budgets of Two Alpine Wetlands on the Northeastern Qinghai—Tibet Plateau

Abstract

Alpine wetlands sequester large amounts of soil carbon, so it is vital to gain a full understanding of their land-atmospheric CO2 exchanges and how they contribute to regional carbon neutrality; such an understanding is currently lacking for the Qinghai—Tibet Plateau (QTP), which is undergoing unprecedented climate warming. We analyzed two-year (2018–2019) continuous CO2 flux data, measured by eddy covariance techniques, to quantify the carbon budgets of two alpine wetlands (Luanhaizi peatland (LHZ) and Xiaobohu swamp (XBH)) on the northeastern QTP. At an 8-day scale, boosted regression tree model-based analysis showed that variations in growing season CO2 fluxes were predominantly determined by atmospheric water vapor, having a relative contribution of more than 65%. Variations in nongrowing season CO2 fluxes were mainly controlled by site (categorical variable) and topsoil temperature (Ts), with cumulative relative contributions of 81.8%. At a monthly scale, structural equation models revealed that net ecosystem CO2 exchange (NEE) at both sites was regulated more by gross primary productivity (GPP), than by ecosystem respiration (RES), which were both in turn directly controlled by atmospheric water vapor. The general linear model showed that variations in nongrowing season CO2 fluxes were significantly (p < 0.001) driven by the main effect of site and Ts. Annually, LHZ acted as a net carbon source, and NEE, GPP, and RES were 41.5 ± 17.8, 631.5 ± 19.4, and 673.0 ± 37.2 g C/(m2 year), respectively. XBH behaved as a net carbon sink, and NEE, GPP, and RES were –40.9 ± 7.5, 595.1 ± 15.4, and 554.2 ± 7.9 g C/(m2 year), respectively. These distinctly different carbon budgets were primarily caused by the nongrowing season RES being approximately twice as large at LHZ (p < 0.001), rather than by other equivalent growing season CO2 fluxes (p > 0.10). Overall, variations in growing season CO2 fluxes were mainly controlled by atmospheric water vapor, while those of the nongrowing season were jointly determined by site attributes and soil temperatures. Our results highlight the different carbon functions of alpine peatland and alpine swampland, and show that nongrowing season CO2 emissions should be taken into full consideration when upscaling regional carbon budgets. Current and predicted marked winter warming will directly stimulate increased CO2 emissions from alpine wetlands, which will positively feedback to climate change.

The impacts of land‐use and climate change on the Zoige peatland carbon cycle: A review

“…In comparatively recent times, prior to the 1930s, the Zoige peatlands were considered to be in a relatively pristine state due to relatively limited anthropogenic impacts, that is, little human usage and at this time, the Zoige peatland area was thought to cover 4605 km 2 (Brierley et al, 2016;Li et al, 2015). In a pristine or intact state, Zoige peatlands are generally characterized by a seasonally fluctuating water table level (WTL) with surface water (waterlogging) present in summer, while falling below surface during winter, with some studies reporting WTL to range between +20 and À90 cm (Cao et al, 2018;Chen et al, 2021;Peng et al, 2015;Song et al, 2021;Zhou et al, 2021). Many have described Zoige peatlands as fens dominated by sedges (Figure 2; Chen et al, 2011Chen et al, , 2021Liu, Zhu, et al, 2019;Yang et al, 2017).…”

“…Although others do not specify the peatland type, peat pH values (pH 6.6-7.0) and vegetation composition also suggest they are minerotrophic fen peatlands (Cao et al, 2018;Peng et al, 2019). Microtopographical differences are present with Carex muliensis and Kobresia tibetica, typically dominating wetter and drier areas, respectively (Cao et al, 2017;Chen et al, 2011;Hao et al, 2011) Pedicularis sp, Potentilla bifurca, Scirpus triqueter, Triglochin palustre, and Trollius farreri (Chen et al, 2021;Hao et al, 2011;Peng et al, 2021;Song et al, 2021;Wang, Li, Li, & You, 2019). More recently, pressure from human activities such as peatland drainage for livestock grazing and peat mining, along with climate change have resulted in degradation of the Zoige peatlands, resulting in a decrease in peatland area, estimated at between 30% and 50% (Xiang et al, 2009;Xiao et al, 2010;Yan & Wu, 2005;Yao et al, 2011).…”

“…Microtopographical differences are present with Carex muliensis and Kobresia tibetica , typically dominating wetter and drier areas, respectively (Cao et al, 2017; Chen et al, 2011; Hao et al, 2011). Other reported species include Blysmus sinocompressus , Caltha palustris , Carex alrofusca , C. meyeriana , C. pamirensis , Cremanthodium pleurocaule , Gentiana formosa , Hippuris vulgaris , Pedicularis sp , Potentilla bifurca , Scirpus triqueter , Triglochin palustre , and Trollius farreri (Chen et al, 2021; Hao et al, 2011; Peng et al, 2021; Song et al, 2021; Wang, Li, Li, & You, 2019).…”