Seasonal and Inter-Annual Variations of Carbon Dioxide Fluxes and Their Determinants in an Alpine Meadow

Abstract

The alpine meadow is one of the most important ecosystems on the Qinghai-Tibet Plateau (QTP) due to its huge carbon storage and wide distribution. Evaluating the carbon fluxes in alpine meadow ecosystems is crucial to understand the dynamics of carbon storage in high-altitude areas. Here, we investigated the carbon fluxes at seasonal and inter-annual timescales based on 5 years of observations of eddy covariance fluxes in the Zoige alpine meadow on the eastern Tibetan Plateau. We found that the Zoige alpine meadow acted as a faint carbon source of 94.69 ± 86.44 g C m−2 y−1 during the observation periods with large seasonal and inter-annual variations (IAVs). At the seasonal scale, gross primary productivity (GPP) and ecosystem respiration (Re) were positively correlated with photosynthetic photon flux density (PPFD), average daily temperature (Ta), and vapor pressure (VPD) and had negative relationships with volumetric water content (VWC). Seasonal variations of net ecosystem carbon dioxide (CO2) exchange (NEE) were mostly explained by Ta, followed by PPFD, VPD, and VWC. The IAVs of GPP and Re were mainly attributable to the IAV of the maximum GPP rate (GPPmax) and maximum Re rate (Remax), respectively, both of which increased with the percentage of Cyperaceae and decreased with the percentage of Polygonaceae changes across years. The IAV of NEE was well explained by the anomalies of the maximum CO2 release rate (MCR). These results indicated that the annual net CO2 exchange in the alpine meadow ecosystem was controlled mainly by the maximum C release rates. Therefore, a better understanding of physiological response to various environmental factors at peak C uptake and release seasons will largely improve the predictions of GPP, Re, and NEE in the context of global change.

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

“…While it is likely that GPP would change, it was not possible to determine by how much. The range in GPP measured for intact Zoige peatland studies was 590-2054 g C m 2 year À1 (Hao et al, 2011;Liu, Zhu, et al, 2019;Yao et al, 2022), while other studies from alpine meadows (which can represent a successional stage of peatland degradation), showed a similarly large range (Wang et al, 2016(Wang et al, , 2022. One study of degradation in alpine meadows suggested that in the initial stages, that is, (0%-20% degradation) GPP may increase in accordance with increased vegetation biomass, but this then declined as degradation increased (Yang et al, 2022).…”

“…Degradation impacts on decomposition rates and exchange of greenhouse gases due to a lowering of the water table, while warming may cause similar effects (Hopple et al, 2020; Ma et al, 2022). Indeed, degradation caused by land‐use and climate change may lead to a weakening the Zoige peatland C sink function (Wang et al, 2022). Numerous experimental studies have been conducted on the effects of land management and climate change on aspects of the Zoige peatland C cycle (Cao et al, 2017; Yang et al, 2014; Yang et al, 2017; Zhou et al, 2021), however, there have been no reviews of the Zoige peatland C cycle to date.…”