Seasonal variations in carbon dioxide exchange in an alpine wetland meadow on the Qinghai-Tibetan Plateau

Abstract

Abstract. Alpine wetland meadow could functions as a carbon sink due to it high soil organic content and low decomposition. However, the magnitude and dynamics of carbon stock in alpine wetland ecosystems are not well quantified. Therefore, understanding how environmental variables affect the processes that regulate carbon fluxes in alpine wetland meadow on the Qinghai-Tibetan Plateau is critical. To address this issue, Gross Primary Production (GPP), Ecosystem Respiration (R eco ), and Net Ecosystem Exchange (NEE) were examined in an alpine wetland meadow using the eddy covariance method from October 2003 to December 2006 at the Haibei Research Station of the Chinese Academy of Sciences. Seasonal patterns of GPP and R eco were closely associated with leaf area index (LAI). The R eco showed a positive exponential to soil temperature and relatively low R eco occurred during the non-growing season after a rain event. This result is inconsistent with the result observed in alpine shrubland meadow. In total, annual GPP were estimated at 575.7, 682.9, and 630.97 g C m −2 in 2004, 2005, and 2006, respectively. Meanwhile, the R eco were equal to 676.8, 726.4, 808.2 g C m −2 , and thus the NEE were 101.1, 44.0 and 173.2 g C m −2 . These results indicated that the alpine wetland meadow was a moderately source of carbon dioxide (CO 2 ). The observed carbon dioxide fluxes in the alpine wetland meadow were higher than other alpine meadow such as Kobresia humilis meadow and shrubland meadow.

Biophysical regulation of carbon fluxes over an alpine meadow ecosystem in the eastern Tibetan Plateau

“…Then, as temperature, LAI, and day length increased, GPP and R eco exhibited a rapidly rising trend in June and July, leading to a strong carbon sink of the ecosystem. Maximum daily NEE (−5.27 g C m −2 day −1 ) was within the range of grassland ecosystems (−1.9~−9.3 g C m −2 day −1 ) (Li et al 2005), and slightly higher than the values (−3.9~−5 g C m −2 day −1 ) found in alpine shrubland, alpine meadow, and alpine wetland ecosystems at Haibei station (Kato et al 2004;Zhao et al 2010;Zhao et al 2006) located at northeastern Tibetan Plateau. The daily maximum R eco (10.24 g C m −2 day −1 ) was almost 1.5~2.2 times larger than that of an alpine wetland ecosystem at Haibei station (Zhao et al 2010).…”

“…At the peak growing stage, NEE sat (−19.8 μmol CO 2 m −2 s −1 ) was close to the maximum value reported from an alpine shrubland meadow (−20.54 μmol CO 2 m −2 s −1 for August) ). However, absolute value of α (0.0343 μmol CO 2 μmol −1 photons) was between that of alpine shrubland meadow (0.0082 μmol CO 2 μmol −1 photons for August) ) and alpine wetland (0.08 μmol CO 2 μmol −1 photons for July) (Zhao et al 2010).…”

“…This is probably due to the significant difference of soil organic carbon content between these two sites. At our site, soil organic carbon content in the top 10 cm was 63.24 g kg −1 , and only 28.06 g kg −1 at Haibei alpine wetland (Zhao et al 2010). After grass senescence, the alpine meadow continuously lost carbon via soil respiration.…”

“…Recent studies on CO 2 exchange have been conducted in the Tibetan Plateau (Kato et al 2004;Zhao et al 2006;Zhao et al 2010;Saito et al 2009;Kato et al 2006). Such as result from eddy covariance measurements shows that alpine meadow in the Tibetan Plateau was currently acting as a carbon sink .…”

Turbulent flux observations and modelling over a shallow lake and a wet grassland in the Nam Co basin, Tibetan Plateau

“…Most long-term observation stations focus on the major land cover types such as alpine steppe, Kobresia pastures and wetlands (Zhao et al 2010), however approximately 45,000 km 2 of the plateau are covered by lakes ). This lake area has been subject to changes in the last decades; the reasons are not well understood due to lack of observational data ).…”