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

L Zhao,S Gu,J Li,S Xu,X Zhao,Y Li,H Zhou

doi:10.5194/bg-7-1207-2010

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 (Reco), 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 Reco were closely associated with leaf area index (LAI). The Reco showed a positive exponential to soil temperature and relatively low Reco 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 Reco 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 (CO2). The observed carbon dioxide fluxes in the alpine wetland meadow were higher than other alpine meadow such as Kobresia humilis meadow and shrubland meadow.

Highlights

Global wetlands occupy an area of 5.3–6.4 M km2 on Earth (Matthews and Fung, 1987; Lappalainen, 1996)
Most recent carbon-budget studies of meadow ecosystems have been conducted in alpine K. humilis meadow or P. fruticosa shrubland ecosystems (Kato et al, 2006; Zhao et al, 2005a, b, 2006) The results shown that alpine Kobresia humilis meadow or Potentilla fruticosa shrubland ecosystems sequester carbon on the Qinghai-Tibetan Plateau, at least under normal climatic conditions (Zhao et al, 2006, 2007; Kato et al, 2006)
Photosynthetic Photon Flux Density (PPFD) reached its annual maximum in the beginning of July and decreased gradually

Summary

Introduction

Global wetlands occupy an area of 5.3–6.4 M km on Earth (Matthews and Fung, 1987; Lappalainen, 1996). Northern wetlands play an important role in the global terrestrial carbon cycle. Development of such wetlands has reduced atmospheric CO2 concentrations and affected the global climate system by reducing the greenhouse effect (Moore et al, 1998). It is estimated that northern peatlands cover 34 600 km of the Earth’s surface and represent a soil carbon stock of 455 Pg C (Gorham, 1991). The deep organic soils stored in wetlands have been accumulating carbon for 4000–5000 years. Temperature increases due to climate change and drainage of wetlands may provide conditions to reverse this trend, leading to overall carbon loss

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