CO2 fluxes and their driving factors over alpine meadow grassland ecosystems in the northern shore of Qinghai Lake, China

doi:10.3724/SP.J.1258.2012.00187

Abstract

Abstract:

Aims Meadow grassland is a dominant vegetation type on the Qinghai-Tibetan Plateau, but its mechanisms controlling the exchange of CO₂ across a spectrum of time scales and carbon budget remain unclear. Our objective was to investigate the main drivers of ecosystem carbon dynamics and understand the potential response to future climate warming.
Methods We used the eddy covariance method for continuously measuring net ecosystem CO₂exchange (NEE) and environmental factors over meadow grassland on the northern shore of Qinghai Lake from July 1, 2010 to June 30, 2011.
Important findings Diurnal changes of NEE were controlled by photosynthetic photon flux density (PPFD) during the middle growing season (May to September), and air temperature (T_a) was the determining factor on diurnal NEE during other periods. The maximum daily CO₂uptake and release rate were 11.37 g CO₂∙m^-2∙d^-1 on July 1 and 4.04 g CO₂∙m^-2∙d^-1 on October 21, respectively. T_a was the primary environmental factor related to daily NEE, and the correlation was described by an exponential-linear equation (R ²= 0.54, p < 0.01). A significant asymptotical response of daily NEE with increasing leaf area index (LAI) and enhanced vegetation index (EVI) was observed. The interaction effect of LAI and T_a was significant (p < 0.05), while main effect of EVI versus T_a was more important (p < 0.001). Respiration quotient (Q₁₀) was 2.42 and ecosystem total respiration (R_eco) consumed 74% of gross primary production (GPP). The proper magnitude of diurnal temperature range (<14.8 ℃) could be propitious to ecosystem carbon sequestration. The meadow grassland acted as carbon sink and absorbed 271.31 g CO₂∙m ^-2from the atmosphere during the study period.

Key words: diurnal temperature range, eddy covariance technique, net ecosystem CO₂ exchange, vegetation indexes, respiration quotient

ZHANG Fa-Wei, LI Ying-Nian, CAO Guang-Min, LI Feng-Xia, YE Guang-Ji, LIU Ji-Hong, WEI Yong-Lin, ZHAO Xin-Quan. CO₂ fluxes and their driving factors over alpine meadow grassland ecosystems in the northern shore of Qinghai Lake, China[J]. Chin J Plant Ecol, 2012, 36(3): 187-198.

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URL: https://www.plant-ecology.com/EN/10.3724/SP.J.1258.2012.00187

https://www.plant-ecology.com/EN/Y2012/V36/I3/187

Figures/Tables 5

Fig. 1 Seasonal variations of air temperature (Ta), vapor pressure deficit (VPD) (A), photosynthetic photon flux density (PPFD), soil temperature at 5 cm depth (Ts) (B), precipitation, leaf area index (LAI) and enhanced vegetation index (EVI) (C).

Fig. 2 Diurnal changes of CO2 fluxes during vegetation growing season (A) and no-growing season (B) over the meadow grassland ecosystem.

Fig. 3 Seasonal variations of net ecosystem CO2 exchange (NEE), ecosystem total respiration (Reco), ecosystem gross primary production (GPP) (A) and their correlation with air temperature (Ta) (B) over the meadow grassland.

Fig. 4 Relationships between net ecosystem CO2 exchange (NEE) and Leaf area index (LAI, A), enhanced vegetation index (EVI, B) and the relative contribution of air temperature (Ta, C) to NEE. NEE/LAI and NEE/EVI represented NEE normalized with LAI and EVI, respectively.

Fig. 5 Correlation between net ecosystem CO2 exchange (NEE) and diurnal temperature range (Td) of non-growing season (A) and growing season (B), growing season vapor pressure deficit (VPD, C) and growing season weekly precipitation (D).

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CO₂ fluxes and their driving factors over alpine meadow grassland ecosystems in the northern shore of Qinghai Lake, China

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