Biophysical effects on the interannual variation in carbon dioxide exchange of an alpine meadow on the Tibetan Plateau

Lei Wang,Huizhi Liu,Yaping Shao,Jihua Sun

doi:10.5194/acp-17-5119-2017

Abstract

Abstract. Eddy covariance measurements from 2012 to 2015 were used to investigate the interannual variation in carbon dioxide exchange and its control over an alpine meadow on the south-east margin of the Tibetan Plateau. The annual net ecosystem exchange (NEE) in the 4 years from 2012 to 2015 was −114.2, −158.5, −159.9 and −212.6 g C m−2 yr−1, and generally decreased with the mean annual air temperature (MAT). An exception occurred in 2014, which had the highest MAT. This was attributed to higher ecosystem respiration (RE) and similar gross primary production (GPP) in 2014 because the GPP increased with the MAT, but became saturated due to the limit in photosynthetic capacity. In the spring (March to May) of 2012, low air temperature (Ta) and drought events delayed grass germination and reduced GPP. In the late wet season (September to October) of 2012 and 2013, the low Ta in September and its negative effects on vegetation growth caused earlier grass senescence and significantly lower GPP. This indicates that the seasonal pattern of Ta has a substantial effect on the annual total GPP, which is consistent with results obtained using the homogeneity-of-slopes (HOS) model. The model results showed that the climatic seasonal variation explained 48.6 % of the GPP variability, while the percentages explained by climatic interannual variation and the ecosystem functional change were 9.7 and 10.6 %, respectively.

Highlights

In the last decade, the carbon dioxide exchange in grassland ecosystems has attracted much attention (Baldocchi, 2008; Huang et al, 2008; Hunt et al, 2004; Jing et al, 2010; Suyker et al, 2003) because grasslands cover 32 % of the global land surface and make a substantial contribution to the carbon cycle on a global scale (Parton et al, 1995)
The soil temperature never decreased below 0 ◦C, and the maximum value was 16.48 ◦C (Fig. 1b)
The key parameters for ecosystem photosynthesis and respiration were determined for the different seasons of each year

Summary

Introduction

The carbon dioxide exchange in grassland ecosystems has attracted much attention (Baldocchi, 2008; Huang et al, 2008; Hunt et al, 2004; Jing et al, 2010; Suyker et al, 2003) because grasslands cover 32 % of the global land surface and make a substantial contribution to the carbon cycle on a global scale (Parton et al, 1995). The annual net ecosystem exchange (NEE) of grasslands has a large range, from −650 to 160 g C m−2 yr−1, due to climate variability and land use changes (Gilmanov et al, 2007; Wang et al, 2016a). Alpine meadows in China are the primary grassland type of the nation and are mainly distributed in the QinghaiTibetan plateau (DAHV and CISNR, 1996; Liu et al, 2008). Several studies of CO2 exchange have been carried out on the Qinghai–Tibetan plateau, where the mean annual air temperature (Ta) is approximately 0 ◦C (Gu et al, 2003; Kato et al, 2006; Shi et al, 2006; Zhao et al, 2006).

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