Articles | Volume 17, issue 8
Research article
20 Apr 2017
Research article |  | 20 Apr 2017

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

Lei Wang, Huizhi Liu, Jihua Sun, and Yaping Shao

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.

Short summary
This study found that the seasonal variation in CO2 exchange over an alpine meadow on the Tibetan Plateau was primarily affected by the seasonal pattern of air temperature, especially in spring and autumn. The annual net ecosystem exchange decreased with mean annual temperature, and then increased when the gross primary production became saturated. This study contributes to the response of the alpine meadow ecosystem to global warming.
Final-revised paper