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

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 (T a ) and drought events delayed grass germination and reduced GPP. In the late wet season (September to October) of 2012 and 2013, the low T a in September and its negative effects on vegetation growth caused earlier grass senescence and significantly lower GPP. This indicates that the seasonal pattern of T a has a substantial effect on the annual total GPP, which is consistent with results obtained using the homogeneityof-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.

Impact of sky conditions on net ecosystem productivity of a “floating blanket” wetland in southwest China

“…The difference in diurnal patterns of NEP under cloudy and sunny conditions was not marked, while NEP under sunny and cloudy conditions was evidently greater than that under overcast conditions. The depression of CO2 uptake at noon, which was found in some grasslands (Wang et al, 2016a;Wang et al, 2017), was not significantly for the diurnal patterns of NEP over study site. There were some reasons, on the one hand, the weather in spring, summer and autumn was mainly cloudy days (Fig.…”

Effects of soil water content on carbon sink strength in an alpine swamp meadow of the northeastern Qinghai-Tibet Plateau

“…The NEE observations from this study were within the NEE ranges of previously studies in the similar alpine swamp meadows located across the QTP (-255.5 -173.2 gC m -2 y -1 ) (Table 2). In addition, the NEE estimates of this alpine swamp meadow show a stronger C sink strength than those from alpine meadows (-161.3 -85.4 gC m -2 y -1 ) (Chai et al, 2017;Wang et al, 2017;Wu et al, 2020), alpine steppes (-30 -21.8 gC m -2 y -1 ) (Wang et al, 2018;Wang et al, 2020a;Wang et al, 2020b;Wu et al, 2010), and alpine shrublands (-14 --67 gC m -2 y -1 ) (Zhao et al, 2005(Zhao et al, , 2006. This is likely a result of the inhibiting effects of the nearly-saturated soil condition over soil respiration rather than by the lower temperatures (Sun et al, 2021).…”

Reply on RC1

“…The NEE observations from this study were within the NEE ranges of previously studies in the similar alpine swamp meadows located across the QTP (-255.5 -173.2 gC m -2 y -1 ) (Table 2). In addition, the NEE estimates of this alpine swamp meadow show a stronger C sink strength than those from alpine meadows (-161.3 -85.4 gC m -2 y -1 ) (Chai et al, 2017;Wang et al, 2017;Wu et al, 2020), alpine steppes (-30 -21.8 gC m -2 y -1 ) (Wang et al, 2018;Wang et al, 2020a;Wang et al, 2020b;Wu et al, 2010), and alpine shrublands (-14 --67 gC m -2 y -1 ) (Zhao et al, 2005(Zhao et al, , 2006. This is likely a result of the inhibiting effects of the nearly-saturated soil condition over soil respiration rather than by the lower temperatures (Sun et al, 2021).…”