Seasonal and inter-annual variations of CO2 fluxes over 10 years in an
alpine wetland on the Qinghai-Tibetan Plateau
Abstract
Alpine wetlands play a sensitive function in global carbon cycle during
the ongoing climate warming, yet the temporal patterns of carbon
dynamics from in situ ground-based long-term observations remains
unclear. Here, we analyzed the continuous net ecosystem CO2 exchange
(NEE) measured with the eddy covariance technique over an alpine
peatland on the northeastern Qinghai-Tibetan Plateau from 2007 to 2016.
The wetland acted as a net CO2 source with a positive NEE (120.4 ± 34.8
gCm-2year-1, Mean ± S.D.), with the mean annual gross primary
productivity (GPP) of 500.3 ± 59.4 gCm-2year-1 and annual ecosystem
respiration (RES) of 620.7 ± 74.2 gCm-2year-1. At the seasonal scale,
the classification and regression trees (CART) analysis showed that
aggregated growing season degree days (GDD) was the predominant
determinant on variations in monthly NEE and monthly GPP. Variations in
monthly RES were determined by soil temperature (Ts). Furthermore,
non-growing season Ts had a significant positive correlation with the
following year annual GPP (p<0.05). Non-growing season RES
only accounted for about 25% of annual RES, but had significant
correlation with annual RES and annual NEE (p<0.05). The
further partial correlation analysis showed that non-growing season air
temperature (Ta, p = 0.05), rather than precipitation (PPT, p = 0.25)
was a predominant determinant on variations in annual NEE. Our results
highlighted the importance in carbon dynamics of climate fluctuations
and CO2 emission from the non-growing season in alpine wetlands. We
speculated that the vast peadlands would positively feedback to climate
change on the Tibetan plateau where the non-growing season warming was
significant.