Potential changes in both the intensity and frequency of extreme drought events are vital aspects of regional climate change that can alter the distribution and dynamics of water availability and subsequently affect carbon cycles at the ecosystem level. The effects of extreme drought events on the carbon budget of peatland in the Zoige plateau and its response mechanisms were studied using an in-field controlled experimental method. The results indicated that the peatland ecosystem of the Zoige plateau functioned as a carbon sink while under the control (CK) or extreme drought (D) treatment throughout the entire growing season. Maximum fluxes of methane (CH₄) emissions and the weakest carbon sink activity from this ecosystem were in the early growth stage, the most powerful carbon sink activity was during the peak growth stage, while the absorption sink activity of carbon dioxide (CO₂) and CH₄ was present during the senescence stage. Extreme drought reduced the gross primary productivity (GPP) and ecosystem respiration (R_e) of the peatland ecosystem by 14.5% and 12.6%, respectively (p < 0.05) and the net ability to store carbon was reduced by 11.3%. Overall, the GPP was highly sensitive to extreme drought. Moreover, extreme drought significantly reduced the CH₄ fluxes of the ecosystem and even changed the peatland from a CH₄ emission source to a CH₄ sink. Subsequent to drought treatment, extreme drought was also shown to have a carry-over effect on the carbon budget of this ecosystem. Soil water content and soil temperature were the main driving factors of carbon budget change in the peatland of the Zoige plateau, but with the increase in soil depth, these driving forces were decreased. The findings indicated that frequent extreme drought events in the future might reduce the net carbon sink function of peatland areas, with an especially strong influence on CO₂.

How to effectively combine remote sensing data with the eddy covariance (EC) technique to accurately quantify gross primary production (GPP) in coastal wetlands has been a challenge and is also important and necessary for carbon (C) budgets assessment and climate change studies at larger scales. In this study, a satellite-based Vegetation Photosynthesis Model (VPM) combined with EC measurement and Moderate Resolution Imaging Spectroradiometer (MODIS) data was used to evaluate the phenological characteristics and the biophysical performance of MODIS-based vegetation indices (VIs) and the feasibility of the model for simulating GPP of coastal wetland ecosystems. The results showed that greenness-related and water-related VIs can better identify the green-up and the senescence phases of coastal wetland vegetation, corresponds well with the C uptake period and the phenological patterns that were delineated by GPP from EC tower (GPP_EC). Temperature can explain most of the seasonal variation in VIs and GPP_EC fluxes. Both enhanced vegetation index (EVI) and water-sensitive land surface water index (LSWI) have a higher predictive power for simulating GPP in this coastal wetland. The comparisons between modeled GPP (GPP_VPM) and GPP_EC indicated that VPM model can commendably simulate the trajectories of the seasonal dynamics of GPP_EC fluxes in terms of patterns and magnitudes, explaining about 85% of GPP_EC changes over the study years (p < 0.0001). The results also demonstrate the potential of satellite-driven VPM model for modeling C uptake at large spatial and temporal scales in coastal wetlands, which can provide valuable production data for the assessment of global wetland C sink/source.

Forest nitrous oxide (N₂O) emission plays an important role in the greenhouse gas budget of forest ecosystems. However, spatial variability in N₂O fluxes complicates the determination of key factors of N₂O fluxes at different scales. Based on an updated database of N₂O fluxes and the main edaphic factors of global forests, the magnitude of N₂O fluxes from forests and the relationships between edaphic factors and N₂O fluxes at different scales were analyzed. According to the results, the average annual N₂O flux of the global forest was 142.91 ± 14.1 mg N m⁻² year⁻¹. The range of total forest estimated N₂O emission was 4.45–4.69 Tg N in 2000. N₂O fluxes from forests with different leaf traits (broadleaved and coniferous) have significant differences in magnitude, whereas the leaf habit (evergreen and deciduous) was an important characteristic reflecting different patterns of N₂O seasonal variations. The main factors affecting N₂O fluxes on the global scale were ammonium (NH₄⁺) and nitrate (NO₃⁻) concentrations. With an increasing scale (from the site scale to the regional scale to the global scale), the explanatory power of the five edaphic factors to N₂O flux decreased gradually. In addition, the response curves of N₂O flux to edaphic factors were diversified among different scales. At both the global and regional scales, soil hydrothermal condition (water filled pore space (WFPS) and soil temperature) might not be the main spatial regulation for N₂O fluxes, whereas soil nutrient factors (particularly NO₃⁻ concentration) could contribute more on N₂O flux spatial variations. The results of site-control analysis demonstrated that there were high spatial heterogeneity of the main N₂O controls, showing N₂O fluxes from low latitude forests being more likely associated with soil WFPS and temperature. Thus, our findings provide valuable insights into the regulatory edaphic factors underlying the variability in N₂O emissions, when modeling at different scales.