Evaluation of Environmental Controls on Terrestrial Net Ecosystem Exchange of CO2: A Global Perspective From the FLUXNET Sites. Issue 22 (26th November 2022)

• Record Type: Journal Article
• Authors: Kong, Zhe; Wang, Tiejun; Han, Qiong; Dai, Yibin; Wang, Lichun; Chen, Xi
• Is Part Of: Journal of geophysical research. Volume 127:Issue 22(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-11-26
• Subjects: net ecosystem exchange of CO2 -- FLUXNET -- boosted regression tree -- temporal scales -- climate regime -- ecosystem type; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2022JD037217
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Net ecosystem exchange (NEE) of CO2 is a key process modulating carbon exchanges between terrestrial ecosystems and the atmosphere; however, it remains a grand challenge to elucidate how the interactions of NEE with environmental variables vary among ecosystems and climate regimes across timescales. The FLUXNET and AmeriFlux data sets were used to diagnose the environmental controls on NEE. Based on the sites with long‐term observations (≥7 years), the results showed that the couplings between NEE and surrounding environments were stronger at daily and monthly scales than at annual scales, highlighting the temporal dependence of environmental variables influencing NEE. Moreover, the boosted regression tree method was applied to quantify the relative impacts of environmental controls on daily NEE variations. It revealed that leaf area index (LAI) and shortwave radiation ( R s ) were the major divers of daily NEE variations at most sites with the average contribution of 35.5% and 27.8%, respectively. Particularly, LAI was the principal control in deciduous broadleaf forested, non‐forested, and arid sites, while R s was the leading factor in evergreen forested sites. Meanwhile, air temperature ( T a ), soil water content (SWC), and vapor pressure deficit (VPD) exerted smaller influences with the average contribution of 14.6%, 13.2%, and 8.9%, respectively. The relative impacts of LAI, R s, SWC, and VPD also varied with aridity index, and mean annual precipitation and T a . Furthermore, NEE was more sensitive to vegetation dynamics in drier climate regions. This study provides additional understanding of how environmental factors regulate NEE dynamics across diverse land surface and climatic conditions. Plain Language Summary: Net ecosystem exchange (NEE) of CO2 can vary along the climate and ecosystem gradients at different timescales. Based on the FLUXNET and AmeriFlux data sets, we quantified the relative contributions of environmental factors to daily NEE variations at different sites around the globe by using boosted regression tree models. We found that the couplings between NEE and environmental factors at daily and monthly scales were stronger than at annual scales at the sites with long‐term observations (≥7 years). Leaf area index and radiation were the major divers of daily NEE variations at most sites. Moreover, the relative impacts of environmental variables on daily NEE variations varied with aridity index, mean annual precipitation, and mean annual temperature. These results are important for understanding the causes of variability in NEE across diverse land surface and climatic conditions. Key Points: Couplings between net ecosystem exchange (NEE) and environmental factors at daily and monthly scales were stronger than at annual scales at long‐term recorded sites At most sites, leaf area index was the principal control on daily NEE of CO2 variations, particularly in drier climate regions Relative importance of environmental factors varied with aridity index, mean annual precipitation, and mean annual temperature