Carbon exchange between terrestrial ecosystems and the atmosphere is one of the most important processes in the global carbon cycle. Understanding the spatial variation and controlling factors of carbon exchange fluxes is helpful for accurately predicting and evaluating the global carbon budget. 

Prof. Yu Guirui compiled global carbon flux data across the Asian, European, North American, South American, African and Oceanian regions to reveal that the spatial variations of carbon exchange fluxes (gross primary production (GPP), ecosystem respiration (Re) and net ecosystem production (NEP)) were mainly controlled by the mean annual temperature (MAT) and the mean annual precipitation (MAP) in China, Asian, Northern Hemispheric regions and at the global scale. These results strongly support the universality of the climate-driven theory from regional to global scale. 

Prof. Yu Guirui also revealed a phenomenon that gross primary production (GPP) and ecosystem respiration (RE) covaried across space regionally and globally. RE/GPP values consistently averaged at 0.87 ± 0.04 along the spatial variations in climate and vegetation index. He further demonstrated that this covariation between GPP and RE across space is largely attributed to the parallel responses of GPP and RE to the common climatic and vegetation factors, but the underlying mechanism lies in productivity as the primary and direct substrate supplier for respiration which fundamentally constrains RE. These results indicate the variation in photosynthate availability is the dominant driver for respiration across space and suggest that the photosynthesis process must be fully considered in the cross-site RE comparisons.

Importantly, Prof. Yu Guirui by integrating eddy covariance observations from ChinaFlux, AsiaFlux, AmeriFlux, CarboEurope and FLUXNET over the past two decades revealed the high carbon dioxide uptake by subtropical forest ecosystems in the East Asian monsoon region. The average forest NEP value in subtropical forests is higher than that in Asian tropical and temperate forests and the same latitudes Europe-Africa and North America forests. It is comparable to that in Southeastern US subtropical forests and intensively managed Western European forests. The total NEP of East Asian monsoon subtropical forests was estimated to be 0.72 ± 0.08 Pg C yr-1 which accounts for 8 % of the global forest NEP. He further revealed that the underlying mechanisms for this high carbon uptake in East Asian monsoon subtropical forests was attributed to the combined effects of the young stand ages, high nitrogen deposition and sufficient and synchronous water and heat availability. This result shows the monsoon forest ecosystems represent another large carbon uptake region in addition to those furnished by mid- and high-latitude European and North American forests, which strongly challenge the traditional view of only temperate- and high-latitude forests contribute a carbon sink in the Northern Hemisphere, and it suggest that the regional distributions of the northern hemisphere's terrestrial carbon sinks are needed to be re-evaluated. 

These related studies have been published in Top international academic journals.
1.Yu, G.R., Chen, Z., Piao, S.L., et al. 2014. High carbon dioxide uptake by subtropical forest ecosystems in the East Asian monsoon region. Proceedings of the National Academy of Sciences of the United States of America, 111, 4910-4915.
2.Yu, G.R., Zhu, X.J., Fu, Y.L., et al. 2013. Spatial pattern and climate drivers of carbon fluxes in terrestrial ecosystems of China. Global Change Biology, 19, 798-810.
3.Chen, Z., Yu, G.R., Ge, J.P., et al. 2013. Temperature and precipitation control of the spatial variation of terrestrial ecosystem carbon exchange in the Asian region. Agricultural and Forest Meteorology, 182-183, 266-276.
4.Chen, Z., Yu, G.R., Zhu, X.J., et al. 2015. Covariation between gross primary production and ecosystem respiration across space and the underlying mechanisms: A global synthesis. Agricultural and Forest Meteorology, 203, 180-190.
5.Zhu, X. J. Yu, G.R., He, H.L., et al. 2014. Geographical statistical assessments of carbon fluxes in terrestrial ecosystems of China: Results from upscaling network observations. Global and Planetary Change, 118, 52-61.                                                   

Fig.1 Estimates of GPP, RE and NEP for 10° latitudinal bins in the Asian region.

(Yu & Chen et al., 2014, PNAS)

Fig.2 The influences of MAT and MAP on the spatial pattern of NEP, GPP and Re in the Asian region. (Chen & Yu et al., 2013, Agricultural and Forest Meteorology).