| Summary: | Vegetation photosynthesis is largely determined by CO2 concentrations, which have significantly accumulated by urbanization. Thus, quantifying urbanization-caused CO2 concentrations’ impact on the terrestrial ecosystem, especially for vegetation photosynthesis (represented by GPP, NPP, NEP, and SIF), is vital. In this study, we firstly examined the effectiveness of the observation minus reanalysis (OMR) method in quantifying urbanization-caused CO2 concentrations and the effect of urbanization on CO2 accumulation from 2009 to 2018. Then, the effect of urbanization-caused CO2 on global vegetation GPP, NPP, NEP, and SIF was calculated and analyzed using terrestrial vegetation radiative transfer and prognostic models. Lastly, the impacts of urbanization-caused CO2 increase in different continents and vegetation types were analyzed, separately. The results demonstrated that: 1) Urbanization-caused CO2 concentrations accumulated for 3.93 ppm during 2009–2018. For carbon fluxes, urbanization-caused GPP, NPP and NEP accumulation increased 1.24 PgC, 0.64 PgC, 0.17 PgC, respectively, while urbanization-caused SIF accumulated 0.07 PWum−1sr−1. 2) From a continental perspective, South America accounted for the most significant urbanization caused GPP, NPP, NEP, and SIF accumulation, because the tropical rainforest climate dramatically assists photosynthesis in Amazon Rainforests. 3) Forests accounted for the most significant urbanization-caused GPP, NPP, NEP, and SIF accumulation (over 35% of global vegetation). 4) SIF is more sensitive to the autumn postponement of photosynthetic activities than GPP, NPP, and NEP. ΔOMR(GPP), ΔOMR(NPP), ΔOMR(NEP) showed the most significant urbanization impact in summertime, but the North Hemisphere’s photosynthesis accumulated dramatically in autumntime shown as rising ΔSIF_OMR, partly due to the delay of the end of the growing season which happens in most northern ecosystems. Thus, this study will be helpful for us to further understand the terrestrial carbon cycle dynamics and the potential for alleviating global climate change.
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