Fig. 2: Governing mechanisms on carbon exchange of urban greenery.

a A diagram showing carbon exchange of plants in the built environment with UHI, higher background CO₂ concentration, and management (irrigation). b Irrigation-induced change of urban gross primary productivity (dGPP_u), led by decrease of air temperature and increase of soil water content. c Irrigation-induced change of urban ecosystem respiration (dR_u), led by decrease of soil temperature and increase of soil water content. d Irrigation-induced change of urban net ecosystem exchange (dNEE_u), resulting from the combinations of dGPP_u and dR_u. e Urban ecosystem respiration as a function of soil temperature and soil water content. The light gray lines in b–d show all possible combinations lead to various types of outcomes. The black solid lines indicate pathway to the strong co-benefit effect. The red dashed lines indicate the pathway to the strong tradeoff effect. Circles in (e) indicate the average R_u before (hollow) and after (solid) irrigation. Arrows indicate the direction of change.