Despite atmospheric vapour pressure deficit (VPD) was demonstrated as significant environmental factors affecting plant photosynthesis and productivity, the regulating mechanism under varying atmospheric evaporative demand was still unclarified. The contribution of stomatal, mesophyll resistance and biochemical limitation imposed on photosynthesis in tomato under varying evaporative demand was highlighted in the present study. Quantitative photosynthetic limitation analysis across a series of

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... D was performed in well-watered tomato, by combining gas exchange and chlorophyll fluorescence. Results: Photosynthetic performance in tomato was gradually depressed with increasing in VPD. Under low VPD condition, stomatal and mesophyll conductance were sufficiently high for CO 2 transport, which facilitated high chloroplast CO 2 concentration for carbon fixation. Stomatal and mesophyll limitation accounted a low fraction, and photosynthetic potential was mostly constrained by biochemical limitation inside chloroplasts under low VPD condition. With increasing in VPD, plant water stress was gradually pronounced and triggered declines in stomatal and mesophyll conductance. Contribution of stomatal and mesophyll limitation on photosynthesis increased gradually with rise in VPD. Consequently, the low CO 2 availability inside chloroplast substantially constrained photosynthesis under high VPD condition. Conclusion: Photosynthetic potential in tomato was mostly constrained by biochemical limitation inside chloroplasts under low VPD condition. CO 2 diffusion limitation in series of stomatal and mesophyll resistance was the key rate-limiting step for photosynthesis under high VPD condition.