| Summary: | Improving leaf photosynthetic capacity is one of the most promising approaches to further boost crop yield. Clarifying factors limiting leaf photosynthetic capacity, especially in C<sub>3</sub> crops, is meaningful for designing strategies to improve it. Leaf net photosynthetic rate (<i>A</i>) is one of the parameters describing leaf photosynthetic capacity. In the present study, physiological factors limiting <i>A</i> in C<sub>3</sub> crops such as rice were discussed and different approaches for <i>A</i> improvement were summarized to provide theoretical guidance for increasing leaf photosynthetic capacity. <i>A</i> will be limited by both CO<sub>2</sub> availability and light intensity over periods from a few hours to several days, and by one of them over shorter intervals. Under current ambient atmospheric conditions, <i>A</i> of C<sub>3</sub> crops is mainly limited by Rubisco activity and the CO<sub>2</sub> concentration in chloroplasts. Leaf nitrogen content affects <i>A</i> by regulating Rubisco content and leaf anatomy; leaf morphological and anatomical traits limit <i>A</i> by impacting stomatal and mesophyll CO<sub>2</sub> diffusion. Further improvements of <i>A</i> in C<sub>3</sub> crops can be achieved by designing or introducing high-activity Rubisco; adjusting leaf nitrogen allocation to optimize leaf anatomy and leaf chemical composition; modifying leaf morphology and anatomy for greater CO<sub>2</sub> diffusion; improving the activity of proteins and enzymes associated with sugar transportation and utilization; introducing C<sub>4</sub> photosynthetic mechanisms and combining high photosynthetic traits by conventional breeding.
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