Improving photosynthetic efficiency in fluctuating light to enhance yield of C3 and C4 crops

Photosynthetic adaptations to light fluctuations do not occur instantaneously, leading to reduced carbon gain and lower productivity in agricultural crops. Enhancing the rapidity of photosynthetic responses to these fluctuations could potentially increase carbon assimilation by 13-32%, indicating a substantial opportunity for yield improvement of major crops. Most crops can be categorized into C-3 or C-4 crops by their photosynthetic pathways. This review provides a comparative overview of the photosynthetic responses of both C-3 and C-4 crops to light fluctuations, highlighting the unique and shared challenges for these two photosynthetic pathways. In C-3 crops, fast adjustments in non-photochemical quenching, stomatal and mesophyll conductance, and Rubisco activation are essential for optimizing photosynthesis under variable light conditions. In contrast, C-4 crops, including maize, sorghum, and sugarcane, benefit from their carbon concentration mechanism under high light conditions but face challenges in coordinating the C-4 and Calvin-Benson-Bassham cycles. Strategies to enhance the activation of pyruvate phosphate dikinase and Rubisco, as well as to improve electron transport capacity and flexibility, could markedly boost the photosynthetic efficiency and productivity. Through a detailed understanding of the distinct mechanisms involved in C-3 and C-4 photosynthesis, this review underscores the need for tailored strategies to optimize the photosynthetic efficiency specific to each crop type. Exploring and leveraging these differences is crucial for propelling agricultural productivity forward.