Impacts of Drought on Photosynthesis in Major Food Crops and the Related Mechanisms of Plant Responses to Drought

Abstract

Drought stress is one of the most critical threats to crop productivity and global food security. This review addresses the multiple effects of drought on the process of photosynthesis in major food crops. Affecting both light-dependent and light-independent reactions, drought leads to severe damage to photosystems and blocks the electron transport chain. Plants face a CO₂ shortage provoked by stomatal closure, which triggers photorespiration; not only does it reduce carbon fixation efficiency, but it also causes lower overall photosynthetic output. Drought-induced oxidative stress generates reactive oxygen species (ROS) that damage cellular structures, including chloroplasts, further impairing photosynthetic productivity. Plants have evolved a variety of adaptive strategies to alleviate these effects. Non-photochemical quenching (NPQ) mechanisms help dissipate excess light energy as heat, protecting the photosynthetic apparatus under drought conditions. Alternative electron pathways, such as cyclical electron transmission and chloroplast respiration, maintain energy balance and prevent over-reduction of the electron transport chain. Hormones, especially abscisic acid (ABA), ethylene, and cytokinin, modulate stomatal conductance, chlorophyll content, and osmotic adjustment, further increasing the tolerance to drought. Structural adjustments, such as leaf reordering and altered root architecture, also strengthen tolerance. Understanding these complex interactions and adaptive strategies is essential for developing drought-resistant crop varieties and ensuring agricultural sustainability.

Keywords: chloroplast; crop; drought; photosynthesis; stress.

Figure 1

Effects of drought stress on the photosynthesis of major food crops. Drought stress not only reduces the rate of light reaction and dark reaction, but also restricts the acquirement of the substances for photosynthesis. Moreover, drought stress results in the accumulation of reactive oxygen species (ROS), which causes various damages in chloroplasts.

Figure 2

Drought stress responses in major food crops, with an emphasis on photosynthesis. Plants respond to drought at various levels to protect photosynthesis and other aspects of plants. NPQ, non-photochemical quenching. CET, cyclic electron transfer. WUE, water use efficiency.

Figure 3

Photorespiration and drought response in C₃ and C₄ plants. The mechanisms of photorespiration and drought response in C₃ (such as rice) and C₄ (such as maize) plants differ. Under drought stress, both C₃ and C₄ plants increase ATP and NADPH consumption and reduce ROS production. There are higher water consumption requirements and increased photorespiration in C₃ plants, while C₄ plants exhibit higher photosynthetic rates and efficiency.