Within‐canopy carbon partitioning to cotton leaves in response to irrigation

When water resources are limited, cotton ( Gossypium hirsutum L.) plants adapt in part through adjustments in carbon allocation strategies, often evident in the leaves within the canopy. The dynamics of leaf carbon accumulation provide insights into how the plant partitions and uses carbon resources, a key aspect of optimizing crop productivity. In this study, we investigated the dynamics of leaf carbon accumulation in two cotton cultivars (Phytogen [PHY] 350 and Stoneville [ST] 5707) across spatial and temporal scales under two different levels of irrigation (low: 178 mm year −1 , high: 356 mm year −1 ) in 2020 and 2021. For each cultivar and irrigation treatment, an increase in leaf mass occurred primarily at the bottom of the canopy early in the season, followed by additional leaf production in the middle of the plant as the season progressed. Irrigation reduction resulted in a canopy with reduced radiation interception, less leaf shading in the lower canopy, and thicker leaves. In contrast, more irrigation created canopies with a larger effective leaf area, increasing total light interception despite increased shading at the canopy base. Additionally, leaf carbon allocation is synchronized with fruit carbon demand at the onset of the first bloom stage for an early‐maturing cultivar. Overall, this study provides valuable insights into the complex relationship between water availability, radiation intensity within the canopy, and leaf carbon dynamics, contributing to a more comprehensive understanding of the plant's overall performance in resource‐constrained environments. Mainstem leaf carbon distribution varies across different node positions within the cotton canopy. Reduced irrigation results in thicker mainstem leaves in the lower portion of the canopy. Leaf and fruit carbon gain are synchronous at the onset of the first bloom stage of an early‐maturing cultivar. When water is scarce, cotton plants change how they use and store carbon, especially in their leaves. This helps the plants survive and grow better. In this study, we looked at how two different types of cotton (Phytogen [PHY] 350 and Stoneville [ST] 5707) handled carbon under two levels of irrigation: low and high. We found that early in the growing season, more leaves grew at the bottom of the plant. Later, leaves started to grow more in the middle of the plant. When less water was available, the plants had fewer, thicker leaves and allowed more sunlight to reach the lower parts of the pl