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.