Biotic Responses to Climate Change and Agricultural Management: Impacts on Belowground Diversity and Leaf Physiology

Soil and plant responses to environmental change play an important role in regulating carbon cycling and ecosystem resilience under a climate change. This dissertation integrates meta-analysis, controlled environment experimentation to examine how temperature, drought, and crop diversity influence soil microbial communities, plant–soil feedback, and photosynthetic performance in cotton-based systems. In Chapter I, a meta-analysis of 44 soil warming studies conducted in dry environments (mean annual precipitation < 1000 mm) showed that warming significantly increased soil respiration and oxidative enzyme activity without altering fungal or bacterial abundance. Warming duration and magnitude were the strongest predictors of microbial responses, suggesting that prolonged and intense warming accelerates soil carbon loss by stimulating microbial decomposition of stable organic matter. In Chapter II, I investigated investigates how crop rotation and root exudation shape microbial community and plant–soil feedback dynamics in a cotton–sorghum rotation system. While cotton exhibited a neutral feedback, sorghum showed strong negative feedback when grown in rotation with cotton. Crop type primarily determined root traits and exudate chemistry, whereas soil microbial legacy influenced community composition and beta diversity. These findings underscore the interplay between crop-specific exudation patterns and microbial legacies in maintaining soil microbial function and long-term soil health. In Chapter 3, controlled-environment experiments explored how temperature and drought interact to affect photosynthetic acclimation in Pima (Gossypium barbadense) and Upland cotton (G. hirsutum). High growth temperature enhanced photosynthetic capacity (Vcmax, Jmax) and shifted the temperature optimum upward, indicating thermal acclimation. Water availability moderated these effects, with species-specific differences – Upland cotton maintained higher photosynthetic capacities and Rubisco activity under combined stress, demonstrating greater resilience to semi-arid conditions. Collectively, this work provides a multi-scale understanding of how warming, crop management, and physiological plasticity govern carbon fluxes in soil-plant systems. By linking microbial activity, rhizosphere chemistry, and photosynthetic adaptation, the dissertation highlights key mechanisms that underpin ecosystem function and crop productivity in the face of global change.