Soil compaction impairs cotton growth and photosynthetic performance even under non-limiting water and nutrient...

Soil compaction represents a critical limitation to global agricultural productivity, yet how its direct effects plant physiological processes remain insufficiently understood. This study assessed how increasing levels of soil compaction influence the physiological performance of cotton (Gossypium hirsutum) under controlled environmental conditions. Three degrees of compaction (DC) were considered: Control - 75% of the maximum soil bulk density (Bd = 1.52 Mg m^-3, non-compacted), DC85 (Bd = 1.66 Mg m^-3) and DC95 (Bd = 1.78 Mg m^-3) corresponded to intermediate and high compaction levels, representing 85% and 95% of the soil's maximum bulk density, respectively. Increasing compaction significantly reduced plant growth and leaf area. Photosynthesis was suppressed due to stomatal closure, which limited CO₂ diffusion into mesophyll tissue, and was accompanied by decreased photochemical and carboxylation efficiencies. Soil compaction promotes on cotton plants increased thermal energy dissipation, reduced electron transport efficiency between Q_A and Q_B, and altered chloroplast ultrastructure, including the number of chloroplasts and organization of thylakoid lamellae. These changes impaired light harvesting and CO₂ fixation. Additionally, high compaction levels led to increased leaf reflectance and reduced sugar content, indicating compromised source activity, although no direct evidence of end-product feedback inhibition was observed. Overall, soil compaction negatively affected photosynthetic performance at multiple levels, morphological, anatomical, biochemical, and photochemical, culminating in reduced carbon assimilation and biomass accumulation in cotton. These findings highlight the critical role of maintaining adequate soil physical conditions to ensure optimal photosynthetic function and crop performance.