Drought severity determines the effectiveness of straw mulching in alleviating water stress during early maize growth

Abstract

Introduction Drought is a major constraint on the early growth and photosynthetic productivity of maize (Zea mays L.), yet whether the physiological benefits of straw mulching depend on drought severity remains unclear. Methods A two-year experiment was conducted in 2025 and 2026 using straw removal and straw mulching under three irrigation levels (135, 105, and 75 mm), representing well-watered, moderate-drought, and severe-drought conditions, respectively. Plant growth, photosynthetic performance, carbon-assimilation enzyme activities, osmotic adjustment, and antioxidant responses were evaluated. Results Increasing drought severity generally reduced leaf area index (LAI), plant height (PH), dry matter accumulation (DW), photosynthetic performance, and carbon-assimilation capacity, while increasing the accumulation of proline, soluble sugars, betaine, malondialdehyde (MDA), and hydrogen peroxide (H2O2), together with antioxidant responses. The physiological effects of straw mulching varied markedly with drought severity. Under moderate drought, mulching more consistently maintained plant growth and photosynthetic performance, preserved carbon-assimilation enzyme activities, and reduced MDA and H₂O₂ accumulation. In contrast, these beneficial responses were substantially weaker and less consistent under severe drought. Across physiological traits, better growth and carbon-assimilation performance were generally associated with lower osmotic and oxidative stress. Multivariate patterns further showed that mulched plants under moderate drought exhibited a physiological profile closer to that under well-watered conditions, whereas plants under severe drought remained distinctly separated despite straw mulching. Discussion Overall, straw mulching provided more consistent physiological protection against moderate drought than severe drought during early maize growth, indicating that drought severity strongly constrains the effectiveness of straw mulching.