Nanoclay- and alginate-based soil amendments preserve photosynthetic function, delay senescence, and reduce oxidative damage in drought-stressed wheat.

INTRODUCTION: Drought stress accelerates leaf senescence, disrupts photosynthetic function, and enhances oxidative damage in wheat, yet the extent to which soil amendments can mitigate these responses remains insufficiently understood. This study examined whether nanoclay (CN), calcium alginate (CG), and nanoclay-calcium alginate composite formulations (CNG) could modulate senescence, redox status, and photosynthetic performance under drought conditions. METHODS: A greenhouse experiment was conducted using wheat grown under regular watering and drought stress conditions. Plants were treated with CN, CG, and CNG composite formulations, and responses were assessed through physiological and biochemical traits related to senescence, chlorophyll status, photosystem II (PSII) performance, oxidative stress, antioxidant enzyme activity, and proline accumulation. Principal component analysis (PCA) was performed to evaluate multivariate treatment effects. RESULTS: Drought caused pronounced physiological and biochemical deterioration in the untreated control, including increased leaf yellowing, chlorophyll depletion, reduced PSII performance, and elevated hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels. Amendment effects were strongly trait dependent. CNG 31, particularly at 1.5%, most consistently delayed drought-induced senescence and reduced oxidative injury, whereas CG treatments were more effective in preserving chlorophyll content and photochemical performance. APX and GPX activities varied among formulations and did not show a uniform drought response, suggesting that mitigation involved differential regulation of redox metabolism rather than a simple increase in antioxidant activity. Proline accumulation was influenced mainly by water regime and showed weaker discrimination among treatments. Principal component analysis revealed clear multivariate separation among droughted treatment groups, reflecting coordinated variation in senescence, oxidative, and antioxidant traits. CONCLUSION: Nanoclay- and alginate-based amendments modulated wheat drought responses through coordinated effects on senescence progression, photosynthetic integrity, and oxidative balance, with formulation-specific differences in the dominant protective mechanisms. These findings highlight the potential of tailored soil amendments to improve wheat resilience under water-limited conditions.