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Biochar Mitigates the Detrimental Effects of Combined Drought and Microplastic Stress on Alfalfa by Modulating Physiological and Molecular Responses
Summary
Drought and microplastic pollution in soil are a one-two punch that stunts crop growth, but this study found that adding biochar (a charcoal-like soil additive made from organic waste) helped alfalfa plants recover, boosting their growth by nearly 40% by improving nutrient uptake and reducing plant stress damage. This matters because as microplastics increasingly contaminate farmland and droughts become more common with climate change, biochar could be a cheap, eco-friendly way to protect crop yields—which ultimately affects food supply and security for everyone.
The terrestrial ecosystem is simultaneously facing multiple stresses, such as drought and microplastics (MPs), which are negatively affecting humans, crop productivity, and environmental quality. Biochar (BC) is a widely used soil amendment that enhances crop productivity and mitigates stress. In this study, we examined how BC alleviates the harmful effects of combined drought and MPs on alfalfa (Medicago sativa L.) plants. The study contained seven treatments: control, DS (60% water holding capacity: WHC), MPs (1%), DS + MPs, DS + BC (2%), MPs + BC (2%), and DS + MPs + BC (2%). Both individual stresses, and particularly their co-exposure, markedly reduced alfalfa growth and biomass yield (44.99%) by decreasing root growth, chlorophyll contents, relative water contents (RWC), and soil nutrient availability, and by increasing malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) production. Biochar effectively mitigated the adverse effects of the individual stresses and their combined exposure. Notably, BC under co-exposure to DS and MPs enhanced biomass yield (39.38%) by increasing photosynthetic pigments, leaf photosynthetic rate (Pn: 21.41%), transpiration rate (Tr: 39.28%), stomatal conductance (gs: 41.10%), and soil nutrient availability (N: 37.17%, P: 34.42%, and K: 34.89%), while decreasing MDA (51.04%) and H₂O₂ (38.84%) production. Biochar also reduced H₂O₂ in alfalfa plants by increasing antioxidant activities (APX: 34.80%, CAT: 55.97%, POD: 59.82%, and SOD: 31.17%) and by increasing the expression of antioxidant genes such as MtAPX (24.27%), MtCAT (17.72%), MtPOD (12.80%), and MtSOD (27.46%). Collectively, these findings suggest that BC mitigates the toxic impacts of combined DS and MPs by modulating antioxidant activities, gene expression, and nutrient availability. Thus, BC appears to be an effective and eco-friendly soil amendment for enhancing crop productivity under combined abiotic stresses. These findings lay the foundation for developing sustainable solutions to counteract multi-stress conditions and enhance crop productivity.