Co-application of biochar and melatonin enhances pea (Pisum sativum L.) performance and alleviates cadmium contamination stress

Sole biochar addition or exogenous melatonin application can decrease cadmium (Cd) toxicity in polluted soils and improve plant performance and growth. Yet the additive effects of biochar and melatonin application on plant growth, oxidative stress modulation and Cd absorption remain unclear. We conducted a pot experiment to study the combined effects of melatonin, biochar and Cd stress on pea (Pisum sativum L.) seedling growth, antioxidant enzyme activities, photosynthesis parameters and Cd uptake. Results showed that Cd addition significantly decreased pea growth, chlorophyll content, net photosynthesis rate (Pn), transpiration rate (Tr), stomatal conductance (gs), and increased intercellular CO2 concentration (ci) and oxidant enzyme activities when compared to non-Cd contaminated treatment. Exogenous applications of the biochar or melatonin alone significantly decreased the harmful effects of Cd stress and promoted pea seedling growth. Moreover, soil remediation with biochar could more effectively improve pea growth, chlorophyll contents, and photosynthesis parameters and contribute to Cd immobilisation; the melatonin treatment alone could more effectively increase antioxidant enzyme activities. The treatments of biochar and melatonin showed an additive result and had the largest promoting in pea growth, antioxidant enzyme activities, and lowest Cd contents in pea tissue and soil. These results indicate that the combined use of melatonin and biochar is more effective at reducing Cd uptake by pea tissues and alleviating Cd harm to pea plants.