Exogenous melatonin alleviates apple replant disease by regulating rhizosphere soil microbial community structure and nitrogen metabolism

Apple replant disease (ARD) is a common soil-borne disease afflicting apple plants. Melatonin is a broad-spectrum ox-ygen scavenger that plays a key role in alleviating stress-induced damage in plants. In this study, we aimed to deter-mine whether adding melatonin to replant soil can promote plant growth by improving the rhizosphere soil environment and nitrogen metabolism. In replant soil, chlorophyll synthesis was blocked, reactive oxygen species (ROS) accumulated in large quantities, and membrane lipid peroxidation was aggravated; this eventually resulted in slow plant growth. However, the application of 200 mu M exogenous melatonin enhanced the tolerance of plants to ARD by up-regulating the expression of antioxidant enzyme-related genes and increasing ROS scavenging enzyme ac-tivity. Exogenous melatonin also increased the absorption and utilization of 15N by increasing the expression of nitro-gen absorption genes and the activity of nitrogen metabolism enzymes. Exogenous melatonin enhanced the soil microbial environment by promoting soil enzyme activity and bacterial richness and decreasing the abundance of sev-eral harmful fungi in rhizosphere soil. Mantel test results showed that soil properties (except for AP) and growth in-dexes were positively correlated with the rate of 15N absorption and utilization. Spearman correlation analysis showed that the above factors were closely related to the richness and diversity of bacteria and fungi, indicating that the composition of microbial communities might play a key role in mediating change in the soil environment and thus affect nutrient absorption and growth. These findings provide new insights into how melatonin enhances ARD tolerance.

Automated summary

Apple replant disease (ARD) is a common soil-borne disease that affects apple plants. The study found that adding melatonin to the replant soil can enhance plant tolerance to ARD by up-regulating the expression of antioxidant enzyme-related genes and increasing ROS scavenging enzyme activity. Melatonin also improves nitrogen absorption and utilization, promotes soil enzyme activity and bacterial richness, and reduces harmful fungi in the rhizosphere soil. These findings provide new insights into how melatonin enhances ARD tolerance.