Earthworms Enhance Crop Resistance to Insects Under Microplastic Stress by Mobilizing Physical and Chemical Defenses

To assess the ecological risk of microplastics (MPs) in agricultural systems, it is critical to simultaneously focus on MP-mediated single-organism response and different trophic-level organism interaction. Herein, we placed earthworms in soils contaminated with different concentrations (0.02% and 0.2% w/w) of polyethylene (PE) and polypropylene (PP) MPs to investigate the effect of earthworms on tomato against <i>Helicoverpa armigera</i> (<i>H. armigera</i>) under MPs stress. We found that earthworms alleviated the inhibitory effects of MPs stress on tomato growth and disrupted <i>H. armigera</i> growth. Compared to individual MPs exposure, earthworm incorporation significantly increased the silicon and lignin content in herbivore-damaged tomato leaves by 19.1% and 57.6%, respectively. Metabolites involved in chemical defense (chlorogenic acid) and phytohormones (jasmonic acid) were also activated by earthworm incorporation. Furthermore, earthworms effectively reduced oxidative damage induced by <i>H. armigera</i> via promoting antioxidant metabolism. Overall, our results suggest that utilizing earthworms to regulate above- and below-ground interactions could be a promising strategy for promoting green agriculture.