A meta-analysis of root herbivore-induced communication cascades affecting above-ground herbivores, parasitoids, and pollinators via host plants

Several research papers over the past three decades have reported the profound influence of root herbivores on above-ground plant-insect interactions. Root-feeding insects significantly alter plant nutrient levels—carbon, nitrogen(N), phosphorus(P), and amino acids(AA)—triggering the production of defensive compounds like terpenoids, phenolics, gossypol, and DIMBOA in shoots. Jasmonate translocation from roots to shoots impairs shoot herbivore performance, while root herbivory suppresses salicylic acid (SA)-mediated defenses, benefiting phloem feeders. Reduced leaf water content and increased abscisic acid (ABA) levels enhance phloem feeder success. Nematode infestations lower AA and N, but increase foliar nicotine, aiding leaf chewers. Mycorrhizal fungi reduce plant N but raise carbon and P, while earthworms increase phytosterols, hindering aphid fecundity. These systemic changes cascade through trophic levels, even affecting hyperparasitoids. This review highlights root herbivory's intricate, cascading effects, reshaping our understanding of plant defense mechanisms and ecological interactions.