Effects of Si and N Addition on Oryza sativa and Its Invasive Grazer Apple Snails (Ampullariidae): Resistance Traits and Feeding Metrics.

Silicon, as a crucial element of plants, contributes to plants' resistance to biotic stresses like herbivore feeding. In tropical and subtropical Asia, the apple snail (Ampullariidae) is an invasive aquatic herbivorous snail in agricultural and wetland ecosystems, like paddy fields, which suffer from heavy nitrogen eutrophication. However, little is known about the potential effects of supplementing rice leaves treated with silicon and nitrogen on the feeding metrics of apple snails (Pomacea spp.). This study conducted a greenhouse experiment to examine the effects of silicon and nitrogen addition on rice seedlings grazed by apple snails, with two levels of silicon addition (0 and 1.5 mM) and three levels of nitrogen addition (0.72, 1.44 and 5.76 mM). The results showed that silicon addition increased plant mass under low and high nitrogen addition, and increased the C/N ratio and tannin content only under the middle nitrogen addition, while it increased the leaf sulfur content of rice at all three levels of nitrogen addition. However, silicon addition significantly decreased the growth of apple snails while significantly increasing flavonoid content and the force of fracture of rice leaves across all nitrogen levels. This study indicates that silicon addition could improve the defense of rice against herbivory by invasive apple snails, providing insights into the protection of wetland crops in the context of eutrophication and biological invasion.