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, may contribute to plants’ resistance to biotic stresses like herbivore feeding. In tropical and subtropical Asia, apple snail (Ampullariidae) is an invasive aquatic herbivorous snail in agricultural and wetland ecosystems, like paddy field, which suffer from heavy eutrophication of nitrogen. However, little is known about the potential effects of feeding rice leaves treated with silicon and nitrogen on the feeding metrics of apple snails. We conducted a greenhouse experiment to examine the effect of silicon and nitrogen addition on rice seedlings as grazed by apple snails, in which two levels (0 and 1.5 mM) of silicon addition and three levels (0.72, 1.44 and 5.76 mM) of nitrogen addition were used. We measured plant growth, leaf element contents and leaf defense characteristics of rice. We determined the snail feeding metrics after feeding in different rice leaves for one week. Silicon addition increased plant mass in the low and high nitrogen addition and increased the C/N ratio only in the middle nitrogen addition. Silicon addition significantly decreased the growth of apple snails while significantly increasing flavonoid content and the force of fracture of rice leaves in all the nitrogen levels. Silicon addition increased the tannin content of rice leaves in the middle nitrogen addition but decreased in high nitrogen treatment. Moreover, silicon addition increased the leaf sulfur content of rice at all three levels of nitrogen addition. Silicon addition could improve the defense of rice against invasive herbivory by apple snails, which sheds insights on the protection of wetland crops in the context of control of eutrophication and biological invasion.