Soybean Aphid Injury Effects on Shoot Nitrogen Components in Glycine max

Abstract

Knowledge of soybean aphid (Aphis glycines Matsumura) effects on soybean [Glycine max (L.) Merr.] shoot N components may improve understanding of how plants are injured by this invasive pest. This 2‐yr field study was conducted to measure soybean aphid effects (initial infestation of 0, 10, 50, or 100 aphids plant−1 at the fifth node [V5] stage) on cumulative aphid‐days as well as resulting soybean aphid populations plant−1, shoot dry weight (DW), nitrate N, and ureide N measured at full bloom (R2), beginning pod (R4), full pod (R5), and beginning seed (R6). Cumulative aphid‐days, which quantifies both the number of aphids present on plants and the duration of their feeding time, were similar across initial aphid infestation treatments. Compared with control plants, aphid feeding injury reduced shoot DW by about 40% and increased shoot nitrate N concentrations by about 45% across all initial infestation rates tested. Shoot nitrate N accumulation was increased about 20% by the 10 aphids plant−1 treatment. In contrast, shoot ureide N concentrations in aphid‐injured plants were similar to levels observed for uninjured plants. This lack of a concentration effect resulted in about a 36% decrease in ureide N accumulation in aphid‐injured plants. These differential responses may result because nitrate N can be absorbed directly from the soil solution while ureide N biosynthesis has a higher energy requirement that cannot be met under severe aphid infestations.