The influence of trophic complexity on preferential uptake of dissolved inorganic and organic nitrogen: a laboratory microcosm experiment

Abstract

AbstractN is a critical element for all living things, including the flora and fauna in aquatic ecosystems. However, N exists in many forms, and some organisms might preferentially use one compound over another. We used 15N tracers in laboratory microcosm experiments to measure preferential uptake of 4 different N compounds (NH4-N, NO3-N, glycine, methionine) by filamentous green algae (Cladophora glomerata; autotrophs), microbes in stream sediment (heterotrophs), and freshwater snails (Physa acuta; consumers) in response to varying trophic complexity. Seven trophic complexity treatments were applied: 3 types of single-organism treatments (filamentous algae, sediment microbes, or snails), three types of 2-organism treatments (filamentous algae + sediment microbes, sediment microbes + snails, filamentous algae + snails), and 1 treatment consisting of all organisms (filamentous algae + sediment microbes + snails). We combined trophic complexity treatments (n = 7) with 1 of 5 15N tracers: control (no 15N),...