Response of an invasive plant, Flaveria bidentis, to nitrogen addition: a test of form-preference uptake

Abstract

Plants differ in their capacity to use various forms of nitrogen (N). Although previous studies have suggested invasive plants alter N availability, few distinguish their responses to various forms and different concentrations of inorganic N. In order to understand how plant preference for N affects invasions, we tested the growth and physiological response of Flaveria bidentis, an invasive plant across north China, to different forms and concentrations of inorganic N. Seedlings of F. bidentis were cultivated in a mothproof screen house to determine if this invader benefits from increased or altered forms of N. 15N-labeled NH4 + and NO3 − were applied to the soil to gain insight into N partitioning in communities invaded by this species. We determined that plant growth and biomass variables, chlorophyll content, and photosynthesis parameters all varied depending on the form of available N. Specifically, N addition altered the biomass allocation pattern of plants, with F. bidentis tending to maximize its reproductive output under increased N availability. Also, F. bidentis had higher 15N–NH4 + recovery across biomass components than both co-occurring native plants, Amaranthus retroflexus and Eclipta prostrata. F. bidentis demonstrated a strong preference for ammonium (NH4 +) over nitrate (NO3 −) and captured at least twice the 15N–NH4 + as the native plants. By comparison, the two native species showed no preferences for the form of N. The greater above-ground biomass of F. bidentis contributed to its higher 15N recovery. We suggest that the ability of F. bidentis to respond rapidly to changes in the N pool, especially in ammonium, may confer a competitive advantage to this species over native species. Our results provide insight into how species-specific N preferences influence the ability of this species to invade a native community.