Abstract: Excessive application of nitrogen (N) fertilizers increases the loss of N via runoff and leaching, resulting in a more serious eutrophication. In a previous study, we screened out a nitrogen-phosphorus enriched plant, the mining ecotype (ME) of Polygonum hydropiper. Studying the root morphology response to inorganic nitrogen addition could be expected to provide a theoretical basis for understanding the absorption and accumulation mechanism of nitrogen in the ME of P. hydropiper. Sand culture experiments were conducted to analyse the N accumulation and root morphology of the P. hydropiper ME supplied with different ammonium nitrogen (NH₄-N) concentrations (25, 50, 75 mg N·L^-1) and different nitrate nitrogen (NO₃-N) concentrations (25, 50, 75 mg N·L^-1). The P. hydropiper ME showed the greatest biomass and N accumulation at 50 mg N·L^-1. The biomass values of the P. hydropiper ME grown in 50 and 75 mg·L^-1 NO₃-N treatments were significantly higher than those in NH₄-N treatments; however, the P. hydropiper ME accumulated more N when grown in the NH₄-N than when grown in the NO₃-N treatments. The root growth of the P. hydropiper ME was greatly inhibited with increasing NH₄-N concentrations in solution. The root system of the P. hydropiper ME showed the greatest length, surface area, and volume when grown in 50 mg·L^-1 NO₃-N. The root growth of the P. hydropiper ME was greater in NH₄-N than in NO₃-N at 25 mg N·L^-1, but this difference was reversed at 50 and 75 mg N·L^-1. In summary, he appropriate NO₃-N concentration promoted the growth of the P. hydropiper ME and the development of lateral roots, resulting in enhanced absorption of N. High concentration of NH₄-N inhibited root growth, but did not reduce N accumulation in the plant.

Key words: Polygonum hydropiper, inorganic nitrogen, root morphology, nitrogen accumulation