Effects of nitrate to ammonium ratio and nitrogen level on growth of an invasive plant <i>Alternanthera philoxeroides</i> in cadmium polluted water

Abstract The performance of invasive plants in cadmium polluted environments has been shown to be affected by high nitrogen availability and forms, but the effect of nitrate to ammonium ratios on invasive plant performance under cadmium stress remains unclear. In a greenhouse experiment, single fragments of Alternanthera philoxeroides were grown in water polluted with cadmium at a concentration of 1 mg L −1 . The experiment involved three nitrogen levels (0.4, 2, and 10 mmol L −1 ) and five ratios of nitrate to ammonium (1:9, 3:7, 5:5, 7:3, and 9:1) to investigate the effects of nitrogen concentration and nitrate to ammonium ratio on the growth of this invasive plant species under cadmium polluted conditions. At a nitrogen concentration of 0.4 mmol L −1 , the ratio of nitrate to ammonium at 1:9 significantly decreased the total biomass. In contrast, at a nitrogen concentration of 10 mmol L −1 , the lowest total biomass was observed when the ratio of nitrate to ammonium was 5:5. The effect on morphology both from nitrogen level and nitrate to ammonium ratio were independent from each other. Our finding suggested that when predicting and managing Alternanthera philoxeroides in cadmium polluted water, it is crucial to consider not only nitrogen concentration levels but also the nitrate to ammonium ratio.