LAUSR

Ammonia has been a major reason of macrophyte decline in the water environment, and ammonium ion toxicity should be seen as universal, even in species frequently labeled as "NH4+ specialists". To study the effects of high NH4+-N stress of ammonium ion nitrogen on tolerant submerged macrophytes and investigate the pathways of nitrogen assimilation in different organisms, Myriophyllum aquaticum was selected and treated with various concentrations of ammonium ions at different times. Increasing of ammonium concentration leads to an overall increase in incipient ammonia content in leaves and stems of plants. In middle and later stages, high concentrations of NH4+ ion nitrogen taken up by M. aquaticum decreased, whereas the content of NO3- ion nitrogen increased. Moreover, in M. aquaticum, the activities of the enzymes nitrate reductase, glutamine synthetase and asparagine synthetase changed remarkably in the process of alleviating NH4+ toxicity and deficiency. The results of the present study may support the studies on detoxification of high ammonium ion content in NH4+-tolerant submerged macrophytes and exploration of tissue-specific expression systems.