Effects Of Ammonia Nitrogen Pulse On Growth And Carbon-nitrogen Metabolism Of Submerged Plants

Ammonia pulse attributed to runoff of urban surface and agriculture following heavy rain is common in inland aquatic systems and can cause profoundly effects on the growth of macrophytes,especially when combined with low light.In this study,three patterns of ammonia nitrogen pulse(high ammonia nitrogen × low frequency,medium ammonia nitrogen × medium frequency,low ammonia nitrogen × high frequency)under different light(50% sunlight and 25% sunlight)applied to examine their effects on the growth of three submerged macrophytes,namely,Myriophyllum spicatum,Potamogeton maackianus,and Vallisneria natans.The results showed that the influence of ammonia nitrogen pulse on the growth and metabolism of submerged plants was related to the pulse patterns and the species of submerged plants.The results are as follows:(1)Ammonia nitrogen pulse caused negative effects on the biomass of the submerged macrphytes,and the effects were species specific and light dependent;the negative effects on biomass of M.spicatum were significantly greater than that on V.natans and P.maackianus,the effects of ammonia nitrogen pulse pattern and experiment phase on the biomass of the species accounted for 9.5% and 81.5%,respectively;the negative effects of ammonia nitrogen pulse on P.maackianus were the strongest at high loading with low frequency(branch number,leaf number,and total branch length decreased significantly),and on V.natans at moderate loading with moderate frequency(ramet number and height decreased significantly),for M.spicatum,no significant differences were found among the three ammonia nitrogen pulse patterns;low light availability did not significantly aggregate the negative effects of ammonia nitrogen pulse on the growth of the submersed macrophytes;under the stress of ammonia nitrogen and low light,submerged plants regulate their own morphological characteristics.(2)Ammonia nitrogen pulse had a certain effect on carbon-nitrogen metabolism in submerged macrophytes.Ammonia nitrogen and free amino acids in stem and leaf tissues of submerged macrophytes increased significantly and carbohydrates decreased,and the effect of ammonia nitrogen pulse on carbon-nitrogen metabolism of P.maackianus and M.spicatum was greater than that of V.natans;there was no significant increase in nitrate nitrogen in stem and leaf tissues under ammonia nitrogen pulse;for M.spicatum,compared with its leaf tissue,the ammonia toxicity was eliminated by consuming carbohydrate in its stem tissue;the negative effects of ammonia nitrogen pulse on P.maackianus were the strongest at high loading with low frequency(ammonia nitrogen and free amino acids in its stem and leaf tissues increased significantly),and on V.natans at moderate loading with moderate frequency(free amino acids in its stem tissues increased significantly),for M.spicatum,the negative effects of ammonia nitrogen pulse on its carbon-nitrogen metabolism were the strongest at high loading with low frequency(ammonia nitrogen and free amino acids in its stem tissue increased significantly);the effect of light on submerged macrphytes was species-specific,and low light significantly exacerbated the stress of ammonia nitrogen pulses on the growth of P.maackianus and M.spicatum,but V.natans had a strong physiological adaptability to low light.Our study contributes to revealing the roles of ammonia nitrogen pulse on the growth of aquatic plants and its species specific effects on the dynamics of submerged macrophytes in lakes.