Effects Of Acid Rain And Eutrophication Combined Stress On N Uptake Mechanism Of Acquatic Plants

Three aquatic plants, Oenanthe javanica,Acorus gramineus and Saururus chinensis wereselected as experimental materials with higher N uptake abilities. Effects of acid rain andeutrophication combined stress on N uptake of acquatic plants were investigated, including rootactivity, nitrate reductase(NR) activity, polyamines contents and N uptake ability and so on. Theresults could provide a reference for restoration and reconstruction of acquatic plants in lakeecosystems and understanding of different N uptake mechanisms of acquatic plants in thecontaminated water body. Main results are described as follows:(1)The root activity of A. gramineus was not reduced with increasing frequency of acid rain.Root activity of S. chinensis was reduced with increasing frequency and intensity of acid rain.The interaction of combined stress had significant influence on root activity of A. gramineus butfewer influence on that of S. chinensis.(2)NR activity was reduced with increasing degree of eutrophication both of A. gramineusand S. chinensis. The simulated acid rain with pH1.78had great influence on NR activity both ofA. gramineus and S. chinensis. NR activity of S. chinensis was reduced with increasing frequencyof acid rain. Increasing frequency of acid rain could induce the increase of bands of NR isozymeand increase NR activity of A. gramineus. Eutrophication and acid rain had interaction on NRactivity.(3)Under acid rain stress, the Put content of S. chinensis increased. Eutrophication and acidrain combined stress had no interaction on it. On the other hand, the Put content of A. gramineusincreased firstly,then decreased with increasing frequency of acid rain.The ratio of (Spd+Spm)/Put rose firstly and then falled,with a great fluctuation. It reachedthe peak value after the fourth acid rain treatment in A. gramineus. The ratio of (Spd+Spm)/Putpresented different trend, with less degree of change in S. chinensis than that in A. gramineus.(4)The root of O. javanica could both absorb more NH₄⁺and NO₃^-, the root of S. chinensisprefer more NH₄⁺, and the root of A. gramineus prefer more NO₃^-.(5)The absorption of NH₄⁺by root of O. javanica could be definitely reduced after differentintensitied of acid rain treatments. They even exhausted NO₃^-under hyper eutrophication level.The root of A. gramineus absorbed more NO₃^-at500μm, and reduced it with increasing degree ofeutrophication, but increased with increasing intensity of acid rain. After pH3.5acid raintreatment with hyper eutrophication level, the root of A. gramineus could absorb NH₄⁺at both500μm and10000μm. The absorption of NH₄⁺by S. chinensis could be reduced with increasingeutrophication level,and increased with increasing distance from the tip of its root.(6) Eutrophication and acid rain combined stress has significant interaction and differentaction ways on the fluxes of NH₄⁺and NO₃^-by O. javanica, A.gramineus and S. chinensis. (7) A.gramineus could be planted in waterbodies with acid rain pollution. S. chinensis couldbe planted in lake wetlands with serious acid rain and eutrophication pollution. O. javanica couldbe planted more suitably in lightly polluted wetlands.