Combined Effects Of Ammonia-nitrogen And Environmental Factors On Submerged Plant Vallisneria Natans

With the rapid development of economy in China,the problem of water pollution is increasingly serious.The input of large amount of watsewater into freshwater environment can lead to the eutrophication of water body,the decrease of biodiversity,and the degradation of water ecosystem function.It badly affects on the environmentol safety and people's health,and seriously hinders the development of economy and society.Using aquatic plants,especially submerged macrophytes,to restorate water ecosystem has been paid more and more attentions,due to the advantages of low cost,easy operation,and beautifying landscape.However,submerged plants are easily affected by various environmental factors.Thus,finding the suitable conditions of recover submerged plants is the key for a successful recovery of the submerged vegetation.Given ammonia nitrogen is the main toxic pollutant of polluted river,many studies focus on the effects of high water column ammonia-N concentrations on aquatic plants.The toxicity of ammonia-N on aquatic plants would also be significantly affected by other environmental factors(such as nutrient factors-sediment nutrient,physical factors-light intensity,chemical factors-chemical oxygen demand(COD)and stress factors-sediment copper).However,the combined effects of these environmental factors and ammonia-N on the aquatic plants were often overlooked.In this study,submerged macrophytes Vallisneria natans were selected as a model plant to discuss the combined effects of ammonia-N and various environmental factors(sediment nutrient,light intensity,COD,and sediment copper(Cu))on submerged plants.Their combined effects were elucidated by a series of growth indexes and physiological indexes.The results indicated that:(1)The combined experiment of ammonia-N and nutrient factor(sediment nutrient)indicated that:When ammonia-N contents of the water column were 0-4 mg L-1,the total biomass of V.natans increased with the increase of exposed time,biomass of roots,leaf,and flower were higher,total chlorophyll(including chlorophyll-a and chlorophyll-b),malondialdehyde(MDA)and free proline contents in leaves increased with the increase of water ammonia-N concentrations;when ammonia-N contents of the water column were 8-16 mg L-1,the total biomass of V.natans decreased with the increase of exposed time,biomass of roots,leaf,flower decreased significantly,total chlorophyll,MDA and free proline contents in leaves decreased with the increase of water ammonia-N concentrations.In addition,the total biomass,the biomass of roots,leaf and flower,the total chlorophyll concentration of plants in high nutrient sediments(0.11%TN)were higher than those in the low nutrient sediments(0.04%TN).The plants that grew in the high level of nutrients produced comparatively more leaf and flower fractions,whereas those that grew in the low-nutrient sediment produced more root fractions.Furthermore,with the increasing of ammonia-N concentration,the biomass,total chlorophyll concentration,MDA contents and free proline contents of V.natans in different nutrient sediments had the similar change trend,indicating that high nutrient sediments could not elevate the threshold value of ammonia-N.(2)The combined experiment of ammonia-N and physical factor(light intensity)indicated that:relative growth rate(RGR,p<0.001),chlorophyll contents(p<0.01),activity of superoxide dismutase(SOD,p<0.001)and peroxidase(POD,p<0.001)were significantly affected by ammonia-N.With the increase of ammonia-N concentrations,RGR of V.natans significantly declined,activity of SOD and POD significantly increased.In low ammonia-N contents(0 and 3 mg L-1)water column,RGR of V.natans was positive value,and chlorophyll contents increased;in high ammonia-N contents(6 mg L-1)water column,RGR was negative value,and chlorophyll contents decreased.In addition,RGR(p<0.001),chlorophyll contents(p<0.05),activity of SOD(p<0.001)and POD(p<0.001)were significantly affected by light intensity.With the decreasing of underwater light intensity(100%-0.75%control underwater light intensity),RGR of V.natans decreased,but all of them were positive value,chlorophyll contents,and activity of SOD and POD significantly increased.Furthermore,the combined effects of ammonia-N and light intensity was also significantly(p<0.05).RGR and chlorophyll contents were lowest and activity of SOD and POD was highest in the combined treatment of high ammonia-N(6mg L-1)and low light(0.75%control underwater light intensity).In addition,RGR of V.natans was negetive value in the combined treatment of medium level of ammonia-N(3mg L-1)and low light(0.75%control underwater light intensity).(3)The combined experiment of water ammonia-N and chemical factor(COD)indicated that:the effects of ammonia-N on RGR,chlorophyll contents,activity of SOD and POD were consistent with the results of the experiment(2)-the combined experiment of ammonia-N and light intensity.In addition,RGR(p<0.001),chlorophyll contents(p<0.001),activity of SOD(p<0.001)and POD(p<0.01)was significantly affected by COD.With the increasing of COD(0-160 mg L-1),RGR of V.natans decrease,and activity of SOD and POD significantly increased.In the medium-low COD treatment(0-80 mg L-1),RGR was positive value,and chlorophyll contents increased;in the high COD treatment(160 mg L-1),RGR was negetive value,and chlorophyll contents decreased.Furthermore,the combined effects of ammonia-N and COD were also significantly(p<0.05).RGR and chlorophyll contents were lowest,activity of SOD and POD was highest in the combined treatment of high ammonia-N(6 mg L-1)and COD(160 mg L-1).In addition,RGR of V.natans was negetive value in the combined treatment of medium level of ammonia-N(3mg L-1)and high COD level(160 mg L-1).(4)The combined experiment of water ammonia-N and stress factor(sediment copper)indicated that:the effects of ammonia-N on RGR,above-biomass,total chlorophyll,non protein thiol(NP-SH)and free proline contents were significantly(p<0.001).With the increase of ammonia-N concentrations,RGR and above-biomass of V.natans significantly declined,and the concentrations of NP-SH and free proline significantly increased.In low ammonia-N contents(0 and 3 mg L-1)water column,RGR of V.natans was positive value,and total chlorophyll contents increased;in high ammonia-N contents(6 mg L-1)water column,RGR was negative value,and total chlorophyll contents decreased.In addition,the effects of sediment Cu on RGR,below-biomass,total chlorophyll and NP-SH contents were significantly(p<0.001).With the increasing of sediment copper(0-225.75 mg kg-1),RGR of V.natans decreased,but all of them were positive values;below-biomass and total chlorophyll contents significantly declined,NP-SH contents significantly increased.Furthermore,the combined effects of ammonia-N and sediment Cu was not significant(p>0.05).RGR and chlorophyll contents were lowest,the contents of NP-SH and free proline was highest in the combined treatment of high ammonia-N(6 mg L-1)and sediment Cu.In addition,RGR of V.natans was negetive value in the combined treatment of medium level of ammonia-N(3mg L-1)and medium-high sediments Cu level(?125.75 mg kg-1).According to above mentioned,it is concluded that the tolerable growth conditions of submerged plant V.natans for single factor as follows:water ammonia-N concentration<6 mg L-1,COD concentration<160 mg L-1,nutrient sediments ?0.11%TN,sediment Cu concentration?225.75 mg kg-1,and light conditions?0.75%underwater light intensity.In addition,the different levels of sediments nutrients can not change the ammonia-N tolerance of V.natans.Each of the following environmental factors such as low level of underwater light intensity(0.75%control underwater light intensity),high levels of COD(160 mg L-1)and sediment Cu(?125.75 mg kg-1)can lead to ammonia-N tolerance value of V.natans significantly reduced.Furthermore,using V.natans for water ecological restoration,the water condition should at least meet the ammonia-N content of<6 mg L-1,and the water condition should meet the ammonia-N content of<3 mg L-1,when light intensity ?0.75%underwater light intensity,or COD?160mg L-1,or sediemnt Cu 125.75 mg kg-1.