Studies On The Genetic Diversity Of Duckweed In The Middle Reaches Of The Yangtze River And Preliminary Utilization Of Resource

Duckweed is the general name of the duckweed family.It is the smallest aquatic angiosperm in the world and dominated by floating.There are a total of 37 species in 5 genera:Lemna,Spirodela,Landoltia,Wolffia,Wolfiella.Duckweed is widely distributed.Except for extremely cold regions(Antactic and Arctic),it is distributed all over the world,especially in subtropical and tropical regions.Duckweed's growth rate is very fast.10 species in 4 genera have been found in China so far.Duckweed can absorb nitrogen,phosphorus and heavy metal ions in wastewater during the growth process,thus can purify and improve water quality and perform wastewater treatment.It can also convert nitrogen and phosphorus pollutants into easy-to-harvest,high-quality safe and high-protein,high-starch resources.It can also be used as feedstock for fermentation of ethanol,so as to truly achieve the goal of high efficiency,economy and resource utilization.In this study,duckweed in the middle reaches of the Yangtze River is selected as experimental material.The main results are as follows:1.A total of 112 duckweed germplasms were collected from 42 natural water bodies in Hubei,Hunan,and Jiangxi provinces in the middle reaches of the Yangtze River.According to the observation of the shape of the fronds and roots,54 germplasms were classified in Lemna,34 germplasms were classified in Spirodela,18 germplasms were classified in Landoltia and 6 in Wolfia.AtpF-AtpH spacer sequence and rpS16 intron sequences of 112 duckweed germplasms were amplified by PCR method.Phylogenetic tree was constructed and analyzed.The results showed that 112 duckweed germplasms belonged to 6 species:Lemna aequinoctialis?Lemna minor?Lemna perpusilla?Spirodela polyrhiza?Landoltia punctata?Wolffia globosa.2.Analysis using DnaSP5.10 showed that the genetic diversity of 112 duckweed germplasms in the middle reaches of the Yangtze River was relatively rich.The number of haplotypes of the chloroplast AtpF-AtpH interval sequence and the rpS16 intron sequence were 11 and 18,respectively.The haplotype diversity was 0.748 and 0.892,the population mutation rates were 0.03439 and 0.03507,the average number of nucleotide differences per Kb was 31.386 and 61.263,the nucleotide diversity was 0.04713 and 0.06623.The rpS16 intron sequence was better than AtpF-AtpH spacer sequences having higher genetic diversity.3.Duckweed germplasms(except Wolffia)in the middle reaches of the Yangtze River were cultivated in the terminal wastewater from a rubber processing factory to see their performance in wastewater treatment.Results indicated that Spirodela polyrhiza species has the highest tolerance in wastewater,and Lemna minor has the second highest tolerance,however,some germplasms has tolerance higher than Spirodela polyrhiza(such as HB0204).Lemna aequinoctialis has the lowest tolerance,while Landoltia has an intermediate tolerance in wastewater.4.Twelve duckweed accessions with good tolerance in the rubber wastewater were chosen to stuy their phosphorus removal capacity.Within 6 days,the phosphorus removal rate could reach 23%?50%depending on accessions.Among them,HB0204 has the highest removal rate and the highest weight gain.5.The growth rate of duckweed in rubber wastewater and culture medium was compared,all strains grew significantly faster in N medium than in wastewater.The Mass of Lemna aequinoctialis increased by 6.56 times in N medium,which is the fastest growth rate in the tested duckweed strains,but it grew only by 1.82 times in the wastewater at the same time period,which was the slowest growth rate in wastewater among the tested duckweed strains.Landoltia grew by 3.54 times in N medium and by 1.73 times in wastewater,W/N is 0.488,which is larger than Lemna aequinoctialis.Spirodela polyrhiza and Lemna minor have a small difference between the growth multiples in the wastewater and in the medium,W/N are 0.62 and 0.65,respectively.Considering the effect of the error,the tolerance of these two species in the rubber wastewater was comparable.The contents of P,Na,and Mg in the wastewater were higher than those in the N medium,and the contents of K,Ca,N,and SO4 were lower than those in the N medium,the content of ferrum is 0,suggesting that lacking ferrum ion may be the factor reducing duckweed growth in the wastewater.6.Different concentration of Fe2+ was added to the rubber wastewater to study the effect of Fe2+ on phophorus removal.The result was positive,the progeny fronds were greener in Fe2+supplemented wastewater,and the absorption efficiency of P was improved.7.Different proportions of dried duckweed powder was added to cassava flour to study its effect on alcohol fermentation.Results indicated that adding 5%to 15%dried duckweed powder in cassava flour increased ethanol yield,and 12.5%dried duckweed powder was the best supplementation ratio,which increased ethanol yield the highest.When the amount of dry duckweed powder reached 20%,the ethanol yield decreased.