| Duckweed is a monocotyledonous floating aquatic.It is widely distributed in rivers,lakes and paddy fields with five genera all over the world.It has strong adaptability,fast reproduction rate and high economic value.It can not only be used as medicine,but also as water cleaner and feed ingredient.The protein and starch content of duckweed can be compared with soybean,while the yield of it is far higher than that of soybean.And the proportion of amino acids in duckweed is also excellent.At present,duckweed has been considered as one of the most potential strategic new non-grain biomass raw materials.More and more attention has been paid to the research on its fermentation to produce ethanol and biogas.Compared with other biological resources,the research and development of duckweed as biomass energy is still in the exploratory stage in the world.Starting from the morphology and geographical distribution of duckweed,the genetic diversity,nutritional value,feeding value and biomass energy utilization value of duckweed were studied in this experiment.A total of 46 accessions of duckweed germplasm resources were collected in Yunnan Province.Through morphological classification and molecular biological identification based on chloroplast rpS16 intron sequences and atpF-atpH spacer sequences,these germplasms are divided into 4 genera and 5 species,namely Spirodela polyrhiza,Landoltia punctata,Lemna perpusilla,Lemna quinoctialis and Wolffia globosa.Among the 5 species,Lemna perpusila is a newly recorded species in southern China.The results of genetic diversity analysis showed that the nucleotide diversity indices of atpF-atpH and rpS16 in chloroplast genome of Yunnan Province were 0.04926 and 0.06298 respectively.The average number of nucleotide differences was 30.914 and 79.963 per Kb,and the haplotype diversity index was 0.862 and 0.893.The selection of fine variety showed that DW2602 is the duckweed strain with the highest protein content,lysine content and sulfur-containing amino acid content.It's protein content up to 44.52%DW and amino acid content is 16.23%DW,second only to the highest 16.61%DW,which can be used as a new plant protein resource.In addition,HL1403 and HB0401 are also rich in 40%of protein,which can be used as high protein or high amino acid plants.When using duckweed as feed protein resource,the weight gain rate of tilapia was higher than that of common feed.When the duckweed content was 20%and the feeding amount was 3%of the fish body weight,the tilapia weight gain rate reached 295.92±1.76%,which is 57.5%more than using common feed,and the specific growth rate reached 3.44±0.01%per day at the end of the experiment.The protein content of duckweed feed mixed with this ratio increased 4.3%,while the fat content decreased 0.9%.The crude fiber content of duckweed feed increased but still within the national standard.The lysine content remained unchanged though the total amount of sulfur-containing amino acids,methionine and cystine,increased 0.1%.Study on the economic value of duckweed being biomass energy producting methane showed that the biogas production peak of anaerobic digestion with duckweed as raw material under the constant temperature condition of 35? was 10-20 days in the middle stage of the experiment.The results showed that duckweed is an ideal raw material for anaerobic digestion with the optimal material ratio of 1:2.5.The cumulative gas production could reach 3350±51.59 ml(113g raw material)with the maximum anaerobic digestion potential up to 194.64±3.00 ml/g·TS and the methane content up to 51.93%,which already achieved burning conditions.In a word,duckweed is a promising plant resource,which deserves further research and development.It is of great significance to study the genetic diversity and comprehensive utilization of duckweed. |
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