| Aquaponics is a modern ecological farming technology that combines aquaculture and hydroponic plant culture to reform and innovate the traditional agricultural model.The principle of application is to achieve a green cycle by recycling the aquaculture wastewater from the aquaculture unit and transforming it into nutrients for plant growth into the hydroponic unit through the decomposition of microorganisms in the system.This experiment investigated the effect of two different hydroponic plants,Ipomoea aquatica and Oenanthe javanica,in water purification and applied to a coupled aquaponics system(CAS),and analyzed the differences between the two hydroponic plants in the aquaponics system by comparing the water purification results and microbial composition.The main results of the study are as follows.1.In the 30-d hydroponic experiment,the single Ipomoea aquatica group was more efficient than the Oenanthe javanica in removing nitrogenous nutrients from the system in the early stage.However,the removal efficiency of nitrogenous nutrients in the Oenanthe javanica group gradually increased in the later stage as the plant growth gradually stabilized.At the end of the experiment,the removal rate of ammonia nitrogen in the Oenanthe javanica group reached 80.59%,nitrite nitrogen 99.73% and nitrate nitrogen 73.44%,which was significantly better than that of the Ipomoea aquatica group(P < 0.05).62.39%.The Ipomoea aquatica group removed 54.88% of ammonia nitrogen,95.18% of nitrite nitrogen and 62.39% of nitrate.The removal efficiency of the mixed group was between that of the single Oenanthe javanica group and that of the single Ipomoea aquatica group.For the removal of phosphorus-containing nutrients,the initial concentration was 10 mg/L.At the end of the experiment,the soluble phosphorus content was 3.67 mg/L in the Ipomoea aquatica group,4.72 mg/L in the Oenanthe javanica group,and 4.29 mg/L in the mixed group.The removal of phosphorus salts in the Ipomoea aquatica group was significantly higher than that in the Oenanthe javanica and mixed groups(P < 0.05).After 16 S r RNA sequencing of plant root samples,it was found that the top ten dominant microbial species in the samples at the genus level were Flavobacterium,Hydrogenophaga,Acidovorax,Cellvibrio,Phreatobacter,Chloroplast,Rhizobacter,Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium,Noviherbaspirillum and Rhodoferax.The percentage of Flavobacterium in Oenanthe javanica roots was significantly different from that of Ipomoea aquatica roots(P < 0.05).The dominant species in the Ipomoea aquatica root microorganism was Hydrogenophaga with12.86%,and the most dominant species in both the mixed and Oenanthe javanica groups was Flavobacterium,with the highest percentage of 17.55% in the single Oenanthe javanica.In terms of species abundance,the mixed group was significantly higher than the single group(P < 0.05).The species abundance of the mixed group was significantly up-regulated by Alpha diversity analysis in a locally homogeneous habitat,and its coverage and diversity increased.2.In the 30 d primary CAS experiment,the relative dissolved oxygen fluctuation level of the Ipomoea aquatica group in the system was relatively stable,and there was no significant difference in p H value.The daily temperature change in the blank group showed the greatest change.In terms of water quality physicochemical indexes,the overall nitrogenous nutrient concentration changes basically showed a trend of first increasing and then gradually decreasing,with the experimental group content significantly lower than the blank group.At the end of the experiment,the total nitrogen content was maintained at 6.54 mg/L in the Ipomoea aquatica group,5.16 mg/L in the Oenanthe javanica group,and 7.47 mg/L in the blank group.The changes of phosphorus nutrient parameters in the system during the experiment were that the content gradually increased during the experiment to reach the highest concentration,with the blank group having a higher relative content.At the end of the experiment,the highest level of total phosphorus was 4.37 mg/L in the Ipomoea aquatica group,3.64mg/L in the Oenanthe javanica group,and 6.08 mg/L in the blank group.The removal rate of total nitrogen in the experimental groups ranged from 1.34% to 38.70%,and the removal rate of total nitrogen in the Oenanthe javanica group was slightly higher than that in the Ipomoea aquatica group,while the blank group had no removal effect.The removal of ammonia nitrogen and nitrite nitrogen ranged from 5% to 50%,with nitrite nitrogen being better than ammonia nitrogen,and the best removal of nitrite nitrogen was 59.62% in the Oenanthe javanica group and 35.06% in the blank group.For the removal of phosphorus-containing nutrients,a maximum of 37.58% could be achieved,and the Ipomoea aquatica group had a better and more stable removal of soluble phosphorus than the Oenanthe javanica group.The growth condition and feeding condition of crucian carp in the system were good.The Oenanthe javanica group gained weight at a significantly higher rate than the Ipomoea aquatica group and the blank group(P < 0.05),increased body weight by 56.29%,and the specific growth rate and fattening degree were better than the blank group and the Ipomoea aquatica group.In 16 S r RNA sequencing of plant root samples and water column samples,the top ten dominant microbial species in the samples at the genus level were Polynucleobacter,Cetobacterium,Phreatobacter,Hydrogenophaga,Mycobacterium,Limnohabitans,Flavobacterium,Saccharimonadales,Novosphingobium and Gemmobacter.The most dominant strain in the water column of the blank group was Cetobacterium accounting for 21.47%.Polynucleobacter was the dominant species in both water bodies of Oenanthe javanica group and Ipomoea aquatica group.The dominant strain of microorganisms in Oenanthe javanica roots was Hydrogenophaga accounting for7.66%.The dominant strain in Ipomoea aquatica roots was Phreatobacter accounting for 13.90%.The species abundance in the experimental group was higher than that in the blank group,and the number of species in the root system microorganisms was higher than that in the water column.The difference in species diversity of plant roots in the Ipomoea aquatica and Oenanthe javanica groups was not significantly different by Alpha diversity analysis in a locally homogeneous habitat.Microbial diversity in the water column was significantly different in the Oenanthe javanica group from the Ipomoea aquatica group and the blank group,and species abundance and evenness in the water column of the Oenanthe javanica group were significantly higher(P < 0.05).This experiment showed that adding plants in this CAS system achieved the requirements and effects for water purification.The efficiency of Oenanthe javanica in removing nitrogen and phosphorus from water bodies at the same density was better than that of Ipomoea aquatica.The growth performance of carp in the Oenanthe javanica group was better than that of Ipomoea aquatica group.The net yield of Ipomoea aquatica was higher than that of Oenanthe javanica in the plant output.The abundance of root microorganisms in the Oenanthe javanica group was higher than that in the Ipomoea aquatica group,and the mixed planting of multiple plants was beneficial to enhance the abundance of root microorganisms and species diversity. |
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