| In this paper,the purification ability of two halophytes Sesuvium portulacastrum and Mesembryanthemum crystallinum and their biological responses were studied under different salinity and nitrogen and phosphorus concentrations.Through indoor hydroponic experiments,the difference in nitrogen and phosphorus absorption capacity of S.portulacastrum and M.crystallinum under salt stress and their own salt tolerance mechanism in response to salt stress were studied.The physiological responses to salt stress were analyzed in terms of the contents of N,P,Na and K ions in plants,the activities of antioxidant protective enzymes and osmotic regulation,and the transcriptome sequence of S.portulacastrum under the three groups of salinity was performed using high-throughput sequencing technology.Through GO and KEGG enrichment analysis,the differential genes and metabolic pathways related to salt tolerance were found.By simulating aquaculture wastewater with different nitrogen and phosphorus concentrations,the difference in nitrogen and phosphorus removal rates and growth physiological changes of S.portulacastrum and M.crystallinum when they continue to grow in eutrophic water were explored.Not only indoor experiments were carried out,but also three-dimensional cultivation experiments of Apostichopus japonicas-Argopecten irradians-S.portulacastrum/M.crystallinum were arranged in outdoor ponds,aiming to explore a new mode of integrated multi-trophic plantation and aquaculture in seawater pond.So as to provide theoretical basis and technical support for further restoration of mariculture areas and to promote the development of seawater agriculture by maximizing the purification ability in seawater environment with appropriate salinity.The main research results are as follows:1.Purification capacity and growth physiological response of S.portulacastrum and M.crystallinum under different salinity(1)There was no significant difference of fresh weight in S.portulacastrum.In M.crystallinum groups,the 30 salinity group had the lowest fresh weight.(2)The Na~+content and Na~+/K~+value of S.portulacastrum increased with the increase of salinity,K~+content in roots increased,while K~+content in stems and leaves decreased.Na~+content of M.crystallinum increased while K~+content decreased.(3)With the increase of salinity,the nitrogen content in the root of S.portulacastrum increased gradually,while the nitrogen content in the stem decreased,and the nitrogen content in the stem and leaf was higher than that in the root;the contents of nitrogen and phosphorus in M.crystallinum decreased gradually.(4)The S.portulacastrum of salinity 0 group had the best nitrogen and phosphorus absorption effect,and the final absorption rate of the high salinity group was significantly lower than that of the low salinity group.M.crystallinum of salinity 10group had the best absorption effect on ammonia nitrogen and nitrate nitrogen,the salinity 0 group had the best absorption effect on phosphorus,and the final absorption rate of the high salinity group was significantly lower than the low salinity group.(5)The activities of POD,CAT and SOD,the content of MDA increased with the increase of salinity.The contents of soluble sugar and Pro did not increase with the increase of salinity.2.The water purification capacity and growth physiological response of S.portulacastrum and M.crystallinum under different nitrogen and phosphorus concentrations.(1)There was no significant difference in RGY and water content among all groups of S.portulacastrum.RGY reached the maximum when N was 5 mg/L,P was 0.5 mg/L,N was 0 mg/L,and P was 0.5 mg/L.In M.crystallinum,RGY in low N/P concentration group was significantly higher than that in high N/P group,and there was no significant difference in water content among all groups.(2)There was no significant difference in the content of Na~+among all groups,and the content of K~+in the low-concentration group was significantly lower than that in the high-concentration group.The content of Na~+in the seawater with N 50 mg/L and P 5mg/L was significantly lower than that in the other groups;The K~+content of M.crystallinum decreased significantly with the increase of N and P concentration.(3)With the increase of N and P concentration,the contents of N and P in S.portulacastrum tended to increase.In M.crystallinum,the N content increased,and the P content increased firstly and then decreased.(4)The absorptivity of S.portulacastrum in seawater with nitrogen concentration of 1and 5 mg/L was generally higher than that in seawater with nitrogen concentration of20 and 50 mg/L.In M.crystallinum,during 0-6d,there was little difference in the absorption rate of ammonia nitrogen among all groups;during 6-15d,the absorption rate of low-N/P concentration group was higher than that in the high-N/P group.The absorption rate of nitrate in M.crystallinum was the best when the concentration of nitrate was 0.5 mg/L.In the experimental stage,in M.crystallinum,the absorption rate of phosphate in different concentration groups fluctuated,and there was no obvious regulations.(5)With the increase of N and P concentration,the activities of POD and SOD in S.portulacastrum decreased at first and then increased,while the activity of CAT increased,and the content of MDA fluctuated.The activities of POD,CAT and SOD showed different changing trends with the increase of N and P concentration,while the content of MDA showed an increasing trend.The soluble sugar content in the leaves of S.portulacastrum increased firstly and then decreased with the increase of N and P concentration,and proline was not sensitive to the change of nitrogen and phosphorus concentration.The content of soluble sugar in the leaves of M.crystallinum fluctuated with the increase of N and P concentration,and the content of proline increased firstly and then decreased.(6)With the increase of N and P concentration,the net photosynthetic rate and electron transport rate of S.portulacastrum fluctuated.The net photosynthetic rate and electron transport rate showed a trend of increasing firstly and then decreasing.3.Transcriptome analysis of S.portulacastrum under different salinities 26,717 Unigenes with annotated information were obtained by transcriptome sequencing of the S.portulacastrum samples.92 differential genes were obtained from0 vs 10 groups,and 2146 DEGs were obtained from 0 vs 35 groups.Under low salt stress,S.portulacastrum did not produce related stress-resistance responses to salt stress.However,under high salt stress,S.portulacastrum enhanced a large number of genes in response to salt stress.GO enrichment analysis showed that differentially expressed genes mainly covered"metabolic process","cellular process","organic metabolic process","tissue process"and other functional subcategories,and that phenylpropanol biosynthesis pathway played an important role in response to salt stress in S.portulacastrum.4.Analysis of water quality and growth of integrated multi-trophic plantation and aquaculture(IMTPA)(1)The concentration of ammonia nitrogen,nitrite nitrogen and total phosphorus in Wudi scallop pond was the highest;The concentrations of ammonia nitrogen and nitrite nitrogen were the lowest in S.portulacastrum pond,and the concentrations of total phosphorus were the lowest in the integrated pond.The height,wet weight and dry weight of S.portulacastrum in Binzhou increased significantly.(2)The concentrations of ammonia nitrogen and nitrite nitrogen in the integrated pond in Dongying decreased significantly,while the concentration of total phosphorus showed an increasing trend during the experiment,and only decreased at the 7th day.The length,width,mass and wet weight of scallop were significantly increased in the integrated pond in Dongying.The wet and dry weight of S.portulacastrum in Dongying increased significantly,while the height and water content decreased. |
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