| Procambarus clarkii is the most cultivated freshwater crayfish in the world.China is the world's largest producer of Procambarus clarkii.At present,the Rice-crayfish culture field is developing rapidly in China,with a total planting and breeding area of more than 10 million mu.However,the relevant theoretical research lags behind,and the changes in the structure and function of rice paddy ecosystem after the superposition and coupling of rice planting and aquaculture are still unknown.In order to explore the impact of Procambarus clarkii farming on rice field ecosystems,with a view to further improving the technology and theoretical system of integrated rice field cultivation models,this study used traditional monoculture rice fields as a control,and selected different areas of the Rice-crayfish culture field and investigation In this paper,the rice farming system of Rice-crayfish culture was investigated from the aspects of water quality,soil quality,phytoplankton,zooplankton,soil microorganisms and primary productivity.The main research results are as follows:1.From march to June,2018,the water-physicochemical factors of IRCC and TRF in 24blocks of nearly 200 mu at four survey stations in Jianghan Plain were sampled and investigated,once every half a month,and 15 physicochemical indicators of IRCC and TRF water were monitored.The results showed that:?1?During the breeding period of Procambarus clarkii,the WT,pH,Turb.,SD,DO,ORP and Cond.in IRCC were 7.24?29.02?,7.56?8.28,7.55?41.69 NTU,0.21?0.55 m,4.26?9.71 mg/L,151.62?247.82 mV and 294.44?433.43?S/cm,respectively.And the WT,pH,Turb,DO,ORP and Cond in TRF were8.73?29.89?,7.90?9.17,2.54?13.40 NTU,7.46?13.22 mg/L,131.65?240.53 mV and 189.95?293.60?S/cm,respectively.With the change of culture time,the WT and Turb of IRCC and TRF gradually increased,and the SD,ORP and Cond showed a downward trend.And the DO content first decreased and then increased.?2?The content variation range of TN,TP,NO3--Nand PO43--P in IRCC were 1.64?3.36 mg/L,0.16?0.32 mg/L,0.08?0.27 mg/L and 0.04?0.13 mg/L,respectively.And the contents of TN,TP,NO3--N and PO43--P in TRF were 1.31?2.27 mg/L,0.07?0.20 mg/L,0.04?0.19 mg/L and 0.02?0.05 mg/L;CODMnn and Chl.a content In IRCC were7.20?16.76 mg/L and 4.89?37.78?g/L,and in TRF were 5.19?6.01 mg/L and 1.03?15.87?g/L,respectively.The contents of NH4+-N?NO2--N and Chl.a in the two types of water gradually increased with time.Compared with TRF,IRCC increased the Trub,Cond,TN,TP,PO43--P,Chl.a and CODMn,and reduced WT,pH and DO.Procambarus clarkii farming increased the nutrient salt content and the nutrient load of water.2.The species composition,density and biomass of plankton in IRCC and TRF paddy fields were investigated,and the primary productivity of the two types of water bodies was measured once a month.The results show that:?1?There were 124 species phytoplankton belongingto 7phylum observed,among which 141 species were from 7 phylum in IRCC,including 15 species of Cyanophyta,85 species of Chlorophyta,23 species of Bacillariophyta,5 species of Pyrrophyta,7 species of Euglenophyta,2 species of Cryptophyta and 4 species of Chrysophyta.The dominant species were mostly Cyanophyta.In TRF,there were 103 species belongingto 7phylum,11 species Cyanophyta,63 species of Chlorophyta,17 species of Bacillariophyta,3species of Pyrrophyta,6 species of Euglenophyta,2 species of Cryptophyta and 1species of Chrysophyta,and the dominant species were mostly Chlorophyta.There were 98 species in total,and the species composition was similar.The variation range of IRCC phytoplankton cell density was 3.79×106?1.73×108 cells/L,TRF was 3.25×105?4.66×107 cells/L,and the Chl.a content of both was 1.03?37.78?g/L.The cell density and algal biomass of IRCC were significantly higher than TRF,and the cell density of both showed an upward trend with time.The mean values of phytoplankton community diversity index?H'?were 2.052 and 1.700,respectively,and the diversity evaluation level was both level III,which is a good level.?2?A total of 54 species of large zooplankton were identified,including 48 species in IRCC,28 species of Cladocera and 20species of Copepod,most of which were Cladocera;39 species of TRF,25 species of Cladocera and 14 species of Copepod,the dominant species are mostly Copepod.There were 33species in total,and the similarity of species composition was high.The population density and biomass of IRCC are significantly higher than that of TRF,and both of them increase with time.The mean values of zooplankton community diversity index?H'?of the two were 1.181 and1.132,respectively,and the diversity evaluation level was level II,which was a general level.?3?The total production,net production and respiration of IRCC are significantly higher than that of TRF,and the primary productivity of them gradually increases with time.The maximum primary productivity of the two types is June,which is 15.49 mg O2/?L·d?and 4.36 mg O2/?L·d?,the smallest in March,1.97 mg O2/?L·d?and 0.49 mg O2/?L·d?.Compared with the rice monoculture model,the integrated culture model of rice shrimp and shrimp cultured in Procambarus clarkii increased the species composition of plankton in the paddy field,making the population density and biomass of algae cells and zooplankton significantly higher than that in the rice monoculture paddy field It has become the dominant species in cultivated rice fields,and farming has also significantly improved the primary productivity of phytoplankton in rice fields.Compared with TRF,IRCC increases the species composition of phytoplankton in rice fields,the population density and biomass increase significantly.Meanwhile,IRCC has also significantly improved the primary productivity of phytoplankton in the rice field.3.Collected the soil in the TRF and IRCC of 2 years,4 years,6 years and 10 years in Honghu City and Qianjiang City,and measured the 11 physical and chemical indicators and the number of microorganisms of soil in TRC,PRC of IRCC and TRF,and tested Functional diversity of soil microbial communities.The results show that:?1?The pH,Cond and water content of the soil were between 6.54 to 7.78,1.82 to 2.16 ms/cm,and 0.30 to 0.55.The contents of TC,TN,NO3--N,NH4+-N,NO2--N and AP all show TRC>PRC>TRF,and the contents of TC,TN,TP,TOC,NH4+-N and NO2--N increased with the increase of years of cultivation,and the contents of NO3--N and AP increased first and then decreased with the increase of years of cultivation.?2?With the increase of planting and breeding years,there was no significant difference in soil microbial biomass,but the microbial diversity index decreased gradually.The utilization of carbon sources by microorganisms increased first and then decreased,PRC>TRC;in PRC,2 years>TRF>4 years>6 years>10 years,in TRC,4 years>2 years>6years>10 years.Procambarus clarkii farming increased the soil nutrient load of the paddy field,caused the soil to accumulate more nutrients such as carbon,nitrogen and phosphorus.With the increase of breeding years,the comprehensive index of soil nutrients gradually increased from medium nutrition to high nutrient levels;the utilization of soil microorganisms for carbon source increased first and then decreased,the diversity index gradually decreased,and the carbon metabolism capacity gradually weakened.4.In order to investigate the impact of residual bait on the paddy field ecosystem,different feeds were used to carry out the soaking test to determine the nutrient release and its impact on water quality.The result shows:After the feed was soaked for 96 hours,the contents of NO3--N,PO43--P,NH4+-N and NO2--N in the water all increased to a higher level,which had a significant negative impact on water quality,resulting in an increase in the nutritional load of the water and a tendency for the water to deteriorate.So as to reduce the negative effect of residual bait on water quality,Chlorella sorokiniana was inoculated into each experimental group after the feed immersion test.After 8 days of culture,NO3--N in the two treatment groups of distilled water and culture raw water Removal rates were 77%and 83%,PO43--P were 62%and 56%,NH4+-N were 92%and 89%;Chlorella OD680nm increased by 0.446 and 0.654,biomass increased by 2.126 g/L and 3.115 g/L.The results showed that the nutrient release of feed immersion could rapidly increase the content of nitrogen and phosphorus,and Chlorella had a better absorption and purification effect on the nutrient enrichment in water.The results of this study confirmed the specific impact of the culture of Procambarus clarkii on the paddy field ecosystem.To a certain extent,the cultivation increased the nutrient content of the paddy field water and increased the fertility of the paddy soil,but it also increased the nutrient load of the water and soil.Increased the species composition,population density and biomass of phytoplankton,and also increased the primary productivity in the rice field.However,the carbon utilization capacity of soil microorganisms increased first and then decreased with the increase of culture time,and the diversity index gradually decreased and the carbon metabolism capacity gradually weakened.The impact of Procambarus clarkii farming on the rice field ecosystem are mixed,and the results of this study can provide data support for objective understanding and evaluation of IRCC. |
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