Effects Of Differnet Straw Returning Treatnments On Macrobenthos In Rice And Shrimp Fields

During rice-shrimp continuous cropping,strawing as a natural organic fertilizer can be returned to the field to reduce the use of chemical fertilizers,thereby reducing the impact on the ecological environment,and at the same time,it can improve the economic benefits of rice and shrimp breeding models.Macrobenthos,as an important part of the rice and shrimp farming ecosystem,participates in the species cycle and energy flow of the rice and shrimp ecosystem through biological disturbance.The dynamic changes of its community structure are affected to a certain extent by the ecological environment of rice and shrimp fields.Using straw to increase soil fertility and promote the growth of large benthic animals can provide natural animal food for crayfish to a certain extent.In this paper,the effects of biological disturbance of crayfish on the community structure and diversity of macrobenthos under different treatments of straw returning to the field were set to set the best straw returning treatment.At the same time,indoor simulation experiments were used to explore the effects of different temperatures on the intensity of crayfish biological disturbances.The results are as follows:1 Effects of different straw C/N treatments on community structure and diversity of macrobenthosDuring the continuous cropping of rice and shrimp,the straw return technology was used to promote the growth of large benthic animals in the rice and shrimp fields to provide natural animal food for crayfish.The optimal C/N is set by changing the community structure of macrobenthos.The C/N of different straws were(0,15/1,25/1,35/1).They are labeled as ck,S1,S2,and S3,and the experimental period is from January 2017 to May 2018.The experimental results found that:1)The total density and biomass of large benthic animals in the treatment group increased significantly,and the density and biomass of the S1 treatment group were significantly higher than those in S2 and S3 after the field was returned(P<0.05).2)The relative importance index is calculated,and the main dominant species of C.fusiformis,C.thursii and S.chinensis are the dominant species.3)Pearson correlation analysis found that soil organic matter,NH4+-N,temperature,and water TP were the main environmental factors affecting the density of dominant species.Studies have shown that S1(15/1)is the most suitable straw treatment group.2 Effects of different straw-returning on macrobenthic community structure and species diversity in rice-shrimp fields during winter and springSediment samples were collected from four Rice-shrimp fields of varying straw-returning.0(ck)?1500 kg/hm~2(S1)?3500 kg/hm~2(S2)and 4500kg/hm~2(S3)straw-returning.From January 24,2019 to July 18,2019,Macrobenthic community structure were analyzed to investigate the reasonable straw-returning in rice-crayfish fields during spring and winter.Before crayfish were released to paddy field on April 28,straw-returning have promoted the significant increase in the density,biomass and species diversity of macrobenthos.Under the influence of crayfish,the macrobenthic density,biomass and species diversity decreased to different degrees.The results showed that:1)Before and after the release of crayfish,Shannon-wiener diversity index is presented as S2>S3>S1>ck and ck>S2>S3>S1 respectively.2)Dominance index showed that Branchiura sowerbyi,Limnodrilus hoffmeisteri,Hippeutis umbilicalis Benson,Physa foncinalis were the main dominant species during the whole experinment.3)Before releasing crayfish,the density and biomass of each treatment group were directly proportional to the amount of straw-returning,showing that S3 was slightly higher than S2,both groups were significantly higher than ck and S1.After the release of crayfish,it was found that the density and biomass of Branchiura sowerbyi,Limnodrilus hoffmeisteri,Hippeutis umbilicalis Benson decreased significantly(P<0.05),suggesting that these might be important natural bait for crayfish.Redundancy analysis(RDA)showed that Soil total phosphorus,Soil bulk density and organic matter were the key factors influencing the macrobenthic community structure during winter and spring.The results of community structure and species diversity changes of each group of macrobenthos showed that S2(3500kg/hm2)was the optimal straw-returning amount under the conditions of this study.3 Effect of crayfish biological disturbance on vertical distribution of particulate matter at different temperaturesUsing laboratory simulation experiments and chemically stable glass beads as tracers,the effects of crayfish bioturbation on the vertical distribution of sediment particles at different temperatures were investigated.After the crayfish were perturbed for two days at 25°C and35°C,the sediment particles were vertically distributed.The experimental results found that:1)At two temperatures,the depth of crayfish disturbance to sediments was mainly concentrated at 1-5?.2)It was found that the temperature and particle mobility had a significant positive correlation between disturbed 3d and 5d sampling,and the particle mobility at 35?was significantly higher than 25?(P<0.05).Perturbation for 10 days,found no correlation between temperature and particle mobility.There was no difference between 35°C and 25°C(P>0.05),and the particle mobility decreased significantly.The research shows that the biological disturbance intensity of crayfish is positively correlated with temperature in a short time,and the longer the time,the smaller the disturbance intensity is and has no correlation with temperature.