Ecological Effects And Functional Mechanism Of Chinese Softshell Turtle(Pelodiscus Sinensis)-Rice Co-culture System

Pelodiscus sinensis commonly is the most traditional freshwater aquaculture varieties raised in China.Due to its delicious taste,rich nutrition and medicinal efficacy,the market demand and production scale of P.sinensis have increased sharply in recent years.The rapid development of Chinese soft-shelled turtle breeding industry has brought many problems at the same time.Because of the expansion of the scale of culture and the increasing of the density of culture,the amount of bait used in production is increasing.At least 10%-20%of the bait was directly dissolved in the aquaculture water,and only 20%-25%was used by the turtle body.About 75%-80%of the bait was mixed into the breeding system,which caused serious environmental pollution and seriously restricted the sustainable and healthy development of the culture industry of P.sinensis.The rice-fishery culture system could put rice cultivation and aquaculture in the same space and time position,and can produce high quality rice and aquatic animals.Rice-fishery culture systems can efficiently utilize agricultural resources(land,water,human resources,etc.)and reduce environmental pollution.This kind of culture system could provide peoples with green and high quality food products and it is an important part of the sustainable development model of green and organic agriculture in the future.In this study,we constructed a complete turtle-rice co-culture system.The changes of yield and quality of culture objects,environmental parameters of culture system,material flow between culture objects and culture systems,and the diversity of microbes in culture system were studied.The aim of this study was to clarify the operation mechanism of turtle-rice co-culture system and to provide the basis for improving and popularizing this culture model.The results are as follows:1.The effects of the turtle-rice co-culture system on the production performance of cultured objects.The growth characteristics of turtles and rice in different treatment groups were studied by statistical method.The yield of rice in turtle-rice co-culture system was significantly higher than that in rice monoculture group(RM)and rice monoculture group with fertilizer(RMF)(P<0.05).The yield of turtles in turtle-rice co-culture system was significantly higher than that in TM(P<0.05).At different sampling time points during the whole breeding period,the length,width and body weight of turtles were higher than those of TM.FCR of TR6(6 turtles/m2)was significantly lower than that of the rest of turtle-rice co-culture and TM(P<0.05).The SGR,WG,DR,NRE and PRE of TR6,TR8 and TRIO were significantly better than those of TR12 and TM(P<0.05).The crude lipid contents of turtles were found no significantly different in the four co culture groups(P>0.05),but were significantly higher than that in the TM groups(P<0.05);The contents of crude ash of turtles in the TR6,TR8,TR10 groups were significantly lower than that in the TM groups(P<0.05).Digestive enzymes in intestinal of TR6,TR8 and TR10 were significantly higher than those of TR12 and TM(P<0.05).The results of weed biomass statistics showed that the weed biomass of turtle-rice co-culture system was significantly lower than that of RM and RMF(P<0.05).The above results indicate that the production performance of the cultured objects can be improved significantly in the turtle-rice co-culture system than that in the TM.It is speculated that the positive interaction between the soft-shelled turtle and the rice is beneficial to the growth and metabolism of both sides.The results of this chapter provide a theoretical basis for further elucidation of the interaction mechanism among the turtle-rice co-culture system.2.The effects of the turtle-rice co-culture system on the aquaculture water environment.Using the method of measuring water quality Indexes,the water quality of each experimental group was analyzed.The NH4+-N,NO2-N,NO3-N,COD,TN and TP of TR12 and TM were significantly higher than those in the rest of turtle-rice co-culture system,RM and RMF(P<0.05).The above water quality indexes of TR6 group were all at the lowest position among the turtle-rice co-culture system during most of the breeding period.Compared with the TM,the average value of NH4+-N,NO2-N,NO3-N,TN,TP and COD in the 90-day culture period of TR6 decreased by 43.79%,54.23%,50.61%,28.17%,41.23%and 19.18%,respectively(P<0.05).The DO in TR6,TR8 and TR10 groups were similar and higher than those in TR12 and TM.Compared with TM,the average DO in the 90-day culture period of TR6 was increased 9.1%.The results showed that the eutrophication of water environment could be controlled in the group of turtle-rice co-culture system,and the water quality of culture water was kept in a good condition.3.The effects of turtle-rice co-culture system on soil physical and chemical propertiesWithout the use of any fertilizer,compound fertilizer,the soil organic matter,soil available P,soil available K,soil NH4+-N and soil NO3-N of TR6,TR8,TR10,TR12 and TM were increased in the culture period.The content of soil organic matter in turtle-rice co-culture system and TM were increased a lot at the end of the breeding experiment.The content of soil organic matter in TR12 group was significantly higher than that in TR6,TR8,TR10 and TM(P<0.05),while the content of soil organic matter in TR6,TR8,and TRIO was significantly higher than that in TM(P<0.05).The soil physical and chemical indexes of RM and RMF were lower than those of turtle-rice co-culture system and TM at the stage of maturity.The soil pH of each group gradually increased throughout the breeding period and was finally kept in the weak acid range.The results indicated that the content of important nutrient elements in turtle-rice co-culture system was higher than that of RM and RMF,which was beneficial to rice root absorption.The results of this part reflect the soil quality changes of turtle-rice co-culture system,and provide theoretical basis for further understanding the mechanism of growth and development of culture objects by soil in turtle-rice co-culture system.4.The effects of turtle-rice co-culture system on soil enzyme activityIn this part,The soil enzymes activity of turtle-rice co-culture system were higher than that of RM,RMF and TM,and the soil enzymes activity of turtle-rice co-culture system were gradually increased with the increasing of culture density and tended to be stable at maturity.The activities of urease,protease,catalase and phosphatase in soil of TR12 and TM groups were higher than those of TR10,TR8 and TR6 groups in most time of culture period.The results of this chapter show that the turtle-rice co-culture system can increase the activities of soil urease,protease,catalase and phosphatase,and promote the growth of rice effectively.It is speculated that the turtle-rice co-culture system can promote the growth and development of rice roots,enhance the ability of rice root metabolism and increase root exudates.In this part of the experiment,the characteristics of soil enzymes activity in different treatment groups were analyzed,which provided a theoretical basis for further analysis of changes of soil quality in turtle-rice co-culture system.5.The effects of turtle-rice co-culture system on the nutrient element metabolism flowIn this chapter,the contents of nutrient elements in culture system were analyzed and the difference of utilization ratio of N,P and K were also analyzed.Compared with the TM,the transformation and absorption ability of trace elements in the diet of turtles was significantly enhanced(P<0.05),and the accumulation of trace elements was increased.The content of trace elements in straw and grain of turtle-rice co-culture system was significantly higher than that of RM and RMF(P<0.05).At the end of the experiment period,the most indices among contents of total nitrogen,total phosphorus and total potassium in the soil,turtles,straw and grain of turtle-rice co-culture system were significantly higher than those in RM,RMF and TM(P<0.05).N,P and K were mainly distributed in cultured soil,and the rest were in straw,grain and turtles.The contents of N,P and K of the culture objects in the turtle-rice co-culture system were higher than those in RM,RMF and TM.Compared with the RM,RMF and TM,the utilization ratio of N,P and K in the turtle-rice co-culture system was significantly increased and slightly decreased with the increasing of culture density.TR6 had the highest utilization rate of N,P and K,which increased 31.86%,15.26%and 2.24%,respectively,compared with the TM group with the same density of culture.The results of this experiment show that under the condition of turtle-rice co-culture system,each culture component has stronger absorption capacity.The results of this chapter provide a theoretical basis for the further analysis of the operating mechanism of turtle-rice co-culture system at the level of metabolic flow of nutrient elements.6.The effects of turtle-rice co-culture system on diversity of bacteria in culturesoil,intestinal tract and feces of turtlesIn this part,high-throughput sequencing technique was used to sequence and analyze the v3-v4 conserved region of 16s rRNA gene for soil microbes of plant root,intestinal microbes and fecal microbes in different treatment groups,and the diversity characteristics of the microbial communities were obtained.The diversity of intestinal and fecal microbial communities of P.sinensis was different among different treatment groups.The dominant genera in BB and DB were Acidobacteria_Gpl,Acidobacteria_Gp3,Anaeromyxobacter,Gemmatimonas and so on.The dominant genera in CB were Acidobacteria_Gpl,Acidobacteria_Gp3,Anaeromyxobacter,Acidobacteria_Gp2 and so on.The significantly different genera between CB and DB were Anaeromyxobacter,Gp3,Nitrospira,Geobacter and Gemmatimonas using STAMP differential analysis.The significantly different genera between GB and HB were Ktedonobacter.The changes of enrichment functional Pathways among different groups were further analyzed.Compared with CB,the higher enrichment functional pathways were Amino Acid Metabolism,Lipid Metabolism,Xenobiotics Biodegradation and Metabolism and Metabolism of Other Amino Acids.Combined with the above results,the DB group has more dominant genera related to nutrient cycling and environmental remediation,while the significant differential functional pathways are also related to the metabolic function of conventional nutrients and micronutrients.This part of the experiment preliminarily clarified the advantages of the turtle-rice co-culture system in root soil,intestinal tract and fecal microbial diversity compared with TM,which provided a theoretical basis for explaining the operation mechanism of the turtle-rice co-culture system.