Effects Of Different Durations And Scales Of Rice-duck Farming Systems On The Physical And Chemical Properties And The Structure Of Algal Communities In Water

Rice-duck farming system is a compound planting and breeding model that combines ecology and agriculture.It can not only control the number of weeds,reduce environmental pollution caused by herbicides,but also promote the development of environmentally friendly agriculture.In the rice-duck farming system,the activities of ducks greatly disturb the water,which affects the physical and chemical properties of the water and the growth of algal;and as an important indicator of water quality evaluation,the study of algal is of great significance for improving the quality of rice fields and surrounding water bodies.At present,the related research on rice-duck farming system mainly focuses on the ecological effects of the system on the control of diseases,pests and weeds,changes in soil nutrients and greenhouse gas changes,etc.There are few studies on the algal ecology of the water in the farming system.Rice-duck farming systems of different durations and scales will affect the physical and chemical properties of the water and the structure of the algal community.Therefore,this study is based on two different durations of rice-duck farming(19 years and 2 years),set three different scales(667m~2,2000m~2,3333m~2)for each year.The treatments were long-term rice-duck farming(OR1,OR3,and OR5)and short-term rice-duck farming(GR1,GR3,and GR5).Traditional rice farming(CK)test field was set up as a comparison.By detecting the physical and chemical properties of the water and high-throughput sequencing of algae,we studied the physical and chemical properties of the water in the rice-duck farming field,the algae diversity and the change of community structure.The differences in the composition and diversity of the algae community in the water under the rice-duck farming systems with different durations and scales were analyzed,and the physical and chemical driving factors leading to the differences were explored.The main findings are as follows:(1)Rice-duck farming significantly affects the physical and chemical properties of paddy field water.Compared with the conventional rice farming system,the average water temperature during the farming period of the rice-duck systems of different farming years was lower.Among them,the long-term rice-duck farming system significantly reduced the water temperature by 1.45℃on average,which is beneficial to the growth and development of rice;The p H value of the water has decreased;the total nitrogen,ammonium nitrogen and soluble potassium concentration of the water in the later period of the rice-duck farming system are greater than that of non-rice ducks.The scale of farming had no significant impact on the physical and chemical properties of the water in the rice-duck system.(2)Rice-duck farming affects the composition,diversity and community structure of algal in the water.The algal communities in the rice-duck farming fields and traditional rice farming fields mainly include euglenophyta,chlorophyta,cyanophyta,streptophytes and diatoms,accounting for about 90%of the total number of algal,among which the dominant species are euglenophyta,chlorophyta and cyanophyta.The long-term and short-term rice-duck farming systems have similarities in the algal community structure.The water algal community structure of the conventional rice farming system is quite different,while the long-term rice-duck farming system of different scales has different algal community structures.The relative abundances of chlorophyta,cyanophyta and diatoms in the long-term and short-term rice-duck farming system were higher than those in the non-rice-duck farming field.The larger the scale of rice-duck farming,the lower the relative abundance of cyanophyta,which helps reduce the risk of eutrophication in the water.For the algal diversity index,the rice-duck farming system is higher than the conventional rice farming system.There is no significant difference between the rice-duck farming system of the same farming years and different scales,but there are significant differences between different farming years:in the early period of farming,the Shannon diversity index of algal in the long-term rice-duck farming system was lower than that of the short-term rice-duck system,and the results were opposite in the late farming period.The Ace richness index of the water of the long-term rice-duck system was higher than that of the short-term rice-duck system.(3)From the perspective of the relationship between species,there are differences in the relationship between the species of algal in different years of rice-duck farming.From the perspective of the entire farming cycle,the core species of algal in traditional rice farming waters is the genus g＿Cyanobium,and the core species of g＿Cyanobium,g＿Choricystis and g＿Choricystis in GR1,GR3 and GR5 rice-duck farming.The core species of algal with OR1,OR3 and OR5 rice-duck farming system are g＿Lepocinclis,g＿Cyanobium and g＿Lepocinclis.(4)The relationship between the algal diversity and the physical and chemical factors of the rice-duck farming system of different durations and scales is quite different.The amount of euglenophyta in the conventional rice farming system was significantly negatively correlated with dissolved oxygen,and the amount of euglenophyta in the GR1rice-duck farming system was significantly negatively correlated with temperature and nitrate nitrogen(P<0.05);the GR3 rice-duck farming system was naked The number of algal was significantly negatively correlated with nitrate nitrogen and soluble potassium(P<0.05);the number of euglenophyta in the OR1 rice-duck farming system was significantly negatively correlated with the number of nitrate nitrogen(P<0.05);the number of euglenophyta in the OR3 rice-duck farming system was significantly correlated with nitrate nitrogen,total phosphorus and soluble potassium(P<0.05);the number of euglenophyta in the OR5 rice-duck farming system was significantly correlated with ammonium nitrogen,nitrate nitrogen,total phosphorus and soluble potassium(P<0.05).Redundancy analysis showed that the environmental factors affecting the algae community in the non-rice-duck farming field were dissolved oxygen in the water during the late period of farming,while the main environmental factors affecting the algae community structure in the rice-duck farming field were soluble potassium and p H.