The Effects Of Rhizobium Inoculation On The Growth Indices Of Chinese Milk Vetch And Its Responses To Different Soil Physichemical Properties In Paddy Fields

Chinese milk vetch(CMV,Astragalus sinicus L.)is widely cultivated in southern agricultural areas,which can effectively play the role of nitrogen fixation,improve biological yield and increase the ability of soil improvement after returning to the field by inoculating rhizobia.Hence,this study studied the effects of varieties,rhizobium strains and soil physical and chemical properties on nitrogen fixation in the symbiotic system of"CMV-rhizobium".The exclusive relationship between CMV and rhizobium,the relationship between soil physical and chemical properties and nodule growth characteristics were revealed.Under the rotation mode in southern Jiangsu,theoretical support was provided for scientific introduction and rational fertilization in actual production,and the role of "rice-CMV" rotation mode was maximized.1.Effect of rhizobium inoculation with different CMV varietiesPot experiments were conducted Xinyang variety,Minzi No.6,Minzi strain 8487711 and Shishou variety four CMV varieties as host plants,inoculated with four kinds of rhizobia(CCBAU2609,M.h.93,medium and Mesorhizobium huakuii rhizobia 7653R,CK)respectively,studied the differences in growth indexes and nodule characteristics of different varieties of CMV after inoculated with rhizobia,and analyzed the reasons.There was no significant difference in plant height and dry weight above and below ground of the four CMV varieties in different treatment groups at seedling stage,but there was significant difference at full flowering stage.In the whole growth period,the growth indexes and root nodule characteristics of the four varieties treated by strain 7653R was better than the others.In the full flowering stage,the biomass of Xinyang variety,Minzi No.6,Minzi 8487711 and Shishou variety increased by 102.82%,182.42%,55.56%and 168.14%respectively compared with the control group.There are some differences in the specificity between CMV varieties and rhizobium strains.Among them,"Minzi No.6-7653R8","Shishou variety-7653R" had the strongest specificity.To a certain extent,it showed that 7653R was a broad-spectrum and efficient rhizobium strain.It is suggested to use it in combination with CMV such as Minzi No.6 and Shishou variety in production so as to play a greater advantage in yield and nitrogen fixation.2.Impacts of different paddy soils on nodule growth characteristics of CMVNodule growth characteristics of CMV differ in response to different soil physical and chemical properties,especially in different paddy soils.This study aimed to analyze-the relationship between nodule characteristics of CMV and soil physical and chemical properties in CMV used in crop rotations with rice in Taihu and Ning-zhen rice growing regions.Correlation analysis and path analysis were used to associate differences in nodule characteristics with particular soil conditions in paddy fields.It was found that root nodule number,nodule weight and nitrogenase activity of milk vetch in rice-CMV crop rotations were affected by soil conditions.Nodule number per plant and the nitrogenase activity in Kunshan sample point were high(86.24-plant-1,1362.73 nmol C2H4·min-1·g-1,respectively),while corresponding values for Danyang sample point were low(1.13·plant-1,9.25 nmol C2H4.min-1·g-1,respectively).Path coefficients for nitrate nitrogen,total nitrogen,organic matter and available phosphorus were generally strongly correlated with nodule number,and organic matter,nitrate nitrogen and available phosphorus were positively correlated(P2=1.629,P1=0.633,P4=0.448)but total nitrogen negatively correlated(P5=-1.138,P represents direct path coefficient of factors).Soil organic matter,nitrate nitrogen and available phosphorus had the greatest positive influence on nodule number,whereas high soil total nitrogen reduced nodule number.There is a synergistic relationship between root nodule characteristics and the soil environment.In practice,appropriate organic fertilizer and phosphate fertilizer should be used to improve the nitrogen fixation capacity in CMV,rather than nitrogen fertilizer.3.Isolation and identification of CMV rhizobium strainsTo further promote the CMV green manure,the study collected CMV from 9 sample points of southern Jiangsu,and isolated 3 strains with the general characteristics of rhizobia from root nodules.Through 16S rDNA sequence analysis to determine their phylogenetic tree after the bacterial identification was taken,which showed that three strains of rhizobia belong to one genus and belong to Rhizobium;DY has higher similarity with strain sp.BAB-3360,reaching 98.36%,KS2-2 has 94.79%similarity with strain Rhizobium sp.SOY7,and WJ has 95.18%similarity with strain Rhizobium sp.GGC10,and KS2-2 and DY are in the same branch,and have close genetic relationship,but have far genetic relationship with WJ.The preliminary isolation and identification of rhizobia isolated from CMV under paddy fields rotation in southern Jiangsu province enriched the resources of rhizobia isolated from CMV in the study area and laid a certain theoretical foundation for future research on molecular mechanism of rhizobia.In conclusion,host plants,rhizobium strains,soil organic matter content and soil fertility level have obvious effects on nodule capability of CMV.The growth of Minzi strains 8487711 and Shishou variety are better than Xinyang variety and Minzi NO.6.The growth characteristics of CMV inoculated with 7653R strain are better than that of other strains.Soil organic matter content,nitrate nitrogen and available phosphorus are the main factors that promote the nodulation ability of CMV,while soil total nitrogen is the main limiting factor,and isolated three strains from CMV in paddy fields soil belong to Rhizobium,what’s more,the strain KS2-2 is closely related to DY.