Exploring The Response Of Soybean Root-Associated Microbial Communities To Dodder Parasitism And The Regulation To Their Interaction By Nitrogen Addition

Soybean is an important economic crop in the world and support China’s economic development.However,dodder parasitism seriously limits the growth and yield of soybean in many areas.Root-associated microbiotas can be beneficial for plants to resist biotic and abiotic stresses.The microbiotas may also plays important roles in alleviating the harmful parasitism.Until now,the responses of the structure and function of the microbial communities in soybean to dodder parasitism is unclear.In this study,the effects and regulation of dodder parasitism on the root-associated microbial communities and secondary metabolites in soybean were investigated using 16 S r RNA and ITS high throughput sequencing and widely targeted metabolome detection techniques;based on soybean genotype and growth stage,the temporal succession patterns of the bacterial communities and core taxa in soybean and dodder were investigated,as well as the nutrient accumulations in different compartments of the plants;the effects of fertilization measures on the root-associated bacterial communities and the important ecological clusters of soybeans with different susceptibilities to dodder were studied in a field experiment;combining high-throughput Geo Chip technology and greenhouse experiments,the effects of different nitrogen sources(chemical nitrogen and biological nitrogen fixation)on the bacterial community and function genes in the rhizosphere of the soybean susceptible to dodder were further studied,and the alleviation effects of the nitrogen sources on the dodder parasitism were analyzed.The main results are as follows:(1)The variations in the root-associated microbial communities of soybean and the soil physicochemical properties in the root zone were analyzed under different parasitism statuses.The results showed that dodder parasitism significantly increased the enrichment and environmental sensitivity of the bacterial and fungal communities in soybean,and the inhibitory parasitism of dodder also significantly promoted the multinutrient accumulations in root zone soil.Network analysis showed that parasitism affected the cooccurrence patterns of the microbial communities,and led to the high complex and unstable in bacterial and fungal communities.Further analysis showed that dodder parasitism promoted the enrichment of Ensifer and Rhizobium in soybean,and enhanced the relationships between these groups and soil factors.However,dodder parasitism also promoted the enrichment of the potentially pathogenic genus,Alternaria.The analysis of root secondary metabolites showed that dodder parasitism significantly increased the content of flavonoids,indicating that the parasitism induced the synergistic responses in secondary metabolites,microbial communities,and soil physicochemical properties in underground of soybean.(2)Based on different soybean genotypes,the temporal changes of root-associated bacterial communities and biomass in soybeans with parasitism were analyzed.The results showed that dodder parasitism significantly reduced the absorption capacity of nitrogen,phosphorus,and potassium nutrients,and reduced the dry matter accumulation and dry matter allocation of soybean leaves,stems,and roots.During the growth stages,parasitism led to the high similarity between the bacterial communities in the rhizosphere and root,as well as in the stem and dodder.Redundancy analysis showed that leaf dry matter in soybean with parasitism can affect the bacterial communities in the rhizosphere,root,and stem of soybean.In addition,the limitations of dodder parasitism on soybean plant traits are influenced by soybean genotype.The nutrient uptake,nutrient accumulation,and dry matter accumulation in leaves,stems,and roots of the soybean susceptible to dodder were more severely inhibited by parasitism,and its root-associated bacterial communities were more sensitive to dodder parasitism.Further analysis showed that Betaproteobacteriales and Rhizobaiales are the core taxa of soybean.The stochastic process dominated the assembly of the core taxa in different root compartments of soybean,and the process was not susceptible to dodder parasitism.(3)Then,we investigated the effects of fertilization measures on the root-associated bacterial communities in soybeans with different susceptibilities to dodder.The results showed that fertilization measures had different effects on the bacterial communities of different soybeans.Fertilization significantly affected the bacterial community in the root zone of susceptible soybean,but significantly affected the bacterial community in the root zone,rhizosphere,and root of resistant soybean.At the order level,the dominant taxa is Rhizobiales,which was sensitive to parasitism.Meanwhile,compared with resistant soybean,the relative abundance of Rhizobiales in susceptible soybean is more sensitive to fertilization measures and soil factors.Network analysis showed that the important ecological cluster in soybean was also composed of Rhizobiales,and the abundance and potential nitrogen cycling functions for the ecological cluster varied among fertilization measures.Compared with resistant soybean,the nitrogen cycling functions of the ecological cluster in susceptible soybeans also varied significantly among fertilization measures.The structural equation model showed that the content of soil nitrogen increased the abundance of the ecological cluster in susceptible soybean.(4)In a greenhouse experiment,nitrogen addition treatment,rhizobia inoculation treatment,and the combined treatment of nitrogen and rhizobia could promoted the root development,nutrient accumulation,and dry matter accumulation of the soybean susceptible to dodder,as well as the growth of dodder.The effect of nitrogen addition was the best.Different treatments significantly affected the rhizosphere bacterial community of soybean.Meanwhile,the treatments increased the α diversity of its bacterial community,but reduced the relative abundance of Ensifer and Pseudomonas.The analysis of multiple nutrient cycling functional genes showed that the nitrogen addition treatment and the combined treatment led to the enrichment of more denitrification genes in soybean rhizosphere.In addition,the abundance of functional genes related to C,N,P,and S in the rhizosphere was significantly positively correlated with the nutrient accumulation and dry matter accumulation of dodder.The structural equation model showed that the α diversity of rhizosphere bacterial community had important contribution to the biomass accumulation of dodder and soybean,and indicated that nitrogen addition can increase the contribution of αdiversity.In summary,this study revealed the inhibitory effect of dodder parasitism on soybean growth and the cascade effect on root-associated microbial communities,and discovered the impact of fertilization measures on the assembly of the important bacterial ecological cluster and their potential functions in soybeans with different susceptibilities to dodder,and demonstrated the promotion of different nitrogen sources on the growth of dodder and soybean.These results provide ideas and references to alleviate the inhibitory effects of parasitic dodder on soybean through nitrogen-fixing microorganisms and nitrogen fertilizer,and provide the theoretical basis for field management of soybean and dodder.