Effects Of Wheat Straw Return On The Soil And Soybean Root-associated Microbial Communities In The Huang-huai Region Of China

Wheat straw return has been widely used in improving soil fertility and crop yield,however,a robust understanding of the impact of wheat straw return on the composition of the soil and root-associated microbial communities under field conditions in a wheat-soybean rotation system in Huang-huai region has remained elusive.Soybean roots provide three different microhabitats at the soil-root interface:rhizosphere,rhizoplane,and endosphere.Plant-associated microorganisms are known to aid in key functions across the entire plant,e.g.,water and nutrient acquisition,stress response,and suppression of pathogens.Therefore,plant holobiomes or plant microbial communities are gaining increased attention.We characterized the effects of wheat straw return on soil bacterial and fungal communities in a wheat-soybean rotation system over a 3-yr period,using Illumina-based 16S rRNA and internal transcribed region(ITS)amplicon sequencing.Wheat straw return significantly affected the ?-diversity of the soil bacterial,but not fungal,community.However,the effect on fungal community composition was stronger than that on bacterial community.It enhanced the relative abundance of the bacterial phylum Proteobacteria and the fungal phylum Zygomycota,but reduced that of the bacterial phylum Acidobacteria and the fungal phylum Ascomycota.Notably,it enriched the relative abundance of nitrogen-cycling bacterial genera such as Bradyrhizobium and Rhizobium.Analysis of soil chemical properties indicated that straw return soils had significantly higher total nitrogen contents than no straw return soils.In addition,the relative abundance of fungal genera containing pathogens was significantly lower in straw return soils relative to control soils,such as Fusarium,Alternaria,and Myrothecium.During two growing seasons in wheat-soybean rotation system at three different sites in Huang-huai region,we tracked the wheat straw return-induced changes in bacterial and fungal community composition in bulk soil,rhizosphere,rhizoplane,and endosphere.PCoA analysis combined with ANOSIM analysis showed that soybean root-associated fungal communities exhibit compositional shifts under wheat straw return but not bacterial communities.Wheat straw returning could not only significantly affect the fungal community composition in bulk soil,but also significantly affect the fungal community composition in rhizosphere and rhizoplane.In addition,wheat straw return not only significantly affected the relative abundance of pathogenic fungi in the bulk soil,but also significantl in rhizosphere and rhizoplane,however,there was no significant effect on the relative abundance of pathogenic fungi in endosphere.The relative abundance of fungal genera containing pathogens was significantly lower after straw return,such as Fusarium,Gibberella and Alternaria,while enriched the relative abundance of Mycosphaerella.A field experiment was conducted to study the effects of short-term(two-year)wheat straw return on soil microbial communities in a wheat-soybean cropping system at three sites from Huang-huai region during four stages(pre-sowing,seedling,podding and maturity).The results showed that soybean growth stages had greater impact on soil bacterial community than fungal community.The response of soil bacterial community to straw return was the strongest at 30 days(seedling stage)after soybean sowing,while the response of fungal community to straw return was the strongest at 60 days(podding stage)after soybean sowing.LEfSe analysis showed that Massilia,Adhaeribacter and Ferruginibacter were significantly enriched in the pre-sowing stage;Acidibacter was significantly enriched in the mature stage.For fungi,Lectera was significantly enriched in the pre-sowing stage,Penicillium was significantly enriched in the seedling stage,and Corynespora was significantly enriched in the mature stage.LAMP detection showed that the detection rate of Fusarium was the highest,and the detection rates of F.graminearum and F.flavum were significantly higher than F.solanacearum.In the soybean maturity stage,the total detection rate of root rot pathogens respectively increased 1-2.3 and 7-12 times in straw return than no straw return treatment,compared with that in 2015.Endophytic microorganisms represents one of the key determinants of plant growth,nutrition and health by providing a lot of functional capacities such as obtain nutrients,suppression of plant pathogens,and resistance to biotic and/or abiotic stresses.Using soybean as a model ecosystem,we investigated the effects of different organs(roots,stems,leaves and pods),genotype(AD203,HD 12,SN16 and ZH13)and field locations(Jining,Suzhou and Xuzhou)on the composition and diversity of endophytic bacteria and fungi communities in soybean using 16S and ITS1 rRNA gene analyses.The results showed that there were significant differences in the composition of endophytic bacteria and fungi communities among the four organs of soybean(root,stem,leaf and pod).The composition diversity of endophytic bacteria and fungi communities in root(underground organ)was significantly different from that in stem,leaf and pod(aboveground organ).Bacterial alpha diversity was highest in stem and pod and lowest in root.Fungal alpha diversity was highest in root and lowest in pod.Plant genotype has the greatest impact on bacterial community composition in stems and the least impact on roots,and the greatest impact on fungal community composition in leaves and the least impact on pods.The field location had the greatest influence on bacterial community composition in roots,while the greatest impact on fungal community composition in stems,and the smallest impact on the bacterial and fungal community in pods.The relative abundance of common soybean pathogens also differs between host organ and genotype.Fusarium and Macrophomina are mainly enriched in soybean roots,Alternaria in soybean leaves,and Colletotrichum in soybean leaves and stems,which may be related to the pathogenic site and disease resistance of soybean varieties.We characterized the endophytic fungal communities associated with the roots and corresponding seeds of soybeans grown in the Huang-Huai region of China.For the roots,we identified 105 and 50 genera by culture-independent and culture-dependent(CD)methods,respectively,and isolated 136 fungal strains from the CD samples.Compared with the 52 soybean endophytic fungal genera reported in other countries,28 of the genera we found were reported,and 90 were newly discovered.Even though Fusarium was the most abundant genus of fungal endophyte in every sample,soybean root samples from three cities exhibited diverse endophytic fungal communities,and the results between samples of roots and seeds were also significantly different.In summary,the wheat straw return has different extent effects on root-associated microbial community composition,not only in bulk soil,but also in rhizosphere,rhizoplane,and endosphere,in a wheat-soybean rotation system in the Huang-huai region.The effects of wheat straw return on soil microbial community composition were also different in different soybean growth stages.In addition,we identified the composition of endophytic microbiome in the below-ground and above-ground organs of soybean,and revealed that the diversity of microbiome community in soybean was affected by the type of organ,genotype and field location.Our results have positive significance in evaluating the ecological,environmental and production benefits of wheat straw return,at the same time,the research results can also be used as a theoretical reference for the government to promote the work of straw return.