Distribution Patterns And Driving Mechanism Of Bacterial And Arbuscular Mycorrhizal Fungal Communities In Soda Saline-sodic Soils In Western Songnen Plain

According to the second national soil census,the total area of saline-sodic soil in China is about 1.5billion acres.The crop yield is low and not stable in saline-sodic region,which threatened the construction of high and stable yield fields.However,the vast saline-sodic region is also an crucial reserve agricultural resource in China.Songnen Plain is an important grain production base and the largest region of soda saline-sodic soils in China.The area and extent of saline-sodic soils were aggravated increasingly in this region,leading to decrease in crop yield and soil productivity,which threatened the crop production in Northeast China.Microorganism are key proponents of soil ecosystem,playing crucial roles in soil organic decomposition,nutrient cycling and protecting plants from abiotic stress.Arbuscular mycorrhizal(AM)fungi are ubiquitous in terrestrial ecosystem,which form mutualism symbiosis with host plants and improve the biotic and abiotic resistance for their host plants.Therefore,a field study was conducted in Western Songnen Plain,Northeast China.Totally,120 soil samples ranging from non-salinity to extremely salinity-sodicity across western Songnen Plain were collected.Soil physiochemical variables,AM fungal biomass,soil bacterial and AM fungal diversity were determined based on Miseq sequencing,morphological methods and network analysis.The conclusion is as follows:(1)Totally,3,564,782 reads were obtained through Miseq sequencing,and 8,282 bacterial OTUs were obtained at 97% similarity threshold.Soil bacterial OTU richness,Shannon diversity and Pielou evenness indices were negatively correlated with soil ESP.PCo A and Mantel test revealed that soil ESP was the key determinant in shaping bacterial community composition and showed dependent effect.In addition,soil p H,organic matter,electrical conductivity,soil moisture and available potassium content all contributed to soil bacterial community composition.Proteobacteria(28.89%),Actinobacteria(19.96%)and Gemmatimonadetes(16.71%)were the predominant phylum in saline-sodic soils.Especially,the relative abundance of Gemmatimonadetes positively correlated with soil ESP,and TITAN analysis indicated that members in this phylum mainly belonged to z+ OTUs.Null model analysis revealed that the deterministic process was the dominant process in shaping bacterial community assembly,and contributed more in moderate and extreme saline-sodic soils than in slight saline-sodic soils.The connectivity and modularity of soil bacterial co-occurrence network was significantly impacted by soil ESP.Along with the increasing ESP,network connectivity and modularity were dramatically decreased,and the modularity increased.The four modules in network showed contrasting response to ESP,and modules dominated by Gemmatimonadetes positively responded to increasing ESP.Bacterial functional attributes and phenotypes were predicted by FAPROTAX and Bugbase.Stress-tolerant and Gram+bacteria increased along with the increasing ESP,while other phenotypes exhibited opposite trend.(2)The microscopy observation demonstrated that AM fungal structures including arbscules,vesicles and hyphae were detected in all samples,indicating that AM fungi could form symbiosis relationship with Leymus chinensis.AM fungal root colonization rate,extraradial hyphal(ERH)density were negatively correlated with soil ESP,while spore density was not correlated with soil ESP.Totally188 AM fungal OTUs were obtained through Miseq sequencing.AM fungal OTU richness,Shannon diversity and Pielou evenness indices were all negatively correlated with soil ESP.PCo A and PERMANOVA analysis revealed that soil ESP was the key determinant in shaping AM fungal community composition.At family level,the top three AM fungal families responded differently to soil ESP.The relative abundance of Glomeraceae generally increased with the increasing ESP,while Claroiglomeraceae exhibited contrasting trend.However,Paraglomeraceae was not related to soil ESP.Compared with abundant AM fungi,rare AM fungi was more sensitive to soil ESP.Random forest analysis indicated that the abundance and community composition of abundant AM fungi contributed more to soil nutrient availability than rare AM fungi.(3)By constructing a co-occurrence network between AM fungi and bacteria(B),the results showed that slight saline-sodic soils had the most complex and largest AM-B co-occurrence network and the most abundant AM-B interactions.However,the AM-B network was less connected in moderate saline-sodic soils.The AM-B positive/negative interaction ratio was significantly lower in moderate saline-sodic soils than in slight saline-sodic soils,indicating that high ESP intensified the competition between AM fungi and bacteria.We further screened bacterial OTUs that positively interacted with AM fungi in the AM-B network and found that the relative abundance of three bacterial OTUs(Acidobacteria sp.,Cryptosporangiaceae sp.,Anaerolineae sp.)was positively correlated with AM fungal spore density,and another OTU(Gemmatimonadetes sp.)was positively correlated with AM fungal ERH.In summary,this study shows that soil ESP is a key factor in determining the diversity and community composition of soil bacteria and AM fungi,and finds that the interactions between AM fungi and soil bacteria may be an important factor affecting the function of mycorrhiza,providing a solid theoretical basis for the efficient use of soda saline-sodic soils in the Songnen Plain.