Community Structure And Adaptation Of Soil Microbiome After Long-term Phosphorus Fertilization

Soil microbiome is directly involved in phosphorus(P)cycling in the soil.It affects crop yield and food quality.Taking full advantage of the biological potential of crops and soil microbioMe is an important strategy to improve phosphorus use efficiency,ensure crop yields,and realize green and sustainable development of agriculture.In recent years,long-term excessive P fertilizer application has led to P accumulation in the soil.This study focuses on whether and how cumulative P influences the community structure and functionality of soil microbiome.Based on the analysis of the diversity and community structure of arbuscular mycorrhizal(AM)fungi and the amount of P-related microbiome in long-term field trial(high vs low P),pot experiments were conducted to study the effect of soil microbiome on crop growth.The effects of different soil microbial groups,host plant species,substrate P supply levels and the rhizosphere effect were considered.The experiments were aimed to uNravel the underlying mechanism of different microbial groups adapted to long-term P fertilization in mining P and affecting crop growth.The results will provide theoretical evidence for developing suitable cropping systems to take full advantage of the potential of soil microbiome to improve P utilization efficiency.The main results are as follows:1.Soil samples in three P treatments of nil P(PO),optimal P(P75,75 kg P2o5 ha-1)and high P(P300,300 kg P2O5 ha-1)were collected during three sampling periods cross maize growth.P fertilization significantly influenced the composition of AM fungi community while no significant influence on diversity was detected.AM fungi taxa are mainly affiliated to Glomeraceae,Diversisporaceae,Paraglomeraceae,Gigasporaceae,Claroideoglomeraceae and Acaulosporaceae.The effect of sampling times was greater than that of P fertilization.In the early growth stage the structure of AM fungi was mainly influenced by the root-shoot ratio,root P content and P concentration.In the later growth stages,AM fungal community was mainly influenced by shoot biomass.The abundances of Firmicutes and Actinobacteria phyla,belonging to phosphate solubilizing bacteria,were significantly higher at later growth stages than that at the early growth stage.2.In order to study the effects of different soil microbiome group of continuous maize monocropping in long-term P fertilization trials on maize growth feedback.Soil microbiome at three P fertilization levels(P0,P75 and P300)were divided into three fractions:AM fungi community,pathogenic/saprobe and original microbial inoculum.The results showed that the shoot biomass of maize plants was the highest in the sterilized treatment,and the lowest in the treatment inoculated with original inoculum.Shoot biomass inoculated with AM fungi and pathogenic/saprobe as intermediate.These results indicate that soil pathogens inhibit plant growth.The benefit of AM fungi is constrained in the soil of continuous maize monocropping systems.The soil inoculated by PO inoculum significantly constrained the maize growth,meanwhile soil inoculated by P300 inoculum did not significantly affect the maize growth compared with P75 inoculum.The results showed that the microbiome with long-term low P stress had negative effect on maize growth,while the microbiome with long-term high P level did not have negative effect on maize growth.3.In order to study the effects of soil microbiome of continuous maize monocropping in long-term P fertilization trials on the growth of different plant species,original and sterilized microbial inoculum at three P fertilization levels(P0,P75 and P300)were inoculated.The results showed that inoculum conferred different benefit to the growth of maize,clover and rape plants.The shoot biomass of maize plants inoculated with PO and P75 original microbial inoculum was significantly higher than that inoculated with the sterilized treatment in the nil P treatment,and the results were the opposite in the P fertilized treatments.While the maize plants inoculated with P300 original microbial inoculum was significantly higher than that inoculated with the sterilized treatment both in the nil P and P fertilized treatments.The shoot biomass of clover plants inoculated with original inoculum were significantly higher than that in the sterilized treatment,while the growth of rape plants was not significantly influenced by the original inoculum compared with sterilized inoculum on both substrate P supply levels,respectively.The activity of acid phosphatase(ALP)and N-acetyl-glucosaminidase(NAG)in soil inoculated by original inoculum with clover was significantly higher than that in maize soil in the same substrate P supply level.The increase of substrate P supply significantly inhibited the clover root colonization but not for maize.However,the expression of ZmPhtl;6 gene in maize roots decreased significantly with the increase of substrate P supply level,which was more sensitive than that of maize root colonization.Overall,the adaptability of soil microbiome in maize continuous cropping system was determined by both the inoculum source and plant species,and the pathogens inhibition in soil could be regulated by selecting suitable crop species.4.The a-diversity(estimated species richness and Shannon-Wiener Index)of rhizosphere bacteria of clover and maize plants decreased continuously from bulk and rhizosphere to rhizoplane.Rhizocompartment was the main driving factor affecting bacterial community,followed by plant species.Certain OTUs of bacterial community were enriched in the rhizosphere and rhizoplane of maize and clover plants.The enriched OTUs belonged to Proteobacteria,Actinobacteria,Bacteroidetes,Chloroflexi and Verrucomicrobia.The relative abundance of Proterbacteria in the rhizoplane of clover plants was significantly higher than that in maize plants,while the relative abundances of other four phyla were opposite.Functional gene prediction indicated that the enriched bacteria in the rhizoplane of maize plants tended to be closely related to carbon metabolism while OTUs in clover plants were more with P metabolism.Significant differences in rhizosphere bacterial communities of maize plants were observed among different inoculum of three P fertilization levels(P0,P75 and P300).The results indicate that host plant species exert strong selections on the assemblages of rhizosphere bacterial communities.In conclusion,long-term P fertilization significantly affected the AM fungi community structure and the number of phosphorus solubilizing bacteria associated with P cycling.Root niche is the key factor affecting bacterial community,and the significant continuous enrichment of bacterial community from bulk soil to root rhizoplane may be related to the plant specific function.The adaptation of soil microbes from high legacy P soil was stronger than that from low legacy P soil.The suitable crop selection for rotation was helpful for microbial effectively developed the function and could guide the optimization of planting pattern.