Mechanism Of Action Of Arbuscular Mycorrhizal Fungal Community In Red Soil On Phosphorus Absorption By Maize Roots Under Organic Fertilizatio

The red soil in the southeast hilly area is the main medium-low-yield soil in China,with low content of organic matter and available phosphorus,poor microbial quantity and functional activity,low plant stress resistance and phosphorus（P）absorption,making the potential production capacity of red soil resources unable to be played.Arbuscular mycorrrhizal fungi（AMF）formed arbuscular structure with cortical cells of infected plant roots,established mutualistic symbionts with plant roots,which affected the plant growth characteristics and P absorption process.The long-term field experiment with manure application was conducted at the Yingtan Red Soil Ecological Experiment Station of the Chinese Academy of Sciences.The total microbial DNA was extracted from rhizosphere,bulk soil and maize roots under four fertilization treatments containing no manure（CK）,low manure with 150 kg N ha^-1y^-1（LM）,high manure with 600 kg N ha^-1y^-1（HM）,and high manure with 600 kg N ha^-1 y^-1and lime(HML,Ca（OH）₂ applied 3000 kg ha^-1 3y^-1),respectively.The alpha diversity and composition of AMF community in the maize roots,rhizosphere and bulk soil were investigated using high-throughput sequencing and quantitative real time polymerase chain reaction（q RT-PCR）.The study provided the comprehensive knowledge of whether and how the AMF community affected the maize growth and P absorption of maize roots in a red soil（derived from Quaternary red clay）.1.Results of high-throughput sequencing showed that:（1）Manure application of increased significantly the nutrient level of red soil,including p H,moisture,organic matter（OM）,total phosphorus（TP）,available phosphorus（AP）and total nitrogen（TN）of rhizosphere and bulk soil increased significantly,and those were the highest under the HML treatments has the best application effect.Soil properties in the rhizosphere and bulk soil under the HML treatment were 1.30-39.69 and 1.08-57.69 times higher than those under the CK treatment,respectively.（2）Manure fertilization significantly improved the alpha diversity of AMF community and reached the maximum under the LM treatment.The Chao1,Richness,and Shannon of AMF community in maize roots,rhizosphere and bulk soil under LM treatment were 1.89-2.05,1.55-2.33 and 1.56-1.83 times larger than those under the CK treatment,respectively.There were no significant differences in AMF diversity between rhizosphere and bulk soil,while they were significantly higher than that in maize roots.（3）The community structure composition analysis showed that the AMF community in maize roots,rhizosphere and bulk soil were dominant by the genera Glomus and Paraglomus.Glomus（52.88%-79.93%）>Paraglomus（0.17%-20.64%）in maize roots.Paraglomus（48.73%-74.23%,32.82%-63.66%）>Glomus（3.00%-29.45%,2.90%-24.85%）in rhizosphere and bulk soil.Principal component analysis（PCA）showed that the AMF community structure was well separated under four fertilization treatments by the PC1 axis.（4）Pearson correlation analysis showed that the alpha diversity（Chao1,Richness and Shannon）,structure（PC1）and dominant genera（Glomus and Paraglomus）of AMF community were significantly correlated with moisture,OM,TN,TP and AP（P<0.05）.Random forest model further showed that p H,OM,TN,TP and AP were main factors affecting AMF diversity and community structure,with contributions of 4.92%-16.13%,3.68%-21.61%,7.78%-19.83%,4.81%-20.05%,6.92%-20.80%,respectively.2.The results of maize growth and mycorrhizal-induced gene expression of phosphorus transporter showed that:（1）At jointing stage of maize,manure treatments significantly promoted the growth of root system,including total root length（Len）,average diameter（Avg D）,surface area（SA）,volume（Vol）,root tip numbers（N Tips）,fork numbers（N Forks）,and cross numbers（N Cross）,as well as the biomass of maize（including plant height,dry weight of maize stem,root and grain）,chlorophyll relative content（SPAD）and the phosphorus utilization efficiency（P%）.（2）The infection rate of AMF on maize roots was significantly higher under CK,HM and HML treatments（28.00%,33.33%and 38.67%,respectively）than that under LM treatment（8.00%）.（3）The sample sequence detected in this study was aligned with the targeted（Zmpht1;6）and the phylogenetic tree of sample sequence compared with the reference genome（Maize,Rice,Arabidopsis thaliana）showed that sample sequence had the highest homology with Zmpth1;6,which was mycorrhizal-induced phosphorus transporter genes of maize.It indicated that sample sequence,a member of Pht1 family in maize,was mycorrhizal-induced gene of phosphorus transporter,named ZEAma;Pht1;6.The ZEAma;Pht1;6 had higher value of gene expression under CK,HM and HML treatments than under LM treatment,and its expression was positively correlated with the infection rate of AMF community（P<0.01）.3.The effects of AMF community on maize growth and P absorption were analyzed by statistical methods.（1）Random forest modeling determined that soil properties in the rhizosphere（OM,TP,AP,p H）,the diversity of AMF（Richness）in the maize roots and rhizosphere,maize aboveground（plant height,dry weight of maize stem and grain,SPAD value）and underground parameters（dry weight of root and root parameters）significantly contributed to P%.（2）Pearson correlation analysis revealed that soil properties of rhizosphere（OM,TP,AP,p H）,AMF diversity（Richness,Shannon,Chao1）and community structure（PC1）in maize roots and rhizosphere,maize aboveground（plant height,dry weight of maize stem and grain,SPAD value）and underground（dry weight of maize root,Vol,Avg D,SA）parameters were significantly associated with P%（P<0.05）.（3）Structural equation modeling（SEM）revealed that OM,TP and p H could indirectly affect the growth of aboveground and underground parts and P%by regulating the AMF diversity（Richness）in maize roots and rhizosphere.The total effects found that soil properties of rhizosphere（OM,TP,p H）,AMF diversity（Richness _R）in maize roots,and growth of aboveground and underground parts of maize significantly affected P%.AMF can regulate plant growth characteristics and soil P absorption process.This study explored the influence of AMF diversity and community structure on the maize growth and P absorption of maize roots,and revealed the biotransformation mechanism of AMF-plant interaction on the efficient utilization of P in red soil.It laid a scientific foundation for the application of AMF in red soil ecosystems.