Effects Of Arbuscular Mycorrhizal Fungi And Nitrogen Addition On Below-ground Processes And The Growth Of Rice Genotypes With Different Root Morphologies

Arbuscular mycorrhizal fungi（AMF）are a kind of plant-growth-promoting fungus that can mutualistic associations with roots of most land plants.Host plants provide carbon sources for the AMF.As a feedback,AMF can absorb mineral nutrients and water from the soil and transfer them to the plant.Numerous studies have shown that the symbiotic relationship between plants and AMF is affected by the plant root morphology.However,it is not clear how the interaction between plants with different root morphologies and AMF influences soil under-ground processes and thus generates feedback to plants.In this study,we selected four rice mutants with different root morphologies（root hairless:rhl1;lateral rootless:iaa11;Kasalath adventitious rootless:arl1 and Wild type:Kas）as the objects to answer the following questions:（1）Effect of AMF on the root morphology of rice with different genotypes;（2）Effects of AMF and nitrogen addition on nitrogen（N）uptake of rice mutants with different root morphologies;（3）Composition of rhizosphere microbial communities among different rice mutants.The main results of the study are as follows:1.Effect of AMF on the root morphology of four rice mutantsWe used pot experiment to explore the effect of AMF on the root morphology of four rice mutants.The results showed that there were significant differences in root morphology among the four rice mutants.The ranking for the number of rice adventitious roots was Kas>iaa11>rhl1>arl1（P<0.05）,with the root tips of iaa11and rhl1 accounting for 8%and 52%of that of Kas respectively.The mycorrhizal dependence of arl1,Kas,rhl1 and iaa11 was 50%,57%,57%and 68%.The average effect size of AMF on arl1,Kas,rhl1 and iaa11 and arl1 specific root length were-10%,-2%,15%and-22%,and the average effect size of AMF on arl1,Kas,rhl1,iaa11 and arl1 root tips were 67%,46%,50%and 88%.These results indicated that the effect of AMF treatment on the root morphology of different rice mutants were different.2.Effects of AMF and N addition on N uptake of rice mutants with different root morphologiesWe used ¹⁵N isotope labeling method to explore the effects of arbuscular mycorrhizal fungi and N treatment（low N:20 ppm;high N:100 ppm）on N uptake of rice mutants with different root morphologies.The results showed that the leaf N concentrations of rhl1,Kas,iaa11 and arl1 under the high N treatment were increased by 60%,72%,128%and 118%,respectively.This result indicated that the addition of N significantly promoted rice N uptake with the most significant effect occurring in iaa11 and arl1.We used effect size as the index to measure ¹⁵N concentration shift in rice shoot under different AMF treatment.The average effect sizes of AMF on rhl1,Kas,iaa11 and arl1 were 17%,31%,42%and 51%under the low N level,indicating that root morphology can alter the effect of AMF on plant N uptake.Compared to the low N treatment,high N significantly downregulated the AMF effect on N uptake,indicating that the N addition may mediate the complementary effect of AMF and root morphology on plant nutrient uptake.3.Composition of rhizosphere microbial community among four rice mutants with different root morphologiesRhizosphere microorganisms play an important role in regulating soil nutrient transformation and plant nutrient uptake.We used 16S r RNA sequencing to analyze the rhizosphere microbial community structure among four rice mutants with different root morphologies.The results showed that the average OTU numbers of rhl1,Kas,iaa11 and arl1 were 2947,2879,2908 and 3737.The average Shannon index of rhl1,Kas,iaa11 and arl1 were 7.9,7.7,7.9 and 8.3.This results indicated that the alpha diversity of arl1 was higher than other three rice.In addition,there were significant differences between rhl1 and iaa11,iaa11 and arl1,rhl1 and arl1 as adonis,anosim and MRPP methond shown.These results indicated that there were differences in the rhizosphere microbial community structure among four rice mutant,which might affect the processes of rhizosphere microbial regulation.In conclusion,our study indicated how AMF affect plants with different root morphologies,how AMF treatment and N addition affects plant nutrient absorption and the differences in rhizosphere microbial community structure of plants with different root morphologies.Our research provides some experimental supports for the functional complementarity between AMF and plants.In the future,we will further explore the mechanism on interaction among rhizosphere microorganisms,AMF and plants nutrient utilization.