Effects Of AMF On The Growth Of Citrus Seedlings And Rhizosphere Soil Microenvironment Under Reduced Fertilization

Citrus is the world's largest fruit and the second largest fruit in China after apples.In production,fertilization is the key technology for citrus cultivation.However,the main citrus production areas in China generally have problems such as fertilization and irrational fertilization structure.For example,excessive application of chemical fertilizers may result in poor soil structure,water pollution,and improper management of citrus cultivation.Therefore,in terms of relative policies and agricultural production requirements,producers urgently need to find a new way.This new method can not only reduce the unreasonable application of fertilizer,but also change the way of fertilizer utilization and increase the utilization rate of fertilizer.Less root plants such as citrus can acquire more nutrients through symbiosis with Arbuscular mycorrhizal fungi(AMF)to adapt to changes in the ecological environment.Using the symbiotic relationship between citrus and AMF,combining AMF with reduced fertilization may not only effectively improve soil compaction,but may also improve soil water supply and fertilization capacity.Therefore,this study is of great significance for improving the excessive fertilization and efficient fertilizer use in current citrus production.In this experiment,detoxification seedlings of citrus [(Citrus unshiu×C.sinensis)×C.reticulate/ C.junos] with one-year old were used as the test material,and the Claroideoglomus etunicatum(C.e)and the Funneliformis mosseae(F.m)were used as the microbial agents.Two-factor(inoculation x fertilization)randomized block design was used in this study.For the part of inoculation,three treatments were conducted as follows:(1)non-inoculation(NAM),(2)inoculation of AMF(C.e),(3)inoculation of AMF(F.m).Additionally,each treatment was set at three levels according to the amount of fertilization: customary fertilization(CK),the reduction of 30% fertilization(A)and the reduction of 60% fertilization(B)compared to CK.The experimental spots were randomly arranged,5 plants per plot,with 5 replicates,totaling 225 stains.In this paper,we mainly studied the vegetative growth,physiological metabolism,rhizosphere soil properties and microbial community structure of citrus seedlings.And then we comprehensively analyzed the effects of AMF on citrus seedling growth and soil microenvironment under reduced fertilization.The main results are as follows:1.Under the three fertilization levels,the roots of citrus seedlings could form a good symbiotic relationship with AMF(C.e and F.m),and the infection rate was inversely proportional to the amount of fertilizer applied.The reduction of 30% fertilization(A)did not affect the growth of citrus seedlings,but the reduction of 60% fertilization(B)significantly inhibited the growth.Inoculation with AMF(C.e and F.m)promoted the growth of citrus seedlings,root development as well as nitrogen,phosphorus and potassium absorption to varying degrees.The reduction of 30% fertilization(A)was best for the growth of citrus seedlings,but the reduction of 60% fertilization(B)had the highest inoculation effect of citrus seedings,and F.m was superior to C.e.2.Under the three fertilization levels,the root activity of citrus seedlings increased firstly and then decreased with the increase of fertilization amount.The reduction of 30% fertilization(A)did not affect the physiological metabolism of citrus,but the reduction of 60% fertilization(B)significantly reduced seedling leaf area,chlorophyll content,and gas exchange parameters,soluble sugar and soluble protein content,glutamine synthetas(GS),nitrate reductase(NR)and acid phosphatase(ACP)activities.Inoculation with AMF(C.e and F.m)significantly promoted the physiological metabolic of citrus seedlings,and these effects enhanced with the reduction of fertilization amount.3.Under the condition of non-inoculation(NAM)treatment,the reduction of 30% fertilization(A)would not affect soil physical and chemical properties,enzyme activity,microflora and glomalin-related soil protein(GRSP)content,while the reduction of 60% fertilization(B)significantly reduced soil physical and chemical properties(organic matter,alkaline nitrogen,available phosphorus,available potassium),glomalin-related soil protein(GRSP)content,and soil enzyme activity(alkaline phosphatase,urease,invertase,cellulase,protease and catalase).Inoculation with AMF(C.e and F.m)can significantly improve the physical and chemical properties of rhizosphere soil and increasing soil enzyme activity.The reduction of 60% fertilization(B)soil index is the best,and the low fertilization level AMF(C.e and F.m)is more significant.4.The dominant bacterial groups in the rhizosphere soil of citrus seedlings were Proteobacteria,Acidophilus and Firmicutes.The abundance of dominant bacteria was significantly different under the three fertilization levels,with the highest bacterial abundance reduced by 30%.The relative abundance of soil eutrophic bacteria was obviously increased after the inoculation of AMF,which had a convergent effect on the value of bacterial community diversity.Ascomycota is the main fungal group in the rhizosphere of citrus seedlings.There is no significant difference in the abundance of Ascomycetes among the three fertilization levels,but customary fertilization(CK)leaded to an increase in the proportion of some potentially pathogenic fungi.Inoculation with AMF(C.e and F.m)could significantly reduce the abundance of pathogenic fungi in citrus rhizosphere soil and promote the growth of beneficial soil fungi.