Distribution Of Arbuscular Mycorrhizal Fungi In Pear Orchards And Their Effects On Growth Of Pyrus Betulaefolia

Arbuscular mycorrhizal fungi(AMF)are widely found in natural ecosystems,and form symbiotic relationships with plant roots.Many studies have shown that AMF can promote the growth of most plants,improve plant water metabolism and nutrient absorption,protect plant roots,and increase yield.The rhizosphere of plants is extremely complex.Besides AMF,there are many other microorganisms,such as plant growth-promoting rhizobacteria(PGPR).It has been reported that arbuscular mycorrhizal fungi can also interact with PGPR,and the coinoculation usually exhibit synergistic effects.One reason is that PGPR affects fungal spore germination,colonization rate and mycelial growth.Nowadays,pear is one of the most economically important fruit crops in China,which contribute to increase of agricultural efficiency,farmers’ income and the construction of new socialist countryside.Pear is a mycorrhizal plant,but AMF resources in pear rhizosphere soils have not been fully studied,and the effect and mechanism of promoting pear tree growth are not very clear,which limits the application of mycorrhizal technology in pear industry.In this paper,high-throughput sequencing technology was used to study the distribution,diversity and influencing factors of AMF in 9 pear gardens in Jiangsu Province,China.The effects and mechanisms of inoculations with AMF and PGPR alone or incombined on the growth of pear seedlings were clarified by using existing AMF strains and PGPR.The main research results are as follows:1.Using high-throughput sequencing technology,195,385 sequences from 54 samples from 9 pear gardens were obtained.After comparison in SILVA and MAAGJAM database,our data showed that a total of 108 OTUs were identified,with the majority belonging to Glomus(>90%).Non-metric multidimensional scaling(NMDS)plots and PERMANOVA based on the Bray-Curtis distance showed a clear separation of soil samples,suggesting significant dissimilarities of the AMF communities among the nine sampling sites.Distance-decay relationship(DDR)curves revealed that both geographical distance and soil properties affect AMF community composition.Canonical correspondence analysis(CCA)and Mantel tests were used to examine the significance of environmental factors in more detail and found that edaphic factors(soil pH,available phosphorus(AP),available potassium(AK),Cu,Zn and Al)and geographical distance correlated with the AMF community composition.Partial CCA demonstrated that soil factors exerted the primary influence on the assembly of the AMF communities in pear orchard soil,while geographical distance was less influential,which was supported by a partial Mantel analysis.pH,Cu and AP were the most significant soil factors that affected AMF communities.Overall,we concluded that soil chemical properties were primary parameters that affected AMF communities,especially in small scales,and changes of soil properties,such as moderate fertilization and avoiding excessive heavy metals may preserve diverse AMF communities in agricultural soils.2.Soil samples were collected from Hushu and Baima pear orchards and pot experiments were carried out.Six different treatments were set up:no inoculation(CK)or single inoculation with bacterium(Rhizobium sp.W33),Glomus etunicatum(G.e)and Funneliformis caledonium(F.c),double inoculation with G.e+W33 and double inoculation with F.c +W33.The effects of different treatments on plant growth,AMF infection rate,infection intensity,plant nitrogen,phosphorus and potassium content and soil nutrient content were studied.The results showed that all treatments significantly promoted the growth of pear seedlings.Among them,compared with CK,coinoculation with F.c+W33 significantly increased plant height,dry weight of root and shoot biomass by 18.08%,80.60%,55.24%and 92.16%,respectively,and showed 92.8%of the infection rate.In Baima soil,G.e treatment showed the most significant effects on plant growth and nutrient uptake.Coinoculation F.c+W33 showed the highest values of the colonization rate and intensity by 92.6%and 60.64%,respectively.Compared with CK,F.c+W33 treatment increased plant height and dry weight of shoot and root by 10.73%,12%and 21%,respectively.Compared with G.e+W33 treatment,G.e treatment increased root length of pear seedlings by 51.52%.F.c+W33 could significantly(P<0.05)increase the levels of neutral phosphatase,urease and sucrase in both tested soils,increasing by 225.74%,154.72%and 259.65%in the Hushu soil,respectively,and by 145.56%,185.42%and 189.15%,respectively in Baima soil.Above in all,we highlighted that W33 and F.c could effectively improve the growth of pear seedlings,and an ideal synergistic effect was found.