| Drought is one of the most serious natural disasters in the world.China is located in a typical monsoon climate region,and the impact of drought disasters is particularly prominent,with Inner Mongolia Autonomous Region being one of the provinces most severely affected by drought.Drought is the main environmental stress that restricts plant growth and development.It can interfere with plant physiological and biochemical processes,thereby inhibiting plant growth and development.Plant rhizosphere and root surface soil microorganisms are the most active components in soil ecosystems,responsible for the cycling of nutrients such as carbon,nitrogen,phosphorus,and sulfur in the soil.They have a direct impact on plant growth and development,and play a crucial role in improving soil quality and maintaining plant health.Amygdalus mongolica is an excellent tree species for desertification prevention and soil erosion reduction,with strong drought tolerance.Its root related microorganisms may play an important role,but its community structure characteristics are rarely studied.This study used a potted water control method and set drought stress conditions for potted experiments.Water was poured every 15 and 30 days as the control group(CK)and drought stress group(MB),respectively,for a total of 120 days of cultivation.The high-throughput sequencing technology was used to analyze the microbial community structure in the rhizosphere and root surface of its seedlings,in order to reveal the impact of drought stress on the diversity of microbial community structure related to the roots of Amygdalus mongolica,and to verify the impact of strains on the growth and development of Amygdalus mongolica through the isolation,identification,functional determination and reverse connection experiments of microorganisms in the rhizosphere and root surface.The main results and conclusions of the study are as follows:1.Plant growth traits under drought stress: Drought stress limits the growth and development of Mongolian almonds.Under drought stress,the plant height and root length significantly decrease by 13.16% and 11.82%,respectively(P<0.05);The number of leaves and lateral roots significantly decreased by 45.59% and 24.64%,respectively(P<0.05);The dry weight of the aboveground and underground parts decreased by 22.85%and 20.93% respectively,with a significant difference(P<0.05).2.Diversity analysis: The Chao1 index of rhizosphere and root surface bacteria in seedlings significantly decreased by 10.63% and 22.97%,respectively(P<0.05);The Shannon index of rhizosphere bacteria increased by 1.08%,while the Shannon index of root surface bacteria decreased by 4.54%,with a significant difference(P<0.05).Under drought stress,the Chao1 index of rhizosphere fungi in seedlings increased by 35.78%,with a significant difference(P<0.05),while the Chao1 index of root surface significantly decreased by 7.46%,and the Shannon index of rhizosphere and root surface significantly decreased by 13.82% and 18.58%,respectively(P<0.05).3.Microbial community structure: The top five phyla of bacteria abundance in rhizosphere soil of CK and MB treatments were Proteobacteria(49.13%～51.16%),Actinobacteria(19.74%～24.55%),Bacteroides(5.94%～7.86%),Planctomycetes(4.58%～6.78%),and Verrucomicrobia(1.83%～2.26%).The relative abundance of Actinomycetes and Bacteroides in rhizosphere soil under MB treatment was higher than that under CK treatment,and the relative abundance of Planctomycetes under CK treatment was higher than that under MB treatment;The relative abundance of Bacteroidetes in rhizosphere soil under MB treatment was significantly higher than that under CK treatment.The genera with relative abundance greater than 5% in the rhizosphere soil treated with CK and MB were Frankia(12.78%～14.99%)and Mesorhizobium(5.41%～5.86%),respectively.The relative abundance of Mesorhizobium,Devosia,Microbacterium,Pseudorhizobium,Streptomyces,Lysobacter,Ohtaekwangia,and Agromyces in rhizosphere bacteria under MB treatment was significantly higher than that under CK treatment;The relative abundance of Pseudomonas,Steroid bacteria,Shinella and Haloferula in CK treatment was significantly higher than that in MB treatment.In the composition of bacterial community on the root surface,CK treatment is consistent with the top 5 phyla rhizosphere of bacteria in the root surface soil of MB treatment,which are Proteobacteria(62.81%～64.30%),Actinobacteria(14.69%～16.99%),Bacteroidetes(4.51%～8.00%),Planctomycetes(3.05%～4.05%),and Verrucomicrobia(1.21%～1.80%).The relative abundance of Bacteroidetes under MB treatment was significantly higher than that under CK treatment.The genus with a relative abundance greater than 5% is Frankia(11.34%～11.67%).The relative abundance of Devosia,Pseudorhizobia,and Neorhizobia under MB treatment was higher than that under CK treatment,while the relative abundance of Steroid and Shinella under CK treatment was higher than that under MB treatment.The top five phyla of fungi abundance in rhizosphere and root surface soil of CK and MB treatments were: Ascomycota(82.21%～93.79%),Mucormycota(1.87%～10.39%),Basidiomycota(3.93%～5.29%),Chytridiomycota(0.16%～1.18%),Zoopagomycota(0.01%).The relative abundance of Ascomycota under MB treatment was significantly higher than that under CK treatment,while the relative abundance of Mucoromycota and Chytridiomycota under CK treatment was significantly higher than that under MB treatment.The genera with relative abundance greater than 5% of rhizosphere fungi treated with CK and MB were Frankia(20.54%～47.47%)and Ilyonectria(8.49%～13.72%),respectively.The relative abundance of Fusarium and Ilyonectria in rhizosphere fungi under MB treatment was significantly higher than that under CK treatment,but the relative abundance of Humicola,Chaetomium,Glomus and Mortierella under CK treatment was significantly higher than that under MB treatment.The top five phyla of fungi abundance in root surface soil of CK treatment and MB treatment were: Ascomycota(89.93%～94.29%),Mucormycota(0.85%～2.86%),Basidiomycota(4.69%～6.71%),Chytridiomycota(0.03%～0.16%),Blastocladiomycota(0.02%).The relative abundance of Basidiomycota and Mucor mycota under CK treatment was higher than that under MB treatment.The genera with relative abundance greater than 5% in the root surface soil fungi treated with CK and MB were Fusarium(31.23%～45.42%)and Ilyonectria(7.74%～15.68%),respectively.The relative abundance of Fusarium and Ilyonectria under MB treatment was significantly higher than that under CK treatment,while Humicola under CK treatment was higher than that under MB treatment.4.Isolation and identification of rhizosphere bacteria: A total of 56 bacterial and 3fungal strains were isolated from the rhizosphere soil samples of CK and MB seedlings.The 44 strains of bacteria isolated from CK belong to 22 genera,with Streptomyces accounting for the largest proportion(16%),Arthrobacter accounting for 14%,and Nocardioides accounting for 11%;The 12 bacterial strains isolated from MB belong to 10 genera,with Streptomyces and Bacillus accounting for the largest proportion,accounting for 17%,and Pseudorhizobium accounting for 8%.Three fungal strains were isolated and purified.The two strains isolated from CK treatment belong to the genus Penicillium,while the one strain isolated from MB belongs to Oidiodendron.Among them,16 genera of Nocardia,Rhizobia,Aeromicrobe,sphingosine box bacteria were isolated only in CK treatment;Pseudomonas,Fictibacilli,Mesorhizobium,Neobacilli,and Oidiodendron were only isolated in MB treatment.5.Result of growth promoting ability test for 16 strains of bacteria: 16 strains corresponding to the genus with increased relative abundance under drought stress were tested for growth promoting ability,which can grow rapidly on Ashby medium.There are14 strains with nitrogen fixation potential,accounting for 87.5%;There are 13 strains with the ability to dissolve calcium phosphate,accounting for 81.3%;There are 5 strains producing IAA,accounting for 31.3%.There are four strains with nitrogen fixation potential,calcium phosphate solubilization ability,and IAA production ability,namely BR001(Microbacterium genus),BR002(Microbacterium genus),BR065(Streptomyces genus),and BR125(Mesorhizobium genus).6.Analysis of the growth promoting effect of 3 strains of bacteria on Amygdalus mongolica seedlings: 16 strains were inoculated and verified,among which 3 strains showed significant growth promoting effects.BR125 had a significant promoting effect on plant height,root length,aboveground dry weight,and underground dry weight of Amygdalus mongolica seedlings;BR002 significantly promoted the elongation of seedling main roots and increased underground dry weight;BR069 has a significant promoting effect on the number of leaves and lateral roots of Mongolian almond seedlings.In summary,drought stress significantly inhibits the growth of Amygdalus mongolica and reduces the abundance of rhizosphere and root surface bacteria,resulting in an increase in rhizosphere bacterial evenness and a decrease in root surface bacterial evenness;At the same time,drought stress reduces the evenness of rhizosphere and root surface fungi,and also reduces the richness of root surface fungi,but the richness of rhizosphere fungi increases.In the community structure,the relative abundance of 8 genera such as Mesorhizobium in rhizosphere bacteria significantly increased;The relative abundance of four genera,including Pseudomonas,decreased significantly;At the same time,in the composition of root surface bacterial communities,the relative abundance of four genera,including Devosia,significantly increased,while the relative abundance of two genera,including Steroidbacter,significantly decreased.The relative abundance of Fusarium and other two genera in rhizosphere fungi significantly increased,but the relative abundance of Humicola and other four genera significantly decreased;In the composition of root surface fungal communities,the relative abundance of Fusarium and other two genera significantly increased,while the relative abundance of Humicola significantly decreased.Strains belonging to 28 genera,including Streptomyces and Penicillium,were isolated and cultured.Among them,strains belonging to Mesorhizobium,Microbacterium,and Streptomyces have varying degrees of promoting effects on the plant height,root length,lateral root number,aboveground dry weight,and underground dry weight of Mongolian almond seedlings,It may be an important microbial resource for alleviating drought stress in Amygdalus Mongolica. |
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