| Ulmus pumila L,with its biological characteristics of cold tolerance,drought tolerance and salinity tolerance,it is one of the main tree species for afforestation in saline and alkali land in sand wasteland.Drought makes it difficult for plant roots to absorb water,causing plant growth to regress.Arbuscular Mycorrhizal fungus(AM)fungi can form a reciprocal community with the root system of host plants,improve the growth and development of host plants,and have important significance for the improvement of terrestrial ecosystem functions.There have been many studies that demonstrate that AM fungi can improve the adverse effects of drought on plants.At present,the process and mechanism of AM fungus adaptation to drought stress of Ulmus pumila L are not clear.Based on this,Funneliformis mosseae(F.m),Claroideoglomus etunicatum(C.e)and Rhizophagus intraradices(R.i)and its mixed strains(F.C.R)were used as experimental agents.Potted elm seedlings were used as experimental materials.Three water gradients were set by means of industrial water control: normal water supply,moderate drought and severe drought.To study the effects of four AM fungi on the growth and drought resistance of Ulmus pumila L seedlings under drought stress,the specific research results of this experiment are as follows:(1)Under different water conditions,F.m.,C.e.,R.i.and F.C.R could infect the roots of Ulmus pumila L seedlings to different degrees,forming a good symbiotic relationship.Although the mycorrhizal infection rate decreased with the increase of drought,it remained between 45.66%-61.39% under severe drought.At the same time,mycorrhizal dependence showed an upward trend with the decrease of water supply,and the dependence of Ulmus pumila L seedlings on mycorrhizal was highest under severe drought stress.The mycorrhizal dependence of four AM fungi on seedlings under severe drought conditions ranged from high to low: mixed agent(199.19%)> Claroideoglomus etunicatum(125.72%)> Rhizophagus intraradices(90.79%)> Funneliformis mosseae(84.86%).(2)Under different water conditions,compared with uninoculated control plants,F.m,C.e,R.i and F.C.R increased plant height,biomass and root-shoot ratio of Ulmus pumila L seedlings to different degrees.AM fungus also promoted the growth and development of Ulmus pumila L seedling root system,the root system vitality of the inoculation treatment group,the number of new roots at the first level and the root length of the longest side were significantly higher than those in the control group,AND AM fungi improved the root morphology,promoted the root system to absorb more water and nutrients,and improved the drought resistance of Ulmus pumila L seedlings.(3)Under drought stress,the relative water content(RWC)of mycorrhizal Ulmus pumila L seedlings was higher than that of control seedlings,and the water saturation deficit(WSD)was significantly lower than that of control.and F.m,C.e,R.i,and F.C.R all promoted the accumulation of soluble protein and soluble sugar in elm seedling leaves,reduced proline(Pro)and malondialdehyde(MDA)content,and increased Ulmus pumila L seedling leaf antioxidant enzyme activity(SOD,POD,CAT).Based on the above indicator analysis,F.m,C.e,R.i and F.C.R can improve the drought resistance of Ulmus pumila L seedlings by improving the water retention,osmotic regulation and antioxidant capacity of Ulmus pumila L seedlings.(4)Drought stress forces Ulmus pumila L seedlings to significantly limit photosynthesis.In drought conditions,the net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs)and chlorophyll(Chl)content of Ulmus pumila L seedlings were increased by inoculation with F.m,C.e,R.i.and F.C.R.The intercellular CO2 concentration(Ci)was decreased.With the increasing degree of drought,the benefit of AM fungi became more significant.(5)There are differences in the drought resistance of different species of AM fungi to Ulmus pumila L seedlings.In this experiment,the cumulative value of the membership function value of Ulmus pumila L seedlings was arranged from largest to smallest as mixed agent(10.578)> Claroideoglomus etunicatum(9.559)> Rhizophagus intraradices(9.196)> Funneliformis mosseae(8.541)>control without inoculation(6.595).It shows that AM fungi can improve the drought resistance of Ulmus pumila L seedlings,and the mixed bacterial agent has strong drought resistance. |
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