| Pinus sylvestris var.mongolica,as an important species for protection forests,has been widely introduced in northern China,and played an important role in wind and sand fixation,soil and water conservation,and ecological restoration.However,large-scale declines and deaths of P.sylvestris plantations have occurred,which are mainly characterized with sluggish growth,withered leaves and regeneration barriers.This severely restricted the ecological,economic and social benefits of P.sylvestris plantations.Ectomycorrhizal fungi(EMF)can form mutually beneficial symbiotes with a variety of higher plants.Ectomycorrhizas have important ecological functions such as improving the water absorption efficiency of plants and enhancing plant stress resistance,and they are of great significance for maintaining the diversity,functionality and stability of forest ecosystems.P.sylvestris is an ectomycorrhiza-dependent species,it is inseparable from the mutually beneficial cooperation of EMF along all growth stages.Therefore,the studies on the ectomycorrhizal fungal diversity and their ecological functions on P.sylvestris are meaningful for understanding the decline and death of P.sylvestris deeply.In this study,the natural forest was used as control group,the P.sylvestris plantations of different age groups(half-mature,nearly-mature,and mature)in the Hulunbuir,Mu Us and Horqin Sandy land were studied for the differences in ectomycorrhizal fungal diversity and community structures and their main driving factors by using molecular biology methods.The key fungi were selected by analyzing the molecular ecological network of the EMF community and the abundance quantitative analysis.The growth adaptability of the experimantal EMF to carbon sources,nitrogen sources,moisture,p H and temperature conditions was explored with pure culture experiments.Inoculating the P.sylvestris seedlings with the experimental EMF to study growth of ectomycorrhizal-seedlings.The growth and physiological metabolism of ectomycorrhizal-seedlings under drought stress were recorded and used to evaluate the drought resistance of ectomycorrhizal-seedlings by fuzzy mathematical membership function analysis and principal component analysis.The main results and conclusions are as follows:(1)The ectomycorrhizal fungi of P.sylvestris were abundant and have obvious regional differences.The ectomycorrhizal fungal diversities of plantations were significantly lower than that of natural forest.The ectomycorrhizal fungal diversity of the plantations in the Mu Us Sandy Land was the highest,following by that of the Horqin Sandy Land.That of the Hulunbeier Sandy Land was the lowest.In the Hulunbuir Sandy Land,the EMF belonged to 2 phyla,22 families,and 27 genera,and Suillus was the dominant genus.In the Mu Us Sandy Land,EMF belonged to 2 phyla,15 families and 18 genera,Rhizopogon was the dominant genus.In the Horqin Sandy Land,EMF belonged to 2 phyla,14 families,and 17 genera,and Wilcoxina was the dominant genus.Differences in ectomycorrhizal fungi community were mainly affected by the spread limitation caused by geographical distance and environmental select brought by the differences in climatic and soil factors.The average sunshine time,soil organic carbon and total nitrogen content were significantly related to the ectomycorrhizal fungal diversity(P<0.01).The ectomycorrhizal fungal community structures were significantly related to temperature and mean precipitation(P<0.01).At the local scale,there were significant differences in the factors that drived and regulated the ectomycorrhizal fungal community during the stand ageing.In addition to the soil organic carbon content,the community structure of the EMF was also significantly related to total nitrogen and total phosphorus content(the Hulunbuir Sandy Land),total phosphorus content(the Mu Us Sandy Land),the soil p H and total soil porosity(the Horqin Sandy Land)(P<0.01).(2)Suillus leteus(Sl),Suillus granulatus(Sg),and Tricholoma sp(Ts)were the fungi for subsequent experiments.In the experiment of exploring the effects of environmental factors on the ectomycorrhizal fungal growth,the three EMF had no significant differences in the preference to carbon source for glucose,sucrose,and starch.NH4 Cl was the optimal nitrogen source for them,and urea nitrogen cannot be used at all.The three EMF had drought tolerance,but their growth was completely inhibited with the water potential of-6.95 Mpa.All the three EMF preferred weakly acidic environment,and Ts had better adaptability to alkaline environment.The optimum growth temperature of the three EMF were 25-35°C,but there were certain differences among the species.Temperatures below 15 °C would significantly inhibit their growth.(3)All the three EMF can form ectomycorrhizas with P.sylvestris seedlings.Ectomycorrhizas had positive effect on plant growth.Ectomycorrhizal-seedlings of the three treatment groups(Sl,Sg,and Ts)showed different growth condition.Seedlings in Sl treatment had the best performance on the radial growth,biomass accumulation,and root growth regulation and the increase of photosynthetic characteristics.The growth promotion effect of Sg treatment showed consistency with Sl,the effect of Sg was slightly lower than Sl but not significantly(P>0.05).Ts treatment had the best performance on high growth and chlorophyll concentration,but negative effect on root activity was showed in the Ts treatment.(4)Ectomycorrhizas can improve the drought resistance of P.sylvestris seedlings.We set the drought stress gradients as the 80%,40%,20%,10%,5% of the saturated soil moisture content(marked as slight,milt,moderate,severe and extremely severe).There was no significant difference in the degree of damage to the three groups of ectomycorrhizal-seedlings among all the drought gradients(P>0.05).Plants resisted drought stress by the composited effect of promoting growth,osmotic adjustment,and producing antioxidant enzymes to eliminate active oxygen damage.The ectomycorrhizal-seedlings of Sl treatment mainly eliminated the damage of reactive oxygen by increasing antioxidant enzyme activity;in addition to improving the antioxidant enzyme effect,the ectomycorrhizal-seedlings of Sg treatment mainly adjusted the osmotic potential by accumulating proline to resist the drought stress;the ectomycorrhizal-seedlings of Ts treatment preferred to promote seedling growth and increase the photosynthesis efficiency to resist the drought stress.Under slight and mild drought stress,the Sl treatment group had the strongest drought resistance;under moderate drought stress,the Ts treatment group had the strongest drought resistance;under severe drought stress,the Ts and Sg treatment groups had the highest drought resistance;under severe drought stress,the Sl treatment group had the strongest drought resistance.Our study gave more evidence on the differences and driving factors of ectomycorrhizal fungal communities in different age groups with various environmental conditions and elucidated the effect of ectomycorrhizal fungi on P.sylvestris seedlings.The results provided strong theoretical support for the construction and sustainable management of P.sylvestris plantation in sandy lands.And it is significant for desertification control in the aeolian sandy areas of northern China. |
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