| Arbuscular mycorrhizal are wildly distributed in the soil,which could form mutualistic symbiotic relationship with most terrestrial plants,playing an significant role in the natural ecosystem.AM fungi and its underground massive hyphal networks could not only improve the quality of rhizosphere soil,increase the tolerance to salt,drought,and heavy metals,but also could enhance the uptake of nutrients and water to promote plant growth.AMF have been extensive used in reconstruction of ecosystem,maintenance of ecological balance and agriculture and forestry production.The fluctuation belts of the Three Gorges Reservoir area have been annually fluctuated for three to six months,leading to serious soil and water loss,low vegetation coverage and ecological stability,so the ecological restoration is difficult.Mulberry(Morus alba L.)have strong ecological adaptation ability and ecological restoration potential,as well as high economic value.Mulberry trees colonized by AM fungi could have the capacity to improve the soil rhizosphere quality,promote the uptake and transportation of minerals and water,and enhance the tolerance to adversity situation.As the growth rhythm of mulberry is reversely directionally coupling with fluctuation of water level in the reservoir,mycorrhizal mulberry trees is considered as a potential ecological restoration strategy to deal with both the waterlogging in winter or early spring and the drought in summer in the fluctuation belts or other fragile ecosystem of the Three Gorges Reservoir area.To explore the ecological restoration potential of mycorrhizal mulberry in the Three Gorges Reservoir,this experiment was firstly conducted to study the survival and vegetative growth of mycorrhizal and non-mycorrhizal mulberry in the hydro-fluctuation belt of Yunyang,and explore the impact of arbuscular mycorrhizal on seedling survival.Then we studied the ecological adaptability and restoration of the mycorrhizal mulberry in fluctuating zone,and analied on the enrichment and distribution of six heavy metals in the root,stem and leaf of the mycorrhizal mulberry and non-mycorrhizal mulberry.We even studied the influence of cadmium on growth effect of mycorrhizal mulberry.The main findings are as follows:1 The ecological adaptability study on mycorrhizal mulberry in the hydro-fluctuation beltMycorrhizal mulberry saplings and mulberry saplings were planted in the Three Gorges Reservoir,mycorrhizal mulberry survival was significantly higher than the control after flooding.Mycorrhizal mulberry and control mulberry survival were 75.0%and 34.0%,and inoculated mulberry infection rate was 40.14%,and 14.92%rate of control mulberry.The survival rate reached at 100%after two years,indicating that arbuscular mycorrhizal fungi can improve the survival rate of early mulberry seedlings in a certain intensity and flooding stress;The study showed that the root sugar content,photosynthetic pigments,proline,soluble sugar and enzyme activity were significantly higher than those in the contrast.These showed that AM fungi significantly promoted the growth of mulberry saplings,and quicken the recovery of mulberry after water logging.2 The enrichment and translocation from soil to mulberryStudies have shown that the single factor pollution index of heavy metals Cd,As,Pb,Cu,Mn,Zn are 0.002,97.916,0.157,0.015,0.008,and the Nemerow comprehensive contamination index was 49.931,showing hydro-fluctuation belt exists serious cadmium pollution,belonging to a serious regional pollution.Though analyzing the on different heavy metal's content and distribution in the root,stem and leaf of mycorrhizal mulberry and the control mulberry,the results show that Arsenic,cadmium and copper manganese mainly accumulate in the root,AM fungi can improve the enrichment capacity of arsenic,cadmium and copper in mulberry,and significantly reduce the migration to the blade;Cadmium mainly accumulated in the roots,but lowly in the stems and leaves;Plumbum is mainly due to air pollution,so it mainly accumulates in the leaves,almost not affected by AMF inoculation;Zinc,manganese and copper in the root stems and leaves have a certain content.3 The exploration on mechanism of mycorrhizal mulberry to heavy metal cadmiumThe consistent mulberry sapling were selected to grow as test materisls,with four diferent treats,to study the influence of AM on mulberry sapling for the absorption of mineral elements under cadmium stress.The results showed that:Cd inhibited the growth of mulberry,but AM inoculation promoted the absorption of N?K;Cd inhibited the absorption of N,but promote the absorption of Ca and Mg.AM reduced the absorption of Ca for the root of mulberry.AM fungi may alleviate the damage of mulberry sapling root under Cd treat,through the immobilization reacting with Cd.4 The resistance mechanism to heavy metal of mycorrhizal mulberryPot experiment was carried in foam box with mulberry saplings inoculated by AMF,with four levels of mycelial growth chambers:0,5,20,40 mg/kg,to study the effects of cadmium on the growth of arbuscular mycorrhizal fungi(Gigaspora rosea Nicol&Schenck).The results showed that the cadmium concentration have an impact on the mycelial growth,the higher the concentration,the lower the mycelium biomass,indirectly affecting the absorption of N,K,Ca,Mg.Mulberry saplings absorb Cd through mycorrhizal hyphae,AMF has certain stress reaction on Cd.Under the low concentration of cadmium treatment,Cd significantly increased the growth of fungal hyphae,but with the increase of Cd concentration,the proliferation of fungi to Cd gradually reduced.Low cadmium concentration promotes plant growth,but mulberry saplings appears yellow leaves,wilting symptoms when Cd concentration grows;When Cd concentration is 5%,migration rate is 8.81%,and mobility is highest in the mulberry.Cd increase the Ca content in the aboveground parts of mycorrhizal mulberry,but reduce the content of K?Mg. |
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