Mechanisms Underlying The Promotion Of Arbuscular Mycorrhiza Fungi To Water Absorption Of Mulberry Roots From Rocky Desertification Habitats

Soil water deficit is the main obstacle factor of plant reconstruction in rocky desertification area of southwest China.Mycorrhizal mulberry?Morus alba L.?could cope with the main ecological barriers during the seasonal drought in the rocky desertification area.So,the mulberry of typical rocky desertification area in Guizhou Province was determined as a research subject.Therefore,the study would mainly solve two key scientific problems:one was to clarify the soil water absorption capacity of mycorrhizal mulberry change with seasonal variation in rocky desertification area,and to reveal the water use strategy;The second was to understand the composition and diversity of AM Fungi Community inside and outside mulberry roots in rocky desertification areas,to demonstrate that dominant fungi can promote water uptake by mulberry roots,and to reveal the mechanism of AM fungi promoting water uptake.Firstly,hydrogen and oxygen stable isotope technique was used to analyzed soil water use ratios and ways of mulberry roots grown at different depths in different karst habitats,and the most active and non-active areas of water absorption of mulberry roots was probed.Furthermore,species diversity in roots and soils were assessed as well as dominant species selected through identifying arbuscular mycorrhizal fungi inside and outside mubelerry roots by the aid of morphology method and modern molecular biology method-454 pyro sequencing in the most active and non-active areas of water absorption.Finally,Pot experiments was tested the effect of inoculation in promoting function of the dominant species for mulberry water absorption.Overall,the study provided the theories for water effective use of mulberry,ecological adaptation of mulberry and ecological restoration in the rocky desertification area.The main results and conclusions are as follows:1.Water use strategy of mulberry in rocky desertification area?D and?¹⁸O in rainwater were more enrichment in the early stage of mulberry growth?spring,from April to June?than in the late growth stages?autumn,from September to November?.With the seasonal variation of rainfall,the?D and?¹⁸O of soil water showed a downward trend.They,which were affected by rainfall and evaporation,also showed the vertical variation.In mulberry stems,?D and?¹⁸O in water were located under the atmospheric precipitation line,and the changes of them were similar to the soil water.It indicated that the water required by mulberry growth mainly came from soil water.Based on the analysis of simple correlation and multivariate linear mixed model,the strategies of absorbing and using soil water by mulberry were different in spring and autumn.In spring,mulberry mainly used soil water from 10-30 cm to 50 to 60 cm.In autumn,it mainly used soil water from 50-60 cm to 0-10 cm.2.Community characteristics of AM fungi in mulberry roots and soil in rocky desertification areaCommunity characteristics of AM fungi were analyzed by 454-pyrophosphate sequencing technique.83 VT species were included in 7 family or 8 genera in mulberry roots and soils.The diversity of AM fungi in mulberry root system after cropland returned to forests for 10 years was higher than that for 1 years.Shannon-wiener index decreased with soil depth.There was a certain correlation between the soil property and the AM fungi diversity.The diversity of AM fungi showed a significant variation due to the effects of interaction among soil property,recovery time and climate.The Glomus was dominant genera in AM fungi communities for mulberry roots and soils.There were two molecular species,that is,both VTX00067?G.mossease=F.mosseae?and VTX00105?G.intraradices=R.intraradices?occured in all samples.3.The effect of AM fungi on water absorption and utilization in mulberry under drought stressThe lack of soil moisture had a certain restriction to mulberry growth.However,AM fungi significantly promoted mulberry growth and increased the water content of mulberry roots,stems and leaves.Under normal water supply and water stress conditions,?¹⁸O contents of organic were significantly reduced in the leaves of mulberry inoculated with AM fungi.There was a significant correlation between?¹⁸O of organic and soil?or mulberry root or stem?moisture.Therefore,?¹⁸O of organic provided an integrated measure of the effect of AM fungi on host plant water relations over the period when the plant tissue was formed.At the same time,AM fungi significantly improved water use efficiency of mulberry.In general,our study confirmed that AM fungi promoted mulberry water uptake and utilization.Meanwhile,the effect of F.mosseae was better than R.intraradices.4.Mechanism of the promotion of AM fungi to water absorption and utilization of mulberry?improving soil aggregates.By contrast analysis,AM fungi significantly increased the percentage content of large aggregates,mean weight diameter?MWD?and geometric mean diameter?GMD?in soils.It indicated that AM fungi improved soil structure and improved the stability of aggregates.Through the analysis of correlation analysis and structural equation model,the water content of mulberry roots was promoted by the improvement of the aggregates.These results showed that the soil porosity and water infiltration capacity were strengthened by AM fungi,leading to more soil water for mulberry roots absorption.?regulating mulberry nutrient status.Mulberry growth was restricted by N and P.However,AM fungi significantly improved soil nutrient availability,and promoted mulberry to uptake more N and P.Therefore,AM fungi alleviated mulberry nutrient limitation,and regulated the distribution of C,N,P and K in soil-mulberry system.Meanwhile,AM fungi enhanced water use efficiency?WUE?through changing the leaf nutrient and stoichiometric ratio in mulberry leaves under the natural drought situation.?regulating the expression of AQPs in mulberry.There were seven aquaporin genes?including 3PIPs and 4 TIPs?to directly control the expression of the protein in the main roots,lateral roots,fibrous roots and leaves of mulberry inoculated by AM fungi.We found that the expressions of AQPs in mulberry inoculated with AM fungi were different under two water conditions.AM fungi could promote mulberry water uptake and utilization by regulating the expressions of PIPs and TIPs in roots and leaves.In a word,the strategies of absorbing and utilizing soil moisture of mulberry trees are different in different growing seasons,which provides an important theoretical basis for sustainable management of rocky desertification mulberry orchards.The variation of community composition and diversity of AM fungi inside and outside mulberry roots is of great significance for understanding AM fungi promoting mulberry growth,improving soil environment and improving the efficiency of mulberry restoration in desertification areas.The dominant strains of AM fungi obtained by preliminary screening of mulberry inoculation showed that AM fungi could promote water uptake and utilization of mulberry by improving soil aggregates,regulating nutrients and regulating the expression of water channel proteins of mulberry trees.The research results provided important theoretical support and new ways for vegetation restoration of ecosystems lacking soil moisture in rocky desertification areas.