Effects Of Arbuscular Mycorrhizal Fungi Inoculation On Dryland Wheat Productivity And Soil Quality And Their Mechanisms

Spring wheat is widely planted in the semi–arid region of Loess Plateau,northwest China.However,regional precipitation is usually low and variable at the critical stage of water demand,when wheat growth requires much water for seed germination and plant development.Therefore,it became a core issue to make full use of the soil deep water for wheat yield and water use.In this region,application of plastic film mulching(PFM)has improved yield and water use efficiency to a certain extent,yet soil quality proved to be decreasing,and there was still a huge space to enhance water productivity.In this case,to explore environment–friendly soil and water management technology is urgently needed.Arbuscular mycorrhizal fungal(AMF)is a kind of soil microorganism,which symbiosis with plant use plant photosynthetic products and helps plant absorb nitrogen,phosphorus and other mineral elements,and enhance plant respond to biotic or abiotic stresses.However,can AMF play a similar role in promoting stress resistance in dryland spring wheat? Can AMF inoculation under plastic film mulching play much better effects? Whether AMF noculation under plastic film mulching have a positive effect on soil quality and crop yield,and what is their physiological and ecological mechanism? The answer to these questions requires systematic experiment to verify.In this study,three AM fungal species,Acaulospora laevis(ID: Sunsex),Glomus monosporum(ID: WUM11)and Glomus intraradices were used.Spores of the three AMF species isolated from the wheat belt in Western Australia were pot–cultured with white clover(Trifolium repens)prior to the experiment.The study was performed to illustrate the effects of AMF on wheat growth,yield formation,water use and sustainability for dryland agriculture under potted water control,field,or intergreting with plastic film mulching in field at the Dryland Agricultural Ecological Experimental Station in Yuzhong County of Gansu from 2011 to 2015.Pot experiment was conducted to assess the inoculation effects of three AMF species on different ploidy wheat cultivars individual water use and yield,and their physiological and ecological mechanism under the condition of different water gradients.Three relatively independent but closely related field trials with spring wheat L8275 and three AM fungal species,were conducted to evaluate effects of AMF inoculation on grain yield,biomass accumulation,water use efficiency(WUE),soil organic carbon and economic profitability in with or without plastic film mulching.Trial 1 inoculated with three AMF species(Acaulospora laevis,Glomus monosporum,and Glomus intraradices)alone or in combination,or without inoculation as the control.Trial 2 included traditional flat planting and plastic film mulching,which was the control Trial of Trial 3.Hence Trial 3 consisted of PFM treatment inoculated with three AMF species(Acaulospora laevis,Glomus monosporum,and Glomus intraradices)alone or in combination,or without inoculation as the control.Major results and innovations were achieved as follows:1.The growth and grain yield of hexaploid spring wheat(L8275)were significantly increased with inoculation of three AMF species,the growth and grain yield of tetraploid spring wheat(DM31)and the 1000-grain weight of diploid spring wheat(MO4)were also significantly enhanced with inoculation of the Acaulospora laevis and Glomus intraradices under different water conditions,which were helpful to improve the adaptation strategy of different wheat genotypes to drought stress.There were different physiological and ecological characteristics due to different AMF that affected on different genotypes of wheat.The results showed that Acaulospora laevis improve host drought tolerance better than that of Glomus intraradices.The benefit effects on improving drought tolerance of hexaploid spring wheat(L8275)among three AMF were Gm > AL> Gi.2.The wheat growth,root colonization rate and grain yield were significantly improved no matter with single or mixed AMF inoculation and in dry or wet year.AMF inoculation not only improved the yield-forming factors such as tiller number,grain number and grain weight per spike,but also affected the R-V index to benefit for increasing the host plant harvest index and grain yield.The results indicated that AMF introduced from Western Australia could also promote the growth and grain yield of dryland spring wheat in the Loess Plateau of China.3.Rhizosphere soil nutrients and five kinds of cultural microbial populations were also measured in this study.The results showed that AMF inoculation significantly affected the number of microflora in rhizosphere soil,and there was close correlation between different microbial groups and soil nutrients.AMF inoculation also increased total nitrogen and available potassium contents,but decreased the content of organic matter and available phosphorus,which was disadvantageous to the soil sustainability in semi–arid rainfed agriculture area.The results further showed that the rainfall played more impacts on soil nutrients and cultural microbial populations than those of AMF inoculation,which indicated that water is the major factor to limit the rhizosphere processes,and AMF inoculation play a micro–regulation on rhizosphere microbes,water and nutrients in rhizosphere soil.4.Importantly,across all the species under PFM,the AMF inoculation increased grain yield and aboveground biomass by 46.6% and 56.5% in wet year 2014,and 16.6% and 27.4% in dry/warm year 2015,respectively,comparing with no AMF inoculation.AMF symbiosis also significantly enhanced harvest index and population fitness,and higher inoculation rates generally led to greater magnitudes of the increases in yield,biomass and WUE.We also quantitatively estimated the economic benefits among various treatments,and found that PFM significantly increased net economic income by 35.8% in 2014 and 245.0% in 2015 respectively,comparing with traditional flat planting,while AMF inoculation further promoted net income averagely by 72.9% in 2014 and 21.7% in 2015 respectively on the basis of CK–2.Meanwhile,the AMF inoculation further significantly increased the contents of SOC by 16.5% in 2014 and 1.9% in 2015,respectively.The results showed that integrated AMF–mulching farming system improved field productivity,economic benefit and soil organic carbon,which may act as an environment–friendly and high–yielding management to ensure wheat production and ecosystem sustainability under climate change.5.Although AMF coupled with plastic film mulching and without plastic film mulching,both agronomic measures could improve dryland farmland productivity,but the mechanism of promoting growth and yield was different.Allometric exponents under AMF coupled with plastic film mulching fall into the threshold range from 0.9 to 1,which means that biomass allocation was much stable while the R–V exponents were close to 1 in two growth years,which could be further maximized the reproductive output under AMF coupled with plastic film mulching.However,the allometric exponents unchanged and the R–V exponents were fall into the threshold range from 0.9 to 1(not close to 1)under plastic film mulching in two years.Whereas AMF not only increased host plant individual size,but also improved more reproductive output than vegetative biomass,which was beneficial to population fitness and yield improvement.6.Wheat aboveground biomass and yield have been improved in field inoculated with AMF and AMF inoculation coupled with PFM.However,soil organic matter content declined in two years under inoculated with AMF,which was not conductive to soil sustainability.AMF coupled with PFM improved soil organic matter,which benefited to soil sustainability,and was a promising farming strategy.The higher contents of Actinomycetes and Dothidemycetes were detected in bacterial and fungal OTUs under AMF coupled with PFM treatments,respectively.AM fungi diversity also improved as the introduced AMF had been colonized in wheat rhizosphere by AMF diversity analysis under AMF coupled with PFM treatments.The results indicated that inoculated with AMF could improve rhizosphere microbial diversity and soil quality to benefit with nutrients cycling and water uptake.In conclusion,in this study,wheat aboveground biomass and yield have been improved under potted water control,and field trials,which verified AMF inoculation,play a beneficial role in promoting dryland spring wheat.Gas exchange parameters,membrane damage,osmotic adjustment,oxidase activity and hormone(ABA)in three spring wheat,L8275,DM31 and MO4 were detected to reveal the main mechanism of AMF on improving wheat growth and yield under drought stress.Field Trials results answered the mechanism of AMF inoculation promoting wheat growth and yield and AMF inoculation technology is feasibility to use in agricultural practice,especially better effects of AMF inoculation coupled with PFM technology.AMF inoculation coupled with PFM technology not only further enhanced wheat yield and economic benefit than PFM,but also increased soil organic carbon content,improved soil microbial diversity and function to improve soil quality,which is beneficial to the sustainable development of semi–arid rain–fed agricultural areas.