Effects Of Arbuscular Mycorrhizal Fungal Inoculation On Dryland Maize(Zea Mays L.)productivity And Soil Organic Carbon And The Relevant Mechanisms Under The Scenario Of Reduced Plastic Film Mulching

In the semiarid Loess Plateau region of Northwestern China,where insufficient precipitation and poor soil fertility are major constraints to increasing crop productivity.Plastic film mulching,which as an efficient farming technology has been extensively used in drought-prone,high altitude and/or high latitude regions.However,the negative effects of plastic mulching have recently received more attention.Due to the increase in plant growth,plants under plastic mulching require more water input.If the evapotranspiration?ET?of plants and soils exceeds the precipitation,the decreasing soil moisture levels can aggravate soil water scarcity in subsoil soil layers.In addition,plastic mulching increases the soil temperature and water and then increase soil organic carbon?SOC?mineralization and thus negatively affect the SOC balance if the increased carbon consumption is not balanced by increased input.Importantly,current plastic mulching practices are usually to cover with new plastic film every year,and a large amount of residual plastic film is directly incorporated into the soil during the cultivation process.To reduce the amount of plastic film usage but still maintain high field productivity and sustainability is a huge practical challenge for dryland agriculture.Soil microbial community plays a crucial role in the agricultural ecosystem.Among these microbes are arbuscular mycorrhizal?AM?fungi,which have come to be viewed not only as plant symbionts,but as essential to both plant and soil,serving as the critical link in the plant-soil continuum.AM fungi may also potentially improve soil health through their external hyphae?EMH?that improve crop water use,sustain soil structure and increase SOC storage.However,in the plastic film mulching system,it is not known whether allochthonous AM fungal inoculation can affect soil AM fungal diversity and thus affect the crop yield and soil labile SOC fractions.We first conducted a meta-analysis based on all available data to evaluate the effect of plastic mulching on maize productivity,soil moisture and soil labile organic C fractions in rain-fed regions;and then field experiment adds the dimension of inoculation with AM fungi to access the effect of reduced plastic film mulching and AM fungal inoculation on soil labile organic C fractions,crop productively and resident AM fungal community composition.The major results were presented as follows:1.Impacts of plastic film mulching on maize productivity,soil water sustainability and soil organic carbon:insights from a meta-analysis in rain-fed regions.1)Plastic mulching significantly and positively impacted both crop yield and WUE.Increased yields and WUE were highest when annual mean precipitation was250-400 mm?142%and 190%?,followed by 400-500 mm?39%and 35%?,500-600mm?34%and 32%?and over 600 mm?22%and 31%?.In the meanwhile,full plastic mulching significantly increased the crop yield and WUE,in comparison with half plastic mulching.The increases in yield and WUE were 48%and 46%,50%and 47%,and 47%and 58%under high,moderate,and low nitrogen applications,respectively.Additionally,increased vegetation growth due to plastic mulching can turn to impact soil water dynamics across growing and fallow seasons,but it did not disrupt the annual equilibrium of SWS.Particularly,more precipitation harvesting and storage at deep soil layer during the non-growing season appeared to fully offset the extra water loss by enhanced evapotranspiration.2)Plastic mulching significantly enhanced the light fraction organic C?LFOC?and particulate organic C?POC?decomposition.The effect size of LFOC and POC were 0.92?0.90-0.94?and 0.96?0.96-0.97?,respectively.However,those of easily oxidizable C?EOC?1.01?0.96-1.07?were not significant.The plastic film mulching increased microbial biomass C?MBC?,and the effect size was 1.12?0.90-1.41?.2.Response of maize yield,soil water storage,SOC fractions and AM fungal communities to different agricultural practices.3)In the second growing season,plastic film mulching treatments?the experiment of plastic mulching combination with straw mulching:the amount of plastic film was 2/3 of the total plastic film mulching;use of plastic film once every 2years coupled with no-tillage practice:the amount of plastic film was 1/2 of the total plastic film mulching?significantly increased soil water storage?SWS?for maize in 0to 60 cm soil profile before sowing,the effects of the combination of plastic mulching and AM fungal inoculation is more significant.In the harvesting stage,plastic mulching significantly increased SWC at 0 to 20 cm soil profile.The soil water content in CK,plastic film mulching,and plastic film mulching combined with AM fungal inoculation was 13.1%,15.4%and 20.1%lower than that of AMF treatment in60 to 200 cm soil layer under non-tillage.4)Plastic mulching significantly increased the leaf area ratio of maize in the second growing season.Inoculation with AM fungi increased the specific leaf area and leaf area ratio under no-tillage.Compared with non-mulching treatment,plastic mulching improved ear length,ear diameter,1000-grain weight,and reduced the bare tip length.Furthermore,plastic mulching significantly increased the maize yield and WUE,which are consistent with the meta-analysis results.In the second growing season,inoculation with AM fungi significantly increased the ear length.Although inoculation with AM fungi did not significantly increase corn yield,water use efficiency and biomass in the first growing season,while AM fungi had a significant growth-promoting effect in the second growing season.5)In this study,across each growing season,the TOC contents remained insignificant differences among various treatments.While the labile organic C differed with different years and treatments.We found that based on alternative double-ridge film mulching?ADM?,AM fungal inoculation?ADM+A?,additional straw mulching?ADMS?and combination with AM fungal inoculation and straw mulching?AMDS+A?significantly increased the content of LFOC in 2016?5.57-15.1%?and 2017?8.46-15.6%?.In addition,compared with ADM and ADM+A,ADMS increased the POC content by 5.82%and 3.80%;and ADMS+A increased POC by 12.4%and 10.5%in 2016,respectively.In 2017,ADMS increased the POC content by 20.4%and 9.19%;and ADMS+A increased POC by 23.7%and 13.0%when compared with ADM and ADM+A treatments,respectively.Moreover,the amount of nitrate-nitrogen?NO₃^--N?and ammonia nitrogen?NH₄⁺-N?in topsoil?0-20cm?was not significantly influenced by straw mulching and AM fungal inoculation.While AM inoculation significantly reduced the content of total nitrogen?TN?and available phosphorus?AP?and significantly increased the content of shoot N and P in2017.Field inoculation with AM fungi appeared to have stimulated EMH production and significantly increased the glomalin-related soil protein?GRSP?content.Shoot and root biomass was also generally affected by AM fungal inoculation and straw mulching.Critically,EMH and GRSP have highly correlated with the soil labile organic C.A significant negative linear relationship between TN and EMH.Shoot N and P were also significantly correlated with EMH and mycorrhizal colonization.6)Our meta-analysis was consistent with our field experiment where full plastic mulching significantly decreased levels of soil POC and LFOC.While positive effects on soil labile organic C were observed when inoculation increased root colonization,EMH and glomalin content,particularly under the non-tillage.AM fungal inoculation significantly increased LFOC content by 12.9%-35.5%and POC content by6.44%-22.3%compared with non-AM fungal treatments,particularly under the no-tillage.AM inoculation treatment significantly increased the shoot N concentration by 10.2%and 9.21%under tillage and no-tillage when compared with the CK,respectively.Notably,AM inoculation significantly increased EMH by16.9-19.8%under non-tillage conditions,in comparison with tillage.Inoculation with F.mosseae strongly increased the relative abundance of F.mosseae detected in rhizosphere soil.Meanwhile,AM fungal root colonization significantly increased with inoculation,indicating successful competition by the inoculant for root niche space against naturally occurring AM fungi at this site.Root mycorrhizal colonization,T-GRSP and EMH were positively correlated with EOC,LFOC,POC and shoot N concentration under no-tillage practices.EMH was positively correlated with LFOC content under tillage conditions.7)Fungicide applications reduced labile organic C,possibly through decreasing EMH,glomalin content and soil AM fungal diversity.Benomyl application significantly decreased the POC,MBC,LFOC content,root mycorrhizal colonization,EMH,EE-GRSP and T-GRSP by 21.1%,8.92%,28.6%,26.0%,49.0%,30.2%and18.3%respectively.Shoot N concentration was reduced by 38.6%following benomyl applications.However,benomyl application significantly increased the NO₃^--N and NH₄⁺-N accumulation in the 0-100 cm soil layers.8)No significant difference in AM fungal richness and Shannon diversity were found between plastic mulching and inoculation with AM fungal and their interactive effect.AM fungal diversity was significantly higher on control plots than fungicide application plots.The community composition of AM fungi was significantly influenced by plastic mulching and fungicide applications,which was strongly correlated to soil organic C fractions?LFOC,POC?,NO₃^--N,TN,and GRSP.Pearson's correlation analysis indicated that MBC,EOC and LFOC were significantly correlated with GRSP content?AM fungal inoculation studies?.EMH significantly positively correlated with POC,and negatively correlated with TN.However,there was no significant relationship between diversity and C fractions.Furthermore,the relationship between AM fungal diversity?alpha diversity,Shannon?and these C fractions were positively correlated under fungicide applications.The adoption of plastic mulching increased crop productivity,while the plastic mulching decreasing the SOC content.We observed a significant positive effect of AM fungal inoculation on soil water storage,maize productivity,and SOC under the scenario of reduced plastic film mulching.Furthermore,a close positive correlation between AM fungal abundance,diversity and labile organic C was also observed.These results may further support the important role of AM fungi in the maintenance of SOC and benefits to plant productivity in agricultural ecosystems.Importantly,AM fungal inoculation can promote plant growth under the plastic mulching,but it did not influence the composition and diversity of indigenous AM fungal communities.AM fungal inoculation may act as an effective farming solution to improve soil organic C fractions under the scenario of reduced plastic film mulching,which correlated to maize productivity.