Study On The Regulation Effects Of Film Mulching Practices On The Growth Of Broomcorn Millet And Soil Environment In Dry Farming Regions

Dry farming areas in northern China play a crucial role in ensuring national food security.Limited rainfall and high spatial and temporal variability have long threatened the stability and sustainability of agricultural production in this region.Several Mulching methods are widely used in the dry farming areas,which can effectively collect rainfall,inhibit evaporation,improve crop productivity and water use efficiency.Broomcorn millet has the characteristics of short growth period,drought and barren tolerance,and has obvious production and regional advantages in dry farming regions.At present,the researches on mulching methods mainly focuses on the increase of yield and income of staple crops.There are no reports on the structure of soil microbial communities,function and metabolic properties in different dry farming regions.Therefore,it is necessary to explore how the film mulching practices in different dryland areas can improve the broomcorn millet productivity and resource utilization efficiency,and clarify the driving mechanism of microbial communities in broomcorn millet fields,so as to provide a basis for promoting the sustainable development of agriculture in dryland areas in northern China.Field experiments were conducted in nine ecological regions in northern China and three ecological regions on the Loess Plateau（Guyuan,Ningxia;Huining,Gansu;Yulin,Shaanxi）from 2020 to 2022.With broomcorn millet“Yumi No.2”as the experimental material,different mulching regimes were set up:（1）ridge-furrow mulching planting（RF,only mulching plastic film on the ridge）,（2）plastic film mulching planting（PFM）,（3）traditional flat planting without mulching（TP,control treatment）.The effects of plastic film mulching on broomcorn millet yield and microbial community in northern China were analyzed,and the key environmental factors affecting broomcorn millet yield were identified.From the perspective of plant-soil-microorganism,the effects of farmland film mulching practices on the broomcorn millet growth,development,photosynthetic characteristics,grain yield,water use efficiency,soil temperature,water and nutrients,microbial community structure,function and metabolism in the three ecological regions on the Loess Plateau were systematically explored.The main results are as follows:（1）The hydrothermal effect formed by film mulching practices promoted the photosynthetic capacity of broomcorn millet leaves,improved the morphogenesis and dry matter accumulation of broomcorn millet,and then improved the grain yield and water use efficiency of broomcorn millet.Compared with TP treatment,PFM treatment has the most significant warming effect.In Guyuan,Huining and Yulin regions,the average soil temperature of PFM treatment increased by 1.0-2.7℃,1.2-4.4℃,and 1.1-3.1℃,respectively,in the two growth seasons of broomcorn millet.In these three regions,film mulching practices can improve the soil moisture content of 0-100 cm soil layer during the growth period of broomcorn millet,as shown by RF>PFM>TP.There are also great differences in soil moisture among different regions.The soil moisture in Yulin region is the lowest,followed by Guyuan and Huining regions.At the same time,both PFM and RF treatments could significantly increase the SPAD content,net photosynthetic rate（Pn）,transpiration rate（Tr）,stomatal conductance（Gs）and intercellular CO₂ concentration（Ci）of the leaves before the filling stage of the broomcorn millet,thereby promoting the growth of the broomcorn millet,increasing the plant height,leaf area and dry matter accumulation in the above-ground dry matter accumulation,and ultimately promoting the increase of the grain yield of the broomcorn millet.In Guyuan,Huining and Yulin regions,PFM and RF increased the average grain yield of broomcorn millet by 15.08%and 24.86%,20.86%and 25.61%,15.75%and 25.57%,respectively,and WUE increased by 16.31%and27.48%,23.21%and 28.80%,15.55%and 28.57%,respectively.Therefore,in the three semi-arid regions,furrow-ridge mulching planting can be used as an agricultural measure with application value.The structural equation model showed that soil moisture content and agronomic traits were the most important environmental factors affecting the grain yield of broomcorn millet,and film mulching practices and regions significantly affected the soil moisture content and agronomic characteristics of broomcorn millet,but had no significant impact on soil temperature.（2）The film mulching practices increased the soil nutrients at the jointing stage of the broomcorn millet,but decreased the soil nutrients at the flowering stage.Meanwhile,the increase of soil temperature and water content in PFM and RF treatments also increased soil microbial carbon and nitrogen limitations.In this study,in three semi-arid regions,at the jointing stage of broomcorn millet,compared with TP treatment,the content of soil organic carbon（SOC）in PFM and RF treatments increased by 19.29%and11.80%on average,the content of total nitrogen（TN）increased by 10.31%and 10.34%on average,the content of ammonium nitrogen（NH₄⁺-N）increased by 184.60%and 26.11%on average,and the content of nitrate nitrogen（NO₃^--N）increased by 25.56%and 19.64%on average,while at the flowering stage of broomcorn millet,the contents of SOC,TN,NH₄⁺-N and NO₃^--N in the soil treated with PFM and RF decreased to varying degrees.Compared with TP treatment,the C,N,P acquisition enzyme activities of PFM and RF treatments increased by 29.02%and 33.68%,19.46%and 13.78%,6.81%and 6.52%,respectively,at the jointing,flowering,and mature stages of broomcorn millet.The growth of soil microorganisms in the three semi-arid regions is limited by nitrogen.In the film mulching practices,the changes of soil temperature and soil nutrients affected microbial carbon and nitrogen limitation.With the increase of the content of SOC,TN and NO₃^--N,the nitrogen limitation gradually alleviated.The structural equation model showed that soil moisture content and soil nutrients were significantly obvious in different regions,and soil temperature had a positive regulation effect on soil nutrients.（3）PFM treatment significantly improved the soil hydrothermal environments and soil quality,thus increasing the crop yield of broomcorn millet and changing the fungal communityαdiversity and structure composition,but do not influence the diversity of bacterial community.The plant height,main spike length,stem diameter,total dry matter weight and 1000-grain weight of PFM treatment increased by 4.93%,11.95%,13.51%,48.52%and 3.57%,respectively.PFM treatment increased the grain yield of broomcorn millet by 7.32%-35.57%,with an average increase of 19.76%.Furthermore,PFM treatment significantly reduced fungal Chao1 and phylogenetic diversity,increased fungalβdiversities,but for bacterialαandβdiversities had no significant.With the increase of longitude and latitude,fungalαdiversities of TP and PFM treatments tends to decrease,but bacterialαdiversities had not changed.In PFM treatment,the relative abundance of Actinobacteriota and Mortierellomycota increased by 4.19%and 22.71%,respectively,while the relative abundance of Bacteroidota decreased by 10.93%.Random forest（RF）analysis indicated that fungalαdiversities,soil temperature,and p H were the most important factors affecting the grain yield of broomcorn millet.PFM treatment decreased the stochastic processes of the fungal community,but had no effect on the assembly process of bacterial community.PFM treatment also reduced the complexity and stability of the bacterial and fungal networks,which was reflected in the lower number of nodes,edges,ACC,and degree.Moreover,PFM also altered the keystone taxa of bacterial and fungal networks.（4）Film mulching practices changed the diversity,composition and structure of bacterial and fungal communities in different compartments of broomcorn millet,and also altered the relative abundance of specific modules in the co-occurrence network and the community assembly processes.In this study,there were significant differences in the community composition at the phylum levels of bacteria and the class levels of fungi in different compartments,growth stages and film mulching practices.Compared with TP treatment,PFM and RF treatments significantly reduced the bacterialαdiversity at jointing stage,whereas significantly increased the fungalαdiversity in rhizosphere soil and roots of broomcorn millet at flowering stages.At the same time,different compartments had the most significant impact on the bacterial and fungal community structure,followed by the growth stages and film mulching practices.Indicator taxa analysis showed more shared and specific species in rhizosphere bacterial and fungal networks.Compared with root bacterial and fungal networks,bulk and rhizosphere soil bacterial and fungal networks have more complex networks,showing more nodes and higher APL values.Compared with TP treatment,PFM and RF treatments significantly reduced the cumulative relative abundance of key species in Module#5 of bulk soil meta-network and Module#7 of root meta-network,while increased the cumulative relative abundance of key species in Module#4 of rhizosphere soil meta-network.In the bulk and rhizosphere soil meta-networks,Actinobacteria and Firmicutes were the keystone taxa,and the relative abundance of Actinobacteria in root meta-networks decreased in the PFM and RF treatments compared to that in the TP treatment.In addition,the bacterial community in bulk soil and the fungal community in bulk,rhizosphere soil and roots are mainly controlled by stochastic processes.Mulching affected the bacterial assembly process in bulk,rhizosphere soil and root compartments,but did not affect the fungal assembly process.（5）Film mulching practices significantly affected the rhizosphere soil nutrient contents,extracellular enzyme activity,microbial community,functional gene abundance and metabolite content in broomcorn millet field.Compared with TP treatment,PFM and RF treatments significantly reduced p H,TN,SOC,NH₄⁺-N and NO₃^--N contents in rhizosphere soil of broomcorn millet at flowering stage,and increased the activities ofβ-N-acetylglucosaminidase,L-leucine aminopeptidase,urease,β-1,4-glucosidase,cellobiohydrolase and alkaline phosphatase,and also increased the relative abundance of genes encoding the enzymes ofβ-1,4-glucosidase and L-leucine aminopeptidase.Mulching significantly changed the microbial community structure,function and metabolic properties of rhizosphere soil.Compared with TP treatment,PFM and RF treatments changed the relative proportion of Level 2 KEGG and Level 3 KEGG functional pathways,and also increased 129 and 132 differential metabolites.PFM and RF treatments also differentially regulated the relative abundance of multiple functional genes during the nitrogen cycling.At the same time,TP and PFM treatments significantly affected three pathways:starch and sucrose metabolism,arachidonic acid metabolism and glycerol phospholipid metabolism;Four pathways with significant effects were identified between TP and RF treatments:starch and sucrose metabolism,arachidonic acid metabolism,glycerol phospholipid metabolism,and tryptophan metabolism.PFM and RF treatments significantly increased the contents of metabolites in starch and sucrose metabolism,glycerol phospholipid metabolism,and arachidonic acid metabolism pathways.PFM and RF treatment also increased the content of metabolites involved in carbohydrate,lipid,nucleotide and amino acid metabolic pathways.Co-occurrence network analysis showed that PFM and RF treatments not only enriched organoheterocyclic compounds,organic acids and derivatives,lipids and lipid-like molecules,and organic oxygen compounds,but also increased their relative abundance in the major modules.In summary,this study clarified that furrow-ridge mulching is a cultivation technique to improve the grain yield of broomcorn millet.Mulching cultivation increased soil nutrients at the jointing stage of broomcorn millet,but decreased soil nutrients at the flowering stage,and also increased soil microbial carbon limitation in the field of broomcorn millet on the Loess Plateau.Meanwhile,mulching cultivation not only changed the diversity,network structure and assembly process of bacterial and fungal communities in different compartments of the broomcorn millet field,but also regulated the abundance of multiple functional genes in the nitrogen cycle and increased the content of metabolites.This study provides important reference values for further understanding the effects of mulching cultivation on the growth of broomcorn millet and the improvement of farmland ecosystem.