| A two factor field experiment was conducted on irrigation level and application times of gamma-polyglutamic acid.Two irrigation levels of 0m3/ha(W1)and 900m3/ha(W2)are set,and the irrigation time is arranged at the huge bellbottom stage.Three gamma-polyglutamate levels were spray twice(T2,at the jointing stage and at huge bellbottom stage,respectively,each with a dosage of 50g/ha),spray once(S1,only at the jointing stage with a dosage of 50g/ha),and control(S0,spray equal amount of distilled water at the two stages).A total of W1CK,W1T1,W1T2,W2CK,W2T1 and W2T2 were composed.The effects of different treatments on summer maize yield and its components(dry matter accumulation and distribution in silking stage and maturity stage,nitrogen,phosphorus and potassium accumulation amount,photosynthetic index in grain-filling stage)were studied.The maize height and stem thickness in the silking stage and filling stage were determined.The diversity and community structure of rhizosphere bacteria and fungi in W2CK,W2T1 and W2T2 was investigated.The main results are as follows:1.The main effects of irrigation and spraying of y-polyglutamic acid(PGA)on summer maize yield,hundred-grain weight and grain number per ear were significant,but only the interaction effects on grain weight per ear was significant With the increase of spraying times,the yield showed an upward trend.Compared with the control group,Spraying PGA once and twice could increase the yield of summer maize by 33.3%and 37.0%,respectively,but there was no significant difference between spraying once and twice.The average yield increase of spraying PGA without irrigation was equivalent to 441m3/ha amount of irrigation at trumpet stage.2.The main effect and interaction effect of irrigation and spraying PGA on dry matter weight of summer maize at silking stage and mature stage and anthesis reached or approached significant level,and spraying PGA significantly improved the above indexes,but there was no significant difference between spraying times.Compared with the control,spraying PGA average increased the dry matter weight by 6.8%,20.1%and 33.0%in silking stage,mature stage and post-anthesis,respectively.The main effect of spraying PGA on dry matter harvest index was not significant,but the interaction effect of irrigation and spraying PGA on dry matter harvest index was significant Although the effects of irrigation and spraying PGA on the transfer of dry matter from vegetative organs to grains from silking stage to maturity stage,the transfer efficiency of dry matter from vegetative organs to grains before flowering,and the contribution rate of dry matter to grains were not significant,but there were significant differences between the two indexes in the treatment combination.Under the condition of irrigation,the yield increased and the rate and amount of transferring to grains decreased with the increase of times of spraying PGA,while there was no significant difference between spraying and non-spraying without irrigation.3.The main effects of irrigation and spraying PGA on N,P and K accumulation in silking stage and mature stage were significant,but only the interaction effects on N accumulation of mature stage was significant.The accumulation of N,P and K in silking stage increased by 12.2%and 22.3%,8.4%and 18.9%,11.7%and 22.8%respectively,the accumulation of P and K in mature stage increased by 1 5.5%and 41.0%,8.5%and 23.4%respectively after spraying PGA once and twice as compared with spraying water.The accumulation of N in mature stage increased by 20.5%and 36.6%,5.6%and 12.7%under the condition of no irrigation and irrigation after spraying PGA once and twice,respectively.The increase effect of no irrigation was higher than that of irrigation.4.The main effects of irrigation and spraying PGA on net photo synthetic rate,stomatal conductance,intercellular CO2 concentration,transpiration rate and SPAD value of leaves were significant or extremely significant,the interactions effects on stomatal conductance and SPAD value were also significant,but the interactions effects on net photosynthetic rate,intercellular CO2 concentration and transpiration rate were not significant.The net photosynthetic rate,intercellular CO2 concentration and transpiration rate increased by 13.1%and 37.9%,4.8%and 10.9%,11.0%and 27.3%respectively after spraying-PGA once and twice.SPAD value and stomatal conductance of polyglutamic acid without irrigation increased by 29.0%and 2.7%respectively after spraying PGA once,and 70.1%and 7.6%respectively after spraying PGA twice.SPAD value and stomatal conductance of polyglutamic acid under irrigation increased by 64.0%and 5.5%after spraying-PGA once,respectively,increased by 157%and 30.2%after spraying PGA once,respectively.5.The main effects of irrigation and spraying PGA at silking stage and mature stage on plant height,stem diameter,leaf length,leaf width and leaf thickness were extremely significant,and the average effects of spraying PGA on the above indexes were positive.The interaction effects of irrigation and spraying PGA on plant height at silking stage and filling stage and leaf length at filling stage were significant or extremely significant,but the interaction effects on other indexes were not significant.6.The bacterial a diversity was not significantly affected by the spray of polyglutamate.The relative abundance of Acidobacteria decreased inW2S1 treatment,while the relative abundance of Actinomycetes and Proteobacteria increased.On the whole,the spraying of polyglutamate had no significant effect on the soil bacterial community structure.SIMPER analysis showed that the spraying of polyglutamate affected the abundance of individual bacteria taxa,the abundance of each one member belonging to Pyrinomonadaceae and Acidobacteria decreased,while the relative abundance of strains belonging to Arthrobacter,Sphingomonas,Streptomyces,and Alternaria increased,which played a role in soil health and nutrient cycle promotion.Based on Spearman correlation network analysis,the keystone taxa in the bacterial network structure belong to Gemmatimonadaceae and Bryobacter,which were closely associated with soil carbon cycle.7.Chao index and Ace index showed that the spraying of polyglutamate significantly reduced the species diversity of soil fungi,and the effect of spraying twice of polyglutamate on the fungal diversity was greater than that of spraying once,with no significant difference between spraying twice and once.Ascomycetes,Mortierellomycota and Basidiomycetes are the main components of soil fungus community.SIMPER analysis showed that the spraying of polyglutamic acid significantly increased the relative abundance of Mortierella and Chaetomium.The keystone fungal taxa in the related network are Metarhizium marquandii,each member classified in Chaetomiaceae and Marasmius,which are of great significance in soil carbon cycleCombined,the improvement of spraying polyglutamate on maize growth was achieved through the reshaping and optimization of fungal community structure. |
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