Mechanism Research And Simulation Analysis Of Bacillus Subtilis Improving Cotton Growth And Salt Tolerance Under Water And Salt Stress

The shortage of fresh water resources and the serious problem of secondary salinization of soil in northwest China seriously threaten agricultural production and economic development.Based on microbial improvement technology,this paper takes cotton,a typical crop in Xinjiang region,as the research object,aims to improve yield and safely utilize brackish water resources,combines Bacillus subtilis with brackish water,fresh water and freshwater deficit irrigation,and studies the effects of water-salt stress treated by different Bacillus subtilis on soil water and salt,soil microenvironment,cotton growth,development and yield.The main conclusions are as follows:（1）The soil volume water content and water holding capacity of cotton root zone could be increased effectively by applying bacteria.The soil volume water content under brackish water,fresh water and fresh water deficit irrigation was higher in the whole growth period of cotton than that under CK treatment,and increased by 46.86%～87.94%and 23.39%～66.83%compared with CK,respectively.The water consumption and water consumption intensity of each growth stage of cotton were also increased by applying bacteria,and the water consumption of cotton during the whole growth stage was increased by 1.55%～7.94%and 0.1 8%～12.53%compared with CK,respectively.The soil volume water content,water consumption and water consumption intensity reached the maximum when the applying bacteria was applied at 3000 g/mu.（2）The soil salt content under brackish water,fresh water and fresh water deficit irrigation under different applying bacteria treatments was lower than that under CK,which was 8.31%～26.49%and 20.49%～44.98%lower than CK,respectively.The desalting rates were 8.5%～19.8%and 20.8%～37.8%,respectively,and the soil salt content was the minimum when the applying bacteria agent was applied at 3000 g/mu,and the desalting effect was the best.The effect of fertilization on soil nutrient change was obvious.When the irrigation treatment was consistent,the soil nutrient content under applying bacteria was lower than that without applying bacteria,which indicated that fertilization promoted the absorption and utilization of soil nutrients by cotton.（3）Different applying bacteria and irrigation treatments had certain effects on soil enzyme activity in 0-40 cm soil layer at each growth stage of cotton.With the increase of the amount of bacteria applied,the soil enzyme activity increased first and then decreased.Soil diversity index and soil bacterial species relative abundance of cotton under different fertilization and irrigation treatments were significantly higher than those under no fertilization,and showed a change pattern of first increasing and then decreasing with the increase of bacteria applied amount.With the advance of growth period,the distribution uniformity of soil bacterial community in root zone of cotton from seedling stage to boll-opening stage became stronger and the stability of community structure became better,and the difference between the composition and distribution of microbial community gradually decreased.Structural equation model analysis showed that the changes of soil bacterial community and soil nutrient in cotton root zone were the key environmental factors affecting cotton yield.（4）The growth indexes（plant height,stem diameter,leaf area index,dry matter accumulation）,physiological indexes（leaf antioxidant enzyme activity,SPAD,chlorophyll fluorescence parameters）,yield and water use efficiency of cotton under brackish water,fresh water and fresh water deficit irrigation were significantly affected by different bacteria applied treatments.And when the bacteria applied at 3000g/mu,all the indexes of cotton are optimal.Under brackish water,fresh water and fresh water deficit irrigation,the growth index,SPAD,leaf antioxidant enzyme activity,yield and water use efficiency of cotton increased first and then decreased with the increase of bacteria applied.The dry matter accumulation of cotton increased by 2.40%～49.27%and 9.63%～50.50%compared with CK,and the yield increased by 3.32%～49.34%and 3.73%～54.67%compared with CK,respectively.Compared with CK,water use efficiency increased by 1.68%～38.30%and 3.61%～41.07%,respectively.The F_v/F_m,F_v/F_o and PI_abs of cotton were higher than those without Bacillus subtilis treatment,which indicated that under Bacillus subtilis,the electron transport efficiency could be improved and the light energy absorbed and captured could be efficiently used in the photosynthesis of cotton,thus enhancing the ability of cotton to resist stress.（5）Based on effective accumulated temperature,the cotton growth model considering brackish water and Bacillus subtilis could accurately fit the growth process of cotton plant height,leaf area index and dry matter accumulation,and the model results had high fitting degree and accuracy.Multiple quadratic regression model was used to establish cotton production model considering the coupling effect of bacterial applied and irrigation,which was used for yield prediction and yield effect analysis.When the applying bacteria was 3000 g/mu treatment under fresh water irrigation,it is the best irrigation bacteria coupling treatment.And the cotton yield reached the maximum under this combination,which was the optimal combination scheme in this experiment.