Screening Of Straw Degrading Microbial Strains And Study On Their Degradation Effects

China is a traditional agricultural country,the annual output of grain ranks the first in the world,and the burning of crop straw and its environmental problems have been concerned by both domestic and foreign governments.Returning crop straw to the field in situ is an important measure for straw utilization and improvement of physical and chemical properties in soil.However,the degradation process of straw is very slow under natural conditions,which affects cultivation and limits its application.Therefore,it is of great significance to screen safe and efficient straw degradation microbial strains and determine the degradation effect for straw returning to the field and improving soil quality.In this paper,the screening and identification of high-efficiency straw degradation microbial strains were carried out,the degradation of corn straw under the condition of liquid fermentation was explored,the optimal growth conditions of each dominant strain were determined,and the degradation effect of straw composite degradation microbial strains was constructed and defined.The main results are as follows:1.Through streak plate method,primary screening of Congo red culture medium and disintegration test of filter paper,5 strains of high-efficiency straw degrading microbial strains were screened out from the straw piles and fresh cow dung samples accumulated and rotted for a long time in the northeast of China.The optimum growth pH?between7.5-8.5?and the optimum growth temperature?between 20?-30??were determined.The strain NF6 can keep a good growth state at 4?and show the characteristics of low temperature resistance.It can be applied to the environment with large temperature difference in the north.2.Through the liquid fermentation experiment of corn straw,the degradation ability of different strains to straw was determined.Among them,strain NX9 has the strongest degradation ability to corn straw and straw hemicellulose,with the degradation rate of53.88%and 48%respectively?15 days?;strain JZ8 has the second,with the degradation rate of 44%;strain JF3 has strong degradation ability to straw cellulose,and the degradation effect of cellulose under the same culture time is significantly greater than other strains,with the overall trend of fast first and then slow,at the 6th-12th days.Compared with cellulose and hemicellulose,the degradation rate of five strains was lower,and the degradation rate of lignin was the slowest.Among them,NF6 had stronger degradation ability of lignin,and the degradation rate of lignin was 37.7%in the whole cultivation process.After morphological observation,physiological and biochemical identification and 16S rDNA sequence analysis,the optimal strain NX9 was identified as Bacillus thuringiensis.3.Through the antagonistic experiment of three strains?NX9,JF3,NF6?with the strongest degradation ability of the three components in the straw under the condition of liquid culture,it was found that there was no inhibition of growth among the three strains.Using them to construct a composite strain,named MJ1,it was found that the composite strain could effectively promote the degradation of corn straw and improve the soil through the simulated experiment of straw decomposition in the field.The contents of organic matter,available nitrogen,phosphorus and potassium play a role in soil fertility.The results of straw degradation experiment with metal Fe²⁺catalysis composite microbial agent showed that the composite strain MJ1 with metal Fe²⁺treatment could significantly accelerate the rate of straw degradation,at the same time,the enhancement of soil organic matter and soil physical and chemical properties was significantly higher than other treatments,and the content of soil organic matter was 9.2%,11%higher than CK;the content of soil available N?P?K were 103.18 mg·kg^-1?128.19 mg·kg^-1?108.91 mg·kg^-1?higher than CK:20.4%?34.8%?29.2%.4.Developed and optimized the straw microbial catalytic degradation process:metal Fe²⁺enhanced the degradation of MJ1 straw.The effect of straw degradation by combining compound microbial strains and metal catalysis is better than that by applying compound microbial strains alone and treatment is better than blank treatment.It can not only accelerate straw returning to the field,improve soil physical and chemical properties,but also improve soil seed germination rate.At the same time of solving the problem of solid waste,it can realize a healthy environmental protection and healthy soil virtuous cycle,with both economic benefits and application.