Screening Of Low-temperature Straw-degrading Trichoderma And Its Effect On Microbial Communities In Straw Degradatio

Returning straw to the field is a major initiative for the effective utilization of straw resources,but straw has a complex structure,especially in northern autumn and winter,where the temperature is relatively low and lasts for a long time,leading to slow decomposition of straw and the accumulation of pathogenic bacteria in the returned plots,which has brought adverse effects on agricultural production.Microorganisms play a decisive role in straw degradation.To improve the degradation rate of straw after returning to the field in winter,reduce the accumulation of pathogenic bacteria in the land where straw is returned to the field,this article screened out Trichoderma strains that degrade straw in low-temperature environments,studied the straw degradation effect of Trichoderma at low temperature environment;test its inhibitory effect on pathogenic bacteria;a Trichoderma agent with microsclerotia as the main component was prepared,and its stress resistance was studied and the culture conditions for producing microsclerotia by fermentation were optimized;on the microbial community during straw degradation in the field was analyzed.The main research results obtained are as follows:（1）86 Trichoderma strains were collected and isolated from Daxing’an Mountains and Changbai Mountains in autumn and winter.11 Trichoderma strains resistant to low temperature were obtained by primary screening at 15℃.A Trichoderma strain C47-3 with straw decomposed at low temperature was obtained after rescreening of its enzyme production ability including cellulase,hemicellulase,and laccase.The strain was identified as Trichoderma paratroviride by morphological observation and molecular biology.（2）To investigate the straw degradation effect of this strain at a low temperature environment,adding this strain to the corn straw fermentation culture medium and cultivating it at a low temperature of 15℃for 15 days had a straw degradation rate of 23.89%,which was17.99%higher than that of the control treatment;in autumn and winter（This article selected November to February of the next year）,the strain was applied to the field for corn straw degradation,and the straw degradation rate was 44.02%,which was 22.72%higher than that of control treatment.Combined with scanning electron microscopy（SEM）,the results showed that the strain could destroy the dense structure of straw to form a large number of fiber fragments and accelerate the degradation process of straw.（3）Trichoderma C47-3 and its volatile substances have inhibitory effects on 8 strains of pathogenic fungi tested,such as Fusarium pseudograminearum,Fusarium solani,Fusarium oxysporum and so on.The inhibitory effect on Botrytis cinerea and Coniothyrium diplodiella was significant after 7 days of confrontation cultivation,with an inhibition rate of 100%;the inhibitory effect on Fusarium pseudograminearum was significant after 5 days of contralateral cultivation,with an inhibition rate of 60.13%.（4）The microsclerotia of Trichoderma has good stress resistance and storage resistance,the results of the experiment showed that the conidia production of the dried microsclerotia preparation was 3.09×10⁴/mg after rehyration,the germination rate of microsclerotia after heat treatment at 50℃for 30 min was 56%,58.33%at 3 h after UV irradiation,and 83%after 1 year of room temperature storage.Single factor experiments showed that glucose and peptone were the best carbon and nitrogen sources for microsclerotia production,and both low and high carbon were not conducive to microsclerotia production.The Plackett-Burman experiment determined that the significant conditional factors affecting the yield of microsclerotia were p H,C/N,carbon source concentration,and NH₄NO₃ concentration.The Box-Behnken experiment showed that the interaction of carbon source concentration and carbon-nitrogen ratio had a significant effect on the yield of microsclerotia,and the theoretical maximum value of microsclerotia yield predicted by the model was 6.42×10² cells/m L.（5）The change of microbial community during straw degradation was analyzed,the results showed that the fungal community:the richness and diversity of fungal communities in straw during each treatment period showed that C47-3 treatment was lower than control treatment,and showed a gradual decreasing trend with increasing treatment time.Ascomycota is an important player in straw decay with high relative abundance during the early stages of treatment,Basidiomycota has a strong ability to decompose refractory organics,with a significant increase in relative abundance at the late stage of treatment.The relative abundance of Trichoderma was increased in the C47-3 treatment group,and the relative abundance of wheat-associated pathogenic fungi such as Fusarium was decreased.The fungal community structure changed significantly during the late treatment period.Bacterial community:The richness and diversity of bacterial communities in straw during each treatment period showed that C47-3 treatment was higher than control treatment.At the late stage of treatment,the relative abundance of Actinobacteria,which can accelerate the process of straw decomposition,increased in each treatment group,and the relative abundance of functional flora related to straw lignin degradation,such as Bacteroidetes,decreased in each treatment group.Streptomyces had a positive effect on lignocellulose degradation,and its relative abundance increased on day 60of C47-3 treatment.The bacterial community structure changed significantly during the late treatment period.