Screening Of Straw Degradation Strains Under Medium-Low Temperature And Their Degradation Effects On Crop Straw

Crop straw returning in situ is an effective technical measure to improve the comprehensive utilization of straw, raise the soil building, and increase the soil fertility. However, straw returning generates many adverse effects for the agricultural operations due to its slow decomposition, which limits its promotion. In order to offer the straw-degradation strain resource and provide technical support for accelerating the straw returning, the isolation of straw degradation microbes and their degrading effect were conducted in this thesis. The main research results are as follows:Three high efficient straw degradation fungi were screened using filter paper digestion method, Congo red stain method and enzyme production capacity comparison method at 15℃conditions. The 3 fungi were Penicillium oxalicum QSH3-3, Fusarium oxysporum DSH2-3 and Chaetomium sp. YSH3-3. Moreover, one fungi combination was constructed by Fusarium oxysporum DSH2-3 and Chaetomium sp.YSH3-3.The three fungi could produce relatively high xylanase, cellulase and ligninase, in which strain QSH3-3 possessed the highest CMCase activity (26.78 U/mL) and xylanase activity (550.37 U/mL), strain DSH2-3 possessed highest laccase activity (468.75 U/L), and strain YSH3-3 have upper FPase activity(13.04 U/mL).After 15 d liquid fermentation at 20℃, corn straw's degradation rates with the treating of strains QSH3-3,DSH2-3,YSH3-3 and fungi combination reached 58%,48%,52% and 53%, respectively, which were higher than the control strain AS3.3711 ranging from 23.1% to 48.7%. Among them, the straw cellulose and hemicellulose degradation abilities of strain QSH3-3 were the strongest, and degradation rate reached 49% and 46%, respectively; the fungi combination processed the strongest degradation ability of lignin, and its degradation rate reached 32%. Combined with scanning electron microscopy (SEM) results, it was shown that the decomposition of straw started from the damage of wax coat in the surface layer and the dense structure, and with the wall occurred over destroyed, straw internal organization began degradation, and eventually the whole straw organization structure presented loose state. In which, the damage degrees of straw density treated by QSH3-3 and fungi combination were relatively higher.The two simulation tests of straw return to field, ploughing straw back and covering straw with soil, were conducted in 10 - 25℃. It was shown that compared with CK, after applying the selected strains the straw decomposition rate increased significantly; however, the degradation abilities of the same strain was different for the straws sourced from different crops, especially for the lignin. In the four kinds of microbial inoculum treatments, the degradation effect of strain DSH2-3 on the wheat straw was better, and the decomposition rate reached 45 - 53% after 50 days; The degradation effect of fungi combination on rice and corn straw presented more significant, and the straw weightlessness rate could reach 50 - 69%.The simulation experiments of wheat, corn, and rice straw returning at 10 - 25℃were utilized to investigate the content changes of organic matter, humus, N, P, and K in soil. The results indicated that the organic matter and humus contents in soil treated with fungi combination were significantly higher than others, organic matter content in the soil could amount to 9.6 - 10.6%, than CK high 10.3 - 17.8%; Soil humus content could reach 6.4 - 9.0%, than CK high 4.5 - 21.6%. The addition of microbial inoculums decreased the rapidly-available N content to varying degrees, however, improved the rapidly-available P and K content. In which, the rapidly-available P content in soil treated with fungi combination reached 143.6 - 200.0 mg/kg,which were 2.25 - 28.1% higher than that in CK; the rapidly-available K content in soil treated with strain YSH3-3 reached 69.0 - 79.7 mg/kg,which were 3.1 - 23.4% higher than that in CK.