Efficient lignin decomposing microbial consortium to hasten rice-straw composting with moderate GHGs fluxes

Abstract

We hypothised that lignin decomposition microbial consortium would make rice-straw decomposition faster as straw contain around 15–24% lignin. In this study, we isolated lignin degrading microbes from four natural sources and based on their ability towards lignin degradation four microbial strains and their combination (2 bacteria (LB 8, LB 18) and 2 fungi (LF 3, LF 9) were selected for rice straw decomposition. During straw decomposition greenhouse gases emission, enzymatic activities (β-glucosidase, cellulase, laccase), reduction in lignin content, weight loss and carbon nitrogen ratio (C:N) were quantified. The β-glucosidase, cellulase and laccase activities were higher in LB 18 + LF 3 consortium as compared to others. The lignin content was also decreased (8.9–9.5 to 6.6–7.9%) continuously from initial to 28th days of composting under LB 18 + LF 3. We found the microbial consortium LB 18 + LF 3 decomposed the rice straw faster as indicated by reduction of C:N ratio and reduction of lignin, hemicellulose and cellulose contents of 60, 19.2, 41.5 and 10.3%, respectively at 28th day from initial compare to other strains/consortium. However, higher, CH₄ and CO₂ fluxes were observed at 28th days after composting (1.36 and 200.7 mg m^− 2 h^− 1) with no significant trend in N₂O flux. Further, the consortium identified could be tested for in-situ straw decomposition with proper moisture management to evaluate its potential in field condition. Therefore, we conclude that use of lignin decomposing microbial consortium has the potential to hasten the composting of rice straw in large scale, so viable option to reduce the menace of straw burning.