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

We hypothesized that lignin decomposition microbial consortium would make rice-straw decomposition faster as straw contain around 15–24% lignin. In this study, we isolated aerobic 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. The greenhouse gases emission, enzymatic activities (β-glucosidase, cellulase, laccase), reduction in lignin content, weight loss and carbon nitrogen ratio (C:N) were quantified during the process of decomposition. The β-glucosidase, cellulase and laccase activities were higher in compost where LB 18 + LF 3 consortium was applied as compared to others. The lignin content was also decreased (8.9–9.5 to 6.6–7.9%) gradually 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 relatively faster than other strains/consortium tested as indicated by lowering 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 of composting compared to initial values. However, higher, methane and carbon dioxide fluxes were also observed at 28th days of composting (1.36 and 200.7 mg m−2 h−1) with no significant trend in nitrous oxide fluxes. 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.