Nitrous Oxide Mitigation And Lignocellulose Degradation In Manure Composting

Composting has been suggested as a sustainable agricultural method for recycling livestock wastes. However, the composting of livestock wastes has been universally regarded as a source of anthropogenic greenhouse gas, yielding annual global nitrous oxide (N2O) emissions. It poses a serious environmental pollution risks as the emissions may contribute to global warming and nitrogen loss. In addition, the period of composting is usually long due to the recalcitrance of lignocellulosic materials. This seriously influences the efficiency of manure disposal effect and limits the usage of the follow-up composting products. In order to realize the resource utilization of livestock manure and meet the increasing requirements of environmental protection and adapt to the rapid development trend of large-scale processing, the effects of biochar amendment during pig manure composting were investigated using the closed chamber technique. Meanwhile, the combined molecular methods were applied to investigate actinomycetal diversity and dynamics in a pilot-scale composting and moreover, we combine 454-pyrosequencing and metagenomics to investigate the function of rice straw-adapted consortia enriched from manure compost in degradation of lignocellulose. Primary results were summarized as follows:(1) We investigated the extent to which biochar addition influences biochemical parameters and N2O emissions during composting using the closed chamber technique. In the current study, biochar amendment increased the kinetics of composting and thereby shortened the required time period. Biochar amendment resulted in a higher pH and C/N values and a lower moisture and EC values compared to the control. Biochar not significantly affected NH4+ and NO3- but NO2--N in this study. The N2O emission rate increased slightly and then declined and the peak occurred in the late composting phase. Most importantly, the treatment with biochar amendment emitted a total of 25.9% less N2O than the control treatment.(2) The extent to which the biochar amendment influences the abundance of the denitrifying community was tested using real-time PCR. The highest copy numbers of all denitrification genes were observed during the cooling and maturing phase; significantly lower copy numbers were measured during the initial mesophilic and thermophilic phases. There were significant differences in denitrifying bacteria numbers when composting with or without biochar amendment. Spearman rank correlations matrix revealed that the N2O emission rates measured in both treatments displayed significant positive correlations with the abundance of nosZ, and nirS gene copy numbers, together with EC and moisture. Interestingly, the correlations were mutual and high between the abundance of all three denitrifying genes (nosZ, nirK and nirS). Based on these interpretations, our findings demonstrated that less N2O-producing and more N2O-consuming bacteria in the the treatment with biochar significantly lowered N2O emissions during the maturation phase of composting.(3) In this study, real-time PCR coupled with denaturing gradient gel electrophoresis (DGGE) and clone library construction were applied to investigate actinomycetal diversity and dynamics in a pilot-scale composting. Quantitative real-time PCR data revealed that the copy numbers of actinomycetal and bacterial 16S rRNA gene increased quickly and then declined, and the ratio of actinomycetal to bacterial 16S rRNA gene numbers (0.86) occurred in the maturing phase of composting, indicating that Actinobacteria were critical to the compost ecosystem. Qualitatively, actinomycetal communities displayed distinct temporal variations during composting. Each sample tends to harbor its own dominant actinomycetal groups. Specifically, pathogenic Corynebacterium species dominated in the initial phase, whereas the genera Saccharomonospora and Thermobifida were abundant in the thermophilic phase. In maturing composts, mesophilic Micrococcineae members were most prevalent. Redundancy analysis indicated that temperature exerted an influence over the actinomycetal communities.(4) This study aims at providing a valuable blueprint that helps to recognize the functioning of microbial compost ecosystem in lignocellulose degradation by applying both 454 pyrosequencing and massive depth metagenomic sequencing. The rice straw-adapted consortia enriched from manure compost contain a distinctive set of microorganisms, primarily actinomycetes. The abundant genes encoding for carbohydrate-metabolising enzymes and carbohydrate transporters (7.3% in COG and 12.1% in KEGG) help explain the ability of this enrichment to utilise carbohydrates. The enzymatic degradation of cellulose is accomplished via synergistic activities of endoglucanase and cellobiohydrolase and β-glucosidase, which are primarily derived from actinomycetes. During this process, Thermobaculum terrenum and Rhodothermus marinus are predominantly responsible for the hydrolysis of the hemicellulose. It is strikingly suggested that the prominent actions of actinomycetal esterase and arabinofuranosidase may facilitate the breakdown of glycosidic bonds. Complete hydrolysis of pectins involves a set of diverse enzymes, including pectin lyase, polygalacturonase, galactosidase, arabinofuranosidase, as well as rhamnosidase. In our study, a range of rare actinomycetes are the major producers of pectin lyase. These results provided technical support and a strong theoretical guidance for rapid and efficient composting of livestock waste.