GREENHOUSE GAS METHANE AND NITROUS OXIDE PRODUCTION AND MIRCOBIAL FUNCTIONING GENE CHARACTERIZATION IN GRASSLANDS AND THE INFLUENCES BY GRAZING LAND MANAGEMENT

Methane and nitrous oxide gases are significantly more potent in their ability to create a greenhouse effect than CO2. Grazing lands can either be a sink or source of GHG depending on management scenarios and climatic conditions. Management of grasslands can have a broad impact on the levels of GHG emissions, as grazing pressure, crop rotations, and levels and types of fertilization inputs can alter microbial communities and influence on GHG production. Methanogens and denitrifying microbial communities are two major groups associated with the production of GHGs. This study attempted to unravel the microbial and geochemical characteristics associated with CH4 and N2O production, and the interplay between the grazing pressure and the fertilizer amendments in the nitrogen fixing clover and nitrate supplemented rye cover grasslands. Using GC analysis of incubated soil samples, this study indicated that surficial soils (0-8 cm) in both clover and rye grasslands contributed the highest production of CH4 and N2O. CH4 production showed significant seasonal changes. High levels of grazing intensity caused a significantly increased CH4 yield, which was particularly true with no nitrogen fertilized lands. Quantitative PCR of methyl coenzyme M reductase (mcrA) gene, one of the genes for methanogenesis pathway, further confirmed theses effects. Increased amendment of nitrogen and carbon of these soils showed that nitrate addition at 100 kg ha-1 after 9 day incubation stimulated CH4 production. Higher nitrate addition, however, could initially suppress methanogenic activities. Organic carbon additions also significantly enhanced CH4 production