Functional Analysis of Copper (Cu) and Soil Ph for the Nosz Gene Abundance and N2o Emissions in Acidic Soils

Nitrous oxide (N2O) emissions from agricultural soils are alarming for global warming and climate change. Conversion of N2O to N2 is carried out only by nosZ gene encoded N2O-reductase which is highly sensitive to acidic pH and limited by copper (Cu) availability. We hypothesized that increasing soil pH and adequate Cu supply to acidic soils can promote the conversion of N2O to N2 and thereby mitigate N2O emissions. Therefore, a microcosm laboratory based study was conducted to test this hypothesis. Cu was applied at the dose of 0, 10, 25 and 50 mg kg-1 to three acidic soils (Soil 1: rice-fallow soil, Soil 2: rice-rapeseed soil, and Soil 3: vegetable soil) without and with dolomite (0 and 5 g kg-1). Cu application substantially enlarged the abundance of nosZ gene and consequently mitigated N2O emissions from three soils. However, application of 25 Cu mg/kg was the most effective to reduce the emissions of N2O. Dolomite executed an increasing influence on soil pH that greatly increased dissolved organic carbon, microbial biomass, and nosZ gene abundance and resulted in decreased N2O emissions. NH4+-N concentration rapidly declined in dolomite treated soil and resulted in accumulation of NO3--N indicating use of N2O as electron acceptor rather than NO3- and thus causing lower emissions. The highest emissions were 0.19 µg N2O-N kg-1 h-1 in Soil 1, 0.34 µg N2O-N kg-1 h-1 in Soil 2, and 0.32 µg N2O-N kg-1 h-1 in Soil 3 in 0 Cu mg/kg treatment at day 15 of the study. The cumulative N2O emissions were lowest (87.42 µg N2O-N kg-1 in Soil 1, 258.96 µg N2O-N kg-1 in Soil 2, and 225.12 µg N2O-N kg-1 in Soil 3) in 25 Cu mg kg-1 with dolomite treatment. These results propose that Cu and dolomite addition to acidic soils may lower N2O emissions.