Environmental impacts on the diversity of methane-cycling microbes and their resultant function

Methane is an important anthropogenic greenhouse gas that is produced and consumed in soils by microorganisms responding to micro-environmental conditions. Current estimates show that soil consumption accounts for 5-15% of methane removed from the atmosphere on an annual basis. Recent variability in atmospheric methane concentrations has called into question the reliability of estimates of methane consumption and call for novel approaches in order to predict future atmospheric methane trends. This review synthesizes the environmental and climatic factors influencing the consumption of methane from the atmosphere by non-wetland, terrestrial soil microorganisms. In particular, we focus on published efforts to connect community composition and diversity of methane-cycling microbial communities to observed rates of methane flux. We find abundant evidence for direct connections between shifts in the methane-cycling microbial community, due to climate and environmental changes, and observed methane flux levels. These responses vary by ecosystem and associated vegetation type. This information will be useful in process-based models of ecosystem methane flux responses to shifts in environmental and climatic parameters

Meta-analysis of environmental impacts on nitrous oxide release in response to N amendment

Atmospheric nitrous oxide (N2O) accounts for approximately 5% of the global greenhouse effect and destroys stratospheric ozone. Soils are the most important source of N2O, which is produced during nitrification and denitrification. To assess the impact of environmental variables and ecosystems on N2O flux, we performed a meta-analysis comparing N2O flux in N amended and matched control plots in non-agricultural soils. We found that N2O release increased with N amendment in the short term. Although there were few studies in shrubland, this ecosystem showed the greatest response. The N2O response to N amendment was greater in year-round studies and in studies with more measurements, but lower in longer studies. The N2O response was greater at higher latitudes and precipitation rates. We also observed an unexpected 55% decline in the N2O response to N amendment over the 23 years covered by the studies. This pattern may reflect a suppression of the N2O response from long-term N deposition accumulation, particularly in temperate regions. Although short-term increases in reactive N entering natural systems may cause positive feedbacks to the release of N2O, this effect may diminish over time in locations with high rates of N deposition