Methane flux in non‐wetland soils in response to nitrogen addition: a meta‐analysis

Abstract

The controls on methane (CH₄) flux into and out of soils are not well understood. Environmental variables including temperature, precipitation, and nitrogen (N) status can have strong effects on the magnitude and direction (e.g., uptake vs. release) of CH₄ flux. To better understand the interactions between CH₄‐cycling microorganisms and N in the non‐wetland soil system, a meta‐analysis was performed on published literature comparing CH₄ flux in N amended and matched control plots. An appropriate study index was developed for this purpose. It was found that smaller amounts of N tended to stimulate CH₄ uptake while larger amounts tended to inhibit uptake by the soil. When all other variables were accounted for, the switch occurred at 100 kg N·ha⁻¹·yr⁻¹. Managed land and land with a longer duration of fertilization showed greater inhibition of CH₄ uptake with added N. These results support the hypotheses that large amounts of available N can inhibit methanotrophy, but also that methanotrophs in upland soils can be N limited in their consumption of CH₄ from the atmosphere. There were interactions between other variables and N addition on the CH₄ flux response: lower temperature and, to a lesser extent, higher precipitation magnified the inhibition of CH₄ uptake due to N addition. Several mechanisms that may cause these trends are discussed, but none could be conclusively supported with this approach. Further controlled and in situ study should be undertaken to isolate the correct mechanism(s) responsible and to model upland CH₄ flux.