Methane and nitrous oxide fluxes in native, fertilized and cultivated grasslands

Abstract

METHANE and nitrous oxide are long-lived, radiatively active trace gases that account for ∼20% of the total anticipated atmospheric warming¹. The atmospheric concentrations of both gases have increased dramatically over the past few decades, and continue to increase at a rate of ∼1.1 and 0.25% yr⁻¹ for CH₄ (ref. 2) and N₂O (ref. 3) respectively. Increased biospheric production is gen-erally suggested as the reason for the increases, but decreases in global sinks may also be important. It has been suggested, for example, that nitrogen fertilization may decrease the rate at which tropical^4,5 and temperate forest soils⁶ take up methane from the atmosphere. Furthermore, the recent extensive changes in land management and cultivation could be contributing to the observed increases in both atmospheric CH₄ and N₂O, as has been suggested for tropical soils⁷. Little information exists on CH₄ uptake in temperate grasslands (which currently occupy ∼8% of the Earth's surface), its relation to N₂O production, or the effect of land management or cultivation^8,9. Here we report measurements of CH₄ uptake and N₂O emissions in native, nitrogen-fertilized and wheat-growing prairie soils from spring to late autumn, 1990. We found that nitrogen fertilization and cultivation can both decrease CH₄ uptake and increase N₂O production, thereby contributing to the increasing atmospheric concentrations of these gases.