METHANE AND NITROUS-OXIDE FLUXES IN NATIVE, FERTILIZED AND CULTIVATED GRASSLANDS

METHANE and nitrous oxide are long-lived, radiatively active trace gases that account for approximately 20% of the total anticipated atmospheric warming 1. The atmospheric concentrations of both gases have increased dramatically over the past few decades, and continue to increase at a rate of approximately 1.1 and 0.25% yr-1 for CH4 (ref. 2) and N2O (ref. 3) respectively. Increased biospheric production is generally 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 soils 6 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 soils 7. Little information exists on CH4 uptake in temperate grasslands (which currently occupy approximately 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.