SOIL PROCESSES AND GLOBAL CHANGE

Contributors to the Intergovernmental Panel on Climate Change (IPCC) g enerally agree that increases in the atmospheric concentration of gree nhouse trace gases (i.e., CO2, CH4, N2O, O-3) since preindustrial time s, about the year 1750, have led to changes in the earth's climate. Du ring the past 250 years the atmospheric concentrations of CO2, CH4, an d N2O have increased by 30, 145, and 15%, respectively. A doubling of preindustrial CO2 concentrations by the end of the twenty-first centur y is expected to raise global mean surface temperature by about 2 degr ees C and increase the frequency of severe weather events. These incre ases are attributed mainly to fossil fuel use, land-use change, and ag riculture. Soils and climate changes are related by bidirectional inte ractions. Soil processes directly affect climatic changes through the production and consumption of CO2, CH4, and N2O and, indirectly, throu gh the production and consumption of NH,, NO,, and CO. Although CO2 is primarily produced through fossil fuel combustion, land-use changes, conversion of forest and grasslands to agriculture, have contributed s ignificantly to atmospheric increase of CO2. Changes in land use and m anagement can also result in the net uptake, sequestration, of atmosph eric CO2. CH4 and N2O are produced (30% and 70%, respectively) in the soil, and soil processes will likely regulate future changes in the at mospheric concentration of these gases. The soil-atmosphere exchange o f CO2, CH4, and N2O are interrelated, and changes in one cycle can im part changes in the N cycle and resulting soil-atmosphere exchange of N2O. Conversely, N addition increases C sequestration. On the other ha nd, soil processes are influenced by climatic change through imposed c hanges in soil temperature, soil water, and nutrient competition. Incr easing concentrations of atmospheric CO2 alters plant response to envi ronmental parameters and frequently results in increased efficiency in use of N and water. In annual crops increased CO2 generally leads to increased crop productivity. In natural systems, the long-term impact of increased CO2 on ecosystem sustainability is not known. These chang es may also-result in altered CO2, CH4, and N2O exchange with the soil . Because of large temporal and spatial variability in the soil-atmosp here exchange of trace gases, the measurement of the absolute amount a nd prediction of the changes of these fluxes, as they are impacted by global change on regional and global scales, is still difficult. in re cent years, however, much progress has been made in decreasing the unc ertainty of field scale flux measurements, and efforts are being direc ted to large scale field and modeling programs. This paper briefly rel ates soil process and issues akin to the soil-atmosphere exchange of C O2, CH4, and N2O. The impact of climate change, particularly increasin g atmospheric CO2 concentrations, on soil processes is also briefly di scussed.