CO2 exchange in an organic field growing barley or grass in eastern Finland

The CO₂ dynamics were measured in an organic soil in eastern Finland during the growing season and wintertime, and the annual CO₂ balance was calculated for plots where barley or grass was grown. During the summer, the CO₂ dynamics were measured by transparent and opaque chambers using a portable infrared gas analyser for the CO₂ analyses. During the winter, the CO₂ release was measured by opaque chambers analysing the samples in the laboratory with a gas chromatograph. Statistical response functions for CO₂ dynamics were constructed to evaluate the annual CO₂ exchange from the climatic data. The net CO₂ exchange was calculated for every hour in the snow‐free season. The carbon balance varied extensively depending on the weather conditions, and type and phenology of vegetation. During the growing season, the grassland was a net source while the barley field was a net sink for CO₂. However, both soils were net sources for CO₂ when autumn, winter and spring were included also. The annual CO₂ emissions from the grassland and barley soil were 750 g CO₂‐C m^?2 and 400 g CO₂‐C m^?2, respectively. The carbon accumulated in root and shoot biomass during the growing season was 330 g m^?2 for grass and 520 g m^?2 for barley. The C in the aboveground plant biomass ranged from 43 to 47% of the carbon fixed in photosynthesis (P_G) and the proportion of C in the root biomass was 10% of the carbon fixed in photosynthesis. The bare soils had 10–60% higher net CO₂ emission than the vegetated soils. These results indicate that the carbon balance of organic soils is affected by the characteristics of the prevailing plant cover. The dry summer of 1997 may have limited the growth of grass in the late summer thus reducing photosynthesis, which could be one reason for the high CO₂ release from this grass field.     

Soil Carbon Dioxide Flux in Antarctic Dry Valley Ecosystems

The Antarctic dry valleys of southern Victoria Land are extreme desert environments where abiotic factors, such as temperature gradients, parent material, and soil water dynamics, may have a significant influence on soil carbon dioxide (CO₂) flux. Previous measurements of soil respiration have demonstrated very low rates of CO₂ efflux, barely above detection limits. We employed a modified infrared gas-analyzer system that enabled detection of smaller changes in CO₂ concentration in the field than previously possible. We measured diel CO₂ fluxes and monitored soil microclimate at three sites in Taylor Valley. Soil CO₂ flux ranged from –0.1 to 0.15 mol m^–2 s^–1. At two of the three sites, we detected a physically driven flux associated with diel variability in soil temperature. At these sites, CO₂ uptake (negative flux) was associated with dropping soil temperatures, whereas CO₂ evolution (positive flux) was associated with increases in soil temperature. These observations are corroborated by laboratory experiments that suggest that CO₂ flux is influenced by physically driven processes. We discuss four potential mechanisms that may contribute to physically driven gas exchange. Our results suggest there are strong interactions between biological and abiotic controls over soil CO₂ flux in terrestrial ecosystems of the Antarctic dry valleys, and that the magnitude of either may dominate depending on the soil environment and biological activity.