Soil carbon cycling at a black spruce (Picea mariana) forest stand in Saskatchewan, Canada

Stored amounts and flow rates of soil carbon were measured simultaneously with soil environmental conditions (temperature and moisture content) periodically during the growing seasons from 1994 to 1995 at two plots (plot A was a dry soil condition, and plot B was a wet condition) in a black spruce (Picea mariana) forest stand in the Prince Albert area of Saskatchewan, Canada. Seasonal trends in litterfall rate and accumulation of the A(0) layer were not observed, while the total and mineral soil respiration rates changed seasonally with soil temperature. There was no significant relationship between soil moisture content and-any how rates or accumulations of soil carbon. Soil respiration and loss of litter might have been very low during the winter (November to early May) because of the frozen soil. The annual soil carbon cycling was analyzed by a compartment model, based on the data obtained in this study. The relative decomposition rate of the A(0) layer and humus in the mineral soil were estimated at 0.0632 yr(-1) and 0.0045 for plot A and 0.0284 yr(-1) and 0.0020 for plot B, respectively. These values indicate that the soil carbon cycling in plot A was about twice as fast as that in plot B. The slower cycling in plot B may be caused by the lower soil temperature and humid soil conditions, since the groundwater level is higher in plot B. The soil in both plots were accumulating carbon, i.e., 0.13 t C ha(-1) yr(-1) for plot A and 0.03 for plot B. The soil carbon cycling in the boreal forest stand was slower because of the lower soil temperature than that reported in the cool- and warm-temperate forests. Soil carbon cycling in the boreal forest predominantly occurred at the surface of the mineral soil, suggesting that the decomposition response of soil organic matter in the boreal forest will be enhanced compared to other climate zone forests because of the large predicted temperature increase in the boreal zone under global warming.