SOIL CARBON CYCLING AT A BLACK SPRUCE (PICEA-MARIANA) FOREST STAND INSASKATCHEWAN, CANADA

Stored amounts and flow rates of soil carbon were measured simultaneou sly with soil environmental conditions (temperature and moisture conte nt) periodically during the growing seasons from 1994 to 1995 at two p lots (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 a rea of Saskatchewan, Canada. Seasonal trends in litterfall rate and ac cumulation of the A(0) layer were not observed, while the total and mi neral soil respiration rates changed seasonally with soil temperature. There was no significant relationship between soil moisture content a nd-any how rates or accumulations of soil carbon. Soil respiration and loss of litter might have been very low during the winter (November t o early May) because of the frozen soil. The annual soil carbon cyclin g was analyzed by a compartment model, based on the data obtained in t his 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 pl ot A and 0.0284 yr(-1) and 0.0020 for plot B, respectively. These valu es 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 ground water level is higher in plot B. The soil in both plots were accumulat ing 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 becau se of the lower soil temperature than that reported in the cool- and w arm-temperate forests. Soil carbon cycling in the boreal forest predom inantly occurred at the surface of the mineral soil, suggesting that t he 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.