Respiration in boreal forest soil as determined from carbon dioxide concentration profile

Soil respiration forms a substantial part of the ecosystem respiration. However, the respiration measurements conducted with chambers on the soil surface do not give information on the vertical distribution Of CO2 sources and its seasonal dynamics. We used permanently installed CO2 probes to determine the CO2 profile in a boreal coniferous forest soil and calculated the CO2 efflux from the concentration profile with a dynamic model. There was an increase in both soil CO2 efflux and soil air CO2 concentration over the 2.5-mo Study period between April 15 and June 30. The CO2 efflux determined from the concentration profile was in relatively good agreement with the CO2 efflux measured by, open dynamic chamber method. We also determined the respiration of different soil horizons and estimated the contribution of recent photosynthate to total respiration. Humus layer and A-horizon contributed 69.9%, B-horizon 19.8%, and C-horizon 10.4% of the total CO2 efflux. The Q(10) values determined over 7-d periods were on average 2.54, 3.66, and 13.14 in A-, B-, and C-horizons, respectively However, when fitted over the whole 2.5-mo time period, the Q(10) values were 3.56, 5.57, and 17.45 in A-, B-, and C-horizons, respectively. Based on the different temperature responses obtained over 7-d and 2.5-mo time periods, we estimated the contribution of recent photosynthate to soil respiration. In April, the respiration originating from recent photosynthate contributed about 2% of the total respiration in the A-, B-, and C-horizons and increased to 32, 35, and 24% by June 30 in the respective soil horizons.