Soil respiration in Siberian Taiga ecosystems with different histories of forest fire

Abstract

Soil respiration includes soil microbial respiration, soil fauna respiration, and plant root respiration, therefore it reflects the biological activity of the soil ecosystems. The Siberian Taiga often experiences serious damage from forest fire, due to the very low precipitation in spring. We measured the soil respiration in five forest soil ecosystems with different histories of forest fire in Yakutsk in August 1997. The dominant tree species was Larix cajanderi, and the soils were Spodosols with a sandy and loamy texture. We also measured the soil respiration in a grassland. At severely burned sites, almost all the trees had fallen, litter and vegetation on the forest floor had burned, other forms of vegetation, including bryophytes or herbs, had invaded. At less severely burned forest sites, the trees were still standing but litter and vegetation on the forest floor had disappeared. Soil temperature, moisture, pH, and EC all increased after severe forest fires, the A-horizon showed a higher organic carbon content and a lower CN ratio. Soil respiration rate ranged from 18 to 397 (10-6 g CO2 m-2 s-1) in the same order reported so far. Soil respiration in severely burned forests was significantly lower than in intact forests, and was similar to that of grassland. Furthermore, mildly burned forests showed soil respiration values intermediate between those of severely burned and intact forests. These findings suggest that tree root respiration is considerably higher than root respiration of other plants or microbial and fauna respiration in soil. Soil microbial respiration was determined by the incubation method under the same temperature and soil moisture conditions as those in situ. Multiple regression analysis for mineral soils showed that the soil microbial respiration increased with the increase of the soil temperature and organic carbon content, that the soil microbial respiration decreased with the increase of pH. Whole soil microbial respiration within 1 m depth was higher in severely burned forests than in intact forests. These findings show that forest fire increased the soil microbial respiration and confirm that the loss of tree root respiration was the main reason for the decrease in soil respiration after severe forest fire. The contribution of tree root respiration to soil respiration was estimated to exceed 50%. Severe forest fire kills trees, and consequently results in a decrease of soil respiration.