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

Soil respiration includes soil microbial respiration, soil fauna respiratio n, and plant root respiration, and therefore it reflects the biological act ivity of the soil ecosystems. The Siberian Taiga often experiences serious damage from forest fire, due to the very low precipitation in spring. We me asured the soil respiration in five forest soil ecosystems with different h istories of forest fire in Yakutsk in August 1997. The dominant tree specie s 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, and other forms of vegetation, including bryophyt es or herbs, had invaded. At less severely burned forest sites, the trees w ere still standing but litter and vegetation on the forest door had disappe ared. Soil temperature, moisture, pH, and EC all increased after severe for est fires, and the A-horizon showed a higher organic carbon content and a l ower 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 simi lar to that of grassland. Furthermore, mildly burned forests showed soil re spiration values intermediate between those of severely burned and intact f orests. These findings suggest that tree root respiration is considerably h igher than root respiration of other plants or microbial and fauna respirat ion in soil. Soil microbial respiration was determined by the incubation me thod under the same temperature and soil moisture conditions as those in si tu. Multiple regression analysis for mineral soils showed that the soil mic robial respiration increased with the increase of the soil temperature and organic carbon content, and that the soil microbial respiration decreased w ith the increase of pH. Whole soil microbial respiration within 1 m depth w as higher in severely burned forests than in intact forests, These findings show that forest fire increased the soil, microbial respiration and confir m that the loss of tree root respiration was the main reason for the decrea se in soil respiration after severe forest fire. The contribution of tree r oot respiration to soil respiration was estimated to exceed 50%. Severe for est fire kills trees, and consequently results in a decrease of soil respir ation.