Dynamics of carbon and nitrogen mineralization in relation to stand type, stand age and soil texture in the boreal mixedwood L. Coˆte´ a,b , S. Brown c , D. Pare´ b,d, *, J. Fyles d , J. Bauhus e a Biodoˆme de Montre´al, 4777 avenue Pierre-de-Coubertin, Montre´al, Que. H1V 1B3, Canada b GREF-interuniversitaire, Universite´ du Que´bec a` Montre´al, C.P. 8888, Succursale Centre-Ville, Montre´al, Que. H3C 3P8, Canada c GREF-interuniversitaire, McGill University, Department of Natural Resource Sciences, Macdonald Campus, Sainte-Anne-de-Bellevue, Que. H9X 3V9, Canada d Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, P.O. Box 3800, Sainte-Foy, Que. G1V 4C7, Canada e Australian National University, Department of Forestry, Canberra, ACT 0200, Australia Accepted 13 December 1999 Abstract In the boreal mixed forest, stand composition generally changes from deciduous to mixed to coniferous stands during post- disturbance succession. Our objective was to determine the influence of forest composition on the quality of soil nitrogen and carbon as determined by C and N mineralization during the course of a long-term in vitro incubation (282 days). Three stand types (Populus tremuloides, Betula papyrifera, and conifers (mixture of Abies balsamea and Picea glauca )), of two ages (50 and 124 years since fire) growing on two soil types (clay and till) were considered. Expressed on an organic C basis, our results showed a greater N mineralization for deciduous than coniferous stands, both in the mineral soil and the forest floor, a higher N mineralization in the mineral soil of older stands as compared with young ones, and in till than in clay soils. Mineralization of C was higher in the forest floor of clay soils as compared to till soils while the opposite was found in the mineral soil. It was also higher in both soil layers of older sites. The observed dierences in N and C mineralization among stand types, stand ages and deposits appeared to be due to dierences in the most labile fraction of soil organic matter because these dierences were observed within 100 days of incubation. The ratio of C mineralized–N mineralized was greater in coniferous than deciduous soils in both soil layers, indicating a lesser quality of organic matter under coniferous stands. Despite significant dierences among the above-listed factors for N and C mineralization on an organic C basis, the pool size of mineralized (or mineralizable) N and C was generally not significantly dierent between the dierent forest and soil types because of an inverse relationship between quality and quantity of soil organic matter. Correlation and multiple regression analysis indicated that clay content (negatively), C–N ratio (negatively), available P as well as exchangeable Mn were related to the mineralization of N. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Boreal forest; Soil carbon; Soil nitrogen; Vegetation dynamics 1. Introduction Boreal forest soils contain large amounts of or- ganic nitrogen of which only a small portion is po- tentially available to the vegetation over a growing season, and the productivity of these forests is often N limited. Fertilization trials have often shown a growth response to N addition in both deciduous (Van Cleve, 1973; Weetman et al., 1978) and coni- ferous boreal stands (Binkley and Ho¨gberg, 1997; Weetman et al., 1978). Apart from soil climate, the rate of N mineralization is dependent upon the chemical characteristics of organic matter that aect the activity of the decomposer community. Soil en- Soil Biology & Biochemistry 32 (2000) 1079–1090 0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S0038-0717(00)00017-1 www.elsevier.com/locate/soilbio * Corresponding author. Fax: +1-418-649-6956. E-mail address: dpare@cfl.forestry.ca (D. Pare´).