Nitrogen availability in soil and forest floor of contrasting types of boreal mixedwood forests

Abstract

Boreal mixedwood forests with varying proportions of coniferous and deciduous species are found throughout the North American continent. Maintenance of a deciduous component within boreal forests is currently favoured, as deciduous species are believed to promote faster nutrient turnover and higher nutrient availability. Results of comparisons of deciduous and coniferous forests are, however, inconsistent in supporting this generalization. We compared indices of soil nitrogen (N) availability in the forest floor and mineral soil of deciduous, mixed, and coniferous stands of boreal mixedwood forest in northwestern Alberta. Deciduous stands had higher N availability, reflected by higher pools of NH 4 -N and inorganic N in the forest floor. Forest floors of deciduous stands also tended to have higher concentrations of microbial N but did not have higher levels of NO 3 -N or higher rates of net nitrification. Mixed stands showed the highest rates of net N mineralization. Soil N availability was more closely related to litter N content than to litter decomposition rate. The variation among the forest types is likely attributable to vegetation, as topography is fairly uniform, stands do not differ in soil texture, and N-availability indices correlated directly with the proportion of deciduous trees. Résumé :Les forêts boréales mélangées, qui contiennent des proportions variables de conifères et de feuillus, sont pré-sentes partout sur le continent nord-américain. On encourage actuellement le maintien d'une composante feuillue dans les forêts boréales croyant que les espèces feuillues favorisent un recyclage plus rapide et une plus grande disponibilité des nutriments. Les résultats de comparaisons entre des forêts résineuses et feuillues sont cependant trop inconsistants pour supporter cette généralisation. Les auteurs ont comparé les indices de disponibilité de l'azote (N) du sol dans la couverture morte et le sol minéral de peuplements feuillus, mélangés et résineux de la forêt boréale mélangée du nordouest de l'Alberta. Les peuplements feuillus avaient une plus grande disponibilité de N reflétée par des pools de N-NH 4 et de N inorganique plus importants dans la couverture morte. La couverture morte des peuplements feuillus avait aussi tendance à avoir de plus fortes concentrations de N microbien mais n'avait pas de niveaux plus élevés de N-NO 3 ou de plus hauts taux de nitrification nette. Les peuplements mélangés avaient les taux de minéralisation nette de N les plus élevés. La disponibilité de N du sol était plus étroitement reliée au contenu en N de la litière qu'à son taux de dé-composition. Les différences entre les types de forêts sont probablement attribuables à la végétation étant donné que la topographie est assez uniforme, que les peuplements ont des sols dont la texture est semblable et que les indices de disponibilité de N sont directement corrélés avec la proportion de tiges feuillues.[Traduit par la Rédaction] Jerabkova et al. 122

Comparing soil biogeochemical processes in novel and natural boreal forest ecosystems

“…The influence of tree species on key biogeochemical processes has been previously documented in Western Canadian forests, including influences on nutrient availability (Prescott et al, 2000c;Prescott and Vesterdal, 2005;Jerabkova et al, 2006), microbial communities (Leckie et al, 2004;Grayston and Prescott, 2005;Hannam et al, 2006), and organic matter characteristics (Hannam et al, 2004). In our study, the importance of the coniferous component in mixed stands was obvious, as the presence of either spruce or pine trees determined how boreal forest soils grouped in terms of nutrient availability.…”

Nitrogen availability from peat amendments used in boreal oil sands reclamation

“…Dissolved organic nitrogen (DON) was calculated by subtracting NH 4 -N and NO 3 -N concentrations from TN. The MBN values were further calculated as DON after fumigation minus DON before fumigation, and MBC as DOC after fumigation minus DOC before fumigation (Jerabkova et al 2006). No conversion factor was used as the primary objective was to compare values among seasons.…”

“…Field measurements of N transformations in boreal forest and peatland soils typically show low rates of net N mineralization and nitrification (Table 1). Deciduous and mixed boreal forest floors are often reported to have higher soil N availability than coniferous forest floors; these differences have been related to lower N concentrations as well as higher lignin content in coniferous litter (Coˆte´et al 2000;Lindo and Wisser 2003;Jerabkova et al 2006). Low mineralization and decomposition rates in peatlands have commonly been assumed to be due to anoxic conditions in these soils.…”

Variability of soil N cycling and N2O emission in a mixed deciduous forest with different abundance of beech

“…Taylor et al 1991;Prescott 2002;Inagaki et al 2004;Miyamoto and Hiura 2008) and soil conditions (Bengtsson et al 2003;Booth et al 2005;Kooijman et al 2008). Distinctive differences were found between conifers and hardwood species with regard to their effects on stocks, distribution and mineralization rates of soil N (Jerabkova et al 2006;Joshi et al 2006;Inagaki et al 2004). In addition, N 2 O emissions were significantly higher in deciduous than in coniferous forests (Ambus et al 2006;Butterbach-Bahl et al 2002).…”