An analysis of litter nitrogen dynamics using artificial soils across a gradient of forest soil disturbances

Abstract

Kranabetter, J. M. and Chapman, B. K. 2004. An analysis of litter nitrogen dynamics using artificial soils across a gradient of forest soil disturbances. Can. J. Soil Sci. 84: 159-167. The release of nutrients from a standard litter is often assumed to be solely a function of its decomposition rate. We tested whether nitrogen release would also be influenced by soil attributes affected by disturbance, such as interactions with soil microflora. Changes in nitrogen contents of decaying litter (Populus balsamifera) were compared across soil compaction and organic matter removal treatments in central British Columbia, using artificial materials to isolate litter bags from contact with forest floors or mineral soil. After 30 mo, nitrogen content of litter was only slightly higher on artificial soils than actual soils, suggesting that most nitrogen had been lost by leaching. A significant interaction, however, was detected in leaf nitrogen content between organic matter removal and soil compaction treatments that was not found on the artificial soils. This difference in nitrogen release led to a range in C:N ratios of 28 to 32 (from an initial C:N ratio of 52) for leaves at 1.5 g (70% mass loss). The differences in nitrogen release were relatively small and will perhaps be less important than other effects of soil disturbance (such as changes in litter quality) on nitrogen cycling. On présume souvent que les déchets forestiers libèrent uniquement leurs éléments nutritifs en fonction de la rapidité avec laquelle ils se décomposent. Les auteurs ont tenté de voir si la quantité d'azote libérée dépend aussi de paramètres affectés par la perturbation du sol comme les interactions avec la microflore tellurique. Pour cela, ils ont comparé la teneur en azote de résidus forestiers en décomposition (Populus balsamifera) selon divers traitements du sol pratiqués dans le centre de la Colombie-Britannique (compactage et retrait de la matière organique) en isolant des sacs de déchets du sol forestier ou minéral grâce à des matériaux synthétiques. Après 30 mois, la concentration d'azote des déchets n'était que légèrement plus élevée dans le sol artificiel que dans le sol naturel, signe que la majeure partie de l'azote se perd par lixiviation. L'interaction sensible entre le retrait de la matière organique et le compactage observée pour la teneur des feuilles en azote dans le sol naturel n'a toutefois pas été relevée dans le sol artificiel. Cet écart au niveau du taux de libération de l'azote donne un ratio C:N variant de 28 à 32 (contre un ratio initial de 52) pour les feuilles de 1,5 g (perte de 70 % de la masse). Les variations au niveau de la libération de N restent relativement faibles et ont peut-être moins d'importance sur le cycle de l'azote que d'autres conséquences de la perturbation du sol (une modification de la qualité des résidus, par exemple).

Effects of organic matter removal, soil compaction and vegetation control on 10th year biomass and foliar nutrition: LTSP continent-wide comparisons

“…Greater nutrient demands by larger trees, together with dilution effects through increased fascicle growth, may account for the negative overall correlations between planted loblolly pine biomass and foliar N and P concentrations (c.f., Zutter et al, 1999), whereas the lack of significant OM treatment effects on planted tree foliar nutrition and biomass at the study level is consistent with much greater variation in soil nutrient availability between sites than among treatments at a given site (e.g., Li et al, 2003;Kranabetter and Chapman, 2004).…”

“…(Li et al, 2003) or may not (Tan et al, 2005;Blumfield et al, 2005;Kranabetter et al, 2006) reduce mineralization rates. Kranabetter and Chapman (2004) showed limited OM-Comp effects on yr 5 litter nitrogen dynamics. Overall, compaction effects on productivity appear more closely related to soil physical properties and competition effects, than to soil nutrient availability.…”

Evidence that Northern Pioneering Pines with Tuberculate Mycorrhizae are Unaffected by Varying Soil Nitrogen Levels

“…There were forest floors present in the soil intact areas, but forest floors were not initially sampled. We know from other work that forest floors in the area are typically around 1 % nitrogen [ 19 ], and we determined nitrogen isotope ratios on forest floor samples taken from a trial located 1.24 km from the Skulow pit site.…”