A growth chamber experiment was conducted with Pinuscontorta Dougl. ex Loud. var. latifolia Engelm. seedlings grown in soil compacted at 0.1, 2.0, 4.0, 6.0, and 8.0 MPa pressure. Three moisture regimes were applied factorially to compaction levels by watering from above or by maintaining 2- or 10-cm water tables at the base of the 40-cm soil columns. All treatments were grown at either 22:14 °C or 26:18 °C (light:dark) for 13 weeks. Soil compaction increased bulk density, penetrometer resistance, and soil CO2 and ethylene. The presence of water tables resulted in elevated soil gravimetric water content, which rose with increased compaction and resulted in reduced penetrometer resistance and soil O2. Increased compaction was associated with decreased needle lengths, root dry weights, and net photosynthesis and increased rates of shoot respiration. Compaction had a small effect on height growth, with the tallest seedlings occurring at the greatest compaction rate. Shoot concentrations of mineral nutrients also decreased as soil compaction increased. Within the water table treatments, increased gravimetric soil water content was generally paralleled by a rise in the negative effects of compaction on growth, root/shoot dry weight ratios, and shoot mineral nutrient concentrations.

Conlin, T. S. S. and van den Driessche, R. 2000. Response of soil CO 2 and O 2 concentrations to forest soil compaction at the Long-term Soil Productivity sites, Central British Columbia. Can. J. Soil Sci. 80: 625-632. The concentrations of soil CO 2 and O 2 at three Long-term Soil Productivity sites located in the Sub-Boreal Spruce biogeoclimatic zone of British Columbia, Canada, were monitored over several growing seasons. These sites were treated with three levels of soil compaction and three levels of organic material removal following forest harvest. Both compaction and depth had a significant effect upon soil CO 2 concentrations and average values increased in response to deeper sampling and compaction. Removal of the forest floor and other organic materials had no significant effect upon soil CO 2 and O 2 concentrations. Mean soil CO 2 concentrations varied from site to site and data collected over three growing seasons also showed that mean CO 2 values in response to compaction fluctuated significantly from year to year. The high levels of soil CO 2 observed in this study (up to 40 000 µL L -1 ), especially in response to the compaction treatments, may have had a substantial effect upon whole plant carbon allocation as well as soil nutrition available to trees growing on the treated plots. Although mean soil O 2 also decreased in response to compaction and sampling depth, these lower concentrations did not approach the levels required to influence plant growth.Key words: Soil, compaction, carbon dioxide, oxygen, long-term soil productivity Conlin, T. S. S. et van den Driessche, R. 2000. Réponse à la compaction des concentrations de CO 2 et de O 2 des sols forestiers aux Emplacements d'observation de longue durée de la productivité du sol dans le centre de la Colombie-Britannique. Can. J. Soil Sci. 80: 625-632. Nous avons surveillé durant plusieurs saisons de croissance l'évolution des concentrations de CO 2 et de O 2 dans le sol à trois placeaux d'observation de longue durée de la productivité du sol dans la zone biogéoclimatique sud-boréale à épinette (épicéa) en Colombie-Britannique (Canada). Ces placeaux étaient exposés à trois intensités de compaction et à trois niveaux d'enlèvement de la couche organique à la suite de la récolte de la forêt. La compaction et la profondeur d'échantillonnage exerçait toutes deux un effet significatif sur les concentrations de CO 2 du sol, les valeurs moyennes augmentant en fonction du degré de compaction et de la profondeur de l'échantillon. L'enlèvement de la couche organique et d'autres matières organiques n'avaient pas d'effets significatifs sur les concentrations de CO 2 et de O 2 du sol. Les concentrations moyennes de CO 2 variaient d'un emplacement à l'autre et en outre leur réaction à la compaction fluctuait significativement d'une année à l'autre. Les concentrations élevées de CO 2 du sol observées (jusqu'à 40 000 µL L -1 ), surtout en réponse à l'intensité de la compaction, pourraient avoir un effet substantiel sur la disponibilité du carbone et des éléments ...

Typha latifolia and Carex rostrata both exhibit rhizospheric iron reduction after iron deprivation while Phragmites australis does not. Examination of T. latifolia and C. rostrata roots showed that these potential sites of iron uptake are surrounded by oxidized rhizospheres. Rhizospheric oxidation by T. latifolia, C. rostrata, and P. australis is more extensively distributed along the root than has been recorded in the past. All three species lower the pH of their rhizospheres: iron starvation increases the rate of acidification in T. latifolia and C. rostrata, but not in P. australis. Observation of the superimposition of oxidative rhizospheres over iron reduction sites supports the hypothesis that oxidation protects the root from reduced toxins. However, it is also possible that root oxidation may play a major role in nutrient procurement by hydrophytes.

A portable delimber-debarker-chipper, designed for in-woods chipping operations, was used to produce waste bark and wood residue from winter-harvested tree-length trembling aspen logs. The residue was then utilized to create leachate, which was subsequently used to treat white spruce, lodgepole pine, paper birch, aspen and Calarnagrostis canadensis seedlings grown in sand-filled pots. Treatment with the leachate significantly decreased height growth and shoot and root dry weights of all species relative to the control treatment. Root:shoot ratios of all tree species except lodgepole pine were increased significantly by application of leachate. The root:shoot ratios of treated C. canadensis were significantly increased during one season, but significantly reduced in the following season. The data indicated that leachate from aspen bark and wood residue contain allelochemical properties that could affect the regenerative capacity of aspen cutblocks harvested for in-woods chipping operations.Key words: aspen, leachate, allelochemistry, Populus tremuloides, in-woods chipping Une Cbrancheuse-Ccorceuse-dkchiqueteuse mobile, conGue pour les opCrations de mise en copeaux en forst, a Ct C utilisCe pour produire des rksidus d'kcorce et de bois provenant de troncs en longueur de peuplier faux-tremble rCcoltCs au cours de l'hiver. Les rCsidus ont Ct C par la suite utilisCs pour crker un mkdium de percolation qui a Ct C utilisC par la suite pour traiter des semis d'Cpinette blanche, de pin lodgepole, de bouleau B papier, de peuplier et de Calamagrostis canadensis cultivCs dans des pots remplis de sable. Le traitement avec le mCdium a entrain6 une diminution significative de la croissance en hauteur et du poids sec de la pousse et des racines de toutes les espkces par rapport au tmitement tCmoin. Les ratios racineslpousse de toutes les espkes d'arbres B l'exception du pin lodgepole ont Ct C augment& de f a~o n significative suite B l'application du mCdium. Les ratios racineslpousse des C. canadensis trait& ont augment6 de f a~o n significative au cours d'une saison, mais Ctaient significativement rCduits la saison suivante. Les donnCes indiquent que le mCdium obtenu B partir de 1'Ccorce et des rCsidus de peuplier contient des ClCments allClochimiques qui pourraient affecter la capacitC rCgCnCratrice des parterres de coupe de peuplier rCcoltC pour des opCrations de dkchiquetage en for&t.

The efflux of CO2 from roots of Pinusbanksiana Lamb., Pinuscontorta Dougl., Piceaglauca (Moench) Voss, Piceamariana (Mill.) B.S.P., and Larixlaricina (Du Roi) K. Koch were measured under anaerobic and aerobic conditions at 5, 15, and 25 °C. Piceamariana showed an anaerobic to aerobic CO2 efflux ratio that was significantly higher than all other species at 5 °C. Larixlaricina showed higher levels of anaerobic and aerobic CO2 efflux rates than the other four species. These data suggest that Piceamariana roots have higher overall increases in fermentation rates with onset of anoxia at 5 °C, and L. laricina roots have high fermentation and respiration rates at 5 °C. These features may be indicative of metabolic adaptations to cold, flooded peatland soils of Canadian boreal forests. A redox dye test showed O2 diffusion from roots of Pinus spp. and L. laricina at each temperature level. Thus these species have some ability to transport O2 to root tissues and sustain limited respiration under anaerobic conditions. Black and white spruce did not show any O2 diffusion from roots at any temperature.