Summary Three clones of Agrostis gigantea were evaluated for their tolerance to cobalt, copper, nickel and zinc. Of the clones originating from a mine waste site in Sudbury, Ontario, one showed tolerance to copper, cobalt, and nickel, the other only to nickel. Neither of these clones showed tolerance to zinc. A clone from a seed supply house lacked tolerance to any of the metals tested. Copper was most toxic to A. gigantea, followed by nickel, cobalt and zinc.

A wide variety of hybrid poplar clones are being introduced for intensive culture biomass production, but the potential clonal or genotypic response to increasing tropospheric carbon dioxide (CO2), ozone (O3), and their interactions are unknown. To study these effects, we exposed five different hybrid Populus clones to increased concentrations of CO2, O3, and CO2 + O3 in open-top chambers for one growing season and determined growth responses. Exposure to elevated CO2 increased height growth, dry mass, and basal area; exposure to O3 decreased all three of these growth responses. Exposure impact differed among the different plant parts (leaf, stem, and roots) and among the clones. These differences were associated with different growth strategies or carbon allocation patterns inherent in the different clones. The fastest growing clones had the greatest response to O3 treatment. The addition of CO2 to the O3 exposure counteracted the negative impact of O3 in all plant components except leaf mass (e.g., CO2 + O3 plant mass equaled control plant mass) in all of the clones. But correspondingly, added O3 negated increased growth from CO2. Genetic variation in response to atmospheric pollutants must be considered even in closely related genotypes found in Populus culture.

Pollutant levels were examined in a boreal forest system that had been exposed to smelter effluents for 50 yr. High levels of Zn, Cu, and Pb were found in the surface soils close to the source (< 10 km) and declined rapidly in a south‐southeast direction. Significant deposition of metals may be occurring at sites up to 35 km from the source. Positive correlations between metals found in the soil and distance from the source implicated the smelter as the source of the metal particulates. The most heavily impacted sites (> 4000 and 1000 mg/kg of Zn and Cu, respectively) showed significant accumulations of metal at lower soil depths. Extraction of soils with diethylenetriaminepentaacetic acid (DTPA) indicated that 50 to 60% and 18 to 36% of the and Cu, respectively, could be in a plant‐available form. Soil pH was not related to distance from the source, indicating that acidification had not taken place; this was confirmed by snow analysis. Data did not indicate that metal levels in the soil have affected the foliar nutrient levels of major tree species. Elevated S levels were found in the foliage of black spruce (Picea mariana Mill.) close to the source but were not apparent for jack pine (Pinus banksiana Lamb.).

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We measured organic matter removal and soil compaction effects on soil surface CO2 efflux (F) from a jack pine (Pinus banksiana Lamb.) forest and developed an analytical framework involving multiplicative response functions to interpret response. Treatments included stem-only harvest (OM0C0), full-tree harvest (OM1C0), full-tree harvest with surface soil removal (OM2C0), full-tree harvest with surface soil removal and soil compaction (OM2C2), and uncut forest (UF). Mean F and calculated F at 10 °C under nonlimiting soil moisture conditions (F10) were greatest in treatments with intact organic surfaces and often larger in the OM2C0 than in the OM2C2. F10 showed strong linear relationships with detrital production in harvested plots, with total near-surface carbon in all plots, and was positively correlated with understory cover. F increased exponentially with soil temperature, with the most and least pronounced responses found in the UF and OM2C0 treatments, respectively. F also responded in parabolic fashion to relative soil water content. In the UF, F was often low in May because of cold soils, but subsequently attained rates equivalent to those of the OM0C0 and OM1C0, despite lower soil temperatures. Three to five growing seasons after treatment, soil temperature and moisture, together with F10, explained 71%–87% of the plot-level variation in F.