Search

Covers with capillary barrier effects (CCBE) are used to prevent acid mine drainage from mine wastes in the short term. However, the long-term efficiency of CCBE can be affected by trees because their roots may reduce the ability of covers to limit oxygen migration and also physically damage the CCBE. Two plant species that are native to boreal Canada, bluejoint (Calamagrostis canadensis) and sheep laurel (Kalmia angustifolia), were selected as bio-barrier species (BBS) to test if they reduce the growth and root system architecture of trees established on mine covers (balsam poplar [Populus balsamifera], willow [Salix spp], and black spruce [Picea mariana]). The experiment was established in 2008 on a mine tailings impoundment located in northwestern Quebec, Canada. Trees were measured for height, diameter, and biomass. Coarse roots were excavated from the plots and digitized in three dimensions. Compared with the control (no BBS), bluejoint strongly decreased tree height and diameter increment, biomass, maximum root depth and radial extension, total root length and volume, and number of second-and third-order tree roots. Height and diameter increment, biomass, maximum root depth and volume, and number of second-order roots of balsam poplar increased with sheep laurel compared with control conditions, whereas willow showed no response to this treatment. Most characteristics of black spruce (except rootto-shoot ratio and number of second-order roots) improved in the presence of sheep laurel compared with the control. Thus, bluejoint was a more efficient BBS than sheep laurel. Bio-barriers comprised of bluejoint can be used as a countermeasure for controlling tree invasion of CCBE. [ABSTRACT FROM AUTHOR]

A debate over the impacts of invasive plants is fueled by varied terminology, ecosystem types, response metrics, and conflicting evidence across scales. We quantify the effects of invading Phalaris arundinacea (Pa) on species richness and abundance in Wisconsin sedge meadows dominated by Carex stricta (Cs). Among species area curves from four nested plots (0.25, 1, 4, and 16 m) in seven sites, Pa stands averaged 48 % fewer species than the adjacent Cs. Species richness was reduced by about half regardless of plot size. Total richness for Pa stands was 50 species compared to 83 for Cs, and Pa stands had consistently lower additive percent cover of subordinate species at all scales. However, resident species responded differentially to Pa invasion. Only one species, Calamagrostis canadensis (a tall clonal grass), had similar importance values (using cover and frequency) in Cs and Pa stands at 0.25 and 16-m scales. Other species declined with Pa invasion, mostly in frequency. Despite losing half of their resident species, sites did not differ significantly in their native exotic richness relationship (NERR). NERR confounds the effects of invasiveness with species' origins, and it under-represents impacts of dominant invaders in wetlands. Debates should be fewer if studies specify if the invader is exotic or native, type of invaded ecosystem, the metric used to assess responses, and the spatial scale. [ABSTRACT FROM AUTHOR]

Canada bluejoint grass [Calamagrostis canadensis(Michx.) P. Beauv., hereafter referred to as bluejoint] outcompetes overstory tree species such as white spruce [Picea glauca(Moench) Voss] by creating a thick litter layer and competing for the available nitrogen (N). This study was conducted to investigate the effects of bluejoint litter layer (with or without litter removal) and N fertilization on soil water and N availabilities using principal component analysis (PCA) and foliar δ15N and δ13C of bluejoint in a plantation in north-central Alberta, Canada. PCA using soil properties and understory growth data demonstrated that N fertilization was more effective in changing the soil environment and resource availabilities for bluejoint growth than litter layer removal. The increase in soil N availability by N fertilization was linked with increased bluejoint foliar δ15N (by around 3‰) in fertilized plots, as a result of greater N isotopic fractionation in the fertilized plots. The more negative δ13C (by around 1‰) of bluejoint in litter layer-removed plots suggested that litter layer removal increased soil water availability, indicating that the litter layer reduced soil water availability on the site. Therefore, results from this and previous studies showed that the litter layer decreased both soil water and N availabilities. Although the exact mechanisms of the benefit of the litter layer for bluejoint remains unknown, bluejoint likely adversely impacted tree growth by competing for N due to its strong N acquisition ability under soil resource-limiting conditions. [ABSTRACT FROM PUBLISHER]

Abstract: A matrix model for age-stage-structured population dynamics of Calamagrostis canescens, a perennial grass species colonizing forest clear-cut areas, was calibrated before from a type of data called ‘identified individuals with unknown parents’ (Logofet, 2008) in order to estimate λ 1, the dominant eigenvalue of the projection matrix. A number of methods were applied to tackle the ‘reproductive uncertainty’ in data, and the output variety contained λ 1 both greater and less than 1 (Logofet, 2008), leaving the estimation uncertain. An ‘adaptation conjecture’ was then proposed that reduced the calibration to a nonlinear constraint maximization problem and provided for a satisfactory outcome. Two reasons have now caused revisiting. First, the maximization technique has been theoretically comprehended. In particular, an existence-uniqueness theorem has been proved that requires the maximizing solution to be reached at a vertex of the polyhedral of constrains. To facilitate searching for the solution in practice, I use the notion of potential-growth indicator and prove R 0 and R 1, the known indicators, to be certain linear functions of the uncertain fertility rates in a general class of projection matrix patterns. To solve a conjugate linear maximization problem under the same constraints as for λ 1 is both theoretically and technically simpler, and this causes a practical benefit from the indication along with calculation. Second, the former uniform (non-specific) estimate of the upper bounds for the status-specific fertility rates has now conceded to the age-stage-specific estimates inferred from a special case study. These more sophisticated constraints produce respectively more accurate calibration, hence a more reliable estimation of λ 1 as the growth potential inherent in the population in a certain environment at a given time. [Copyright &y& Elsevier]

C4 photosynthesis is particularly successful at high light intensities and high temperatures, but is relatively rare when the average growing season temperature is less than about 15°C. We tested the hypothesis that rapidly reversible photoprotection enables some C4 species to tolerate cool climates, by focusing on two questions: (1) Do chlorophyll fluorescence responses differ seasonally between co-occurring C3 and C4 grasses in the field? (2) Does xanthophyll-mediated photoprotection differ between the two pathways? Spartina pectinata (C4) and Calamogrostis canadensis (C3) were sampled in a herbaceous fresh-water meadow in New Brunswick, Canada (45°N 66°W). Non-photochemical thermal energy dissipation (Φ NPQ) and the epoxidation state of the xanthophyll cycle (EPS) were used as indicators of photoprotection. We observed no differential susceptibility to chronic photoinhibition (i.e. photodamage) between the C3 and C4 species, except potentially during spring emergence. On average, C. canadensis showed higher levels of protective dynamic photoinhibition throughout the growing season, but S. pectinata had greater Φ NPQ and lower EPS during seasonal and daily temperature minima. The low Rubisco capacity of C4 species is a potential limiting factor to C4 success at high latitudes, but our findings suggest that it is unlikely via a photoinhibitory feedback mechanism. [ABSTRACT FROM AUTHOR]

Background and aims: Canada bluejoint grass is a strong competitor for water and N against young white spruce trees in regenerating boreal forests in moist habitats. We investigated foliar δC and δN responses of white spruce to understory removal and N fertilization to infer treatment effects on soil water and N dynamics. Methods: An experiment with understory removal and N fertilization as the main and split-plot treatments was conducted in a 13-year-old white spruce plantation in the boreal region for 2 years. Soil N availability, gravimetric soil moisture content, tree growth, foliar C and N concentrations, and foliar δC and δN values were determined. Results: Foliar δC was increased by understory removal in the second year and by N fertilization in the first year. There was a positive ( P < 0.01) relationship between foliar δC and N concentration, suggesting that understory removal and N fertilization improved tree growth via increased N availability and thus increased carboxylation rate of photosynthesis. The positive correlation ( P < 0.01) of foliar δN with foliar N concentration and with available soil N indicated that understory removal and N fertilization facilitated N isotope fractionation accompanying increased soil N turnover. Conclusions: Foliar δC and its relationship with other variables suggested that understory removal and N fertilization improved white spruce growth mainly through enhanced carboxylation rate due to greater N availability rather than increased stomatal conductance. Specifically, understory removal and N fertilization increased soil N availability and subsequently induced N loss from the system, leading to a higher N concentration and δN in the foliage. Control of competing vegetation and N fertilization could be used as management tools to reduce N limitation. [ABSTRACT FROM AUTHOR]