Search

Background and aims: Changes in water availability during the growing season are becoming more frequent due to climate change. Our study aimed to compare the fine-root acclimation capacity (plasticity) of six temperate tree species aged six years and exposed to high or low growing season soil water availability over five years. Methods: Root samples were collected from the five upper strata of mineral soil to a total soil depth of 30 cm in monoculture plots of Acer saccharum Marsh., Betula papyrifera Marsh., Larix laricina K. Koch, Pinus strobus L., Picea glauca (Moench) Voss and Quercus rubra L. established at the International Diversity Experiment Network with Trees (IDENT) field experiment in Sault Ste. Marie, Ontario, Canada. Four replicates of each monoculture were subjected to high or low water availability treatments. Results: Absorptive fine root density increased by 67% for Larix laricina, and 90% for Picea glauca, under the high-water availability treatment at 0–5 cm soil depth. The two late successional, slower growing tree species, Acer saccharum and Picea glauca, showed higher plasticity in absorptive fine root biomass in the upper 5 cm of soil (PIv = 0.36 & 0.54 respectively), and lower plasticity in fine root depth over the entire 30 cm soil profile compared to the early successional, faster growing tree species Betula papyrifera and Larix laricina. Conclusion: Temperate tree species show contrasting acclimation responses in absorptive fine root biomass and rooting depth to differences in water availability. Some of these responses vary with tree species successional status and seem to benefit both early and late successional tree species. [ABSTRACT FROM AUTHOR]

Purpose: Most plants interact with soil biota that positively or negatively affect seedling performance. These plant-soil feedbacks (PSFs) can strongly affect recruitment, potentially for years after death. We tested whether PSFs persisted following death for Populus tremuloides Michx. (aspen) and if these effects were environment dependent using soils collected from live and dead aspen and heterospecific Picea glauca (Moench) Voss in 24 stands across two ecosystems. Methods: We conducted a greenhouse experiment using soils from 24 aspen stands. At each stand, we collected soil from three trees of each tree type and used live and sterilized versions of these soils to inoculate aspen seedlings. We then recorded mortality and growth of the seedlings over three months. Results: Live inocula reduced aspen survival and growth relative to sterilized inocula, suggesting that pathogens drive PSF. Plant responses to live and dead aspen inocula were correlated across environments; however, responses to aspen and heterospecific Picea inocula were uncorrelated, suggesting that specialized pathogens may drive PSF. Conclusions: Pathogen-driven negative PSFs can persist for multiple years irrespective of the environment, potentially limiting the regeneration of aspen stands following dieback. Persistent PSFs thus have potential to cause lagged effects on population and community dynamics. [ABSTRACT FROM AUTHOR]

Purpose: The objective of this study was to compare the accumulation over time of organic carbon (C) in soil and vegetation of abandoned agricultural lands left to natural vegetation succession or afforested with planted white spruce (Picea glauca (Moench) Voss) in Abitibi (Canada). The agricultural areas of this region originated from the clearing of forested lands in the late 19th -early 20th centuries. The aim was to determine whether afforestation of such lands is a relevant tool for C sequestration and climate change mitigation. Methods: Field and laboratory measures for tree, shrub and herbaceous strata, woody debris and soil down to a 50 cm depth were carried out on abandoned agricultural lands that were either left to natural succession or planted, to determine total C stocks. The experimental design was a chronosequence covering 50 years, with sites representing various stages following agriculture abandonment and plantation. Results: There was no significant difference in the amount of C stored by lands that were either planted or left to natural succession over a 50-year time period. Both types of lands were found to be net C sinks. Abandoned lands left to natural succession stored 1.3 times more C in the soil compared with afforested lands, while the latter stored twice as much C in aboveground biomass. Conclusions: These results put into perspective the use of afforestation to increase land C sinks and suggest that natural succession might also play a role in land management practices in the context of climate change mitigation. [ABSTRACT FROM AUTHOR]

Aims: The Sub-Boreal Pine-Spruce xeric-cold (SBPSxc) biogeoclimatic region in British Columbia, Canada is characterized by weakly-developed soils, thin organic forest floor and limited plant-available nitrogen. Yet, lodgepole pine trees are thriving in this region unaffected by these nitrogen-limitations, which led us to hypothesize that endophytic nitrogen-fixing bacteria could be playing a potential role in sustaining pine tree growth. Methods: We evaluated these endophytes in a yearlong greenhouse experiment with their native host (lodgepole pine) for in planta nitrogen-fixation (15N isotope dilution assay) and growth-promotion (length and biomass). These endophytes were also evaluated with a foreign host native to the SBPSxc region (hybrid white spruce) in another yearlong greenhouse trial. Results: Each bacterial strain considerably enhanced seedling length and biomass of pine and spruce along with fixing significant amount of nitrogen from atmosphere (15–50%). Notably, Caballeronia sordidicola HP-S1r strain fixed 49–50% of the host nitrogen from atmosphere and enhanced seedling length and biomass by up to 1.5-fold and 4-fold, respectively. Conclusions: Endophytic bacteria could be playing a crucial role in the survival of lodgepole pine trees in the SBPSxc region by providing them with significant amounts of fixed nitrogen. Their effectiveness with a foreign host (hybrid white spruce) shows the lack of plant x microbe specificity, indicating their potential role in supporting the growth of multiple boreal forest trees. [ABSTRACT FROM AUTHOR]

Aims: Soil water availability is important for tree growth and varies with topographic position and soil depth. We aim to understand how two co-occurring tree species with distinct rooting and physiological characteristics respond to those two variables during two climatically distinct growing seasons. Methods: Growing season (May to September) sap and transpiration fluxes were monitored using heat ratio method sap flow sensors on Populus tremuloides and Picea glauca in 2014 and 2015 growing along a hillslope with two different soil cover depths providing different rooting spaces. Results: Across the two growing seasons, a shallow rooting space was the main factor limiting aspen's leaf area and cumulative sap flux, whereas responses of white spruce were more limited by topographical position. Generally, sap and transpiration fluxes decreased with the season; however, a large precipitation event during the 2015 summer triggered a significant recovery in sap and transpiration fluxes in white spruce, while in aspen this response was more muted. Conclusions: The two species distinct rooting and physiological characteristics produced contrasting water uptake and water use dynamics in response to rooting space, soil water availability and climate, inviting a more detailed exploration of sap flux and its interactions with climatic and edaphic variables. [ABSTRACT FROM AUTHOR]

Background and Aims: Abandoned lands are increasingly used to establish fast-growing tree plantations, and are often rapidly colonized by a high density of herbaceous undergrowth. These weeds are generally removed since they compete with trees for resources, in particular soil nutrients. However, mixing herbaceous litter with the litter of planted trees could also stimulate the activity of decomposers and associated nutrient release due to an increase of litter quality (lower C:N ratio), plant diversity (more diverse litter traits) and water holding capacity. The objective was to determine the impact of herbaceous litter on the litter decomposition process of white spruce and hybrid poplar litters alone or in mixtures. Methods: Litter mass loss rate, nutrient release and decomposer communities were monitored on single and mixed-species litters using litterbags during two years in three plantations types (hybrid poplar, white spruce and mixed plantations). Litters within mixtures were separated by species to identify species-specific responses of leaf mass loss. Results: N release of all litter types increased with the presence of herbaceous litter. This finding could be linked to the greater abundance of decomposers and fungal biomass brought about by the herbaceous litter. Addition of herbaceous litter had no effect on spruce litter mass loss but had positive effects on poplar and mixed spruce/poplar litter mass loss. Abundance of fungi and mites was more affected by litter quality, whereas the abundance of collembola was more affected by the diversity of resources than by litter quality. Conclusions: In these 10-year plantations with poplar, increased litter mass loss for poplar and mixed litters and N release associated to the presence of herbaceous litter showed that weeds may change soil C sequestration and N cycling. [ABSTRACT FROM AUTHOR]

Background and aims: Soil pH is among the major environmental factors affecting plant growth. Although the optimum range of soil pH for growth and the tolerance of pH extremes widely vary among plant species, the pH tolerance mechanisms in plants are still poorly understood. In this study, possible mechanisms were examined to explain the differences in tolerance of boreal plants to root zone pH. Methods: In the controlled-environment solution culture experiments, we compared growth, physiological parameters and tissue nutrient concentrations in aspen, white spruce and tamarack seedlings that were subjected to 8 weeks of root zone pH treatments ranging from 5.0 to 9.0. Results: The pH treatments had little effect on dry weights and net photosynthesis in white spruce seedlings despite reductions in transpiration rates at higher pH levels. In aspen and tamarack, both the growth and physiological parameters significantly decreased at pH higher than 6.0. The chlorosis of young tissues in aspen and tamarack was associated with the reductions in foliar concentrations of several of the examined essential nutrients including Fe and Mn. Although the plants varied in their ability to deliver essential nutrients to growing leaves, there was no direct correlation between tissue nutrient concentrations, chlorophyll concentrations and plant growth. The results also demonstrated strong inhibition of transpiration rates by high pH. Conclusions: The results suggest that high root zone pH can upset water balance in pH sensitive species including aspen. Although the uptake and assimilation of essential elements such as Fe and Mn contribute to plant tolerance of high soil pH, we did not observe a direct relationship between growth and foliar nutrient concentrations to account for the observed differences in growth. [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]

Sub-alpine environments consist of altitudinal gradients associated with dramatic changes in plant growth and community composition, but the role of soil feedbacks and microbe interactions is largely unknown. Here, we examine the influence of the overall soil microbial community, with a focus on ectomycorrhizal and dark septate endophytic root colonizing fungi, from low, mid, and high elevations on the growth of Pinus contorta and Picea glauca × engelmannii. The influence of the soil microbial community was tested on seedlings from the same three elevations in order to determine 'home' versus 'away' effects on conspecifics of differing elevations. The low elevation soil was the most fertile and harbored a soil microbial community with an overall negative effect on seedling growth. In contrast, the high elevation soil was the least fertile and had a microbial community that enhanced seedling growth. However, only the soil microbial community in the highest elevation soil resulted in a stronger influence on the native P. contorta seedlings than seedlings originating from lower elevations. Despite the overall influence of the soil microbial community, ectomycorrhizal colonization was significantly correlated with P. glauca × engelmannii growth rates, but colonization by dark septate endophytes showed no relationship with seedling growth. The results provide evidence that plant-soil microbial community relationships are dependent on soil environment. Moreover, our results provide further support for the importance of soil microbes in facilitating seedling growth toward the edge of their elevational range. [ABSTRACT FROM AUTHOR]

Soil nitrogen (N) supply and uptake by regenerating trees is an important ecosystem attribute but difficult to quantify in partial-cut forests where light availability varies. The foliar attributes of N concentration (N%) and N per unit area (Na) may help characterize the influence of soil nutrition, but ideally the relationship between soils and foliage would be tested separately by species across well-defined light gradients. To do this, we examined foliar attributes of four tree species across gradients of light availability in 12 year-old partially-cut forests in northwest British Columbia, Canada. There were no differences in forest floor or mineral soil N mineralization rates across the light gradients, and for western hemlock ( Tsuga heterophylla) and hybrid white spruce ( Picea glauca x sitchensis), this consistent level of soil N supply corresponded with unchanging foliar N%. In contrast, foliar N% of Betula papyrifera (paper birch) and Thuja plicata (western redcedar) declined with shading, perhaps due to shifts in root-shoot biomass allocation for B. papyrifera, and climatic constraints on shade tolerance for T. plicata. Leaf δ13C approached an asymptote at approx. 40% full light for the coniferous species, but increased linearly with light for B. papyrifera. Foliar Na was linearly correlated with leaf δ13C for three species, reflecting the dual effect of light and nutrition on photosynthesis processes, and suggesting that foliar Na may be a simple parameter to integrate both resource constraints on regenerating saplings. These results demonstrate both support for and limits to foliar attributes among species in isolating soil N effects against light constraints in partial-cut forests. [ABSTRACT FROM AUTHOR]

Demonstrates that colonization with Hebeloma crustuliniforme increases water conductance and limits shoot sodium uptake in white spruce seedlings. Inoculation of Picea glauca seedlings; Resistance mechanisms in ectomycorrhizal plants growing in salinized soil.

This study examined how the availability of inorganic nitrogen (N) modified the anatomical characteristics of white spruce (Picea glauca (Moench) Voss) roots related to their hydraulic properties. Seedlingswere grown for one growing season in 4 L capacity pots filled with sand under one of three N levels: low (10 ppm), medium (50 ppm) and high (125 ppm). First order lateral roots with intact tips were sampledfrom dormant seedlings in October. Root segments were collected from4, 10, and 14 cm distances above the root tip for fixation and sectioning and for maceration. Additional specimens were collected from the 4 and 14 cm distances for maceration and scanning electron microscopy of xylem pits. Root diameter and surface area occupied by the xylem in root cross sections increased basipetally in all treatments but exceptions were found. Higher N-levels significantly increased root diameter and surface area occupied by the xylem. In the two higher N treatments secondary root development was more advanced near the root tip than in the low N treatment. There was a strong positive correlation between root diameter and cross-sectional root area occupied by the xylem (30-50% of the root cross section) but not in portions with little secondary development. Non-conducting space within the xylem occupied 10-13% of its cross-sectional surface. Tracheids of the primary xylem were larger, had larger lumens but thinner cell walls than those of the secondary xylem. Low N treatment seedling tracheids had smaller total cross-sectional area, less lumen, and less cell wall surface area than the two other N treatments. Tracheid diameter means were between 19-20 Mum in the high and medium N treatments, and 15.2 ??m in the low N treatment. The range was 4.5-51.3 Mum. Tracheid lengthwas not significantly affected by N. The average tracheid was about 1000 Mum long, and the range was 110-3530 Mum. Pit-border diameters ranged between 4.1-20.6 Mum (average 10-11 Mum) and were not affected by t [ABSTRACT FROM AUTHOR]

Thirty-two one-year-old white spruce (Picea glauca (Moench) Voss) seedlings were grown outdoors for one season in 35 L pots buried in thesoil. The pots were vertically split in half. One compartment (mineral) was filled with loamy sand. The bottom of the other compartment (organic) was filled with 10 cm sand topped with 15 cm of organic substrates. Two seedling types (16 seedlings each), (i) polystyroblock-grown and (ii) peat-board grown with mechanical root pruning had their root systems split approximately in half into each of the vertical compartments. Controlled-release (26-12-6 N-P-K) fertilizer was added to one or to none (control) of the compartments. Above-ground growth was positively affected by fertilizer placed in either soil compartmnent. Nutrient content of the foliage was greater in fertilized than inunfertilized seedlings; N and P concentrations were significantly increased. Bud reflushing occurred frequently in fertilized seedlings. Unfertilized container-grown seedlings had the fewest roots in eithersoil compartment. Unfertilized mechanically-pruned seedlings had significantly greater root length, root surface area, and more root tipsin mineral than in organic compartments. They also had more P in current-year leaves than did unfertilized container-grown seedlings. Fertilizer added to mineral compartments significantly affected root growth in these compartments only, whereas when added to organic compartments it affected root growth in both compartments. Root systems of the two seedling types were differently affected by fertilizer: in mechanically-pruned seedlings, the number of roots was reduced but theirlength and diameter increased; in container-grown seedlings, root proliferation was stimulated and this increased total root length and root surface area. Five ectomycorrhizal morphotypes were identified. E-strain was the most abundant. Except for Cenococcum, all morphotypeswere present in nursery stock prior to planting. Changes in distribution o [ABSTRACT FROM AUTHOR]