Boreal Forest Plants Research Articles

Condensed tannins mediate the effect of long-term nitrogen addition on soil nematodes in a boreal spruce forest

Fertilization and combustion of fossil fuels have increased nitrogen (N) deposition over the last decades. Most boreal forests are N-limited; thus, increased N availability may have considerable implications for boreal forest food web structure and functioning. Soil biota are important drivers of ecosystem processes through their effect on carbon (C) and nutrient cycling. Among these, nematodes are ubiquitous in soil and respond quickly to environmental changes. They are thus useful in determining changes in ecosystem status. Boreal forest plants produce large quantities of condensed tannins (hereafter tannins), and these may decrease following N addition. As defence compounds, tannins may alter soil community structure by reducing microbial activity and deter microfauna. Using nematodes as indicators, we here investigated the linkages between N-induced changes in soil food web and soil tannin concentration. We utilized an experimental site where N has been added since 2003 at a rate of ca. 37 kg N ha−1 year−1. This have resulted in a shift in the understory, and consequently a 23 % lower soil tannin concentration. Fertilization led to a less structured nematode community dominated by bacterivores. Channel Index was 35 % lower in fertilized plots, indicating an increasing decomposition dominance by bacteria. Furthermore, the dominance of bacteria appears to have been inhibited by soil tannin concentrations in the fertilized plots. Overall, our study demonstrate that soil community structure strongly changes upon increased N availability, and lower soil tannin concentrations further facilitate the dominance of bacteria.

Overexpression of the HcPT1.1 transporter in Hebeloma cylindrosporum alters the phosphorus accumulation of Pinus pinaster and the distribution of HcPT2 in ectomycorrhizae.

Ectomycorrhizal (ECM) fungi are associated with the roots of woody plants in temperate and boreal forests and help them to acquire water and nutrients, particularly phosphorus (P). However, the molecular mechanisms responsible for the transfer of P from the fungus to the plant in ectomycorrhizae are still poorly understood. In the model association between the ECM fungus Hebeloma cylindrosporum and its host plant Pinus pinaster, we have shown that the fungus, which possesses three H+:Pi symporters (HcPT1.1, HcPT1.2 and HcPT2), expresses mainly HcPT1.1 and HcPT2 in the extraradical and intraradical hyphae of ectomycorrhizae to transport P from the soil to colonized roots. The present study focuses on the role of the HcPT1.1 protein in plant P nutrition, in function of P availability. We artificially overexpressed this P transporter by fungal Agrotransformation and investigated the effect of the different lines, wild-type and transformed ones, on plant P accumulation, the distribution of HcPT1.1 and HcPT2 proteins in ectomycorrhizae by immunolocalization, and 32P efflux in an experimental system mimicking intraradical hyphae. Surprisingly, we showed that plants interacting with transgenic fungal lines overexpressing HcPT1.1 did not accumulate more P in their shoots than plants colonized with the control ones. Although the overexpression of HcPT1.1 did not affect the expression levels of the other two P transporters in pure cultures, it induced a strong reduction in HcPT2 proteins in ectomycorrhizae, particularly in intraradical hyphae, but still improved the P status of host plant shoots compared with non-mycorrhizal plants. Finally, 32P efflux from hyphae was higher in lines overexpressing HcPT1.1 than in the control ones. These results suggest that a tight regulation and/or a functional redundancy between the H+:Pi symporters of H. cylindrosporum might exist to ensure a sustainable P delivery to P. pinaster roots.

Individual response traits of understory plants vary along linked-press and compounded-pulse disturbance gradients in northern temperate and boreal forests

Community-weighted means (CWM) and functional dispersion (FDis) of response traits of woody and herbaceous understory plants in northern temperate and boreal forest communities were studied to determine how these traits respond to linked-press (i.e., climate, historic fire regimes, and silviculture systems) and compounded-pulse (i.e., harvest, site preparation, and release treatments) disturbances. We used fifth year post-harvesting disturbance data from the NEBIE plot network (NEBIE), a large-plot field experiment in northern temperate and boreal forests in Ontario, Canada. To analyze treatment effects, a randomized complete block design was assumed. Treatments were applied in a semi-operational manner to two-hectare experimental units. Individual response traits were affected by linked-press and compounded-pulse disturbances in unique ways, with logarithmic (stress-gradient hypothesis) or hump-shaped (intermediate disturbance hypothesis) patterns typically observed. Some traits (i.e., lateral spread of clones, seed weight) did not differ between disturbance types. Results suggest that all interactions between linked-press and compounded-pulse disturbances typically exert non-linear effects on CWM and FDis of individual plant response traits for both woody and herbaceous understory plants in boreal and temperate forests. Specific responses varied with trait, understory layer, and type of disturbance.

Phytocoenotical behaviour of nemoral and boreal-nemoral plant species in taiga zone communities

Phytocoenotic behaviour of 14 nemoral or boreal-nemoral vascular plant species is analyzed in the middle- and southern-taiga subzones in comparison with that in the broadleaved-forest zone, based upon the set of 1669 relevés made in European Russia in 1996–2018. The nemoral species are mainly represented by shadow mesoeutrophic plants from the “corteges” of Tilia cordata s. l. and Fagus sylvatica. The more light-demanding plants from the Quercus robur “cortege”, either mesotrophic, or mesoeutrophic, more often demonstrate the boreal-nemoral type of zonal distribution. In the boreal-forest zone, linden and beech companions are typical for the southern-boreal nemoral-herb / sorrel spruce (Picea abies s. l.) forests on placors as well as the valley / riparian tall-herb forests, including the middle-boreal ones. The oak companions also inhabit grass-feathermoss pine (Pinus sylvestris) forests, besides the spruce forest types mentioned. Species from all the named “corteges” are also common in the small-leaved forests. The Betula companions which grow together with the nemoral plants in boreal forests could also be subdivided into the two florogenetical groups, namely a) the boreal, originally subalpine plants and b) the boreal-nemoral ones, originally oak companions. Species from the latter group often become widespread and dominant in the small-leaved forests; a good example is provided by Aegopodium podagraria. The rank correlation (Spearman rS) analysis shows the projective cover increase is connected with either the growing season warmth supply, or the climate oceanicity for both nemoral and boreal-nemoral species. These effects are most sound in the placor community sequence from broadleaved forests to sorrel and then bilberry-feathermoss spruce ones but weakened in the tall-herb forests on rich soil and completely levelled in the aspen (Populus tremula) forests. Carbonate bedrock outcrops contribute to nemoral species survival in the areas they inhabited during the climatically favourable epochs; they also favoured the migration of these species during the interglacials. Individualization of coenotic patterns of nemoral species at their distribution limits does not contradict to joint occurrence of such plants in relict / extrazonal locations.

Wild Boar Effects on Fungal Abundance and Guilds from Sporocarp Sampling in a Boreal Forest Ecosystem.

Simple SummaryNative wild boar populations are expanding across Europe, causing concern due to their significant soil disturbances and considerable impact on ecosystems. However, little is known about how wild boar activities affect other organisms. This study investigated the effects of wild boars on the abundance of fungal sporocarps and their respective fungal guilds (i.e., symbiotic, saprophytic and pathogenic) in boreal forests in Sweden. We selected 11 forested sites in central Sweden: six with and five without the presence of wild boar. We determined the presence or absence of wild boar and rooting intensity at each site. Simultaneously, we investigated the abundance of fungal sporocarps and their fungal guilds. We found that the presence of wild boar and rooting intensity were associated with the abundance of fungal sporocarps. Wild boar rooting was positively correlated with saprotrophic fungi and negatively with symbiotic fungi. Pathogenic fungi were more abundant in plots with no rooting but in the presence of wild boar. We conclude that wild boar represents a recurrent disturbance agent and, based on sporocarp abundance, could eventually affect entire fungal populations.Native wild boar (Sus scrofa) populations are expanding across Europe. This is cause for concern in some areas where overabundant populations impact natural ecosystems and adjacent agronomic systems. To better manage the potential for impacts, managers require more information about how the species may affect other organisms. For example, information regarding the effect of wild boar on soil fungi for management application is lacking. Soil fungi play a fundamental role in ecosystems, driving essential ecological functions; acting as mycorrhizal symbionts, sustaining plant nutrition and providing defense; as saprotrophs, regulating the organic matter decomposition; or as plant pathogens, regulating plant fitness and survival. During autumn (Sep–Nov) 2018, we investigated the effects of wild boar (presence/absence and rooting intensity) on the abundance (number of individuals) of fungal sporocarps and their functional guilds (symbiotic, saprotrophic and pathogenic). We selected eleven forested sites (400–500 × 150–200 m) in central Sweden; six with and five without the presence of wild boar. Within each forest, we selected one transect (200 m long), and five plots (2 × 2 m each) for sites without wild boar, and ten plots for sites with boars (five within and five outside wild boar disturbances), to determine the relationship between the intensity of rooting and the abundance of sporocarps for three fungal guilds. We found that the presence of wild boar and rooting intensity were associated with the abundance of sporocarps. Interestingly, this relationship varied depending on the fungal guild analyzed, where wild boar rooting had a positive correlation with saprophytic sporocarps and a negative correlation with symbiotic sporocarps. Pathogenic fungi, in turn, were more abundant in undisturbed plots (no rooting) but located in areas with the presence of wild boar. Our results indicate that wild boar activities can potentially regulate the abundance of fungal sporocarps, with different impacts on fungal guilds. Therefore, wild boar can affect many essential ecosystem functions driven by soil fungi in boreal forests, such as positive effects on energy rotation and in creating mineral availability to plants, which could lead to increased diversity of plants in boreal forests.

Foliar stable isotope ratios of carbon and nitrogen in boreal forest plants exposed to long-term pollution from the nickel-copper smelter at Monchegorsk, Russia

Long-term exposure to primary air pollutants, such as sulphur dioxide (SO2) and nitrogen oxides (NOx), alters the structure and functions of forest ecosystems. Many biochemical and biogeochemical processes discriminate against the heavier isotopes in a mixture; thus, the values of δ13C and δ15N (i.e. the ratio of stable isotopes 13C to 12C and that of 15 N to 14 N, respectively) may give insights into changes in ecosystem processes and identify the immediate drivers of these changes. We studied sources of variation in the δ13C and δ15N values in the foliage of eight boreal forest C3 plants at 10 sites located at the distance of 1–40 km from the Monchegorsk nickel-copper smelter in Russia. From 1939‒2019, this smelter emitted over 14,000,000 metric tons (t) of SO2, 250,000 t of metals, primarily nickel and copper, and 140,000 t of NOx. The δ13C value in evergreen plants and the δ15N value in all plants increased near the smelter independently of the plant mycorrhizal type. We attribute the pollution-related increase in the foliar δ13C values of evergreen species mainly to direct effects of SO2 on stomatal conductance, in combination with pollution-related water stress, which jointly override the potential opposite effect of increasing ambient CO2 concentration on δ13C values. Stomatal uptake of NOx and root uptake of 15N-enriched organic N compounds and NH4+ may explain the increased foliar δ15N values and elevated foliar N concentrations, especially in the evergreen trees (Pinus sylvestris), close to Monchegorsk, where the soil inorganic N supply is reduced due to the impact of long-term SO2 and heavy metal emissions on plant biomass. We conclude that, despite the uncertainties in interpreting δ13C and δ15N responses to pollution, the Monchegorsk smelter has imposed and still imposes a great impact on C and N cycling in the surrounding N-limited subarctic forest ecosystems.

Mixed evidence for the small‐island effect in a replicated colonisation experiment

AbstractAimPlant species richness increases with island/patch area, but the effect of spatial scale on the shape of the species‒area relationship remains debatable. We asked whether the small‐island effect (SIE; i.e. different relationship between island area and species richness on smaller compared to larger plots) occurs in plants naturally colonising extremely small de novo plots.LocationNorthern Europe.MethodsWe established 16 experimental plots with bare ground (two plots of each of eight sizes, from 2 to 0.01 m2) in each of four localities, and monitored colonisation of these plots by vascular plants from 2008 to 2010. We modelled species‒area relationships in these plots by linear and breakpoint regressions, and we analysed plant functional traits with respect to plot size.ResultsSmall‐seeded plants were over‐represented among the primary colonisers, and plant functional traits changed with plot size. On average, the number of plant species was six times greater in our largest (2 m2) than in our smallest (0.01 m2) plots. The SIE was observed in half of our analyses; the semi‐log models identified SIE more often than the log‐log models did (71.1% and 28.9% of all analyses respectively).ConclusionsThe evidence for the small‐island effect in boreal forest plants colonising patches of bare ground is mixed. Despite extremely small patch size and habitat uniformity, half of our data showed a “classic” species‒area relationship. Our findings hint that the probability of SIE occurrence increases with decreases in the species pool of primary colonisers and with decreases in the time from the beginning of colonisation. We suggest that the analysis of plant functional traits in study systems where SIE does occur be conducted to uncover the drivers of this interesting biogeographical phenomenon.

Siberian plants shift their phenology in response to climate change.

Siberia has undergone dramatic climatic changes due to global warming in recent decades. Yet, the ecological responses to these climatic changes are still poorly understood due to a lack of data. Here, we use a unique data set from the Russian 'Chronicles of Nature' network to analyse the long-term (1976-2018) phenological shifts in leaf out, flowering, fruiting and senescence of 67 common Siberian plant species. We find that Siberian boreal forest plants advanced their early season (leaf out and flowering) and mid-season (fruiting) phenology by -2.2, -0.7 and -1.6days/decade, and delayed the onset of senescence by 1.6days/decade during this period. These mean values, however, are subject to substantial intraspecific variability, which is partly explained by the plants' growth forms. Trees and shrubs advanced leaf out and flowering (-3.1 and -3.3. days/decade) faster than herbs (-1day/decade), presumably due to the more direct exposure of leaf and flower buds to ambient air for the woody vegetation. For senescence, we detected a reverse pattern: stronger delays in herbs (2.1days/decade) than in woody plants (1.0-1.2days/decade), presumably due to the stronger effects of autumn frosts on the leaves of herbs. Interestingly, the timing of fruiting in all four growth forms advanced at similar paces, from 1.4days/decade in shrubs to 1.7days/decade in trees and herbs. Our findings point to a strong, yet heterogeneous, response of Siberian plant phenology to recent global warming. Furthermore, the results highlight that species- and growth form-specific differences among study species could be used to identify plants particularly at risk of decline due to their low adaptive capacity or a loss of synchronization with important interaction partners.

Can Larvae of Forest Click Beetles (Coleoptera: Elateridae) Feed on Live Plant Roots?

Simple SummaryDetailed natural history information is still lacking for many species of soil-dwelling invertebrates. We asked whether the larvae (wireworms) of two click beetle species, which are most abundant in European boreal forests, feed on live roots of forest plants. The weight of root pieces of downy birch, Scots pine, Norway spruce and wavy hair-grass, offered to wireworms in a laboratory experiment, did not decrease, indicating that these larvae did not consume live root tissues. Therefore, Athous subfuscus and Dalopius marginatus should be excluded from the lists of forest pests damaging tree roots.The life histories of many soil-dwelling invertebrates remain poorly studied. The larvae of two click beetle species, Athous subfuscus and Dalopius marginatus, which are most abundant in European boreal forests, are both classified as omnivorous and are included in lists of root-damaging pests. Nevertheless, we are not aware of any direct proof of their ability (or inability) to consume plant roots. In this study, we asked whether these larvae actually feed on the roots of forest plants in the absence of other food sources. Live roots of boreal forest plants, including trees (Betula pubescens, Picea abies and Pinus sylvestris) and grass (Deschampsia flexuosa), were offered to click beetle larvae in a two-month microcosm experiment. The weight of roots placed in vials with the wireworms did not decrease, indicating that the larvae of these click beetle species did not feed on live roots, even in the absence of other food sources. This suggests that the feeding niches of A. subfuscus and D. marginatus larvae are narrower than previously thought and do not include live plant tissues. Therefore, these click beetle species should be excluded from the lists of forest pests damaging tree roots.

Effect of plant-derived smoke water and potassium nitrate on germination of understory boreal forest plants

This experiment assessed the effects of plant-derived smoke water, potassium nitrate (KNO3), and their combined effect on germination of cold-stratified and non-stratified seed from 18 native boreal forest plant species. Seeds were treated with smoke water diluted to 1:20, 0.1% KNO3, and smoke water + KNO3. Nine species responded positively to smoke water; these responses were dependent on the type of stratification, and three of these species only had a positive response to smoke water + KNO3 solution. Five species responded positively to KNO3 and four of those were associated with smoke water + KNO3 solution. Smoke water induced germination of several species, but only for seeds that had been previously cold-stratified. Vaccinium myrtilloides Michx. had the largest increase in germination using smoke water and the most reduced germination using KNO3. The interactions between smoke water, KNO3, and stratified seeds are not well understood. The effects and applications of smoke water and KNO3 (or other nitrogen sources) should be further researched to determine alternative approaches to restoration of disturbed boreal forest ecosystems.

Growth environment and organ specific variation in in-vitro cytoprotective activities of Picea mariana in PC12 cells exposed to glucose toxicity: a plant used for treatment of diabetes symptoms by the Cree of Eeyou Istchee (Quebec, Canada)

BackgroundThe Cree of Eeyou Istchee (James Bay area of northern Quebec) suffer from a high rate of diabetes and its complications partly due to the introduction of the western lifestyle within their culture.As part of a search for alternative medicine based on traditional practice, this project evaluates the biological activity of Picea mariana (Mill.) Britton, Sterns & Poggenb. needle, bark, and cone, in preventing glucose toxicity to PC12-AC cells in vitro (a diabetic neurophathy model) and whether habitat and growth environment influence this activity.MethodsThree different organs (needle, bark, and cone) of P. mariana were collected at different geographical locations and ecological conditions and their 80% ethanolic extracts were prepared. Extracts were then tested for their ability to protect PC12-AC cells from hyperglycaemic challenge at physiologically relevant concentrations of 0.25, 0.5, 1.0 and 2.0 μg/mL. Folin-Ciocalteu method was used to determine the total phenolic content of P. mariana extracts.ResultsAll extracts were well-tolerated in vitro exhibiting LD50 of 25 μg/mL or higher. Extracts from all tested organs showed a cytoprotective concentration-dependent response. Furthermore, the cytoprotective activity was habitat- and growth environment-dependent with plants grown in bog or forest habitats in coastal or inland environments exhibiting different cytoprotective efficacies. These differences in activity correlated with total phenolic content but not with antioxidant activity. In addition, this paper provides the first complete Ultra-Performance Liquid Chromatography-quadrupole time-of-flight (UPLC-QTOF) mass spectrometry analysis of Picea mariana’s bark, needles and cones.ConclusionsTogether, these results provide further understanding of the cytoprotective activity of Canadian boreal forest plants identified by the Cree healers of Eeyou Istchee in a cell model of diabetic neuropathy. Their activity is relevant to diabetic peripheral neuropathic complications and shows that their properties can be optimized by harvesting in optimal growth environments.

Expanding and testing fluorescent amplified fragment length polymorphisms for identifying roots of boreal forest plant species.

Premise of the StudyIdentifying roots to species is challenging, but is a common problem in ecology. Fluorescent amplified fragment length polymorphisms (FAFLPs) can distinguish species within a mixed sample, are high throughput, and are inexpensive. To broaden the use of this tool across ecosystems, unique size profiles must be established for species, and its limits identified.MethodsFragments of three noncoding cpDNA regions were used to create size profiles for 193 species common to the western Canadian boreal forest. We compared detection success among congeners using FAFLPs and Sanger sequencing of the trnL intron. We also simulated and experimentally created communities to test the influence of species richness, cpDNA regions used, and extraction/amplification biases on detection success.ResultsOf the 193 species, 54% had unique size profiles. This value decreased when fewer cpDNA regions were used. In simulated communities, ambiguous species identifications were positively related to the species richness of the community. In mock communities, some species evaded detection owing to poor extraction or amplification. Sequencing did not increase detection success compared to FAFLPs for a subset of 24 species across nine genera.DiscussionWe recommend FAFLPs are best suited to confirm rather than discover species occurring belowground.

Major disturbances test resilience at a long-term boreal forest monitoring site.

The impact of disturbances on boreal forest plant communities is not fully understood, particularly when different disturbances are combined, and regime shifts to alternate stable states are possible after disturbance. A long‐term monitored semi‐natural forest site subject to intense combined storm and bark beetle damage beginning in 2005 provided an opportunity to investigate the postdisturbance development of the vegetation community. Previous studies suggest that a shift from Picea abies to Fagus sylvatica domination was possible.We analyzed pre‐ and postdisturbance vegetation data to investigate to what extent vascular plant species abundances, diversity, traits, and community composition have changed. We were particularly interested in differences between remaining apparently unaffected areas (potential refugia) and disturbed areas, and in signs of consistent change over time in community composition in response to disturbance that could indicate an impending regime shift.We found that the vegetation community present in the refuge areas has remained substantially intact through the period of disturbance. Nonrefuge areas diverged from the refuges in community composition and showed increased taxonomic and functional diversity. Despite this, and an increase in deciduous tree species (particularly F. sylvatica), P. abies has shown strong postdisturbance regeneration. The refuges may be important in the apparent ongoing recovery of the disturbed areas to a P. abies‐dominated state similar to that found predisturbance. This fast recovery is interpreted as evidence of a system resilient to a potential shift to a deciduous‐dominated state. Synthesis: Our results show that even powerful combined disturbances in a system with multiple stable states can be insufficient to initiate a regime shift. Resilience of the P. abies‐dominated forest community is increased by the survival of refuge areas functioning as a form of ecological memory of the previous ecosystem state. The results also demonstrate the value of data generated by long‐term monitoring programs.

Effects of undergrowth removal and edge proximity on ground beetles and vascular plants in urban boreal forests

Effects of undergrowth removal and edge proximity on ground beetles and vascular plants in urban boreal forests

Soil invertebrate avoidance behavior identifies petroleum hydrocarbon contaminated soils toxic to sensitive plant species.

In recent years, laboratory soil toxicity testing has advanced with the introduction of ecologically relevant boreal forest soil invertebrate and plant species, as well as increased adoption of avoidance toxicity tests. In this study, we investigated the toxicity of a binary petroleum hydrocarbon (PHC) mixture to six agronomic and boreal forest plant species (Elymus lanceolatus, Lactuca sativa, Medicago sativa, Raphanus sativus, Pinus banksiana and Picea glauca) and the avoidance response of five soil invertebrate species (Eisenia fetida, Enchytraeus crypticus, Folsomia candida, Oppia nitens and Hypoaspis aculeifer). We assessed concentration addition and independent action mixture toxicity reference models, with potential interactions, using observed responses from the mixture and individual component toxicity endpoints from literature. Our key finding was soil invertebrate avoidance of PHC-contaminated soil was in the similar range of growth measurements for plant species sensitive to PHC-contaminated soils. This study further supports the inclusion of avoidance tests in toxicity test batteries for assessing PHC toxicity as invertebrate avoidance response appears to be linked to plant growth and informative of plant habitat quality.

Above- and belowground fluxes of methane from boreal dwarf shrubs and Pinus sylvestris seedlings

The contribution of boreal forest plants to the methane (CH4) cycle is still uncertain. We studied the above and belowground CH4 fluxes of common boreal plants, and assessed the possible contribution of CH4 producing and oxidizing microbes (methanogens and methanotrophs, respectively) to the fluxes. We measured the CH4 fluxes and the amounts of methanogens and methanotrophs in the above- and belowground parts of Vaccinium myrtillus, Vaccinium vitis-idaea, Calluna vulgaris and Pinus sylvestris seedlings and in non-planted soil in a microcosm experiment. The shoots of C. vulgaris and P. sylvestris showed on average emissions of CH4, while the shoots of the Vaccinium species indicated small CH4 uptake. All the root-soil-compartments consumed CH4, however, the non-rooted soils showed on average small CH4 emission. We found methanotrophs from all the rooted and non-rooted soils. Methanogens were not detected in the plant or soil materials. The presence of plant roots seem to increase the amount of methanotrophs and thus CH4 uptake in the soil. The CH4 emissions from the shoots of C. vulgaris and P. sylvestris demonstrate that the plants have an important contribution to the CH4 exchange dynamics in the plant-soil systems.

Boreal forest plant species responses to pH: ecological interpretation and application to reclamation

Reclamation following oil sands mining in northeastern Alberta (Canada) creates adverse reforestation soil conditions, including extreme pH values. We elucidated pH tolerance limits of boreal plant species and how pH affects nutrient uptake in these plants. We measured growth, gas exchange, and foliar nutrient concentration of 15 common northern boreal forest plants after eight weeks exposure to root zone pH ranging from 5.0 to 9.0. Cluster analyses were used to group these species based on their pH responses. Based on their growth and gas exchange responses to pH, the 15 plant species could be divided into five groups, each of which contained species that commonly co-occur in particular boreal forest site types. For the foliar nutrient responses to pH, the 15 species could be grouped into only two categories; both showed decreases in foliar N, P, Fe and Zn concentration with increasing pH, with a more pronounced effect on the group that included trembling aspen, paper birch and chokecherry. The evidence of differential adaptation to pH by habitat type suggests the importance of soil pH as a factor affecting boreal plant species distribution and could be helpful for selection of species suitable for reclamation of sites with altered soil pH.

Thawing seasonal ground ice: An important water source for boreal forest plants in Interior Alaska

AbstractLittle is known about the ecological impacts of permafrost degradation on water fluxes in boreal ecosystems, such as those in Interior Alaska. Low plant water stress suggests a reliance on a diversity of water sources. In addition to rainfall, we hypothesize that deep soil water derived from thawing seasonal ground ice (TSGI) supports plants during dry periods. We analyzed water stable isotopes from soils, plants, ice, and rain collected from stable and unstable permafrost sites. We found that TSGI provides a background water source for plants during wet years (at least 10–20%) and a stable source during dry years (at least 30–50%) and early in the growing season (60–80% in wet and dry years). Plant water uptake patterns “track” the soil thawing front, using deep and shallow layers in wet years and deep layers during dry years. This plasticity allows boreal plants to cope with seasonal drought and exploit available water sources. The availability of TGSI depends on the amount of rainfall the prior year and on permafrost stability. Thawing permafrost may reduce the buffering capacity of TGSI due to less seasonal ice from greater drainage and/or a deeper active layer. This study demonstrates the importance of two buffering mechanisms for plants to cope with rainfall variability within boreal forest underlain by permafrost—availability of TSGI and plasticity in water uptake patterns. We suggest that plant utilization of stored water may be why evapotranspiration in northern latitudes can exceed growing season precipitation.

Evaluating Land–Atmosphere Coupling Using a Resistance Pathway Framework

Abstract This paper presents a methodology for examining land–atmosphere coupling in a regional climate model by examining how the resistances to moisture transfer from the land to the atmosphere control the surface turbulent energy fluxes. Perturbations were applied individually to the aerodynamic resistance from the soil surface to the displacement height, the aerodynamic resistance from the displacement height to the reference level, the stomatal resistance, and the leaf boundary layer resistance. Only perturbations to the aerodynamic resistance from the soil surface to the displacement height systematically affected 2-m air temperature for the shrub and evergreen boreal forest plant functional types (PFTs). This was associated with this resistance systematically increasing the terrestrial and atmospheric components of the land–atmosphere coupling strength through changes in the partitioning of the surface energy balance. Perturbing the other resistances did contribute to changing the partitioning of the surface energy balance but did not lead to systematic changes in the 2-m air temperature. The results suggest that land–atmosphere coupling in the modeling system presented here acts mostly through the aerodynamic resistance from the soil surface to the displacement height, which is a function of both the friction velocity and vegetation height and cover. The results show that a resistance pathway framework can be used to examine how changes in the resistances affect the partitioning of the surface energy balance and how this subsequently influences surface climate through land–atmosphere coupling. Limitations in the present analysis include grid-scale rather than PFT-scale analysis, the exclusion of resistance dependencies, and the linearity assumption of how temperature responds to a resistance perturbation.

Forest management regulates temporal change in the cover of boreal plant species

We analysed the driving forces of temporal change in the cover of boreal forest plant species in Finland over 21years (1985–2006). Our study focused on the effects of forest cuttings of different intensity, i.e. regeneration cuttings (RC) and intermediate cuttings (IC), on 11 common understory species (including vascular plants, mosses and lichens) and their recovery after cuttings. General linear models (LM) were applied in modelling the change in the cover of plant species. The plant species displayed contrasting responses to RC and IC in accordance with their light demand, which also accounted for their recovery rate after cutting disturbance. After RC of old forest, shade and semi-shade tolerant species (herb Oxalis acetosella, moss Hylocomium splendens, dwarf shrub Vaccinium myrtillus) decreased strongly in cover (>70%) and recovered relatively slowly, but increased (40–100%) after IC. Species adapted to semi-light conditions (mosses Dicranum polysetum and Pleurozium schreberi, dwarf shrub Vaccinium vitis-idaea) decreased rather strongly (20–60%) after RC, but recovered relatively fast, reaching their old-forest cover level at a stand age of ca. 30years. These species also increased after IC. In contrast, light-demanding species (dwarf shrubs Empetrum nigrum and Calluna vulgaris, grass Deschampsia flexuosa) increased after RC and decreased after IC. Cladina lichens decreased across the country. In general, early successional light-demanding species increased and late successional shade-tolerant species decreased after RC. IC favoured all but the most light-demanding species. Species-specific responses to cuttings showed considerable variation within plant functional groups (e.g. dwarf shrubs, herbs, mosses). Cuttings determined the principal change in vegetation, while only slight signals of the effect of climate warming were found in few species. The legacy of forest management deserves special attention when e.g. tracking the effect of global change on vegetation.