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Boron deficiency, manifested as shoot dieback, is a problem in conifer stands growing on soils with high nitrogen availability in Fennoscandia. Earlier observations on Norway spruce (Picea abies L. Karst.) suggest that freezing tolerance is decreased by boron deficiency. Here, the effect of boron fertilization on cold acclimation of Norway spruce was studied in a young stand with initially low boron status two years after fertilization. Buds, stems, needles and roots were collected at five sampling times during cold acclimation and subsequently exposed to series of freezing temperatures. Lethal temperatures of organs were assessed by electrolyte leakage method (EL) and visual scoring of damage (VS). Freezing tolerance of buds was measured also by differential thermal analysis (DTA). The mean boron (B) concentration in needles was 4 mg kgâ1 in unfertilized and 21 mg kgâ1 in B-fertilized trees while critical level of B deficiency is considered to be 5 mg kgâ1. The risk for increased freezing injuries in the low-B trees was not evident since all trees achieved cold hardiness that would be sufficient in central Finland. At two sampling times out of five, shoots or stem of B-fertilized trees were slightly more freezing tolerant than non-fertilized trees. However, the present study does not give strong evidence for the hypothesis that decreased freezing tolerance in B deficiency would be a triggering factor for leader dieback in Norway spruce at the B levels studied.

Two-year-old silver birch (Betula pendula) saplings were grown for a third growing season in controlled-environment rooms (dasotrons) at three soil temperatures (5, 10, and 20 °C). All trees grew the first flush of leaves, but the growth of the second flush was almost completely inhibited at the two lower temperatures. The dry weight of the second-flush leaves was 50 times larger at 20 °C than at 5 and 10 °C, with about 100 times more nitrogen. Root growth was less affected than shoot growth. Chlorophyll content, net assimilation rate and stomatal conductance were lower at low soil temperatures. The value of the cytoplasm resistance estimated from the electric impedance spectra was lower at 5 °C than at 10 or 20 °C. Leaf water potential was highest at the lowest soil temperature, and intercellular carbon dioxide concentration was only slightly lower in saplings growing in cooler soil. We conclude that the effect of long-term exposure to cold soil on net assimilation and growth was not caused by stomatal closure alone. It is likely to be additionally mediated by the limited nitrogen acquisition at the low soil temperatures, and perhaps additionally by some other factor. As the growth depression of aboveground parts in response to low soil temperature was more significant in silver birch than what has earlier been found in conifers, the relative changes in air and soil temperature may eventually determine whether birch will become more dominant in boreal forests with climate change.

The non-destructive evaluation of plant root growth is a challenge in root research. In the present study we aimed to develop electrical impedance spectroscopy (EIS) for that purpose. Willows (Salix myrsinifolia Salisb.) were grown from cuttings in a hydroponic culture in a growth chamber. Root growth was monitored at regular intervals by a displacement method and compared with the EIS parameters of the plants. To measure its impedance spectrum (IS) (frequency range from 40 Hz to 340 kHz) each plant was set in a measuring cell filled with a solution of the hydroponic culture. The IS was measured using a two-electrode measuring system. A silver needle electrode was connected to the stem immediately above the immersion level and a platinum wire was placed in the solution. The measurements were repeated twice weekly for a root growth period of one month. The IS of the entity consisting of a piece of stem, roots and culture solution were modelled by means of an electric circuit consisting of two ZARC-Cole elements, one constant-phase element, and a resistor. On the plant basis, an increase in root volume by growth correlated with a reduction in the sum of resistances in the ZARC-Cole elements (mean Pearsonâs correlation coefficient r = â0.70).

One-year-old seedlings (two sowing times), two-year-old seedlings and 14- and 18-year-old cuttings of Norway spruce (Picea abies (L.) Karst.) were exposed to shortening photoperiod (initially 16 h), lengthening photoperiod (initially 6 h) and constant short photoperiod (6 h) treatments with uniform temperature conditions in growth chambers. The timing of bud burst was examined. In all plants, shortening photoperiod treatment seemed to promote bud burst compared with other treatments. This effect was clearest in the oldest material. The results suggest that, in addition to temperature sum, the accumulated duration of the light period may promote bud burst of Norway spruce.

The productivity of Scots pine ( L.) under changing climatic conditions in the southern part of Finland was studied by scenario analysis with a gap-type forest ecosystem model. Standard simulations with the model predicted an increased rate of growth and hence increased productivity as a result of climatic warming. The gap-type model was refined by introducing an overwintering sub-model describing the annual growth cycle, frost hardiness, and frost damage of the trees. Simulations with the refined gap-type model produced results conflicting with those of the standard simulation, i.e., drastically decreased productivity caused by mortality and growth-reducing damage due to premature dehardening in the changing climate. The overwintering sub-model was tested with frost hardiness data from Scots pine saplings growing at their natural site 1) under natural conditions and 2) under elevated temperature condition, both in open-top chambers. The model predicted the frost hardiness dynamics quite accurately for the natural conditions while underestimating the frost hardiness of the saplings for the elevated temperature conditions. These findings show that 1) the overwintering sub-model requires further development, and 2) the possible reduction of productivity caused by frost damage in a changing climate is less drastic than predicted in the scenario analysis. The results as a whole demonstrated the need to consider the overwintering of trees in scenario analysis carried out with ecosystem model for boreal conditions. More generally, the results revealed a problem that exists in scenario analysis with ecological models: the accuracy of a model in predicting the ecosystem functioning under present climatic condition does not guarantee the realism of the model, nor for this reason the accuracy for predicting the ecosystem functioning under changing climatic conditions. This finding calls for the continuous rigorous experimental testing of ecological models used for assessing the ecological implications of climatic change.Pinus sylvestris

Two dynamic models predicting the development of frost hardiness of Finnish Scots pine ( L.) were tested with frost hardiness data obtained from trees growing in the natural conditions of Finland and from an experiment simulating the predicted climatic warming. The input variables were temperature in the first model, and temperature and night length in the second. The model parameters were fixed on the basis of previous independent studies. The results suggested that the model which included temperature and photoperiod as input variables was more accurate than the model using temperature as the only input variable to predict the development of frost hardiness in different environmental conditions. Further requirements for developing the frost hardiness models are discussed.Pinus sylvestris

According to a recently presented hypothesis, the predicted climatic warming will cause height growth onset of trees during mild spells in winter and heavy frost damage during subsequent periods of frost in northern conditions. The hypothesis was based on computer simulations involving a model employing air temperature as the only environmental factor influencing height growth onset. In the present study, the model was tested in the case of eastern Finnish Scots pine ( L.) saplings. Four experimental saplings growing on their natural site were surrounded by transparent chambers in autumn 1990. The air temperature in the chambers was raised during the winter to present an extremely warm winter under the predicted conditions of a double level of atmospheric carbon dioxide. The temperature treatment hastened height growth onset by two months as compared to the control saplings, but not as much as expected on the basis of the previous simulation study. This finding suggests that 1) the model used in the simulation study needs to be developed further, either by modifying the modelled effect of air temperature or by introducing other environmental factors, and 2) the predicted climatic warming will not increase the risk of frost damage in trees as much as suggested by the previous simulation study.Pinus sylvestris

The ability of one-year old Scots pine ( L.) seedlings to reharden during the dehardening period was studied. Naturally hardened quiescent seedlings were preconditioned at 0°C for ten days and then placed in chambers at different forcing temperatures with different light regimes. The forcing periods were followed by cool periods. Changes in frost hardiness were monitored at intervals using freeze tests of whole plants. Frost hardiness was assessed by three methods: impedance, survival and growth retardation. Dehardening seemed to be a partially reversible process, i.e. in some growing conditions slight rehardening was found.Pinus sylvestris

The relationships between bud dormancy and frost hardiness were examined using two-year-old L. seedlings. The chilling temperatures used were +4 and -2°C. To examine the dormancy release of the seedlings, a forcing technique was used. Frost hardiness was determined by artificial freezing treatments and measurements of electrical impedance. At the start of the experiment, the frost hardiness of the seedlings was about -25°C. After the rest break, the seedlings kept at +4°C dehardened until after eight weeks their frost hardiness reached -5°C. At the lower chilling temperature (-2°C) the frost hardiness remained at the original level. When moved from +4 to -2°C, seedlings were able to reharden only after the time required for bud burst in the forcing conditions had reached the minimum.Pinus sylvestris

Excess water in the rooting zone critically reduces tree growth and may even kill trees; however, the relative importance of damage to roots versus aboveground parts and the time course of damage are not well understood. We studied the dynamics of fine-root growth and mortality of 7-year-old Scots pine (Pinus sylvestris L.) saplings affected by a 5-week period of waterlogging (WL) during the growing season. Two out of six WL-exposed saplings survived the treatment. After 1-2 weeks of WL, the mortality of the first-order short roots (usually mycorrhizas) started to increase and the production of these roots started to decrease. WL decreased the longevity of short and long roots. Total root length (especially of fine roots with a diameter Key words: carbon sequestration, growth, forest hydrology, hypoxia, phenology, survival analysis. L'exces d'eau dans la zone d'enracinement reduit dangereusement la croissance et peut meme entrainer la mort des arbres. Cependant, l'importance relative des dommages aux racines comparativement aux parties aeriennes et l'evolution temporelle des dommages ne sont pas bien comprises. Nous avons etudie la dynamique de la croissance et de la mortalite des racines fines de gaules de pin sylvestre (Pinus sylvestris L.) agees de sept ans, plantees dans un substrat gorge d'eau (WL) pendant cinq semaines durant la saison de croissance. Deux des six gaules exposees au traitement WL ont survecu. Apres une a deux semaines, la mortalite des racines courtes du premier ordre (habituellement des mycorhizes) a commence a augmenter et la production a diminuer dans le traitement WL. Le traitement WL a reduit la longevite des racines courtes et des racines longues. La longueur totale des racines (particulierement celle des racines fines avec un diametre < 0,5 mm), la longueur specifique des racines fines, la masse anhydre totale des racines (incluant la souche) et la conductance hydraulique des racines (flux inverse) etaient plus faibles chez les gaules du traitement WL que chez les gaules temoins a la fin de l'experience. Cependant, plusieurs caracteristiques des racines etaient semblables chez les gaules qui ont survecu au traitement WL et les gaules temoins. Etant donne l'importance capitale des racines fines pour la croissance des arbres et la sequestration du carbone, on devrait tenir compte de leurs reactions a une nappe phreatique elevee pour l'amenagement et l'utilisation durable des tourbieres boreales boisees, p. ex. en maintenant un couvert forestier permanent et en entretenant les reseaux de fosses. [Traduit par la Redaction] Mots-cles : sequestration du carbone, croissance, hydrologie forestiere, hypoxie, phenologie, analyse de la survie., Introduction An elevated water table associated with waterlogging (WL) in the rooting zone is a growth-limiting factor for trees in large areas of the boreal zone, especially on peatlands (Kozlowski [...]

Electrical impedance characteristics of plant cells are dependent on such physiological factors as physiological condition, developmental stage, cell structure, nutrient status, water balance and temperature acclimation. In the measurements also such technical and physical factors as type of electrodes, frequency, geometry of the object, inter-electrode distance and temperature have an effect. These factors are discussed especially with respect to the impedance method in frost resistance studies of plants. The PDF includes an abstract in Finnish.

Tree roots comprise a huge carbon pool. Their dynamics are driven by environmental factors and thereby affected by climate change. We studied the effects of soil temperature on root and shoot phenology and their linkages in Norway spruce (Picea abies (L.) Karst.). Saplings were grown in controlled-environment rooms for three simulated growing seasons (GS1, GS2, and GS3). Soil-temperature treatments of 9, 13, 18, and 21[degrees]C were applied during GS2. Root growth was monitored with minirhizotrons and commenced in all treatments simultaneously. Temporal growth patterns of short and long roots were usually bimodal. Root growth was very low during the coldest treatment of GS2 but increased during GS3 as an aftereffect. During GS3, growth of short roots continued later after colder treatments than warmer treatments. Reduced sink strength of roots and increased carbohydrate accumulation into needles at 9[degrees]C during GS2 probably enabled compensatory root growth under restored temperatures during GS3. Soil temperature did not affect shoot phenology, and root and shoot phenology varied between growing seasons; thus, the linkage of root and shoot phenology was inconsistent. In warmer soil, root longevity was shorter and turnover rate was higher than in colder soil. This can further affect soil carbon dynamics and ecosystem carbon cycling in boreal forest ecosystems. Key words: climate change, fine-root dynamics, fine-root survival, minirhizotron, Picea abies. Les racines des arbres constituent un immense reservoir de carbone. Leur dynamique est regie par des facteurs environnementaux et par consequent influencee par les changements climatiques. Nous avons etudie les effets de la temperature du sol sur la phenologie des racines et des pousses, ainsi que leurs liens, chez l'epicea commun (Picea abies (L.) Karst.). Des gaules ont ete cultivees dans des chambres a environnement controle en simulant trois saisons de croissance (GS1, GS2 et GS3). Des traitements avec une temperature du sol de 9,13,18 et 21[degrees]C ont ete appliques durant GS2. La croissance des racines a ete suivie avec des minirhizotrons. La croissance des racines a debute simultanement dans tous les traitements. Les patrons temporels de croissance des racines courtes et longues etaient normalement bimodaux. La croissance des racines etait tres faible dans le traitement le plus froid durant GS2 mais a augmente apres coup durant GS3. La croissance des racines courtes s'est aussi poursuivie plus tard apres les traitements plus froids que plus chauds durant GS3. La reduction de l'importance du puits que representent les racines et l'accumulation accrue des hydrates de carbone dans les aiguilles a 9[degrees]C durant GS2 ont probablement permis la croissance compensatoire des racines lors de la restauration de la temperature dans le cas de GS3. La temperature du sol n'a pas influence la phenologie des pousses et la phenologie des racines et des pousses variait selon la saison de croissance; par consequent, le lien entre la phenologie des pousses et des racines etait incoherent. La longevite des racines etait plus courte et le taux de renouvellement etait plus eleve dans les sols plus chauds comparativement aux sols plus froids. Cela peut influencer la dynamique du carbone dans le sol et le recyclage du carbone de l'ecosysteme dans les ecosystemes forestiers boreaux. [Traduit par la Redaction] Mots-cles: changements climatiques, dynamique des racines fines, survie des racines fines, minirhizotron, Picea abies., Introduction On a global scale, land and ocean surface temperatures have increased ca. 0.9[degrees]C since the late 19th century (Intergovernmental Panel on Climate Change (IPCC) 2014). For the boreal zone, [...]

In the future management and sustainable use of boreal forests, it is crucial to consider the rate and strength of tree responses to an elevated water table and the concurrent oxygen limitations, especially in peatlands. We examined the response dynamics of 7-year-old Scots pine (Pinus sylvestris L.) seedlings to a 5-week waterlogging (WL) treatment during a growing season in a root lab (dasotron) experiment. WL took place after shoot elongation had ended but while growth of the trunk diameter was still in progress. Trunk sap flow and needle water potential started to decrease immediately after the onset of WL, while the first signs in needle gas exchange--seen as decreases in the potential efficiency of photosystem II, the rates of light-saturated net assimilation and transpiration, and increased needle respiration--were observed after 3 weeks of WL. New needles responded to WL more strongly than the old ones. Drainage with consequent re-oxygenation of the soil caused a further decrease in sap flow. We conclude that through negative feedback on transpiration and net photosynthesis, WL during the growing season is harmful for Scots pine, leading to potential growth losses or even dying of trees within a few weeks of WL. Key words: hypoxia, hydrology, peatland forestry, photosynthesis, sap flow. Pour l'amenagement futur et l'utilisation durable des forets boreales, il est essentiel de tenir compte du taux et de la robustesse de la reaction des arbres a l'elevation de la nappe phreatique et a l'appauvrissement simultane en oxygene, particulierement dans les tourbieres. Nous avons etudie la dynamique des reactions de semis de pin sylvestre (Pinus sylvestris L.) ages de 7 ans a un engorgement du sol d'une duree de 5 semaines au cours d'une saison de croissance lors d'une experience dans un laboratoire racinaire (dasotron). L'engorgement du sol est survenu apres que l'elongation des pousses eut ete completee mais pendant que la croissance en diametre du tronc etait toujours en cours. Le flux de seve dans le tronc et le potentiel hydrique des aiguilles ont commence a diminuer immediatement apres le debut de l'engorgement du sol, tandis que les premiers signes dans les echanges gazeux foliaires, visibles par la diminution de l'efficacite potentielle du photosysteme II, les taux de transpiration et d'assimilation nette a saturation lumineuse, ainsi que par l'augmentation de la respiration des aiguilles, ont ete observes apres 3 semaines d'engorgement du sol. Les nouvelles aiguilles ont reagi plus fortement a l'engorgement du sol que les vieilles aiguilles. Le drainage suivi de la reoxygenation du sol a cause une nouvelle diminution du flux de seve. Nous concluons que par l'intermediaire d'une retroaction negative sur la transpiration et la photosynthese nette, l'engorgement su sol durant la saison de croissance est nefaste pour le pin sylvestre et entraine des pertes potentielles de croissance ou meme la mort des arbres apres quelques semaines. [Traduit par la Redaction] Mots-cles: hypoxie, hydrologie, foresterie des tourbieres, photosynthese, flux de seve., Introduction Excess water, with consequently declined soil aeration, is one of the limiting factors in tree growth in the boreal zone, especially in the peatlands that extend to about 10% [...]