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Short-term (three to four years) effects of forest harvesting on soil solution chemistry were investigated at two Norway spruce sites in southern Norway, differing in precipitation amount and topography. Experimental plots were either harvested conventionally (stem-only harvesting, SOH) or whole trees, including crowns, twigs and branches were removed (whole-tree harvesting, WTH), leaving residue piles on the ground for some months before removal. The WTH treatment had two sub-treatments: WTH-pile where there had been piles and WTH-removal, from where residues had been removed to make piles. Increased soil solution concentrations of NO3–N, total N, Ca, Mg and K at 30 cm depth, shown by peaks in concentrations in the years after harvesting, were found at the drier, less steep site in eastern Norway after SOH and WTH-pile, but less so after WTH-removal. At the wetter, steeper site in western Norway, peaks were often observed also at WTH-removal plots, which might reflect within-site differences in w...

Decomposition of the finest harvest residues is important for the carbon and nutrient cycle in forest ecosystems both before and after tree felling. We assumed that decomposition is dependent on harvest residue fraction and chemistry, soil temperature and moisture, and aimed at determining decomposition rates and nutrient dynamics of needles, twigs and fine roots from newly felled Picea abies trees in two sites with different climate and topography. Decomposition of needles, twigs and fine roots in mesh bags was followed for up to six years and four years in harvesting sites in eastern and western Norway, respectively. The western site had a more humid climate and a steeper terrain than the eastern site. The mass loss after two years was significantly higher for needles (49–59%) than for twigs and fine roots (29–38%). Between sites, there was no significant difference between mass loss for neither needles nor twigs. Nitrogen accumulated in needles during the first year, but 35% of initial needle N had been released after three years. The initial needle and twig decomposition rate was dependent on soil moisture and topographic aspect. During the first three years, needle lignin concentrations retarded whereas P concentrations stimulated needle mass loss. For twigs, P concentrations stimulated mass loss, whereas higher soil temperatures reduced it. Lignin and P concentrations of plant parts and soil temperature were the most important factors for the first three-year mass loss. The slow release of nutrients shows the importance of remaining needles, twigs and fine roots as a long-time nutrient source in the ecosystems under study.

Several studies have looked at how individual environmental factors influence needle morphology in conifer trees, but interacting effects between drought and canopy position have received little attention. In this study, we characterized morphological responses to experimentally induced drought stress in sun exposed and shaded current-year Norway spruce needles. In the drought plot trees were suffering mild drought stress, with an average soil water potential at 50 cm depth of -0.4 MPa. In general, morphological needle traits had greater values in sun needles in the upper canopy than in shaded needles in the lower canopy. Needle morphology 15 months after the onset of drought was determined by canopy position, as only sun needle morphology was affected by drought. Thus, canopy position was a stronger morphogenic factor determining needle structure than was water availability. The largest influence of mild drought was observed for needle length, projected needle area and total needle area, which all were reduced by ~27% relative to control trees. Needle thickness and needle width showed contrasting sensitivity to drought, as drought only affected needle thickness (10% reduction). Needle dry mass, leaf mass per area and needle density were not affected 15 months after the onset of mild drought. Our results highlight the importance of considering canopy position as well as water availability when comparing needle structure or function between conifer species. More knowledge about how different canopy parts of Norway spruce adapt to drought is important to understand forest productivity under changing environmental conditions.

Predicted increases in the frequency and duration of drought are expected to negatively affect tree vitality, but we know little about how water shortage will influence needle anatomy and thereby the trees’ photosynthetic and hydraulic capacity. In this study, we evaluated anatomical changes in sun and shade needles of 20‐year‐old Norway spruce trees exposed to artificial drought stress. Canopy position was found to be important for needle structure, as sun needles had significantly higher values than shade needles for all anatomical traits (i.e., cross‐sectional needle area, number of tracheids in needle, needle hydraulic conductivity, and tracheid lumen area), except proportion of xylem area per cross‐sectional needle area. In sun needles, drought reduced all trait values by 10–40%, whereas in shade needles, only tracheid maximum diameter was reduced by drought. Due to the relatively weaker response of shade needles than sun needles in drought‐stressed trees, the difference between the two needle types was reduced by 25% in the drought‐stressed trees compared to the control trees. The observed changes in needle anatomy provide new understanding of how Norway spruce adapts to drought stress and may improve predictions of how forests will respond to global climate change.

Trees must respond to many environmental factors during their development, and light is one of the main stimuli regulating tree growth. Thinning of forest stands by selective tree removal is a common tool in forest management that increases light intensity. However, morphological and anatomical adaptations of individual shoots to the new environmental conditions created by thinning are still poorly understood. In this study, we evaluated shoot morphology (shoot length, needle number, projected leaf area) and anatomy (tracheid lumen area, tracheid number, tracheid dimensions, xylem area, potential hydraulic conductivity) in three Norway spruce (Picea abies/L./Karst.) families exposed to different thinning regimes. We compared shoot characteristics of upper-canopy (i.e. sun-exposed) and lower-canopy (i.e. shaded) current-year shoots in a control plot and a plot thinned to 50 % stand density the previous year. One tree per family was chosen in each treatment, and five shoots were taken per canopy position. We found that upper-canopy shoots in both plots had higher values than lower-canopy shoots for all studied parameters, except lumen roundness and tracheid frequency (i.e. tracheid number per xylem area). Thinning had little effect on shoot morphology and anatomy 1 year after thinning, except for small but significant changes in tracheid dimensions. Needles were more sensitive to altered light conditions, as projected leaf area of shoot, needle number and leaf hydraulic conductivity changed after thinning. Differences between upper- and lower-canopy shoots did not seem to be influenced by thinning and were almost the same in both plots. Our results suggest that lower-canopy shoots require several years to modify their morphology and anatomy to new light conditions following thinning. The slow light adaptation of the lower canopy may be of practical importance in forest management: thinned stands may be predisposed to drought stress because newly exposed shoots experience increased illumination and transpiration after thinning.

Global warming will most likely lead to increased drought stress in forest trees. We wanted to describe the adaptive responses of fine roots and fungal hyphae, at different soil depths, in a Norway spruce stand to long-term drought stress induced by precipitation exclusion over two growing seasons. We used soil cores, minirhizotrons and nylon meshes to estimate growth, biomass and distribution of fine roots and fungal hyphae at different soil depths. In control plots fine roots proliferated in upper soil layers, whereas in drought plots there was no fine root growth in upper soil layers and roots mostly occupied deeper soil layers. Fungal hyphae followed the same pattern as fine roots, with the highest biomass in deeper soil layers in drought plots. We conclude that both fine roots and fungal hyphae respond to long-term drought stress by growing into deeper soil layers.

Drought-induced tree susceptibility is a major risk associated with climate change. Here we report how an 11-week drought affected tracheid structure, gene expression, and above- and belowground growth in 5-year-old Norway spruce trees (Picea abies) under controlled conditions. The canopy of trees subjected to severe drought had significantly less current-year needle biomass, and fewer tracheids and tracheid rows in current-year shoots compared to fully watered control trees. Belowground tissues were more strongly affected by drought than aboveground tissues. In fine roots (

Conifer needles are extraordinarily variable and much of this diversity is linked to the water transport capacity of the xylem and to xylem conduit properties. However, we still know little about how anatomical characteristics influence the hydraulic efficiency of needle xylem in different parts of the crown. In this study we evaluated needle function and anatomy in Norway spruce families exposed to different light conditions. We measured tracheid and needle characteristics of sun-exposed and shaded current-year needles in two experimental plots: a control plot and a thinned plot with 50% reduction in stand density. Sun-exposed needles had a larger tracheid lumen area than shaded needles, and this was caused by a larger maximum tracheid lumen diameter, while the minimum lumen diameter was less plastic. Sun-exposed needles had also higher theoretical hydraulic conductivity than shaded needles. Thinning leads to increased radiation to the lower branches, and presumably exposes the upper branches to stronger water stress than before thinning. Thinning affected several needle parameters both in sun-exposed and shaded needles; tracheid lumens were more circular and minimum tracheid lumen diameter was larger in the thinned plot, whereas maximum tracheid lumen diameter was less plastic on both plots. This study demonstrates that needle xylem structure in Norway spruce is clearly influenced by the light gradient within the tree crown.

Dissolved aluminium (Al) in soils, mobilized by acid deposition, is considered a threat to forest health through hampering root growth and nutrient uptake. Since the end of the 1980s dissolved Al in forest soil water plays a key role in the assessment of critical loads of acid deposition. So far, most evidence for toxicity of dissolved Al in forest soil water is based on nutrient solution studies and pot experiments. Here, we present results from one of the few in situ ecosystem-scale forest manipulation experiments to study the effect of Al on mature forest trees. A plotwise addition of dilute AlCl3 was conducted during seven years in an even-aged spruce forest (Picea abies) in an area in Norway with low acid deposition. Soil solution concentrations of Al were increased to potentially toxic levels (up to 500 μmol L−1) and base cation (Ca + Mg + K) to inorganic Al ratios in the soil solution in the root zone were mostly below 1 in the Al-addition treatments. In the control treatment (only water addition) Al concentrations did not exceed 15 μmol L−1 and base cation to inorganic Al ratios were above 1. The toxic effects of Al on fine root growth and plant growth found in hydroponic studies and pot trials are not confirmed by this field manipulation. However, magnesium (Mg) contents in needles decreased significantly and persistently in plots with elevated Al concentrations, whereas the needle Ca content did not respond. The depletion of the Mg content in needles is suggested to be due to antagonistic effects of high Al concentrations at the root surface, consistent with observed reductions in Mg to Al ratio of inner bark. This study clearly supports a role for Al in critical load functions for forests as dissolved Al causes a decrease in uptake of Mg. However, other signs of reduced forest vitality were not observed. Soil base cation status may need to be included in risk evaluations of forest health under acid deposition.

Root cap development in cereals and legumes is self-regulated by a repressor that accumulates in the extracellular environment, and immersing the root tip into water results in renewed cap development. By exploiting this phenomenon, root cap mitosis and differentiation can be synchronously induced among populations. In Pisum sativum L., messenger RNA (mRNA) differential display revealed changes in expression of approximately 1% of the sample mRNA population within minutes of induced cap turnover. This profile changes sequentially over a period of 30 min, then stabilizes. Microarray analysis of Medicago truncatula root caps confirmed changes in expression of approximately 1% of the target population, within minutes. A cell specific marker for cap turnover exhibited the same temporal and spatial expression profile in the gymnosperm species Norway spruce (Picea abies) as in pea. Induced cap development provides a means to profile cell-specific gene expression among phylogenetically diverse species from the early moments of mitosis and cellular differentiation.

Fine roots (

Organic acid anions exuded from roots of Picea abies (Norway spruce) seedlings grown on glass beads in the presence and absence of mycorrhiza (Laccaria bicolor) and aluminum (Al) at pH 3.9 were measured. We wanted to test if the roots exuded more organic acid anions when exposed to Al and if mycorrhization influenced the exudation. Oxalate was exuded in far higher amounts than any other organic acid anion, with a maximum rate of 1.7 nmol (mg root DW) -1 d -1 . Mycorrhizal roots exuded significantly more oxalate than non-mycorrhizal roots. The presence of Al did not enhance oxalate exudation. We conclude that the oxalate exuded constitutively by Picea abies/Laccaria bicolormay lead to rhizosphere oxalate concentrations that are relevant for Al resistance.

Considerable knowledge exists about the effect of aluminium (Al) on root vitality, but whether elevated levels of Al affect soil microorganisms is largely unknown. We thus compared soils from Al-treated and control plots of a field experiment with respect to microbial and chemical parameters, as well as root growth and vitality. The field experiment was established in a 50-year-old Norway spruce (Picea abies L.) stand where no Al or low concentrations of Al had been added every 7–10 days during the growth season for 7 years. Analysis of soil solutions collected using zero tension lysimeters and porous suction cups showed that Al treatment lead to increased concentrations of Al, Ca and Mg and lower pH and [Ca + Mg + K/Al] molar ratio. Corresponding soil analyses showed that soil pH remained unaffected (pH 3.8), that exchangeable Al increased, while exchangeable Ca and Mg decreased due to the Al treatment. Root in-growth into cores placed in the upper 20 cm of the soil during three growth seasons was not affected by Al additions, neither was nutrient concentration or mortality of these roots. The biomass of some taxonomic groups of soil microorganisms, analyzed using specific membrane components (phospholipid fatty acids; PLFAs), was clearly affected by the imposed Al treatment, both in the organic soil horizon and in the underlying mineral soil. Microbial community structure in both horizons was also clearly modified by the Al treatment. Shifts in PLFA trans/cis ratios indicative of short term physiological stress were not observed. Yet, aluminium stress was indicated both by changes in community structure and in ratios of single PLFAs for treated/untreated plots. Thus, soil microorganisms were more sensitive indicators of subtle chemical changes in soil than chemical composition and vitality of roots.

Here we report on low molecular weight organic acids in root exudates and soil solutions of Norway spruce and silver birch grown in rhizoboxes, sterile microcosms and the field. Monocarboxylic acids dominated in all three experimental systems. Formic, shikimic and oxalic acids were found in both spruce and birch microcosms. Fumaric acid was exclusive for spruce, while lactic, malonic, butyric and phthalic acids were only found in the birch microcosms. In spruce rhizoboxes oxalic, lactic, formic, butyric and pthalic acids were found. In addition, citric, adipic, propionic, succinic and acetic acids were observed in the rhizosphere of birch. Behind root windows in the field, only oxalic and lactic acids were found in the rhizosphere of spruce fine roots, whereas also formic and phthalic were observed close to birch fine roots, all at low concentrations. The rhizosphere of mycorrhizal short roots of birch contained butyric acid along with the acids observed for birch fine roots. Our results emphasise that characteristics of both the trees e.g. species, developmental stage, root density, mycorrhizal status, and the experimental system, i.e. growth conditions are important for the composition and the amount of organic acids. We conclude that the rhizosphere of birch contains more organic acids at higher concentrations than spruce.

Summary • Aluminium (Al) stress reduces plant growth. However, some species such as Norway spruce (Picea abies) seem to tolerate high Al concentrations. The aim of this study was to investigate characteristics possibly involved in Al tolerance in Norway spruce seedlings. • Seedlings (10-d-old) were exposed to Al3+ concentrations of 0.5 and 5 mm for up to 168 h. The effect of Al stress on root growth, cell morphology and Al distribution, callose production, and peroxidase and chitinase activity was analysed. • Root growth decreased after 1 d and 2 d with 5 and 0.5 mm Al, respectively. Callose concentration increased strongly after 6 h treatment with 5 mm Al. The activity of many peroxidase and chitinase isoforms decreased after 1–24 h exposure of both treatments. Several isoforms increased after 48–168 h exposure to 5 mm Al. • We postulate that, with external Al concentrations 0.5 mm or lower, an increased production above constitutive levels of peroxidase or chitinase is not required for Al tolerance in young Norway spruce seedlings. High constitutive levels of peroxidase and chitinase in this species may be part of this Al tolerance.

Organic acids such as malate, citrate and oxalate have been hypothesized to be involved in the long-term podzolization process and also to offer short-term protection to plants and microorganisms against aluminium under acid soil conditions. However, the reactions of organic acids in soil remain poorly understood. The aim of this study was to characterize the reactions of citrate and oxalate in Picea abies forest soils of contrasting Al status. 14 C-labelled citrate and oxalate were added to soil at low levels close to steady state organic acid soil solution concentrations and their fate followed over a subsequent 24 h period. Organic acid decomposition was greatest in surface horizons (t1/2a 0.5 h) compared to subsurface horizons (t1/2a 8 h) and the long-term field addition of Al to soil did not influence the mineralization rate or biomass-C yield by the microbial community. In experiments where the levels of Al were manipulated in the laboratory, only at high Al concentrations ($5 mM) was organic acid mineralization significantly affected. Similar experiments with non-Al complexing glucose indicated that this effect could be attributable to a direct Al complexation effect on the organic acids and partly due to an indirect toxic effect of Al on the microorganisms themselves. In conclusion, while the release of organic acids from plants may offer protection against rhizotoxic Al, the efficiency of this mechanism will be reduced by the rhizosphere microbial community. q 2001 Elsevier Science Ltd. All rights reserved.

[b][u]Background and Aims[/u][/b][br/] [br/] Forest trees directly contribute to carbon cycling in forest soils through the turnover of their fine roots. In this study we aimed to calculate root turnover rates of common European forest tree species and to compare them with most frequently published values.[br/] [br/] [b][u]Methods[/u][/b][br/] [br/] We compiled available European data and applied various turnover rate calculation methods to the resulting database. We used Decision Matrix and Maximum-Minimum formula as suggested in the literature.[br/] [br/] [b][u]Results[/u][/b][br/] [br/] Mean turnover rates obtained by the combination of sequential coring and Decision Matrix were 0.86 yr−1 for Fagus sylvatica and 0.88 yr−1 for Picea abies when maximum biomass data were used for the calculation, and 1.11 yr−1 for both species when mean biomass data were used. Using mean biomass rather than maximum resulted in about 30 % higher values of root turnover. Using the Decision Matrix to calculate turnover rate doubled the rates when compared to the Maximum-Minimum formula. The Decision Matrix, however, makes use of more input information than the Maximum-Minimum formula.[br/] [br/] [b][u]Conclusions[/u][/b][br/] [br/] We propose that calculations using the Decision Matrix with mean biomass give the most reliable estimates of root turnover rates in European forests and should preferentially be used in models and C reporting.

Conifers and other trees are constantly adapting to changes in light conditions, water/nutrient supply and temperatures by physiological and morphological modifications of their foliage. However, the relationship between physiological processes and anatomical characteristics of foliage has been little explored in trees. In this study we evaluated needle structure and function in Norway spruce families exposed to different light conditions and transpiration regimes. We compared needle characteristics of sun-exposed and shaded current-year needles in a control plot and a thinned plot with 50% reduction in stand density. Whole-tree transpiration rates remained similar across plots, but increased transpiration of lower branches after thinning implies that sun-exposed needles in the thinned plot were subjected to higher water stress than sun-exposed needles in the control plot. In general, morphological and anatomical needle parameters increased with increasing tree height and light intensity. Needle width, needle cross-section area, needle stele area and needle flatness (the ratio of needle thickness to needle width) differed most between the upper and lower canopy. The parameters that were most sensitive to the altered needle water status of the upper canopy after thinning were needle thickness, needle flatness and percentage of stele area in needle area. These results show that studies comparing needle structure or function between tree species should consider not only tree height and light gradients, but also needle water status. Unaccounted for differences in needle water status may have contributed to the variable relationship between needle structure and irradiance that has been observed among conifers.

International audience; High soil acidity and elevated soil Al concentrations limit plant growth in many terrestrial ecosystems. Aluminium toxicity can be ameliorated by Ca. Thus, Ca/Al molar ratios in soil solution and in plant tissues have been proposed as superior indicators than Al concentration itself for evaluating the Al toxicity stress to trees (Cronan & Grigal, J Environ Qual 1995;24:209-226). This article presents an overview of publications since 1995 where the reduced Ca/Al ratio in fine tree roots has been used as an indicator of stress for Al and/or soil acidity. The main aim of this review was to evaluate the use and the critical threshold of the fine root Ca/Al ratio as a potential indicator for Al toxicity stress to trees in acid soils. Based on the reviewed literature, the fine root Ca/Al molar ratio was strongly negatively related to Al stress in small tree seedlings in controlled environments, whereas the response was not clear under field conditions where other environmental factors interact. Fine root Ca/Al ranged from 0.03 to 17 in tree seedlings and from 0.1 to 18 in mature trees depending on experimental and site conditions, as well as the tolerance and uptake mechanisms of the different tree species. Fine root Ca/Al was positively related to the soil solution Ca/Al molar ratio. Fine root Ca/Al ratios were related positively to fine root length, growth, specific root length, and biomass, and negatively to root diameter, callose formation, respiration chain activity, starch concentration, and root necromass. A number of relationships have been also found between the fine root Ca/Al and above-ground seedling and/or mature tree growth and nutrient uptake. The critical thresholds for the Ca/Al fine root ratio of 0.2 suggested by Cronan and Grigal (1995) is estimated to represent 90% risk of inverse impact on root and above-ground tree growth. Values of Ca/Al molar ratio in the fine roots of mature trees were only rarely determined below the critical 0.2. The caveats for the use and the interpretation of Ca/Al ratio in fine roots have been addressed in detail. A protocol for root processing and elemental analysis to obtain reliable and comparable results of Ca and Al concentrations in roots is also provided. The article concludes with recommendations for a wider use of the Ca/Al ratio in roots as a bioindicator of Al toxicity to trees in acid soils.

Toxic effects of aluminium (Al) on Picea abies (L.) Karst. (Norway spruce) trees are well documented in laboratory-scale experiments, but field-based evidence is scarce. This paper presents results on fine root growth and chemistry from a field manipulation experiment in a P. abies stand that was 45 years old when the experiment started in 1996. Different amounts of dissolved aluminium were added as AlCl 3 by means of periodic irrigation during the growing season in the period 1997–2002. Potentially toxic concentrations of Al in the soil solution were obtained. Fine roots were studied from direct cores (1996) and sequential root ingrowth cores (1999, 2001, 2002) in the mineral soil (0–40 cm). We tested two hypotheses: (1) elevated concentration of Al in the root zone leads to significant changes in root biomass, partitioning into fine, coarse, living or dead fractions, and distribution with depth; (2) elevated Al concentration leads to a noticeable uptake of Al and reduced uptake of Ca and Mg; this results in Ca and Mg depletion in roots. Hypothesis 1 was only marginally supported, as just a few significant treatment effects on biomass were found. Hypothesis 2 was supported in part; Al addition led to increased root concentrations of Al in 1999 and 2002 and reduced Mg/Al in 1999. Comparison of roots from subsequent root samplings showed a decrease in Al and S over time. The results illustrated that 7 years of elevated Al tot concentrations in the soil solution up to 200 μM are not likely to affect root growth. We also discuss possible improvements of the experimental approach.

Keywords: Norway spruce; microcosms; pH stability; silver birch; solid growth medium

Parallel to the long-term studies, greenhouse experiments were done to elucidate the connection between soil acidification and germination/ seedling development of the most common Norwegian forest tree species. Preliminary results that showed that the aluminum concentration increased in seedlings when soil pH decreased (Teigen, unpublished), initiated greenhouse and growth chamber experiments on the effects of Al on seedling growth.

The response to aluminium concentrations was evaluated for birch seedlings (Betula pendula Roth, formerly Betula verrucosa Ehrh.) by using a growth technique that provides stable internal concentrations of nutrients in plants. Aluminium was added as aluminium nitrate and aluminium chloride and pH was kept at 3.8±0.2 by adding HCl or NaOH. The seedlings were grown in two different series of nutrient treatments, either with near-optimum conditions (relative addition rate 25% day−1) or with constant nutrient stress (relative addition rate 10% day−1) before the aluminium addition. Growth reduction occurred at aluminium concentrations greater than 3 mM, and lethal effects at aluminium concentrations greater than 15 mM. In plants subjected to near-optimum conditions before aluminium addition, the internal nutrient concentrations decreased with increasing aluminium concentration for all macronutrients. The concentration of the macronutrients N, K and P decreased gradually with increasing aluminium concentration, while the concentration of Ca and Mg decreased fairly abruptly when aluminium concentrations exceeded 1 mM. The same tendency was observed in nutrient stressed birch seedlings, but the pattern was more scattered. Relative growth rate of the seedlings was not affected by a low Ca/Al ratio. In all treatments, the molar Ca/Al ratio in/on the roots was below 0.2 at the end of the experiments. As decrease in growth occurs only at high aluminium concentrations, there is no reason to suggest that aluminium in acid soils is growth limiting for natural birch stands.