Four years of ozone exposure at high or low phosphorus reduced biomass in Norway spruce

Saplings of one clone of Norway spruce (Picea abies) were planted in pots and exposed to charcoal filtered (CF) air, non-filtered (NF) air or NF air plus extra ozone (NF+; ambient × 1.4) in open-top chambers (OTCs). The lowest and highest ozone concentrations were combined with low phosphorus (LP) supply. Ambient air plots without OTCs, and with and without pots, were also included. A long-term study was conducted with 756 trees (3–7 years old) harvested successively over four growing seasons. Ozone had a negative impact on tree growth, both in the high phosphorus (HP) supply and in the LP treatments. The ozone-induced decrease in biomass of the whole tree (NF+ relative to CF) was approximately 5% after four seasons, irrespective of phosphorus status. The corresponding decrease in biomass caused by LP, relative to HP, was 20% whatever the ozone treatment. LP also caused a shift in the shoot to root ratio, where root growth was favoured at the expense of the shoot. A weak effect of ozone treatment on the shoot to root ratio, favouring shoot growth, was found after three seasons, but was totally surpassed by the opposite effect of LP in the fourth season. The effect of OTCs and pots is also discussed.     

The effect of previously infested spruce needles on the growth of the green spruce aphid, Elatobium abietinum, and the effect of the aphid on the amino acid balance of the host plant

The effect of chlorosis induced in needles of Sitka and Norway spruce by the green spruce aphid on growth of the aphid is investigated, and the effect of infestation of the aphid on amino acid levels in Sitka spruce foliage is reported. On both Sitka and Norway spruce green spruce aphids were heavier when reared on chlorotic (previously infested) needles than when reared on green (previously uninfested) needles. The effect was more pronounced on Sitka than on Norway spruce. Infestation of the aphid altered the amino acid balance of Sitka spruce foliage but not the concentration of total amino acids. Possible causes of chlorosis, the influence of individual amino acids on aphid growth, the potential effect of chlorosis on outbreaks of the aphid and the differences in susceptibility of Sitka and Norway spruce to damage by the aphid are discussed.     

Freezing stress and membrane injury of Norway spruce (Picea abies) tissues

Effects of sub-zero temperatures (−5 to −35°C) on the tissues of needles, buds and shoots of Norway spruce [ Picea abies (L.) Karst.] were studied. The freezing caused increased efflux of cellular electrolytes. Freezing injury of the primordial shoots and 1-year-old shoots was the result of the spontaneous freezing of a deep supercooled cellular water. The crystallization injures the cellular membranes leading to the loss of semipermeability and to the drastic efflux of K⁺. In the needles there was no deep supercooling of water and two patterns of changes in the membranes, depending upon the range of the applied temperatures, could be distinguished. At 0 to – 25°C, which do not kill the cells, we observed a disturbance in the membrane semipermeability as monitored by electrolytes efflux within a few hours after thawing of the needles. At lower temperatures (−35°C) we observed irreversible loss of the membrane semipermeability, and death of the tissue. Those changes occurred 10 h after thawing and were probably caused by the released lytic enzymes and some toxic compounds, which acted on the cellular membranes.     

Diurnal Changes in Microscopic Structures of Mesophyll Cells of Norway Spruce, Picea abies(L.) Karst., and the Effects of Ozone and Drought

Microscopy has been used to diagnose the effects of air pollutantson conifers. As sampling may be slow, it is important to knowwhether the structure of needles changes during the day. Usinglight- and electron microscopy, diurnal changes in the structureof mesophyll cells of current year needles from 6-year-old Norwayspruce saplings were studied on one day in early autumn, 1995.Saplings had been grown in open-top chambers and exposed toozone and drought stress during the 1992–1995 growingseasons. In all treatments, the proportion of cells with smallcytoplasmic vacuoles and with large cytoplasmic lipid depositsdecreased during the day. Mitochondria increased in size fromearly morning to midday, after which time they shrank progressively.Ozone affected the shape of mitochondria: the proportion oftube-shaped mitochondria decreased from early morning in controlsaplings, whereas it increased in ozone-treated saplings. Starchaccumulated during the day, but to a lesser extent in drought-stressedsaplings than well-watered controls. Microbodies were smallerin drought-stressed saplings than in controls early in the morning,but their size then increased compared to that of the controls.Cellular and sub-cellular disorganization, probably due to sub-optimalfixation procedures, were detected in all treatments, especiallyin the morning, but these decreased later, particularly in well-wateredsaplings. Results show that microscopy is a sensitive and validtool for studying stress responses in plants. However, the timeof sample collection must be considered and documented to avoidmisleading conclusions due to actual diurnal changes and fixationproblems. Copyright 2001 Annals of Botany Company Diurnal changes, drought, light microscopy, mesophyll cells, needles, Norway spruce, Picea abies, ozone, transmission electron microscopy     

Productivity and vitality of spruce stands: dynamic feedback simulation for responses to different annual and seasonal levels of magnesium supply from soil

Responses of Norway spruce stands to gradually decreased annual magnesium supply from soil, with two seasonal courses, are evaluated by computer simulation. At low supply, magnesium concentrations in the needles are reduced to levels inducing chlorosis, but annual growth of new needles remains at the same level as stands with adequate magnesium. Above-ground permanent biomass shows a decreased annual production with lower supply, mainly because of shorter net carbon gain caused by decreased assimilation which is due to magnesium deficiency in needles. An additional but less important reason is the magnesium deficiency in stem and branch cambium, which is most severe during summer at low magnesium supply rates. The interaction of magnesium and carbon balance is emphasized.Modeling and simulation are not used for prediction but to test the consistency of scientific hypotheses.     

Effects of drought and waterlogging on ultrastructure of Scots pine and Norway spruce needles

Effects of water stress on needle ultrastructure of 2-year-old Scots pine (Pinus sylvestris L.) and 5-year-old Norway spruce [Picea abies (L.) Karst.] seedlings were studied in greenhouse experiments. Drought stress was induced by leaving seedlings without watering, and waterlogging stress was produced by submerging the seedling containers in water. Needle samples for ultrastructural analyses were collected several times during the experiments, and samples for nutrient analyses at the end of the experiments. In drought stress, plasmolysis of mesophyll and transfusion parenchyma tissues, aggregation of chloroplast stroma and its separation from thylakoids and decreased size and abundance of starch grains in needles of both species were observed. The concentration of lipid bodies around the chloroplasts were detected in pine needles. Calcium and water concentrations in spruce needles were lower by the end of the experiments compared to controls. In waterlogging treatment, swelling of phloem cells in pine needles and large starch grains, slight swelling of thylakoids and increased translucency of plastoglobuli in chloroplasts of both species studied were observed. The phosphorus concentration in pine needles was higher while phosphorus, calcium and magnesium concentrations in spruce needles were lower in the waterlogging treatments compared to controls. Typical symptoms induced by drought stress, e. g. aggregation of chloroplast stroma and its separation from thylakoids, were detected, but, in waterlogging stress, ultrastructural symptoms appeared to be related to the developing nutrient imbalance of needles.     

Effects of ozone on organic acids in needles of Norway spruce and Scots pine

Summary The effect of ozone, needle age, and season on the pH of homogenate and acid contents of Scots pine and Norway spruce needles is presented. In addition enzyme activities of cytochrome C-oxidase (cyt. C-ox), phosphoenolpyruvate-carboxylase (PEPC), shikimic acid-dehydrogenase (SHDH) and malate-dehydrogenase (MDH) were measured in Scots pine needles. In freshly sprouted spruce needles the level of quinic acid is high and the pH of the needle homogenate is low. Shikimic acid starts at low levels, increases with increasing needle age and becomes dominant, whereas the quinic acid content decreases. Malic acid has a marked seasonal trend; no trend was found in citric acid. Ozone (200 g/m³) decreased shikimic acid and quinic acid, whereas pH, malic acid and citric acid increased. Ozone (100 g/m³) had a similar effect, except in the current-year spruce needles. In Scots pine needles ozone led to increased enzymatic activities of cyt. C-ox, PEPC and SHDH, and a decrease in the activity of MDH. This effect was more pronounced in summer than in autumn, but the visible damage was greater in autumn. These effects can be found with other stresses and are not specific for ozone.     

Quantification of ozone influx and apoplastic ascorbate content in needles of Norway spruce trees (Picea abies L., Karst) at high altitude

The objective of the present study was to investigate whether peak concentrations of ozone can deplete the apoplastic ascorbate pool of needles from Norway spruce trees (Picea abies L. Karst.) and, thereby, contribute to damage to forest trees. Twigs of forest trees grown at high altitude (1950m above sea level; Mt Patscherkofel, Austria) were enclosed in situ in chambers and fumigated for 5-5 or 17 h with ozone concentrations ranging from 60 to 798 nmol mol^?1. Adjacent branches were fumigated with filtered air. Ozone influx into the foliage ranging from 1-7 to 17nmolm^?2s^?1 had little effect on whole-needle ascorbate or glutathione contents. However, apoplastic ascorbate decreased by about 30% when the needles were exposed to environmentally relevant ozone concentrations and increased about 3-fold at higher ozone concentrations. This response suggests the induction of ascorbate as a protective system and may also be important under field conditions. Needles of spruce trees from high altitude that were exposed to chronically increased ozone concentrations contained significantly higher apoplastic ascorbate concentrations than needles from spruce trees from lower altitudes with lower mean atmospheric ozone concentrations. The results show that peak concentrations of ozone do not act in spruce via a depletion of the apoplastic ascorbate pool.     

Influence of elevated ozone and limited nitrogen availability on conifer seedlings in an open-air fumigation system: effects on growth, nutrient content, mycorrhiza, needle ultrastructure, starch and secondary compounds

Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies Karst.) seedlings were exposed to realistically elevated O₃ levels in open‐air experiments over three growing seasons. The total O₃ exposure doses were 1.2 × (1991), 1.5 × (1992) and 1.7 × (1993) ambient levels. During the 1992 and 1993 growing seasons pine and spruce seedlings received two different levels of nitrogen supply. Effects on growth, mycorrhiza formation, needle ultrastructure, primary and secondary compounds were studied. Ozone exposure had only slight effects on biomass production, growth height and nutrient content of studied conifers. Higher nitrogen availability improved growth of the seedlings and resulted in higher concentration of nitrogen in needles. In Scots pine O₃ exposure did not have effects on quantity of total mycorrhizas and short roots, while higher nitrogen availability decreased quantity of mycorrhizas and short roots. In both tree species O₃ exposure induced O₃‐related ultrastructural symptoms, e.g. granulation and dark staining of the chloroplast stroma in the needle mesophyll cells, at both nitrogen availability levels. Ozone exposure and nitrogen availability did not have significant effects on starch concentrations in either tree species. Concentrations of some individual terpenes were higher in O₃‐exposed needles, while concentrations of individual and total resin acids, total phenolics and catechins were not affected by O₃ exposure. Nitrogen availability did not have substantial effects on concentrations of monoterpenes. By contrast, concentrations of some individual and total resin acids were lower in pine needles and higher in spruce needles with higher nitrogen availability, while phenolic concentration in spruce needles decreased at higher nitrogen availability. The results suggest that realistically elevated levels of O₃ in the field can have some negative effects on the mesophyll ultrastructure of conifer needles, but carbon allocation to root and shoot growth and secondary metabolites are not affected substantially.     

Growth and reproduction of aphids and levels of free amino acids in Scots pine and Norway spruce in an open-air fumigation with ozone

To estimate the susceptibility of conifer seedlings to aphids under future tropospheric ozone levels, Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings were exposed to ambient and elevated ozone levels in an open-air exposure system. Growth and reproduction of the aphids Schizolachnus pineti and Cinara pinea on Scots pine and Cinara pilicornis on Norway spruce were monitored. Levels of free amino acids in foliage and young shoots were used as indicators of host plant quality. In elevated treatment plots the ozone doses were between 1.2 and 1.7 times the dose in ambient plots in 1990–93. Half of the seedling material in 1992–93 was subjected to nitrogen fertilization treatment to evaluate the effects of increased N deposition. In 1990, population density of S. pineti on pine did not differ between ambient and elevated ozone treatments during growing season, but remained higher in the elevated ozone plot than in the ambient plot at the end of the growing season. This was associated with elevated levels of glutamic acid in foliage. In August 1992, the numbers of S. pineti were consistent between the two ambient ozone plots, but deviated highly between the two ozone-fumigated plots. Glycine concentration in pine foliage was elevated by ozone, but free amino acid concentrations were not related to aphid performance. In 1993, ozone and nitrogen did not significantly affect the relative growth rate (RGR) of S. pineti or C. pinea nymphs on Scots pine, but glutamic acid concentration in foliage was increased by nitrogen fertilization. On Norway spruce, fecundity of C. pilicornis females was higher in elevated ozone treatment, but RGR of nymphs was not affected in 1992. In 1993, RGR of C. pilicornis nymphs was increased by nitrogen fertilization in June, but not affected by ozone. Nitrogen fertilization increased the levels of total free amino acids, aspartic acid, glutamic acid and proline in elongating shoots of Norway spruce, and ozone reduced the concentrations of valine and γ-butyric acid. Our results suggest that availability of nitrogen from soil has a stronger impact on the concentrations of free amino acids in conifer seedlings than ozone. Some episodes of high ozone concentration may increase free amino acids in foliage. Aphid response to ozone was extremely variable, in agreement with previous laboratory experiments. The expected 20–70% increase in ambient concentrations of tropospheric ozone may in some occasions enhance aphid performance on Scots pine and Norway spruce seedlings, but in most cases the ozone effect on the susceptibility of conifer seedlings to sucking insect pests is not important.     

Ribulose-l,5-bisphosphate carboxylase activity and influence of air pollution in spruce

Methods were established, which render possible a simultaneous determination of ri-bulose-l,5-bisphosphate (RuBP) carboxylase (EC 4.1.1.39) activity and chlorophyll content of Norway spruce (Picea abies Karst.) needles from a detergent-containing aqueous crude extract. Spruce RuBP carboxylase was tentatively characterized with regard to kinetic properties. Recovery experiments employing purified wheat RuBP carboxylase proved quantitative extraction of the enzyme from spruce foliage. Five timber stands consisting of 35–62 years old spruce, two of which exhibited the typical symptoms of recent spruce decline, were compared. For the needle generations 1 to 4 the enzyme activities as well as chlorophyll and protein concentrations were determined. The results do not indicate an involvement of RuBP carboxylase in spruce decline.     

Damage caused by the Green Spruce Aphid to Norway and Sitka spruce needles

Three-month-old needles of Sitka spruce were less susceptible to Elatobium abietinutn than 15-month-old needles. Symptoms appeared after longer aphid feeding times but only a proportion of damaged needles fell. After short feeding periods symptoms appeared in more Norway spruce needles than in Sitka spruce, whereas longer feeding periods resulted in more needles producing symptoms in the Sitka spruce. The symptoms took 4—6 days longer to appear in Norway spruce, and needle fall followed a longer feeding period than on Sitka spruce. Following 72 h feeding, needle fall occurred more quickly on Sitka spruce than on Norway spruce. The time taken for needle fall to occur was inversely related to the feeding time in Sitka spruce but such a response was not evident in Norway spruce. The results are discussed in relation to the differences exhibited in the probing behaviour of the aphid on the two spruces.     

Combined effects of loose wood ash and carbon on inorganic N and P, key organisms, and the growth of Norway spruce seedlings and grasses in a pot experiment

The effects of wood ash on the growth of Norway spruce seedlings and grasses, nitrogen and phosphorus leaching, and soil fauna were investigated at two levels of carbon availability in a greenhouse experiment simulating harvested boreal forest. While sucrose-C amendment reduced grass biomass regardless of wood ash by 88%, the shoot and root biomass of spruce seedlings increased by 38% and 370%, respectively. Despite the large variation in above-ground biomass, C addition did not alter the concentration of water extractable ammonium nitrogen in humus, but it counteracted the ash-induced increase in soil phosphate concentration. C addition reduced the proportion of bacterial-feeding nematodes in the nematode community. Wood ash reduced enchytraeid size, but their biomass was not affected. Carbon treatment was crucial for enchytraeids probably because amended pots were moister than controls. Small compensatory grass growth following harvest implied that soil fauna made little nitrogen available to plants in one growing season. The results support the hypothesis that C availability may be an important determinant of nutrient retention, and has the potential to control plant competition in intensively harvested forests.     

Does the azimuth orientation of Norway spruce (Picea abies/L./Karst.) branches within sunlit crown part influence the heterogeneity of biochemical,structural and spectral characteristics of needles?

The goal of this study was to determine if selected biochemical, structural and spectral properties of Norway spruce needles are influenced by the azimuth orientation of the branch. Three youngest needle age classes from 20 mature (100 years old or older) Norway spruce trees were sampled from upper branches of the sunlit production crown part from each of the 4 cardinal azimuth orientations. Photosynthetic pigments, soluble phenolic compounds and selected spectral and structural characteristics were determined for each needle age class. The content of photosynthetic pigments and soluble phenolic compounds did not differ among needles from different azimuth-oriented branches, nor did the optical reflectance indices Normalized Difference Vegetation Index (NDVI), Transformed Chlorophyll Absorption in Reflectance Index (TCARI)/Optimized Soil-Adjusted Vegetation Index (OSAVI), Red Edge Inflection Point (REIP) and Landsat Thematic Mapper bands 5 and 4 (TM5/TM4). No variation in volume properties, tissue volume proportions and cross-section shape characteristics of 3rd-year needles rejected our hypothesis that there would be variation in needle structural properties according to the azimuth orientation of branches. Consequently, we concluded that a random sampling of similar-aged needles within the sunlit production crown part may be used to study biochemical or structural and spectral needle properties of a mature Norway spruce growing in forest stands without a significant slope. In addition, the results obtained from a branch of one azimuth orientation should be representative for the whole sunlit portion of the crown. Consequences of these findings for Norway spruce health monitoring using remote sensing techniques are discussed.     

Interactions between green spruce aphid (Elatobium abietinum (Walker)) and Norway and Sitka spruce under high and low nutrient conditions

1 Green spruce aphid (Elatobium abietinum) is a serious pest of spruce (Picea spp.) in north‐west Europe, causing defoliation of one‐year‐old and older needles. 2 Relationships between population development of E. abietinum, needle loss and tree growth were compared for five pure genotypes of Sitka spruce and mixed‐genotype material of Sitka and Norway spruce, grown under high and low nutrient conditions. 3 Despite wide differences in flushing date between spruce genotypes, E. abietinum populations peaked on the same date on each genotype and on the mixed‐genotype material, irrespective of nutrient supply. 4 Larger aphid populations developed on trees grown under high nutrient conditions than under low nutrients. However, more needles were lost per aphid in the low nutrient treatment and overall defoliation rates in the two nutrient treatments were similar. 5 Total aphid numbers differed significantly between Sitka spruce genotypes within nutrient treatments, but not in relation to bud‐burst or needle terpene content. Reductions in height growth caused by infestation were greater (15–44%), and related to mean aphid densities and defoliation, in the low nutrient treatment, but were smaller (11–27%) and not related to aphid density and defoliation in the high nutrient treatment. 6 Development of E. abietinum populations was similar on Norway and Sitka spruce, but Norway spruce lost fewer needles. However, the effects of infestation on tree growth were more closely related to aphid density and were similar for Norway and Sitka spruce. 7 Infestation caused a decrease in total root dry weight of Norway and Sitka spruce in proportion to the reductions observed in above‐ground growth.     

Effects of elevated pCO2 and/or pO3 on C-, N-, and S-metabolites in the leaves of juvenile beech and spruce differ between trees grown in monoculture and mixed culture.

Three and four-year-old saplings of beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.) grown in monoculture and mixed culture were exposed in phytotrons to (1) ambient air, (2) elevated pO(3), (3) elevated pCO(2), or (4) elevated pCO(2) plus elevated pO(3). After 5 months, the contents of soluble sugars, starch, soluble amino compounds, non-structural proteins (NSP), as well as reduced (GSH) and oxidized (GSSG) glutathione were determined in the leaves of both species in order to assess the effects of the gaseous regimes on primary metabolism. Elevated pO(3) did not affect sugar and starch levels in beech leaves in monoculture, but significantly increased sugar levels in beech leaves grown in mixed culture. In spruce needles, sugar levels tended to be enhanced in both culture types. Individual and combined exposure of elevated pCO(2) led to an increase in non-structural carbohydrate (soluble sugars plus starch) levels in beech and spruce leaves of both culture types. Differences in the responses of non-structural carbohydrate levels to elevated pCO(2) between beech and spruce were apparent from different contributions of sugars and starch to the increase in carbohydrate levels. Exposure to elevated pCO(2) and/or elevated pO(3) did not affect the levels of soluble amino compounds and NSP in beech leaves, but reduced amino compound levels in spruce needles of both culture types. Elevated pO(3) increased GSH levels in the leaves of both tree species in both culture types, while GSSG levels in monoculture were reduced in beech leaves, but significantly enhanced in spruce needles. Elevated pCO(2) reduced GSSG levels in beech and spruce leaves in monoculture, and GSH levels in spruce needles of both culture types. The combination of elevated pCO(2) and pO(3) increased GSSG levels in beech leaves of both culture types and in spruce needles in monoculture, but reduced GSH levels in spruce needles of both culture types. Apparently, under each gaseous regime, the culture type significantly altered primary metabolism of the leaves of beech and spruce.     

Magnesium deficiency in young Norway spruce (Picea abies [L.] Karst.) trees induced by NH4NO3 application

Young Norway spruce trees were grown in 94 pots (2 per pot) on soil substrate derived from granite with low Mg saturation and were fertilized with different amounts of NH₄NO₃ (in total 25, 61, and 97 kmol N ha^-1) over a period of four years, partly at an experimental station, partly at a high-elevation site in the Bavarian Forest. A fourth set of trees received 9.4 kmol Mg ha^-1 in addition to 25 kmol N. Depending on the treatment, needle chlorosis developed in the course of the experiment. Improved light conditions after three years accelerated the yellowing process. The chlorotic Norway spruce trees showed a severe Mg deficiency and an imbalanced N:Mg ratio. The shoot length increment, the stem diameter, and the needle weights however were not influenced by the fertilization. Excessive applications of NH₄NO₃caused the substrate to become depleted of Mg. The successful experimental induction of the characteristic tip yellowing of older needles of Norway spruce growing on acidic soils at higher altitudes allowed hypotheses on the causes and processes of this type of forest decline to be tested.     

Does timing of boron application affect needle and bud structure in Scots pine and Norway spruce seedlings?

Loss of apical dominance is a well-known boron (B) deficiency symptom in trees. Recent field studies indicate that B deficiency may cause irreversible damage in emerging leader buds leading to bushy growth, and changes in developing needles in mature Norway spruce trees. We experimentally studied if timing of B application affects needles and buds of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings with low initial B levels. The treatments were: no B (B0); B supply from the beginning of the simulated summer (B1); starting soon after bud burst (B2) and starting at the occurrence of first needle primordia in new spruce buds (B3). At the end of the experiment, B concentration in B1 was 23 mg kg⁻¹ (pine) or 17 mg kg⁻¹ (spruce) and lower in the later applications. In B0 it was at deficiency limit. In B0, B2 and B3, there were fewer sclerenchyma cells, and cavities occurred in vascular cylinders in pine needles, and in spruce buds there were more tanniferous cells in the primordial shoots compared to B1. Furthermore, in all but B1 there was cell collapse in the bud apex of some spruce seedlings. The experimentally induced changes were the same as earlier reported in B deficient conifers in the field, and indicate, similarly as in the field that adequate B is necessary throughout the growing season for healthy growth, particularly for spruce. The differences between spruce and pines are due, at least partly, to the differences in time frame of needle development and in the differences in development of conducting tissues in the buds.     

Ameliorating effect of UV-B radiation on the response of Norway spruce and Scots pine to ambient ozone concentrations

Elevated levels of both ozone and UV-B radiation are typical for high-altitude sites. Few studies have investigated their possible interaction on plants. This study reports interactive effects of O₃ and UV-B radiation in four-year-old Norway spruce and Scots pine trees. The trees were cultivated in controlled environmental facilities under simulated climatic conditions recorded on Mt Wank, an Alpine mountain in Bavaria, and were exposed for one growing season to simulated ambient or twice-ambient ozone regimes at either near ambient or near zero UV-B radiation levels. Chlorotic mottling and yellowing of current year needles became obvious under twice-ambient O₃ in both species at the onset of a high ozone episode in July. Development of chlorotic mottling in relation to accumulated ozone concentrations over a threshold of 40 nL L^–1 was more pronounced with near zero rather than ambient UV-B radiation levels. In Norway spruce, photosynthetic parameters at ambient CO₂ concentration, measured at the end of the experiment, were reduced in trees cultivated under twice-ambient O₃, irrespective of the UV-B treatment. Effects on photosynthetic capacity and carboxylation efficiency were restricted to trees exposed to near zero levels of UV-B radiation, and twice-ambient O₃. The data indicate that UV-B radiation, applied together with O₃, ameliorates the detrimental effects of O₃. The data also demonstrate that foliar symptoms develop more rapidly in Scots pine than in Norway spruce at higher accumulated ozone concentrations. Symbols and abbreviations: LSD, least significant difference; PAS300, UV-B irradiance weighted according to the plant action spectrum of Green et al. (1974) normalized at 300 (nm); AOT40, (AOT = accumulated over threshold) reflects the sum of hourly ozone concentrations above 40 nL L^–1 during daylight hours (> 50 Wm^–2) ( Kärenlampi & Skärby 1996 ); A₃₅₀, net photosynthesis at ambient CO₂; G₃₅₀, stomatal conductance for water vapour at ambient CO₂; A₂₅₀₀, net photosynthesis at saturating CO₂ (maximal potential photosynthetic activity); CE, carboxylation efficiency; ROS, reactive oxygen species; RuBP, ribulose 1,5-bisphosphate; Rubisco, ribulose 1,5-bisphosphate carboxylase/oxygenase; GLM, general linear model.     

The use of different soil nitrogen sources by young Norway spruce plants

 Three-year-old Norway spruce trees were planted into a low-nitrogen mineral forest soil and supplied either with two different levels of mineral nitrogen (NH₄NO₃) or with a slow-release form of organic nitrogen (keratin). Supply of mineral nitrogen increased the concentrations of ammonium and nitrate in the soil solution and in CaCl₂-extracts of the rhizosphere and bulk soil. In the soil solution, in all treatments nitrate concentrations were higher than ammonium concentrations, while in the soil extracts ammonium concentrations were often higher than nitrate concentrations. After 7 months of growth, ¹⁵N labelled ammonium or nitrate was added to the soil. Plants were harvested 2 weeks later. Keratin supply to the soil did not affect growth and nitrogen accumulation of the trees. In contrast, supply of mineral nitrogen increased shoot growth and increased the ratio of above-ground to below-ground growth. The proportion of needle biomass to total above-ground biomass was not increased by mineral N supply. The atom-% ¹⁵N was higher in younger needles than in older needles, and in younger needles higher in plants supplied with ¹⁵N-nitrate than in plants supplied with ¹⁵N-ammonium. The present data show that young Norway spruce plants take up nitrate even under conditions of high plant internal N levels. Received: 1 April 1998 / Accepted: 9 October 1998