Response of needle sulphur and nitrogen concentrations of Scots pine versus Norway spruce to SO2 and NO2

The results of two field studies and an open-top chamber fumigation experiment showed that the response of mature Scots pine to SO(2) and NO(2) differed from that of mature Norway spruce. Moreover, the response of pine seedlings to SO(2) and NO(2) differed from that of mature trees. The greater increase in the needle total S concentrations of pine suggested more abundant stomatal uptake of SO(2) compared to spruce. Both pine seedlings and mature trees also seemed to absorb more N from atmospheric deposition. Mature pine was able to assimilate SO(4)(2-) derived from SO(2) into organic S more effectively than mature spruce at the high S and N deposition sites, whereas both pine and spruce seedlings accumulated SO(4)-S under NO(2)+SO(2) exposure. Spruce, in turn, accumulated SO(4)-S even when well supplied with N. Net assimilation of SO(4)(2-) in conifer seedlings was enhanced markedly by elevated temperature. To protect the northern coniferous forests against the harmful effects of S and N deposition, it is recommended that the critical level for SO(2) as a growing season mean be set at 5-10 microg m(-3) and NO(2) at 10-15 microg m(-3), depending on the 'effective temperature sum' and/or whether SO(2) and NO(2) occur alone or in combination.     

Crown condition of Norway spruce in relation to sulphur and nitrogen deposition and soil properties in southeast Norway

Atmospheric deposition of sulphur and nitrogen compounds may lead to enhanced leaching of base cations, accumulation of nitrogen in organic matter, lowered pH and increased concentration of toxic aluminium in soil, which in turn may affect the vitality of forest trees. A general monitoring of forest condition has been initiated in many European countries, partly in order to reveal stresses caused by acidification. However, forest condition is also affected by many other factors. This paper examines a seven-year series of crown-condition data from Local County Monitoring Plots in Norway spruce stands in Norway. Average, time trend and lability variables were calculated for crown density and crown colour for each plot. Wet deposition of sulphate, ammonium and nitrate for each plot were estimated using data from the national air and precipitation monitoring programmes. Soil data are based on soil sampling within the plots. The analysis gave no evident support for the hypothesized negative effect on crown condition from sulphur and nitrogen deposition and related alterations in soil.     

Physiology of young Norway spruce

In the Hohenheim experiment young spruce (Picea abies L. Karst.) were exposed to low levels of SO(2) and/or O(3) and acid precipitation. At the end of a five-year experimental period (1983-88) the following physiological parameters were examined: water soluble thiols, ascorbic acid, glutathionereductase activity and pigment content. Exposure to SO(2), leads to an increase in thiol content, to a slight decrease of ascorbic acid and to a pronounced decrease of pigments. O(3) exposure increases the content of ascorbic acid and decreases the thiols and the glutathione-reductase activity with no change in the pigment content. The combined exposure to SO(2), and O(3) results in the most distinct deviations compared to the control chamber response. These needles show the highest increase of ascorbic acid and thiols, the dry weight is decreased as is the glutathione-reductase activity and the pigment content is reduced. Consequences of these physiological alterations for the plant's health are discussed.     

Fluxes of oxidised and reduced nitrogen above a mixed coniferous forest exposed to various nitrogen emission sources

Concentrations of nitrogen gases (NH(3), NO(2), NO, HONO and HNO(3)) and particles (pNH(4) and pNO(3)) were measured over a mixed coniferous forest impacted by high nitrogen loads. Nitrogen dioxide (NO(2)) represented the main nitrogen form, followed by nitric oxide (NO) and ammonia (NH(3)). A combination of gradient method (NH(3) and NO(x)) and resistance modelling techniques (HNO(3), HONO, pNH(4) and pNO(3)) was used to calculate dry deposition of nitrogen compounds. Net flux of NH(3) amounted to -64 ng N m(-2) s(-1) over the measuring period. Net fluxes of NO(x) were upward (8.5 ng N m(-2) s(-1)) with highest emission in the morning. Fluxes of other gases or aerosols substantially contributed to dry deposition. Total nitrogen deposition was estimated at -48 kg N ha(-1) yr(-1) and consisted for almost 80% of NH(x). Comparison of throughfall nitrogen with total deposition suggested substantial uptake of reduced N (+/-15 kg N ha(-1) yr(-1)) within the canopy.     

Norway spruce and spruce shoot aphid as indicators of traffic pollution

Two-year-old Norway spruce (Picea abies (L.) Karst) seedlings were exposed to traffic emissions along roadsides with three different traffic densities and speed limits; highway, street and a quiet local road. The responses of the exposed seedlings as a host plant and those of spruce shoot aphid (Cinara pilicornis Hartig) were studied. The concentrations of soluble N and free amino acids, defence chemicals (total phenolics, monoterpenes) were analysed, and aphid growth and reproduction were studied. Along the highway, street and at the local road control site, the atmospheric concentrations of black carbon (BC) and oxides of N (NO(x)) were measured for 1 week during the experiment. The BC data indicate deposition of organic particulate compounds along the highway and street. The NO(x) concentrations along the highway and street showed great diurnal variation, but the average NO(x) concentrations were relatively low. Thus, no changes in N metabolism or growth of the exposed Norway spruce seedlings were found. Along the street, the concentrations of many individual free amino acids, such as proline, as well as total amino acid concentrations, were lower than at the associated control site. Correspondingly, there was also no increase in spruce shoot aphid mean relative growth rate. The aphid reproduction, however, increased along the highway and is suggested to be due to more conducive microclimatic conditions at the exposure site or lack of natural enemies. No changes in defence chemicals (total phenolics, monoterpenes) in relation to the traffic exposure were found. Instead, the microclimatic conditions (temperature, solar irradiation) seemed to affect the concentration of total phenolics.     

The effects of SO2 fumigation on the nitrogen metabolism of aseptically grown spruce seedlings

Aseptically grown spruce seedlings were cultivated in a hydroponic system, where the roots were separated from the shoots by a gastight, silicone material. The plants were fumigated with four SO(2) concentrations (93, 190, 270 and 530 microg m(-3)) for nine weeks. Up to 270 microg m(-3) of SO(2), an inhibition of nitrogen metabolism (enzyme activities of nitrate reductase (NR) and glutamine sythetase (GS) and nitrate content) in the shoot was compensated by a stimulation in the root, while nitrogen uptake was unaffected. Only the treatment with 530 microg m(-3) of SO(3) decreased enzyme activities, nitrate content in both roots and shoots as well as nitrate uptake, and inhibited the growth of plants. Increases in the content of thiols and superoxidismutase activity are discussed in terms of SO(2) detoxification.     

The effects of excess nitrogen deposition on young Norway spruce trees. Part I the soil

The effects of wet-deposited nitrogen on soil acidification and the health of Norway spruce were investigated in a pot experiment using an open-air spray/drip system. Nitrogen was applied as ammonium ((NH(4))(2)SO(4)) or nitrate (HNO(3)/NaNO(3)) in simulated rain to either the soil or the foliage for a period of two years five months. Symptoms of forest decline were not reproduced. Adverse effects relating to soil acidification and N saturation were observed and depended on the chemical form of N. The plant-soil system absorbed most of the soil-applied NH(+)(4) at doses of up to 65 kgN ha(-1) year(-1) but only 54% at a dose of 125 kgN ha(-1) year(-1). About 60% of soil-applied NO(-)(3) was absorbed in all treatments. Ammonium treatments acidified the soil, increased base cation leaching, and mobilised acidic cations. Nitrification was not the major source of acidity, however. Nitrate inputs increased soil pH. Critical loads calculated using current criteria were 60-120 and 30-60 kgN ha(-1) year(-1) for ammonium and nitrate, respectively. Ammonium is more likely to damage forest ecosystems, however, illustrating the need for care in the definition of critical loads.     

The effects of excess nitrogen deposition on young Norway spruce trees. Part II the vegetation

The effects of wet-deposited nitrogen on soil acidification and the health of Norway spruce were investigated in a pot experiment using an open-air spray/drip system. Nitrogen was applied as ammonium ((NH(4))(2)SO(4)) or nitrate (HNO(3)/NaNO(3)) in simulated rain to either the soil or the foliage. Symptoms of forest decline as observed in the field were not reproduced, and there was no evidence of direct toxicity. Treatments did, however, have significant effects on tree nutrition. Both NH(+)(4) and NO(-)(3) treatment applied to the foliage lowered foliar K concentrations. NH(+)(4) to a greater extent. Soil-applied NH(+)(4) reduced foliar Mg concentrations and increased foliar Al and Fe. Soil-applied NO(-)(3) significantly reduced foliar P concentrations, and at high doses prevented the alleviation of P deficiency by fertiliser. These effects could be important in some field situations. Ammonium deposition is predicted to be more damaging than nitrate deposition, although the latter may be critical for forests where P status is marginal, such as in parts of the British uplands.     

Long-term exposure to enhanced UV-B radiation has no significant effects on growth or secondary compounds of outdoor-grown Scots pine and Norway spruce seedlings

The effects of long-term enhanced UV-B radiation on growth and secondary compounds of two conifer species were studied in an outdoor experiment. Scots pine (Pinus sylvestris) seedlings were exposed for two growing seasons and Norway spruce (Picea abies) seedlings for three growing seasons to supplemental UV-B radiation, corresponding to a 30% increase in ambient UV-B radiation. The experiment also included appropriate controls for ambient and increased UV-A radiation. Enhanced UV-B did not affect the growth of the conifer seedlings. In addition, neither the concentrations of terpenes and phenolics in the needles nor the concentrations of terpenes in the wood were affected. However, in the UV-A control treatment the concentrations of diterpenes in the wood of Scots pine decreased significantly compared to the ambient control. Apparently, a small increase in UV-B radiation has no significant effects on the secondary compounds and growth of Scots pine and Norway spruce seedlings.     

Simulations of stomatal conductance and ozone uptake to Norway spruce saplings in open-top chambers

A simulation model was developed to estimate the stomatal conductance and ozone flux to Norway spruce saplings in open-top chambers. The model was parameterized against needle conductance measurements that were made on 4-6-year-old spruce saplings, grown in open-top chambers, in July-September during three different seasons. The spruce saplings were either maintained well watered or subject to a 7-8 week drought period in July-September each year. The simulated conductance showed a good agreement with the measured conductance for the well-watered as well as the drought stress-treated saplings. The simulations were significantly improved when different vapour pressure deficit (VPD) functions were applied for well-watered and drought-stressed spruce saplings. The cumulated ozone uptake which was calculated from the conductance simulations showed less variation between years, compared to the cumulative ozone exposure index AOT40 (accumulated exposure over a threshold of 40 ppb or nl l(-1)) for the corresponding time periods. Measurements in May 1995 demonstrated the occurrence of long-term 'memory-effects' from the drought stress treatments on the conductance. Memory-effects need to be considered when simulation models for stomatal conductance are to be applied to long-lived forest trees under a multiple stress situation.     

Nitrate reductase activity of needles of Norway spruce fumigated with different mixtures of ozone, sulfur dioxide, and nitrogen dioxide

Four-year-old spruce clones (Picea abies (L.) Karst.) cultivated in sand and provided with a complete nutrient solution, or a solution deficient in magnesium and calcium, were exposed to the pollutant mixtures SO(2)/NO(2), O(3)/NO(2), and O(3)/SO(2)/NO(2), at realistic concentrations for 32 weeks. Fumigation caused a slight increase of total N contents in current year needles, whereas in one-year-old needles N concentrations did not change. The response of nitrate reductase activity to pollutant stress depended on needle age and nutrient supply, respectively. In one-year-old needles fumigation resulted in a significant inhibition of enzyme activity, particularly in Mg and Ca deficient trees. The combination of all three components proved to be most effective in causing a decrease by 60% compared to the control. In contrast, nitrate reductase activity was stimulated in current year needles, especially by O(3)/NO(2) and O(3)/SO(2)/NO(2). Changes in the activity of nitrate and nitrite reductases are considered as a factor contributing to the high phytotoxic potential of pollutant combinations with NO(2).     

Limited compensation of ozone stress by potassium in Norway spruce

The effects of potassium fertilization and ozone stress were investigated in a clone of Picea abies (L.) Karst, by studies of the uptake of CO(2) by the crowns, the element content, on leaching of the youngest needles, and the longevity of the needles. All plants were exposed to 0.075 microl litre(-1) SO(2) from January to April 1986. The average ozone concentrations applied during the subsequent growing season (May-December) were 0, 0.027, 0.050 and 0.100 microl litre(-1). Half of the trees received liquid fertilizer applications from April to July 1986. CO(2) uptake by the crowns was significantly reduced in non-fertilized plants at ozone doses of 100-200 microl litre(-1) h, whereas similar reductions were recorded in fertilized plants only above an ozone dose of 300 microl litre(-1) h. Independent of the fertilization, however, the concentrations of calcium, magnesium and nitrogen in the needles increased in parallel with the ozone dose, whilst potassium, phosphorus and sulphur showed little response to ozone. In both nutrient regimes, the diffusive loss of elements from chloroform-washed needles was similar and tended to be reduced at the highest ozone concentration, when relating the leachate to the corresponding element content in the needles. Needles formed in the highest ozone treatment were significantly shed during the succeeding year, regardless of the nutrient supply. It appears that increased potassium supply has little compensating effect on ozone stress in spruce.     

Effects of simultaneous ozone exposure and nitrogen loads on carbohydrate concentrations, biomass, and growth of young spruce trees (Picea abies)

Spruce saplings were grown under different nitrogen fertilization regimes in eight chamberless fumigation systems, which were fumigated with either charcoal-filtered (F) or ambient air (O3). After the third growing season trees were harvested for biomass and non-structural carbohydrate analysis. Nitrogen had an overall positive effect on the investigated plant parameters, resulting in increased shoot elongation, biomass production, fine root soluble carbohydrate concentrations, and also slightly increased starch concentrations of stems and roots. Only needle starch concentrations and fine root sugar alcohol concentrations were decreased. Ozone fumigation resulted in needle discolorations and affected most parameters negatively, including decreased shoot elongation and decreased starch concentrations in roots, stems, and needles. In fine roots, however, soluble carbohydrate concentrations remained unaffected or increased by ozone fumigation. The only significant interaction was an antagonistic effect on root starch concentrations, where higher nitrogen levels alleviated the negative impact of ozone.     

The use of light and electron microscopy to assess the impact of ozone on Norway spruce needles

Light (LM) and transmission electron (TEM) microscopy were used to study previously specified ozone symptoms in the foliage of Norway spruce. The three youngest green needle generations from twenty mature trees in two stands on sites of different soil fertility at Asa, southern Sweden, were sampled in 1999. The critical dose of ozone, expressed as AOT40, was 6,362 ppb.h. LM showed ozone-specific symptoms: decreased chloroplast size with electron dense stroma advancing gradually from the outer to the inner cell layers, being most severe in the needle side facing the sky. The symptoms were expressed as ozone syndrome indices at the needle generation, tree and stand levels. The index had higher values at the low fertility site. TEM was used to confirm the LM results. The study shows that LM can be used for diagnosis of the impact of ozone on conifers in the field.     

Regional variation in surface properties of Norway spruce and scots pine needles in relation to forest decline

Measurements of leaf wettability (contact angle), amounts of epicuticular wax and of surface dust are reported for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L) Karst) trees growing at 12 sites in Europe from SW Germany to NE Scotland. At each site, three year classes (current year, 1 and 2-year-old) of needles were sampled from the mid-crown of up to 12 trees. Trees were selected at random from two strata, those showing visible decline symptoms (i.e. loss of needles or discoloration) and those apparently healthy. Needles for analysis were taken from apparently healthy (green) shoots in both cases. There were no significant differences between 'declining' and 'healthy' trees within sites, suggesting that leaf surface properties reflect environmental exposure rather than plant response. There were significant differences between sites, particularly for Norway spruce, which may be related to environmental factors including air pollution. Contact angles were consistently smaller at low-altitude sites in Britain and The Netherlands than at high-altitude sites in Germany where forests show decline symptoms. Leaf wettability decreased (contact angles increased) with wax amount and increased with dust amount. Leaf surface properties integrate environmental influences over long periods, and may be useful in identifying sites 'at risk' of developing decline symptoms, but causal relationships cannot be deduced without further direct experimentation.     

Persistent effects of ozone on needle water loss and wettability in Norway spruce

Four-year-old, seed-grown trees of Norway spruce (Picea abies (L.) Karst.) were exposed in open-top chambers to charcoal-filtered air (8 h daily mean 54 microg O(3) m(-3)) over three consecutive summers (1986-1988). In mid-May 1988, before the third season of fumigation and more than 7 months after exposure to ozone the previous summer had terminated, daily rates of transpiration from intact shoots and water loss from excised needles were measured together with the amount of wax on the needle surface. In mid-July, 92 days after the beginning of the third year of exposure, the wettability of needles was assessed by measuring the contact angle of water droplets on the surface of needles. Exposure to 156 microg O(3) m(-3) resulted in a 16% increase in daily transpiration in current year's needles and a 28% increase in 1-year old needles. These effects were associated with slower stomatal closure in response to increasing water deficit in the needles previously exposed to 156 microg m(-3) ozone. The long-lasting nature of such ozone-induced effects could predispose trees to drought and winter desiccation. No significant effects of ozone were found on the amount of wax covering the needle surface, but a marked increase in the wettability of needles exposed to ozone was observed. The far reaching physiological consequences of these effects in the field and the possibility that similar disturbances may contribute to the decline of high-altitude forests of Norway spruce in Europe are discussed.     

Fluxes of inorganic and organic arsenic species in a Norway spruce forest floor

To identify the role of the forest floor in arsenic (As) biogeochemistry, concentrations and fluxes of inorganic and organic As in throughfall, litterfall and forest floor percolates at different layers were investigated. Nearly 40% of total As(total) input (5.3g Asha(-1)yr(-1)) was retained in Oi layer, whereas As(total) fluxes from Oe and Oa layers exceeded the input by far (10.8 and 20g Asha(-1)yr(-1), respectively). Except dimethylarsinic acid (DMA), fluxes of organic As decreased with depth of forest floor so that <10% of total deposition (all <0.3g Asha(-1)yr(-1)) reached the mineral soil. All forest floor layers are sinks for most organic As. Conversely, Oe and Oa layers are sources of As(total), arsenite, arsenate and DMA. Significant correlations (r>/=0.43) between fluxes of As(total), arsenite, arsenate or DMA and water indicate hydrological conditions and adsorption-desorption as factors influencing their release from the forest floor. The higher net release of arsenite from Oe and Oa and of DMA from Oa layer in the growing than dormant season also suggests microbial influences on the release of arsenite and DMA.     

Response of spinach and kidney bean plants to nitrogen dioxide

Different responses of spinach and kidney bean plants to various concentrations of NO(2) in the light and in the dark were shown. Spinach is more resistant than NO(2) than kidney bean. It is not only due to its greater tolerance to NO(2)(-) accumulated in leaves, but also to its stronger ability to metabolize NO(2)(-). The injury of spinach induced by the exposure to high concentration NO(2) in the light was not caused by the accumulation of NO(2)(-), but concerned the large amount of accumulated NH(3). The primary causes of NH(3) accumulation were that the activity of nitrite reductase was not affected by the fumigation on the one hand, and the activities of glutamine synthetase and glutamate synthase were inhibited on the other.     

Photosynthetic and stomatal conductance responses of Norway spruce and beech to ozone, acid mist and frost--a conceptual model

Two-year-old beech and Norway spruce seedlings were exposed to a combination of ozone and acid mist treatments in open-top chambers in Scotland during the months of July through to September 1988. Replicate pairs of chambers received charcoal-filtered air (control), ozone-enriched air (140 nl ozone litre(-1)) or 140 nl ozone litre(-1) plus a synthetic acid mist (pH 2.5) composed of ammonium nitrate and sulphuric acid. Field measurements of assimilation and stomatal conductance were made during August. In addition, measurements of assimilation and conductance were made during September in the laboratory. Light response curves of assimilation and conductance were determined using a GENSTAT nonrectangular hyperbolic model. During February 1988/9 the Norway spruce were subject to a four day warming period at 12 degrees C and the light response of assimilation determined. The same plants were then subject to a 3-h night-time frost of -10 degrees C. The following day the time-course of the recovery of assimilation was determined. It was found that ozone fumigation did not influence the light response of assimilation of beech trees in the field, although stomatal conductance was reduced in the ozone-fumigated trees. The rate of light-saturated assimilation of Norway spruce was increased by ozone fumigation when measured in the field. Measurements of assimilation of Norway spruce made during the winter showed that prior to rewarming there was no difference in the rate of light-saturated assimilation for control and ozone-fumigated trees. However, the ozone plus acid mist-treated trees exhibited a significantly higher rate. The 4-day period of warming to 12 degrees C increased the rate of light-saturated assimilation in all treatments but only the ozone plus acid mist-treated trees showed a significant increase. Following a 3-h frost to -10 degrees C the control trees exhibited a reduction in the rate of light-saturated assimilation (Amax) to 80% of the pre-frost value. In comparison, following the frost, the ozone-fumigated trees showed an Amax of 74% of the pre-frost value. The ozone plus acid mist-treated trees showed an Amax of 64% of the pre-frost trees. The time taken for Amax to attain 50% of the pre-frost value increased from 30 min (control) to 85 min for ozone-fumigated trees to 190 min (ozone plus acid mist). These results are discussed in relation to the impact of mild, short-term frosts, which are known to occur with greater frequency than extreme, more catastrophic frost events. A simple conceptual framework is proposed to explain the variable results obtained in the literature with respect to the impact of ozone upon tree physiology.     

A cumulative ozone uptake-response relationship for the growth of Norway spruce saplings

Norway spruce saplings [Picea abies (L.) Karst.] were exposed during four growing seasons to different ozone treatments in open-top chambers: charcoal filtered air (CF), non-filtered air (NF) and non-filtered air with extra ozone (NF+, 1.4xambient concentrations). The CF and NF+ ozone treatments were combined with phosphorous deficiency and drought stress treatments. The total biomass of the trees was harvested at different intervals during the experimental period. The ozone uptake to current-year needles of the Norway spruce saplings was estimated using a multiplicative stomatal conductance simulation model. There was a highly significant correlation between the reduction of total biomass and the estimated cumulative ozone uptake, which did not vary when different thresholds were applied for the rate of ozone uptake. The reduction of the total biomass was estimated to 1% per 10 mmol m(-2) cumulated ozone uptake, on a projected needle area basis.