Effects of low-level long-term ozone fumigation and acid mist on photosynthesis and stomata of clonal Norway spruce (Picea abies (L.) Karst.)

Four clones of 3-year-old Norway spruce (Picea abies (L.) Karst.), grown on two soils, were from July 1986 to September 1987 exposed to ozone fumigation (50 microg m(-3) as a control, 100 microg m(-3) plus peaks between 130 and 360 microg m(-3) as treatment) and acid mist of pH 3.0 (versus mist pH 5.6 in the control). Climatic conditions, identical for both control and treatment, followed a diurnal and seasonal pattern characteristic of medium high altitudes of the Bavarian Forest, an area affected by the new-type forest decline. Gas-exchange measurements were carried out on the plants from December 1986 until the end of the 14-month's exposure using a series of climate-controlled minicuvettes. ANOVA of the four clones investigated towards the end of the experiment gave hints of a treatment-related depression of the photosynthetic capacity of the previous year's needles (age-class 1986). Within this age-class only one of the clones (11) showed a significant treatment effect, indicating an age-class dependence and a genetic influence of the treatment-related depression of the photosynthetic capacity. The current year's flush was not impaired through the ozone and acid mist exposure. Analysis also revealed clear effects of soil, clone and needle age on photosynthetic parameters.     

Effects of ozone, acid mist and soil characteristics on clonal Norway spruce (Picea abies (L.) Karst.)--an introduction to the joint 14 month tree exposure experiment in closed chambers

This paper introduces a series of publications referring to a single 14-month laboratory study testing the hypothesis that the recent decline of Norway spruce (Picea abies (L.) Karst.) at higher elevations of the Bavarian Forest and comparable forests in medium-range mountains and in the calcareous Alps is caused by an interaction of elevated ozone concentrations, acid mist and site-specific soil (nutritional) characteristics. The effect of climatic extremes, a further important factor, was not included as an experimental variable but was considered by testing of the frost resistance of the experimental plants. Results of these individual studies are presented and discussed in the following 14 papers. Plants from six pre-selected clones of 3-year-old Norway spruce (Picea abies (L.) Karst.) were planted in April 1985 in an acidic soil from the Bavarian Forest, or a calcareous soil from the Bavarian Alps. After a transition period, plants were transferred, in July 1986, into four large environmental chambers and exposed for 14 months to an artificial climate and air pollutant regime based on long-term monitoring in the Inner Bavarian Forest. The climatic exposure protocol followed realistic seasonal and diurnal cycles (summer maximum temperature, 26 degrees C; total mean temperature, 9.8 degrees C; winter minimum, -14 degrees C; mean relative humidity, 70%; maximum irradiance, 500 W m(-2); daylength summer maximum, 17 h; winter minimum, 8 h). Plants were fumigated with ozone, generated from pure oxygen (control: annual mean of 50 microg m(-3); pollution treatment: annual mean of 100 microg m(-3) with 68 episodes of 130-360 microg m(-3) lasting 4-24 h), and background concentrations of SO(2) (22 microg m(-3)) and NO(2) (20 microg m(-3)); windspeed was set at a constant 0.6 m s(-1). Plants were additionally exposed to prolonged episodes of misting at pH 5.6 (control) and pH 3.0 (treatment). Simulation of the target climatic and fumigation conditions was highly reliable and reproducible (temperature +/-0.5 degrees C; rh+/-10%; ozone+/-10 microg m(-3);SO(2) and NO(2)+/-15 microg m(-3)).     

Biochemical response of Norway spruce (Picea abies (L.) Karst.) towards 14-month exposure to ozone and acid mist: effects on amino acid, glutathione and polyamine titers

Two clones of Norway spruce were exposed to elevated ozone levels (100 microg m(-3) with episodes of 130-360 microg m(-3)) in combination with acidic mist (pH 3.0) for two vegetation periods. The plants did not exhibit any visible injury, but levels of several amino acids and polyamines were altered in comparison with control plants (50 microg m(-3) ozone, mist of pH 5.6), the changes being pronounced in clone 14. Total free amino acids as well as methionine titers were increased in clone 14. Asparagine was significantly increased in clone 11 and less so in clone 14. Arginine, which comprised more than 50% of the free amino acids in spruce needles, was not changed by the exposure regime applied. Reduced glutathione was significantly increased in all clones/soil/needle age combinations (average increase 50%). Free soluble putrescine was enhanced by 50-200% in clone 14, but remained unchanged in clone 11. Conjugated putrescine was significantly, and conjugated spermidime was slightly, increased in both clones, whereas other polyamines did not responde to the treatment.     

Influence of soil substrate and ozone plus acid mist on the frost resistance of young Norway spruce

The needles of clonal Norway spruce grown in environmental chambers on two different soils (an acidic soil 1 and a calcareous soil 2) and exposed to two levels of ozone fumigation (a low level combined with neutral mist = control, and an elevated one combined with acid mist = treatment) were analyzed for their frost hardiness. No effect of ozone was observed on either the development of frost resistance during the hardening phase or on the decrease in frost resistance during the dehardening phase. The preliminary results of Brown et al. (1987) and Barnes and Davidson (1988), which indicated that ozone treatment predisposes plants to winter injury, could thus not be confirmed. Frost resistance was, however, distinctly influenced by the content of the mineral nutrients of the soils. The pronounced K(+) deficiency of the needles of the trees growing on the neutral soil (Alps) had less effect on the development of frost resistance than did the Ca(++) and Mg(++) deficiency of the needles of the trees grown on the acidic soil 1 (Bavarian Forest). The variability of frost resistance between the different clones on soil 1 was partly attributed to fluctuations in the mineral nutrient content of the needles, rather than to a genetic predisposition.     

Impact of ozone, acid mist and soil characteristics on growth and development of fine roots and ectomycorrhiza of young clonal Norway spruce

As part of the joint 14-month exposure experiment on Norway spruce (Picea abies (L.) Karst.) sensitivity to pollution (two levels of ozone plus acid mist) of growth and development of the fine-root system and of mycorrhizae, have been investigated in two forest soils from areas showing forest decline. This study shows that differences in fine-root biomass and the occurrence of species of ectomycorrhizae were mainly due to prevailing conditions within the acid or calcareous substrate. The pollution treatment resulted in higher numbers of short root tips in only one soil, whereas the percentage of ectomycorrhizal roots with a well-developed mantle was low (10-23%) in both soils, irrespective of exposure of trees to ozone and acid mist. There was no consistent response, with the two clones examined, in terms of mycorrhizal frequency, beaded short roots and renewed growth. Regarding the effects on root growth, data cannot be used unrestrictedly for extrapolation to a more complex field situation.     

Mineral and nutrient supply, content and leaching in Norway spruce exposed for 14 months to ozone and acid mist

The nutrient contents of an acid and a calcareous soil, as well as the foliar contents of four clones of Norway spruce grown on these soils, were evaluated during a 14-month exposure to low level ozone (100 microg m(-3) + peaks between 130 and 360 microg m(-3)) plus acid mist (pH 3.0). Whilst distinct differences could be established between and within clones depending on soil types and genotype, only few pollutant-related effects were observed. Leaching losses from foliage were generally low compared to field studies. The data obtained with young trees in an artificial environment do not support the hypothesis that enhanced leaching from foliage may contribute to nutrient deficiencies in mature stands of Norway spruce.     

Effects of acid mist on mature grafts of Sitka spruce. Part I. Frost hardiness and foliar nutrient concentrations

Mature grafts of five clones of Sitka spruce (Picea sitchensis Bong. Sarg.) were exposed to simulated acid mist composed of an equimolar mixture of sulphuric acid and ammonium nitrate at pH 2.5 and pH 5.0 in open-top chambers from May to November 1991. Treatments were applied on consecutive days, four times a week. The pH 2.5 treatment provided an overall dose three times higher than that received by forests in upland areas of Britain. Frost hardiness was assessed in November by freezing detached current year shoots at a range of temperatures and assessing the rate of electrolyte leakage Foliar nutrient concentrations were determined on the same shoots. Acid mist at pH 2.5 significantly reduced frost hardiness in four of the five clones; the temperature causing 50% shoot death (LT50) was increased by 0 to 7 degrees C. The clones varied in their level of hardiness, one clone being exceptionally frost sensitive. The frost hardiness of the frost sensitive clone was found to be less perturbed by acid mist than the hardiness of the more frost resistant clones. Mature grafts showed a smaller reduction in hardiness at an equivalent dose than that found previously with Sitka spruce seedlings. Compared with seedlings, grafts had lower absolute concentrations of foliar sulphur. Exposure to acid mist at pH 2.5 increased %S in current year foliage by <0.05% compared with absolute increases of more than 0.10% in current year foliage of seedlings. We conclude that the effect of acid mist on frost hardiness is likely to be less on mature trees than on seedlings and that the increased frost risk to mature trees of Sitka spruce from occult deposition alone is small.     

Effects of ozone, acid mist and soil characteristics on clonal Norway spruce (Picea abies (L.) Karst.)--overall results and conclusions of the joint 14 month tree exposure experiment in closed chambers

This paper summarizes and evaluates the main findings of 14 preceding papers related to the joint 14-month tree-exposure experiment carried out by the 'Munich Working Party on Air Pollution' at the GSF, Munich, FRG, from July 1986 to September 1987. The experiment tested the hypothesis that an interaction of ozone/acid mist/soil/extreme climatic conditions is the cause of decline of Norway spruce (Picea abies (L.) Karst.) at higher altitudes of the Inner Bavarian Forest. The main findings of the individual studies are presented and their implications for the hypothesis are discussed. Clear effects of soil and genetic factors (differences between clones), for example on growth and frost resistance were found. Treatment with O(3)/acid mist was shown to have effects on plant biochemistry, physiology, histology/ cytology, and growth. The wide scattering of these effects, and the lack of a consistent pattern of response across all clones does not permits a firm conclusion on the validity of the experimental hypothesis. These effects were not confounded by the nutrient stresses imposed during the initial exposure period and were not found to be cumulative during repeated treatments, as was proposed by the hypothesis. It is concluded that the experimental evidence does not indicate that ozone/acid mist are major factors to explain the Norway spruce decline on acidic sites at higher altitudes of the Inner Bavarian Forest and probably similar forest areas.     

Cytological observations on spruce needles after prolonged treatment with ozone and acid mist

Light and electron microscopic studies of four clones of 5-year-old Picea abies trees subjected to ozone and acid mist treatment showed, that: (1) Clones respond differently to the treatment, with clone 14 the most sensitive clone. (2) Main effects were observed in the mesophyll; the vascular strand showed minor cellular changes. (3) Needle shape and ratio of intercellular area to cross section was clone- age-dependent, with a clear increase in intercellular space associated with the treatment (clone 14 and 11 only). (4) Accumulation of tannins in vacuoles was clone-specific. (5) Strong starch formation was found in all samples; in clones 14 and 133 this formation was enhanced by the treatment in older needles, if number of starch grains per cell was calculated. (6) The accumulation of plastoglobules in plastids depended on clone and age, with the older needles containing more globules. In clones 11 and 133, the treatment led to an increase in the number of plastoglobules. (7) Grana stacking in all clones and both needle ages subjected to ozone and acid mist was significantly reduced. The observed changes in the ultrastructure of needle tissue are comparable to those found in field investigations with similar conditions, or phytotron studies evaluating pollution effects on spruce trees.     

Influence of soil substrate and ozone plus acid mist on the pigment content and composition of needles from young Norway spruce trees

The influence of an ozone + acid mist treatment on photosynthetic pigments has been examined with the needles of the (Picea abies) clones 11, 14, 16, and 133 by spectrophotometric analysis of the total pigment extract and of single components upon HPLC separation (Part A), and in terms of a detailed pigment analysis of the 1987 and 1986 needles of clone 14 by TLC (Part B). Clone 14 had been already analysed prior to the onset of the experiment. At the end of the 14-month experiment, which incorporated frost events during a simulated winter period, neither symptoms corresponding to those of spruce Type I or IV decline, nor those of ozone damage could be observed. However, the 1986 needles of the trees on soil 1, which exhibit an adequate nutrient content, showed zonal chlorosis independently of the ozone + acid mist treatment. Analysis of variance of chlorophyll contents and needle ages showed a clear reduction to nearly 50% in the 1986 needles of clone 11, soil 1, and clone 16, soil 2. In contrast, clones 14 and 16 (soil 1) formed significantly more chlorophylls during the shorter exposure time in the 1987 flush. The detailed analysis of the individual pigment components of clone 14 needles provided no evidence for a destructive influence of the treatment on the chlorophylls, xanthophylls and beta-carotene in the two needle generations which had developed during the experiment, in spite of the distinct K deficiency of the 1986 needles of the trees on soil 2 and the common chlorosis of the needles of the trees on soil 1. The observed increase in violaxanthin content upon O(3)-treatment observed in clone 14 can be considered as an expression of the protective function of the xanthophylls against photooxidative processes. In conclusion, the observed differences in the chlorophyll and carotenoid contents are better correlated with the individual clone and soil character than with the ozone + acid mist treatment. Comparing the results of the pigment analyses of the needles the differences in the pigment concentrations reflect the N and K contents (Pfirrmann et al., 1990), which differ significantly between the clones. Thus it is not possible to pool the pigment data of all clones without considering the different nutrient levels.     

Biochemical response of Norway spruce (Picea abies (L.) Karst.) towards 14-month exposure to ozone and acid mist: part I--Effects on polyphenol and monoterpene metabolism

Three-year-old clonal Picea abies (L.) Karst. plants, grown either on a sandy (No. 1) or on a calcareous (No. 2) soil, were treated with ozone (100 microg m(-3) and peaks of up to 360 microg m(-3)) and acid mist (pH 3.0) over two vegetation periods. Needles of the current (1987) and previous (1986) year were analysed at the end of the experiment for biosynthetic enzymes and in vivo activity of the phenylpropanoid pathway, for products of polyphenol metabolism (clones 11 and 14), and for mono- and sesquiterpenes (clones 14 and 16). 1. Polyphenol metabolism. The activity of cinnamyl alcohol dehydrogenase, an enzyme of the lignin pathway, was increased by the treatment by up to 83% in the needles of both age classes. Chalcone synthase was measured in mature tree material for the first time. This enzyme, as well as phenylalanine ammonia-lyase activities and the content of catechin, astringin, isorhapontin, picein and p-hydroxyacetophenone, exhibited no significant treatment-dependent differences. However, soil and age-class dependent differences occurred. Pulse-labelling experiments with l[U-(14)C]phenylalanine and [2-(14)C]acetate were carried out at four different stages of shoot development and showed label incorporation into (+)-catechin and proanthocyanidins. There was no effect of the ozone and acid mist treatment. 2. Monoterpenes. The content of needle terpenes was generally diminished by the ozone and acid mist treatment. Other factors tested, such as clone, needle age and soil, exerted a highly significant influence on the content of most of the needle monoterpenes.     

Effects of acid mist on needles from mature Sitka spruce grafts. Part II. Influence of developmental stage, age and needle morphology on visible damage

Mature grafts of five Sitka spruce (Picea sitchensis (Bong.) Carr.) clones were exposed to simulated acid mist comprising an equimolar mixture of H(2)SO(4) and NH(4)NO(3) (1.6 and 0.01 mol m(-3)) at pH 2.5 and 5.0. Mist was applied to potted plants growing in open-top chambers on consecutive days, four times a week, at a precipitation equivalent of 1 mm per day. The total exposure to polluted mist was equivalent to three times that measured at an upland forest in SE Scotland. The aim of the experiment was to characterize the response of juvenile foliage produced by physiologically mature grafts (on seedling root stock) and compare it with the behaviour of juvenile foliage on seedlings. Development of visible foliar damage was followed through the growing season. Measurements of needle length, diameter, weight, surface area, surface was weight and wettability were made on current year needles to determine whether particular foliar characteristics increased susceptibility to injury. Significant amounts (> 10%) of visible needle damage was observed on only one of the five clones. Damage was most severe on the clone with the most horizontal branch and needle habit, but over the five clones there was no relationship between angle of branch display and damage. Likewise no combination of needle characteristics (length, width, area, amount of wax) was indicative of potential susceptibility. A comparison with previous acid misting experiments using seedlings suggests that juvenile foliage on physiologically mature trees is equally susceptible to visible injury as juvenile seedling foliage. Data of budburst differed among clones, and in this experiment exerted the over-riding influence on development of injury symptoms. Foliage exposed to a combination of strong acidity and high sulphate concentrations over the few weeks immediately following budburst suffered most visible injury. The absence of significant amounts of visible damage in UK forests probably reflects the general low susceptibility to visible injury of Sitka spruce exposed to acid mist.     

Response of sugar maple to multiple year exposures to ozone and simulated acidic precipitation

Potted sugar maple seedlings were exposed to ozone and acidic precipitation in open-top chambers for three consecutive growing seasons. Periodic measurements of photosynthesis, dark respiration, through-fall and soil solution chemistry, and annual measurements of the weight of plant parts were made. Experimental treatments caused few and minor effects on above- or below-ground growth of the seedlings, even after three growing seasons. There were trends for reduced photosynthesis in trees exposed to elevated concentrations of ozone and increased photosynthesis in those exposed to the lowest pH simulated rain treatment. The chemistries of soil-solutions and through-fall were not altered significantly by treatment. Although major effects were not observed, sugar maple may respond to exposures that take place over a significant part of its life cycle.     

Direct damage to vegetation caused by acid rain and polluted cloud: definition of critical levels for forest trees

The concept of critical levels was developed in order to define short-term and long-term average concentrations of gaseous pollutants above which plants may be damaged. Although the usual way in which pollutants in precipitation (wet deposition) influence vegetation is by affecting soil processes, plant foliage exposed to fog and cloud, which often contain much greater concentrations of pollutant ions than rain, may be damaged directly. The idea of a critical level has been extended to define concentrations of pollutants in wet deposition above which direct damage to plants is likely. Concentrations of acidity and sulphate measured in mountain and coastal cloud are summarised. Vegetation at risk of injury is identified as montane forest growing close to the cloud base, where ion concentrations are highest. The direct effects of acidic precipitation on trees are reviewed, based on experimental exposure of plants to simulated acidic rain, fog or mist. Although most experiments have reported results in terms of pH (H(+) concentration), the accompanying anion is important, with sulphate being more damaging than nitrate. Both conifers and broadleaved tree seedlings showing subtle changes in the structural characteristics of leaf surfaces after exposure to mist or rain at or about pH 3.5, or sulphate concentration of 150 micromol litre(-1). Visible lesions on leaf surfaces occur at around pH 3 (500 micromol litre(-1) sulphate), broadleaved species tending to be more sensitive than conifers. Effects on photosynthesis and water relations, and interactions with other stresses (e.g. frost), have usually been observed only for treatments which have also caused visible injury to the leaf surface. Few experiments on the direct effects of polluted cloud have been conducted under field conditions with mature trees, which unlike seedlings in controlled conditions, may suffer a growth reduction in the absence of visible injury. Although leaching of cations (Ca(2+), Mg(2+), K(+)) is stimulated by acidic precipitation, amounts leached are small compared with root uptake, unless soils have been impoverished. This aspect of the potential effects of acidic precipitation is best considered in terms of the long-term critical-load of pollutants to the soil. Given the practical difficulties in monitoring cloud water composition, a method for defining critical levels is proposed, which uses climatological average data to identify the duration and frequency of hill cloud, and combines this information with measured or modelled concentrations of particulate sulphate in the atmosphere, to derive cloud water concentrations as a function of cloud liquid water content. For forests within 100 m of the cloud base the critical levels of particulate sulphate, corresponding to solution concentrations in the range 150-500 micromol litre(-1), are in the range 1-3.3 microg S m(-3). These concentrations are observed over much of central Europe, suggesting that many montane forests are at risk of direct effects of fossil-fuel-derived pollutants in cloud.     

Variation in ozone sensitivity among clones of Betula pendula and Betula pubescens

Forty clones of Betula pendula and 6 clones of Betula pubescens, originating from southern and central Finland, were ranked in order of ozone sensitivity according to visible injuries, growth and leaf senescense under low ozone exposure. The plants were fumigated in natural climatic conditions using an open-air exposure system during two growing seasons. Control plants were grown under ambient air, and the elevated-ozone exposures were 1.6x the ambient in 1994 and 1.7x the ambient in 1995. The differences in ozone sensitivity among clones were large. Ozone tolerance was related to thicker leaves and higher stomatal density as compared to sensitive clones. Ultrastructural ozone-induced symptoms were found in chloroplasts of sensitive clones. Increased number of visibly injured leaves on fumigated plants was correlated with reduced leaf formation, foliage area, shoot dry wt and number of stomata, and increased yellowing of leaves. The results suggest that a considerable proportion of birch trees, showing high sensitivity to ozone, are at risk if ambient ozone exposures increase.     

No general effect of ozone on foliar nutrient concentrations in mature scions of grafted Picea abies trees

The effect of ozone (< 10, 200, or 400 microg m(-3)), on foliar nutrient concentrations of Picea abies were determined by fumigating potted grafts from mature trees (> 55 and 125 years), representing six clones, in open-top chambers at two locations in Norway. The concentration of nutrients in needles of grafted plants were significantly affected by clone and location. Generally, the concentrations of nutrients were not affected by ozone, but a significant increase in the concentrations of potassium and iron in two of the clones were found. These two clones were the only ones injured (yellow needles) by the fumigation.     

Simulated Effects of Acidic Solutions on Element Dynamics in Monsoon Evergreen Broad-leaved Forest at Dinghushan,China - Part 1: Dynamics of K,Na, Ca,Mg and P (7 pp)

Background, Aim and Scope Acid deposition has become a concern in south China in recent years. This phenomenon has increased to a dramatic extent with the large use of cars and coal- fueled power plants. As a consequence, soils are becoming acidified and their element dynamics will change. A decrease in the nutrient availability will lead to slower plant growth and maybe to a change in the forest type with current species being replaced by new ones with less nutrient requirements. Because of these reasons, it is important to understand how the dynamics of elements will change and what mechanism is part of the process. This knowledge is important for modeling the acidification process and either finding ways to counter it or to predict its consequences. The primary purpose of this study was to provide information about how the dynamics of K, Na, Ca, Mg and P are affected by acid deposition in a typical forest in southern China. Materials and Methods: Experimental soils and saplings were collected directly from the monsoon evergreen broad-leaved forest in Dinghushan. All saplings were transplanted individually into ceramic pots in August 2000 and placed in an open area near their origin site. Pot soils were treated weekly from October, 2000 to July, 2002 with an acidic solution at pH 3.05, pH 3.52, pH 4.00 or pH 4.40, or with tap water as a control. The concentrations of SO42-, NO3-, K+, Na+, Ca2+, Mg2+ and available P and the pH were measured in soil and leachate samples taken at different times. The sapling leaves were collected and their element concentrations were measured at the end of the experiment. Results: Concentrations of soil exchangeable Ca and Mg decreased quickly over time, although only Ca showed changes with the acidic solution treatment and soil exchangeable K was stable because of soil weathering. Leaching of K, Mg and Ca was dependent upon the treatment acidity. Soil available P decreased slowly without any correlation with the acidity of the treatment. All the NO3- added by the treatment was taken up by the plants, but the SO42- added accumulated in the soil. Discussion: Amongst the plant species, Schima superba was little affected by the treatment, the leaf P content was affected in Acmena acuminatissima plants and Cryptocarya concinna was the most susceptible species to soil acidification, with a marked decrease of the leaf K, Ca and Mg concentrations when the treatment acidity increased. Conclusions: Simulated acid deposition affected the dynamics of K, Ca and Mg in the monsoon evergreen broad-leaved forest. The dynamics of Ca in the soil and of K, Mg and Ca in the soil leachates were affected by the acidic solution treatment. If such a soil acidification occurs, Cryptocarya concinna will be amongst the first affected species, but Schima superba will be able to sustain a good growth and mineral nutrition. Recommendations and Perspectives: Acid deposition will lead to imbalance the nutrient elements in the evergreen broad-leaved forest because of accelerated leaching losses of soil exchangeable Ca and Mg. Measures should be developed to slow down soil acidification or nutrient decrease.     

Stem growth reduction in mature Sitka spruce trees exposed to acid mist

An eighteen-year-old clone of Sitka spruce (Picea sitchensis (Bong.) Carr) growing in the field was used to evaluate the whole tree response of 'mature' Sitka spruce to acid mist treatment. The mist, an equimolar mixture of H(2)SO(4) and NH(4)NO(3) at pH 2.5 with or without particles (soda glass ballotini < 20 microm diameter), was applied twice weekly (equivalent to 4 mm precipitation week(-1)) throughout the growing season, May-November 1990-1992. The annual dose of S, N, H applied as mist (at 51, 48 and 3.3 kg ha(-1), respectively) was 2.5 times that measured in the Scottish uplands. Throughout the experiment there was no evidence of visible injury symptoms, yet there was a highly significant reduction (p < 0.02) in the stem-area increment relative to the stem area at the start, measured using vernier dendrometer bands. There was no significant difference between the (acid mist + particle) and the acid mist only treatments. The mean relative stem-area increment over two complete growing seasons (1991-1992) was 65% for control trees, but only 53% for acid-misted trees.     

Acid mist and ozone effects on the leaf chemistry of two western conifer species

Seedlings of Jeffrey pine (Pinus jeffreyi) and giant sequoia (Sequoiadendron gigantea) were more susceptible to leaf chemical changes following exposure to acid mist (pH 3.4-2.0) or acid mist/ozone combinations, than to ozone alone (0.1-0.2 microl/litre), when plants were exposed to alternating doses of these pollutants for 6-9 weeks. Under acid mist treatment, leaves exhibited higher levels of nitrogen and sulfur, two elements applied in acid mist. In addition, levels of foliar sodium, and, in the case of giant sequia, potassium, as well, increased under acid mist treatment. Iron and manganese were also mobilized, resulting in significant increases in these elements in pine, and decreases in manganese in giant sequoia foliage. The acid treatment also reduced chlorophyll b concentrations in pine, and, to a less significant extent, in giant sequoia. Calcium, magnesium, barium and strontium were differentially accumulated in giant sequoia compared to Jeffrey pine. Under acid mist treatment, all of these elements (except strontium) declined in concentration in giant sequoia, with calcium showing the most significant trend. The more extensive changes in leaf chemistry induced by acid mist are consistent with earlier observations of significant changes in spectral reflectance of these seedlings after 3 weeks of fumigation. Limited foliage samples collected from these two species in 1985 and 1986 in Sequoia/Kings Canyon National Parks in the southern Sierra Nevada do not in themselves indicate any clearcut or severe effects of ozone alone on leaf chemistry of these species, but a mild influence of nitrate-laden acid deposition, possibly in combination with ozone, is consistent with the rise in nitrogen and lignin levels in Jeffrey pine on sites observed to have moderate visible injury symptoms. No firm conclusions about effects of pollutants on leaf chemistry in these field sites is possible without further study.     

Ozone-induced nitrate formation in needles and leaves of Picea abies, Fagus sylvatica and Quercus robur

Much attention has been paid to ozone as a major cause of novel forest decline in Europe. In combination with acidic mist, O(3) has been observed to increase ion leaching. Besides cations lake Mg(2+), Ca(2+), K(+), NH(4)(+), considerable amounts of nitrate were found to be leached by acidic mist from needles of Norway spruce. Controlled fumigation experiments, with 100, 300, and 600 microg O(3)m(-3) over 22 days continuously, have led to a nitrate accumulation of 94.1 +/- 14.8, 119.4 +/- 28.7 and 198.9 +/- 14.9 microg NO(3)(-1) g(-1) FW, respectively, in leaves of Quercus robur. Similar values were found in leaves of Fagus sylvatica and current and previous year needles of Picea abies. Nitrate levels of controls receiving charcoal filtered air were well below 40 microg NO(3)(-) g (-1) FW. Statistically significant elevated nitrate levels were observed after only 48 h of continuous fumigation with 600 microg O(3)m(-3), in all tree species tested, and after 144 h in the 100 microg O(3)m(-3) treatment. In another experiment, trees of Picea abies were kept in two charcoal (C) and two Purafil plus charcoal (P/C) ventilated chambers, and fumigated with O and 500 microg O(3)m(-3) in cabinets of each filter-type in order to eliminate NO(x) from chamber air. After 29 days of continuous ozone fumigation, NO(3)(-) accumulation in needles amounted to 102.0 +/- 37.7 and 137.4 +/- 40.5 microg g(-1) FW in P/C and C-filtered chambers, respectively. Nitrate contents of controls were below 30 microg NO(3)(-)g(-1) FW at the end of the experiment. No significant differences in NO(3)(-) accumulation between filter treatments were observed. Since NO(x) was reduced by more than 95% in the Purafil/charcoal versus the charcoal treatment, NO(3)(-) accumulation in needles can be attributed predominantly to the influence of ozone and not to direct NO(2) uptake of needles by the possible oxidation of NO to NO(2) in the presence of ozone.