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.     

Clone and soil effects on the growth of young Norway spruce during 14 months exposure to ozone plus acid mist

Five clones of 3-year old Norway spruce (Picea abies [L.] Karst), planted in a soil from the Bavarian Forest (pH 4.4) or a soil from the Calcareous Bavarian Alps (pH 6.9), were exposed for two successive vegetation periods, in closed environmental chambers, to a pollution treatment consisting of acidic mist (pH 3.0) plus ozone levels of 100 microg m(-3) with episodes of 130-360 microg m(-3); control trees were exposed to mist of pH 5.6 and ozone levels of 50 microg m(-3). Climatic and pollution protocols followed the diurnal and seasonal pattern characteristic for the Inner Bavarian Forest in Southern Germany, an area affected by the new-type forest decline. Biometric parameters were strongly related to clone and soil. Pollution treatment had a limited effect on only a few growth parameters. The stem diameter growth increment of two clones was reduced by pollution treatment in both soils, a third clone was affected in the acidic soil only. Two other clones were not affected at all. Stem volume increment of three clones, calculated as D(2)H, was reduced by pollution treatment in the neutral soil, a fourth clone was affected in the acidic soil only. Bud break was either delayed (two clones) or accelerated (two other clones) by treatment. Depending on soil and clone, needle yellowing was observed in previous years' needles in both treatment and control trees exposed to increased light intensities. The 'spotted' yellowing was not identical to symptoms found in forest decline areas and was most likely a consequence of nutrient deficiencies during the vegetation period preceding the experiment. The results of this experiment are discussed with regard to field observations and forest productivity. The complex pattern of growth responses resulting from interactions between air pollution, soil and genetic factors is considered to reflect different susceptibilities of trees to air pollutants.     

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.     

No general ozone-specific indicator among the hexane- and dichloromethane-soluble components of Picea abies needles exposed to ozone in open-top chambers

The effect of ozone (< 10, 200 or 400 microg m(-3) on hexane- and dichloromethane-soluble components of Picea abies needles was determined by fumigating potted grafts from mature trees. The trees (>55 and 125 years, 2.5 m high), representing six clones of Norway spruce, were fumigated in open-top chambers at two locations in Norway for one growth season. The needles were extracted with hexane and dichloromethane; 142 compounds from the hexane extract and 164 silylated compounds from the dichloromethane extract were analysed by gas chromatography although no identifications were made. The concentration of four of the compounds from the hexane extract changed with ozone dose in a way that made them promising as indicators, but the present analytical method could not verify this possibility. None of the other 302 compounds qualified as a general indicator of ozone stress in Norway spruce, as none changed its concentration with ozone dose consistently in all romets of all clones. Most of the variation in the experiment is mainly attributable to genetic variation and to climate.     

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.     

Effects of acid rain on growth and nutrient concentrations in Scots pine and Norway spruce seedlings grown in a nutrient-rich soil

The effects of artificially applied acid precipitation on growth and nutrient concentrations of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies [L.] Karst.) seedlings were investigated in a long-term acid irrigation experiment in field conditions. Seedlings of northern and southern origin were planted in boxes containing peat and composted soil rich in nutrients, and sprinkler irrigated with water acidified with nitric and sulphuric acids to pH 3 or pH 4 for periods varying from two to three and a half growing seasons during 1986-1989. Water irrigated (pH 5.4-7.6) and non-irrigated groups of seedlings were also included in the experiment. At the end of the experiment needles, main and lateral shoots and roots were collected from the seedlings for the determination of height growth and biomass partitioning, and for the analysis of S, N, Mg, P, K, Ca, Mn and Fe concentrations. The treatment effects compared to the irrigated control were studied using multivariate analyses of variance and covariance. In the pine seedlings the total dry matter production increased by 25-70% compared with the irrigated controls when the total wet deposition to the seedlings exceeded 67 kg S ha(-1) and 36 kg N ha(-1) (e.g. after two growing seasons' exposure of the pH 3 treatment). The increase was mainly due to an increase in needle dry weight (54-72% greater at pH 3) and root weight (20-65% greater at pH 3), whereas the height growth or shoot weight growth were less affected. The northern provenance pine seedlings responded more clearly to the pH 3 irrigation than the southern ones. The treatments had no consistent effects on any of the growth variables studied in the spruce seedlings, however. The pines had higher root and foliage Ca concentrations as a result of the acid irrigation, whereas in spruce, acid rain decreased the Ca concentration in needles and shoots. Root Mn and Fe concentrations were higher in both species as a result of the pH 3 treatment. A higher soil conductivity and Ca concentration resulted from the prolonged pH 3 treatment. The results strongly support the hypothesis that the long-term growth and nutrient allocation response of conifers to acid precipitation is dependent both on the tree species and on the nutritional status of the soil.     

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.     

Air pollution, precipitation chemistry and forest health in the Retezat Mountains, Southern Carpathians, Romania

In the Retezat Mountains concentrations of O3, NO2 and SO2 in summer season 2000-2002 were low and below toxicity levels for forest trees. While NH3 concentrations were low in 2000, the 2001 and 2002 concentrations were elevated indicating possibility for increased N deposition to forest stands. More than 90% of the rain events were acidic with pH values <5.5, contributing to increased acidity of soils. Crown condition of Norway spruce (Picea abies) and European beech (Fagus sylvatica) was good, however, defoliation described as >25% of foliage injured increased from 9.1% in 2000 to 16.1% in 2002. Drought that occurred in the southern Carpathians between fall 2000 and summer 2002 and frequent acidic rainfalls could cause the observed decline of forest condition. Both Norway spruce and European beech with higher defoliation had lower annual radial increments compared to the trees with low defoliation. Ambient O3 levels found in the Retezat did not affect crown condition of Norway spruce or European beech.     

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.     

Trichloroacetic acid cycling in Sitka spruce saplings and effects on sapling health following long term exposure

Trichloroacetic acid (TCA, CCl(3)COOH) has been associated with forest damage but the source of TCA to trees is poorly characterised. To investigate the routes and effects of TCA uptake in conifers, 120 Sitka spruce (Picea sitchensis (Bong.) Carr) saplings were exposed to control, 10 or 100 microg l(-1) solutions of TCA applied twice weekly to foliage only or soil only over two consecutive 5-month growing seasons. At the end of each growing season similar elevated TCA concentrations (approximate range 200-300 ng g(-1) dwt) were detected in both foliage and soil-dosed saplings exposed to 100 microg l(-1) TCA solutions showing that TCA uptake can occur from both exposure routes. Higher TCA concentrations in branchwood of foliage-dosed saplings suggest that atmospheric TCA in solution is taken up indirectly into conifer needles via branch and stemwood. TCA concentrations in needles declined slowly by only 25-30% over 6 months of winter without dosing. No effect of TCA exposure on sapling growth was measured during the experiment. However at the end of the first growing season needles of saplings exposed to 10 or 100 microg l(-1) foliage-applied TCA showed significantly more visible damage, higher activities of some detoxifying enzymes, lower protein contents and poorer water control than needles of saplings dosed with the same TCA concentrations to the soil. At the end of each growing season the combined TCA storage in needles, stemwood, branchwood and soil of each sapling was <6% of TCA applied. Even with an estimated half-life of tens of days for within-sapling elimination of TCA during the growing season, this indicates that TCA is eliminated rapidly before uptake or accumulates in another compartment. Although TCA stored in sapling needles accounted for only a small proportion of TCA stored in the sapling/soil system it appears to significantly affect some measures of sapling health.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Factors influencing 2,4-D sorption and mineralization in soil

This study quantified 2,4-D [(2,4-dichlorophenoxy)acetic acid] sorption and mineralization rates in five soils as influenced by soil characteristics and nutrient contents. Results indicated that 2.4-D was weakly sorbed by soil, with Freundlich distribution coefficients ranging from 0.81 to 2.89 microg(1 - 1/n) g(-1) mL(1/n). First-order mineralization rate constants varied from 0.03 to 0.26, corresponding to calculated mineralization half-lives of 3 and 22 days, respectively. Herbicide sorption generally increased with increasing soil organic carbon content, but the extent of 2,4-D sorption per unit organic carbon varied among the soils due to differences in soil pH, clay content and/or organic matter quality. Herbicide mineralization rates were greater in soils that sorbed more 2,4-D per unit organic carbon, and that had greater soil nitrogen contents. We conclude that the effect of sorption on herbicide degradation cannot be generalized without a better understanding of the effects of soil characteristics and nutrient content on herbicide behavior in soil.