Rasterelektronenmikroskopische Untersuchungen an Stomata von Fichten- und Tannennadeln nach Begasung und saurer Beregnung1

Scanning electron microscopical investigations on stomatal wax plugs of fir and spruce needles after fumigation and acid rain treatment Alterations of stomatal wax plugs of fir and spruce needles have been investigated in order to demonstrate the effects of different air pollutants. After acid rain treatment, and in addition to SO₂ fumigation, heavily melted wax crystals were observed. It is assumed that acid rain causes mainly the changes of the stomatal wax plugs.     

Environmental Effects on Norway Spruce Needle Wax

In spring, tubular wax structures were observed on the needle surfaces of new Norway spruce needles and also on previous-year needles. In young plants, as in mature trees, the fusing and eroding of the wax tubes on needles of increasing age had taken place in relation to their exposure, particularly to wind and precipitation. The quantity of needle wax and certain fractions of the extracted wax differed in mature trees at two field sites and in young clonal plants. No difference in wax quantity and only small differences in wax composition occurred among young plants which had undergone different treatments (fumigation with O³, SO², ambient air, filtered air, or planting at the sites). Environmental effects on wax structure, wax quantity and the presence of certain compounds in the wax were identified.     

A method for quantifying changes in the epicuticular wax structure of Norway spruce needles

A method for quantifying changes in the epicuticular wax structure of spruce needles (Pieea abies) has been developed for the scanning electron microscope. This evaluation system, based on a five-point scale, classifies only the epistomatal waxes of current-year needles. Two criteria, the different crystal wax forms and the amount of changed wax as a percentage of the total stomatal area have been used for classification. Statistically significant results (accuracy below ± 10% at 5% error level) were obtained under the following conditions. Mixed needle samples were taken from two adjacent trees per site. These were in a dominant and predominant social position in the stand. The needles were collected from the 7^th whorl of sun crowns exposed to all wind directions. The wax quality was determined by evaluating three stomata per needle. One stoma was investigated at the needle base, one m the middle and the third at the apex of the needle. 24 needles were evaluated per site. SEM-Investigations of needle waxes of 25 Austrian forest sites with no local emission source (background sites) showed, that the mean wax quality ranged from 1.6 to 4.1, according to this classification method. Stepwise multiple regression analyses with site characteristics and element contents of the needles (nutrient elements, heavy metals) confirmed correlations between the wax quality and the manganese- and sulphur-content of the needles and also the average degree of crown defoliation.     

Effects of nursery environment on needle morphology of Pinus monticola Dougl. and implications for tree improvement programs

Statistically significant differences were found in 14 needle traits of western white pine (Pinus monticola Dougl.) seedlings grown from the same seed orchard source in the three nurseries in northern Idaho. Traits with significant variation included needle length and width, number of stomatal rows, number of stomata per row, total stomata per needle, adaxial surface area, stomatal density, major axes of stomata, stomatal shape, stomatal area, stomatal occlusion, epistomatal wax degradation, weight of wax per dry weight of needle, and the contact angles of water droplets placed on adaxial needle surfaces. Wax crystallites on needle surfaces were hollow and tubular and the amount of surface wax appeared to be associated with surface wettability. Our results may have important implications for tree improvement programs that require successful inoculation of nursery-grown seedlings with spores of Cronartium ribicola J. C. Fisch. ex Rabenh. to reliably screen white pines for resistance to blister rust.     

Morphology of epicuticular waxes in Pinus pinea needles in relation to season and pollution-climate

Micromorphological change of the epicuticular wax structure in Pinus pinea needles was analysed by scanning electron microscope and the relationships between the rates of wax weathering over seasons and the pollution-climate at one urban and two rural sites arediscussed.     

The effect of the exclusion of dry and wet deposition on visible symptoms and accumulation of sulphur and fluoride by Picea abies needles near point‐sources

The effect of air pollutants on conifers was studied throughout the year near industrial point‐sources using two types of half‐open chambers for excluding wet or dry deposition around selected trees. Results indicate that pollutant uptake from dry deposition and wash‐off effect by rain have overriding influence in the internal accumulation of pollutants by needles. The exclusion of wet deposition substantially enhanced pollutant accumulation in the needles and suggests that wet deposition itself has a minor direct effect on accumulation near point‐sources. Near the fertilizer plant the trees growing in filtered air exhibited fewer visible symptoms and had lower accumulations of fluoride. This suggests that decreasing the gaseous air pollutants would improve the condition of conifers at this site. Results suggest also that besides high needle pollutant content, winter conditions are needed to facilitate visible injury development.     

Effects of Filtered Air and Misting Treatments on Cuticles of Red Spruce Needles on Whiteface Mountain,N.Y.

Two sets of large (8-20 m tall) red spruce (Picea rubens Sarg.) trees growing on Whiteface Mountain, N.Y., were used in branch chamber experiments. In the summer of 1988, the treatments were made on four healthy trees and consisted of: (1) open branches (N), and in chambers that were supplied with either: (2) ambient air (A); (3) charcoal-filtered air (T); or (4) charcoalfiltered air and deionized water misting when the forest was immersed in ambient cloud water (M). Each tree had all of the treatments. The treatments for the second year (summer of 1989) were made on four declining trees and consisted of: (1) open branches (NC) and chambers supplied with either (2) ambient air and mist (AA), (3) synthetic acid mist and ambient air (SA), (4) distilled water mist and ambient air (DA), (5) synthetic acid mist with filtered air (SF), and (6) distilled water mist with filtered air (DF). Foliar properties measurcd included: (1) microreflectivity, a measure of surface wax properties; (2) cuticle thickness; (3) cutinized cell wall thickness; (4) total cuticular layer thickness: (5) the mass of surface wax extracted from needle samples; and (6) contact angles, a measure of surface wetting. In addition, needles were collected and measured from healthy trees at lower and higher elevations. In the first experiment, reflectance from the wax in the stomata1 antechambers in treatment M was statistically significantly greater than all the other treatments. The cuticles of needles in treatment M were also statistically significantly thicker than the cuticles measured in all the other treatments (40% thicker than for the open branches). A plot of cuticular layer against elevation showed that the two filtered chambers (M and T) provided environments for cuticle development that mimic lower elevations. In 1989 the weather was cooler and more moist, and although the trees used in 1989 were declining, the results were similar to those of 1988. However, the additional treatments with synthetic acid mist resulted in reduced cuticle thickness. While the cuticles of the chamber trees growing at 1,170 m were, except for treatment M and T, generally thicker in 1989 than in 1988, they were still considerably thinner than those of spruce trees growing at the lower elevations. These results suggest regional scale air and precipitation quality have detrimental effects on red spruce needles at Whiteface Mountain.     

Über den Einfluß fluorhaltiger Fabrikabgase auf den Phenolgehalt von Fichtennadeln

The effect of industrial fluoride air pollutants on the phenolic contents of Norway spruce needles . Potted Norway spruce trees of two clones were exposed under natural conditions at various distances from an industrial fluoride source. The new needles were analysed periodically for their phenolic content. The group of trees closest to the fluoride source contained the highest amount of phenols.     

Untersuchungen zur Biologie,Morphologie und Verbreitung von Herpotrichia parasitica (Hartig) E. Rostrup (vormals Trichosphaeria parasitica Hartig)1

Studies on thc biology, morphology ancl clistribution of Herpotrichin parasitica (Hartig) E. Rostrup (Trichosphaeria parasitica Hartig) 1. Distribution and morphology. H. paratsitica (Hartig) E. Rostrup (Impcrfcct stage Pyrcnochaeta parasitica Freyer ct van der Aa) occurs in Southern Bavaria on European silver fur. Thc Fungus produces thick cushions of mycelium on the under sidcs of shoots and ovcr thc stomatal rows on needles, penctrates bark tissue as well as necdlcs and causes dcath of needles. Spores of both stagcs gcrminate vcry well in water under various conditions; pycnosρores germinated on silvcr fir needles undcr laboratory Conditions.     

Verschmutzung von Blatt- und Nadeloberflächen im Nahbereich einer Autobahn und deren Einfluß auf den stomatären Diffusionswiderstand

Pollution of leaf and needle surfaces near a highway and its effect on stomatal diffusive resistance. Young clones of several trees and shrubs were exposed on the dividing strip of a highway in spring 1976. After three months, surfaces of leaves and needles were extremely polluted and their stomata occluded. During warm dry days in June and July stomatal diffusive resistance in aspen, birch, alder and ash showed a significant (P<0.02) decrease compared to control plants. Compared with the control, temperature on the strip was higher in the soil but not in the air. It is suggested that this pollution effect may cause an increased water stress and reduced growth of plants in dry, hot periods.     

SEM-observations on the structural degradation of epistomatal waxes in Picea abies (L.) Karst.—and its possible role in the “Fichtensterben”

The structural degradation of the epistomatal waxes was studied with the scanning electron microscope in needles of five trees of Picea abies (L.) Karst. differing in their symptoms of decline. The shedding of needles was found to be related to the degree of occlusion of stomates and to occur when about 80 to 90 % of stomates became occluded by a flat and solid wax cover resulting from the structural degradation of the epistomatal wax crystalloids. While this structural degradation stage was not reached before the seventh year in the trees classified as healthy, degradation was dramatically accelerated in the declining trees. The physiological consequences of such structural obstruction could explain many results so far obtained in declining trees.     

Epicuticular wax content of western white pine is involved in Cronartium ribicola resistance

The introduction of Cronartium ribicola, the causative agent of white pine blister rust, has been devastating for white pines in North America, including western white pine. Among the observed partial resistance responses to white pine blister rust is a mechanism referred to as difficult-to-infect (DI), which is characterized by lower frequency of infection spots on needles and a lower incidence of branch and stem cankers than susceptible host plants. Parents with the DI trait were selected and bred to produce nine full-sib families. Progeny were propagated and cloned using in vitro techniques in controlled environmental conditions. Explants were inoculated with a single strain of C. ribicola and characterized by using a disease assessment index (DAI), which was used to compare DI full-sib families to several other full-sib families (from Idaho) selected for other partial resistance traits. Most DI families had significantly lower DAI scores and higher epicuticular wax content. When the wax was removed from the surface of needles, the DAI of all full-sib families increased. Scanning electron microscopy revealed that stomata in DI full-sib families are mostly occluded by epicuticular wax. The results of this study suggest that the DI resistance mechanism of western white pine is related to needle surface epicuticular wax, which likely hinders the penetration of stomata by fungal hyphae. The occurrence and magnitude of this trait in the breeding population remains unknown, and special assessment technique for large-scale screening will have to be developed.     

Predisposition of trees to drought stress by ozone

This paper reviews research on the effects of ozone on stomatal behavior, and draws attention to the direct link between stomatal function and air pollution. Contradictory results concerning the effects of air pollutants on stomatal activity are attributed to the use of univariate statistical treatments of data. Alternative experimental methods that subject stomata to a functional test are described. These methods verify the hypothesis that ozone predisposes trees to drought stress. It is proposed that ozone directly attacks the walls of guard and subsidiary cells, leading to impairment of the sensory mechanism of the stomata.     

Effects of simulated acid deposition on the surface structure of Norway spruce and silver fir needles

Treatments with acidified solutions of pH 3.5 cause alterations in the wax structure of the needles of silver fir and Norway spruce. The wax structures, especially those of the stomata, once they have been damaged, are not capable of complete reorganization even if the needle is repeatedly treated with distilled water.     

Impacts of seasonal air and soil temperatures on photosynthesis in Scots pine trees

Seasonal courses of light-saturated rate of net photosynthesis (A360) and stomatal conductance (gs) were examined in detached 1-year-old needles of Scots pine (Pinus sylvestris L.) from early April to mid-November. To evaluate the effects of soil frost and low soil temperatures on gas exchange, the extent and duration of soil frost, as well as the onset of soil warming, were manipulated in the field. During spring, early summer and autumn, the patterns of A360 and gs in needles from the control and warm-soil plots were generally strongly related to daily mean air temperatures and the frequency of severe frost. The warm-soil treatment had little effect on gas exchange, although mean soil temperature in the warm-soil plot was 3.8 degrees C higher than in the control plot during spring and summer, indicating that A360 and gs in needles from control trees were not limited by low soil temperature alone. In contrast, prolonged exposure to soil temperatures slightly above 0 degrees C severely restricted recovery of A360 and especially gs in needles from the cold-soil treatment during spring and early summer; however, full recovery of both A360 and gs occurred in late summer. We conclude that inhibition of A360 by low soil temperatures is related to both stomatal closure and effects on the biochemistry of photosynthesis, the relative importance of which appeared to vary during spring and early summer. During the autumn, soil temperatures as low as 8 degrees C did not affect either A360 or gs.     

Seasonal CO(2) assimilation and stomatal limitations in a Pinus taeda canopy

Net CO(2) assimilation (A(net)) of canopy leaves is the principal process governing carbon storage from the atmosphere in forests, but it has rarely been measured over multiple seasons and multiple years. I measured midday A(net) in the upper canopy of maturing loblolly pine (Pinus taeda L.) trees in the piedmont region of the southeastern USA on 146 sunny days over 36 months. Concurrent data for leaf conductance and photosynthetic CO(2) response curves (A(net)-C(i) curves) were used to estimate the relative importance of stomatal limitations to CO(2) assimilation in the field. In fully expanded current-year and 1-year-old needles, midday light-saturated A(net) was constant over much of the growing season (5-6 &mgr;mol CO(2) m(-2) s(-1)), except during drought periods. During the winter season (November-March), midday A(net) of overwintering needles varied in proportion to leaf temperature. Net CO(2) assimilation at light saturation occurred when daytime air temperatures exceeded 5-6 degrees C, as happened on more than 90% of the sunny winter days. In both age classes of foliage, winter carbon assimilation accounted for approximately 15% of the daily carbon assimilation on sunny days throughout the year, and was relatively insensitive to year-to-year differences in temperature during this season. However, strong stomatal limitations to A(net) occurred as a result of water stress associated with freezing cycles in winter. During the growing season, drought-induced water stress produced the largest year-to-year differences in seasonal CO(2) assimilation on sunny days. Seasonal A(net) was more drought sensitive in current-year needles than in 1-year-old needles. Relative stomatal limitations to daily integrated A(net) were approximately 40% over the growing season, and summer drought rather than high temperatures had the largest impact on summer A(net) and integrated annual CO(2) uptake in the upper crown. Despite significant stomatal limitations, a long duration of near-peak A(net) in the upper crown, particularly in 1-year-old needles, conferred high seasonal and annual carbon gain.     

Association of Eucalyptus globulus leaf anatomy with susceptibility to Teratosphaeria leaf disease

Resistance of Eucalyptus globulus juvenile foliage to Teratosphaeria leaf disease (TLD) damage has been shown to be under genetic control. Constitutive traits of juvenile leaves such as stomatal density (counted with wax on and with wax removed), total phenolics, total leaf wax, leaf mass per area (LMA) and leaf anatomical features were assessed to determine differences between pairs of resistant and susceptible families. Anatomic features assessed included cuticle, epidermis, palisade spongy mesophyll and total leaf thickness, as well as palisade cell size, shape and intercellular airspace. One interprovenance, one intraprovenance and two within‐family contrasts were used to compare resistant and susceptible pairs of families of Australian origin. The more resistant families had a significantly higher LMA and smaller percentage airspace compared with susceptible families. It is argued that one of the mechanisms by which E. globulus resists TLD involves the closely packed palisade mesophyll cells that increases LMA and reduces airspace, thereby restricting pathogen spread once infection has occurred.     

Peroxidase-Aktivität in Fichtennadeln unter Schadgasbelastung im Freiland und in Expositionskammern

Zusammenfassung Die Gesamt-Peroxidase-Aktivit?t in grünen, optisch gesunden Nadeln der Fichte (Picea abies L.) wurde im Freiland am Standort “Postturm” (Forstamt Farchau/Ratzeburg) in Tages- und Langzeitkinetiken und bei kurzfristigen Schadstoffspitzenwerten von SO₂ und Ozon untersucht. Parallel hierzu wurde der Wasserhaushalt der Nadeln, die Klimabedingungen und Lichtintensit?ten erfa?t. Unter kontrollierten Bedingungen erfolgte eine Behandlung mit Einzelschadgasen sowie eine Kombinationsbegasung von SO₂ und NO₂ auf die POD-Aktivit?t in Nadeln eines Fichtenklons. Die Ergebnisse zeigen, da? die POD-Aktivit?t Schwankungen unterworfen ist, jedoch keine signifikanten Aktivit?ts?nderungen in Abh?ngigkeit von der Schadgasbelastung zeigt. Die Untersuchungen führen zu dem Ergebnis, da? die Gesamt-POD-Aktivit?t im überstand des Gewebehomogenats von Fichtennadeln als Indikator für eine Umweltbelastung mit Schadgasen ungeeignet ist, da die Aktivit?t dieses Enzyms von zu vielen Faktoren abh?ngig ist.

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Activity of peroxidase in spruce needles in presence of gaseous pollutants in the field and under controlled conditions

Summary The activity of soluble peroxidase (POD, EC 1.11.1.7.) in green needles of about 100-year-old trees of Norway spruce (Picea abies L.) at the location “Postturm” near Ratzeburg, Northern Germany, was studied in relation to transitory increased concentrations of gaseous air pollutants (SO₂ up to 260 ppb in winter, and O₃ up to 130 ppb in summer). Significant changes of POD activity in response to pollution could not be observed. POD activity did not show diurnal variation, but seasonal changes, and changes in response to sunlight (sun needles versus shade needles) and in relation to needle age were observed as well as great variation between individual trees. Moreover, seven-year-old cloned spruce trees were exposed to SO₂, O₃ and NO₂ in growth chambers under simulated climatic outdoor conditions. Consistent with the field studies no changes in POD activity in response to the gaseous pollutants could be observed, although the concentrations applied were higher than in the field. It is, therefore, concluded that the activity of soluble POD is not a suitable indicator for the tested gaseous pollutants.

     

Ten-year exposure to elevated CO2 increases stomatal number of Pinus koraiensis and P. sylvestriformis needles

Stomatal number and stomatal conductance are important structural and functional parameters for the assessment of carbon assimilation and water use under elevated CO₂. We studied stomatal density, number of stomatal rows and stomatal conductance of Pinus sylvestriformis and P. koraiensis needles exposed to elevated CO₂ (500 μmol mol^?1 CO₂) in open-top chambers for 10 years (1999–2009). Elevated CO₂ increased stomatal density on P. sylvestriformis by 10.8 % (13.5 % on abaxial surface and 8.0 % on adaxial surface) and the number of stomatal rows on P. koraiensis by 7.9 % (5.0 % in 1-year-old needles and 10.7 % in current-year needles). Increased stomatal density for P. sylvestriformis and number of stomatal rows for P. koraiensis indicate that elevated CO₂ increases stomatal number in both tree species. Needle age significantly influenced stomatal density and number of stomatal rows in P. koraiensis but not in P. sylvestriformis. For both species, elevated CO₂ did not significantly affect stomatal conductance but increased water use efficiency. The increase in stomatal number is not accompanied by significant changes in stomatal conductance at elevated CO₂ for both tree species suggesting that there may be no direct relationship between stomatal conductance and stomatal numbers.     

Ultrastructure of mesophyll cells of spruce needles exposed to O3 alone and together with SO2

Mesophyll cells of spruce [Picea abies (L.) Karst.] needles fumigated for two months with O₃ alone and together with SO₂ were studied with electron microscope. The observations showed the specific type of injuries for both pollutants, the dependency of severity of injuries both on the concentration of the pollutant and the duration of daily exposure as well as enhanced effects with combined O₃ and SO₂ in the older needles.