Photosynthetic performance,chloroplast pigments,and mineral content of various needle age classes of spruce (Picea abies) with and without the new flush: an experimental approach for analysing forest decline phenomena

Summary Damage in the older needles of Norway spruce [Picea abies (L.) Karst.] in the Fichtelgebirge (NE Bavaria, FRG) appears to result primarily from nutrient imbalances rather than from direct effects of air pollutants on the mesophyll of the needles. Support for this conclusion was obtained by altering the nutrition of older needles through the removal of terminal buds on several branches from a damaged and an undamaged spruce tree in spring. Various photosynthetic parameters, as well as the chloroplast pigment and nutrient concentrations, of 1- to 3-year-old needles on manipulated branches were compared with those of branches on which the new flush was allowed to develop during the course of the growing period. Removal of terminal buds affected only the 1-year-old needles. Elimination of the new flush resulted in a higher Ca and Mn content of the needles of the undamaged tree. This treatment also resulted in an increase of the photosynthetic capacity (under saturating light and CO₂ conditions), carboxylation and light use efficiency, as well as net photosynthesis under natural conditions of the 1-year-old needles on the yellow chlorotic tree. This was accompanied by higher chlorophyll concentrations and an increase in Mg, Ca, Mn, and Zn content, and no visible signs of chlorosis developed in the experiment. By contrast, the needles of twigs in which the new flush was allowed to develop exhibited reductions in mineral content in the middle of the year. This was especially true for the elements Mg and Ca, and was accompanied by needle chlorosis and a depression of the capacity of photosynthesis. Thus it appears that there is a close relationship between the development of needle damage and nutrient imbalances in spruce. The retranslocation of elements from the 1-year-old needles to the new flush seems to play a major role in the development of needle bleaching. This approach thus supports the hypothesis described above and confirms a preliminary test with a similar experimental design, which had been conducted earlier.     

Characterization of the short needle phenomenon in red spruce

Red spruce trees (Picea rubens Sarg.) occasionally produce short twigs bearing short needles. The frequency of short needle cohorts is positively correlated with both elevation and defoliation and they are found in greater numbers on trees that regularly experience winter injury. Short needles are smaller, have lower fresh and dry weights, and reduced volumes compared with normal needles. They have reduced cross-sectional areas due to smaller areas of stelar and mesophyll tissue systems. Individual mesophyll cells, however, have the same cross- and longitudinal sectional areas. On a weight or volume basis, both short and normal needles contain similar amounts of chlorophyll and carotenoid pigments. When pigment concentration was calculated on a unit needle or a needle area base, short needles contain more pigment than normal needles. Short needles appear to have a greater photosynthetic efficiency as determined by fluorescence measurements.     

Antioxidants and Manganese Deficiency in Needles of Norway Spruce (Picea abies L.) Trees

Chlorotic and green needles from Norway spruce (Picea abies L.) trees were sampled in the Calcareous Bavarian Alps in winter. The needles were used for analysis of the mineral and pigment contents, the levels of antioxidants (ascorbate, glutathione), and the activities of protective enzymes (superoxide dismutase, catalase, ascorbate peroxidase, monodehydroascorbate radical reductase, dehydroascorbate reductase, glutathione reductase). In addition, the activities of two respiratory enzymes (glucose-6-phosphate dehydrogenase, NAD-malate dehydrogenase), which might provide the NADPH necessary for functioning of the antioxidative system, were determined. We found that chlorotic needles were severely manganese deficient (3 to 6 micrograms Mn per gram dry weight as compared with up to 190 micrograms Mn per gram dry weight in green needles) but had a similar dry weight to fresh weight ratio, had a similar protein content, and showed no evidence for enhanced lipid peroxidation as compared with green needles. In chlorotic needles, the level of total ascorbate and the activities of superoxide dismutase, monodehydroascorbate radical reductase, NAD-malate dehydrogenase, and glucose-6-phosphate dehydrogenase were significantly increased, whereas the levels of ascorbate peroxidase, dehydroascorbate reductase, glutathione reductase, and glutathione were not affected. The ratio of ascorbate to dehydroascorbate was similar in both green and chlorotic needles. These results suggest that in spruce needles monodehydroascorbate radical reductase is the key enzyme involved in maintaining ascorbate in its reduced state. The reductant necessary for this process may have been supplied at the expense of photosynthate.     

The ion concentration of dew condensed on Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) needles

Summary Dew droplets collected with pipettes from coniferous needles were analysed for their ionic composition. Almost all samples of dew taken from Scots pine trees (Pinus sylvestris) showed significantly higher ion concentrations than those taken from Norway spruce trees (Picea abies). This can be explained by the micromorphology of the needle surface. The higher microscale roughness of the wax layer of a pine needle causes a more efficient flux of atmospheric aerosol particles compared to the spruce needle surface. Dew on coniferous needles is shown to be capable of maintaining pH values below 3 for several hours.     

Activity and activation state of ribulose-1,5-bisphosphate carboxylase of spruce trees with varying degrees of damage relative to the occurrence of novel forest decline

The aim was to determine whether a reduced carboxylation efficiency in needles of damaged spruce trees (Picea abies), is derived from a direct impairment of the ribulose-1,5-bisphosphate carboxylase (RuBP carboxylase) or there is an indirect inhibition of the RuBP carboxylase. In 1985, 1986 and 1987 measurements of RuBP carboxylase activity were carried out at three locations. Trees of different ages and degrees of damage were examined. RuBP carboxylase was assayed using both a rapid extraction method to determine the initial activity and an in vitro test after total activation to determine the total activity. The activation state was calculated as the ratio of initial activity to total activity.Within three vegetation periods the total activity in needles of damaged and apparently healthy or slightly damaged spruce trees indicated no definite difference in the annual average. On the other hand, in damaged needles a continued decline of the actual activation of RuBP carboxylase was established. The observation of continued depression of the activation state of the enzyme in needles of damaged spruce trees can possibly be due to a reduced photosynthetic electron transport rate.The measurements of the soluble protein content indicate a tendency to increased amounts in the needles of damaged trees. In accordance, a considerable increase of the activity of some enzymes like glutamine synthethase, phosphoenol-pyruvate carboxylase, and catalase could be noticed. However, there is no clear connection between the RuBP carboxylase and the content of soluble proteins.Abbreviations chl chlorophyll a+b, dw-dry weight, i.a-initial activity - P-700 reaction center of photosystem I - PVP polyvinylpyrrolidone 25 - RuBP ribulose-1,5-bisphosphate - RuBPCase ribulose-1,5-bisphosphate carboxylase - t.a. total activity     

Contents of ATP and ADP in needles of Norway spruce in relation to their development,age, and to symptoms of forest decline

Summary Pool sizes of ATP and ADP were analysed in freeze-stopped, lyophilised homogenates of needles from Norway spruce [Picea abies (L.) Karst.]. Control experiments in which possible changes in adenylate pools during sample acquisition were investigated did not reveal significant differences between needles taken from branches in situ or within a 30-min period after cutting off a branch. In addition, pool sizes of ADP and ATP were not affected by changes in light intensity (between 60 and 1500 E^*-m^-2*s^-1), which inevitably occur when samples have to be taken from the upper region of older trees. Levels of ATP and ADP showed considerable seasonal changes (May through October) with the highest ratios of ATP/ADP in developing needles. In general, there was a tendency towards increased ratios of ATP/ADP with increasing needle age. This observation was corroborated by analyses of needles from spruce trees of different age and growing under different conditions. Needles from declining trees or from trees specifically fumigated with low concentrations of ozone and sulphur dioxide had significantly increased ratios of ATP/ADP compared to controls. The results are discussed with respect to physiological responses connected with natural senescence and induced ageing.     

Inhibition of photosynthesis in current-year needles of unfertilized and fertilized Norway spruce [Picea abies (L.) Karst.] during autumn and early winter

Inhibition of photosynthesis was followed during autumn and early winter in current-year sun and shade needles of unfertilized and fertilized Norway spruce [Picea abies (L.) Karst.] by simultaneous measurements of photosynthetic O₂ evolution and chlorophyll a fluorescence at 20 °C. The CO₂-saturated rate of O₂ evolution was generally higher in sun needles of fertilized trees than in those of unfertilized trees over a wide range of incident photon flux densities (PFDs). Furthermore, the maximum photo-chemical efficiency of photosystem (PS) II, as indicated by the ratio of variable to maximum fluorescence (F_V/F_M) was generally higher for sun needles of fertilized trees. The depression of f_v/f_m during frost periods was more pronounced in sun needles than in shade needles, indicating that winter inhibition in Norway spruce is strongly light-dependent. However, the inhibition of the rate of O₂ evolution at high PFDs in needles of fertilized trees during early winter was partly independent of the light regime experienced by those needles in the field, which appeared to result in a pronounced decrease in the proportion of oxidized PS II reaction centres in shade needles. A nearly identical linear relationship between the quantum yield of PS II electron transport determined by chlorophyll fluorescence and the quantum yield of O₂ evolution (gross rate of O₂ evolution/PFD) was obtained for the investigated types of needles during autumn and early winter. Except for shade needles of fertilized trees, this appeared to be largely achieved by adjustments in thermal energy dissipation within PS II.     

Stand characteristics of ozone-stressed populations of Pinus jeffreyi (Pinaceae): extent,development, and physiological consequences of visible injury

The development and physiological consequences of ozone-induced visible injury was investigated in native populations of Jeffrey pine (Pinus jeffreyi) that were exposed to chronic levels of anthropogenic ozone. Stand structure analyses demonstrated that the expression of visible ozone injury symptoms within self-regenerating populations of Jeffrey pine was highly variable. Of the 975 trees surveyed, 90% exhibited some degree of visible injury and 10% were classified as resistant to ozone. Needles of the most sensitive trees developed a chlorotic mottle characteristic of ozone injury 1 year after their initiation and prematurely abscised in their third year (normal needle retention is 5–6 years). Average needle retention was not different between diameter size categories but was the most variable within the smallest size category and the least variable in the largest size category. Gas exchange measurements indicated a negative correlation between photosynthetic rate and needle surface area covered by chlorotic mottle. Chlorophyll fluorescence kinetics of the current-year needles did not differ between symptomatic and asymptomatic trees but did differ between the oldest needles, suggesting an uncontrolled physiological decline in needles about to abscise in sensitive trees. The high degree of variability of ozone-induced visible injury coupled with the reduction of physiological capacity associated with visible injury suggest that mixed conifer forests growing in polluted regions could potentially undergo shifts in community structure if sensitive Jeffrey pine individuals were to experience differential mortality as a result of ozone exposure. Intraspecific variation in ozone sensitivity may potentially lead to increased population tolerance to oxidative air pollutants, but long-term population analyses will be required to address genetic changes in response to ozone stress.     

Photosynthetic Characteristics of Eastern Dwarf Mistletoe (Arceuthobium pusillum Peck) and its Effects on the Needles of Host White Spruce (Picea glauca [Moench] Voss)

Abstract: We studied the biochemical composition and photosynthetic characteristics of the aerial parasite eastern dwarf mistletoe (Arceuthobium pusillum) and the effect of infection on the needles of host white spruce (Picea glauca) in a coastal forest stand in Maine, USA. Eastern dwarf mistletoe was capable of photosynthetic oxygen evolution; however, rates were low and were exceeded by respiratory oxygen consumption at all light intensities through full sunlight. Therefore, eastern dwarf mistletoe acts as a net sink for host photosynthate. Relative to those of uninfected trees, needles from infected branches of white spruce were significantly smaller in terms of length, fresh weight, maximum cross section and the diameter of the vascular cylinder. Needles of uninfected and infected trees did not differ in terms of fresh weight to dry weight ratio, nor in nitrogen, soluble sugar or starch content. Needles of infected trees possessed significantly less α-carotene and neoxanthin, but did not otherwise differ from uninfected needles in terms of chlorophyll and carotenoid composition. Since specific physiological roles for α-carotene and neoxanthin have not been described, the functional significance of the decreases in their content is not known. Photosynthetic capacities of needles from infected and uninfected white spruce did not differ significantly, as measured by oxygen evolution. These findings suggest that dwarf mistletoe infection does not substantially perturb host white spruce source-sink balance at the end of the growing season and that carbon exchange dynamics between the host and parasite are unlikely to fully explain the detrimental effects of infection on white spruce.     

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

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

Seasonal variation in the monoterpenes in needles of Picea abies (L.) Karst.

Summary This investigation was conducted to obtain information about the fluctuations in composition and amount of needle monoterpenes during the development of spruce needles. Studies conducted with two Norway spruce clones clearly revealed the existence of fluctuations. In juvenile needles, the amounts of the oxygenated terpenes increase constantly with age during the first 2 months of needle growth. The hydrocarbon terpenes dominate within the first weeks, some of them even showing a very distinct first maximum within the first 3 weeks after bud burst. All terpenes, including the oxygenated ones, have a maximum in June/July, which favours the hypothesis of a substitution of the hydrocarbons later on. There are significant changes even in mature needles of Norway spruce. The terpene level of 1-year-old needles of the clonal trees increased from spring to early summer and then dropped again towards winter. In addition, fluctuations in mature needles were shown for a set of ten wild trees. Needles of the same age class, which emerged in 1986, were sampled 4 times from 1986 to 1988. The needle terpene concentrations of the 1 -year-old needles were considerably lower in spring at the time of bud burst than in autumn. The terpene level of older needles thus seems to be influenced by biosynthetic and catabolic activities.     

Photosynthetic performance and nutrient status of Norway spruce [Picea abies (L.) Karst.] at forest sites in the Ore Mountains (Erzgebirge)

Summary Photosynthetic performance of several needle age classes of Norway spruce trees [Picea abies (L.) Karst.] in highly SO₂-polluted and heavily damaged forest sites was measured at two different locations in the Ore Mountains (Erzgebirge, Krusne Hory) during early summer. The carboxylation efficiency showed a dramatic drop from current-year's needles to 1-year-old needles with only a slight further decrease with increased needle age. The light use efficiency also revealed these characteristics. For both parameters, no linear decrease with needle age could be found. In contrast, the maximum photosynthetic capacity (A₂₅₀₀) decreased linearly with time and revealed a good correlation with the total sulfur content of the needles. Absolute values measured for A₂₅₀₀ were approximately 50% lower than those of comparable trees in the nearby Fichtelgebirge. Mineral deficiencies or acute nutrient imbalances of the needles were not detected. In contrast to the situation in the forests of the Fichtelgebirge, a direct effect of gaseous SO₂ on the trees in the Ore Mountains seems plausible.This paper is dedicated to our teacher Professor Otto Ludwig Lange on the occasion of his 65th birthday     

The effect of ozone on the yellowing process of magnesium-deficient clonal Norway spruce grown under defined conditions

During two vegetation periods, young clonal spruce trees (Picea abies (L.) Karst.) with sufficient and poor magnesium (Mg) supply were exposed in the environmental chambers of the GSF phytotron to three levels of ozone (daily means: 18-22, 88-130, and 135-190 microg m(-3); 10% reduction at night). Previous year's needles were examined at 4-week intervals with respect to their contents of Mg, Ca, K, Mn, N, P, and chlorophyll (Chl), various parameters of Chl fluorescence, and the stability of the isolated light-harvesting Chl-a/b-protein complex LHC II. The needles of the two nutrition variants contained more than 0.53 or less than 0.27mg Mg g(-1) needle dry matter, respectively. The ratio of variable to maximal Chl-a fluorescence of the dark-adapted needles, Fv/Fm, and the photoinhibitory quenching of Fv after light treatment, SVi.v, were affected by the Mg content of the needles rather than the ozone levels. Changes of the Chl content and the behavior of the LHC II allowed differentiating between a slow process of needle yellowing occurring under Mg deficiency only, and a rapid process of needle yellowing occurring under the combined action of Mg deficiency and ozone pollution. Only the rapid yellowing process was accompanied by destabilization of the LHC II, and the degree of destabilization was correlated with the ozone concentration present in the days before sampling. The results are consistent with observations obtained at a research site in the Central Black Forest (J Plant Physiol 161 (2004) 423).     

Magnesium deficiency treatment causes reductions in photosynthesis of well-nourished Norway spruce

In order to investigate effects of magnesium deficiency on Norway spruce [Picea abies (L.) Karst.] photosynthesis, 100 well-nourished 5-year-old spruce trees were grown in sand culture, individually supplied with circulating nutrient solutions. Mineral nutrients were added to the nutrient solutions in optimal quantities and optimal relations to nitrogen. Magnesium was supplied at 0.203, 0.041 and 0.005 mM in order to simulate optimal nutrition, moderate deficiency and severe deficiency. Parameters of photosynthetic gas exchange, chlorophyll, magnesium and starch concentrations were determined in current-year and 1-year-old needles during one growing season. By mid May — 6 months after onset of the Mg deficiency treatments in late autumn — CO₂-assimilation rates of 1-year-old needles were significantly decreased independent of the severity of the deficiency treatment, whereas the chlorophyll concentrations did not differ from the controls. The occurrence of yellowing symptoms during July did not further influence the Mg deficiency effect on photosynthesis. In contrast to 1-year-old needles, significant reductions of photosynthesis and chlorophyll in current-year needles were only caused by severely deficient Mg supply. Mg deficiency affected carboxylation efficiency but not light use efficiency. From the accumulation of starch in the needles, up to 30-fold of the controls, the conclusion has been drawn that reactions of CO₂-fixation were affected by reduced carbohydrate export. The light-dependent pigment reduction, leading to the typical tipyellowing of needles, clearly reflects a secondary effect of Mg deficiency.     

Seasonal development of the photosynthetic performance of Norway spruce (Picea abies [L.] Karst.) under magnesium deficiency

In order to investigate the influence of different magnesium nutrition on photosynthesis, one hundred 6-year-old spruce trees derived from one clone were planted in October 1990 into a special out-door experimental construction, where they were cultivated in sand culture with an optimal supply of nutrients, except magnesium, via circulating nutrient solutions. Magnesium was added to the nutrient solutions in three different concentrations, varying from optimal to severe deficient supplies. During the first vegetative period in 1991, photosynthetic performance and carboxylation efficiency were measured under saturating light, controlled CO₂ conditions, optimal temperature and humidity, using a minicuvette system.During summer, the trees under moderate magnesium deficiency developed tip yellowing symptoms on older needles, while the youngest needles remained green with unchanged chlorophyll contents. Trees under severe magnesium deficiency showed yellowing symptoms on all needle age classes combined with decreased chlorophyll contents in the youngest needles as well. In comparison with the controls, the photosynthetic performance of the 1-year-old needles was significantly lower in both deficiency treatments. The same was observed in the youngest needles of the trees under severe deficiency. Trees under moderate deficiency treatment decreased in photosynthetic performance during the summer without reduction of chlorophyll contents. The reduction of photosynthetic rates corresponded to a decrease in carboxylation efficiency, which is taken as a measure of the activity of the enzyme ribulose-1,5-bisphosphate carboxylase. This reduction, together with the observed increase of carbohydrate contents in needles of trees growing under magnesium deficiency, led to the assumption that the photosynthetic carbonfixation is reduced as a consequence of the accumulation of carbohydrates.     

Developmental disorders in buds and needles of mature Norway spruce, Picea abies (L.) Karst., in relation to needle boron concentrations

Dieback of the terminal shoot and consequently bushy growth induced by boron deficiency have been reported widely throughout the world in several tree species. Recently, similar growth damage was documented in half of the young spruce stands in eastern Finland. To clarify the role of B deficiency, the light microscopic structure of emerging buds and of developing and previous-year needles of mature Norway spruce (Picea abies L. Karst.) from damaged (D stand), partly damaged (PD stand) and healthy (H stand) stands were analysed. The samples, on which needle nutrient concentrations were also determined, were taken seven times between early spring (April) and early winter (November). Cell death characterized by precipitation of the cell content, possibly due to the release of tannins after membrane rupture, was seen in the apex of emerging buds, and this led to fatal damage in about half of the buds in the trees from the D stand, where the needle B concentration was well below the deficiency level of 4–5 mg kg⁻¹. Furthermore, an increase in living cells that accumulated tannins in the vacuoles, which is a common stress and/or defense reaction, was found in the primordial shoots of buds and in the differentiating needles in the PD and D stands. The increase in the areas of the central cylinder and of the xylem found in the needles indicate structural plasticity during needle differentiation to drought. The time frame for bud emergence from late May up to mid-September means that an adequate B supply is necessary throughout the summer in order to avoid fatal bud damage and thus bushy growth of the trees.     

Seasonal dynamics of chlorophyll and microelement content in developing conifer needles of <Emphasis Type="Italic">Abies sibirica</Emphasis> and <Emphasis Type="Italic">Picea abies</Emphasis>

Composition of microelements and photosynthetic pigment content (chlorophylls (Chl) a and b) were monitored in growing needles of spruce (Picea abies (L.) Karst.) and Siberian fir (Abies sibirica Ledeb.) during spring-autumn vegetation period. The dynamics of fresh weight and needle length for the first-year needles of spruce and fir revealed a number of shared and species-specific features in growth patterns of photosynthetic organs. In the beginning of growth period (in May), the needles elongated rapidly, while June–July were marked by the increase in needle weight. In P. abies the needle weight accumulated rapidly (specific growth rates μ_max up to 0.20 day⁻¹) over a short period (14 days), while in A. sibirica the needle weight increased slower (μ_max ≤ 0.11 day⁻¹) but over a longer period (≥30 days). The dynamics of Chl a and Chl b content and their ratio were identical in needles of both species over the growth period, although changes in Chl a were pronounced stronger than those in Chl b. In spring (May), a relatively high total Chl content per needle dry weight was noted. In summer (June–August), the total Chl content declined appreciably. In autumn (September–November), the total chlorophyll content in first-year needles increased slightly. Microelements were classified into two groups according to seasonal dynamics of their relative content in first-year needles. The first group includes Ba, Mn, Zn, B, Cu, Co, Cr, Pb, and Mo, whose relative content had a distinctive maximum in July, coincident with the peak in Chl content. The second group comprises Ni, V, Ag, Be, Cd, and As, whose relative content was minimal at this period. Seasonal changes in microelement composition were similar for the two conifer species examined, which is likely due to different physiological values of various microelements for photosynthetic organs.     

Bacterial (Bacillus thuringiensis subsp. thuringiensis and B. thuringiensis subsp. kurstaki) Entomocidal Preparations Decrease Chlorophyll Accumulation in Larch Needles

Chlorophyll a plus b content and absorption spectra of the homogenates from the cotyledonary leaves of 30-day-old seedlings of two larch species, Larix gmelinii (Rupr.) Rupr. and L. sibirica Ldb. were studied. The seedlings were grown on Perlite containing aqueous solutions of entomocidal biopreparations isolated from Bacillus thuringiensis subsp. thuringiensis (bitoxybacillin) and B. thuringiensis subsp. kurstaki (lepidocide) at various final concentrations (2, 6, and 12 g/l). Changes in the form of chlorophyll absorption spectra induced by biopreparations were established. A marked inhibition of pigment accumulation in the needles dependent on the biopreparation concentration was noted. At a low concentration (2 g/l), the biopreparations virtually did not affect the chlorophyll content; an increase in their concentrations resulted in a decrease in chlorophyll content in leaves by 20% (at 6 g/l) and 40% (at 12 g/l). It is concluded that bitoxybacillin and lepidocide inhibited the chlorophyll accumulation in larch needles to a similar extent.     

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

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

Leaf age as a factor in anatomical and physiological acclimative responses of Taxus baccata L. needles to contrasting irradiance environments

To evaluate the acclimative ability of current-year and previous-year needles of a shade tolerant conifer Taxus baccata L. to contrasting irradiance conditions, seedlings were raised under 27% solar irradiance and at 3 years of age they were transferred to an experimental garden and grown for one season under full irradiance (HL), 18% irradiance (ML) or 5% irradiance (LL). Whereas previous year needles did not change anatomically, current year needles in HL were thicker and had a thicker palisade and spongy mesophyll, and greater leaf mass per area than ML or LL needles. LL needles had greater nitrogen concentration than HL needles irrespective of age but only previous year LL needles also had an increased N per area content, thanks to their lack of reduction in LMA. Adjustment of chlorophyll and carotenoid content occurred in both needle age classes with LL and ML needles having much higher concentrations but, in current year needles, only slightly higher per area content than HL needles. Chlorophyll a/b ratio was not affected by age or irradiance. These modifications had no significant effect on photosynthetic capacities, which did not significantly differ between the age classes in HL or LL treatment and between treatments. On the other hand, high growth irradiance resulted in a greater photochemical yield, photochemical quenching, apparent electron transport rate and inducible non-photochemical quenching in needles formed in the current season. In previous year needles, however, only inducible NPQ was enhanced by high irradiance with other parameters remaining identical among treatments. To test sensitivity to photoinhibition, at the end of the summer plants from the three irradiance levels were transferred to a HL situation and F _v/F _M was determined over the following 18 days. Sensitivity to photoinhibition was negatively related to growth irradiance and previous year needles were less photoinhibited than current year needles. Thus, differences in acclimation ability between needle age classes were most pronounced at the level of anatomy and light reactions of photosynthesis, both of which showed almost no plasticity in previous year needles but were considerably modified by irradiance in current year needles.