Life expectancy of spruce needles under extremely high air pollution stress: performance of trees in the Ore Mountains

Summary Photosynthetic performance of Norway spruce needles [Picea abies (L.) Karst.] was measured over a 1-year period. The trees grew in an area of heavy air pollution and forest decline on a mountain ridge in the eastern Ore Mountains (Czech Republic). Photosynthetic capacity, as well as light use efficiency, decreased dramatically with time, starting in July (2 months after bud-break) to finally reach zero (respiration only) by February of the following year. Two months later all needles from upper crown parts were shed. Needles from lower crown parts, on the other hand, were undamaged. The chlorophyll and Mg content decreased transiently during the cold season, with Mg reaching deficiency thresholds during winter. However, total sulfur, as well as organic and sulfate S increased with time. The increase was higher in needles from the upper parts of the crown, which were exposed to windy air throughout the year, than in the lower parts of the crown, which were covered by grass during summer and by snow during most of the winter.     

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     

Somatic embryogenesis in conifers: The role of carbohydrate metabolism

Summary Somatic embryogenesis represents a promising tool for mass propagation of elite genotypes of conifers. The efficiency of the technique strongly depends on cultivation conditions, with the exogenous saccharide supply being one of the most important factors. Different types and concentrations of saccharides have been empirically evaluated with respect to production of acceptable numbers and quality of somatic embryos for particular conifer species. Only a few recently published papers have focused on deeper studies of carbohydrate metabolism, enabling insight into the physiological background of the crucial effects of carbohydrates. Generally, saccharides are known to serve as carbon and energy sources, osmotic agents, stress protectants, and signal molecules in plants. This review collects and critically discusses the experimental data on exogenous saccharide supplies, resulting endogenous levels, and key enzyme activities obtained from the most thoroughly described genus Picea. In conclusion, it stresses the necessily to broaden the studies and consider the unltiple roles of saccharides during conifer somatic embryogenesis.     

Detoxification of dissolved SO2 (bisulfite) by terricolous mosses

BACKGROUND AND AIMS: The widespread calcifuge moss Pleurozium schreberi is moderately tolerant of SO2, whereas Rhytidiadelphus triquetrus is limited to calcareous soils in regions of the UK that were strongly affected by SO2 pollution in the 20th century. The proposition that tolerance of SO2 by these terricolous mosses depends on metabolic detoxification of dissolved bisulfite was investigated. METHODS: The capacities of the two mosses to accelerate loss of bisulfite from aqueous solutions of NaHSO3 were studied using DTNB [5, 5-dithio-(2-nitrobenzoic acid)] to assay bisulfite, and HPLC to assay sulfate in the incubation solutions. Incubations were performed for different durations, in the presence and absence of light, at a range of solution pH values, in the presence of metabolic inhibitors and with altered moss apoplastic Ca2+ and Fe3+ levels. KEY RESULTS: Bisulfite disappearance was markedly stimulated in the light and twice as great for R. triquetrus as for P. schreberi. DCMU, an inhibitor of photosynthetic electron chain transport, significantly reduced bisulfite loss. CONCLUSIONS: Bisulfite (SO2) tolerance in these terricolous mosses involves extracellular oxidation using metabolic (photo-oxidative) energy, passive oxidation by adsorbed Fe3+ (only available to the calcifuge) and probably also internal metabolic detoxification.     

The role of photophosphorylation in SO2 and SO 3 2- inhibition of photosynthesis in isolated chloroplasts

Sulphur dioxide inhibits noncyclic photophosphorylation in isolated envelope-free chloroplasts. This inhibition was shown to be reversible and competitive with phosphate, with an inhibitor constant of K_i=0.8mM. The same inhibition characteristics were observed when phosphoglycerate (PGA)- or ribulose-1,5-bisphosphate (RuBP)-dependent oxygen evolution was examined in a reconstituted chloroplast system in the presence of SO ₃ ^2- . Using an ATP-regenerating system (phosphocreatine-creatine kinase), it was demonstrated that the inhibition of PGA-dependent oxygen evolution is solely the result of inhibited photophosphorylation. It is concluded that at low SO₂ and SO ₃ ^2- concentrations the inhibition of photophosphorylation is responsible for the inhibition of photosynthetic oxygen evolution.Abbreviations Chl chlorophyll - PGA D-3-phosphoglyceric acid trisodium salt - Pi inorganic phosphate - RuBP D-ribulose-1,5-bisphosphoric acid tetrasodium salt     

Light conditions inside developing buds affect floral induction

Buds of Pinus sylvestris L. and Picea abies (L.) Karst. were pierced with optical fibres allowing natural light to the vicinity of apical domes. Induction of female strobiles was achieved. Since bud scales absorb more red than far-red light, the treatment may have increased the far-red light absorbing form of phytochrome.Abbreviations Pfr far-red light absorbing form of phytochrome     

Estimating photosynthetic rate and annual carbon gain in conifers from specific leaf weight and leaf biomass

Summary Canopy photosynthesis is difficult to measure directly or to predict with complex models demanding knowledge of seasonal variation in environmental and physiological properties of the canopy. Trees in particular offer a challenge with their large, aerodynamically rough and seasonally-changing canopy properties. In this paper we assess the possibility of using specific leaf weight to predict seasonal and annual net photosynthetic rate in deciduous (Larix sp.) and evergreen (Picea abies) conifers.Annual photosynthetic rate and specific leaf weight of different positions of the crown in both species were highly correlated (r ²=0.930). Annual carbon uptake by different segments in a mature P. abies crown was closely related to leaf biomass. The relationship was improved by adjusting the leaf biomass of each segment in regard to its specific leaf weight relative to the maximum found in the canopy. The adjustment accounted for associated differences in photosynthetic activity. This combined structural index (leaf biomassxrelative specific leaf weight) could, when calibrated, predict the total annual carbon uptake by different parts of the crown. If direct measurements of photosynthesis are not available, the combined structural index may still serve as a comparative estimator of annual carbon uptake.     

Seasonal changes in light transmission by bud scales of spruce and pine

A bundle of optical fibres and a photometer were used to measure light transmission through bud scales of Norway spruce [Picea abies (L.) Karst.] and Scots pine (Pinus silvestris L.). Percentage transmission increases with wavelength from none below 480 nm to 3% the far-red. Transmission of all wavebands measured was lowest in late summer and winter and highest in the autumn and spring. For most of the year in pine, and only from July to September in spruce, there is a depression of red light (660–670 nm) transmission. This affects the ratio of 660/730 nm light penetrating the apical domes. This ratio is lowest in July and August, at the time of initiation of female strobili. The seasonal variation in transmission of light by bud scales is discussed in relation to the possible consequences for the control of flowering.     

The heterogeneous levels of linkage disequilibrium in white spruce genes and comparative analysis with other conifers

In plants, knowledge about linkage disequilibrium (LD) is relevant for the design of efficient single-nucleotide polymorphism arrays in relation to their use in population and association genomics studies. Previous studies of conifer genes have shown LD to decay rapidly within gene limits, but exceptions have been reported. To evaluate the extent of heterogeneity of LD among conifer genes and its potential causes, we examined LD in 105 genes of white spruce (Picea glauca) by sequencing a panel of 48 haploid megagametophytes from natural populations and further compared it with LD in other conifer species. The average pairwise r(2) value was 0.19 (s.d.=0.19), and LD dropped quickly with a half-decay being reached at a distance of 65 nucleotides between sites. However, LD was significantly heterogeneous among genes. A first group of 29 genes had stronger LD (mean r(2)=0.28), and a second group of 38 genes had weaker LD (mean r(2)=0.12). While a strong relationship was found with the recombination rate, there was no obvious relationship between LD and functional classification. The level of nucleotide diversity, which was highly heterogeneous across genes, was also not significantly correlated with LD. A search for selection signatures highlighted significant deviations from the standard neutral model, which could be mostly attributed to recent demographic changes. Little evidence was seen for hitchhiking and clear relationships with LD. When compared among conifer species, on average, levels of LD were similar in genes from white spruce, Norway spruce and Scots pine, whereas loblolly pine and Douglas fir genes exhibited a significantly higher LD.     

Performance of two Picea abies (L.) Karst. stands at different stages of decline

Summary A declining Picea abies (L.) Karst. stand produced as much foliage and branches as a healthy stand but less stemwood at a similar leaf area index and climate. Nutrient analyses revealed that most biomass components at the declining site had lower concentrations of calcium and magnesium, but similar nitrogen and potassium (except for lower potassium in younger needles) and higher phosphorus, manganese and aluminum than the respective components at the healthy site. Comparison of these data with the results from studies on the nutrition and growth of P. abies seedlings (Ingestad 1959) led to the conclusion that the healthy stand is in a balanced nutritional state, while trees at the declining stand have only 56% of the foliar magnesium concentration required to permit growth at a rate which could be achieved at their nitrogen status. It appears that acidic deposition, which involves an input of nitrogen and a leaching of cations from the soil, causes an imbalance in the availability of nitrogen and magnesium. Growth is eventually reduced as magnesium becomes limiting.     

Quantitation of gibberellins A1, A3, A4, A9 and an A9-conjugate in good- and poor-flowering clones of Sitka spruce (Picea sitchensis) during the period of flower-bud differentiation

The levels of endogenous gibberellin A₁ (GA₁), GA₃, GA₄, GA₉ and a cellulase-hydrolysable GA₉-conjugate in needles and shoot stems of Sitka spruce [Picea sitchensis (Bong.) Carr.] grafts with different coning or flowering histories were estimated by combined gas chromatography-mass spectrometry selected ion monitoring using deuterated GA₃, GA₄ and GA₉ as internal standards. The samples were taken at the approximate time of the start of flower-bud differentiation, i.e. when the shoots had elongated approx. 95% of the final length. The needles of the good-flowering clones contained 11–12 ng per g fresh weight (FW) and 15–28 ng· (g FW) ^–1 of GA₉-conjugate and GA₉, respectively. The shoot stems of the same material contained no detectable amounts of GA₉-conjugate and 11–15 ng-(g FW)^–1 of GA₉. The amounts of GA₉-conjugate and GA₉ were apparently lower in the poor-flowering clones, the needles containing 4–9 ng-(g FW)^–1 and 7–17 ng·(g FW)^–1, respectively. Also in this material the shoot stems contained no detectable amounts of GA₉-conjugate. The amounts of GA₄ were very small in both materials, ranging from 1–1.6 ng-(g FW)^–1. The good-flowering clones contained no detectable amounts of the more polar gibberellins, GA₁ and GA₃. The poor-flowering clones, on the other hand, contained high levels of GA₁₅ 17–19ng·(gFW)^–1 in the needles and 10–13 ng·(g FW) ^–1 in the shoot stems, and also smaller amounts of GA₃, 2–3 ng·(g FW)^–1 in the needles and approx. 1 ng·(g FW)^–1 in the shoot stems. The results demonstrate differences in GA-metabolism between the poor- and the good-flowering clones. The higher amounts of GA₉-conjugate and GA₉ might indicate a higher capacity for synthesizing GA₄ in the good-flowering material. This synthesis does not, however, result in a build-up of the GA₄-pool, maybe because of a high rate of turnover. Gibberellin A₄ was apparently neither hydroxylated to GA₁ nor converted to GA₃ in the goodflowering material, as was the case in the poor-flowering material. This might indicate that gibberellin metabolism in the poor-flowering material is directed towards GA₁ and GA₃, GAs preferentially used in vegetative growth.Abbreviations FW fresh weight - GA_n gibberellin A_n - HPLC high-performance liquid chromatography     

Stomatal SO2 uptake and sulfate accumulation in needles of Norway spruce stands (Picea abies) in Central Europe

Monthly uptake rates and the annual deposition of gaseous SO₂ via the stomata of six Norway spruce canopies (Picea abies (L.) Karst.) in Germany (Königstein im Taunus, Witzenhausen, Grebenau, Frankenberg, Spessart, Fürth im Odenwald) were calculated (i) from statistical response functions of stomatal aperture depending on meteorological data, and (ii) from the synchronously measured SO₂ immission at these stands. The stomatal response functions had been derived on the basis of thorough stomatal water conductance measurements in the field. Calculations of the SO₂ conductance of spruce twigs and SO₂ uptake rates via stomata need continuously measured complete data sets of the (i) light intensity, (ii) air temperature, (iii) air humidity and (iv) SO₂ concentration in spruce forests from all the year. These data were recorded half hourly in different German spruce forests. The apparent needle water vapour pressure difference and transpiration rates were calculated from meteorological data. Additional use of canopy through flow data in dry years allowed the estimation of the mean stomatal conductance for H₂O and SO₂ of whole spruce canopies. The annual SO₂ uptake of a mean unit needle surface in spruce forests was 32% of the SO₂ uptake rate of exposed needles at the top of spruce crowns. There is significant SO₂ uptake all the year. The mean SO₂ dose at all sites and years received through the stomata was (0.25±0.07) mol SO₂ m^-2 (total needle surface) (nPa Pa^-1)^-1 (annual mean of SO₂ immission; 1 nPa (SO₂) Pa^-1 (air) = 1 ppb) day^-1 (vegetation period per year). Comparison of calculated SO₂ uptake rates into needles with measured SO₄ ^2- accumulation rates in needles from the mentioned sites and additionally from Würzburg, Schneeberg (Fichtelgebirge) and from three sites in the eastern Erzgebirge (Höckendorf, Kahleberg, Oberbärenburg) revealed that oxidative SO₂ detoxification (SO₄ ^2- formation) dominates only at sites with high SO₂ immission and short vegetation periods. Under these conditions 70 to 90% of the annual stomatal SO₂ uptake is detoxified via SO₄ ^2- accumulation in needles. Cations are needed for neutralization of accumulating SO₄ ^2- which are inavailable to support growth. Thus, SO₂ induces a dominant and competitive additional nutrient cation demand, cation deficiency symptoms and enhanced needle loss (spruce decline symptoms) mainly at sites, where the ratio R=(SO₂ immission): (length of the vegetation period) is higher than R=0.07 nPa Pa^-1 day^-1. Correlation analysis of the relative needle loss versus the SO₂-dependent SO₄ ^2- formation rate revealed a significant increase of needle loss at the 98% level (Student). At sites with small SO₂ immission and long vegetation periods (R<0.07 nPa Pa^-1 day^-1) reductive SO₂ detoxification via growth (and/or phloem export of SO₄ ^2-) is not kinetically overburdened. Under these conditions only 30% of the annual SO₂ uptake is detoxified via SO₄ ^2- formation and spruce decline is small or absent. On the basis of the critical value R0.07 nPa Pa^-1 day^-1 recommended SO₂ immission limits can be deduced on a mere ecophysiological basis. These deduced values are close to the proposed SO₂ immission limits of the IUFRO, WHO and the UNECE.     

Gas exchange and SO2 fumigation studies with irrigated and unirrigated field grown Diplacus aurantiacus and Heteromeles arbutifolia

Summary Experiments were performed on an evergreen (Heteromeles arbutifolia) and a drought deciduous shrub (Diplacus aurantiacus) to determine, 1) whether approaches for evaluating SO₂ absorption by leaves in laboratory studies could be extended to field studies, 2) the effects of irrigation on metabolism and SO₂ responses of the study species during a season when water was limiting, 3) to interpret SO₂ responses on the basis of SO₂ flux rates. Laboratory-developed approaches for evaluating SO₂ absorption by leaves were found to be suitable for use with field plants, despite field plants having lower gas exchange rates. Supplementing water during times of deficit did not override all the biological and environmental factors that limited photosynthesis (A). Irrigation increased leaf longevity of D. aurantiacus, and stomatal conductance to water vapour (g); g was also shown to increase with H. arbutifolia on irrigation. Irrigation profoundly influenced plant response to SO₂. Unwatered D. aurantiacus had only a small g and therefore a reduced capacity to absorb SO₂ and respond to SO₂; which resulted in apparent SO₂ avoidance. Water availability and SO₂ both affect g and therefore, SO₂ flux rates into the mesophyll. Different ambient SO₂ concentrations of 8.3 and 26.2 mol m^-3 (0.2 and 0.6 ppm) were both found to result in similar SO₂ flux rates into the leaf, due to variations in g in response to water availability. Changes in g did not always result in changes in A, implying that carbon fixation may be little affected by some SO₂ exposures, although still potentially affecting such processes as maintenance of leaf water potential, transpirational cooling and nutrient uptake.Abbreviations SO₂ sulphur dioxide - A net photosynthesis - E transpiration - g stomatal conductance to water vapour - W Water vapour mole fraction difference between the leaf and air - WUE water use efficiency (mol CO₂ uptake per mol H₂O transpired)     

Abscisic acid in shoots and roots of Scots pine (Pinus sylvestris L.) seedlings grown in controlled long-day and short-day environments

Scots pine (Pinus sylvestris L.) seedlings grown in nutrient solution in controlled-environment chambers were used. The effects of a shortday (SD, early autumn) treatment on growth and the content of free and alkaline hydrolysable abscisic acid (ABA) in shoots and roots were investigated. The weekly relative growth rates of seedlings grown continuously under long-day (LD, summer) conditions were stable at approx. 0.08 g g^–1 d^–1 between weeks four and eight from germination. Weekly relative growth rates of seedlings transferred to SD conditions decreased rapidly to a then stable level of approx. 0.04 g g^–1 d⁰¹. Shoot elongation ceased within two weeks of SD treatment. The content of both free and alkaline hydrolysable ABA was approx. 40–50% higher in shoots of seedlings grown for five weeks in LD plus one week in SD than in shoots of seedlings grown for five or six weeks in LD. Two additional weeks of SD did not change the free ABA content. Three weeks in simulated late autumn (SD but decreased temperatures) and three weeks in simulated winter (lower light intensity and temperature) further increased the content of free ABA in the shoots. A transfer back to LD conditions reduced the ABA content to a level equal to the level found during the first LD period. The recovery of radioactive ABA at certain times after application ofr[³H] ABA was the same in shoots and roots of LD-grown and SD-treated seedlings.Abbreviations ABA abscisic acid - LD long day(s) - RGR₇ weekly relative growth rates - SD short day(s)     

Detoxification of N-(phosphonoacetyl)-L-aspartate by carrot cells in suspension culture

Phototropic reversal of Phycomyces sporangiophores can be elicited by a change to darkness during steady-state phototropism. The reversal lasts 25–30 min under these conditions. Control experiments show that the reversal is not caused by gravitropism. Tropic reversal is also elicited by the removal of a barrier during an avoidance response, showing that the reversal occurs at the output of the sensory transduction chain.     

p-Coumaric acid — a monomer in the sporopollenin skeleton

Sporopollenin obtained from wings of Pinus mugo (Turra) pollen was analysed by pyrolysis mass spectrometry. In the spectrum, mass peaks which are characteristic for p-coumaric acid were dominant. p-Coumaric acid was the main degradation compound when the wing material was treated by a gentle method using AII₃, and also when the remaining residue of the treated sporopollenin material was saponified. It is therefore assumed that p-coumaric acid is a genuine structural unit in the sporopollenin skeleton. In addition, the effects of AII₃ treatment indicate that the p-coumaric acid might be bound by ether linkages.Abbreviations HPLC high-performance liquid chromatography - MS mass spectrometry - TLC thin-layer chromatography     

Interactions of SO2 with other environmental stresses in influencing leaf gas exchange

Summary Leaves of two field growing co-occuring perennial shrubs (drought-deciduous Diplacus aurantiacus and the evergreen Heteromeles arbutifolia) from the Californian chaparral were exposed to small doses of SO₂. During this exposure the leaf environment was manipulated to determine how the presence of SO₂ alters the response of gas exchange to other environmental stresses. The data show that no direct changes in stomatal conductance (g) or net assimilation rate (A) could be attributed to short-term (7 h) SO₂ (4.2 mol m^-3, 0.1 l l^-1) exposure. D. aurantiacus leaves possessed features which demonstrate that they were sensitive to changes in environment e.g. light flux and atmospheric relative humidity. The interspecific differences in stomatal sensitivity to water vapour were extremely important, as relative humidity is a major factor influencing carbon fixation and the rate of pollutant absorption. Conditions of high relative humidity and high xylem water potentials are suggested to pre-dispose leaves of D. aurantiacus to greater pollutant doses than the more stomatally-conservative evergreen, H. arbutifolia. In the presence of SO₂ there was some indication of increased g for both D. aurantiacus and H. arbutifolia as W became smaller. This SO₂-effect was only obvious as increasing atmospheric humidity induced further stomatal opening. The important consequences of an SO₂ enhanced g, were a reduction in WUE, which may cause earlier leaf abscission and a concomitant decline in productivity.Abbreviations A net photosynthesis - A _max maximum rate light saturated photosynthesis - E transpiration; g stomatal conductance to water vapour - QY apparent incident quantum yield - W water vapour mole fraction difference between the leaf and the air - SO₂ Sulphur dioxide - WUE water use efficiency (mol CO₂ fixed per mol H₂O^-1 transpired)     

Differences in the response sensitivity of stomatal index to atmospheric CO2 among four genera of Cupressaceae conifers

Background and Aims

The inverse relationship between stomatal density (SD: number of stomata per mm² leaf area) and atmospheric concentration of CO₂ ([CO₂]) permits the use of plants as proxies of palaeo-atmospheric CO₂. Many stomatal reconstructions of palaeo-[CO₂] are based upon multiple fossil species. However, it is unclear how plants respond to [CO₂] across genus, family or ecotype in terms of SD or stomatal index (SI: ratio of stomata to epidermal cells). This study analysed the stomatal numbers of conifers from the ancient family Cupressaceae, in order to examine the nature of the SI–[CO₂] relationship, and potential implications for stomatal reconstructions of palaeo-[CO₂].

Methods

Stomatal frequency measurements were taken from historical herbarium specimens of Athrotaxis cupressoides, Tetraclinis articulata and four Callitris species, and live A. cupressoides grown under CO₂-enrichment (370, 470, 570 and 670 p.p.m. CO₂).

Key Results

T. articulata, C. columnaris and C. rhomboidea displayed significant reductions in SI with rising [CO₂]; by contrast, A. cupressoides, C. preissii and C. oblonga show no response in SI. However, A. cupressoides does reduce SI to increases in [CO₂] above current ambient (approx. 380 p.p.m. CO₂). This dataset suggests that a shared consistent SI–[CO₂] relationship is not apparent across the genus Callitris.

Conclusions

The present findings suggest that it is not possible to generalize how conifer species respond to fluctuations in [CO₂] based upon taxonomic relatedness or habitat. This apparent lack of a consistent response, in conjunction with high variability in SI, indicates that reconstructions of absolute palaeo-[CO₂] based at the genus level, or upon multiple species for discrete intervals of time are not as reliable as those based on a single or multiple temporally overlapping species.     

Sulfur accumulation in western wheatgrass exposed to three controlled SO2 concentrations

Summary Sulfur concentrations of western wheatgrass tillers and individual leaves were measured from plants exposed to four SO₂ concentrations (9, 52, 105 and 183 g·m^–3). Sulfur concentration of plants was a linear function of either time of exposure or concentration.Young leaves and the youngest portion of leaves contained less sulfur than their older counterparts irregardless of whether they had or had not been exposed to SO₂.Current hypotheses which relate plant sensitivity to amount of sulfur taken up do not apply for western wheatgrass.