bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photosynthetic performance, chloroplast pigments and mineral content of Norway spruce (Picea abies (L.) Karst.) exposed to SO2 and O3 in an open‐air fumigation experiment
Authors: WEDLER M. , WEIKERT R. M. , LIPPERT M. 
Published: April 2006

ABSTRACTPhotosynthetic performance, mineral content and chloroplast pigments were investigated in August‐September 1988 and 1989 in Norway spruce trees (Picea abies (L.) Karst.) exposed to SO2, and O3 in an open‐air fumigation facility at Liphook, England. The data do not suggest a treatment effect on the mineral content of the needles in terms of nutrient leaching from the foliage. In addition, there were no direct SO2 and/or O3 effects on the content and/or composition of the chloroplast pigments. However, the long‐term application of SO2 resulted in a depression of net photosynthesis under light saturation and ambient CO2 (A 340) which was probably caused by a treatment‐related depression of the carboxylation efficiency (CE). In 1989, the supposed treatment effects were apparently masked by an insufficient N‐supply and probably also by low water availability during summer. However, fumigation appeared to accelerate an N‐deficiency‐related decrease of CE, stomatal closure and the age‐dependent development of the chlorophyll content of the needles. In 1989, an observed depression of the photosynthetic capacity (A2500) was in part accompanied by a decrease in light use efficiency (α), suggesting an enhanced photosensitivity resulting from the impact of several possible interacting stresses (drought, N deficiency and fumigation). The results support the general conclusion that long‐term low‐level SO2 dosage adversely affects the photosynthetic performance of the needle, whether directly or indirectly, and may also interact with other environmental stresses. The findings of our investigations are discussed with regard to the hypothesis of forest decline in the mountain regions of the Fichtelgebirge (north‐eastern Bavaria, Germany).
Leaf surface properties of Norway spruce needles exposed to sulphur dioxide and ozone in an open‐air fumigation system at Liphook
Authors: CAPE J. N. , SHEPPARD L. J. , BINNIE J. 
Published: April 2006

ABSTRACTSamples of current‐year and 1‐year‐old foliage were taken from Norway spruce (Picea abies (L.) Karst.) trees in April 1991, 4 months after a 3–4 year controlled fumigation with O3 and SO2 in the open at Liphook, south‐east England. Trees were grown in seven plots, and treated in a factorial design with three levels of SO2 and two levels of O3 (ambient and c. 1.3 × ambient), with an extra ambient air plot. All statistical analyses were made on plot means.Leaf wettability, as measured by the contact angle of water droplets, was significantly affected by needle age and by SO2 treatment (P≤0–05. in older needles, decreasing with increasing SO2 concentration. There was no effect of O3 on wettability, and no effect of any treatment on amounts of surface wax extracted by immersion of needles in chloroform. Electrolyte leakage rates from detached current‐year needles were not affected by prior exposure to O3, but decreased significantly (P= 0.034) with increasing exposure to SO2. There was no detectable effect of fumigation on the rate of water loss from detached needles. Similarly, there was no effect of fumigation on the dry weight/fresh weight ratio of needles. The total sulphur content of needles increased significantly (P≤0.0001) with exposure to SO2 and with needle age. Amounts of water‐extractable sulphate, however, varied greatly among plots, but with no pattern with respect to fumigation treatment.It is concluded that leaf wettability and electrolyte leakage rates may be good indicators of the persistent effects of SO2 on Norway spruce growing in the open air, and that the observed changes in leaf surface properties in response to SO2 fumigation have implications for the processes, both biotic and abiotic, that occur on leaf surfaces.
Effect of open‐air fumigation with sulphur dioxide and ozone on phyllosphere and endophytic fungi of conifer needles
Authors: MAGAN N. , KIRKWOOD I. A. , MCLEOD A. R. , SMITH M. K. 
Published: April 2006

ABSTRACTThe phyllosphere microbial populations inhabiting the needles of three conifer species, Scots pine (Pinus sylvestris L.), Sitka spruce (Picea sitchensis L.) and Norway spruce (Picea abies (L.) Karst.), exposed to SO2 and O3, in an open‐air fumigation experiment were analysed over a 3 year period using serial dilution after washing, direct plating and a fluorescein diacetate (FDA) enzyme assay. Total fungal populations ranged from 102 to 105 colonyforming units (CPU) g−1 fresh weight of needles. The dominant fungi isolated from needles varied with tree species and isolation technique; Aureobasidium pullulans (de Bary) Arnaud was most common on Scots pine and Norway spruce and white yeasts on Sitka spruce using the dilution plating method. However, direct plating of needle segments onto culture media indicated that Sclerophoma pythiophila (Corda) Hohnel was dominant on Scots pine and A. pullulans on Sitka and Norway spruce. Green needles of Sitka spruce were found to be endophytically colonized by Rhizosphaera kalkhoffii Bubak, but seldom by Lophodermium piceae (Fuckel) Hohn during extensive sampling in 1990. Statistical analyses revealed significant differences (P<0.05) between plots in the 3 year mean of the total fungal populations or the fungal biomass (FDA assay) on all three tree species. Differences between plots were also observed for a number of dominant component species. Data were also analysed for treatment effects. A significant effect of SO2 treatment was observed on the total fungal populations on Sitka spruce (P<0.05) which were reduced markedly by the low‐SO2 treatment, while the O3 treatment caused a significant increase in total fungal numbers on Scots pine (P<0.05). The FDA activity on needles of both Scots pine and Sitka spruce was noticeably higher in the 03‐only treatment plot, but the overall O3 effect was not significant. Treatment effects were also detected on the occurrence of component species. The serial dilution method revealed an SO2 effect (P<0.05) of a reduction in the occurrence of pink yeasts on Sitka spruce and an O3 effect (P<0.05) of an increase in the occurrence of S. pythiophila on Sitka spruce (P<0.01) but a decrease of Epicoccum nigrum Link and Cladosporium spp. on Scots pine. The direct‐plating method revealed an SO2 effect of an increase in S. pythiophila on Norway spruce (P<0.05). Ozone treatment caused a significant increase in the isolation of a black strain of A. pullulans on Norway spruce (P<0.05). Endophytic colonization of Sitka spruce needles by R. kalkhoffii was found to be increased on two occasions by O3 exposure.
Effects of sulphur dioxide and ozone on stilbenes and disease resistance in spruce trees from the Liphook Forest Fumigation Project
Authors: PEARCE R. B. , McLEOD A. R. 
Published: April 2006

ABSTRACTLevels of the stilbene glucosides astringin and isorhapontin, the main constitutive antifungal compounds in bark tissues of spruce trees, were not altered in young Picea sitchensis (Bong.) Carr. or Picea abies (L.) Karst. trees exposed to sulphur dioxide and ozone in the Liphook Forest Fumigation Project. These trees had received computer‐controlled fumigation treatments with two levels of SO2 (long‐term means 13 and 22nmol mol−1) or one level of O3 (1–3.times ambient), or a combination of these treatments, from spring until December.Resistance of bark tissues from these trees to colonization by the root‐ and butt‐rot pathogen Heterobasidion annosum (Fr.) Bref., assessed in vitro using excised stem lengths, was not significantly altered in fumigated plants compared with those exposed to ambient pollutant levels only. This study therefore provided no evidence for altered disease resistance in P. abies and P. sitchensis trees exposed to SO2 and O3.
The effects of open‐air fumigation with sulphur dioxide on the decomposition of sycamore (Acer pseudoplatanus L.) leaf litters from polluted and unpolluted woodlands
Authors: NEWSHAM K. K. , INESON P. , FRANKLAND J. C. 
Published: April 2006

ABSTRACTSycamore (Acer pseudoplatanus L.) leaf litters from 15 woodlands exposed to a broad range of ambient sulphur dioxide (SO2) concentrations were fumigated with environmentally realistic concentrations (ll‐20nmol mol−1) of SO2, for 166 d in an open‐air fumigation experiment. Fumigation of the sycamore litters significantly increased sulphate‐S and proton leaching, and decreased calcium, magnesium and potassium concentrations in leachates and leaf tissues. Leaf litters from relatively unpolluted woodlands showed a tendency to lose higher amounts of sulphate‐S, calcium, magnesium and nitrate‐N in leachates than litters from polluted sites when exposed to elevated levels of SO2 in treatment plots.Fumigation inhibited the decomposition rates (CO2 evolution) of the leaf litters. Marked changes in the composition of the saprotrophic fungal communities in SO2‐fumigated leaf litters were also recorded, but fungal communities and responses to SO2, were similar between woodlands. There was no evidence from our data to suggest that resistance to SO2, was developed in decomposer mycofloras in woodlands more frequently polluted by the gas.
Populations of root‐feeding aphids in the Liphook forest fumigation experiment
Authors: SALT D. T. , WHITTAKER J. B. 
Published: April 2006

ABSTRACTThree species of root aphid (Pachypappa vesicalis Koch, Pachypappa tremulae L. and Prociphilus (Stagona) xylostei De Geer) were found feeding on Norway spruce [Picea abies (L.) Karsten] that were exposed to elevated concentrations of O3, and/or SO2 in a field manipulation experiment at Liphook, England. The experiment exposed conifer trees to controlled concentrations of these gases between 1987 and 1990. Root‐aphid populations feeding on Norway spruce were monitored in autumn 1990, the third year of fumigation and in autumn 1991, 10 months after fumigation had ceased. In 1990 the numbers of aphids in the high‐SO2, high‐SO2+ O3 and O3 treatments were significantly less than in ambient plots. Although after fumigation had ceased in 1991 the ambient plots still had higher numbers than the treatment plots, most of these differences were no longer statistically significant. In all plots sampled, total numbers of root aphids were higher in 1991 than in 1990. These results indicate that the numbers of root aphids in the experiment were negatively related to pollution levels. This relationship is the same as that shown in controlled laboratory experiments and is the converse of that generally reported in experiments using shoot‐feeding aphids.
A reinterpretation of stomatal responses to humidity
Authors: MONTEITH J. L. 
Published: April 2006

ABSTRACTThe stomatal conductance (g) for single leaves and the equivalent canopy conductance for stands of vegetation are often represented in models as empirical functions of saturation vapour pressure deficit or relative humidity. The mechanistic basis of this dependence is very weak. A reanalysis of 52 sets of measurements on 16 species supports the conclusion of Mott & Parkhurst (1991, Plant, Cell and Environment 14, 509–515) that stomata respond to the rate of transpiration (E) rather than to humidity per se. In general, ∂g/∂E is negative and constant so that the relation between g and E can be defined by two parameters: a maximum conductance gm obtained by extrapolation to zero transpiration, and a maximum rate of transpiration Em obtained by extrapolation to zero conductance. Both parameters are shown to be functions of temperature, CO2 concentration, and soil water content. Exceptionally, transpiration rate and conductance may decrease together in very dry air, possibly because of patchy closure of stomata.
The cellular pathway of photosynthate transfer in the developing wheat grain. II. A structural analysis and histochemical studies of the pathway from the crease phloem to the endosperm cavity
Authors: WANG H. L. , OFFLER C. E. , PATRICK J. W. 
Published: April 2006

ABSTRACTIn the developing wheat grain, photosynthate is transferred longitudinally along the crease phloem and then laterally into the endosperm cavity through the crease vascular parenchyma, pigment strand and nucellar projection. In order to clarify this cellular pathway of photosynthate unloading, and hence the controlling mechanism of grain filling, the potential for symplastic and apoplastic transfer was examined through structural and histochemical studies on these tissue types. It was found that cells in the crease region from the phloem to the nucellar projection are interconnected by numerous plasmodesmata and have dense cytoplasm with abundant mitochondria. Histochemical studies confirmed that, at the stage of grain development studied, an apoplastic barrier exists in the cell walls of the pigment strand. This barrier is composed of lignin, phenolics and suberin. The potential capacity for symplastic transfer, determined by measuring plasmodesmatal frequencies and computing potential sucrose fluxes through these plasmodesmata, indicated that there is sufficient plasmodesmatal cross‐sectional area to support symplastic unloading of photosynthate at the rate required for normal grain growth. The potential capacity for membrane transport of sucrose to the apoplast was assessed by measuring plasma membrane surface areas of the various cell types and computing potential plasma membrane fluxes of sucrose. These fluxes indicated that the combined plasma membrane surface areas of the sieve element–companion cell (se–cc) complexes, vascular parenchyma and pigment strand are not sufficient to allow sucrose transfer to the apoplast at the observed rates. In contrast, the wall ingrowths of the transfer cells in the nucellar projection amplify the membrane surface area up to 22‐fold, supporting the observed rates of sucrose transfer into the endosperm cavity. We conclude that photosynthate moves via the symplast from the se–cc complexes to the nucellar projection transfer cells, from where it is transferred across the plasma membrane into the endosperm cavity. The apoplastic barrier in the pigment strand is considered to restrict solute movement to the symplast and block apoplastic solute exchange between maternal and embryonic tissues. The implications of this cellular pathway in relation to the control of photosynthate transfer in the developing grain are discussed.
Effects of continuous leaf wetness on photosynthesis: adverse aspects of rainfall
Authors: ISHIBASHI M. , TERASHIMA I. 
Published: April 2006

ABSTRACTAbove‐ground parts of Phaseolus vulgaris L. plants were treated with artificial misty rain (‘rain’) in a growth chamber to investigate the effects of leaf wetness on photosynthetic performance. The following results were obtained. (1) Stomata closed completely within 2 min of the onset of continuous ‘rain’ application and gradually opened to half the original aperture by 60 min. The rate of CO2 exchange measured on such wet leaves changed in parallel with the changes in stomatal aperture and attained 60 to 70% of the control level by 1h. (2) The dependence of the rate of leaf photosynthesis, A, on the intercellular CO2 concentration, ci [A(ci) relationship], examined in thoroughly dried leaves which had been treated with ‘rain’ did not change until after 4 h of treatment. However, leaves treated for 6h showed discernible decreases in A at high ci (ci>500μmolmol −1). The photosynthetic rate of leaves treated with ‘rain’ for 24 h was reduced at all ci, and A at the ambient CO2 concentration of 350μmolmol−1 was 60 to 70% of that of the control level. The rate of photosynthesis did not recover even after 3 d of treatment of the plants in a dry environment. These results clearly indicate that leaf wetness causes not only instantaneous suppression of photosynthesis but also chronic damage to the photosynthetic apparatus. Potential effects of leaf wetness on photosynthetic performance in nature are also discussed.
Two modes of bicarbonate utilization in the marine green macroalga Ulva lactuca
Authors: AXELSSON L. , RYBERG H. , BEER S. 
Published: April 2006

ABSTRACTThe green marine macroalga Ulva lactuca L. was found to be able to utilize HCO3− from sea water in two ways. When grown in flowing natural sea water at 16°C under constant dim irradiance, photosynthesis at pH8.4 was suppressed by acetazolamide but unaffected by 4,4′‐diisothiocyanostilbene‐2,2′‐disulphonate. These responses indicate that photosynthetic HCO3− utilization was via extracellular carbonic anhydrase (CA) ‐mediated dehydration followed by CO2 uptake. The algae were therefore described as being in a ‘CA state’. If treated for more than 10 h in a sea water flow‐through system at pH9.8, these thalli became insensitive to acetazolamide but sensitive to 4,4′‐diisothiocyanostilbene‐2,2′‐disulphonate. This suggests the involvement of an anion exchanger (AE) in the direct uptake of HCO3−, and these plants were accordingly described as being in an ‘AE state’. Such thalli showed an approximately 10‐fold higher apparent affinity for HCO3− (at pH9.4) than those in the ‘CA state’, while thalli of both states showed a very high apparent affinity for CO2. These results suggest that the two modes of HCO3− utilization constitute two ways in which inorganic carbon may enter the Ulva lactuca cells, with the direct entry of HCO3−, characterizing the ‘AE state’, being inducible and possibly functioning as a complementary uptake system at high external pH values (e.g. under conditions conducive to high photosynthetic rates). Both mechanisms of entry appear to be connected to concentrating CO2 inside the cell, probably via a separate mechanism operating intracellularly.
Water movement through Quercus rubra I. Leaf water potential and conductance during polycyclic growth
Authors: REN Z. , SUCOFF E. 
Published: April 2006

ABSTRACTTwo experiments examined simultaneous changes in leaf area (AL), root length (Lr), stomatal conductance (gs), leaf water potential (ΨL), transpiration and hydraulic plant conductance per unit leaf area (G) during the first three shoot cycles of northern red oak (Quercus rubra L.) grown under favourable and controlled conditions. Each shoot cycle consisted of bud swell, stem elongation, leaf expansion and rest; roots grew almost continuously. The gs of all leaves decreased substantially while leaves of the newest flush were expanding and increased modestly when seedling leaf area remained constant. Overall, gs decreased. The ΨL of mature leaves decreased during leaf expansion and increased by an equivalent amount during intervening periods. Possible explanations for the paired changes in gs and ΨL are considered. Changes in G closely paralleled those of canopy gs. These parallel changes during polycyclic seedling growth should act to keep seedling ΨL relatively constant as plant size increases and thereby help prevent ΨL from dropping to levels that would cause runaway embolism.
Evaluation of the heat pulse velocity technique for measurement of sap flow in rainforest and eucalypt forest species of south‐eastern Australia
Authors: BARRETT D. J. , HATTON T. J. , ASH J. E. , BALL M. C. 
Published: April 2006

ABSTRACTSap flow in the stems of two cut saplings each of Eucalyptus maculata (a canopy eucalypt forest tree), Doryphora sassafras and Ceratopetalum apetalum (both canopy rainforest trees of south‐eastern coastal Australia) was measured by the heat pulse velocity technique and compared with water uptake from a potometer. Scanning electron micrographs of wounding caused by implantation of temperature sensor and heater probes into the sapwood showed that wounding was similar in rainforest and eucalypt species and was elliptical in shape. A circular wound has been implicitly assumed in previous studies. Accurate measurements of sapling water use were obtained using the smaller transverse wound dimension rather than the larger longitudinal dimension because maximum disruption of sap flow through the xylem vessels occurred in the transverse plane. Accurate measurements of sap flux were obtained above a minimum threshold sap velocity. These velocities were 15·7,10·9 and 9·4 cm h−1 for E. maculata, C. apetalum and D. sassafras, respectively. Below the threshold sap velocity, however, sap flow could not be accurately calculated from measurements of heat pulse velocity. The minimum threshold sap velocity appeared to be determined by probe construction and xylem anatomy. Despite the elliptical wounding and inaccurate measurement of sap flow below the threshold sap velocity, total sap flow over the experimental period for two saplings of each species was within 7% of water use measured by the potometer.
Temperature‐dependent changes of electric potential differences on opposite sides of the tepals of Eranthis in relation to thermonastic responses
Authors: HEJNOWICZ Z. , TREBACZ K. , SIEVERS A. 
Published: April 2006

ABSTRACTElectric potential differences (PDs) across the plasma membrane in cells of tepals of Eranthis hyemalis (L.) Salisb. were recorded under a regime in which the temperature was changed rapidly between two levels of approximately 8 and 19°C. The warming of an intact tepal resulted in a transient small increase in the magnitude of PD followed by a substantial long‐lasting depolarization. Upon cooling the reverse response occurred: a small transient depolarization was followed by a substantial hyperpolarization. These responses were more pronounced in the epidermis on the abaxial side of the tepal than in that on the adaxial side, indicating an electrophysiological dorsiventrality of the tepals which may be related to thermonastic movements through differential proton secretion on the two sides.
Abscisic acid concentrations and fluxes in droughted conifer saplings
Authors: JACKSON G. E. , IRVINE J. , GRACE J. , KHALIL A. A. M. 
Published: April 2006

ABSTRACTWe present the first study of abscisic acid (ABA) concentrations and fluxes in the xylem sap of conifers during a drought cycle. In both Pinus sylvestris and Picea sitchensis the concentration of ABA in the sap rose 11‐fold as the drought progressed. There were clear diurnal trends in this concentration, which reached its maximum (6–8.ininol ABA m−3) near the middle of the day. The fluxes of ABA were calculated by multiplying the xylem ABA concentration by the sap flow rate. The ABA fluxes in the droughted plants in the middle of the day were usually no higher than those of the controls, as a result of the very low sap flow in the droughted plants at that time. However, the ABA flux in the droughted plants was higher than in the controls in the morning, and we postulate that the stomata are responding to these ‘morning doses’Stomatal conductance, gs, could not be related statistically to leaf turgor or to the ABA flux. However, £s did display a negative exponential relationship with ABA concentration in the xylem.Pinus displayed more acclimation to drought than Picea, Its ABA concentration rose and its stomatal conductance fell at day 6 of the drought, as opposed to day 17 for Picea, and its osmotic potential fell during the drought treatment.