bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrogen allocation in ponderosa pine seedlings exposed to interacting ozone and drought stresses
Authors: TEMPLE PATRICK J. , RIECHERS GEORGE H. 
Published: April 2006

summaryNitrogen (N) resorbed from foliage before leaf abscission is a significant source of N for new leaves. The widely distributed photochemical air pollutant ozone (O3) accelerates foliar senescence and leaf abscission and therefore could interfere with the process of N resorption. The objective of this study was to determine the effects of O. and drought stress on the N economy of ponderosa pine (Pinus ponderosaLaws.), a species highly susceptible to O Potted ponderosa pine trees (2‐yr‐old) were exposed for 3 yr to three concentrations of O3and two soil water regimes in open‐top chambers in the Sierra Nevada mountains of California. One‐third of the trees was harvested at the end of each exposure season and each age class of needles, branches, stems, coarse roots, fine roots, and leaf litter was analysed for N. Exposure to a seasonal O3mean of 88 ppb increased N concentrations in pine foliage, particularly in current‐year needles. Current‐year foliage from well‐watered (WW) trees exposed to elevated O averaged 34% higher N than that from trees in charcoal‐filtered (CF) chambers. Drought‐stressed (DS) trees from all O3treatments averaged 10% higher N in current‐year needles than WW seedlings. Resorbed N from older age classes of needles from WW trees increased from 32% of current‐year needle N in CF seedlings to 51% of current‐year N in the high O3treatment. Nitrogen resorbed from older needles of DS trees increased from 15% in CF to 38% of current‐year N in the high O3treatment. Thus O3‐injured ponderosa pine seedlings increased resorption of N from older needles and increased partitioning of N to current‐year foliage. The increased N in current‐year needles facilitated increased rates of photosynthesis in these needles, thus partly compensating for the O3‐induced loss of older leaves.
Morphological and molecular variation in natural populations of Betula
Authors: HOWLAND D. E. , OLIVER R. P. , DAVY A. J. 
Published: April 2006

summaryMolecular variation within morphologically variable natural populations of Betula pendula Roth, (diploid) and Betula pubescens Ehrh. (tetraploid) was investigated using RFLP and RAPD techniques. RFLP analysis of rDNA showed a high degree of polymorphism within and between individuals of both cytotypes in spacer length variation. Analysis of randomly amplified genomic DNA fragments, within one population, showed little differentiation between cytotypes. In East Anglian populations, diploid and tetraploid Betula are distinct neither on the basis of morphological nor molecular characters.
Variation in moisture contents between bulk soil and the rhizosheath of wheat (Triticum aestivum L. cv. Wembley)
Authors: YOUNG I. M. 
Published: April 2006

summaryThere is conflicting evidence as to whether rhizosheath soil can be wetter or drier than bulk soil. The gravimetric moisture contents of bulk soil and the rhizosheath of wheat were determined for plants grown in a glasshouse over a range of dry bulk densities (1.0, 1.1 and 1.3 Mg m−3). Plants were also grown in soil at 1.1 Mg m−3 at 15 °C in a controlled environment. No significant differences in soil moistures over the initial dry bulk density range examined were found. Overall, rhizosheath soil was significantly (P < 0.05) wetter than bulk soil. In the second experiment, under controlled environment conditions, significant differences (P < 0.05) were found only at the lowest depth range examined. The mechanism behind preferential wetting of the rhizosheath is examined with reference to other work on transfer of water to soil from roots, physical changes in the rhizosheath, and root exudates. The most likely explanation of these results is that the presence of mucigel within the rhizosheath increases the water‐holding capacity of that soil.
Influence of ectomycorrhizal infection on the rhizosphere pH around roots of maritime pine (Pinus pinaster Soland in Ait.)
Authors: RIGOU L. , MIGNARD E. , PLASSARD C. , ARVIEU J. C. , REMY J. C. 
Published: April 2006

summaryThis study examined the influence of mycorrhizal infection on ionic exchanges by roots, by measuring rhizosphere pH and the quantities of protons released by roots of mycorrhizal and non‐mycorrhizal pine (Pinus pinaster × Suillus collinitus). The effect of inoculation was measured around individual roots and compared with the effect on the root system as a whole, with root heterogeneity thus being taken into account in structural terms and in terms of functioning. Inoculation enhanced significantly the capacity of roots to release protons in a medium with a neutral pH, but the strength of reaction varied with the part of the root involved. This enhancement could possibly be used to improve the bioavailability of compounds not readily soluble in particular chemical conditions of the soil.
Attributes of the nitrogen uptake systems of maize (Zea mays L.): maximal suppression by exposure to both nitrate and ammonium
Authors: JACKSON W. A. , VOLK R. J. 
Published: April 2006

summaryHigher plants arc commonly exposed to rapid changes in the amounts and proportions of ammonium and nitrate in their root environment. Some of the potential consequences of such changes have been determined by examining the suppressive effects of growing maize (Zea mays L.) seedlings with a high concentration (3 mM) of nitrogen on the subsequent uptake of nitrogen from a more dilute (0.2 mM) solution. To document the interactive role of nitrate and ammonium supply in suppression, ratios of these ions in the growth solution were maintained at 3:0, 2:1, 1:2 and 0:3. Rates of nitrate and ammonium uptake were then measured during initial (0–1 h) exposure to 0.2 mM KNO3 or NH4NO3 and hourly during a subsequent 7 h period of adaptation to the dilute solutions.Maximal suppression of nitrate uptake occurred only when both nitrate and ammonium were present (2: 1 and 1:2) during prior growth. Nitrate uptake rates increased two‐ to three‐fold as the seedlings adapted to the dilute KNO3 solution, but the presence of ammonium with nitrate in the prior growth solution restricted the rate and extent of recovery from suppression. Recovery was further restricted when ambient ammonium was present during the adaptation period. Neither the magnitude of suppression nor the rate and extent of recovery was readily explained by (a) the proportion of nitrate and ammonium present during prior growth, (b) carbohydrate concentrations in root and shoot tissues, (c) concentrations of nitrate and ammonium in the root tissue, or (d) indirect effects of ammonium on potassium uptake.Total nitrate reduction by the entire plant in the 8 h adaptation period decreased as the proportion of ammonium in the prior growth solution increased. Ambient ammonium restricted nitrate reduction only in seedlings previously grown entirely with ammonium. Thus the effect of ambient ammonium on nitrate reduction by the whole plant differed substantially from that on nitrate uptake. Since nearly all the ammonium taken up by the roots was assimilated, as well as that generated by nitrate reduction, it appears that carbohydrate supply did not limit the observed uptake of ammonium and nitrate. The accumulation in roots of both nitrate and specific metabolites of ammonium serving as negative electors could account for most of the observations.
Canopy gas exchange and growth of upland pasture swards in elevated CO2
Authors: WOLFENDEN J. , DIGGLE P. J. 
Published: April 2006

summaryVegetation monoliths (450 × 450 mm) from two contrasting upland grassland communities were grown in Solardomes in either ambient air or ambient air enriched with 250 ppm CO2 During the first two growing seasons measurements of canopy gas exchange showed that rates of photosynthesis of limestone swards were enhanced by growth in elevated CO2, by approx. 50% during spring and early summer. Although canopy respiration was also greater in elevated CO2 the overall effect was an average increase of 33% in net CO2 assimilation. Enhanced respiration rates persisted into the autumn, whereas the effect on photosynthesis diminished through the growing season, so that in September swards growing in high CO2 had net photosynthesis rates similar to, or even lower than those in ambient air. This response varied between swards of differing species composition. In acidic grassland no significant effects of CO2 on respiration or net CO2 uptake rates were detected at any time.The above ground productivity of limestone grassland was measured in several harvests throughout both seasons, and was not affected by CO2 concentration at any time. Similarly, the acidic grassland, harvested at the end of the second season, showed no significant effect of CO2 on above‐ground biomass. The results suggest that increasing atmospheric CO2 concentration is unlikely to cause large changes in net primary productivity in these grasslands.
Characterization of acid invertase from the snow mould Monographella nivalis: a mesophilic enzyme from a psychrophilic fungus
Authors: CAIRNS ANDREW J. , HOWARTH CATHERINE J. , POLLOCK CHRISTOPHER J. 
Published: April 2006

summaryA soluble acid invertase was extracted by mechanical disruption of mycelium of the psychrophile Monographella nivalis grown on sucrose in submerged culture. The crude preparation was stable to incubation at pH 6.2 for 1 h at temperatures up to 47 °C and was stable to handling at room temperature. Half of the initial activity was lost after 1 h at 52 °C and all activity was lost after 1 h at 57 °C. A single isoform with activity against sucrose was detected on both native PAGE and IEF activity gels, exhibiting an isoelectric point of pH 3.6. The activity bound tightly to Concanavalin A‐sepharose and was not displaced by 500 mM α‐methyl mannopyranosidase indicating the enzyme to be a mannose‐containing glycoprotein. By gel filtration, the apparent Mr was determined at 195 kDa. The invertase was purified 106–fold by salt precipitation. The partially purified enzyme exhibited maximal activity at pH 4.2 and apparent Michaelis constants for sucrose of 1.2, 2.0 and 2.6 mM at 3, 9 and 15 °C. The activity increased exponentially with temperature in the range 7–55 °C. Q10 fell with increased temperature giving values of 1.96 between 5 and 15 °C and 1.60 between 40 and 50 °C. Maximal activity was recorded at 55 °C. Arrhenius analysis of temperature data in the range 7–52 °C produced a continuous linear relationship. The activation energy for sucrose hydrolysis was 38.8 kJ mol−1. The thermal stability and thermal kinetic properties of the invertase were similar to those of invertases from mesophilic organisms. The invertase catalysed fructosyl transfer at 13% of the molar activity against sucrose when assayed under conditions analogous to those in culture. The major fructan products were neokestose, isokestose, kestose and an unidentified tetrasaccharide. Traces of larger fructans were also detected. The transient accumulation of fructan in cultures of M. nivalis can he explained as a side reaction of invertase activity. The enzymological and physiological data do not suggest a cryoprotective function for fructan during the growth of the fungus.
The structure and function of the vegetative mycelium of ectomycorrhizal plants
Authors: BENDING GARY D. , READ DAVID J. 
Published: April 2006

summaryThe nutrient mobilizing activities of mycelia of two ectomycorrhizal fungi, Suillus bovinus (Fr.) O. Kuntze and Thelephora terrestris (Ehrh.), were investigated in transparent root observation chambers to which were added discrete weighed samples of organic matter collected from the fermentation horizon of a pine‐forest soil. The mycelia grew from mycorrhizal plants of Pinus sylvestris L. over a homogeneous humified peat and colonized the introduced fermentation horizon organic matter (FHOM). The chronology of intensive mycelial exploitation of the FHOM was followed, and its nutrient status was monitored before and after colonization by the fungal mycelia. The time from initial colonization to early senescence of mycelial patches was c. 40 d. Colonization by S. bovinus reduced concentrations of nitrogen (N), phosphorus (P) and potassium (K.) in FHOM by 23, 22 and 30%, respectively, whereas colonization by T. terrestris led to decreases of N and K of 13 and 21 % respectively, but did not change P concentration. There were increases in calcium and magnesium concentration following colonization by terrestris. Analyses of the inorganic N pool of uncolonized FHOM incubated separately suggested that mineralization rates were inadequate to explain the loss of N from the colonized material. The carbon to nitrogen ratio of material colonized by both fungi increased greatly relative to that in uncolonized material. The significance of these nutrient transfer processes is discussed in relation to element cycling processes in boreal forest ecosystems.
Lack of competition between Frankia and Glomus for infection and colonization of roots of Casuarina equisetifolia (L.)
Authors: SEMPAVALAN J. , WHEELER C. T. , HOOKER J. E. 
Published: April 2006

summary Casuarina eqisetifolia (L.) (L.) seedlings, grown with a limiting supply of mineral N and P, were inoculated with either Frankia or Glomus fasciculatum E3 and subjected to delayed inoculation with the second microsymbiont. Comparison with seedlings inoculated simultaneously with both microsymbionts showed that neither the development of nodules nor mycorrhizal colonization was delayed when seedling were pre‐inoculated for periods of up to 60 d with either Glomus or Frankia, respectively.Mycorrhizal colonization was affected when inoculation with Frankia was delayed for 60 d. Thus, a 60 d delay in Frankia inoculation of Glomus‐inoculated seedlings resulted in a lower percentage mycorrhizal colonization of the root system than in seedlings inoculated earlier with Frankia or simultaneously with Glomus. A similar delay in Glomus inoculation of Frankia‐inoculated seedlings resulted in a 50% reduction in the colonization of the roots with Glomus 60 d after inoculation. Delayed inoculation with either microsymbiont had no long‐term effect on subsequent nodulation.There was a highly significant, linear relationship between log10 (nodule number per plant/%Glomus root colonization) and the time (days) after Frankia or Glomus inoculation, indicating a high degree of coordination between nodulation, mycorrhizal colonization and seedling growth in mineral deficient conditions.These data indicate a co‐operative, but not a competitive interaction between Frankia and Glomus for nodulation and mycorrhizal colonization of Casuarina.
Nitrogen supply as a limiting factor determining the sensitivity of Populus tremuloides Michx. to ozone stress
Authors: PELL E. J. , SINN J. P. , JOHANSEN C. VINTEN 
Published: April 2006

summarySeedlings of trembling aspen (Populus tremuloides Michx.) were grown at six rates of supplemental nitrogen (N). Five of the N rates were sub‐optimal to optimal for growth, whilst the sixth provided an excess of N with no additional growth benefit. The biomass of plants stressed by ozone (O3) in open‐top chambers was significantly reduced at optimal rates of N. Plants which received sub‐optimal or excess N showed no significant effects of O3 on biomass accumulation. Ozone induced two compensatory responses; increased shoot/root ratio and accelerated senescence, at all N rates. Growth rate was strongly influenced by the amount of N supplied, and O3‐induced reductions in total biomass were highly correlated with growth rate. We concluded that when growth rate was small as a result of N limitation, compensatory responses to O3 stress were sufficient to prevent detectable losses in biomass.
Does CO2 modify the effect of SO2 on variegated leaves of Chlorophytum comosum (Thunb) Bak?
Authors: NIEWIADOMSKA EWA , MISZALSKI ZBIGNIEW 
Published: April 2006

summaryStomatal aperture and conductance were greater in the green parts of Chlorophytum comosum (Thunb) Bak var. variegatum leaves than in the white parts. A strong decrease in net photosynthesis (PN) was measured in green parts of the leaves after fumigation with 80 μ 1−1 SO2 for 45 min. However, the inhibitory effect of SO2 on PN was less expressed at 1000 μl−1 CO2 than at 0 and 380μl 1−1 CO2. The decrease in PN after exposure to SO2 was accompanied by closure of the stomata, both in the green and white parts of the leaves, at all tested CO2 concentrations (0, 380 and 1000μl 1−1).Superoxide dismutase (SOD) activity strongly increased at 1000μl l−1 CO2 both in the green and white parts of the leaves as compared with 0 and 380 μl 1−1 CO2, indicating better adaptation to oxidative stress. Exposure to 80μl 1−1 SO2 increased SOD activity at 0 and 380μl 1−1 CO2 but not at 1000μl l−1 CO2.
Effects of ambient ozone on seedlings of Fagus sylvatica L. and Picea abies (L.) Karst
Authors: BRAUN SABINE , FLÜCKIGER WALTER 
Published: April 2006

summaryThe effect of unfiltered versus filtered air was tested on tree seedlings at different sites with prevailing ozone pollution, at different altitudes. Growth and biomass data from different experiments were evaluated in relation to ozone dose above 40 nl l−1during the exposure time. In beech (Fagtis sylvatica L.), biomass was significantly correlated with ozone dose whereas shoot length was not. There was no change in shoot/root ratio but there were more significant reductions in fine root biomass than in shoot biomass. The effect of ozone was cumulative within the duration of the experiments, i.e. from a few months to three years. A cumulative dose of 7 μl 1−1h > 40 nl l−1Per growing season, calculated for 24 h day−1, corresponded to a 10% biomass reduction within three years. Seedlings grown in unfiltered air also exhibited much more severe symptoms of frost injury following a cold winter with rapid temperature change. Laboratory experiments suggest that winter desiccation may have played a more important role than low temperatures, but that medium frost temperatures may cause more latent injuries in seedlings exposed to ambient air. Water loss of detached leaves from unfiltered air was significantly higher later m the season. Both increased chlorosis and premature leaf fall were observed in the beech seedlings grown in unfiltered air, but in different years. The biomass of spruce [Picea abies (L.) Karst.] showed a tendency towards a reduction, but this was not significant within the dose range tested. Three years of fumigation, however, caused increased chlorosis also in the spruce seedlings. Tests with low temperatures suggest that the vitality of the spruce seedlings during winter may also be impaired by the ambient air pollution.
Effects of short‐term ozone exposure on the carbon economy of mature and juvenile Douglas firs [Pseudotsuga menziesii (Mirb.) Franco]
Authors: SMEULDERS S. M. , GORISSEN A. , JOOSTEN N. N. , VAN VEEN J. A. 
Published: April 2006

summaryEffects of short‐term ozone exposure of mature trees were compared with those of seedlings. Both 25‐yr‐old Douglas firs [Pseudotsuga menziesii (Mirb.) Franco] and 3‐yr‐old Douglas fir seedlings were exposed to 0, 200 and 400 μgm−1ozone for about 1.5 wk and then labelled with 14CO2 to study the effect on net photosynthesis, translocation and partitioning of assimilates.In the seedling experiment, two identical growth cabinets with separated shoot and root compartments were used for ozone fumigation and 14C‐labelling. Seedlings were harvested and HC contents in the needles (subdivided into starch, ethanol‐soluble and residue fractions), branches, roots, root/soil respiration and soil residue were determined, together with the total starch content of the needles. Ozone increased the retention of 14C‐photosynthates in the needles. Translocation of carbon to the branches and roots seemed to be inhibited by the highest ozone treatment. The increased 14C‐retention was mainly recovered in the residue fraction of the needles. Total starch content of the needles decreased in the highest ozone treatment.In the experiment with mature trees, terminal shoots were fumigated with ozone and labelled with 14C using three small branch chambers. Carbon distribution was studied after harvest of the branches. Total 14C contents in the needle fractions and the branches were determined, together with the total starch content of the needles. Ozone was found to inhibit net 14CO2 assimilation as well as translocation of 14C‐labelled assimilates from exposed needles to the branch. No effects of ozone were found on the partitioning of 14C among the starch, ethanol‐soluble, and residue fractions of the needles, although amounts in the ethanol‐soluble fraction tended to increase after exposure to ozone.The results indicate that mature and juvenile Douglas firs respond in a similar way to short‐term ozone exposure with regard to carbon translocation. If this similarity also applies to other species, then results from phytotron experiments on ozone and translocation of carbon might gain importance with respect to extrapolation to forest ecosystems.
Exposure of red spruce seedlings to acid mist: importance of droplet composition just prior to drying periods
Authors: HELLER L. I. , SHAW A. J. , JACOBSON J. S. 
Published: April 2006

summaryTwo‐year‐old red spruce(Picea rubensSarg.), raised from seed collected at five locations from Maine to North Carolina, were exposed in a greenhouse to either sulphuric or nitric acid mist (median pH 2–85). Exposures were performed three times a day, four days a week over an eleven‐week period during the growing season. Each exposure consisted of 4 h of misting followed by a 3.75 h drying period. Immediately before each drying period, acidic droplets were either left to dry directly on the foliage or were removed by a 15 min deionized water(diw)rinse.When sulphuric acid droplets dried directly on the foliage, visible injury developed and to a lesser degree the same was true for nitric acid. When acidic droplets were replaced withdimbefore each drying period, foliar injury did not develop despite misting for hundreds of hours at pH values well within the range that has caused visible injury in previous experiments. When acidic droplets dried directly on foliage, needle dry weight was reduced, but differences between sulphuric and nitric acid exposure were not found. No treatment effects were found on terminal shoot length. Treatment responses among seedlings from different seed resources were similar, with greater variation found within provenances than between provenances. We conclude that the composition of liquid on foliage at the end of wet deposition events and the processes occurring during drying periods are important factors in determining the response of red spruce to acidic cloudwater.