bluuebunny/crossref_metadata_2025 huggingface dataset:
Tansley Review No. 82. Strategies of arbuscular mycorrhizal fungi when infecting host plants
Authors: BONFANTE PAOLA , PEROTTO SILVIA
Published: April 2006

summary

Arbuscular mycorrhizal (AM) fungi are ancient Zygomycetes, thought to have colonized the first land plants; today, they are associated with the roots of about 80% of plant species. The symbiosis they form is potentially valuable not only for developmental programmes based on low‐input agriculture, but also as a complex experimental model, where both fungal and host plant growth are regulated. Here we review some recent progress m the area of cell and molecular biology of arbuscular mycorrhizas. Particular attention is given to strategies followed by AM fungi when, as obligate biotrophs, they establish a successful symbiosis with their host plants. Four topics are analysed: (i) parameters controlling fungal growth in the absence and presence of the host root, Le. events of DNA replication and timing of the cell cycle; (ii) mechanical and enzymatic mechanisms which allow the fungus to colonize root tissues, maintaining host viability; (iii) morphological changes induced by AM fungus host cells and, in particular, the formationde novoof a subcellular compartment termed the interface, and (iv) modifications of plant gene expression during fungal colonization, including those involving structural, symbiotic and defence‐related genes.

ContentsSummary3I.Introduction3II.Fungal growth and activatioti of the cell cycle5III.Molecular basis of the colonization process9IV.Plant and fungal morphogenesis during the infection process12V.AM fungi change the pattern of gene expression in host plants17VI.Conclusions18Acknowledgements470References
Partitioning and flows of ions and nutrients in salt‐treated plants ofLeptochloa fuscaL. Kunth
Authors: JESCHKE W. DIETER , KLAGGES SABINE , HILPERT ANDREA , BHATTI A. SAEED , SARWAR G.
Published: April 2006

summary

An empirically based modelling technique, based on the relative immobility of Ca2+in phloem, was used quantitatively to describe uptake, flow in xylem and phloem, and partitioning of K+, Na+, Mg2+, and Cl−for a 13‐d period at the end of vegetative growth of the main shoot inLeptochloa fusca(L.) Kunth grown in presence of 100 mM NaCl. The model incorporated data on net increments of the ions in the root, the stem, individual leaf sheaths and laminae (blades), and tillers, secretion of salt by glandular hairs on sheaths and laminae, and the molar ion:Ca ratios in the xylem sap. Molar ratios of uptake of Na:Cl:K were 1.27: 1.12:1, indicating an uptake selectivity of 11.3 in favour of K+against Na+. The flow pattern of K+ in the main shoot featured relatively low permanent deposition (22% of the intake into the shoot in the stem axis and 10% in leaves) but a high return flow via phloem to the root (67%) followed by cycling of K+. In the whole plant a large share (72%) of K+uptake was utilized for growth of tillers but K+cycling from shoot to root amounted to 96% of uptake. The flow pattern of Na+featured a somewhat smaller commitment (62%) to deposition in tillers. In the main shoot 33% of Na+intake was deposited in the stem and 35% in leaves. In these the sheaths incorporated by far the larger (2.8‐fold) share compared with the laminae. Of the total Na1intake, 9%, was excreted by salt glands (3.3‐fold more by laminae than sheaths) and only 31% was translocated to the root via phloem. Flows and partitioning of Cr were similar to those of Na+, but phloem transport was larger (60% of intake into the main shoot) than that of Na+. The flow patterns are discussed in relation to changes in ion concentrations of leaves with leafage and in relation to salinity tolerance. It is suggested that besides salt secretion a high efficiency in K+utilization contributes to the performance of this halophyte in presence of salt
Hydraulic conductivity of concentric root tissues of Agave deserti Engelm. under wet and drying conditions
Authors: NORTH GRETCHEN B. , NOBEL PARK S.
Published: April 2006

summary

Water moves from the root surface to the root xylem through a series of tissues, each with properties that influence the root radial hydraulic conductivity (LR). To determine LR for intact roots, root hydraulic conductivity (LR) and axial (xylem) conductance (Kh) were measured for root segments of the desert succulent Agave deserti Engelm. As layers were successively removed, LR was calculated for each layer by considering the conductivities in series. For the distal root region, no single tissue limited LR under wet conditions, although the suberized exodermis and sclerenchyma/endodermis were more limiting per cross‐sectional area of the root than were the cortex and stele. At midroot under wet conditions, LR for the cortex was higher than in the distal region, and cortical cells were dead. After 28 d in drying soil, LR for the suberized layers decreased by over 70% and thereby became more limiting to LR of the intact segment, consistent with increases in extracted lipids in these layers. During drying, intercellular lacunae formed in the cortex due to cellular collapse, and cortical LR decreased. After 7 d of re‐wetting following drying, LR increased for all tissues, but not to its value under wet conditions, reflecting persisting losses in conductivity, especially in the suberized layers. Thus, new apical growth and the development of new laterals are necessary for the complete restoration of root system conductivity. Within 20 mm of the root tip, substantial uptake of the apoplastic tracer 8‐hydroxy‐1,3,6‐pyrenetrisulphonic acid (PTS) occurred, although the exodermis restricted PTS uptake further than 20 mm back from the root tip under wet conditions and all along the root after drying. When the exodermis was removed, PTS moved freely through the cortex in both distal and midroot regions, further suggesting that the cortical apoplast is a significant pathway for radial water flow.
Activities of free radical processing enzymes in dry sunflower seeds
Authors: REUZEAU C. , CAVALIE G.
Published: April 2006

summary

Changes in the lipid peroxidation and the enzymatic activities of the oxygen radical detoxification were studied in dry seeds of sunflower (Helianthus annuus L.) and related to their germinability. There was a positive relationship between the total dehydrogenase activity extracted from whole seeds and germination at both 25 °C and 10 °C. Catalase and superoxide dismutase activities in embryonic axes and germination at 10 °C were negatively correlated. Glucose‐6‐phosphate dehydrogenase and total peroxidase activities were higher in seeds showing high germination capacity. A high malondialdehyde content and a high total glutathione content, were found in cotyledons of dry seeds exhibiting no germination capacity. A net decrease (20%) in the activities of catalase and glucose‐6‐phosphate dehydrogenase was found in these cotyledon fragments. Glutathione reductase and glutathione peroxidase activities were increased by 20 and 50%, respectively. Kinetic properties of glucose‐6‐phosphate dehydrogenase were also affected; the apparent Km for NAD+ was lower in seeds unable to germinate than in seeds with a high germination ability. Oxidative stress appeared to affect seed quality by lowering antioxidant defence capacity; the collapse of the oxygen radical detoxification system appeared to be the result of the ineffectiveness of the glucose‐6‐phosphate dehydrogenase activity; its potential role in oxidative stress tolerance and seed germination ability is discussed.
Continuous monitoring of gas exchange in open‐top chambers in pollution experiments: methodological aspects
Authors: DAUDET F.‐A. , CLAUSTRES J. P.
Published: April 2006

summary

As part of an experiment on effects of atmospheric pollution on the physiology of spruce trees (Picea abies (L.) Karsten), a method for continuous monitoring of gas exchange of young trees grown in Open Top Chambers (OTC) was developed. The basic principles and feasibility of this method are first presented in detail. The installation of a fine perforated polyethylene net over the top of the OTC, in order to reduce ingress of outer air, made it possible satisfactorily to monitor the gas exchange of the trees over long periods. Examples are given of typical measurements of net assimilation and transpiration fluxes for an experimental canopy of 15 young spruce trees to show diurnal and seasonal variation.
Nitrogen allocation in ponderosa pine seedlings exposed to interacting ozone and drought stresses
Authors: TEMPLE PATRICK J. , RIECHERS GEORGE H.
Published: April 2006

summary

Nitrogen (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

summary

Molecular 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

summary

There 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

summary

This 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

summary

Higher 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

summary

Vegetation 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

summary

A 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

summary

The 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

summary

Seedlings 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

summary

Stomatal 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

summary

The 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

summary

Effects 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

summary

Two‐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.
Interactions between drought and elevated CO2 on growth and gas exchange of seedlings of three deciduous tree species
Authors: TSCHAPLINSKI T. J. , STEWART D. B. , HANSON P. J. , NORBY R. J.
Published: April 2006

summary

Interactions between elevated atmospheric CO2 and drought on growth and gas exchange of American sycamore (Platanus occidentalis L.), sweetgum (Liquidambar styraciflua L.) and sugar maple (Acer saccharum Marsh.) were investigated using 1‐yr‐old seedlings, planted in 8 1 pots and grown in four open‐top chambers, containing either ambient air or ambient air enriched with 300 μmol mol−1CO2. Two soil moisture regimes were included within each chamber: a ‘well‐watered’ treatment with plants watered daily and a ‘drought’ treatment in which plants were subjected to a series of drought cycles. Duration and depth of the drought cycles were determined by soil matric potential. Mean soil water potential at rewatering for the water‐stressed seedlings under ambient CO2 for sugar maple, sweetgum and sycamore was −0.5, −0.7 and −1.8 MPa, respectively, compared with > −0.1 MPa for all well–watered plants.

Elevated CO2 increased relative growth rate of well‐watered sugar maple by 181%, resulting in a 4.3‐fold increase in total plant dry weight after 81 d, compared with 1.4 and 1.6‐fold increases for sweetgum and sycamore, respectively, after 69 d. Although elevated CO2 increased net CO2 assimilation rate of sugar maple by 115%, there was a 10‐fold increase in leaf area which contributed to the growth response. Although drought did not eliminate a growth response of sugar maple to elevated CO2 it greatly reduced the elevated CO2‐induced enhancement of relative growth rate. In contrast, relative growth rates of sweetgum and sycamore were not significantly increased by elevated CO2. Drought, under elevated CO2, reduced leaf area of all three species to a greater extent than it reduced net CO2 assimilation rate. The response ranged from no effect in sugar maple to a 40 % reduction in sycamore, with sweetgum exhibiting an intermediate response. Results indicate that drought may alter the growth response, gas exchange and water relations of tree species growing in an elevated CO2 atmosphere. Under high nutrient and water availability, sugar maple may benefit the most (of the three species studied) from a CO2‐ enriched atmosphere, but productivity gains will be limited if frequent drought is prevalent.
Effects of high nitrogen concentrations on ectomycorrhizal structure and growth of seedlings of Picea abies (L.) Karst.
Authors: BRUNNER IVANO , SCHEIDEGGER CHRISTOPH
Published: April 2006

summary

High nitrogen concentrations are known to affect ectomycorrhizal and ectomycorrhizal fungi in field and laboratory experiments. Using NH/ as a nitrogen source in the growth pouch system, a variety of structural modifications were documented on first order lateral roots of Picea abies (L.) Karst. seedlings. Root cells increased in size and number at high levels of NH4+resulting in a hypertrophic appearance of roots in both uncolonized seedlings and in those inoculated with mycelia of the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull, ex St. Amans) Quel. A fungal mantle surrounded short roots of inoculated seedlings, and the outer walls of epidermal and cortical cells were often thickened when in contact with fungal hyphae. No Hartig net developed, although intracellular penetration of fungal hyphae into epidermal and cortical cells frequently occurred. At moderate NH4+concentrations, Hartig net development was incomplete, but occasional intracellular penetration of Hartig net hyphae into epidermal and cortical cells occurred. The addition of high levels of NH4+after ectomycorrhizal development resulted in ectomycorrhizas with distinctly altered apical structures. None of the various NH4+concentrations resulted in significantly different plant dry weights after two months of exposure, either with or without fungal inoculation. After four months, dry weight, root length and branching indices were higher in both inoculated plants and those exposed to high nitrogen. The root/shoot ratio and number of short roots per seedling were high with fungal inoculation. Shoot nitrogen levels after two and four months and the Ca levels after 4 months were higher with increasing NH4+in the nutrient solution. Other mineral elements were not influenced by nitrogen concentrations and fungal inoculation.
Variations in habitat, season, flower traits and pollinators in dimorphic Narcissus tazetta L. (Amaryllidaceae) in Israel
Authors: ARROYO JUAN , DAFNI AMOTS
Published: April 2006

summary

Narcissus tazetta shows a genetically‐based discrete polymorphism for style length similar to that well known in heterostylous plants. Plants are either short‐ (S) or long‐styled (1). In Israel, marsh populations are dominated by S plants and hill populations by L plants. Populations differ in size, flowering time and duration, flower orientation, inflorescence display, vegetative reproduction, and pollinators. The main visitors to flowers in marshes are hawkmoths, whereas in the hills they are visited by short‐tongued insects: solitary bees and hoverflies. The pollination efficiency of these insects was investigated by studying foraging behaviour, visit rate, and pollen deposition on stigmas. Our findings are consistent with the hypothesis of lower efficiency of pollination of S flowers by short‐tongued insects, resulting in the exclusion of this morph from the hills. Additionally, we considered the possibility that there might be pollination ecotypes corresponding to the two habitats (marsh and hill) and examined variation in a set of continuous flower traits related to pollination biology. Flower tube length was the only trait showing a distinct difference between the two habitat types. Although the concentration of nectar was not different between habitats, L flowers presented more concentrated nectar than S flowers. Such a difference in nectar concentration may he of adaptive value for the pollination of the L flowers by short‐tongued pollinators in the hills.
Low genetic diversity in the Scottish endemicPrimula scoticaHook.
Authors: GLOVER BEVERLEY J. , ABBOTT RICHARD J.
Published: April 2006

summary

Primula scoticaHook., a rare Scottish endemic, is threatened with extinction due to habitat destruction. A survey of genetic variability within the species was conducted on five populations from the Orkney islands and nine from the Scottish mainland. Isozyme analysis revealed variation between individuals at only one of 15 enzyme encoding loci examined, while a survey of DNA sequence variation via RAPD analysis revealed no genetic diversity either within or between a subsample of four populations surveyed. Individuals exhibited a ‘fixed’ heterozygous genotype at seven of the enzyme encoding loci, indicating thatP. scoticais of allopolyploid origin. Despite the high level of heterozygosity per individual and the biochemical diversity that may stem from it, the species remains restricted to a very specific habitat. Implications for the conservation of the species are considered, including the need for habitat protection.
Pollination ecology and patch‐dependent reproductive success of the rare perennialGentiana pneumonantheL.
Authors: PETANIDOU T. , DEN NIJS J. C. M. , OOSTERMEIJER J. G. B. , ELLIS‐ADAM A. C.
Published: April 2006

summary

The reproductive behaviour ofGentiana pneumonantheL., a rare plant species in The Netherlands, was studied in a relatively large wet heathland population during summer 1989. The species co‐occurred with the grassMolinia caeruleaand co‐flowered withErica tetralixandCalluna vulgaris.The flowering period lasted from July to October, peaking in late August to late September. Flowers are protandrous. The species appeared to be self‐compatible, but spontaneous self‐pollination was strongly limited. Hand‐crossing and hand‐selfing resulted in the same amount of seed set as in natural pollination. Reproductive success was dramatically reduced late in the season. Pollination was achieved sternotribically by the speciesBombus pascuorum, which visited the flowers for nectar. In the study area, three patch types were distinguished: co‐dominated byErica, byCallunaandErica, and byMolinia, respectively. Frequency of visits toGentianawas highest in theErica‐patch. However, this did not result in a higher seed set. In theMolinia‐patch seed set was reduced. However, in theMolinia‐patch the mean number of ovules was greater than in the others (as high as in plants raised indoors and in cross‐pollinated plants). Fruits from theCalluna‐patch had less ovules than those from theErica‐patch. We conclude that, in this remnant population,Gentianais not pollination‐limited. However, it is likely that in theMolinia‐patch geitonogamy is frequent, which may lead to inbreeding depression. The greater number of ovules observed inMolinia‐patches may reflect an excess of nutrients available there, relative to theCalluna‐patch where there may be reduced water availability.
Enzyme activities in isolated root plasma membranes from a stand of Norway spruce in relation to nutrient status and ammonium sulphate application
Authors: ROSENGREN‐BRINCK ULRIKA , MAJDI HOOSHANG , ASP HAKAN , WIDELL SUSANNE
Published: April 2006

summary

The effect of ammonium sulphate application (100 kg N ha −1y −1) on the chemistry of the rhizosphere, fine roots and needles was studied using a Norway spruce stand. Data were also collected on enzyme activities in isolated root plasma membranes as well as on Ca and K uptake in fine roots. Application of ammonium sulphate decreased both pH and Al concentration whereas Ca/Al molar ratio as well as Ca and SO4 concentrations in the soil: water extracts increased. By contrast, no treatment effect was found either for the plasma membrane‐bound ATPase activity or the glucan synthase II (GS II) activity, or for the uptake of Ca or K. Independently of treatment, increased activity of the H‐+ ATPase in fine roots was correlated with a higher Ca/Al molar ratio of the rhizosphere soil and increased root length density. Increased root length density was also linked to lower Al concentration of both rhizosphere soil and fine roots. The stress‐related enzyme GS II in fine roots showed increased activity as the P concentration in the roots decreased and was positively linked to increased K uptake. Thus, plasma membranes could be isolated from forest roots and reliably used in enzyme activity assays. Furthermore, the relations between different parameters could be determined, although data were collected only from selected parts of the intact forest ecosystem.
Response of red alder seedlings to CO enrichment and water stress
Authors: HIBBS DAVID E. , CHAN SAMUEL S. , CASTELLANO MICHAEL , NIU CHIH‐HAO
Published: April 2006

summary

Red alder (Alnus rubra Bong.) is a nitrogen‐fixing pioneer tree species of the Pacific Northwest of North America. We investigated the response of different seed sources of red alder to elevated atmospheric CO2 and to varied levels of water stress. Seeds were stratified, germinated and grown for up to 147 d under ambient (350 //.I I−1) or elevated (700 ftl I−1) CO2.

There were no significant interactions of seed source latitude with either treatment, although seedlings from more northerly sources were larger. Elevated CO2 and low moisture stress resulted in larger plants with more leaf area; effects of the two factors appeared additive. Effects of both factors on biomass allocation, including root: shoot ratios, were small or nonsignificant. Elevated CO2 decreased specific nitrogenase activity and generally increased photosynthesis (A) and stomatal conductance (g). The ratio A: g, potential water use efficiency, also increased when plants were under water stress. Elevated CO2 appears to improve drought tolerance in red alder.

Overall, these results indicate that red alder would benefit in total plant growth from increased ambient CO2 and could tolerate changes in precipitation.
Atmospheric CO2, soil nitrogen and turnover of fine roots
Authors: PREGITZER KURT S. , ZAK DONALD R. , CURTIS PETER S. , KUBISKE MARK E. , TEERI JAMES A. , VOGEL CHRISTOPH S.
Published: April 2006

summary

In most natural ecosystems a significant portion of carbon fixed through photosynthesis is allocated to the production and maintenance of fine roots, the ephemeral portion of the root system that absorbs growth‐limiting moisture and nutrients. In turn, senescence of fine roots can be the greatest source of C input to forest soils. Consequently, important questions in ecology entail the extent to which increasing atmospheric CO2may alter the allocation of carbon to, and demography of, fine roots. Using microvideo and image analysis technology, we demonstrate that elevated atmospheric CO2increases the rates of both fine root production and mortality. Rates of root mortality also increased substantially as soil nitrogen availability increased, regardless of CO2concentration. Nitrogen greatly influenced the proportional allocation of carbon to leaves vs. fine roots. The amount of available nitrogen in the soil appears to be the most important factor regulating fine root demography inPopulustrees.
Effects of ozone on stomatal conductance and photosynthesis in populations of Plantago major L.
Authors: REILING K. , DAVISON A. W.
Published: April 2006

summary

British populations of Plantago major L. differ in ozone resistance. As stomata regulate ozone uptake it is possible that some of this variation in ozone resistance is the result of differences in stomatal behaviour. This paper reports a comparative study of the effects of ozone exposure on the stomatal conductance (gs), net CO2 uptake (A) and intercellular CO2 concentration (C1) of 28 populations over a 5 d period under controlled conditions. The ozone exposure was 70 ml 70 nl1−1 for 7 h d−1 while controls in charcoal filtered air received < 5 ml 1−2. There was no relationship between mean or maximum stomatal conductance in charcoal filtered air and ozone resistance. Ozone reduced gs in all populations within hours of the start of fumigation, but particularly so in the more sensitive ones, then over the next 4 d the pattern changed as the effect on the sensitive populations decreased. The effect on the resistant populations remained more constant. Conductance measurements made in the dark period showed that the stomata did not close completely, and that in ozone fumigated plants gs was on average 75% of that in control plants. Although the resistant populations showed a large reduction in gs, ozone had no effect on A or C, indicating that closure was not caused by reduced photosynthesis and higher C. It is argued that closure was probably caused by direct effects on the guard cells. In sensitive populations ozone reduced A to around 50–60% of the controls on day 1 but only to 70–80% of the controls on day 5. The recovery might have been caused by the decreasing effect on gs but as the uptake of ozone would have increased at the same time it might have been related to acclimation.
Influence of nitrogen supply on the response of clones of birch (Betula pendula Roth.) to ozone
Authors: PÄÄKKÖNEN E. , HOLOPAINEN T.
Published: April 2006

summary

Clonal birch (Betula pendula Roth.) seedlings were exposed to slightly higher than ambient levels of ozone and different levels of nitrogen supply under open‐field conditions in three experiments: (1) three 2‐year‐old clones exposed to ozone and 74/150 kg N ha−1 y−1 for two growing seasons, (2) three 2‐year‐old clones under a corresponding exposure regime for one growing season and (3) one 2‐year‐old clone exposed to ozone and 37/74/150 kg N ha−1 y−1 for one growing season. The cumulative ozone exposures were 1–5 x (1992) and 1–7 x (1993) higher than ambient levels. In these experiments no significant differences between the clones were found in their response to each treatment. Ozone exposure reduced the mean leaf size and the leaf area, accelerated autumn yellowing and loss of leaves, and increased the palisade layer thickness. High nitrogen availability increased the height growth, the mean leaf size, the leaf area, the shoot/root ratio, the leaf water content and the stem dry weight, but decreased the number of leaves and the leaf dry mass per area, and retarded autumn senescence of leaves. It also reduced the leaf and palisade layer thickness and increased the intercellular space of the palisade layer. Significant interactions between ozone and nitrogen supply were found as an increase in leaf biomass production, root dry weight and spongy intercellular space, and as a decrease in leaf loss, yellowing of leaves and palisade layer thickness. The results suggest that sufficient nitrogen supply can confer the birch with greater resistance to ozone.