bluuebunny/crossref_metadata_2025 huggingface dataset:
Pollen–pollen interactions in Betula pendula in vitro
Authors: PASONEN H. L. , KÄPYLÄ M.
Published: March 2003

Direct pollen interactions, as well as interactions mediated by a recipient, can have a remarkable influence on pollen fertilization ability. Under conditions of pollen competition it could be advantageous if pollen grains interfered with the germination of other pollen. The aim of this study was to find out if there are direct negative or positive pollen–pollen interactions between pollen grains from genetically slightly different donors. The in vitro germinability of the pollen from several Betula pendula Roth clones was investigated. The pollen interactions between the clones were examined pairwise by using equal pollen mixtures. In three of the eight cases the germination percentage of the pollen mixture was significantly higher than the average germination percentage of the separate clones that formed the mixture, which indicates some type of interaction between the pollen populations. We found only positive interactions between the pollen of clones. This study also documented density‐dependent germination of pollen grains in vitro (=pollen population effect). Adding an aqueous pollen extract to the incubation medium increased the germination percentages of poorly germinating pollen and small pollen populations. Germination‐stimulating effects were found to exist both with fresh and dead pollen. Such direct pollen–pollen interactions could be explained by specific water‐soluble substances diffusing from pollen grains.
Immunocytochemical studies of the infection mechanisms of Botrytis fabae II. Host cell wall breakdown
Authors: COLE L. , DEWEY F. M. , HAWES C. R.
Published: March 2003

Immunoelectron microscopy using the anti‐pectin monoclonal antibody JIM 7 confirmed earlier observations that pectin degradation is a primary event in the process of host cell wall breakdown during the development of chocolate spot disease (causal agent: Botrytis fabae (Sard.)) of broad bean. Close examination of infected and non‐infected Vicia faba L. leaves indicated a loss of JIM 7‐labelling, and therefore, methyl‐esterified pectin, from swollen walls of infected and contiguous epidermal cells. Modified mesophyll walls also possessed less methyl‐esterified pectin than healthy walls. Enzymes which attack methyl‐esterified pectin appeared to be most active in regions of host tissue close to sites of fungal infection.

Ultrastructural studies using the enzyme, cellobiohydrolase conjugated to gold (CBH1‐Au) revealed that the cellulose microfibrils of outer epidermal walls of non‐infected V. faba leaf tissue were heavily masked by other components of the plant cell wall. Such material was most probably pectin because the cellulose microfibrils of swollen epidermal and modified mesophyll walls of infected host tissue were heavily labelled with CBH1‐Au. These results were confirmed by double‐labelling studies using JIM 7 and CBH1‐Au. At early stages of the infection process, limited cellulose degradation was observed in infected leaf tissue.

Double‐labelling experiments using the monoclonal antibody BC‐KH4 directed against Botrytis matrices and a marker for the plant cell wall (JIM 7 or CBH1‐Au) confirmed previous observations that the fungal matrices extended through modified host walls and degenerate cytoplasm. It is suggested that the wall‐modifying action of the pectin‐degrading enzymes produced during the infection process might facilitate pervasion of matrix material associated with the infection hyphae through host cell walls. Possible role(s) of such matrix material during the post‐penetration processes of the V. faba–B. fabae relationship are discussed.
Effects of solar radiation on the endemic Mediterranean red alga Rissoella verruculosa: photosynthetic performance, pigment content and the activities of enzymes related to nutrient uptake
Authors: FLORES‐MOYA ANTONIO , GÓMEZ IVÁN , VIÑEGLA BENJAMÍN , ALTAMIRANO MARÍA , PÉREZ‐RODRÍGUEZ EDUARDO , MAESTRE CRISTINA , CABALLERO ROSARIO M. , FIGUEROA FÉLIX L.
Published: March 2003

The effects of full‐spectrum solar radiation and of solar radiation deprived of total u.v. radiation (λ<395 nm) on the endemic Mediterranean red alga Rissoella verruculosa (Bertoloni) J. Agardh were studied in situ in early summer, from sunrise to sunset. Photosynthetic performance, pigment content and the activities of enzymes related to nutrient uptake, were monitored under both radiation conditions throughout a daylight period.

The doses of solar radiation, measured on the day during which the experiments were carried out (24 June 1997), were 9228·25, 1109·70 and 13·03 kJ m−2 for PAR (λ=400–700 nm), u.v.‐A (λ=315–400 nm) and u.v.‐B (λ=280–315 nm), respectively. Under these conditions, a clear daily variation in photosynthetic performance was found. However, no significant differences were detected between the two radiation conditions. At noon, strong sunlight impaired O2 evolution by 75%, but complete recovery occurred during the afternoon, reaching similar values to those measured in the early morning. By contrast, photoinhibition of optimal quantum yield (Fv/Fm), and the relative electron transport rate was followed by only a slight recovery during the afternoon. The rate of photosynthesis in air (simulating emersion conditions), estimated by CO2 exchange, showed a negative balance at noon, which was accentuated in plants exposed to the full‐solar spectrum.

Significant changes in the activities of nitrate reductase and carbonic anhydrase were found throughout the day under both radiation conditions. In thalli receiving solar radiation deprived of u.v., total CA activity decreased throughout the day. However, in thalli exposed to full‐spectrum solar radiation, the activity of the enzyme tended to increase in the afternoon, correlating with an increase in NR activity.
Nutrient exchange in an Antarctic macrolichen during summer snowfall–snow melt events
Authors: CRITTENDEN P. D.
Published: March 2003

Concentrations of NH4+, NO3−, PO43−, K+, Ca2+ and Mg2+ in snow meltwater resulting from summer snow showers were monitored before and after its passage through monospecific stands of the Antarctic macrolichen Usnea sphacelata R. Br. The sampling was conducted under field conditions near Casey Station in East Antarctica between January and March. Total snow deposition during the 61‐d period was 44±1 mm (rainfall equivalent depth) delivering 362±10, 87±2 and 9±1 μmol m−2 of NH4+, NO3− and PO43−, respectively. Meltwater that had percolated through U. sphacelata was depleted in NH4+ and NO3− equating with a retention by the lichen of 87 and 92%, respectively, of the total wet deposition of these ions. Lichen‐modified meltwater was slightly enriched in PO43−, but because the volume of the lichen percolate was smaller than that of the original snow deposition, the lichen achieved a net gain of 9% of the total P deposited. Lichen percolate was also enriched in metal cations. Potassium loss associated with the melting of the heaviest snowfall (18 mm) was equivalent to only 0·05% of the total K in the lichen suggesting that ion loss did not signal significant cellular damage. There was also a progressive increase in NH4+ concentration in unmodified meltwater from 3 to 21 nmol ml−1 over a 3‐d period whereas levels in the lichen‐modified meltwater remained unchanged at 4 nmol ml−1. This enrichment in NH4+ might have resulted from dry deposition onto the melting snow pack of NH3 emitted from nearby penguin rookeries. During the study, tagged thalli of U. sphacelata made a 2% loss in dry mass although they appeared healthy and, at the end of the study, showed an effective quantum yield (ΔF/Fm′) comparable with field material. The results are discussed in relation to the time of year that is likely to be most suitable for lichen growth in this continental Antarctic environment and the potential growth‐led demand for N in U. sphacelata.
Clonality and genetic variation in Amylostereum areolatum and A. chailletii from northern Europe
Authors: VASILIAUSKAS RIMVYDAS , STENLID JAN , THOMSEN IBEN M.
Published: March 2003

Genetic variation within and between vegetative compatibility groups (VCGs) of Amylostereum areolatum (Fr.) Boid. and Amylostereum chailletii (Pers.: Fr.) Boid. isolates was investigated. DNA fingerprints were made using the M13 core sequence as a primer. A total of 53 isolates of A. areolatum and 57 isolates of A. chailletii from Lithuania, Sweden, Denmark and Great Britain were studied. In all cases isolates belonging to the same VCG showed identical DNA banding patterns, suggesting that VCGs correspond to clones. In A. areolatum the vast majority of the isolates (spread by Sirex juvencus L.) were assigned to dispersive clones, that have wide geographical distribution (i.e. the same genotypes were detected in Lithuania, Sweden and Denmark), with low genetic variation between the different clones. By contrast, A. chailletii population structure was consistent with the spread of airborne basidiospores produced by outcrossing. Only a small fraction of A. chailletii isolates studied, could be assigned to dispersal clones with a local distribution, spread by Urocerus gigas L. Overall, M13 fingerprinting detected low genetic differentiation in both species in the samples we studied.
Editorial
Authors: Ayres Peter
Published: March 2003

New Phytologist welcomes this month, and introduces, its new Managing Editor, Jonathan Ingram. He comes to New Phytologist from Elsevier Science's Trends in Plant Science, where he has worked as Assistant Editor since the highly successful launch of that magazine in January 1996.

Jonathan's introduction to plant science, at Oxford over 10 years ago, was through the excellent tuition of Vernon Butt in a traditional botany degree. He then took a DPhil with Andrew Smith and Chris Leaver, learning biochemical and molecular research methods while studying malate decarboxylation associated with Crassulacean acid metabolism. He subsequently moved to the Max Planck Institute for Breeding Research in Cologne, Germany, where he did research with Dorothea Bartels into the molecular mechanism of drought tolerance in the resurrection plant Craterostigma plantagineum, specifically the role of sucrose‐phosphate synthase.

These are challenging times in science publishing, particularly as technological advances force rapid change, but there are also many exciting new opportunities. Jonathan's experience and background will help New Phytologist remain in the vanguard of plant journals, while maintaining its traditions of scientific excellence and friendly service to authors and readers, traditions carefully nurtured by his predecessor David Stribley.

We wish David improved health and a happy retirement.
Do Striga hermonthica‐induced changes in soil matric potential cause the reduction in stomatal conductance and growth of infected maize plants?
Authors: TAYLOR A. , SEEL W. E.
Published: March 2003

Maize (Zea mays L.) plants parasitized by the root hemi‐parasitic angiosperm, Striga hermonthica (Del.) Benth., consistently display a range of symptoms similar to those found in droughted plants. The mechanisms by which these changes occur are largely unknown. However, S. hermonthica has unusually high rates of transpiration, and stomata which are relatively insensitive to water deficit. Consequently, it has often been suggested that the parasite might cause a severe depletion of the available water in the host's rooting zone. To determine whether the lower stomatal conductance and retarded growth of infected plants could be a result of parasite‐induced water deficit, we have monitored the matric potential of the growth medium, water use, growth and stomatal conductance of infected vs. uninfected maize plants.

Host plant height and stomatal conductance of parasitized plants were significantly lower than those of control plants from 31 or 37 d after planting (d.a.p.) respectively. However, there was no indication of an increase in the rate of water depletion in the rooting zone of infected plants until approx. 63 d into the parasitic association. In fact, from 39 until 59 d.a.p. infected plants used less water than uninfected control plants, probably the result of the plants having fewer expanded leaves during part of this period, combined with the lower stomatal conductance exhibited by the infected plants from day 37 onwards. Leaf RWC of infected plants was unchanged in comparison with that of uninfected plants, therefore the change in stomatal conductance was not a response to dehydration of the leaf tissue. Our results indicate that parasitism by S. hermonthica does not cause an increase in water uptake/use in the host until well after most of the symptoms of infection have become fully established. It is highly unlikely, therefore, that the observed effects on the host are primarily due to soil water deficit.
15N natural abundance in fruit bodies of different functional groups of fungi in relation to substrate utilization
Authors: GEBAUER G. , TAYLOR A. F. S.
Published: March 2003

Natural abundances of 15N and N concentrations of 34 fruit bodies from 24 species of ectomycorrhizal and saprophytic fungi were measured in a temperate Central European mixed forest stand. The fungi of the two life forms are known to be capable of utilizing different types of N sources (organic N compounds from the humus, inorganic N from the soil and N from litter or wood) differing by their 15N natural abundance values. Based on the two life forms and the three different N sources, four functional groups of fungi were distinguished: (1) ectomycorrhizal fungi capable of utilizing organic N from the humus; (2) ectomycorrhizal fungi known to depend on inorganic N compounds in the soil; (3) saprophytes capable of utilizing organic N from the humus; and (4) saprophytes utilizing N from dead wood or litter. Large differences were found between species in the δ15N values (−3.0 to 3.3‰) and in the N concentrations (0.84 to 6.61 mmol eq N g dw−1) of the fruit bodies. In most cases fungi were more enriched in 15N than their respective bulk N source was. Fungi living in humus, and presumably having access to organic N compounds (groups 1 and 3), were significantly more enriched in 15N than fungi which are known to depend on inorganic N (e.g. Laccaria, group 2), or fungi living on litter or wood (group 4), irrespective of whether they were ectomycorrhizal or saprophytic species. Fungi living in humus had significantly higher N concentrations than fungi living on litter or wood.
Strategies of thermal adaptation by high‐latitude cyanobacteria
Authors: TANG EVONNE P. Y. , VINCENT WARWICK F.
Published: March 2003

Although mat‐forming cyanobacteria dominate many freshwater ecosystems in the Arctic and Antarctic, their optimal temperature for growth (Topt) is usually much higher than the temperature range of their native habitat. The present study compared the temperature dependence of growth, pigment composition and absorbance, photosynthesis and photosynthate partitioning for two strains of cyanobacteria with contrasting Topt values; Phormidium subfuscum, isolated from McMurdo Ice Shelf, Antarctica, and Phormidium tenue, collected from the Kuparuk River in the tundra region of northern Alaska. Phormidium subfuscum grew between 5 and 20°C with a Topt of 15°C whereas P. tenue showed detectable growth from 10 to 40°C and a Topt of 30°C. Light utilization efficiency, photosynthetic capacity and the irradiance at the onset of light saturation increased with increasing temperature up to Topt in both strains. The cellular concentrations of chlorophyll a (Chl a) and carotenoid (CAR) and the in vivo absorbance maxima for Chl a, CAR, C‐phycocyanin and allophycocyanin changed little for P. subfuscum but all these variables increased across the temperature range up to Topt for P. tenue. Neither P. subfuscum nor P. tenue showed changes in relative carbon allocation with varying temperature, suggesting that gross biochemical alterations are not a characteristic of temperature acclimation in these cyanobacteria. We conclude that the eurythermal cyanobacterium P. tenue optimizes growth over a wide range of temperatures by adjusting its light‐capturing as well as carbon fixation characteristics, whereas stenothermal P. subfuscum relies on changes in carbon fixation without concomitant shifts in pigment content.
Carbon gain in a multispecies canopy: the role of specific leaf area and photosynthetic nitrogen‐use efficiency in the tragedy of the commons
Authors: SCHIEVING FEIKE , POORTER HENDRIK
Published: March 2003

Models have been formulated for monospecific stands in which canopy photosynthesis is determined by the vertical distribution of leaf area, nitrogen and light. In such stands, resident plants can maximize canopy photosynthesis by distributing their nitrogen parallel to the light gradient, with high contents per unit leaf area at the top of the vegetation and low contents at the bottom. Using principles from game theory, we expanded these models by introducing a second species into the vegetation, with the same vertical distribution of biomass and nitrogen as the resident plants but with the ability to adjust its specific leaf area (SLA, leaf area∶leaf mass). The rule of the game is that invaders replace the resident plants if they have a higher plant carbon gain than those of the resident plants. We showed that such invaders induce major changes in the vegetation. By increasing their SLA, invading plants could increase their light interception as well as their photosynthetic nitrogen‐use efficiency (PNUE, the rate of photosynthesis per unit organic nitrogen). By comparison with stands in which canopy photosynthesis is maximized, those invaded by species of high SLA have the following characteristics: (1) the leaf area index is higher; (2) the vertical distribution of nitrogen is skewed less; (3) as a result of the supra‐optimal leaf area index and the more uniform distribution of nitrogen, total canopy photosynthesis is lower. Thus, in dense canopies we face a classical tragedy of the commons: plants that have a strategy to maximize canopy carbon gain cannot compete with those that maximize their own carbon gain. However, because of this strategy, individual as well as total canopy carbon gain are eventually lower. We showed that it is an evolutionarily stable strategy to increase SLA up to the point where the PNUE of each leaf is maximized.
A mechanical perspective on foliage leaf form and function
Authors: NIKLAS KARL J.
Published: March 2003

The mechanical behaviour of large foliage leaves in response to static and dynamic mechanical forces is reviewed in the context of a few basic engineering principles and illustrated in terms of species drawn from a variety of vascular plant lineages. When loaded under their own weight or subjected to externally applied forces, petioles simultaneously bend and twist, and thus mechanically operate as cantilevered beams. The stresses that develop in petioles reach their maximum intensities either at their surface or very near their centroid axes, where they are accommodated either by living and hydrostatic tissues (parenchyma and collenchyma) or dead and stiff tissues (sclerenchyma and vascular fibres) depending on the size of the leaf and the species from which it is drawn. Allometric analyses of diverse species indicate size‐dependent variations in petiole length, transverse shape, geometry and stiffness that accord well with those required to maintain a uniform tip‐deflection for leaves with laminae differing in mass. When dynamically loaded, the laminae of many broad‐leaved species fold and curl into streamlined objects, thereby reducing the drag forces that they experience and transmit to their subtending petioles and stems. From a mechanical perspective, the laminae of these species operate as stress‐skin panels that distribute point loads more or less equally over their entire surface. Although comparatively little is known about the mechanical structure and behaviour of foliage leaves, new advances in engineering theory and computer analyses reveal these organs to be far more complex than previously thought. For example, finite‐element analyses of the base of palm leaves reveal that stresses are decreased when these structures are composed of anisotropic as opposed to isotropic materials (tissues).
Effects of excess nitrogen on frost hardiness and freezing injury of above‐ground tissue in young oaks (Quercus petraea and Q. robur)
Authors: THOMAS F. M. , AHLERS U.
Published: March 2003

The effects of excess nitrogen (N) on the frost hardiness and freezing injury of bark and buds were tested in 2‐yr‐old sessile oaks (Quercus petraea) and pedunculate oaks (Q. robur) that had been grown outdoors in sand culture with normal or luxurious N supply during the growing season. Some trees from both N treatments were subjected to drought stress in summer, whereas others were adequately watered. Between January and March, whole plants were exposed to artificial freezing treatments at −25 °C of different durations (10 d, 21 d, or two periods of 4 d interrupted by an 8 d frost‐free period, referred to as a freeze–thaw cycle). The frost hardiness and freezing injury of the bark were determined by two different versions of the electrolyte leakage method (calculation of an index of injury, I−25, from the relative conductivity after a fixed time; and measurement of the electrolyte leakage rate). In addition, the vitality of bark and buds was assessed visually with the 2,3,5‐triphenyltetrazolium chloride (TTC) method. In comparison with the control, the oaks that had been luxuriously supplied with N exhibited distinctly higher N concentrations and lower C:N ratios in their leaves and bark, higher relative shoot increments, delayed leaf discoloration in autumn, and earlier budbreak in spring. Oaks kept outdoors during the winter were frost‐hardy from December until the end of February without showing differences between species or N treatments. In comparison with the pedunculate oak, the sessile oak was more susceptible to freezing injury induced by prolonged artificial freezing or by the freeze–thaw cycle. Increased freezing injury in trees with high N supply was detected only by the TTC test of the bark of sessile oaks subjected to the freeze–thaw cycle. In all oaks, except for the pedunculate oaks grown with normal N, the freeze–thaw cycle resulted in significantly lower frost hardiness, as indicated by increased I−25 values. This treatment also led to increased freezing damage of bark and buds, as revealed by the TTC test. In drought‐stressed oaks, the electrolyte leakage rate was significantly elevated after the freeze–thaw cycle. It is concluded that, in the sessile and pedunculate oaks, the water supply before frost stress and the course of the temperature in winter have a greater effect on frost hardiness and freezing damage than excess N.
Budgeting for the wood‐wide web
Authors: Sen Robin
Published: March 2003

How appropriate that at the turn of a century that has overseen a second industrial revolution in agriculture, there is an increasing appreciation of the central role played by the mycorrhizal symbiosis, first described in the latter part of the nineteenth century (Frank, 1885). Simply stated, nearly all families of plants form root symbiotic organs, termed mycorrhizas, with soil fungi belonging to all the main phyla, namely Zygomycotina, Ascomycotina, Basidiomycotina and the Fungi Imperfecti (Harley & Harley, 1987). The importance of this symbiosis in controlling plant nutrient status and growth is well established (Smith & Read, 1997), but a report in this issue now provides, long awaited, nitrogen and phosphorus budgets for mycorrhizal trees (Perez‐Moreno & Read, pp. 301–309).
Physiological anatomy and function of the membranous grass ligule
Authors: CHAFFEY NIGEL
Published: March 2003

Of the three component organs of the grass leaf – blade, sheath and ligule – the ligule is the least studied and the least understood. Traditionally, it has been assumed to act in a passive way in protecting the culm and leaves that it encloses from the entry of water, dust and harmful spores. However, ultrastructural and cytochemical studies of the membranous ligules of several taxa, particularly Lolium species, have challenged that rather simplistic view and suggest that these ligules play a more active role in the life of the grass plant as a secretory tissue. This review summarizes the evidence for the latter notion, assesses the validity of both the passive and active hypotheses of membranous ligule function and notes similarities between membranous grass ligules, root caps and lycopsid ligules.
Zinc tolerance and accumulation in metallicolous and nonmetallicolous populations of Arabidopsis halleri (Brassicaceae)
Authors: BERT V. , MACNAIR M. R. , DE LAGUERIE P. , SAUMITOU‐LAPRADE P. , PETIT D.
Published: March 2003

Zinc tolerance was investigated in five populations of Arabidopsis halleri (syn.: Cardaminopsis halleri) raised from
seeds collected from contaminated and uncontaminated sites. Tolerance was measured by determining the
concentration which inhibited root growth (EC100). A. halleri populations from contaminated and uncontaminated
sites were found to be Zn‐tolerant compared with the Zn‐nontolerant species Arabidopsis thaliana and A. lyrata
subsp. petraea. At very high Zn concentrations, populations of A. halleri from uncontaminated sites were slightly
less Zn‐tolerant than those from contaminated sites. These observations support the hypothesis that in A. halleri,
Zn tolerance is largely a constitutive property. One population from an uncontaminated site and one population
from a contaminated site were studied for Zn uptake. Zinc content was measured in shoots and roots using a
colorimetric test under laboratory conditions. The results showed that whatever their origin, individuals from both
populations are Zn accumulators compared with the nonaccumulator species A. thaliana. Moreover, the
population from the uncontaminated area accumulated Zn in its shoots and roots more quickly than the population
from the contaminated site. These results suggest that, in A. halleri, Zn accumulation to very high concentration is a constitutive property.
Global patterns of root turnover for terrestrial ecosystems
Authors: GILL RICHARD A. , JACKSON ROBERT B.
Published: March 2003

Root turnover is a critical component of ecosystem nutrient dynamics and carbon sequestration and is also an important sink for plant primary productivity. We tested global controls on root turnover across climatic gradients and for plant functional groups by using a database of 190 published studies. Root turnover rates increased exponentially with mean annual temperature for fine roots of grasslands (r2 = 0.48) and forests (r2 = 0.17) and
for total root biomass in shrublands (r2 = 0.55). On the basis of the best‐fit exponential model, the Q10 for root
turnover was 1.4 for forest small diameter roots (5 mm or less), 1.6 for grassland fine roots, and 1.9 for shrublands.
Surprisingly, after accounting for temperature, there was no such global relationship between precipitation and
root turnover. The slowest average turnover rates were observed for entire tree root systems (10% annually),
followed by 34% for shrubland total roots, 53% for grassland fine roots, 55% for wetland fine roots, and 56% for
forest fine roots. Root turnover decreased from tropical to high‐latitude systems for all plant functional groups.
To test whether global relationships can be used to predict interannual variability in root turnover, we evaluated
14 yr of published root turnover data from a shortgrass steppe site in northeastern Colorado, USA. At this site
there was no correlation between interannual variability in mean annual temperature and root turnover. Rather,
turnover was positively correlated with the ratio of growing season precipitation and maximum monthly
temperature (r2 = 0.61). We conclude that there are global patterns in rates of root turnover between plant groups and across climatic gradients but that these patterns cannot always be used for the successful prediction of the relationship of root turnover to climate change at a particular site.
Elevated CO2 and conifer roots: effects on growth, life span and turnover
Authors: TINGEY DAVID T. , PHILLIPS DONALD L. , JOHNSON MARK G.
Published: March 2003

Elevated CO2 increases root growth and fine (diam. 2 mm) root growth across a range of species and
experimental conditions. However, there is no clear evidence that elevated CO2 changes the proportion of C
allocated to root biomass, measured as either the root∶shoot ratio or the fine root∶needle ratio. Elevated CO2 tends
to increase mycorrhizal infection, colonization and the amount of extramatrical hyphae, supporting their key role
in aiding the plant to more intensively exploit soil resources, providing a route for increased C sequestration. Only
two studies have determined the effects of elevated CO2 on conifer fine‐root life span, and there is no clear trend.
Elevated CO2 increases the absolute fine‐root turnover rates; however, the standing crop root biomass is also
greater, and the effect of elevated CO2 on relative turnover rates (turnover∶biomass) ranges from an increase to
a decrease. At the ecosystem level these changes could lead to increased C storage in roots. Increased fine‐root
production coupled with increased absolute turnover rates could also lead to increases in soil organic C as greater
amounts of fine roots die and decompose. Although CO2 can stimulate fine‐root growth, it is not known if this
stimulation persists over time. Modeling studies suggest that a doubling of the atmospheric CO2 concentration
initially increases biomass, but this stimulation declines with the response to elevated CO2 because increases in assimilation are not matched by increases in nutrient supply.
Plant–plant interactions and soil moisture might be important in determining ozone impacts on grasslands
Authors: NUSSBAUM S. , BUNGENER P. , GEISSMANN M. , FUHRER J.
Published: March 2003

Ozone effects on plant species mixtures could depend on the characteristics of the species involved, their mixing ratio, or on environmental conditions. Predicting long‐term effects on the dynamics of plant communities requires an understanding of the interactions involved. The present experiment was designed to determine the effects of ozone on grassland species in relation to mixing ratio and soil water content (irrigation) using binary mixtures. The grass Trisetum flavescens was grown in potted replacement‐series mixtures with Centaurea jacea (Experiment A)
or Trifolium pratense (Experiment B). The plants were exposed to three concentrations of ozone in open‐top
chambers in two irrigation treatments. Total above‐ground dry weight over three growth periods was measured.
The competitive ability of T. flavescens was expressed as the competitive ratio (CRT). In Experiment B, total
above‐ground dry weight was reduced by elevated ozone and by reduced soil moisture, and significant interactions
were found for ozone × irrigation and ozone × ratio. In Experiment A these effects were not significant. Under well
watered conditions, CRT tended to be reduced by elevated ozone in Experiment A, but increased significantly in
Experiment B, indicating the importance of the competing species in modifying the ozone effect on T. flavescens. In both experiments reduced irrigation decreased the magnitude of ozone effects on biomass production, which could be related to observed reductions in specific leaf conductance. The results suggest that under well watered conditions the effect of elevated ozone on the competitive balance between species depends on the species mixture, but that the mixing ratio is less important.
Impacts of increased nitrogen supply on high Arctic heath: the importance of bryophytes and phosphorus availability
Authors: Gordon C. , Wynn J. M. , Woodin S. J.
Published: March 2003

• This study investigates effects of nitrogen and phosphorus on high Arctic heath vegetation, particularly bryophytes.

• Heath communities received factorial combinations of nitrogen (0, 10 and 50 kg ha−1 yr−1) and phosphorus (0 and 5 kg ha−1 yr−1) in five applications per growing season, for 8 yr.

• Nitrogen decreased lichen cover but did not affect cover of any other functional type. However, just 10 kg ha−1 yr−1 increased the proportion of physiologically active bryophte shoots, and decreased their nitrate assimilation capacity. Phosphorus had greater effects, and the combination of both nutrients altered species composition. Individual bryophyte species displayed contrasting responses to fertilization, suggesting that they should not be grouped as a single functional type.

• The ‘critical load’ of nitrogen for Arctic heath lies below 10 kg ha−1 yr−1. Nitrogen and phosphorus are colimiting in this sytem, so the critical load of nitrogen will be lower where phosphorus availability is greater. Responses of vegetation to any increase in net mineralisation due to soil warming will depend on the ratio in which nitrogen and phosphorus availabilities increase. The effects of nutrient enhancement are very persistent.
Nutrient economy of red pine is affected by interactions between Pisolithus tinctorius and other forest‐floor microbes
Authors: Koide Roger T. , Kabir Zahangir
Published: March 2003

The influence of interactions between the mycorrhizal fungus, Pisolithus tinctorius
, and saprotrophic organisms on nutrient transfer to host red pine (
Pinus resinosa ) seedlings is presented here.

Red pine seedlings were grown axenically, and with P. tinctorius and forest‐floor microbes (both individually and in combination), in two experiments varying in nitrogen availability. Root and shoot growth, as well as tissue nitrogen and phosphorus content, were analyzed after harvesting.

At low nitrogen availability, forest‐floor microbes, but not P. tinctorius
, significantly reduced seedling nitrogen content. Moreover,
P. tinctorius
did not ameliorate this negative effect. However, seedling phosphorus content increased with forest‐floor microbes and
P. tinctorius
individually, and these combined to give an additive effect. Forest‐floor microbes and
P. tinctorius , individually, significantly increased seedling nitrogen and phosphorus contents at high nitrogen availability, interacting to give additive and synergistic effects on nitrogen and phosphorus content, respectively.

The effect of ectomycorrhizal fungi on host‐plant nutrition might depend strongly on the nutrient status of coexisting saprotrophic soil microbes. When nutrients are not limiting, their beneficial effects on host nutrition may be additive or synergistic.
Intracellular calcium oxalate crystal structure in Dracaena sanderiana
Authors: Pennisi Svoboda V. , McConnell Dennis B. , Gower Laurie B. , Kane Michael E. , Lucansky T.
Published: March 2003

• The chemistry, crystallography and ultrastructure of intracellular calcium oxalate deposits in the angiosperm, Dracaena sanderiana are reported here.

• Crystalline deposits extracted from mature leaves and leaf primordia of D. sanderiana were studied by scanning electron microscopy and X‐ray powder diffractometry techniques, and compared with X‐ray standards for calcium monohydrate and calcium oxalate dihydrate.

• Intracellular calcium oxalate deposits were of two types; calcium oxalate monohydrate raphides or solitary calcium oxalate dihydrate crystals. Raphide‐containing cells exhibited lamellate sheaths around the chamber walls, mucilage‐like materials surrounding the developing crystal chambers, and paracrystalline bodies with closely spaced subunits within the chambers. The intracellular calcium oxalate dihydrate crystals usually displayed typical tetragonal‐dipyramidal morphology, but development of some unusual crystal faces occasionally occurred.

• Two intracellular hydrate forms of calcium oxalate (monohydrate and dihydrate) exist in D. sanderiana. The elaboration of crystal vacuoles derived from rough endoplasmic reticulum and modified crystals with energetically unfavourable faces suggest that precipitation of calcium oxalate dihydrate in D. sanderiana cells might be biologically controlled.
Ectomycorrhizal protection of Pinus sylvestris against copper toxicity
Authors: Van Tichelen Katia K. , Colpaert Jan V. , Vangronsveld Jaco
Published: March 2003

Change in the copper (Cu) sensitivity of Pinus sylvestris
is presented, in response to the ectomycorrhizal fungi,
Suillus bovinus
and
Thelephora terrestris , common mycobionts on metal contaminated sites.

Seedlings grown under phosphorus (P) limitation were exposed to a range of Cu concentrations. Plant and fungal development, P nutrition, sorption of Cu on roots and external mycelia as well as transfer of Cu to shoots were assessed.

Root growth and P nutrition were severely inhibited in nonmycorrhizal pines at elevated Cu compared with mycorrhizal plants. Excess Cu had little effect on the development of mycorrhizal roots and mycelia. Thelephora terrestris
was less sensitive to Cu stress than
S. bovinus
. The extraradical mycelium of
S. bovinus
retained large amounts of Cu. However, binding of Cu in fungal tissue was not a prerequisite for low Cu sensitivity since
T. terrestris
absorbed considerably less Cu that
S. bovinus .

Both ectomycorrhizal fungi protect P. sylvestris against Cu toxicity; a benefit that was not due to a metal dilution effect. The mechanisms of mycorrhizal amelioration of Cu toxicity are probably diverse and species‐dependent.
Elevated CO2 increases sorghum biomass under drought conditions
Authors: Ottman M. J. , Kimball B. A. , Pinter P. J. , Wall G. W. , Vanderlip R. L. , Leavitt S. W. , LaMorte R. L. , Matthias A. D. , Brooks T. J.
Published: March 2003

Atmospheric CO2 concentration is expected to increase by 50% near the middle of this century. The effects the free air CO2 enrichment (FACE) is presented here on growth and development of field‐grown grain sorghum (Sorghum bicolor) at ample (wet) and limiting (dry) levels of irrigation water at Maricopa, AZ, USA.

 Daytime CO2 mole fractions were 561 and 368 µmol mol−1 for the FACE and control treatments, respectively. Irrigation plus precipitation averaged 1132 mm for the wet plots and 396 mm in the dry plots.

 During the growing season, FACE increased biomass accumulation in the dry plots but the effects in the wet plots were inconsistent. At final harvest, FACE increased total yield from 999 to 1151 g m−2 in the dry plots and had no effect in the wet plots.

 If atmospheric CO2 continues to increase, total sorghum yield is likely to be higher in the future in areas where water is limited.
Influence of coumarin on the net nitrate uptake in durum wheat
Authors: Abenavoli M. R. , De Santis C. , Sidari M. , Sorgonà A. , Badiani M. , Cacco G.
Published: March 2003

The effects are reported here of coumarin, an allelopathic compound, on root anatomy and growth, nitrate uptake and translocation to the shoot, as well as respiration in Triticum durum (cv. Simeto) seedlings.

 Wheat seedlings were grown in nitrogen‐free hydroponic culture; after 6 d, coumarin (at concentrations of 0, 25 µM, 0.1, 1, 2.5 and 5 mM) and/or nitrate (50 µM) were added to the nutrient solution.

 Coumarin, in the range 25 µM–1 mM, decreased the relative growth rate of roots and increased the area of the root vessels. Within this concentration range, coumarin alone did not significantly affect net nitrate uptake. In seedlings exposed simultaneously to 100 µM coumarin and to 50 µM nitrate, the net nitrate uptake was significantly stimulated. In the presence of nitrate, even the lowest coumarin concentration tested significantly stimulated nitrate translocation from the root to the shoot.

 The effects of low coumarin concentrations on root vessel size could explain this observation, though specific interactions between coumarin and systems regulating nitrate uptake and transport within the root cell cannot be excluded.
Signalling in the cereal aleurone: hormones, reactive oxygen and cell death
Authors: Fath Angelika , Bethke Paul C. , Belligni Maria V. , Spiegel Yoav N. , Jones Russell L.
Published: March 2003

The cereal aleurone is widely used as a model system to study hormonal signalling. Abscisic acid (ABA) and gibberellins (GAs) elicit distinct responses in aleurone cells, ranging from those occurring within minutes of hormone addition to those that require several hours or days to complete. Programmed cell death is an example of a response in aleurone layers that is hormonally regulated. GAs promote cell death and cells in intact aleurone layers begin to die 24 h after GA treatment, whereas cell death of aleurone protoplasts begins 4 d after GA treatment. ABA prevents aleurone cell death and addition of ABA to cells pretreated with GA can delay cell death. Aleurone cells do not follow the apoptotic route of programmed cell death. Cells treated with GA, but not ABA, develop large, acidic vacuoles containing a spectrum of hydrolases typical of lytic compartments. Enzymes that metabolize reactive oxygen species are also present in aleurone cells, but ascorbate peroxidase, catalase and superoxide dismutase become less abundant after treatment with GA; activity of these enzymes increases or remains unchanged in ABA‐treated cells. We propose a model whereby reactive oxygen species accumulate in GA‐treated cells and lead to peroxidation of membrane lipids and plasma membrane rupture.

Abbreviations

RO, reactive oxygen species; HR, hypersensitive response; PSV, protein storage vacuole; PCD, programmed cell death; CAT, catalase; SOD, superoxide dismutase; APX, ascorbate peroxidase.
Phenology of roots and mycorrhiza in orchid species differing in phototrophic strategy
Authors: Rasmussen Hanne N. , Whigham Dennis F.
Published: March 2003

• The mycorrhiza of orchids represents an energy source that may replace or supplement photosynthesis. Dependency on mycotrophy in adult life stages would thus be expected to be inversely related to the prevalence of phototrophic structures.

• The phenology of underground parts and mycorrhizal infection were monitored in five terrestrial species differing in leaf phenology (and thus in phototrophic strategy): Goodyera pubescens (evergreen), Tipularia discolor (wintergreen), Galearis spectabilis and Liparis lilifolia (summergreen) and Corallorhiza odontorhiza (chlorophyll deficient), growing sympatrically in a North American deciduous forest.

• Mycorrhizal infection was extensive in T. discolor roots and C. odontorhiza rhizomes. Only the proximal part of roots was infected in G. pubescens, and mycorrhizal colonisation was patchy in roots and tubers of G. spectabilis and localized in the rhizome in L. lilifolia. Mycotrophic roots were long‐lived (1.5–3 yrs) determinate structures and mycorrhizal infection reached maximum intensity 2–6 months after development. Mycotrophy appeared to be active all year round in mature organs.

• The phenology of mycotrophic roots and patterns of mycorrhizal infection were not related to the leafy season. The hypothesis that phototrophic and mycotrophic nutrition alternate through the seasons could not be confirmed.
Are xylem radial development and hydraulic conductivity in downwardly‐growing grapevine shoots influenced by perturbed auxin metabolism?
Authors: Lovisolo Claudio , Schubert Andrea , Sorce Carlo
Published: March 2003

Downwardly‐growing grapevine shoots have smaller and more frequent vessels than upwardly‐growing ones and, as a consequence, a lower hydraulic conductivity. Here, grapevine ( Vitis vinifera L.) shoot growth orientation was manipulated to test whether downward shoot orientation negatively affects vessel growth in the apex via a shortage of water and nutrients.

The orientation of the central vine shoot portion was inverted by two consecutive 135° bends, resulting in double‐bent N‐shaped vines; the central downward shoot portion was of different lengths in the experimental treatments to induce increasing reductions of shoot conductivity. These treatments reduced shoot conductivity and water flow, but had no effects on vessel development and frequency in the apex.

In a second experiment, auxin concentration was assessed in shoots of upwardly‐ and downwardly‐growing plants. IAA concentration at the apical internodes was higher in downwardly‐oriented shoots than in shoots growing upwards. In addition, a higher density and a lower vessel diameter were observed in the lower, than the upper side, of the downwardly‐oriented shoot, suggesting increased accumulation of auxin in the lower side.

These results suggest that the downward orientation induces accumulation of auxin in the apex, which in turn affects the density and the size of the xylem vessels, causing reduction of hydraulic conductivity.
Plant growth and competition at elevated CO2: on winners, losers and functional groups
Authors: Poorter Hendrik , Navas Marie‐Laure
Published: March 2003

The effects of increased atmospheric CO2 concentrations on vegetative growth and competitive performance were evaluated, using five meta‐analyses. Paying special attention to functional groups, we analysed responses at three integration levels: carbon economy parameters, vegetative biomass of isolated plants, and growth in competition. CO2 effects on seed biomass and plant‐to‐plant variability were also studied. Underlying the growth stimulation is an increased unit leaf rate (ULR), especially for herbaceous dicots. This is mainly caused by an increase in the whole‐plant rate of photosynthesis. The increased ULR is accompanied by a decrease in specific leaf area. The net result of these and other changes is that relative growth rate is only marginally stimulated. The biomass enhancement ratio (BER) of individually grown plants varies substantially across experiments/species, and size variability in the experimental populations is a vital factor in this. Fast‐growing herbaceous C3 species respond more strongly than slow‐growing C3 herbs or C4 plants. CAM species and woody plants show intermediate responses. When grown in competition, C4 species show lowest responses to elevated CO2 at high nutrient conditions, whereas at low nutrient levels N2‐fixing dicots respond relatively strongly. No systematic differences were found between slow‐ and fast‐growing species. BER values obtained for isolated plants cannot be used to estimate BER of the same species grown in interspecific competition – the CO2 response of monocultures may be a better predictor.

Contents

Summary
175

I.
Introduction
176

II.
Materials and Methods
177

III.
Factors underlying the growth response
178

IV.
Variation in biomass enhancement ratio
181

V.
Functional groups of species
184

VI.
The response in a more natural environment
188

VII.
An outlook
192

VIII.
Conclusions
193

Acknowledgements
193

References
193

Appendices
196
Comparative analysis of Canadian, American and Swedish bankruptcy policy: why do governments legislate consumer debt?
Authors: McGregor Sue , Klingander Birgitta , Lown Jean
Published: March 2003

Comparative research in consumer bankruptcy law is scarce. After profiling bankruptcy statistics in each country, the paper compares bankruptcy laws in Canada, United States and Sweden across 20 criteria and then analyses the predominate ideology underlying each law: deviant behaviour modification, consumer protection or social safety net. There is obvious tension between ideologies in each country with the punitive, deviant behaviour modification paradigm the most pervasive across all three countries. There is much we can learn from a comparative policy analysis approach, leading to the conscious development of bankruptcy policy from discernible, declared ideologies. Seven areas for future research are proposed.