bluuebunny/crossref_metadata_2025 huggingface dataset:
The Holocene at Lac de Creno, Corsica, France: a key site for the whole island
Authors: REILLE M. , GAMISANS J. , ANDRIEU‐PONEL V. , De BEAULIEU J.‐L.
Published: March 2003

Two Holocene lake sequences from Lac de Creno, Corsica were analysed on the basis of 119 pollen spectra and with the support of 13 14C‐calibrated dates. The lower part of one of these sequences, corresponding to the late‐
glacial period, has been published previously. The first third of the Post‐glacial is characterized by very particular forest dynamics, namely the absence of a role for deciduous Quercus and Corylus, the presence of mesophilous vegetation types dominated by Taxus, and the major forest role of Erica arborea at lower and mean altitude. At about 7440 cal BP, the occurrence of a major anthropogenic action brought about significant changes in the vegetation, notably an increase of deciduous Quercus and the expansion of Quercus ilex. Later, three major human‐induced events are identified: the first, at about 2290 cal BP, is the cause of a short local expansion of Abies; the second, at about 1150 cal BP, is the degradation of deciduous forests to the benefit of Fagus; the third, at about 310 cal BP, corresponds to the disappearance of Fagus and its replacement by Pinus. Pollen data indicate that Q. ilex, Abies and Fagus are not indigenous in Corsica but spread there during the Postglacial ; this probably took place at about 6980 cal BP for Q. ilex.
Direct interaction between the arbuscular mycorrhizal fungus Glomus intraradices and different rhizosphere microorganisms
Authors: FILION M. , ST‐ARNAUD M. , FORTIN J. A.
Published: March 2003

Arbuscular mycorrhizal (AM) fungi can reduce the incidence and importance of plant root diseases caused by pathogens. The mechanisms involved are not well characterized. We used an in vitro experimental system to test the hypothesis that the extraradical mycelium of AM fungi can interfere directly with microorganisms in the mycosphere and directly or indirectly reduce the population of plant pathogens. This system permitted the isolation of soluble substances released by the extraradical mycelium of Glomus intraradices. The AM fungus was grown on Daucus carota transformed roots in one compartment, while only the extraradical mycelium was allowed to grow in a second compartment. A freezing and centrifugation technique was developed for the extraction and concentration of substances present in the compartment containing only the AM fungal mycelium. Four soil‐inhabiting microorganisms were selected, and conidial germination (fungi) or growth (bacteria) of these was studied in the presence and absence (control) of the extract. In comparison with the control, the results indicated that both the growth of Pseudomonas chlororaphis and the conidial germination of Trichoderma harzianum were stimulated in the presence of the AM fungal extract. In contrast, conidial germination of Fusarium oxysporum f. sp. chrysanthemi was reduced while the growth of Clavibacter michiganensis subsp. michiganensis was not affected. The measured effects in general were directly correlated with extract concentration. Differences in pH were noted between the extract containing substances released by the AM fungus and the non‐AM control, but no significant influence of the pH on growth or conidial germination was noted, confirming that substances released by the AM fungus in the growth medium is the main factor explaining differential growth of the microorganisms tested. The results suggest that direct interactions exist between AM fungi and soil microorganisms, which might lead to changes in microbial equilibrium detrimental to pathogens.
Nuclear magnetic resonance imaging in studies of gravitropism in soil mixtures
Authors: ANTONSEN FRANK , JOHNSSON ANDERS , FUTSAETHER CECILIA , KRANE JOSTEIN
Published: March 2003

Gravitropic responses of oat coleoptiles were measured in different growth media; humid air, natural soil and artificial soil (glass beads). The oat coleoptiles in soil and glass beads were monitored by NMR imaging, while those in humid air were imaged in darkness with an infrared‐sensitive charge‐coupled device (CCD) camera. The present study shows for the first time that gravitropic experiments can be performed in artificial soil using NMR imaging as a convenient and suitable recording method. Not only was it possible to follow the gravitropic curvatures in natural soil, but the artificial soil allowed plant images of sufficient spatial and temporal resolution to be recorded. The advantages of using artificial soil in magnetic resonance imaging studies are that the iron content of glass beads is very low compared with natural soil, and that the artificial soil matrix can easily be standardized with regard to particle size distribution and nutrient content. Two types of glass beads were used, the diameter of the small and the large beads being 300–400 and 420–840 μm, respectively. The growth rate of the coleoptiles in soil and in big beads was roughly the same and only slightly lower than in humid air, whereas small beads reduced the growth rate by approx. 16%. The bending rate of the coleoptiles during the gravitropic response was reduced by c. 65% in soil and 75% in bead mixtures relative to bending in air. It should be noted, however, that the maximum curvature of the coleoptile tip was of the same order in all cases, about 35°. This value may represent the largest possible curvature of the organ. The potential of NMR imaging to study how plant organs penetrate the soil under the influence of gravitropism, mechanical impedance and thigmotropism is also discussed.
Localized elongation of roots of cotton follows establishment of arbuscular mycorrhizas
Authors: TORRISI V. , PATTINSON G. S. , McGEE P. A.
Published: March 2003

In an experiment to determine the influence of mycorrhizal colonization on root development, fertilized seedlings of cotton were grown in long tubular pots. Inoculation of soil with an isolate of Glomus mosseae at 10, 25 or 40 cm below the soil surface resulted in spread of arbuscular mycorrhizas up and down the root system, and localized elongation of roots following colonization. Specific root length was not influenced by colonization. Increases in local root density at the point of inoculation were observed, though total root mass in relation to shoot mass declined following initiation of mycorrhizas.
Low‐light carbon balance and shade tolerance in the seedlings of woody plants: do winter deciduous and broad‐leaved evergreen species differ?
Authors: WALTERS MICHAEL B. , REICH PETER B.
Published: March 2003

An appendix is available for this article which was not included in the print edition of the Journal. The appendix may be found at the rear of the full text, PDF version of the article.

A popular conceptual model asserts that shade tolerance is characterized by morphological and physiological traits that enhance the net rate of carbon capture in low light. We tested this model by quantitatively reviewing growth, leaf lifespan, CO2 exchange and morphological data from 76 studies on woody seedlings grown under conditions of low light. Data were placed into three tolerance categories (intolerant, intermediate, tolerant), two light categories (less than 4% and 4–12%) and two leaf phenology categories (broad‐leaved evergreen and winter deciduous). For both evergreen and deciduous groups, intolerant species had traits conferring greater growth potential than tolerant species in both light categories. These traits included greater leaf mass ratio, leaf area ratio, specific leaf area and mass‐based photosynthetic rates above light compensation. However, in 0–4% light, growth rates were similar for intolerant and tolerant species, because low light together with higher respiration rates for intolerant species limited the expression of their growth potential differences. Deciduous and evergreen intolerant species were similar in many respects. However, both intermediate and tolerant deciduous species had markedly lower leaf mass ratios and higher root mass ratios than intermediate and tolerant evergreen species. In addition, deciduous species and intolerant evergreens must cope with as much as sixfold higher leaf turnover rates than tolerant evergreen species. Thus, rather than maximizing growth rates in low light, tolerant evergreen species minimize biomass loss through long leaf lifespans and low respiration rates. Tolerant deciduous species also minimize biomass losses by minimizing whole‐plant respiration rates but they accomplish low biomass turnover though low leaf mass ratio and not low leaf turnover rates. Furthermore, unlike most tropical evergreens, tolerant deciduous species can gain large fractions of their total growing season carbon during short periods when the overstory is leafless and then allocate this carbon to storage (as reflected by high root mass ratios) rather than new leaves. In conclusion, we found no support for the low‐light‐enhanced carbon capture model of shade tolerance as viewed strictly from the perspective of physiological growth capacity. This can be explained by the disadvantages to net growth and survival of maintaining a high growth potential at low light, because high growth potential results in greater rates of whole‐plant respiration, tissue turnover, herbivory and mechanical damage and in decreased storage. Thus, shade tolerance can be characterized by traits that maximize survival and net growth, where net growth includes losses to all agents.
Specific leaf area and leaf dry matter content as alternative predictors of plant strategies
Authors: WILSON PETER J. , THOMPSON KEN , HODGSON JOHN G.
Published: March 2003

A key element of most recently proposed plant strategy schemes is an axis of resource capture, usage and availability. In the search for a simple, robust plant trait (or traits) that will allow plants to be located on this axis, specific leaf area is one of the leading contenders. Using a large new unpublished database, we examine the variability of specific leaf area and other leaf traits, the relationships between them, and their ability to predict position on the resource use axis. Specific leaf area is found to suffer from a number of drawbacks; it is both very variable between replicates and much influenced by leaf thickness. Leaf dry‐matter content (sometimes referred to as tissue density) is much less variable, largely independent of leaf thickness and a better predictor of location on an axis of resource capture, usage and availability. However, it is not clear how useful dry matter content will be outside northwest Europe, and in particular in dry climates with many succulents.
Leaf anatomy enables more equal access to light and CO2 between chloroplasts
Authors: EVANS JOHN R.
Published: March 2003

The function of a leaf is photosynthesis, which requires the interception of light and access to atmospheric CO2 while controlling water loss. This paper examines the influence of leaf anatomy on both light capture and CO2 diffusion. As photosynthetic metabolism is spread between many chloroplasts, a leaf faces the challenge of matching light capture by a given chloroplast with the metabolic capacity of that chloroplast. Chloroplasts nearest the leaf surface receive the greatest irradiance and therefore absorb more light per unit chlorophyll than chloroplasts in the centre of a leaf. Electron transport and carbon fixation capacities per unit of chlorophyll decline with increasing depth in the leaf, to compensate for the decline in light absorbed per unit chlorophyll. Many key photosynthetic protein complexes in chloroplasts have nuclear encoded genetic information. Consequently, all chloroplasts within a given cell have a similar metabolic complement, which limits the potential gradient of photosynthetic capacity per unit chlorophyll across the leaf. A simple model couples light absorption through the leaf (based on the Beer–Lambert law) with the profile of chlorophyll through a leaf and the gradient in photosynthetic capacity. It is validated by comparison with 14CO2 fixation profiles through spinach leaves obtained in various studies. The model can account for published 14C fixation profiles obtained with blue, red and green light of different irradiances and white light applied in different combinations to the adaxial and abaxial surfaces of spinach leaves. The model confirms that spongy mesophyll increases the apparent extinction coefficient of chlorophyll compared to palisade tissue. The palisade tissue nearest the surface which receives light facilitates the penetration of light to a greater depth, while spongy mesophyll promotes scattering to enhance light absorption, thus reducing the gradient in light absorbed per unit chlorophyll through a leaf. CO2 fixation faces a diffusional limitation, which necessitates Rubisco to be spread evenly across the cell walls exposed to intercellular airspace. Mesophyll cell structure reflects the need to have a large cell surface per unit volume exposed to airspaces. The regular array of columnar cells in palisade tissue, or cell lobing in monocot leaves, results in greater exposed surface per unit tissue volume than spongy mesophyll. The exposed surface area per unit leaf area scales with photosynthetic capacity such that the difference in CO2 partial pressure between substomatal cavities and the sites of carboxylation within chloroplasts is, on average, independent of photosynthetic capacity of the leaf. However, Rubisco specific activity declines as the Rubisco content per unit leaf area increases due to greater internal diffusional limitations.
Infection time and density influence the response of sorghum to the parasitic angiosperm Striga hermonthica
Authors: GURNEY A. L. , PRESS M. C. , SCHOLES J. D.
Published: March 2003

Two cultivars of sorghum (CSH‐1 and Ochuti) were grown in the presence and absence of the root hemiparasite Striga hermonthica in uniform conditions in the field in Kenya, Africa. S. hermonthica had a marked influence on growth and photosynthesis of ‘CSH‐1’; however, ‘Ochuti’ showed a less severe response to infection and tolerance of the parasite. The variation in genotype response might be partly explained by later attachment of the parasite and a lower level of infection. Laboratory studies were used to determine the importance of both variables in determining host response to infection. Early infection by S. hermonthica had a more negative effect on the host than late infection. The level of parasite biomass supported by the host also influenced host productivity but the relationship was nonlinear. Low degrees of parasite infection had a proportionately much greater effect on host grain weight than at greater parasite loading. Early infection of ‘Ochuti’ in laboratory conditions resulted in lower stem dry weight than in uninfected plants but not in smaller total plant biomass or lower rates of photosynthesis. In conclusion, the time of parasite attachment affected host performance and might explain much of the variation in host sensitivity both within and between studies. The level of parasite infection affected host performance to a lesser extent. In addition, late attachment and low levels of infection might have implications for control management strategies.
Diurnal changes in xylem pressure of the hydrated resurrection plant Myrothamnus flabellifolia: evidence for lipid bodies in conducting xylem vessels
Authors: SCHNEIDER H. , THÜRMER F. , ZHU J. J. , WISTUBA N. , GESSNER P. , LINDNER K. , HERRMANN B. , ZIMMERMANN G. , HARTUNG W. , BENTRUP F.‐W. , ZIMMERMANN U.
Published: March 2003

The resurrection plant Myrothamnus flabellifolia has the ability to recover from repeated prolonged and extreme desiccation cycles. During the dry state the inner walls of the xylem vessels seemed to be covered, at least partly, by a lipid film as shown by Sudan III and Nile Red staining. The lipid film apparently functioned as an ‘internal cuticle’ which prevented the adjacent parenchyma ray cells from complete water loss. The hydrophobic nature of the inner xylem walls was supported by the finding that benzene ascended as rapidly as water in the xylem of dry Myrothamnus branches. On watering, numerous lipid bodies were found in the water‐conducting vessels, presumably formed from the lipid film and/or from lipids excreted from the adjacent living cells into the vessels. The presence of lipid bodies within the vessels, as well as the hydrophobic properties of the inner xylem walls, could explain the finding that the xylem pressure of hydrated, well watered plants (measured both under laboratory and field conditions with the xylem pressure probe) never dropped below c. −0.3 MPa and that cavitation occurred frequently at low negative xylem pressure values (−0.05 to −0.15 MPa). The xylem pressure of M. flabellifolia responded rapidly and strongly to changes in relative humidity and temperature, but less obviously to changes in irradiance (which varied between 10 and c. 4000 μmol m m−2 s−1). The morphological position of the stomata in the leaves could explain the extremely weak and slow response of the xylem pressure of this resurrection plant to illumination changes. Stomata were most abundant in the furrows, and were thus protected from direct sunlight. Simultaneous measurements of the cell turgor pressure in the leaf epidermal cells (made by using the cell turgor pressure probe) revealed that the xylem and the cell turgor pressure dropped in a ratio of 1:0.7 on changes in the environmental parameters, indicating a quite close hydraulic connection and, thus, water equilibrium between the xylem and cellular compartments. An increase in irradiance of c. 700 μmol m−2 s−1 resulted in a turgor pressure decrease from 0.63 to 0.48 MPa. Correspondingly, the cell osmotic pressure increased from 1.03 to 1.22 MPa. From these values and by assuming water equilibrium, the osmotic pressure of the xylem sap was estimated to be 0.25–0.4 MPa. This value seems to be fairly high but may, however, be explained by the reduction of the water volume within the vessels due to the floating lipid bodies.
Diurnal regulation of photosynthesis in understory saplings
Authors: SINGSAAS ERIC L. , ORT DONALD R. , DeLUCIA EVAN H.
Published: March 2003

Photosynthetic rates of plants grown in natural systems exhibit diurnal patterns often characterized by an afternoon decline, even when measured under constant light and temperature conditions. Since we thought changes in the carbohydrate status could cause this pattern through feedback from starch and sucrose synthesis, we studied the natural fluctuations in photosynthesis rates of plants grown at 36 and 56 Pa CO2 at a FACE (free‐air‐CO2‐enrichment) research site. Light‐saturated photosynthesis varied by 40% during the day and was independent of the light‐limited quantum yield of photosynthesis, which varied little through the day. Photosynthesis did not correspond with xylem water potential or leaf carbohydrate build‐up, but rather with diurnal changes in air vapor‐pressure deficit and light. The afternoon decline in photosynthesis also corresponded with decreased stomatal conductance and decreased Rubisco carboxylation efficiency which in turn allowed leaf‐airspace CO2 partial pressure to remain constant. Growth at elevated CO2 did not affect the afternoon decline in photosynthesis, but did stimulate early‐morning photosynthesis rates relative to the rest of the day. Plants grown at 56 Pa CO2 had higher light‐limited quantum yields than those at 36 Pa CO2 but, there was no growth–CO2 effect on quantum yield when measured at 2 kPa O2. Therefore, understory plants have a high light‐limited quantum yield that does not vary through the day. Thus, the major diurnal changes in photosynthesis occur under light‐saturated conditions which may help understory saplings maximize their sunfleck‐use‐efficiency.
Ontogenic changes of thioredoxins f and m, and of their targets fructose‐1,6‐bisphosphatase and NAD(P)‐malate dehydrogenase, of pea plants grown under light stress conditions
Authors: PAGANO EDUARDO A. , CHUECA ANA , HERMOSO ROSARIO , LAZARO JUAN JOSE , LOPEZ‐GORGE JULIO
Published: March 2003

The transcript (mRNA) level and the protein content (as determined by enzyme‐linked immunosorbent assay) of thioredoxins (Trx) f and m, and of their targets, chloroplast fructose‐1,6‐bisphosphatase (FBPase) and NAD(P)‐
malate dehydrogenase (NADP‐MDH), increase over the ontogeny of pea plants grown under normal conditions, showing their highest values before flowering (40 d growth). The clearest results appear in apical, but also in middle leaves. Enzyme activites of FBPase and NADP‐MDH were lowest just before flowering. In the case of FBPase this was probably a mechanism to facilitate triose‐phosphate export to the cytosol for sucrose synthesis. The likely function of NADP‐MDH is to supply the cytosol, via the malate translocator, with the NAD(P)H necessary for UTP regeneration in the sucrose biosynthetic pathway. Both the Fv/Fm ratio and the net photosynthetic rate (IRGA) decreased at saturating irradiance (16 h photoperiod) and under sub‐saturating continuous light. However, the Fv/Fm quotient recovered to normal values after several days adaptation to high light. A similar recovery was also observed in net photosynthesis, although normal levels were never obtained. Under light‐stress conditions the concentration of Trxs f and m, and of the targets FBPase and NADP‐MDH, were somewhat lower than those of unstressed plants. Even though the levels of the corresponding transcripts (mRNAs) are similar in upper leaves from control and light‐stressed plants, those of the middle and basal leaves from plants grown under high light were substantially higher than those of the control plants. In addition to the well‐documented transcriptional regulation of nuclear‐coded chloroplast proteins, these results seem to indicate the existence of an additional post‐transcriptional control.
Zinc and cadmium hyperaccumulation by Thlaspi caerulescens from metalliferous and nonmetalliferous sites in the Mediterranean area: implications for phytoremediation
Authors: ESCARRÉ J. , LEFÈBVRE C. , GRUBER W. , LEBLANC M. , LEPART J. , RIVIÈRE Y. , DELAY B.
Published: March 2003

Growth, tolerance and zinc and cadmium hyperaccumulation of Thlaspi caerulescens populations from three metal
contaminated soils and three normal soils were compared under controlled conditions. Individuals of six
populations were cultivated on five soils with increasing concentrations of zinc (50–25000 μg g−1) and cadmium
(1–170 μg g−1). There was no mortality of normal soil populations in the four metal‐contaminated soils, but plant
growth was reduced to half that of populations from metal‐contaminated soils. However, in noncontaminated soil,
the growth of individuals from normal soils was greater than that of individuals from metal‐contaminated soils.
Individuals from normal soils concentrated three times more zinc in the aboveground biomass than those from
metal‐contaminated soils, but the latter accumulated twice as much cadmium. We conclude that populations of
T. caerulescens from both normal and metal‐contaminated soils are interesting material for phytoextraction of zinc and cadmium, but to optimize the process of phytoextraction it is necessary to combine the extraction potentials of both type of populations.
Physiological impacts of Mg deficiency in Pinus radiata: growth and photosynthesis
Authors: LAING WILLIAM , GREER DENNIS , SUN OSBERT , BEETS PETER , LOWE ALISON , PAYN TIM
Published: March 2003

This paper reports the effects of nutrient magnesium (Mg) concentrations on the growth and photosynthetic physiology of clonal Pinus radiata from four female parents (families) known to differ in their tolerance to Mg
deficiency and in their needle Mg concentrations. Plants were grown in flowing nutrient solutions with 2 mg l−1
(control) and 0.8 mg l−1 (low) Mg. Plant growth, needle Mg concentration, photosynthesis, chlorophyll fluorescence and carotenoid pigment content were measured. At low Mg, needle Mg concentration was about half that of control plants, height growth was reduced 15–25%, and the needles showed strong visual characteristics of Mg deficiency. Photosynthesis was also halved, and was associated with closure of the stomata under low Mg and with reductions in the residual conductance. In needles from plants grown at low Mg, photochemical yield was reduced both in the light and in the dark, and was strongly dependent on needle Mg concentrations below a threshold concentration of 0.02–0.025% (d. wt basis). The electron transport rate (ETR) at saturating photon flux density in low‐Mg‐grown needles was reduced to about half that of their Mg controls, but the photon efficiency of ETR was unaffected by the Mg concentration the plants were grown in. Photosynthetic quenching was markedly reduced and non‐photosynthetic quenching was increased following growth in low Mg. Growth under low Mg also increased levels of zeaxanthin. Although family differences in growth and photosynthetic physiology were present, few family × Mg interactions were significant. We conclude that Mg deficiency probably affects growth through severe reductions in photosynthesis.
Tansley Review No. 111
Authors: CAKMAK ISMAIL
Published: March 2003

Zinc deficiency is one of the most widespread micronutrient deficiencies in plants and causes severe reductions in crop production. There are a number of physiological impairments in Zn‐deficient cells causing inhibition of the growth, differentiation and development of plants. Increasing evidence indicates that oxidative damage to critical cell compounds resulting from attack by reactive O2 species (ROS) is the basis of disturbances in plant growth caused by Zn deficiency. Zinc interferes with membrane‐bound NADPH oxidase producing ROS. In Zn‐deficient plants the iron concentration increases, which potentiates the production of free radicals. The Zn nutritional status of plants influences photooxidative damage to chloroplasts, catalysed by ROS. Zinc‐deficient leaves are highly light‐sensitive, rapidly becoming chlorotic and necrotic when exposed to high light intensity. Zinc plays critical roles in the defence system of cells against ROS, and thus represents an excellent protective agent against the oxidation of several vital cell components such as membrane lipids and proteins, chlorophyll, SH‐containing enzymes and DNA. The cysteine, histidine and glutamate or aspartate residues represent the most critical Zn‐ binding sites in enzymes, DNA‐binding proteins (Zn‐finger proteins) and membrane proteins. In addition, animal studies have shown that Zn is involved in inhibition of apoptosis (programmed cell death) which is preceded by DNA and membrane damage through reactions with ROS.

contents

Summary
185

I.
introduction
186

II.
effect of zinc on production of reactive oxygen species
186

III.
membrane damage by reactive oxygen species
193

III.
membrane damage by reactive oxygen species
193

V.
involvement of zinc in plant stress tolerance
199

VI.
conclusions
199

Acknowledgements
200

References
200
The impact of elevated CO2 and global climate change on arbuscular mycorrhizas: a mycocentric approach
Authors: FITTER A. H. , HEINEMEYER A. , STADDON P. L.
Published: March 2003

Arbuscular mycorrhizal (AM) symbioses are a potentially important link in the chain of response of ecosystems to elevated atmospheric [CO2]. By promoting plant phosphorus uptake and acting as a sink for plant carbon, they
can alleviate photosynthetic down‐regulation. Because hyphal turnover is likely to be fast, especially in warmer
soils, they can also act as a rapid pathway for the return of carbon to the atmosphere. However, most experiments
on AM responses to [CO2] have failed to take into account the difference in growth of mycorrhizal and non‐
mycorrhizal plants; those that have done so suggest that AM colonization of roots is little altered by [CO2], although this issue remains to be resolved. Very little is known about the effects of other factors of global environmental change on mycorrhizas. These issues need urgent attention. It is also necessary to understand the potential for the various AM fungal taxa to respond differentially to environmental changes, including carbon supply and soil temperature and moisture, especially because of the differential abilities of plant and fungal species to migrate in response to changing environments. Indeed, there is a need for a new approach to the study of mycorrhizal associations, which has been too plant‐centred. It is essential to regard the fungus as an organism itself, and to understand its biology both as an entity and as part of a symbiosis.
Building roots in a changing environment: implications for root longevity
Authors: EISSENSTAT D. M. , WELLS C. E. , YANAI R. D. , WHITBECK J. L.
Published: March 2003

Root turnover is important to the global carbon budget as well as to nutrient cycling in ecosystems and to the success of individual plants. Our ability to predict the effects of environmental change on root turnover is limited by the difficulty of measuring root dynamics, but emerging evidence suggests that roots, like leaves, possess suites of interrelated traits that are linked to their life span. In graminoids, high tissue density has been linked to increased root longevity. Other studies have found root longevity to be positively correlated with mycorrhizal colonization and negatively correlated with nitrogen concentration, root maintenance respiration and specific root length. Among fruit trees, apple roots (which are of relatively small diameter, low tissue density and have little lignification of the exodermis) have much shorter life spans than the roots of citrus, which have opposite traits. Likewise, within the branched network of the fine root system, the finest roots with no daughter roots tend to have higher N concentrations, faster maintenance respiration, higher specific root length and shorter life spans than secondary and tertiary roots that bear daughter roots. Mycorrhizal colonization can enhance root longevity by diverse mechanisms, including enhanced tolerance of drying soil and enhanced defence against root pathogens. Many variables involved in building roots might affect root longevity, including root diameter, tissue density, N concentration, mycorrhizal fungal colonization and accumulation of secondary phenolic compounds. These root traits are highly plastic and are strongly affected by resource supply (CO2, N, P and water). Therefore the response
of root longevity to altered resource availability associated with climate change can be estimated by considering
how changes in resource availability affect root construction and physiology. A cost–benefit approach to predicting
root longevity assumes that a plant maintains a root only until the efficiency of resource acquisition is maximized.
Using an efficiency model, we show that reduced tissue Nconcentration and reduced root maintenance respiration,
both of which are predicted to result from elevated CO2, should lead to slightly longer root life spans. Complex interactions with soil biota and shifts in plant defences against root herbivory and parasitism, which are not included in the present efficiency model, might alter the effects of future climate change on root longevity in unpredicted ways.
Matsutake – morphological evidence of ectomycorrhiza formation between Tricholoma matsutake and host roots in a pure Pinus densiflora forest stand
Authors: GILL WARWICK M. , GUERIN‐LAGUETTE ALEXIS , LAPEYRIE FRÉDÉRIC , SUZUKI KAZUO
Published: March 2003

There has been conflicting debate over many years regarding the trophic status of Matsutake. Here we examined the morphology, structure and ultrastructure of Pinus densiflora roots collected from a Tricholoma matsutake Shiro
within a pure Japanese red pine stand. Molecular investigations (PCR–RFLP analyses) indicated that T. matsutake
was the highly dominant fungus within both the Shiro and the colonized root tips, suggesting that reported root
morphology modifications can be attributed to T. matsutake infection. The external morphology of Matsutake‐colonized roots is consistent with previous descriptions. The presence of extraradical mycelium, mantle, and
intracortical Hartig net hyphae indicates clearly that T. matsutake forms an ectomycorrhizal association with P.
densiflora in naturally occurring Shiros. The elucidation, for the first time, of the Hartig net ultrastructure at the
host–fungus interface provides further and convincing evidence of a conventional ectomycorrhizal association.
The progressive blackening, observed from base to tip in dominant mycorrhizal types, due to increased deposition
of polyphenol and subsequent necrosis, appears to be a result of infection. However, the presence of highly
nucleated vascular tissue indicates the viability of the vascular cylinder in these roots bearing necrotic cortices.
Such a preponderance of black necrotic cortical tissues among colonized roots may reflect some atypical behaviour
of T. matsutake.
What are the effects of nitrogen deficiency on growth components of lettuce?
Authors: BROADLEY M. R. , ESCOBAR‐GUTIÉRREZ A. J. , BURNS A. , BURNS I. G.
Published: March 2003

Relationships between nitrogen (N) content and growth are routinely measured in plants. This study determined the effects of N on the separate morphological and physiological components of plant growth, to assess how N‐limited growth is effected through these components. Lettuce (Lactuca sativa) plants were grown hydroponically under contrasting N‐supply regimes, with the external N supply either maintained continuously throughout the period of study, or withdrawn for up to 14 d. Richards' growth functions, selected using an objective curve‐fitting technique, accounted for 99.0 and 99.1% of the variation in plant dry weight for control and N‐limited plants respectively. Sublinear relationships occurred between N and relative growth rates under restricted N‐supply conditions, consistent with previous observations. There were effects of treatment on morphological and physiological components of growth. Leaf weight ratio increased over time in control plants and decreased in N‐ limited plants. Shoot:root ratio followed a similar pattern. On a whole‐plant basis, assimilation of carbon decreased in N‐limited plants, a response paralleled by differences in stomatal conductance between treatments. Changes in C assimilation, expressed as a function of stomatal conductance to water vapour, suggest that the effects of N limitation on growth did not result directly from a lack of photosynthetic enzymes. Relationships between plant N content and components of growth will depend on the availability of different N pools for remobilization and use within the plant.
Low leaf‐level response to light and nutrients in Mediterranean evergreen oaks: a conservative resource‐use strategy?
Authors: VALLADARES FERNANDO , MARTINEZ‐FERRI ELSA , BALAGUER LUIS , PEREZ‐CORONA ESTHER , MANRIQUE ESTEBAN
Published: March 2003

We have explored leaf‐level plastic response to light and nutrients of Quercus ilex and Q. coccifera, two closely
related Mediterranean evergreen sclerophylls, in a factorial experiment with seedlings. Leaf phenotypic plasticity,
assessed by a relative index (PI = (maximum value ‐ minimum)/maximum) in combination with the significance
of the difference among means, was studied in 37 morphological and physiological variables. Light had significant
effects on most variables relating to photosynthetic pigments, chlorophyll fluorescence and gas exchange, whereas
nutrient treatment had a significant effect in only 10% of the variables. Chlorophyll content was higher in the
shade whereas carotenoid content and nonphotochemical quenching increased with light. Nutrient limitations
increased the xanthophyll‐cycle pool but only at high light intensities, and the same interaction between light and
nutrients was observed for lutein. Predawn photochemical efficiency of PSII was not affected by either light or
nutrients, although midday photochemical efficiency of PSII was lower at high light intensities. Photosynthetic
light compensation point and dark respiration on an area basis decreased with light, but photosynthetic capacity
on a dry mass basis and photochemical quenching were higher in low light, which translated into a higher nitrogen
use efficiency in the shade. We expected Q. ilex, the species of the widest ecological distribution, to be more plastic
than Q. coccifera, but differences were minor: Q. ilex exhibited a significant response to light in 13% more of the
variables than Q. coccifera, but mean PI was very similar in the two species. Both species tolerated full sunlight and moderate shade, but exhibited a reduced capacity to enhance photosynthetic utilization of high irradiance. When compared with evergreen shrubs from the tropical rainforest, leaf responsiveness of the two evergreen oaks was low. We suggest that the low leaf‐level responsiveness found here is part of a conservative resource use strategy, which seems to be adaptive for evergreen woody plants in Mediterranean‐type ecosystems.
Flooding tolerance of Carex species in relation to field distribution and aerenchyma formation
Authors: VISSER E. J. W. , BÖGEMANN G. M. , VAN DE STEEG H. M. , PIERIK R. , BLOM C. W. P. M.
Published: March 2003

The flooding tolerance of Carex species was studied in relation to their field distribution and their capacity to form
root aerenchyma under controlled conditions. In an alpine meadow, six Carex species were selected which were
distributed in a clear zonation correlating with water content of the soil. Carex sempervirens and C. ferruginea were
only found on nonflooded soil, the latter species preferring moister conditions. Carex davalliana and C. nigra were
both associated with water‐saturated soil, whereas C. limosa and C. rostrata preferred partially submerged
conditions. Carex davalliana and C. limosa were bound to flooded soils with a relatively high redox potential and
horizontally flowing groundwater. Carex rostrata and C. nigra grew in stagnant soil‐flooded conditions with low
soil redox potentials. The amount of aerenchyma in the roots of all species increased when grown in oxygen‐deficient stagnant agar. This increase in root porosity, combined with increased root diameter, presumably
improved internal aeration of the roots. Although all species survived experimental soil flooding, partial
submergence was lethal to C. sempervirens and, surprisingly, also to the wetland species C. davalliana. Carex
ferruginea showed a reduced growth rate during partial submergence. The three other species, all wetland plants,
reached highest biomass production under soil‐flooded and partially submerged conditions, with slower
growth on free‐draining soil. It is concluded that aerenchyma is not constitutive in the Carex species under study,
and is best developed in Carex species from wetlands. Species with less aerenchyma perform poorly when soil‐flooded, but conditions of partial submergence could even affect species with a considerable amount of root aerenchyma.
Pollen from Lake Sedmo Rilsko reveals southeast European postglacial vegetation in the highest mountain area of the Balkans
Authors: BOZILOVA E. D. , TONKOV S. B.
Published: March 2003

A lacustrine sequence from Lake Sedmo Rilsko (altitude 2095 m) in the northwest of Rila Mountain, Bulgaria, was analysed on the basis of 84 pollen spectra and three 14C accelerator mass spectrometry dates. The lower part
of the sequence (413–530 cm) corresponds to the Late‐glacial. Three phases, two stadial and one interstadial, are
characterized by the dominance of mountain–steppe herb vegetation composed of Artemisia, Chenopodiaceae and
Poaceae, with single trees of Pinus and shrub land of Juniperus and Ephedra. The identification of pollen grains
of Abies, Quercus robur‐type, Corylus, Acer, Fagus and other mesophilous trees suggests that they survived the
harsh Late‐glacial conditions in refuges below an altitude of 1000 m, where moisture was sufficient for their
growth. In the early Holocene period, Betula forests at high altitudes and, below them, closed deciduous forests
with Quercus, Tilia, Ulmus and Corylus, occurred from 11800 until approx. 6700 cal. BP. The formation of the
coniferous belt dominated by Pinus sylvestris, Pinus peuce and Abies alba lasted from between 6700 and 5000 cal.
BP. The forest dynamics in the Subboreal and the Subatlantic ended with the invasion of Fagus sylvatica and Picea
abies after approx. 4500 and 3300 cal. BP, respectively. Indications of anthropogenic activities, expansion of agriculture in the lowland foothills, and livestock grazing in the mountain meadows and pastures, are clearly evident from the pollen diagram from 2400 cal. BP onwards.
Scaling ozone effects from seedlings to forest trees
Authors: Samuelson Lisa , Kelly J. Michael
Published: March 2003

Biospheric ozone has become a widely distributed air pollutant, and a growing body of research indicates that ozone impacts forest health and productivity. Ozone effects are mediated by the ozone concentration present in the external environment and the movement of ozone into the leaf via the stoma. The cumulative dose received by the plant is, in the simplest terms, a function of ambient ozone concentration and stomatal conductance to water vapor. This relationship is important in understanding ozone flux into the leaf and subsequent ozone response in plants. Here, current progress in understanding ozone uptake in juvenile and mature trees is examined. Through an analysis of two long‐term case studies, the significant uncertainty in assessing ozone effects on forests is pinpointed to be the scaling of ozone sensitivity from controlled seedling studies to large forest trees. A rigorous statistical and monitoring approach, which includes ozone uptake as a cause variable, may provide the missing information on processes that are known to be important to risk assessment of ozone impacts on forest trees.ContentsSummary21I.Introduction221.Background222.Characterization of ozone exposure223.The need for scaling23II.Scaling from seedling to tree, evidence from aQuercus rubracase study241.Study background242.Facilities and measurements243.Ozone exposure dynamics244.Above‐ground processes255.Below‐ground processes266.A process modelling exercise277.Conclusions28III.Scaling from chamber to forest, evidence from a field case study291.Study background292.Field sites and measurements303.Ozone exposure dynamics304.Stomatal conductance and ozone uptake in forest trees305.Conclusions32IV.Evidence from a scaling exercise33V.Concluding remarks36Acknowledgements37References37
Trehalose induces resistance to powdery mildew in wheat
Authors: Reignault PH. , Cogan A. , Muchembled J. , Lounes‐Hadj Sahraoui A. , Durand R. , Sancholle M.
Published: March 2003

• Reduction in the degree of powdery mildew infection of wheat leaves is observed after treatments with trehalose, a nonreducing disaccharide commonly found in a wide variety of organisms, including fungi.

• Wheat (Triticum aestivum) cv. Sideral plants grown in phytotrons were inoculated withBlumeria graminisf.sp.tritici. In addition to degree of infection, the effect of trehalose solution was further investigated using light and fluorescence microscopy and enzyme assays.

• Infection in wheat leaves was reduced by 50 and 95% with trehalose solution (15 g l−1) following a single spraying and three sprayings, respectively; in a detached leaf assay, trehalose was effective at concentrations as low as 0.01 g l−1. Trehalose did not inhibit conidial germination and differentiation of appressoria (in vitroor on the leaf epidermis), but enhanced papilla deposition in epidermal cells. Trehalose also enhanced phenylalanine ammonia‐lyase (PAL) and peroxidase (PO) activities; both markers of plant defence responses. However, the level of three cinnamyl alcohol dehydrogenase (CAD) activities (conyferyl,p‐coumaryl and sinapyl alcohol dehydrogenase) was unchanged.

• Trehalose treatment of wheat confers resistance toB. graminisinfection by activating plant defence responses (e.g. papilla deposition, PAL and PO activities).
Linking wood density with tree growth and environment: a theoretical analysis based on the motion of water
Authors: Roderick Michael L. , Berry Sandra L.
Published: March 2003

• An hydraulic model of a tree stem is presented to help understand how the carbon storage in ecosystems varies with changing environmental conditions.

• The model is based on the assumption that a tree stem is a collection of parallel pipes and was used to (qualitatively) predict how the mass concentration of dry matter ([D]) would vary with water temperature (via changes in viscosity), nitrogen supply and atmospheric CO2.

• There was qualitative agreement between model predictions and observed gross trends. The model predicted that the flow rate would be relatively insensitive to variations in [D] in angiosperm stems; this was consistent with observations. It is concluded that other factors need to be considered to explain variations in [D] in angiosperm wood. The flow rate of water through gynmosperm stems was predicted to be very sensitive to variations in [D] and the model explained why [D]; decreases with decreases in water temperature, decreases with increases in nitrogen supply and increases with elevated CO2.

• The model captured some of the important underlying relations linking water transport with wood density and environment and qualitative testing of the model is recommended.
Short photoperiods induce fructan accumulation and tuberous root development in Dahlia seedlings
Authors: Legnani Garry , Miller William B.
Published: March 2003

• The effect is reported here of photoperiod on fructan accumulation in the tuberous roots of Dahlia sp. cv. Sunny Rose seedlings.

• Growth parameters were measured of shoots and roots on glasshouse‐grown dahlia seedlings subjected to either short day (SD) or long day (LD; 4 h night photoperiod interruption) light regimes. The carbohydrate concentrations of tuberous roots was analysed by high performance anion exchange chromatography.

• Total plant dry weight was unaffected by photoperiod. The LD treatment inhibited tuberous root development but increased shoot dry weight. Tuberous root tissue of SD seedlings showed a 156% increase in total fructan (inulin) concentration compared with LD tuberous root tissue, which had higher reducing sugar concentrations than SD tuberous roots. A wide range of oligomers increased during the SD treatment.

• Sucrose appears to be the regulating factor in fructan metabolism in dahlia. Photoperiod is a valuable tool for studying fuctan metabolism in vivo, as it provides a nondestructive means of regulating sucrose partitioning.
Free‐air CO2 enrichment (FACE) of a poplar plantation: the POPFACE fumigation system
Authors: Miglietta Franco , Peressotti Alessandro , Vaccari Francesco Primo , Zaldei Alessandro , DeAngelis Paolo , Scarascia‐Mugnozza Giuseppe
Published: March 2003

A new design of free‐air CO2 enrichment (FACE) is presented that has been used to expose a poplar plantation to elevated atmospheric CO2 concentrations in other‐wise unaltered conditions, in the open.

 This system releases pure CO2 at high velocity, through a large number of small gas jets, causing rapid mixing between CO2 and air. The theoretical and practical aspects of this design are described, with emphasis on the fluid mechanics of air–CO2 mixing in sonic jets. Field performance data, including spectral analysis of short‐term fluctuations in CO2 concentrations as well as temporal and spatial CO2 control, are reported for the European project POPFACE facility.

 Temporal and spatial performances of the operational POPFACE systems were adequate with average long‐term CO2 mole fractions on target. Averages over 1 min measured in the centre of the rings were within ±20% and ±10% of the target concentration for > 91% and > 75% of the time, respectively.

 The data presented provide convincing evidence that a pure‐CO2 FACE system can achieve reliable control, in terms of the quality of the CO2 control, with significant simplification of construction and reduced capital cost.