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At least 487 records · Page 27Linked to original sources
PubMed2003

Phytophthora pseudosyringae sp. nov., a new species causing root and collar rot of deciduous tree species in Europe.

In several studies of oak decline in Europe, a semi-papillate homothallic Phytophthora taxon was consistently isolated, together with other Phytophthora species, from rhizosphere soil samples. It was also found associated with necrotic fine roots and stem necroses of Fagus sylvatica and Alnus glutinosa. Due to morphological and physiological similarities, the semi-papillate isolates were previously identified as P. syringae by various authors. The morphology, physiology and pathogenicity against fine roots of Quercus robur, Q. petraea and F. sylvatica, bark of A. glutinosa, leaves of Ilex aquifolium and apple fruits of this Phytophthora species are described and compared with those of related and similar Phytophthora species, namely P. ilicis, P. psychrophila, P. quercina, P. citricola and P. syringae. The phylogenetic placement on the basis of ITS and mtDNA sequence data was also examined. Isolates of this taxon produce colonies with stellate to rosaceous growth patterns and limited aerial mycelium on various agar media. Antheridia are predominantly paragynous. In water culture catenulate hyphal swellings and semi-papillate caducous sporangia, that are usually limoniform, ellipsoid or ovoid, are formed abundandly, mostly in lax or dense sympodia. This taxon is a moderately slow growing, low temperature species with optimum and maximum temperatures around 20 and 25 degrees C, respectively. Tested isolates are moderately aggressive to fine roots of oaks and beech, highly aggressive to holly leaves and apple fruits, and slightly pathogenic to alder bark. Thirteen tested isolates had an identical and distinct ITS sequence which was more similar to that of P. ilicis and P. psychrophila than any other known taxa. On the basis of their unique combination of morphological characters, colony growth patterns, cardinal temperatures for growth, growth rates, pathogenicity to oaks, beech, alder, apple and holly, their host range, and ITS and mtDNA sequences the semi-papillate caducous Phytophthora isolates from oaks, beech and alder are clearly separated from related and similar Phytophthora spp., and described as a new species, P. pseudosyringae sp. nov.

Alnus↗
PubMed2005

Foraging behaviour of Armillaria rhizomorph systems.

The foraging behaviour of Armillaria rhizomorph systems is poorly understood owing to their cryptic position within the soil. We investigated foraging in a homogeneous environment (i.e. agar), finding that rhizomorph systems of the more parasitic species, A. mellea, A. ostoyae, and A. tabescens, lacked melanin and the approximately cylindrical cord-like form observed in the field. In contrast, rhizomorph systems of the more saprotrophic species, A. calvescens, A. gallica, and A. sinapina, developed radially resembling those in the field. For the three saprotrophic Armillaria species, the number of rhizomorph tips, total rhizomorph length and total rhizomorph surface area were significantly positively correlated with increasing rhizomorph system diameter and elapsed time in two developmental tests. However, the fractal dimension (D), used as a measure of foraging intensity, was temporally invariable, suggesting that one component of foraging behaviour is innate. In a heterogeneous environment (i.e. sand) and in the absence of a potential nutrient source, we observed that rhizomorph systems of A. gallica most often developed asymmetrically. While rhizomorph foraging was unresponsive to the lateral placement of an uncolonised stem segment, we were able to demonstrate directional growth toward an uncolonised Quercus velutina stem segment placed above or below the colonised source stem segment. When neighboring rhizomorph systems were conspecific genets of A. gallica, we observed that the growth of one rhizomorph system was directed toward zones unoccupied by its neighbour. However, the foraging intensity of the neighbouring genets, as measured by fractal dimension (D), was unaffected by the proximity of a neighbour. When neighbouring rhizomorph systems represented different species (A. gallica and A. mellea), A. gallica rhizomorph systems produced more total length and more foraging tips but concentrated their rhizomorph production away from the neighbouring A. mellea genet. In contrast, A. mellea rhizomorph systems produced significantly more foraging tips per unit length, both overall and in the zone of confrontation with the neighbouring A. gallica genet. Our observations are consistent with field observations of territoriality among Armillaria genets, and provide evidence that rhizomorph systems of more parasitic Armillaria spp. are able to compete effectively with the larger rhizomorph systems of more saprotrophic Armillaria species.

Agar↗
PubMed2003

Diplopyrone, a new phytotoxic tetrahydropyranpyran-2-one produced by Diplodia mutila, a fungus pathogen of cork oak.

A new phytotoxic monosubstituted tetrahydropyranpyran-2-one, named diplopyrone (1), was isolated from the liquid culture filtrates of Diplodia mutila, a plant pathogenic fungus causing a form of canker disease of cork oak (Quercus suber). Diplopyrone was characterized, using spectroscopic and chemical methods, as 6-[(1S)-1-hydroxyethyl]-2,4a,6,8a-tetrahydropyran[3,2-b]pyran-2-one. The absolute stereochemistry of the chiral secondary hydroxylated carbon (C-9), determined by application of Mosher's method, proved to be S. Diplopyrone assayed at a 0.01-0.1 mg/mL concentration range caused necrosis and wilting on cork oak cuttings. On a nonhost plant, tomato, diplopyrone caused brown discoloration or stewing on the stem.

Italy↗
PubMed2006

Diplobifuranylones A and B, 5'-monosubstituted tetrahydro-2H-bifuranyl-5-ones produced by Diplodia corticola, a fungus pathogen of cork oak.

Two new 5'-monosubstituted tetrahydro-2H-bifuranyl-5-ones, named diplobifuranylones A and B (1 and 2), were isolated from the culture filtrates of Diplodia corticola, the causal agent of a canker of cork oak (Quercus suber). The same fungus also produced eight known metabolites, namely, the diplopyrone, (3S,4R)-trans- and (3R,4R)-cis-4-hydroxymellein, sapinofuranone B and its (S,S)-enantiomer, and sphaeropsidins A-C. Diplobifuranylones A and B (1 and 2) were characterized, using spectroscopic and chemical methods, as two diastereomeric 5'-(1-hydroxyethyl)-3,4,2',5'-tetrahydro-2H-[2,2']bifuranyl-5-ones. While the relative stereochemistry of the two metabolites (1 and 2) was deduced by NOESY and ROESY experiments, the absolute stereochemistry of the chiral carbon of the hydroxyethyl side chain at C-5', determined by application of Mosher's method, proved to be S and R in 1 and 2, respectively. Assayed on a nonhost plant, diplobifuranylones A and B did not show phytotoxic activity. In an Artemia salina larvae lethality bioassay neither 1 nor 2 was toxic at the highest concentration tested (300 microg/mL).

Animals↗
PubMed2003

Antioxidants in the midgut fluids of a tannin-tolerant and a tannin-sensitive caterpillar: effects of seasonal changes in tree leaves.

The seasonal decline in foliar nutritional quality in deciduous trees also effects the availability of essential micronutrients, such as ascorbate and alpha-tocopherol, to herbivorous insects. This study first examined whether there are consistent patterns of seasonal change in antioxidant concentrations in deciduous tree leaves. Alpha-tocopherol concentrations increased substantially through time in late summer in sugar maple (Acer saccharum), red oak (Quercus rubra), and trembling aspen (Populus tremuloides). However, seasonal change in the concentrations of other antioxidants differed between each species: P. tremuloides had higher levels of ascorbate and glutathione in the spring, Q. rubra had higher levels of glutathione but lower levels of ascorbate in the spring, and A. saccharum had lower levels of both ascorbate and glutathione in the spring. To test the hypothesis that tannin-tolerant caterpillars maintain higher concentrations of antioxidants in their midgut fluids than do tannin-sensitive species, we measured antioxidants in Orgyia leucostigma (a spring- and summer-feeding, tannin-tolerant species) and Malacosoma disstria (a spring-feeding, tannin-sensitive species) that were fed tree leaves in the spring and summer. The midgut fluids of O. leucostigma larvae generally had higher concentrations of antioxidants in the summer than did those of M. disstria, and were significantly higher overall. The results of this study are consistent with the hypothesis that higher concentrations of antioxidants form an important component of the defenses of herbivores that feed on mature, phenol-rich tree leaves. Some limitations of the interpretation of total antioxidant capacity are also discussed.

Acer↗
PubMed2004

Trace element analyses in an epiphytic lichen and its bark substrate to assess suitability for air biomonitoring.

Total concentrations of Cd, Cr, Fe, Ni, Pb and Zn were compared from October 1996 to April 1998 in Physcia biziana (Massal.) Zhalbr. v. leptophylla Vezda and in the bark of Quercus ilex L. sampled from the same trees at an urban park. Trace metal concentrations were also measured in the bark covered by the lichen thalli. The lichens showed significantly higher Cr, Fe, Ni and Zn concentrations than both uncovered and covered barks. By contrast, both types of barks had higher concentrations of Cd and Pb than lichens. Trace elements showed a wide temporal variation of concentrations both in the lichens and barks. No relationship was found between the analysed matrices as regards the time course of trace element concentrations.

Air Pollutants↗
PubMed2004

Induced defensive response of myrtle oak to foliar insect herbivory in ambient and elevated CO2.

The rising level of atmospheric CO2 has stimulated several recent studies attempting to predict the effects of increased CO2 on ecological communities. However, most of these studies have been conducted in the benign conditions of the laboratory and in the absence of herbivores. In the current study, we utilized large octagonal chambers, which enclosed portions of an intact scrub-oak community to investigate the interactive effects of CO2 and insect herbivory on myrtle oak, Quercus myrtifolia. Specifically, we assessed the effects of ambient and elevated CO2 (2x current concentrations) on percent foliar nitrogen, C:N ratio, total relative foliar tannin content, and the presence of leaf damage caused by leaf mining and leaf chewing insects that feed on myrtle oak. Total foliar N declined and C:N ratios increased significantly in oaks in elevated CO2 chambers. The percentages of leaves damaged by either leafminers or leaf chewers tended to be lower in elevated compared to ambient chambers, but they co-occurred on leaves less than expected, regardless of CO2 treatment. Leaves that had been either mined or chewed exhibited a similar wounding or defensive response; they had an average of 25 and 21% higher protein binding ability, which is correlated with tannin concentration, compared to nondamaged control leaves, respectively. While the protein-binding ability (expressed as total percent tannin) of leaves from elevated CO2 was slightly higher than from leaves grown in ambient chambers, this difference was not significant.

Animals↗
PubMed2004

Seasonal variation in the content of hydrolyzable tannins, flavonoid glycosides, and proanthocyanidins in oak leaves.

Oaks have been one of the classic model systems in elucidating the role of polyphenols in plant-herbivore interactions. This study provides a comprehensive description of seasonal variation in the phenolic content of the English oak (Quercus robur). Seven different trees were followed over the full course of the growing season, and their foliage repeatedly sampled for gallic acid, 9 individual hydrolyzable tannins, and 14 flavonoid glycosides, as well as for total phenolics, total proanthocyanidins, carbon, and nitrogen. A rare dimeric ellagitannin, cocciferin D2, was detected for the first time in leaves of Q. robur, and relationships between the chemical structures of individual tannins were used to propose a biosynthetic pathway for its formation. Overall, hydrolyzable tannins were the dominant phenolic group in leaves of all ages. Nevertheless, young oak leaves were much richer in hydrolyzable tannins and flavonoid glycosides than old leaves, whereas the opposite pattern was observed for proanthocyanidins. However, when quantified as individual compounds, hydrolyzable tannins and flavonoid glycosides showed highly variable seasonal patterns. This large variation in temporal trends among compounds, and a generally weak correlation between the concentration of any individual compound and the total concentration of phenolics, as quantified by the Folin-Ciocalteau method, leads us to caution against the uncritical use of summary quantifications of composite phenolic fractions in ecological studies.

Carbon↗
PubMed2004

Distribution of genomic regions differentiating oak species assessed by QTL detection.

Pedunculate oak and sessile oak are two sympatric interfertile species that exhibit leaf morphological differences. We aimed to detect quantitative trait loci (QTLs) of these traits in order to locate genomic regions involved in species differentiation. A total of 15 leaf morphological traits were assessed in a mixed forest stand composed of Quercus petraea and Q. robur and in a full-sib pedigree of Q. robur. The progeny of the full-sib family were vegetatively propagated in two successive experiments comprising 174 and 216 sibs, and assessments were made on two leaves collected on each of the 1080 and 1530 cuttings corresponding to the two experiments. Traits that exhibited strong species differences in the mixed stand tended also to have higher repeatability values in the mapping population, thus indicating higher genetic control. A genetic map was constructed for QTL detection. Composite interval mapping with the one QTL model was used for QTL detection. From one to three QTLs were detected for 13 traits. In-depth analysis of the QTLs, controlling the five morphological traits that exhibited the highest interspecific differences in the mixed stand, indicated that they were distributed on six linkage groups, with two clusters comprising QTLs of at least two discriminant traits. These results were reinforced when error 1 for QTL detection was set at 5% at the chromosome level, as up to nine clusters could be identified. In conclusion, traits involved in interspecific differentiation of oaks are under polygenic control and widespread in clusters across the genome.

Analysis of Variance↗
PubMed2003

Environmental monitoring of historical change in arsenic deposition with tree bark pockets.

ICP-MS analysis recorded historical change (c. 1846 to 2002) in the arsenic concentration of bark included within the trunks (tree bark pockets) of two Japanese oak trees (Quercus crispula), collected at an elevated location approximately 10 km from the Ashio copper mine and smelter, Japan. The arsenic concentration of the bark pockets was 0.016 +/- 0.003 microg cm(-2) c. 1846 (n = 5) and rose 50-fold from c. 1875 to c. 1925, from approximately 0.01 to 0.5 microg cm(-2). The rise coincided with increased copper production in Ashio from local sulfide ores, from 46 tons per year in 1877 to 16,500 tons per year in 1929. Following a decline in arsenic concentration and copper production, in particular during the Second World War, a second peak was observed c. 1970, corresponding to high levels of production from both local (6,000 tons per year) and imported (30,000 tons per year) ores, smelted from 1954. Compared to the local ores, the contribution of arsenic from imported ores appeared relatively low. Arsenic concentrations declined from c. 1970 to the present following the closure of the mine in 1974 and smelter in 1989, recording 0.058 +/- 0.040 microg cm(-2) arsenic (n = 5) in surface bark collected in 2002. The coincident trends in arsenic concentration and copper production indicated that the bark pockets provided an effective record of historical change in atmospheric arsenic deposition.

Air Pollutants↗
PubMed2005

Results on quantitative trait loci for flushing date in oaks can be transferred to different segregating progenies.

Flushing date (bud burst) is one of the most important traits for the adaptation to different environments and climates in the temperate zone. Because of their wide geographic distribution, Quercus robur L. and Q. petraea (Matt.) Liebl. are suitable as model plants to study the genetic basis of bud burst. QTLs (Quantitative Trait Loci) with comparatively large effects have been mapped in a former study in a Q. robur x Q. robur full-sib family (French cross). In the present study, we performed a Bulked Segregant Analysis (BSA) in the F (1) progeny comprising 144 seedlings derived from a cross between a single Q. robur tree as common seed parent and five different pollen donors both from Q. robur and Q. petraea (Q. robur x Q. spp., Diekholzen crosses). In addition, markers linked to two bud burst QTLs with comparably strong effect in the above-mentioned full-sib family (French cross) were tested for their association with bud burst in the Q. robur x Q. spp. (Diekholzen) progeny. Using three microsatellite markers as anchor points, we could map QTLs on linkage group 7 and on linkage group 2, together explaining 16.2 % of the total phenotypic variance (PVE) in 1999 and 38.1 % in 2003. Out of 10 markers that segregated in both mapping progenies, four markers including the two microsatellite markers, showed a significant effect on bud burst in both materials. At microsatellite loci ssrQpZAG1/5 (linkage group 7) and ssrQpZAG119 (linkage group 2) alleles associated with early (allele 166 bp in ssrQpZAG1/5) and late bud burst (allele 57 bp in ssrQpZAG119) in the Q. robur x Q. robur full-sib family (French cross) showed a highly significant association with the same polarity of the effect in the Q. robur x Q. spp. (Diekholzen) progeny. The usefulness of these markers for marker-assisted selection in full-sib and half-sib families is discussed.

Genetic Linkage↗
PubMed2003

Maturation and germination of oak somatic embryos originated from leaf and stem explants: RAPD markers for genetic analysis of regenerants.

Experiments were performed to determine the influence of maturation medium carbohydrate content on the rates of germination and plantlet conversion (root and shoot growth) of somatic embryos from four embryogenic lines derived from leaf or internode explants of Quercus robur L. seedlings. The conversion rate was favoured by high carbohydrate content as long as the maturation medium contained at least 2% sucrose, which was necessary for healthy embryo development. Given this, sorbitol and mannitol favoured the conversion rate more efficiently than sucrose, the highest rate, 32%, being achieved by medium with 6% sorbitol and 3% sucrose. Maturation treatment did not affect the root or shoot lengths of converted embryos. In supplementary experiments, 2 weeks of gibberellic acid treatment between maturation and germination treatments did not improve germination rates, but did reduce root length and the number of leaves per regenerated plantlet. In the four embryogenic lines tested, plant recovery rate was enhanced by inclusion of benzyladenine into the germination medium following culture of the embryos on maturation medium with 6% sorbitol and 2-3% sucrose. In embryogenic systems it is important to assess the uniformity of the regenerants. Random amplified polymorphic DNA (RAPD) analysis using 32 arbitrary oligonucleotide primers was performed to study variability in DNA sequences within and between four embryogenic lines. No intraclonal nor interclonal polymorphism was detected between embryogenic lines originating from different types of explant from the same seedling, but every one of the primers detected enough polymorphism among clones originating from different plants to allow these three origins to be distinguished. No differences in DNA sequences between regenerated plantlets and their somatic embryos of origin were detected, but a nodular callus line that had lost its embryogenic capacity was found to be mutant with respect to three other clones originating from the same plantlet. This study shows that high carbohydrate levels in the maturation medium significantly increase plant conversion of oak somatic embryos, which exhibit no variation in DNA sequences when proliferated by secondary embryogenesis.

Carbohydrates↗
PubMed2004

Manipulation of the onset of ectomycorrhiza formation by indole-3-acetic acid, activated charcoal or relative humidity in the association between oak microcuttings and Piloderma croceum: influence on plant development and photosynthesis.

A Petri dish system in which development of oak (Quercus robur L.) microcuttings is stimulated by the late stage ectomycorrhizal (EM) fungus Piloderma croceum J. Erikss. & Hjortst. in a long pre-symbiotic stage was optimised to allow synchronous, rhythmic plant growth. Addition of indole-3-acetic acid or activated charcoal to the medium caused an early and more intensive EM formation coupled with suppression of most developmental effects of P. croceum. Leaf area, chlorophyll fluorescence, and content were compared in inoculated and uninoculated plants grown at two relative humidity levels (45 and 95%) and under consideration of three possible answers to inoculation, that is, no or EM formation after the 1st or the 2nd shoot flush. The culture conditions for uninoculated plants were suboptimal, leading toward photochemical stress reflected by a non photochemical quenching (qE) increase and a reduced Chl content at the end of the assay. Prior to EM formation, inoculation itself enhanced the optimal (Fv/Fm) and effective (phiPSII) quantum yield in leaves of the 1st shoot flush under reduced relative humidity. It also fully protected the plants against stress during the complete assays. The results indicate that inoculated plants only form EM once they have acquired a sufficient development level and C-providing capacity. However, the fungus actively improves the development and photosynthesis of plants up to the pre-mycorrhizal stage, helping them to reach this capacity.

Charcoal↗
PubMed2006

Demography and recruitment limitations of three oak species in California.

We review published studies on the demography and recruitment of California oak trees and focus on the widespread dominant species of the foothill woodlands, Quercus douglasii, Q. lobata, and Q. agrifolia, to ascertain the nature and strength of evidence for a decline in populations of these species. The vast majority of studies have been of short duration (less than three years), focused on the acorn and seedling life stages, and conducted at few locations within each species geographic range. We summarize the extensive body of research that has been conducted on the biological and physical factors that limit natural seedling recruitment of oaks. The oak "regeneration problem" has largely been inferred from current stand structure rather than by demographic analyses, which in part reflects the short-term nature of most oak research. When viewed over longer periods of time usingfield surveys or historical photos, the evidence for a regeneration problem in foothill oaks is mixed. Q. douglasii shows very limited seedling or sapling recruitment at present, but longer term studies do not suggest a decline in tree density, presumably because rare recruitment is sufficient to offset low rates of mortality of overstory individuals. Q. agrifolia appears to be stable or increasing in some areas, but decreasing in areas recently impacted by the disease Phytophthora ramorum. Evidence from the few available studies is more consistent in suggesting long-term declines in foothill populations of Q. lobata. Long-term monitoring, age structure analysis, and population models are needed to resolve the current uncertainty over the sustainability of oak woodlands in California.

Animals↗
PubMed2002

Physiological responses of beech and sessile oak in a natural mixed stand during a dry summer.

Responses of CO2 assimilation and stomatal conductance to decreasing leaf water potential, and to environmental factors, were analysed in a mixed natural stand of sessile oak (Quercus petraea ssp. medwediewii) and beech (Fagus svlvatica L.) in Greece during the exceptionally dry summer of 1998. Seasonal courses of leaf water potential were similar for both species, whereas mean net photosynthesis and stomatal conductance were always higher in sessile oak than in beech. The relationship between net photosynthesis and stomatal conductance was strong for both species. Sessile oak had high rates of photosynthesis even under very low leaf water potentials and high air temperatures, whereas the photosynthetic rate of beech decreased at low water potentials. Diurnal patterns were similar in both species but sessile oak had higher rates of CO2 assimilation than beech. Our results indicate that sessile oak is more tolerant of drought than beech, due, in part, to its maintenance of photosynthesis at low water potential.

Carbon Dioxide↗
PubMed2006

Comparison of leaf life span, photosynthesis and defensive traits across seven species of deciduous broad-leaf tree seedlings.

BACKGROUND AND AIMS: Leaf life span, photosynthetic parameters and defensive traits were compared across seven species of deciduous broad-leaved tree seedlings native to northern Japan to test the "cost-benefit hypothesis" that more productive leaves are more susceptible to herbivore attack than less productive leaves. METHODS: Studies were made on three early successional species, Alnus hirsuta, Betula maximowicziana and Betula platyphylla "japonica"; one mid-successional species, Ostrya japonica, and three late-successional species, Carpinus cordata, Quercus mongolica 'grosseserrata' and Acer mono. Photosynthetic parameters and defensive traits (total phenolics, condensed tannin and toughness) of leaves were measured for each species, and a bioassay test with Eri silkmoth larvae (Samia cynthia ricini) was undertaken to evaluate differences between species in susceptibility to herbivore attack. KEY RESULTS: Early successional species have a shorter leaf life span (62-88 d) than late successional species (155-187 d). Leaf nitrogen content and light-saturated photosynthetic rate per unit leaf area (P(sat)-area) and per unit leaf mass (P(sat)-mass) were negatively correlated with leaf life span. The nitrogen content of early successional species was about 30 mg g(-1) and that of late successional species was about 16 mg g(-1). Leaf toughness and the C/N ratio were positively correlated with leaf life span, although condensed tannin was not correlated with leaf life span. The bioassay test showed that the number of days the larvae survived was negatively correlated with leaf life span. Average survival of larvae feeding on leaves of A. hirsuta, which has the shortest leaf life span, was 14.4 d and that of Q. mongolica, which has the longest leaf life span, was 6.6 d. The number of days of larval survival was positively correlated with leaf nitrogen content. There was no correlation between days of larval survival and defensive traits. CONCLUSIONS: These results indicate that species with a shorter leaf life span have higher photosynthetic productivity and are more susceptible to herbivore attack than species with a longer leaf life span. This supports the "cost-benefit hypothesis".

Acer↗
PubMed2002

The hydraulic conductance of the angiosperm leaf lamina: a comparison of three measurement methods.

A comparison was made of three methods for measuring the leaf lamina hydraulic conductance (K(lamina)) for detached mature leaves of six woody temperate angiosperm species. The high-pressure method, the evaporative flux method and the vacuum pump method involve, respectively, pushing, evaporating and pulling water out of the lamina while determining the flow rate into the petiole and the water potential drop across the leaf. Tests were made of whether the high-pressure method and vacuum pump method measurements of K(lamina) on single leaves were affected by irradiance. In Quercus rubra, the high pressure method was sensitive to irradiance; K(lamina) measured under high irradiance (>1200 micro mol m(-2) s(-1 )photosynthetically active radiation) was 4.6-8.8 times larger than under ambient laboratory lighting (approximately 6 micro mol m(-2) s(-1 )photosynthetically active radiation). By constrast, the vacuum pump method was theoretically expected to be insensitive to irradiance, and this expectation was confirmed in experiments on Hedera helix. When used in the ways recommended here, the three methods produced measurements that agreed typically within 10%. There were significant differences in species' K(lamina); values ranged from 1.24x10(-4) kg s(-1) m(-2) MPa(-1) for Acer saccharum to 2.89x10(-4) kg s(-1) m(-2) MPa(-1) for Vitis labrusca. Accurate, rapid determination of K(lamina) will allow testing of the links between K(lamina), water-use, drought tolerance, and the enormous diversity of leaf form, structure and composition.

Acer↗
PubMed2003

Cavitation, stomatal conductance, and leaf dieback in seedlings of two co-occurring Mediterranean shrubs during an intense drought.

Seedling shrubs in the Mediterranean semi-arid climate are subjected to intense droughts during summer. Thus, seedlings often surpass their limits of tolerance to water stress, resulting in the loss of hydraulic conductivity due to xylem cavitation. The response in terms of stomatal conductance, vulnerability to cavitation, leaf dieback, and survival were analysed in two co-occurring seedlings of mastic tree (Pistacia lentiscus L.) and kermes oak (Quercus coccifera L.) during an intense drought period. Both species reacted to drought with steep decreases in stomatal conductance before the critical water potential brought about the onset of cavitation events. Q. coccifera showed wider safety margins for avoiding runaway embolism than P. lentiscus and these differences could be related to the particular drought strategy displayed by each species: water saver or water spender. The limits for survival, resprout capacity and leaf dieback were also analysed in terms of loss of conductivity. By contrast with previous studies, the species showing higher seedling survival in the presence of drought also showed higher susceptibility to cavitation and operated with a lower safety margin for cavitation. Both species showed a leaf specific conductivity (LSC) threshold below which leaf biomass had to be regulated to avoid runaway embolism. However, each species displayed a different type of response: P. lentiscus conserved total leaf area up to 100% loss of LSC, whereas Q. coccifera continuously adjusted leaf biomass throughout the drought period in order to maintain the LSC very close to the maximum values recorded without loss of conductivity. Both species maintained the capacity for survival until the loss of conductivity was very nearly 100%.

Climate↗