bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of a natural source of very high CO2 concentration on the leaf gas exchange, xylem water potential and stomatal characteristics of plants of Spatiphylum cannifolium and Bauhinia multinervia
Authors: FERNÁNDEZ MARÍA DOLORES , PIETERS ALEJANDRO , DONOSO CAROLINA , TEZARA WILMER , AZKUE MERCEDES , HERRERA CECILIA , RENGIFO ELIZABETH , HERRERA ANA
Published: March 2003

The effect of a very high CO2 mole fraction (27000–35000 μmol mol−1) on photosynthesis and water relations was studied during the dry and the rainy season in plants of Spatiphylum cannifolium (Dryand.) Schott and Bauhinia multinervia (H.B.K.) DC. growing near natural cold CO2 springs. Xylem water potential in plants of both species was lowered by drought, high CO2 growth‐concentration decreasing it further in S. cannifolium. In plants of both species growing under high CO2 concentration photosynthetic rates measured at a CO2 mole fraction of 1000 μmol mol−1 were higher than in plants growing at ambient CO2 mole fraction and measured at 350 μmol mol−1. The response was the result of a direct effect of CO2 on the photosynthetic machinery. Changes in carboxylation efficiency in response to high CO2 were found during the rainy season, with an increase in S. cannifolium and a decrease in B. multinervia; a significant interaction between growth CO2 concentration and season in B. multinervia resulted from significant effects of both factors. An increase in intrinsic water‐use efficiency due to high CO2 was determined in both species by an increase in photosynthetic rate as well as a decrease in leaf conductance. In high‐CO2 plants of S. cannifolium a 71% decrease in stomatal density and 73% in stomatal index suggested that CO2 affected stomatal initiation, whereas in B. multinervia an 85% decrease in stomatal index and a 72% decrease in stomatal density indicated that CO2 influenced stomatal initiation as well as epidermal cell expansion. Our results indicate that very high CO2 concentrations did not inhibit photosynthesis in these species, and that growth under high CO2 allowed plants to attain carbon balances higher than those of plants growing under low CO2. This was particularly so during the dry season, since the photosynthetic rates at the corresponding ambient concentration were higher in plants nearer the springs, and carboxylation efficiency and some stomatal characteristics of both species apparently acclimated to high CO2, but patterns were not consistent and bore no obvious relationship to photosynthetic capacity.
Impacts of ozone on forests: a European perspective
Authors: SKÄRBY LENA , RO‐POULSEN HELGE , WELLBURN FLORENCE A. M. , SHEPPARD LUCY J.
Published: March 2003

In comparison with the effects of extended drought periods or severe nutrient stress, those of ozone are generally much milder, at least with respect to growth. However, there is substantial evidence from experiments, in the main using young saplings, that O3 does impose a stress on forest trees under European conditions. Decreased chlorophyll contents and photosynthetic rates, changes in carbon allocation, increased antioxidant activity, and reductions in biomass due to O3 have often been recorded, particularly in fast‐growing species. Furthermore, 3 appears to weaken the trees' resilience to a range of biotic and abiotic stresses. Interactions between O3 and climatic stress, in particular drought and frost hardiness, are likely to result in potentially detrimental effects.

A link between the occurrence of O3 and forest damage is not unequivocally established in Europe, and the problem remains of extrapolating and/or scaling up from studies on seedlings to predict responses to O3 of mature trees and forest stands, because we know so little about acclimation to O3. An accurate assessment is also lacking of the magnitude of the O3 effect on European trees both in terms of the forest areas affected and its extent. In this review we suggest that C allocation is the key factor underlying the responses of trees to O3. Stomata also play a key role, since the acquisition of C must be achieved while an effective control over water consumption is retained.
Branched absorbing structures (BAS): a feature of the extraradical mycelium of symbiotic arbuscular mycorrhizal fungi
Authors: BAGO B. , AZCÓN‐AGUILAR C. , GOULET A. , PICHÉ Y.
Published: March 2003

The present work describes the morphogenesis and cytological characteristics of ‘branched absorbing structures’ (BAS, formely named arbuscule‐like structures, ALS), small groups of dichotomous hyphae formed by the extraradical mycelium of arbuscular mycorrhizal (AM) fungi. Monoxenic cultures of the AM fungus Glomus intraradices Smith & Schenck and tomato (Lycopersicum esculentum Mill.) roots allowed the continuous, non‐destructive study of BAS development. These structures were not observed in axenic cultures of the fungus under different nutritional conditions or in unsuccessful (asymbiotic) monoxenic cultures. However, extraradical mycelium of G. intraradices formed BAS immediately after fungal penetration of the host root and establishment of the symbiosis. The average BAS development time was 7 d under our culture conditions, after which they degenerated, becoming empty septate structures. Certain BAS were closely associated with spore formation, appearing at the spore's substending hypha. Branches of these spore‐associated BAS (spore‐BAS) usually formed spores. Electron microscopy studies revealed that BAS and arbuscules show several ultrastructural similarities. The possible role of BAS in nutrient uptake by the mycorrhizal plant is discussed.
In situ studies of water relations and CO2 exchange of the tropical macrolichen, Sticta tomentosa
Authors: ZOTZ G. , BÜDEL B. , MEYER A. , ZELLNER H. , LANGE O. L.
Published: March 2003

Diel (24‐h) time courses of CO2 exchange, water relations, and microclimate of the foliose lichen, Sticta tomentosa (Swartz) Ach., and responses to experimentally manipulated conditions were measured at a forest edge in a lower montane rainforest in Panama.

Similar to earlier observations on two other rain forest lichens, daily desiccation suppressed net photosynthesis (NP) during the period when irradiation was highest. Not surprisingly, the light response curves of NP showed saturation at rather low light levels. Rehydration was associated with an initial resaturation burst of short duration, which could be demonstrated both under natural conditions and experimentally. This additional loss of CO2 seems too low to be ecologically relevant. Moreover, high thallus hydration was also detrimental to NP: at maximum water content net CO2 uptake was depressed by >50%. Although NP was well adapted to the prevailing high temperatures, the latter also stimulated dark respiration. On average, almost 60% of the diurnal carbon gain was lost during the night.

In spite of these limitations, the integrated 24‐h C gain was quite high, on average 0·5% of the thallus C content. Whilst these figures were determined for horizontally exposed samples, we also assessed the role of different exposures on photosynthetic performance. Diel C gain was highest under conditions of semi‐shade (westerly exposure), which allowed long periods of activity, whilst much higher irradiance at other exposures could not be utilized for photosynthetic production: easterly exposed thalli dried out even faster than horizontally exposed samples.
Effects of phosphorus availability and vesicular–arbuscular mycorrhizas on the carbon budget of common bean (Phaseolus vulgaris)
Authors: NIELSEN KAI L. , BOUMA TJEERD J. , LYNCH JONATHAN P. , EISSENSTAT DAVID M.
Published: March 2003

Low phosphorus availability is often a primary constraint to plant productivity in native soils. Here we test the hypothesis that root carbon costs are a primary limitation to plant growth in low P soils by assessing the effect of P availability and mycorrhizal infection on whole plant C budgets in common bean (Phaseolus vulgaris L.). Plants were grown in solid‐phase‐buffered silica sand providing a constant supply of low (1 μm) or moderate (10 μm) P. Carbon budgets were determined weekly during the vegetative growth phase. Mycorrhizal infection in low‐P plants increased the root specific P absorption rate, but a concurrent increase in root respiration consumed the increased net C gain resulting from greater P uptake. The energy content of mycorrhizal and non‐mycorrhizal roots was similar. We propose that the increase in root respiration in mycorrhizal roots was mainly due to increased maintenance and growth respiration of the fungal tissue. Plants grown with low P availability expended a significantly larger fraction of their total daily C budget on below‐ground respiration at days 21, 28 and 35 after planting (29–40%) compared with plants grown with moderate P supply (18–25%). Relatively greater below‐ground respiration in low P plants was mainly a result of their increased root∶shoot ratio, although specific assimilation rate was reduced significantly at days 21 and 28 after planting. Specific root respiration was reduced over time by low P availability, by up to 40%. This reduction in specific root respiration was due to a reduction in ion uptake respiration and growth respiration, whereas maintenance respiration was increased in low‐P plants. Our results support the hypothesis that root C costs are a primary limitation to plant growth in low‐P soils.
Intracellular pH stability in the aquatic resurrection plant Chamaegigas intrepidus in the extreme environmental conditions that characterize its natural habitat
Authors: SCHILLER PETRA , HARTUNG WOLFRAM , RATCLIFFE R. GEORGE
Published: March 2003

Chamaegigas intrepidus Dinter (syn. Lindernia intrepidus (Dinter) Oberm.) is a poikilohydric aquatic plant that lives in rock pools on granitic outcrops in Central Namibia. The pools are only filled intermittently during the summer rains, and the plants can pass through 15–20 rehydration/dehydration cycles during a single wet season. Rehydrated plants also have to cope with substantial diurnal fluctuations in the pool pH as a result of photosynthetic CO2 uptake. We have used in vivo31P NMR spectroscopy to investigate the effect of external pH and dehydration (low water potential) on intracellular pH in the roots and submerged leaves of C. intrepidus. Increasing the external pH from 6 to 10 had no effect on the steady state cytoplasmic and vacuolar pH values of submerged leaves, but caused a slight alkalinization of the root cytoplasm. Similarly dehydration with PEG‐600 at either pH 6 or pH 10 had no effect on the cytoplasmic pH of the leaves, but it did cause a small alkalinization of the leaf vacuoles at pH 10. These results imply an unusually effective regulation of intracellular pH, consistent with the adaptation of C. intrepidus to the extreme environmental conditions of its habitat. The NMR analysis also showed that dehydration had no effect on the inorganic phosphate and phosphocholine pools, and this was taken to indicate that the cell membranes were well protected from the effects of the low water potential.
Molecular diversity of ericoid mycorrhizal endophytes isolated from Woollsia pungens
Authors: LIU G. , CHAMBERS S. M. , CAIRNEY J. W. G.
Published: March 2003

One hundred and sixty‐eight sterile endophytic mycelia were isolated from roots of four Woollsia pungens (Cav.) F. Muell. (Epacridaceae) plants collected from a field site in New South Wales, Australia. All isolates formed typical ericoid mycorrhizal structures when inoculated onto roots of Vaccinium macrocarpon Ait. (Ericaceae). Microsatellite‐primed PCR fingerprints generated using the primers (GTG)5 and (GACA)4 indicated that considerable genetic diversity exists within the endophyte population. It was estimated that a minimum of 43 genetically distinct mycelial genets were present in the root systems of the sampled W. pungens population, with most genets confined to individual plants. Two genets, however, were present within the root systems of two adjacent plants. While most genets were represented by less than eight isolates, three genets contained up to 41 isolates, suggesting that root system colonization by some endophytic mycelia might be extensive.
TIP1 is required for both tip growth and non‐tip growth in Arabidopsis
Authors: RYAN EOIN , GRIERSON CLAIRE S. , CAVELL ALISON , STEER MARTIN , DOLAN LIAM
Published: March 2003

TIP1 is a gene defined by an X‐ray induced allele tip1–2 and a previously described EMS‐induced allele tip1−1. TIP1 is involved in plant cell growth. tip1–2 plants display growth defects throughout the plant and exhibit defects in both root‐hair and pollen‐tube growth. tip1–2 plants are partly male sterile resulting from a combination of pollen germination and pollen‐tube defects; their root‐hairs are short, exhibit a tendency to branch and 2–4 hairs can initiate from each hair cell. They are also slightly dwarf in stature as a result of a general decrease in cell growth indicating that TIP1 activity is required for general cell growth. We propose a role for TIP in both the initiation and maintenance of growth in tip‐growing cells. In addition TIP1 activity is required for normal cell expansion (non‐tip cell growth) indicating that TIP1 is not exclusively involved in tip‐growth.
Relationship between active oxygen species and cardenolide production in cell cultures of Digitalis thapsi: effect of calcium restriction
Authors: PARANHOS A. , FERNÁNDEZ‐TÁRRAGO J. , CORCHETE P.
Published: March 2003

Elimination of calcium ions from the medium of undifferentiated cell cultures of Digitalis thapsi increased cardenolide production and induced extracellular H2O2 accumulation, as measured by the quenching of pyranine fluorescence. The addition of catalase reduced the response and the inclusion of superoxide dismutase enhanced the loss of fluorescence. This suggested that, besides H2O2, the superoxide anion was also formed before dismutating to H2O2. Additionally, exogenous H2O2 or superoxide dismutase stimulated cardenolide production whereas the addition of catalase markedly reduced it. These results point to a connection between H2O2 and cardenolide formation. The absence of calcium did not alter the levels of lipid peroxidation products; however, changes in the antioxidant system of D. thapsi cells were observed. Catalase activity was extremely low in control cultures and remained unaltered upon calcium elimination. Ascorbate peroxidase activity was not modified in calcium‐free cultures. By contrast, calcium deprivation stimulated superoxide dismutase activity and strongly inhibited glutathione reductase activity. Also, a significant decrease in reduced glutathione was observed. These responses were emulated by treatment of the cultures with the glutathione biosynthesis inhibitor buthionine sulfoximine and by ethyleneglycol‐bis‐β‐aminoethyl ether and LaCl3. All these results indicate that the depletion of extracellular calcium induces changes in the redox state of cells and suggest that this alteration stimulates cardenolide formation in D. thapsi cultures.
The effect of increased deposition of atmospheric nitrogen on Calluna vulgaris in upland Britain
Authors: CARROLL J. A. , CAPORN S. J. M. , CAWLEY L. , READ D. J. , LEE J. A.
Published: March 2003

Regular (monthly) additions of NH4NO3 (4–12 g N m−2 yr−1) were made over a period of 8 yr (1989–98) to areas of moorland in North Wales dominated by the ericaceous shrub Calluna vulgaris. Results from the early stages of the experiment (1990–94) have shown marked and dose‐related increases in shoot extension and canopy height in response to the nitrogen treatments, with significantly higher shoot nitrogen contents. The nitrogen‐related stimulation in the growth of the C. vulgaris canopy over this period has resulted in large accumulations of litter on the high‐nitrogen‐treated plots (6.6 kg m−2 in plots treated with 12 g N m−2 yr−1, compared with 3.8 kg m−2 for the water controls). Litter nitrogen concentrations were also significantly increased at the higher rates of nitrogen addition, leading to a doubling of the total return of nitrogen to the litter layer over the experimental period. These changes in vegetation structure were associated with large reductions in the abundance of the bryophyte and lichen species normally present under the untreated canopy. Results since 1994, however, show little increase in shoot extension in response to the nitrogen treatments, with no clear dose response to increasing levels of addition. These findings are associated with a dose‐related increase in the susceptibility of the nitrogen‐treated areas of the C. vulgaris canopy to late winter injury, characterized as browning of the shoot tips in early to late spring. These results indicate that deleterious effects are now accumulating as a result of the long‐term addition of nitrogen to these moorland plots.
Auxin transport inhibitors act through ethylene to regulate dichotomous branching of lateral root meristems in pine
Authors: KASKA D. D. , MYLLYLÄ R. , COOPER J. B.
Published: March 2003

Many soil fungi colonize the roots of pines to form symbiotic organs known as ectomycorrhizas. Dichotomous branching of short lateral roots and the formation of coralloid organs are diagnostic of ectomycorrhizas in many pine species, although the regulation of these changes in root morphology is not well understood. We used axenic root cultures of six pine species to examine the role of auxin, cytokinin, ethylene and nutrients in the regulation of root architecture. Surprisingly, extensive dichotomous and coralloid branching of lateral roots occurred spontaneously in Pinus taeda, P. halepensis and P. muricata. In P. sylvestris, P. ponderosa and P. nigra, treatment with auxin transport inhibitors (ATIs), the ethylene precursor 1‐aminocyclopropane‐1‐carboxylic acid (ACC) or the ethylene‐releasing compound 2‐chloroethylphosphonic acid (CEPA or ethephon) induced extensive dichotomous branching and coralloid organ formation. Formation of both spontaneous and ATI‐induced coralloid structures was blocked by treatment with an ethylene synthesis inhibitor L‐α‐(2‐aminoethoxyvinyl)glycine; this inhibition was reversed by either ACC or CEPA. In addition, the induction of this unique morphogenetic pattern in pine root cultures was regulated by nutrient levels. The morphology and anatomical organization of the chemically induced dichotomous and coralloid structures, as well as the regulation of their formation by nutrient levels, show a striking similarity to those of ectomycorrhizas.
Development of N2‐fixing nodules on the wetland legume Lotus uliginosus exposed to conditions of flooding
Authors: JAMES EUAN K. , SPRENT JANET I.
Published: March 2003

Seeds of the wetland legume, Lotus uliginosus, were germinated and grown in vermiculite which was either continuously flooded or well‐drained. Plants from both treatments were infected by Mesorhizobium loti strain DUS341 via a ‘classical’ root hair pathway, although some flooded plants appeared to be infected via enlarged epidermal cells. Subsequent to infection by M. loti, nodule meristems, which had developed within the root outer cortex, were penetrated by infection threads that released bacteria into the meristematic cells. The infection threads and infection droplets were immunogold labelled with monoclonal antibodies (MAC265 and MAC236) that recognize epitopes (at approx. 155/170 and 170/210 kDa, respectively) on a glycoprotein component of the matrix that surrounded the bacteria within the threads or droplets. Although labelling of infection threads or infection droplets with MAC236 was stronger than that with MAC265, both antibodies strongly labelled material occluding intercellular spaces in the cortices of developing nodules that had not yet expressed nitrogenase (as determined by a lack of signal after immunogold labelling with an antibody raised against nitrogenase component II). After 60 d, nitrogenase activity, shoot and root dry weights, and nodule fresh weight per plant did not differ between the treatments. After a further 30 d submergence, the flooded stems developed extensive aerenchyma and there was profuse development of (nodulated) adventitious roots. Nodules also formed at the junction of adventitious roots and the subtending stem and these were connected vascularly to a small stalk of tissue which gave rise to both a nodule and an adventitious root. The flooded nodules had prominent lenticels, and possible air pathways from the atmosphere to the nitrogen‐fixing bacteroids are discussed.
Measurement of leaf longevity of 14 species of grasses and forbs using a novel approach
Authors: CRAINE J. M. , BERIN D. M. , REICH P. B. , TILMAN D. G. , KNOPS J. M. H.
Published: March 2003

Grasses and forbs are often classified into separate functional types, although systematic differences between the types have only been verified for a few functional traits. Since leaf longevity has been shown to be a key trait linking plant ecophysiology, whole‐plant growth and ecosystem resource cycling, we compared the leaf longevity of 14 species to determine if there were consistent differences between grasses and forbs or other functional classifications, such as persistence of leaves into winter. Leaf longevity was assessed in 6‐yr‐old monoculture plots in central North America by tagging and sequentially monitoring the phenological states of whole forb leaves and sections of grass leaves. This new approach enables a calculation of leaf longevity unbiased by the manner in which grass leaves grow and provides a more accurate comparison between grasses and forbs. Lupinus perennis had the shortest leaf longevity (4 wk) and Koeleria cristata, Poa pratensis, and Solidago rigida the longest (13–14 wk). Average leaf longevity for the 14 species was c. 9 wk, with no significant differences between grasses and forbs nor between current alternative functional classifications.
Leaf structure and defence control litter decomposition rate across species and life forms in regional floras on two continents
Authors: CORNELISSEN JOHANNES H. C. , PÉREZ‐HARGUINDEGUY NATALIA , DÍAZ SANDRA , GRIME J. PHILIP , MARZANO BARBARA , CABIDO MARCELO , VENDRAMINI FERNANDA , CERABOLINI BRUNO
Published: March 2003

There is some evidence that traits of fresh leaves that provide structural or chemical protection (‘defence’) remain operational in the leaf litter and control interspecific variation in decomposition rate in or on the soil. We tested experimentally whether the negative relationship between foliar defence and litter decomposition rate is fundamental, i.e. whether it is seen consistently across higher plant species and life forms, and whether it is repeated in the floras of geographically and climatically distinct areas separated by an ocean. We employed the published results of two outdoor litter bag experiments, in which we simultaneously compared the relative mass losses (‘decomposibility’) of leaf litters of a wide range of plant species. One experiment was in Córdoba, Argentina, and included 48 Argentine species typical of the dry, subtropical landscapes along a steep altitudinal gradient. The other was in Sheffield, UK, and hosted 72 British species typical of the temperate–Atlantic landscape there. We linked the two experiments through a similar experiment in Sheffield that hosted litters of subsets of both the Argentine and British species. We also tested fresh leaves of all species from the same areas for tensile strength (‘toughness’) and relative palatability to generalist herbivorous snails in multi‐species ‘cafeteria’ experiments. Both in Argentina and in Great Britain there were highly significant correlations between leaf palatability (r=0.61; 0.73) or leaf tensile strength (r=−0.60; −0.60) and litter mass loss across all species. These relationships could be explained by variation both between and within broad life‐form groups. Specific leaf area (area∶dry mass) of fresh leaves was consistently correlated only with litter mass loss within British life form groups. We illustrated the possible ecosystem consequences of these relationships by comparing functional traits of British species differing in leaf habit. In comparison with deciduous species, evergreens generally had innately slow growth, which corresponded to their longer‐lived leaves of lower specific leaf area, higher tensile strength and lower palatability to generalist invertebrate herbivores. Correspondingly, evergreens produced more resistant leaf litter. Thus, slow‐growing evergreens might maintain their position in infertile ecosystems through leaf traits that help them to conserve their nutrients efficiently and to keep nutrient mineralization low, thereby not allowing potentially fast‐growing deciduous species to outcompete them.
The effect of defoliation intensity and history on photosynthesis, growth and carbon reserves of two conifers with contrasting leaf lifespans and growth habits
Authors: VANDERKLEIN DIRK W. , REICH PETER B.
Published: March 2003

The effects of partial defoliation on photosynthesis, whole‐seedling carbon allocation, partitioning and growth were studied for two species with contrasting foliar traits. Field‐grown seedlings of deciduous Japanese larch (Larix leptolepis) and evergreen red pine (Pinus resinosa) were defoliated by hand in early summer for 2 consecutive years. In the first year (1990), seedlings were defoliated by removing the distal 0, 25, 50 or 75% of each needle. In the second year (1991), seedlings were defoliated either 0 or 50%, regardless of previous defoliation treatments. Defoliation had little effect on photosynthesis and starch concentration in whole seedlings of either species in the first year. In the second year, photosynthesis increased in both species in response to the 1991 defoliation treatment, and in red pine also increased in response to the 1990 defoliation treatment. Further, in 1991 both larch and pine had decreased whole‐seedling total non‐structural carbohydrate concentrations in all seedlings that were defoliated at least once over the 2‐yr period. This decrease was noted mostly in the starch component of the non‐structural carbohydrates, and was similar in both species. In 1991, biomass was similarly decreased in both species in response to 1991 defoliation. Both species showed overcompensation in total and component biomass in seedlings defoliated by 25% in 1990. Overall, the results do not support the widely held belief that evergreen trees are substantially more affected than deciduous trees by defoliation.
Analysis of genetic structure of a Suillus grevillei population in a Larix kaempferi stand by polymorphism of inter‐simple sequence repeat (ISSR)
Authors: ZHOU ZHIHUA , MIWA MAKOTO , HOGETSU TAIZO
Published: March 2003

Clones of ectomycorrhizal fungi can colonize new areas through production of vegetative mycelium or spore dispersal, but the relative importance of these processes in nature is not known. In this study, sporocarps of an ectomycorrhizal fungus, Suillus grevillei, were mapped and sampled from a Larix kaempferi stand at the foot of Mt Fuji. DNA was extracted directly from each sporocarp, and DNA polymorphism was analysed by polymerase chain reaction (PCR) amplification of inter‐simple sequence repeat (ISSR) regions primed by (GTG)5, (GCC)5 and (GACA)4. Different sensitivities to detect polymorphism were found among the three primers, with (GACA)4 showing the highest sensitivity. Forty seven sporocarps were analysed by the three ISSR primers and divided into 34 genets based on combination of PCR fingerprints. In the population 28 genets were represented by individual sporocarps. In most cases, sporocarps grown in aggregation (within a circle of 50 cm diameter) showed some different ISSR band patterns. These results suggest that genets of S. grevillei at the test site are relatively small. The genetic similarities between the 34 genets were also calculated and similarity groups were determined by the criterion that all similarity F values of genets within a group were not <80%. In general, the genets within a similarity group located close to each other. The results of multiple different but highly related genets in a small area suggest that the population of S. grevillei in this stand is not spread and maintained by clonal mycelium extension but is reproduced by spore dispersal.
LINGRA‐CC: a sink–source model to simulate the impact of climate change and management on grassland productivity
Authors: RODRIGUEZ D. , VAN OIJEN M. , SCHAPENDONK A. H. M. C.
Published: March 2003

A simulation model for the prediction of grassland (Lolium perenne) productivity under conditions of climate change is described and validated for grass growing in the Wageningen Rhizolab, Wageningen, The Netherlands. In this work the model was used to study the impact of different management strategies on the productivity of grassland under present and increased atmospheric CO2 concentrations. In LINGRA‐CC simulated key processes are light utilization, leaf formation, leaf elongation, tillering and carbon partitioning. The daily growth rate is determined by the minimum of a sink and a source term. As in a previous model (LINGRA), the potential growth of the sink depends on the mean daily temperature, and can be modified by the effects of the availability of assimilates on tillering. The growth of roots is calculated from the amount of carbohydrates the shoot is unable to utilize when the number or activity of the sinks is small (overflow hypothesis). The main difference between LINGRA and LINGRA‐CC is the way the source of assimilates for growth is calculated. Assimilate production depends on intercepted radiation, and a photosynthetic light‐use efficiency (LUE) calculated as a function of CO2, temperature, light intensity and the Rubisco concentration of upper leaves. Other differences are that in LINGRA‐CC, the specific shoot area for new growth depends on the level of reserves. Data from two independent experiments with L. perenne swards, grown in enclosures at two levels of CO2 during 1994 and 1995, were used to calibrate and validate the model, respectively. The model predicted well the observed amounts of harvested biomass, and the dynamics of the leaf area index, tiller number and specific shoot area. LINGRA‐CC was used to study the effects of different combinations of cutting interval and cutting height on biomass production, at ambient (350 μmol mol−1 CO2) and double (700 μmol mol−1 CO2 ) CO2 conditions. Under both ambient and doubled CO2, maximum biomass was produced with cuttings of leaf area index >1, and at cutting intervals of 20 and 17 d for ambient and increased CO2 environments, respectively. Under high CO2 conditions the cutting interval for maximum yield was 15% shorter than at ambient CO2. However, the gain in harvested biomass obtained by reducing the cutting interval by 3 d under high CO2 conditions was negligible.
Bacteria associated with Stagonospora (Septoria) nodorum increase pathogenicity of the fungus
Authors: DEWEY F. M. , WONG Y. LI , SEERY R. , HOLLINS T. W. , GURR S. J.
Published: March 2003

In studies with a laboratory isolate of the fungal pathogen Stagonospora (Septoria) nodorum three different isolates of bacteria were closely associated with the fungus. Bacteria were also closely associated with fresh isolates of S. nodorum obtained from artificially and naturally infected field material. Although a range of bacteria was isolated, only one type of bacterium was found to be associated with each isolate of S. nodorum. In co‐inoculation studies with pycnidiospores of the fungus on detached leaves, some of the bacterial isolates significantly increased the pathogenicity of the fungus, particularly Xanthomonas maltophilia, Sphingobacterium multivorum, Enterobacter agglomerans and Erwinia amylovora. Evidence is presented indicating that one of the ways that the ‘helper bacteria’ may assist in the establishment of infections is by the production of lipases that were not detected in germinating fungal spores.
Apoplasmic barriers and their significance in the exodermis and sheath of Eucalyptus pilularis–Pisolithus tinctorius ectomycorrhizas
Authors: VESK PETER A. , ASHFORD ANNE E. , MARKOVINA ANNE‐LAURE , ALLAWAY WILLIAM G.
Published: March 2003

The apoplasmic permeability of ectomycorrhizal roots of intact Eucalyptus pilularis seedlings infected with Pisolithus tinctorius on aseptic agar plates was examined using the nonbinding fluorochrome 8‐hydroxypyrene‐1,3,6‐trisulphonate and lanthanum ions in conjunction with anhydrous freeze substitution and dry sectioning. Most mycorrhizas formed in the air above the agar surface, and in these the sheath rapidly became nonwettable and impermeable to the fluorochrome but was nevertheless permeable to lanthanum ions. In a few mycorrhizas which developed in contact with the agar the sheath remained permeable to both tracers when fully developed. This increased hydrophobicity of the sheath in mycorrhizas in the air above the agar surface might be explained by deposition of hydrophobins, but nevertheless it still allows an apoplasmic pathway for radial movement of ions. Regardless of their sheath permeation both apoplasmic tracers were always found throughout the Hartig net and were arrested at the Casparian bands and suberin lamellae of the exodermis. It is concluded that the fluorochrome must have moved longitudinally along the Hartig net which is a region of higher permeability than the sheath. Casparian bands in the exodermis of ectomycorrhizal roots have similar properties to those in nonmycorrhizal roots in excluding solutes and their exclusion of lanthanum ions indicates that they are not permeable to ions. The data do not support the concept of a totally sealed apoplasmic exchange compartment, but the differential permeability suggests that the sheath might allow radial transfer of ions but block loss of sugars and organic molecules of similar size.
Piceirhiza bicolorata– the ectomycorrhizal expression of the Hymenoscyphus ericae aggregate?
Authors: VRÅLSTAD TRUDE , FOSSHEIM TONJE , SCHUMACHER TROND
Published: March 2003

The mycobionts of Piceirhiza bicolorata, a distinct ectomycorrhizal morphotype of conifers and hardwoods, have
been identified by internal transcribed spacer 1 (ITS1) nuclear ribosomal DNA (rDNA) sequence comparison of
the fungi involved. Samples of Piceirhiza bicolorata were obtained from seedlings of Picea abies, Pinus sylvestris,
Betula pubescens, Populus tremula, Quercus robur and Salix phylicifolia. In an initial screening, the fungus amplified
with universal ITS primers from ectomycorrhizal root samples of P. bicolorata shared approx. 95% ITS1
sequence identity with the ericoid mycorrhizal fungus Hymenoscyphus ericae. A total of 77 out of 88 (= 87.5%)
DNA samples (i.e. 52/56 root samples and 25/32 axenic culture isolates) of P. bicolorata were successfully
amplified with a taxon‐selective primer designed for exclusive amplification of H. ericae‐like strains. Forty‐seven
amplicons were sequenced, yielding 15 different ITS1 genotypes that differed by 1–14 nucleotide character state
changes. An inferred ITS1 phylogeny (maximum parsimony) showed that a single major evolutionary lineage of
P. bicolorata embraced the historically important H. ericae isolates in a 100% bootstrap‐supported clade. The 15
P. bicolorata genotypes were positioned in four subclades, roughly corresponding to morphological groups of P.
bicolorata isolates observed in axenic culture. Culture isolates of H. ericae and P. bicolorata share some common
morphological features including slow, dense growth and formation of short aerial hyphal aggregates. Our results
suggest that members of the H. ericae aggregate participate in the formation of the distinct ectomycorrhizal
morphotype P. bicolorata. This opposes the widely accepted discrimination of ericoid and ectomycorrhizal
mycobionts of the boreal forest ecosystem. The high prevalence of the P. bicolorata morphotype on pioneer
seedlings of P. sylvestris, B. pubescens and S. phylicifolia at a copper mine spoil was remarkable. Hypotheses of
possible nutrient mobilization and detoxification potentials of the fungal associates of P. bicolorata are discussed.
We hypothesize that ericoid and ectomycorrhizal plants may share mycobionts of the H. ericae aggregate.
Pattern in root meristem development in angiosperms
Authors: CLOWES F. A. L.
Published: March 2003

Roots of angiosperms differ in the behaviour of their apical meristems, and this diversity has been studied through the patterns of differentiation in a range of families. Except for three families of the Nymphaeales, all dicotyledons derive the epidermis wholly or partially with the root cap. In closed meristems the inner cell layer of the cap complex forms the epidermis; in open meristems, where cortex and cap are intermittently of common origin, linkages between the epidermis and the cap predominate. Roots of most monocotyledons derive the epidermis as the outer layer of the cortex. Nymphaeaceae, Cabombaceae and Barclayaceae resemble monocotyledons in this respect, and this applies even in the species with open meristems, in which a cleft forms between the cap and the rest of the apex. This feature fits with the close relationship between the Nymphaeales and monocotyledons revealed by other data. But none of the other Magnoliidae with close links to Liliidae has this type of epidermis. The Nymphaeales are also almost unique among dicotyledons in having trichoblasts in a vertical pattern. This results from transverse divisions of epidermal cells giving two conspicuously different daughters. The smaller and most densely staining one later bears a root hair. This is the way trichoblasts develop in many monocotyledons. The only other dicotyledons found with trichoblasts in vertical patterns are in the Piperaceae, though their closed meristems derive the epidermis in the normal dicotyledon pattern. All other dicotyledons that bear trichoblasts develop them in radial patterns probably related to the radial disposition of cells across the cortex. This pattern is more widespread than was previously known, though it can occur only in roots with closed meristems. In plants of both subclasses with vertical patterns of trichoblasts, it is usually the proximal daughter of the initiating mitosis which becomes the trichoblast. But it is the distal daughter in Juncaceae, Restionaceae, Cyperaceae and Poaceae. Vertical patterns differ further as to whether the atrichoblast daughters divide after initiation, thus changing the alternation of trichoblasts and atrichoblasts along a file of epidermal cells. Monocotyledons and the Nymphaeaceae can produce trichoblasts in open or closed meristems. In some embryos and root primordia the epidermis becomes discrete from cortex and cap and remains so in the meristems. This has now been found in six aquatic genera of the Liliidae, but reports of it occurring elsewhere are probably due to misinterpretation of sections. Discrete epidermises differentiate into trichoblasts and atrichoblasts in Hydrocharitaceae, but not in Araceae or Lemnaceae.
Seedling mortality of metal hyperaccumulator plants resulting from damping off by Pythium spp.
Authors: GHADERIAN Y. S. MAJID , LYON ANTHONY J. E. , BAKER ALAN J. M.
Published: March 2003

Seedling mortality of Alyssum serpyllifolium ssp. lusitanicum and A. murale, both nickel hyperaccumulators, was
reduced by increasing concentrations of metal within plant tissues when inoculated with the fungi Pythium
mamillatum or P. ultimum, both of which cause damping‐off disease of seedlings. Pythium mamillatum, isolated
from nickel‐rich serpentine soil, was more tolerant of nickel than P. ultimum, isolated from low‐metal control soil,
and was more pathogenic than P. ultimum towards seedlings containing high concentrations of metal. These results support the hypothesis that metal hyperaccumulation by plants is closely linked to increased protection against disease.
Metal hyperaccumulation: a model system for coevolutionary studies
Authors: Pollard A. J.
Published: March 2003

Recent years have seen a flurry of research activity concerning the hyperaccumulation of heavy metals by plants. Much of the interest in hyperaccumulation has been fueled by the commercial potential of phytoremediation, the use of plants to clean up contaminated soils (Baker et al., 1994; Salt et al., 1995; Chaney et al.,
1997, 2000). These applications have in turn spurred many
studies of the genetics and physiology of metal uptake (e.g.
Krämer et al., 1996; Lasat et al., 1996; Salt & Krämer,
1999; Baker et al., 2000; see also Krämer, 2000; Lombi et al.,
2000). Although phytoremediation provides an intriguing
and potentially profitable backdrop, the ecology
and evolution of hyperaccumulation in natural populations
are interesting subjects in their own right. Two papers in
this issue (Ghaderian et al., pp. 219–224; Davis & Boyd, pp. 211–217) are exciting contributions to the growing consensus that hyperaccumulation may act as a defense against herbivores and pathogens, and suggest that hyperaccumulation may become a model system for research in this area.
Pollen representivity of montane forest taxa in south‐west Uganda
Authors: MARCHANT ROBERT , TAYLOR DAVID
Published: March 2003

Results presented in this paper demonstrate the relationship between two data sets from Mubwindi Swamp, south‐west Uganda. The first data set is from a survey of dryland montane forest within the immediate catchment and the second is in the form of pollen spectra recovered from surface samples of sediment. Numerical analysis grouped pollen types encountered into five categories, according to their level of representivity when compared with abundances of the same taxa in the sampled vegetation: under representative, moderately under representative, representative, moderately over representative, and over representative. The northern part of Mubwindi Swamp also yielded a 5‐m‐long sequence of organic‐rich sediments (core MB6) from which sub‐fossil pollen and radiocarbon data have been previously obtained. This provides an opportunity to apply calibration factors derived from modern pollen–vegetation relationships to sub‐fossil pollen data that were obtained from the same site. These calibration factors effectively down‐weighted the influence of over representative pollen types and permitted the discrimination of a phase of forest disturbance that had not previously been so clearly visible in sub‐ fossil pollen data.
Nitrogen and phosphorus availability limit N2 fixation in bean
Authors: LEIDI E. O. , RODRÍGUEZ‐NAVARRO D. N.
Published: March 2003

Availability of nitrogen (N) and phosphorus (P) might significantly affect N2 fixation in legumes. The interaction
of N and P was studied in common bean (Phaseolus vulgaris), considering their effects on nodulation and N2
fixation, nitrate reductase activity, and the composition of N compounds in xylem sap. The effect of N on the
uptake of P by plants was estimated by analysing rhizospheric pH and P concentration in xylem sap and in plant
shoots. Inoculated bean plants were grown in pots containing perlite/vermiculite in two experiments with
different amounts of P and N. In a third experiment, bean plants were grown on two soil types or on river sand
supplied with different concentrations of N. At harvest, shoot growth, number of nodules and mass, and
nitrogenase activity were determined. Xylem sap was collected for the determination of ureides, amino acids,
nitrate and phosphate concentration. At low nitrate concentration (1 mM), increasing amounts of P promoted both
nodule formation and N2 fixation, measured as ureide content in the xylem sap. However, at high nitrate
concentration (10 mM), nodulation and N2 fixation did not improve with increased P supply. Glutamine and
aspartate were the main organic N compounds transported in the xylem sap of plants grown in low nitrate, whereas
asparagine was the dominant N compound in xylem sap from plants grown in high nitrate. Nitrate reductase
activity in roots was higher than in shoots of plants grown with low P and high N. In both soils and in the sand
experiment, increased application of N decreased nodule mass and number, nitrogenase activity and xylem ureides
but increased the concentration of asparagine in xylem sap. Increasing P nutrition improved symbiotic N2 fixation
in bean only at low N concentrations. It did not alleviate the inhibitory effect of high nitrate concentration on N2
fixation. A decrease in plant P uptake was observed, as indicated by a lower concentration of P in the xylem sap
and shoots, correlating with the amount of N supplied. Simultaneously with the specific inhibition of N2 fixation,
high nitrate concentrations might decrease P availability, thus inhibiting even further the symbiotic association
because of the high P requirement for nodulation and N2 fixation.
Does elevated ozone have differing effects in flowering and deblossomed strawberry?
Authors: DROGOUDI P. D. , ASHMORE M. R.
Published: March 2003

Fruiting and deblossomed plants of strawberry (Fragaria×ananassa) were exposed to 92 ppb ozone or filtered air in open‐top chambers for 69 d. Flower and fruit production, relative growth rate of leaf area, leaf gas exchange and plant biomass were investigated. Ozone caused an initial acceleration in inflorescence production, which was followed by a reduction in inflorescence production, fruit set, and, later, individual fruit weight, although total fruit yield was not affected before the end of the fumigation period. Ozone accelerated leaf senescence and had a greater negative effect on the rate of photosynthesis in older than in younger leaves in fruiting and deblossomed plants, but the response of net photosynthesis to ozone did not differ between the two groups of plants. Relative growth rate of leaf area was the first parameter to be reduced by ozone fumigation, with the effect being significant in fruiting, but not in deblossomed, plants. Final above‐ground biomass was also significantly decreased by ozone in fruiting plants, but not in deblossomed plants. Root and crown biomass were not significantly affected by ozone fumigation in either fruiting or deblossomed plants.
Modelling the germination of Stellaria media using the concept of hydrothermal time
Authors: GRUNDY A. C. , PHELPS K. , READER R. J. , BURSTON S.
Published: March 2003

The germination characteristics of Stellaria media (common chickweed) were investigated over a range of constant temperatures and degrees of moisture stress in order to assess the suitability of hydrothermal time as a basis for modelling germination under field conditions. Maximum percentage germination occurred over a much narrower temperature range around the optimum temperature than previously seen for cultivated crop seed. The entire final percentage germination response to temperature in water was well described by two probit curves, and this model was extended to describe the data at all water potentials at a temperature close to the optimum. The implications of the reduction in germination at nonoptimal temperatures are discussed with respect to the interpretation of germination progress curves and conditional dormancy. After adjusting for maximum percentage germination, a hydrothermal time model was found to fit the data set well within the conditions normally encountered in horticultural seedbeds. This separation of the final percentage germination presents a flexible modelling approach that allows for the different levels of dormancy typically expressed within weed populations. By contrast with many previously reported species, S. media had a synchronous germination rate within the population at any given temperature/water potential combination. This synchronous germination of at least a proportion of the population over a wide range of temperature and water potentials might have ecological significance for the opportunistic germination behaviour of this weed species.