bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of elevated CO2, water and nutrients onPicea sitchensis(Bong.) Carr seedlings
Authors: TOWNEND JOHN
Published: April 2006

summary

Sitka spruce (Picea sitchensis(Bong.) Carr.) seedlings were grown from seed for one year in naturally lit growth chambers with either ambient or ambient + 250 ppm concentrations of CO2. In the following year the plants were grown in the same CO2treatments for the whole growing season at two concentrations of nutrients and were either well‐watered or subjected to a long‐term, gradually increasing drought.

Elevated CO2increased significantly growth in all treatments except the well‐watered, unfertilized treatment. The relative increases in end‐of‐year biomass in the elevated CO2treatment compared with the ambient treatment were: well‐watered, fertilized + 52%, well‐watered, unfertilized +19%, droughted, fertilized+ 44%, and droughted, unfertilized + 49%.

Growth analysis revealed that treatment effects on both unit leaf rates and leaf area duration were important in determining the final masses of the plants. Plants growing in elevated CO2had increased relative growth rates in the first half of the growing season but only slightly increased or even slightly decreased relative growth rates in the later part of the growing season in all water × nutrient treatments.

Overall there was a significant CO2× water × nutrient interaction on end‐of‐year biomass. A combination of small nutrient concentration and adequate water supply led to the smallest growth response to elevated CO2.
Ozone induction of extensin mRNA in Scots pine, Norway spruce and European beech
Authors: SCHNEIDERBAUER A. , BACK E. , SANDERMANN H. , ERNST D.
Published: April 2006

summary

Fumigation of tree seedlings and saplings with ozone increased the mRNA level of extensin, a hydroxyprolinerich cell wall glycoprotein. European beech (Fagus sylvatica L.), Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) seedlings and saplings of various ages were treated with ozone concentrations from 20 nl l−1 up to 200 nl l−1 for 1 h up to several weeks. A strong increase of extensin transcript levels was detected within a few hours of fumigation. The induction occurred in needles and hypocotyls of Scots pine, needles of Norway spruce and leaves of European beech. Hypocotyls and roots with high levels of constitutive lignification were not induced. The degree of lignification in hypocotyls of equally old pine and spruce seedlings correlated with the degree of ozone‐induced transcription of extensin genes.
Attempted isolation and success in the culturing of a broad spectrum of lichen‐forming and lichenicolous fungi
Authors: CRITTENDEN P. D. , DAVID J. C. , HAWKSWORTH D. L. , CAMPBELL F. S.
Published: April 2006

summary

Isolation into pure culture was attempted on 1183 species (2238 specimens) of lichen‐forming and lichenicolous fungi from diverse ecosystems and systematic groups (covering 14 ascomycete orders, 77 families and 280 genera), in 20 countries. Four hundred and ninety three species (42%) were successfully isolated either from ascospores (or basidiospores, or conidia) or photobiont‐free fragments from thallus macerates. Of the total number of isolation attempts from ascospores (1609) and thallus fragments (719), 30% and 32% respectively were successful. The reasons for failure to isolate from ascospores were: ascospores did not germinate (43%) > ascospores were not discharged (30%) > ascospores germinated but growth was not sustained (19%) > discharged spores were heavily contaminated (8%). 59% of isolation failures with fragments were due to lack of growth and 41% were due to contamination. The orders from which mycobionts were most readily isolated were the Ostropales (70% of species attempted were isolated), Dothideales (63%), Pertusariales (53%) and Lecanorales (45%); those orders least readily yielding isolates were Vemicariales (10%), Gyalectales (20%), Arthoniales (30%), Lichinales (29%) and Peltigerales (27%). Members of the Lecanorales comprised c. 60% of species collected of which Porpidiaceae (80% of species successfully isolated), Cladoniaceae (69%), Lecideaceae (67%), Rhizocarpaceae (62%), Umbilicartaceae (60%), Ramalinaceae (60%) and Lecanoraceae (54%) were comparatively successful families and Alectoriceae (18%), Catillariaceae (8%), Pannariaceae (8%) Collemataceae (7%), and Micareaceae (6%) were least successful.

Of those species containing a cyanobacterium (either as the primary photobiont or in cephalodia), only 22% yielded isolates compared with 46%, and 43%, of lichens containing only a chlorococcoid photobiont or Trentepohlia, respectively. Success was even lower (17%) in species containing a cyanobacterium as the primary photobiont. Among non‐cyanobacterial lichens, isolation of mycobionts was achieved in 56% of fruticose species collected compared with 43% and 40% for crustose/squamulose and foliose taxa respectively. Mycobionts of fruticose lichens cultured particularly readily from fragments, with 56% of green algal species to which this method was applied coming into culture compared to 37% of non‐cyanobacterial foliose species. Lichenicolous fungi cultured less readily, with only 31% of species yielding isolates.

In many species viability of ascospores varied between collections. Weather conditions at the time of collection, environmental conditions during transportation, and developmental stage of ascomata of pyrenocarpous lichens might partly explain this variation.
Physiological ecology of cyanobacteria in microbial mats and other communities
Authors: STAL LUCAS J.
Published: April 2006

summary

In this review some aspects of the physiological ecology of cyanobacteria are discussed by taking a microbial mat as an example. The majority of microbial mats are built and dominated by cyarsobacteria which are primary producers at the basis of the microbial foodweb in microbial mats. These micro‐scale ecosystems are characterized by steep and fluctuating physico‐chemical gradients of which those of light, oxygen and sulphide are the most conspicuous. Light is strongly attenuated in the sediment, and owing to constant sedimentation, the mat‐forming cyanobacteria have to move upwards towards the light. However, at the sediment surface, light intensity, particularly in the u.v. part of the spectrum, is often deleterious. The gliding movement of the cyanobacteria, with photo‐ and chemotaxis, allows the organism to position itself in a thin layer at optimal conditions. The organic matter produced by cyanobacterial photosynthesis is decomposed by the ruicrobial community. Sulphate‐reducing bacteria are important in the end‐oxidation of the organic matter. These organisms are obligate anaerobes and produce sulphide. Gradients of sulphide and oxygen move up and down in the sediment as a response to diurnal variations of light intensity. Cyanobacteria, therefore, are sometimes exposed to large concentrations of the extremely toxic sulphide. Some species are capable of sulphide‐dependent anoxygenic photosynthesis. Other cyanobacteria show increased rates of oxygenic photosynthesis in the presence of sulphide and have mechanisms to oxidize sulphide while avoiding sulphide toxicity. Iron might play an important role in this process. Under anoxic conditions in the dark, mat‐forming cyanobacteria switch to fermentative metabolism. Many species are also capable of fermentative reduction of elemental sulphur to sulphide. The gradients of sulphide and oxygen are of particular importance for nitrogen fixation. Very few microbial mats are formed by heterocystous cyanobacteria, which are best adapted to diazntrophic growth. However, these organisms probably cannot tolerate greater concentrations of sulphide or anoxic conditions or both. Under such conditions non‐heterocystous cyanobacteria become dominant as diazotrophs. These organisms avoid conditions of oxygen supersaturation. In the ecosystem, nitrogen fixation and photosynthesis might be separated temporally as well as spatially. In addition, non‐heterocystous diazotrophic cyanobacteria have mechanisms at the subcellular level to protect the oxygen‐sensitive nitrogenase from inaction.

CONTENTS

Summary
1

I.
Introduction
2

II.
Microbial mats
3

III.
Cyanobacteria in light gradients
7

IV.
Dark metabolism
10

V.
Interactions with sulphide
13

VI.
Nitrogen fixation
16

VII.
References
28
Apoplastic permeability of sclerotia of Sclerotium rolfsii, Sclerotium cepivorum and Rhizoctonia solani
Authors: YOUNG NICOLA , ASHFORD ANNE E.
Published: April 2006

summary

Intact mature sclerotia of Sclerotium rolfsii sacc, and Sclerotium cepivorum Berk, produced in culture are impermeable to the apoplastic tracer sulphorhodamine G. Both of these species produce sclerotia with rinds. Some movement of sulphorhodamine into sclerotia of Rhizoctonia solani Kühn, which have no rind, occurred but the fluorochrome was arrested after permeation of at most the outer five layers of cells. In all cases, low permeability depended on an intact outer layer, and when sclerotia of each species were bisected to provide direct access of sulphorhodamine to all tissue layers, the fluorochrome permeated the cell walls and extracellular matrix (where present) of many cells within the sclerotium. A marked reduction in permeability of intact sclerotia occurs at maturity in a number of species and might he important in long‐term Survival.
Dynamics of thermogenesis and structure of epidermal tissues in inflorescences of Arum maculatum
Authors: BERMADINGER‐STABENTHEINER EDITH , STABENTHEINER ANTON
Published: April 2006

summary

The temporal dynamics and spatial distribution of heat production by inflorescences of Arum maculatum L. were investigated by infra‐red thermography. Two centres of (teat production, the appendix and the male flowers, and three thermogenic phases, two of the male flowers and one of the appendix, could be observed. On the first day of flowering, when the spathe was still firmly closed, the male flowers became thermogenic (= first thermogenic phase Of the in florescence) and reached surface temperatures of 4.1–8.0 °C above ambient temperature. Afterwards the spathe unfolded and the appendix started heating to temperatures of 5.0–14.0 °C above ambient temperature (second thermogenic phase of the inflorescence). On the second day of flowering the male flowers revealed a second temperature maximum of 0.5–601 °C above ambient temperature third thermogenic phase of the inflorescence) which was followed by the release of the pollen grains. When the male flowers started heating, a fruit‐like and pleasant scent became evident and continued until the heat production in the male flowers stopped. Only during the heating phase of the appendix was this fruit‐like scent overlaid by the dung‐like odour typical of many aroid species. The surface of the spadix and the inner surface of the basal bulb (floral chamber) as investigated by scanning electron microscopy were characterized by smooth epidermal cells of papillate shape. These cells were rurgid before the onset of flowering and heat production and collapsed afterwards. Distinct intercellular spaces creating a lacunose epidermis (‘Lückenepidermis‘) were observed between the papillate epidermal cells of the inner surface of the basal bulb (floral chamber). This coincided with a high density of stomata on its outer surface. It is suggested that, beside other pathways, these structures contribute to the maintenance of sufficient oxygen support of the captured insects and the thermngenic tissues inside the floral chamber.
Impact of a fungal pathogen, Colletotrichum coccodes on growth and competitive ability of Abutilon theophrasti
Authors: DITOMMASO ANTONIO , WATSON ALAN K.
Published: April 2006

summary

The combined effects of planting density and of different inoculation frequencies ofColletotrichum coccodes (Wallr.) Hughes on growth and competitive performance of Abutilon theophrasti Medik. were studied using a soybean‐A. theophrasti target‐neighbour design in a controlled environment. In both trials of the experiment, A. theophrasti inoculated at the highest planting density (four plants per ppt) suffered significantly greater reductions in height (41%) than did A. theophrasti at the lowest density (one plant per pot) (7%). Above‐ground biomass and leaf area reductions, however were significantly greater at the highest density for only one of the trials. Soybean plants grown with inoculated A. theophrasti at the two highest planting densities had a significantly greater above‐ground biomass (61%) and leaf area (68%) than did plants grown with uninoculated A. theophrasti at the same densities. By contrast, at the two lower densities, soybean above‐ground biomass and leaf area were not increased significantly fallowing inoculation. Either one or two C. coccodes inoculations caused the greatest reductions in A. theophrasti growth compared with uninoculated plants. Conversely, three applications of the fungus generally resulted in less severe disease symptoms and resulted in the smallest decreases in A. theophrasti growth. Induced systemic resistance following two inoculations might have played an important role in limiting disease. However, the significantly greater biomass and height of A. theophrasti plants subjected to the triple C. caicudes treatment, compared with plants receiving either one or two inoculations in one of the trials, provides some evidence of a possible compensatory response in .4. theophrasti. The relevance of these findings for biological weed control is examined.
Increased growth efficiency ofQuercus albatrees in a CO2‐enriched atmosphere
Authors: NORBY RICHARD J. , WULLSCHLEGER STAN D. , GUNDERSON CARLA A. , NIETCH CHRISTOPHER T.
Published: April 2006

summary

Forests have a prominent role in the global carbon cycle, but their response to a changing atmosphere cannot be measured directly. Experimental observations of small trees in CO2‐enriched atmospheres must be interpreted carefully if they are to be relevant to the potential responses of forest trees. We grew1white oak (Quercus albaL.) saplings for four complete growing seasons in open‐top chambers with different partial pressures of atmospheric CO2White oak saplings produced 58% more dry mass in 50 Pa CO2and 135% more in 65 Pa, compared with plants in ambient (35 Pa) CO2Although this result might suggest a substantial potential for increased carbon storage in forests, the large difference in growth rate could be attributed to a stimulation of growth very early in the experiment. There was not a sustained effect of C2on relative growth rate after the first year, and the increased absolute growth rate could persist only so long as leaf area could increase, a condition that would not occur indefinitely in a forest. Nevertheless, annual stem wood production per unit area (growth efficiency) was 37 %, greater in elevated CO2. This increase in growth efficiency, a response that is consistent across diverse studies, implies a potential increase in carbon sequestration by forests, subject to critical assumptions about forest canopy development in a CO2‐enriched atmosphere
Effects of CO2 enrichment, leaf position and clone on stomatal index and epidermal cell density in poplar (Populus)
Authors: CEULEMANS R. , VAN PRAET L. , JIANG X. N.
Published: April 2006

summary

The effects of CO2, enrichment and leaf position on stomatal characteristics (stomatal density, stomatal index and stomatal pore length) and epidermal cell density were examined for two different Populus clones, Beaupre and Robusta, grown from cuttings in open‐top chambers under ambient and elevated atmospheric CO2 conditions. Both clones had amphistomatous leaves, and stomatal density was significantly larger on the abaxial leaf surface than on the adaxial. Significant interactions between CO2 enrichment, leaf position and clone were observed for most stomatal and epidermal characteristics. A significant reduction of the number of stomata mm−2 under elevated CO2 was observed in expanding leaves near the upper portion of the plant for both leaf surface sides and in both clones. For the abaxial leaf side only, this reduction under elevated CO2, was accompanied by a similar reduction of the stomatal index in both clones. In mature leaves on the middle and lower portion of the plants, there was no significant effect of the CO2 treatment on stomatal density. In young, expanding leaves near the upper part of the plant there were significant interactions between the CO2 treatment and leaf surface side for epidermal cell density. The latter increased under elevated CO2 at the abaxial leaf surface, but decreased at the adaxial surface on the upper part of the plant. Total epidermal cell numbers of mature, fully expanded leaves increased under elevated CO2, in both clones. The observation that interactions with leaf age and/or leaf position significantly confound the CO2, treatment effect on stomatal and epidermal cell densities, might contribute to the elucidation of the problem of the phenomenon of stomatal density reduction under elevated atmospheric CO2.
Root‐induced iron oxidation, pH changes and zinc solubilization in the rhizosphere of lowland rice
Authors: KIRK G. J. D. , BAJITA J.B.
Published: April 2006

summary

Rice plants (Oryza sathiva L., cv. IR34) were grown with their roots sandwiched between cylinders of an anaerobic low‐Zn Mollisol. After periods of root‐soil contact of up to 12 d (total plant age c. 28 d) the profiles of different Zn fractions, reduced and oxidized Fe, and pH in the soil near the root plane' were determined. The concentration of easily plant‐extractable Zn in the soil (measured by extraction in I M KCl) was negligible, and so it was necessary for the plants to induce changes in the soil to solubilize Zn. After 6 d, there was a substantial accumulation of Zn associated with organic matter and amorphous ferric hydroxide within 4–5 mm of the root plane. Over the next 6 d, the accumulation continued but there was a substantial depletion of the accumulated fractions within 2 mm of the root plane. The zones of accumulation and depletion coincided with zones of Fe(III) accumulation and soil acidification in which the pH decreased from the bulk soil value of 7.3 by over 0.2 pH units; i.e. a two‐fold increase in H+ concentration, The acidification was the result of H+ released from the roots to balance excess intake of cations over anions, and H+ generated in the oxidation of Fe(H) by root‐released O2. At the high pH and CO., pressure of the experimental soil (7.3 and c. 0.9 kPa. respectively), soil acidity diffusion is fast and consequently the pH drop at the root surface was small. The rate of Fe oxidation peaked before 6 d, but the acidification and Zn accumulation continued beyond 6 d unabated. It is concluded that Fe oxidation released Zn from highly insoluble fractions, and that this Zn was re‐adsorbed on Fe(OH)3 and on organic matter in forms that were acid‐soluble and therefore accessible to the plants.
Estimates of fungal biomass in Scots pine stands on an urban pollution gradient
Authors: MARKKOLA A. M. , OHTONEN R. , TARVAINEN O. , AHONEN‐JONNARTH U.
Published: April 2006

summary

Biomasses of ectomycorrhizal and saprotrophic fungal communities partitioned into sporophores and non‐reproductive structures were estimated in mature Scots pine (Pinus sylvestris L.) stands along an urban nitrogen and sulphur pollution gradient in northern Finland. The average total biomass of fungi varied in the four pollution zones from 14.6 to 20.2 g d. Wt kg−1 soil d. wt and from 73.3 to 108.0 g d. Wt m−2, the mycelia of both mycorrhizai and saprotrophic fungi in the soil comprising 72–80% of the total. The annual carbon allocation to the fungal communities was calculated to vary between 9 and 26% of the estimated annual carbon assimilation at the Scots pine sites. The size of the mean fungal biomass fractions decreased in the following sequence: mycelia in the soil > fungal biomass in fine roots estimated in terms of chitin > sclerotia > fungal biomass in fine roots estimated in terms of ergosterol > sporopbores of mycorrhizal fungi > sporophores of saprotrophie fungi. A positive correlation was obtained between the number of Scots pine mycorrhiza and the average sporophore yield of mvcorrhiaal fungi for three successive years. Tbe sporophore biomass of the mycorrhizal fungi was smaller at the most polluted than at the least polluted sites. The total fungal biomass allocation was not affected by urban pollution.
Assessment of photosynthetic radiation‐use efficiency with spectral reflectance
Authors: PEÑUELAS JOSEP , FILELLA IOLANDA , GAMON JOHN A.
Published: April 2006

summary

Reflectance changes at 531 nm, associated with the zeaxanthin‐antheraxanthin‐violaxanthin interconversion and the related thylakoid energization, are widespread among plant species. We evaluated an index based on 531 nm reflectance (‘PRI’, Photochemical Reflectance Index calculated as (R531− R570)/(R531+ R570)) as an indicator of efficiency of photosynthetic radiation use in seven species representing both C3 and CAM photosynthetic pathways. Leaves exposed to a dark‐lighted ark transition in a steady‐state laboratory gas exchange system exhibited nearly parallel changes in PRI and PS II quantum yield (ΔF/Fm′). Similar PRI and ΔF/Fm′ responses were seen in leaves exposed to diurnally changing sunlight levels outdoors. PRI was linearly related to ΔF/Fm′, and both ΔF/Fm′ and PRI were exponentially related to instantaneous efficiency of photosynthetic radiation‐use in different species over a range of different field conditions. These results extend previous studies by indicating a functional relationship between PRI. ΔF/Fm′, and photosynthetic radiation‐use efficiency. The narrow‐band PRI index offers a simple, portable means of assessing PS II radiation‐use efficiency, analogous to ΔF/Fm′, and with the potential for remote applications at scales larger than the leaf.
A three‐dimensional representation of the relationship between penetration of u.v.‐B radiation and u.v.‐screening pigments in leaves of Brassica napus
Authors: ÅLENIUS CAMILLA M. , VOGELMANN THOMAS C. , BORNMAN JANET F.
Published: April 2006

summary

A three‐dimensional (3–D) representation of the penetration of u.v.‐B (280–320 nm) radiation using fibre‐optic microprobes, and of the spectrophotometric analysis of u.v.‐.screening pigments in leaves of Brassira napus, L. ev. Ceres is presented. In this way the results from radiation measurements were directly related to the distribution of u.v.‐screening pigments. Brasssica napus was grown in a greenhouse chamber with a photon flux density of 740μmol m−2 s−1 photosynthetieally active radiation (400–700 nm) with or without the addition of u.v.‐B radiation. The amount of u.v‐B added was equivalent to 9 kJ m−2 d−1 biologically effective u.v.‐B. Growth parameters measured lncluded leaf thickness and dry weight. Ultraviolet‐B radiation stimulated the accumulation of increased amounts of screening pigments, located mostly beneath the adaxial surface of the leaf. Leaf dry weight decreased by 15% in u.v.‐treated plants and, on a dry weight basis, chlorophyll content increased by 19% in treated leaves. The chlorophyll profiles within leaves from both control and u.v.‐treated plants showed an increase from the adaxial surface to a plateau in the middle of the leaf, at a leaf depth of c. 150–320μm. Relatively large amounts of 285 nm radiation penetrated into leaves of u.v.‐B treated plants to sites located within the initial 40μm of the leaf. Thus, despite the presence of additional screening pigments, u.v.‐B radiation was capable of reaching potential targets within the epidermis and mesophyll.
Mesophyll structure during leaf development in Ballota acetabulosa
Authors: PSARAS G. K. , RHIZOPOULOU S.
Published: April 2006

summary

Mesophyll structure and water relations were studied in expanding and expanded dorsiventral leaves of Ballota acetabulosa Benth., a wild perennial shrub from the Mediterranean. The spongy mesophyll was developed earlier than the palisade in expanding leaves and exhibited a larger internal exposed surface. By contrast, in fully expanded leaves the internal exposed surface was much larger in the palisade than in spongy mesophyll. The development of chloroplasts in cells of both mesophyll tissues, as well as their arrangement along the cell walls exposed to intercellular canals, coincided with the formation of intercellular spaces. Leaf expansion appears to be positively related to increasing internal exposed surface and declining water potentials. As a result, mature leaves possess a high ratio of internal exposed surface per leaf area and low values of turgor. It is considered that an increase in the internal exposed surface might be an adaptive feature for small‐leaved shrubs, grown under water deficiency.
Exudation rate and hydraulic conductivity of maize roots are enhanced by soil drying and abscisic acid treatment
Authors: ZHANG JIANHUA , ZHANG XIAOPING , LIANG JIANSHENG
Published: April 2006

summary

When young maize seedlings were fed with abscisic acid (ABA) into their root systems, the exudation rate from roots through cut stems was enhanced more than leaf diffusive resistance. Enhanced root exudation was also observed when mildly droughted plants were re‐watered. To compare the mechanisms involved in this response under these two treatments, we examined solute transport in exudates and in situ whole root hydraulic conductivity following ABA feeding to the roots or soil drying/re‐watering treatment. Increases of both solute concentration and delivery rate in the exudates of pre‐droughted plants appeared to account for about half of the enhanced exudation rate. ABA‐fed plants showed only a marginal increase of solute delivery rate and in fact a somewhat reduced concentration of solutes in their exudates. In situ root hydraulic conductance, assessed by the pressure‐How method on undisturbed roots, was greatly increased by ABA or soil drying treatments. The results indicate that drought‐induced ABA in roots improved root hydraulic conductivity and raised root pressure when droughted plants were re‐watered.
Ammonium toxicity and nitrate response of axenically grown Dactylorhiza incarnata seedlings
Authors: DIJK EEUWE , ECK NELLY
Published: April 2006

summary

The response to ammonium‐ and nitrate‐nitrogen of seedlings of the calcicole orchid species Dactylorhiza incarnata (L.) Soó was tested in axenic in vitro culture of c. 3‐momh‐old protocorms. A pronounced toxicity of ammonium ions was observed. Seedlings raised from plants of a coastal population (f. dunensis (Druce) Soó) and those from plants of an inland population (f. incarnata) showed a different response to nitrogen form. Although ammonium toxicity was similar for seedlings of both sites, those of the coastal population showed a positive response to nitrate ions whereas those of the inland population did not. These differences could not be interpreted unequivocally as population differentiation. Ammonium toxicity was reduced in alkaline conditions. Yields increased with increasing pH and reached a maximum at pH 8.0. Calcium concentrations of 1 mM were optimal, but calcium levels did not affect the ammonium response. Seedlings did not respond to potassium concentrations in the range of 0.0–4.0 mM superimposed on a basal level of 0.4 mM. No interaction could be demonstrated between ammonium toxicity and potassium levels. Response to pH and ammonium provides a plausible mechanism for the sensitivity of the species to soil decalciftcation and decrease in seepage intensity of calcium rich groundwater in the field.
The biology of mycorrhiza in the Ericaceae
Authors: KERLEY SIMON J. , READ DAVID J.
Published: April 2006

summary

In acid mor‐humus soils of heathland ecosystems fungi are a significant part of the soil biomass. In these organic soils chitin and hyphal wall hexosamines are major potential sources of nitrogen (N). The ability of the ericoid mycorrhizal fungus Hymenoscyphus ericae (Read) Korf & Kernan to degrade purified chitin and the hexosamines, N‐acetylglucosamine, glucosamine and galactosamine when supplied as sole sources of N, was investigated in aseptic liquid culture. The fungus grew rapidly on all the organic N sources, producing the largest dry weight increase when supplied with galactosamine and similar yields on the other nitrogenous sources. Mycelial N contents of fungus grown on the hexosamines reflected the dry weight yields with the fungus grown on galactosamine haying the highest N content. After 20 d only tract quantities of N‐acetylglucosamine and glucosamine were present in culture filtrate, and 15% of the galactosamine remained at the final harvest. Plants of Vaccinium macrocarpon Ait. and Calluna vulgaris (L.) Hull were grown aseptically in the mycorrhizal or non‐mycorrhizal condition on agar media containing chitin or a hexosamine and compared with yields and N contents in the absence of an N source. It was revealed that significant quantities of N were transferred to the host in the mycorrhizal condition that led to enhanced growth rates. The highest yields of V. macrocarpon were observed with N‐acetylglucosamine, with the other hexosamines giving yields slightly below that on chitin. The yields were reflected in the calculation of the percentage of available substrate present in the plant; up to 40% of the N‐acetylglucosamine was present in the plants after 40 d.
Cadmium toxicity in Nostoc UAM208: protection by calcium
Authors: FERNANDEZ‐PIÑAS F. , MATEO P. , BONILLA I.
Published: April 2006

summary

The interactive effects of cadmium (Cd) and calcium (Ca) on growth, photosynthesis (O2 evolution), nitrogenase, respiration, developmental cycle and Cd bioaccumulation by the N2 fixing cyanobacterium Nostoc UAM208 have been studied. Ca was found to exert a detoxifying role towards Cd inhibition of these physiological processes. Finally, the mechanisms by which Ca might protect the cyanobacterium against Cd toxicity are discussed.
Fungal biomass in roots and extramatrical mycelium in relation to macronutrients and plant biomass of ectomycorrhizal Pinus sylvestris and Alnus incana
Authors: EKBLAD ALF , WALLANDER HÅKAN , CARLSSON ROLF , HUSS‐DANELL KERSTIN
Published: April 2006

summary

We studied the effects of macronutrients on the production and distribution of fungal biomass and plant biomass in ectomycorrhizal (Paxillus involutus (Fr.) Fr.) or non‐mycorrhiza] Pinus sylvestris L, and Alnus incana (L.) Moench. Fungal biomass was measured as ergosterol content in roots and extramatrical mycelium, Alnus infants was nodulated with Frankia. All six macronutrients were varied according to a two‐level fractional factorial design, The plants were grown in pots during two growing periods in a growth chamber. Levels of N, P and sometimes K and interactions between them, had highly significant effects, whereas Ca. Mg and S had no significant effects. The production of extramatrical mycelial biomass peaked when P was low and other nutrients were high. This investment in extramatrical mycelium resulted in a 660%, higher biomass in mycorrhizal compared with non‐mycorrhizal P. sylvestris at this nutrient regime. The proportion of fungal biomass in roots was stable in P. sylvestris hut more variable in A. incana. Alnus incana grew less when mycorrhizal then when non‐mycorrhizal. The growth responses to mycorrhiza and to the different nutrient treatments were evident at the end of the first growing period. Non‐mycorrhizal P. sylvestris did not respond to P limitation by a production of proportionally more roots. This might be a reflection of an obligate dependency on mycorrhiza for effective P uptake. By contrast, the root/shoot ratio in both mycorrhizal and non‐mycorrhiza] P. sylvestris decreased strongly in response to increased N. The opposite root/shoot response was found in Alnus incana, and the ratio decreased strongly in response to increased P and increased in response to increased N.
Contrasting effects of elevated CO2 and water deficit on two native herbs
Authors: FERRIS RACHEL , TAYLOR GAIL
Published: April 2006

summary

This study investigated the effects of carbon dioxide (CO)2 enrichment and soil water deficit on the water use efficiency (WUE) and growth of Sanguisorba minor Scop, (salad burnet I and Anthyllis vulneraria L. (kidney vetch), growing in controlled environments. Instantaneous WL E (IWUE) increased in both species in elevated CO2, with a higher average increase in unwatered (UW) A. vulneraria over the drying cycle. Total plant WUE of A. vulneraria increased in elevated CO, and under water deficit: the UW plants in elevated CO., had higher WUE and reduced water loss. By contrast, thee was only an effect of water supply on S. minor: total plant WUE increased and water loss decreased in the UV plants in both CO2, treatments. Total apparent root length (ARL) of both species increased with CO2, enrichment and in UW S. minor total ARL was increased. By contrast, for A. vulneraria, total ARL of UV plants increased in ambient CO2, but decreased in elevated CO2 as compared with well‐watered (WW) plants. Shoot dry weight (SDW) and root dry weight increased in both species (WW and UW) with CO2. enrichment. For UW S. minor, SDW decreased relative to WW plants in both CO2 treatments. By contrast, ANOVA showed no significant effect of water supply on SDW of A. vulneraria. Leafier length increased in both species in elevated CO2, and decreased following drought. Cell wall tensiometric extensibility (%P) increased in expanding leaves of S. minor in elevated CO., and for both species %P decreased in the UW plants as compared with those WW. Leaf water potential (f) of both species was lower in growing leaves of WAV plants in elevated CO2 Water deficit reduced the Ψ of growing leaves in both CO2, treatments. The different responses of these species suggest that in a drier, enriched CO2, environment survival in a community might depend on their ability to maintain growth at the same time as conserving water.
Chemical changes in selected wetland plant species with increasing Fe supply, with specific reference to root precipitates and Fe tolerance
Authors: SNOWDEN R. E. D. , WHEELER B. D.
Published: April 2006

summary

A range of wetland plant species (44) was screened in solution culture experiments for sensitivity to large concentrations of supplied Fe. Two distinct root precipitates were observed (see ‘Appendix’ for a tabulated summary of symptoms). Energy dispersive spectroscopy showed that an ochreous precipitate was probably a hydrated ferric oxide whilst a pale yellow or yellow‐grey one was an Fe‐P solid, possibly a ferric phosphate. Ochre precipitates were found almost exclusively cm the roots of Fe‐tolerant species and were particularly intense on the most tolerant ones, Monocotyledonous species (generally more Fe‐tolerant than dicotyledonous species and with higher root porosities), tended to produce ochre most freely. The Fe‐P precipitate was frequently found on roots of the less tolerant species and was particularly abundant on the most sensitive ones. Blackening of roots (with flaccidity I, another common response of roots of Fe‐sensitive plants exposed to large Fe concentrations, was not a result of any obvious external precipitate. There was no evidence that differential pH changes induced by roots helped to determine either Fe tolerance or the nature of the root precipitate observed. Roots of all species tested caused the pH of an agar medium to rise. Elevated Ft‐ supply resulted in greater external acid phosphatase activity in roots of two test species. The increase corresponded with the species' mean relative growth rate (RGR) (and presumed P requirement), and with me fertility of sites in which it grows. Chemical analyses of shoots and roots of four species of differing Fe tolerance showed that, with increasing Fe supply, mean shoot Fe concentrations increased significantly whereas for most other elements (except Na and Zn) a significant reduction in concentrations in the shoot was observed. Mean root concentrations of most elements also fell significantly with increasing Fe supply, though for three of the four test species there was a significant increase in root P concentrations. It is clear that only some wetland plant species form ochreous root precipitates when grown in Fe‐rich conditions, and have an effective Fe‐exclusion mechanism. Growth of those species that lack this capacity is affected adversely by high Fe concentrations. This might be owing both to direct effects of Fe uptake and to indirect effects, particularly of Fe upon P metabolism. No evidence was found to suggest chat the Fe‐tolerant species examined could accommodate higher tissue Fe concentrations than the Fe‐sensitive species.
Resource partitioning to growth, storage and defence in nitrogen‐fertilized Scots pine and susceptibility of the seedlings to the tarnished plant bug Lygus rugulipennis
Authors: HOLOPAINEN JARMO K. , RIKALA RISTO , KAINULAINEN PIRJO , OKSANEN JARI
Published: April 2006

summary

We tested how variable nitrogen availability affects the above‐and below‐ground growth of first‐year Scots pine (Pinus sylvestris L.) seedlings and carbon allocation to defensive allelochemicals and storage. Concentrations of free ammo acids were considered as indicators of nutritive quality. Suitability of seedlings for polyphagous Lygus rugulipennis Popp. (Heteroptera: Miridae) was tested with oviposition preference and nymphal growth experiments. At the end of the growing season, needle length increased while root hiomass decreased with elevated N fertilization, but shoot length was not affected. Concentration of starch in needles and roots, representing carbon storage, was not significantly affected by N fertilization, although there was a decrease in the starch concentration of needles when nitrogen input increased. Nitrogen fertilization significantly increased the pool of total and non‐essential ammo acids in the shoots. Arginine, proline and glutamine were the individual ammo acids most affected by elevated N. Of the carbon‐based defence compounds, total resin acid concentrations in shoots were significantly reduced with elevated nitrogen in 9‐wk‐old seedlings. Palustric acid and neoabietic acid were the most affected individual) resin acids, where as foliar monoterpenes were not influenced by N availability. Total phenolics in shoot and root showed variable response. The increasing effect of nitrogen on the oviposition rate of Lygus females was almost linear. Mean relative growth rate of the nymphs was significantly affected by the level of N fertilization. but the mortality of nymphs was high in all treatments. The results suggest that in nitrogen‐rich environments the needle growth of small Scots pine seedlings is improved, but their Susceptibility to insect attack is increased and they remain less defended as predicted by the carbon/nutrient balance hypothesis. Total phenolics and resin acids, representing phenylalanine and mevalonic acid pathways, respectively, were both reduced by increased nitrogen availability. Together with the simultaneous increase of foliar free nitrogen in the form amino acids, the nutritive value of seedlings is ameliorated and this might explain susceptibility of nursery‐grown. N fertilized seedlings to polyphagous Lygus bugs.
Auxin action and auxin‐binding proteins
Authors: NAPIER RICHARD M. , VENIS MICHAEL A.
Published: April 2006

The plant growth regulator auxin mediates an enormous range of developmental and growth responses, some of which are manifest rapidly and others manifest only after considerable lag periods. The protein that perceives auxin, the auxin receptor, has been sought by many laboratories and the search has identified a good number of candidates. However, a receptor must not only bind auxin, but also transduce the auxin stimulus into the responses we recognize. Finding evidence for this second condition has always proved very demanding. A key requisite is a convenient assay for auxin activity and preferably one involving a rapid response because this is likely to be linked directly to the perception event. For one auxin‐binding protein (ABP1) there is growing evidence that it is a functional auxin receptor. The assays used in this work have been rapid auxin‐induced changes in protoplast electrophysiology. There are many other responses induced rapidly by auxin for which a link to ABP1 has yet to be established. We have reviewed the whole range of rapid auxin‐mediated responses and by doing so we hope to have provided a comprehensive picture of the many events to which a receptor (or receptors) must connect. Against this framework we match the known properties of all putative receptors, including ABP1. Not only have we tried to identify auxin‐binding proteins unlikely to be receptors, but we also highlight the remaining gaps in our understanding of the more likely receptor candidates.

Contents

Summary
167

I.
Introduction
168

II.
Gene activation
168

III.
Mutants
179

IV.
Auxin‐induced elongation growth
179

V.
Other auxin‐binding proteins
191

VI.
Auxins and signal transduction
192

VII.
Overview
194

Acknowledgements
195

References
195
Interacting effects of soil fertility and atmospheric CO2 on leaf area growth and carbon gain physiology in Populus×euramericana (Dode) Guinier
Authors: CURTIS PETER S. , VOGEL CHRISTOPH S. , PREGITZER KURT S. , ZAK DONALD R. , TEERI JAMES A.
Published: April 2006

Two important processes which may limit productivity gains in forest ecosystems with rising atmospheric CO2are reduction in photosynthetic capacity following prolonged exposure to high CO2 and diminution of positive growth responses when soil nutrients, particularly N, are limiting. To examine the interacting effects of soil fertility and CO2 enrichment on photosynthesis and growth in trees we grew hybrid poplar (Populus × euramericana) for 158 d in the field at ambient and twice ambient CO2 and in soil with low or high N availability. We measured the timing and rate of canopy development, the seasonal dynamics of leaf level photosynthetic capacity, respiration, and N and carbohydrate concentration, and final above‐ and belowground dry weight.

Single leaf net CO2 assimilation (A) increased at elevated CO2 over the majority of the growing season in both fertility treatments. At high fertility, the maximum size of individual leaves, total leaf number, and seasonal leaf area duration (LAD) also increased at elevated CO2, leading to a 49% increase in total dry weight. In contrast, at low fertility leaf area growth was unaffected by CO2 treatment. Total dry weight nonetheless increased 25% due to CO2 effects on A. Photosynthetic capacity (A at constant internal p(CO2), ((C1)) was reduced in high CO2 plants after 100 d growth at low fertility and 135 d growth at high fertility. Analysis of A responses to changing C1 indicated that this negative adjustment of photosynthesis was due to a reduction in the maximum rate of CO2 fixation by Rubisco. Maximum rate of electron transport and phosphate regeneration capacity were either unaffected or declined at elevated CO2. Carbon dioxide effects on leaf respiration were most pronounced at high fertility, with increased respiration mid‐season and no change (area basis) or reduced (mass basis) respiration late‐season in elevated compared to ambient CO2 plants. This temporal variation correlated with changes in leaf N concentration and leaf mass per area. Our results demonstrate the importance of considering both structural and physiological pathways of net C gain in predicting tree responses to rising CO2 under conditions of suboptimal soil fertility.
Submerged batch culture of the psychrophile Monographella nivalis in a defined medium; growth, carbohydrate utilization and responses to temperature
Authors: CAIRNS ANDREW J. , HOWARTH CATHERINE J. , POLLOCK CHRISTOPHER J.
Published: April 2006

An asporogenous strain of the pink snow mould fungus, Monographella nivalis (Schaffnit) E. Müller, anamorph Gerlachia nivalis (Ces. ex Sac.) W. Gams & E. Müller (Syn. Fusarium nivale Ces. ex Sacc.), grew at 5 °C on a denned salts medium plus vitamins and utilized a variety of simple and polymeric carbohydrates as the sole carbon and energy source. Mycelium was grown at temperatures between 3 and 15 °C in aerated submerged fermentation culture in chemically defined medium plus sucrose. Optimum growth rates of 0·035–0·033 h‐1 occurred between 9 and 12 °C. Growth in a simple medium showed that all biochemical and physiological processes necessary for growth were functional at 3 °C. The growth performance of the organism at low temperatures was no better than would be expected from extrapolation of mesophilic growth responses to temperature. The optimum growth temperature of 9–12°C showed that some biochemical or physiological process was impaired above 12 °C.

Uptake and incorporation of 35S‐methionine by mycelium at different temperatures showed that general protein synthesis increased up to 25 °C, and hence was not responsible per se for the sensitivity to temperatures above 12 °C. Heat shock proteins were synthesized at the relatively low temperature of 25 °C, consistent with the low temperature optimum for growth. When grown with sucrose as the sole carbon source, the mycelium catalyzed the extracellular hydrolysis of sucrose, releasing glucose and fructose together with a small amount of fructan trisaccharides and a trace of tetra‐ and penta‐saccharides. Fructan accumulation was transient, corresponding with maximal rates of sucrose hydrolysis. Most biomass formation occurred in the absence of fructan in the culture, hence fructan was not necessary for growth at low temperature and did not appear to function as a cryoprotectant. Invertase activity was mostly (60–70%) bound to mycelium; the remainder was free in the culture supernatant. The regulation of invertase expression appeared to be by sucrose‐induction, rather than by end‐product repression. Rates of sucrose hydrolysis in culture were temperature‐sensitive and were markedly depressed above 12 °C, indicating inhibition of invertase formation.
Colonization of wheat (Triticum vulgare L.) by N2‐fixing cyanobacteria
Authors: GANTAR M. , KERBY N. W. , ROWELL P. , OBREHT Z. , SCRIMGEOUR C.
Published: April 2006

Two cyanobacterial soil isolates, Nostoc 2S9B and Anabaena C5, that had previously been shown to form different types of association with the roots of wheat plants grown in liquid culture, were tested for heterotrophic nitrogenase activity and the ability to colonize the roots of plants grown in sand. Nostoc 2S9B showed substantial nitrogenase activity when associated with the roots of plants grown in liquid culture in medium free of combined N, even with the roots maintained and with assays performed in the dark (29 % of the rate shown by root‐associated Nostoc 2S9B grown and assayed in the light). When grown heterotrophically in the dark, at the expense of fructose, free‐living Nostoc 2S9B showed a similar nitrogenase activity to root‐associated Nostoc 2S9B in the dark. In contrast, Anabaena C5 showed no nitrogenase activity in the dark, under these conditions.

When three different wheat cultivars were grown in sand that had previously been surface‐inoculated with Nostoc 2S9B or with the cultured symbiotic cyanobacterium Nostoc LBG1, isolated from the bryophyte Anthoceros, there was colonization of the plant roots; there was no colonization of roots by Anabaena C5 under these conditions. Some increases in plant biomass and nitrogen content were observed, but these were dependent on the wheat cultivar and cyanobacterial inoculum used.

Wheat plants grown in sand that had been pre‐inoculated with Nostoc 2S9B, Nostoc LBG1 or Anabaena C5 in medium free of combined N had lower δ15N values in both roots and shoots than plants grown under identical conditions without a cyanobacterial inoculum. The observed 15N/14N fractionation indicates that N2 fixed by the cyanobacteria contributed to the nitrogen economy of the wheat plants, irrespective of whether they were closely associated with the plant roots.