bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling root architecture: are there tradeoffs between efficiency and potential of resource acquisition?
Authors: BERNTSON G. M.
Published: April 2006

summary

A model is presented that examines the role of variations in the size of root systems as well as size‐independent aspects of architecture on both the efficiency (volume of soil exploited per unit volume of root) and potential of exploitation (volume of soil exploited). This model is unique in that it explores the architecture of actual root systems rather than statistical approximations of root systems. This design allows the assessment of variations m root system size and size‐independent aspects of architecture in realistic covarying combinations. Root systems of Senecio vulgaris L. grown in ambient and double‐ambient atmospheric CO2 concentrations and two watering regimes were used to parameterize the model.

There was a clear trade‐off between the efficiency and potential of exploitation. Large root systems showed high exploitation but low exploitation efficiency. Inversely, small root systems showed low potential and high efficiency. Overall, the potential of soil exploitation was more strongly correlated with all measured aspects of root architecture than was efficiency. Root system size (total length or number of root tips) was much more highly correlated with patterns of soil exploitation, efficiency and potential, than were size independent aspects of architecture. These findings art important to studies of root architecture, demonstrating that studies of root system architecture need simultaneously to measure root system size, size‐independent aspects of architecture and in situ patterns of deployment (e.g. trajectories of growth) to understand the functional significance of root architecture.
Non‐hydraulic root‐to‐shoot signalling in mycorrhizal and non‐mycorrhizal sorghum exposed to partial soil drying or root severing
Authors: EBEL ROBERT C. , STODOLA ANN J. W. , DUAN XIANGRONG , AUGÉ ROBERT M.
Published: April 2006

summary

Our objectives were (1) to determine if arbuscular mycorrhizal symbiosis could modify leaf response to non‐hydraulic root‐to‐shoot communication of soil drying in Sorghum bicolor (L.) Moench, and (2) to compare the sensitivity of leaf growth and stomatal conductance (Cs) to the non‐hydraulic signal. Seedlings were grown in a greenhouse with root systems split among four pots. Treatments were applied in a 2 (colonized or not colonized by Glomus intraradices Schenck & Smith) × 2 (roots severed or dried) × 4 (roots in 0, 1, 2 or 3 pots dried or severed) experimental design. Plants with roots in three pots dried or severed showed reduced leaf elongation, Cδ and leaf water potential (Ψ) compared with fully watered (control) plants and thus were probably hydraulically affected by root treatment. Drying of severing roots in one pot did not affect leaf elongation, Cδ or Ψ in either mycorrhizal or non‐mycorrhizal plants. In non‐mycorrhizal plants having two pots dried, final leaf area and total leaf length were reduced by 18 and 10%, respectively, relative to controls. Stomatal conductance of these half‐dried non‐mycorrhizal plants remained unchanged, suggesting that the decrease in leaf growth was not hydraulically induced. Non‐mycorrhizal plants having roots severed in two pots continued to have leaf growth similar to that of the controls, suggesting that growth reductions in half‐dried non‐mycorrhizal plants did not result from a reduction in root water gathering capacity. Mycorrhizal symbiosis appeared to eliminate inhibition of leaf growth that was not hydraulically induced, because mean leaf area and total leaf length were not reduced in half‐dried mycorrhizal plants, relative to controls. However, final leaf area of mycorrhizal plants having one or two pots dried was negatively correlated with the product of drying rod mass and the time for which roots were exposed to mild drought, suggesting that mycorrhizal plants were also susceptible to growth inhibition that was not hydraulically induced. Reductions in leaf extension rate that were not hydraulically induced, when viewed as a function of actual soil matric potential, were similar in mycorrhizal and non‐mycorrhizal plants, suggesting that the differences in overall growth inhibition between half‐dried mycorrhizal and non‐mycorrhizal plants may have been related to differences in soil drying rate.
The development of mycorrhizal infection in cucumber: effects of P supply on root growth, formation of entry points and growth of infection units
Authors: BRUCE A. , SMITH S. E. , TESTER M.
Published: April 2006

summary

This paper describes an experiment in which the effects of soil phosphorus (P) on root growth and mycorrhizal colonization of Cucumis salivus L. were studied. The aim was to determine the relative contributions of root growth, formation of new infections and growth of infections within the root to the % colonization. Plants were harvested daily between 7 and 24 d. Added P had no effect on root or shoot f. wt or on root length up to 14 d. After that time plants given additional P grew well, but those with no added P grew poorly and showed signs of P deficiency. Increase in root length with added P was due both to an increase in the number of root apices produced per unit length of root per unit time and to an increase in the mean rate of extension of those apices. Effects of P on the % colonization of the roots by the mycorrhizal fungus Glomus intraradices Schenk and Smith were apparent before any effects on root length were observed. The length of the lag phase was not affected by addition of P. The rate of formation of new entry points was similar with and without added P up to 15 d, and reduction in % colonization up to this time could be attributed entirely to reduction in the rate of growth of infection units within the roots. Later, there was a marked increase in the rate of formation of (secondary) entry points in the absence of added P, which was not observed when P was added. At 15, 20 and 25 d, additional plants were harvested to quantify the development of arbuscules and vesicles in colonized regions of the roots. At all three times, numbers of arbuscules and vesicles were lower with added P. We conclude that at very early stages of colonization P exerts its effect via reduced growth of infection units. After approx. 2 wk, an increase in the rate of growth in length of roots and low rates of formation of secondary infections also contribute to the low values of % colonization.
Mycorrhizal fungus propagules in the jarrah forest
Authors: BRUNDRETT MARK C. , ABBOTT L. K.
Published: April 2006

summary

Seasonal variations in the capacity of propagules of vesicular‐arbuscular mycorrhizal (VAM) and ectomycorrhizal (ECM) fungi to form associations in natural habitat soils were investigated by bioassays. These bioassays involved bait plants which? were grown in intact cores of forest soil to assess mycorrhiza formation by hyphal networks and other propagules of YAM or ECM fungi. Soil cores were collected from the same positions along a transect at different times of the year from a diverse sclerophyllous forest community dominated by Eucalyptus marginato (jarrah) and E. calophylla (marri) trees in the mediterranean (winter rainfall) climatic zone of Western Australia. Seasonal fluctuations in mycorrhiza formation by propagules of VAM or ECM fungi, or colonization by particular VAM endophytes (identified by their morphology within roots), were not substantial. Thus hyphal networks and other mycorrhizal fungus propagules in this soil maintained u similar capacity to colonize roots throughout the rear, even during extended periods of summer drought. It appeared That low light levels in the glasshouse could reduce the capacity of bait plants to form mycorrhizas during the winter. Substantial spatial variability in mycorrhizal fungus inoculum levels between the transect locations where cores were collected persisted through time, but variations in the relative cover of host or non–host plants at these locations were not sufficient to explain these patterns.
Spatial distribution and temporal persistence of discrete genotypes of the ectomycorrhizal fungus Laccaria bicolor (Maire) Orton
Authors: DE LA BAST1DE PALL Y. , KROPP BRADLEY R. , PICHÉ YVES
Published: April 2006

summary

A field study was conducted to determine the spatial distribution and temporal persistence of Laccaria bicolor (Maire) Orton genotypes associated with naturally colonized Norway spruce [Picea abies (L.) Karst.] in a plantation. Groups of sporophores around three trees Were mapped and collected over two to tour consecutive autumn seasons to isolate cultures and determine their genetic relatedness by mating type and randomly amplified polymorphic. DNA (RAPD) analysis. Annual sporophore distribution varied significantly on all sites, with an increase in the mean radial distance from the trees over the study period. Sporophore distribution was discontinuous and characterized by clumped groupings around trees. Sporuphores with the same mating type and disparate distributions were present on each of two sites during the sample period. RAPD analysis for each of the six random primers detected the same DNA polymorphisms for all dikaryotic isolates tested from a given site over the sample period. These results provide evidence that a single genetic individual of L. bicolor can remain associated with a host root system for at least 3 yr and vary significantly in us spatial distribution. This is the first instance in which the persistence of specific genotypes of an early–stage ectomycorrhizal fungus has been demonstrated for a tree colonized by natural sources of inoculum. The implications of these findings are discussed in relation to the ecology and succession of ectomycorrhizal fungi.
Ericoid endophytes of Western Australian heaths (Epacridaceae)
Authors: HUTTON B. J. , DIXON K. W. , SIVASITHAMPARAM K.
Published: April 2006

summary

The presence of ericoid endophytes was Confirmed in hair roots of 14 species of Epacridaceae native to the mediterranean south‐west of Western Australia. The phenology of infection was followed in 2‐yr‐old seedlings of Astroloma xerophyllum D.C. (Sond.) and showed increasing infection up to a peak (40% of hair roots infected) in late winter and a decline to zero infection during summer (December February). Over 400 isolates of root‐inhabiting fungi of 14 species from seven genera of native Epacridaceae were obtained. All isolates were dark‐coloured, sterile and slow growing tin potato dextrose agar. Based on morphological characteristics, eight isolates were selected for further investigation. Detailed analysis of morphological and cultural features was used to create three groups, two of which were infective with cuttings of the common Epacridaceae species. Lysinema ciliatum. The groupings based on rnorphological characteristics were reflected in the pectic zymogram patterns of the isolates. Pectic zymogram analysis of ericoid fungi revealed that none of the Australian isolates matched fungi known to be infective with Ericaceae [Hymenoscyphus ericae (Read) Korf. & Kernen and Oidiodendron spp.] even though all isolates appeared morphologically similar with similar growth rates.
Initial association between Helianthemum and Terfezia is enhanced by low iron in the growth medium
Authors: KAGAN‐ZUR VARDA , RAVEH ERAN , LISCHINSKY SMADAR , ROTH‐BEJERANO NURIT
Published: April 2006

summary

Activated charcoal added to artificial growth medium enhances initial association between the mycelium of the desert truffle Terfezia leonis Tul. and the roots of Helianthemum sessiliforum (Defs). Pers. in vitro. This is due, at least in part, to adsorption of iron.
Characterization of developmental phases of the woody perennial shrub, Solanum aviculare Forst.
Authors: JAMES A. C. , MANTELL S. H.
Published: April 2006

summary

Developmental phases which occur during the growth of seedlings through to flowering in the woody perennial shrub, Solanum aviculare Forst., were characterized. Bud position, as determined by nodes and height to flower, was correlated with the characteristics of heterophylly, leaf anatomy, phyllotaxy, diameter of the shoot apex, dry matter content and chlorophyll content. The existence of developmental phases was confirmed by comparing the performances of axillary buds of the pre‐ and post‐flowering (anthocladial shoots) phenotypes which were either left to develop in situ, following decapitation of plants, or ex situ on subsequently rooted severed shoots (ramets). Performances of in situ buds differed from ex situ buds in both adults and juveniles, indicating that flowering had not been initiated prior to excision. Ramets and shoots derived from the ninth node above the cotyledons of seedlings required similar nodes and heights above their own root systems before phase change occurred; the excision and rooting of axillary buds from these positions did not appear to promote maturation in terms of nodes and height to flower. Conversely, the excision of anthocladial axillary buds promoted floral induction when compared to the performance of their counterpart buds which developed in situ, indicating a difference in competence of juvenile and mature anthocladial buds.
Cytoplasmic polarity and endoplasmic microtubules associated with the nucleus and organelles are ubiquitous features of food‐conducting cells in bryoid mosses (Bryophyta)
Authors: LIGRONE ROBERTO , DUCKETT JEFFREY G.
Published: April 2006

summary

An ultrastructural survey of food conducting cells in the gametophytes and sporophytes of bryoid mosses, including the highly specialized leptoids of Polytrichales, has revealed that, without exception, these cells have a polarized organization and contain an axial system of endoplasmic microtubules (MTs). The orientation of polarity is highly consistent with the putative direction of the source to sink gradient, with distal cellular ends, i.e. those toward the sink, containing denser cytoplasm than proximal ends. In most cases the nucleus is spindle‐shaped and also lies at the distal end. Longitudinal arrays of MTs are associated with the nuclear envelope. These MTs extend into the cytoplasm for long distances and may come into contact with the plasma membrane lining the terminal walls at the distal ends. Cortical MTs are absent. The endoplasmic MTs are closely associated with a variety of organelles including mitochondria, plastids. endoplasmic reticulum and membrane‐bounded tubules and vesicles. The organelles aligned along the MT bundles lie within longitudinal cytoplasmic strands clearly visible with light microscopy. The discovery of cytoplasmic polarity and endoplasmic MTs as distinctive features of food conducting cells of mosses sets these cells apart from the sieve elements of vascular plants. The MT‐organelle associations, as observed in the food conducting cells of mosses, are hitherto undescribed in plants but are reminiscent of MT arrays functioning in organelle transport in neuronal axons and other animal and fungal systems.
Tansley Review No. 74 Control of organogenesis at the shoot apex
Authors: LYNDON ROBERT F.
Published: April 2006

summary

The processes involved in the formation of primordia on the shoor apex are those controlling (1) growth rate, (2) division plane. (3) surface microstructure, and (4) extensibility of the surface. Changes in growth rate and division planes may accompany primordium formation but are considered as probably not in themselves being causal. Changes in surface microstructure may be necessary to delimit the position and area occupied by an incipient primordium. However, attention is directed to changes in surface extensibility as perhaps being the overriding factor in primordium formation. Nevertheless, the position and form of the primordia will also depend on growth rate, division plane, and surface microstructurc being permissive. The relative importance of these four sets of processes may differ from species to species and from one stage of development to another. Chemical and metabolic changes within the apex may first be necessary to determine whether the surface can extend sufficiently for any primordia to form at all, but their positions and time of initiation may depend more on the other factors. The surface microstructure may become more important when patterning is detailed and precise as it is in the developing flower, whereas a less precise mechanism dependent on localized induction of synthesis of a morphogen (auxin?) may provide sufficient information to determine the general position and liming of primordium initiation in vegetative apices. In determining the pattern of primordia on the apex, primordial area at initiation is important and reasons for believing that auxin may be involved in determining this are summarised. The different developmental pathways of primordia seem to diverge from the moment of initiation. Developmental fate of primordia is determined by the hamcotic genes which may in fact be heterochronic genes. How these regulatory genes control the processes involved in differentiation of different types of primordia is so far unknown.

Contents

Summary
1

I.
Introduction
2

II.
The mechanism of primordium formation: what causes an outgrowth of the apical surface?
2

III.
The positions of successive primordia: what determines their size and localization, so giving rise to pattern?
11

IV.
What determines the developmental pathways of the primordia once initiated?
13

V.
Conclusions
15

VI.
Acknowledgements
16

VII.
References
16
The vascular architecture of the fruit receptacle of red raspberry determined by 3D NMR microscopy and surface‐rendering techniques
Authors: WILLIAMSON B. , GOODMAN B. A. , CHUDEK J. A. , HUNTER G. , LOHMAN J. A. B.
Published: April 2006

summary

The three‐dimensional structure of the vascular system in tht fruit receptacle of red raspberry was determined using NMR microscopy in combination with computer techniques which highlight the surfaces of specific tissue types. The surface‐rendering technique is particularly valuable in situations, where there are large differences in image characteristics between the tissue of interest and the rest of the specimen, and thus ideal for the delineation of ilic vascular tissue in the raspberry receptacle. This was shown to consist of a conical network of bundles with a spiral pattern of gaps; tht carpellury traces emereed from the proximal end of each gap. The inner xylem and outer phloem tissues each appeared as a pair of fused columns in the surface‐rendered images, and each carpellary trace had a separate supply from the xyiern and phloem.
The host‐pathogen system of Gremmeniella abietina (Lagerb.) Morelet and Scots pine; effects of non‐pathogenic phyllosphere fungi, acid rain and environmental factors
Authors: RANTA HANNA , NEUVONEN SEPPO
Published: April 2006

summary

Scots pine seedlings (1‐yr‐old) were inoculated either once, or three times, with the conidia of two saprophytic Honmmema species. After these inoculations, the seedlings were inoculated later with conidia of the pathogenic fungus Gremmeniella abietina (Lagerb.) Morelet. Seedlings received irrigation with simulated acid rain at pH 3, with water of pH 6. or no irrigation, during and after the inoculation treatments, The severity of the symptoms caused by G. abietina, and rhe isolation frequency of endophytic (symptomless) G. abietina and the saprophytes, were measured 11 months after G. abietina inoculation. The isolation frequencies of the two Hormunema species increased significantly in the seedlings inoculated three times with saprophyte conidia. Irrigation treatments did not affect the saprophytes. The disease symptoms caused by G, abietina were positively correlated with tree density. Symptomless G, abietina was isolated most often from the seedlings that had received irrigation at pH b. The isolation frequency was lowest in seedlings with acidic irrigation. The seedlings inoculated three times with conidia of Hormonema sp. 1 had a lower frequency of G. abietina isolations than other seedlings, but the difference was not statistically significant.
The effect of an insect herbivore and a rust fungus individually, and combined in sequence, on the growth of two Rumex species
Authors: HATCHER P. E. , PAUL N. D. , AYRES P. G. , WHITTAKER J. B.
Published: April 2006

summary

The chrysomelid beetle Gastrophysa viridula and the rust fungus Urmnyces rumicis both occur on leaves of Rumex crispus and R. obtusifolius. We investigated the effect of beetle grazing or rust infection individually and when combined in sequence on the growth of their hosts in the field. Singly, beetle or rust reduced leaf area and plant biomass; the effect was greater on R. crispus, and rust caused greater damage than the beetle. Beetle grazing with subsequent rust infection caused damage no greater than that caused by rust alone, although on R. obtusifolius damage was greater than that from beetle grazing alone. Rust infection of R. obtusifolius with subsequent beetle grazing produced damage similar to that from other treatments; involving rust infection. In R. crispus this treatment produced the greatest reduction in biomass, The reductions in root and total plant weight from rust infection with subsequent beetle grazing were accurately predicted by a model including the damage produced by beetle and rust alone and the length of time each was present on the plant. This model also predicted accurately the damage to R. obtusifolius from the beetle followed by rust treatment, but over‐estimated by up to 40% the damage to R. crispus. This can be explained mainly by an inhibition of rust infection by beetle grazing.
Distribution patterns of number of nuclei in conidia from heterokaryons of Heterobasidion annosum (Fr.) Bref. and their interpretation in terms of genomic conflict
Authors: RAMSDALE MARK , RAYNER ALAN D. M.
Published: April 2006

summary

Ratios of nuclear genotypes observed in conidia from heterokaryotic strains of Heterobasidion annosum (Fr.) Bref., obtained from pairings between sympatrically derived, sib‐related and non‐sib‐related homokaryons, commonly deviated from 1:1. Ratios were temporally stable, and the genotypes examined could be ranked in a strict dominance hierarchy, linked both to the relatedness of the association partners and to the growth rates of the parental homokaryons. Parental homokaryons and sibrelated heterokaryons produced conidia with a mean number of nuclei of about two, whereas non‐sib‐related‐d heterokaryons produced conidia that were predominantly uninucleate. Moreover, whereas conidia containing more than one nucleus germinated most rapidly when derived from homokaryons or sib‐related heterokaryons, uninucleate conidia germinated more readily if derived from non‐sib‐related heterokaryons. In a study of naturally occurring heterokaryons, distribution patterns of the number of nuclei in conidia were found to be similar to those of the homokaryons. The possible interpretation of these findings in terms of inter‐nuclear genomic conflict is discussed.
Effects of nitrogen on the response of loblolly pine to drought
Authors: GREEN THOMAS H. , MITCHELL ROBERT J. , GJERSTAD DEAN H.
Published: April 2006

summary

Effects of drought on carbon and nitrogen dynamics and biomass allocation patterns of loblolly pine (Pinus taedaL.) seedlings grown under 4 different nitrogen levels were determined Nitrogen stress caused an increase in root‐shoot ratio. increased Foliar and mot Starch concentration, decreased soluble sugar concentration, and decreased free amino acid concentration in well‐watered seedlings. Drought cent‐rally caused an increase in foliar hexoses and decreases in foliar find root starch and root hexoses. while not affecting foliar free amino acids. However, nitrogen stress arid drought interactedinaffecting carbohydrate pools and seedling morphology. Foliar starch reserves in high‐N seedling were rapidly metabolized under drought, white N‐deficient seedling maintained similar starch concentrations throughout the drought stress cycle. After one drought cycle, the N‐induced difference in root:shoot ratio was no longer significant. These results suggest that N‐stressed seedlings partition a higher percentage of fixed carbon to storage, and that (his storage pool is less available For immediate Use than in seedlings grown under adequate N.
Exposure of Norway spruce to ozone increases the sensitivity of current year needles to photoinhibition and desiccation
Authors: MIKKELSEN T. N. , RO‐POULSEN H.
Published: April 2006

summary

Physiological effects of ozone exposure over three consecutive growing seasons on current year needles of Norway spruce were studied in open‐top chambers, during daily Fumigation cycles in the summer, and after the termination of ozone fumigation in autumn 1990. The trees were exposed to two levels of ozone: charcoal filtered air and non‐filtered air to which 30 nl I−1 of ozone was added in three consecutive years from 1988 to 1990, daily from May to September (8 hours a day). Photosynthesis, stomatal conductance, transpiration and chlorophyll fluorescence were studied on selected days. Significant decreases in net photosynthesis and chlorophyll fluorescence (FN/FM) were found during periods with co‐occurrence of high ozone concentrations And high light intensities, indicating interactions between effects of ozone and photoinhibition. After termination of fumigation enhanced rates of photosynthesis were seen in the trees which had been exposed to ozone. A significant decrease in FN/FM was found for twigs from ozone treated trees when exposed to severe desiccation.
Tolerance and co‐tolerance of the grassChloris barbataSw. to mercury, cadmium and zinc
Authors: PATRA JITA , LENKA MAHESWAR , PANDA BRAHMA B.
Published: April 2006

summary

Races ofChloris barbataSw. from a mercury‐contaminated site in the vicinity of a chloralkali plant and from a non‐contaminated site were tested for their relative tolerance to mercury, cadmium and zinc. Pre‐rooted tillers of each of the races were grown in calcium nitrate solution, Ca(NO3)2, 4H2O, l gl−1with or without HgCI2(0.001, 0.01, 0.05, 0.1 and mgl−1), CdSO4.8H2O (0.05, 1.0, 2.5 and 5 mg l−1and ZnSO47H2O (1, 5, 10, 20 and 40 mg l−1) for a period of 5 d, Metal tolerance was evaluated by the effects of the metal on root elongation. Races from the contaminated site were found to be metal‐tolerant, as indicated by higher tolerance indices (TIs) than races from the non‐contaminated site. Mercury and cadmium at lower concentrations and zinc at all concentrations stimulated root growth in tolerant races, resulting in a TI of more than 100%. This indicated a requirement of the metal ion for better root growth. Compared to non‐tolerant races, the tolerant races exhibited higher catalase, peroxidase and acid phosphatase activities as well as higher thiol levels. The over‐all study thus indicated that races ofC. barbatafrom the mercury‐contaminated site were not only tolerant to mercury but also co‐tolerant to cadmium and zinc. Biochemical studies provided evidence that the tolerant races were physiologically distinct from the intolerant races.
Tansley Review No. 76 Helper bacteria: a new dimension to the mycorrhizal symbiosis
Authors: GARBAYE J.
Published: April 2006

summary

The symbiotic establishment of mycorrhizal fungi on plant roots is affected in various ways by the other microorganisms of the rhizosphere, and more especially by bacteria. This review discusses the case of some of these bacteria which consistently promote mycorrhizal development, leading to the concept of ‘mycorrhization’ helper bacteria (MHBs). Examples of MHB evidence are given from the literature, with special reference to the Douglas fir (Pseudotsuga menzeisii Mirb. Franco) Laccaria laccata Scop, ex Fr. ectomycorrhizal combination which has been more extensively studied.

The fungal specificity of some MHBs and the various mechanisms underlying their effect are discussed, considering five hypotheses: effects on the receptivity of the root, effects on the root‐fungus recognition, effects on the fungal growth, modification of the rhizospheric soil, and effects on the germination of the fungal propagule.

MHBs are then considered for their ecological and evolutionary implications, and examples of practical applications in forest nurseries are given: when added to the fungal inoculum, MHBs can improve the success of ectomycorrhizal inoculation of planting stocks with fungi selected for their outstanding growth stimulation after outplanting.

The conclusion points out a number of fundamental questions which remain unanswered about mycorrhization helper bacteria and suggests some investigation priorities in this new field of mycorrhiza research.

Contents

Summary
197

I.
Introduction
197

II.
Evidence for helper bacteria
198

III.
Fungus‐specificity of MHBs
200

IV.
Mechanisms underlying the MHB effect
201

V.
Ecological and evolutionary implications of MHBs
205

VI.
Practical applications of MHBs
206

VII.
Conclusions and perspectives
208

Acknowledgements
208

References
208
The effects of mycorrhizal infection on components of plant growth and reproduction
Authors: LU XIAOHONG , KOIDE ROGER T.
Published: April 2006

summary

We studied the effects of mycorrhizal infection by Glomus etunicatum Becker & Gerd. and P amendment (three levels) on growth and reproduction of Abutilon theophrasti Medic. Mycorrhizal infection increased total leaf area, but individual leaf size was more‐affected than leaf number. Mycorrhizal infection decreased the time taken to initiate flowering, increased the total duration of flowering, and increased seed production by increasing the number of flowers produced, the proportion of flowers producing fruits, and the number of seeds per fruit. Seeds produced by mycorrhizal plants were also heavier and contained more N and P than those produced by non‐mycorrhizal plants, P amendment generally had similar influences to mycorrhizal infection, but seed P content was far more plastic in response TO P amendment than to mycorrhizal infection. The various components of reproduction were not uniformly affected by either mycorrhizal infection or P amendment. The most phenotypically plastic reproductive components were fruit production and seed P content. The least plastic components were seed weight and seed N content.
Effects of O3 on the stomatal behaviour of Egyptian varieties of radish (Raphanus sativus L. cv. Baladey) and turnip (Brassica rapa L. cv. Sultani)
Authors: HASSAN I. A. , ASHMORE M. R. , BELL J. N. B.
Published: April 2006

summary

The effects of O2 (80 nl 1−1) on the photosynthetic rate (A) and stormatal conductance (g) of Egyptian varieties of radish (Raphanus sativus L. ev. Baladey) and turnip (Brassica rapa L. ev. Sultani) were examined. Exposure to O3decreased A in both species, while gs was increased in radish and decreased in turnip. The effect of different concentrations of O3, (50, 100, 150 nl l−1 on radish was examined and it was found that A decreased, while g, increased, with increasing concentrations of O3.

Scanning electron microscopy (SEM) of fumigated leaves showed that the increase in gs in radish resulted from the collapse of epidermal cells. Counts of the percentage of stomata which were fully open demonstrated that 80 nl 1−1 O3 caused an increase of 18% in radish and a decrease of 14% in turnip. The proportion of opened stomata was found to increase with increasing O3 concentration in radish.
Comparative investigations of cuticular permeability of conifer needles from healthy and damaged trees
Authors: SCHREIBER LUKAS
Published: April 2006

summary

Using pentachlorophenol (PCP) and conifer needles, rates of cuticular PCP uptake and effective leaf surface areas were measured, and PCP permeances of the cuticular membranes were calculated. Needles from healthy and damaged conifer trees of the species Picea abies (L.) Karst., Pinus sylvetris L. and Abies alba Mill. were Investigated. Significant differences of the rates of cuticular uptake, effective leaf surface areas and permeances of the cuticular membranes between healthy and damaged trees were not evident. Thus, it must be concluded that damaged cuticular transport harriers of the needles cannot have contributed to the damage symptoms observed with the trees investigated in this study. However, it was found that increasingly older spruce needles had significantly higher permeances, indicating a decrease of cuticular barrier properties with needle age. Additionally, due to larger effective leaf surfaces spruce needles of higher altitudes (1100 m above sea level) possessed higher rates of cuticular transport compared to needles from lower altitudes (400 m above sea‐level). Therefore, these findings might help to understand why older needles and trees growing in higher Geographical sites are more sensitive to detrimental environmental influences causing symptoms of novel forest decline.
Light, chlorophyll, carboxylase activity and CO2 fixation at various depths in the chlorenchyma of Opuntia ficus–indica (L.) Miller under current and elevated CO2
Authors: NOBEL PARK S. , CUI MUYI , ISRAEL ALVARO A.
Published: April 2006

summary

Mature cladodes of Opuntia ficus‐indica (L.) Miller have a thick chlorenchyma (about 4 mm) with a relatively high chlorophyll convent (0.65 gm−2), suggesting that light may be greatly attenuated and hence CO2 fixation negligible in the inner part of this tissue. Indeed, blue light (400–470 nm) and red light (670–685 nm)were 99% attenuated in the outer 2 mm of the chlorenchyma when the cladodes developed under both current and elevated CO2 Concentrations. Nevertheless, the nocturnal acidity increase and 14C accumulation following a brief exposure to 14CO2 at night decreased only 22 to 47% for a layer 2–3 mm deep in the chlorenchyma of this CAM plant. Under a particular growth CO2, the activities of both ribulose‐1,5‐bisphosphate carboxylase/oxygenase and phosho‐enolyruvate carboxylase were similar for each of the outer three 1‐mm‐thick layers of the chlorenchyma. Therefore, although the light level and total chlorophyll decreased sharply with depth and the chlorophyll a/b ratio also decreased. Substantial CO2 fixation apparently occurs throughout most of the chlorenchyma. When O. ficus‐indica was grown under 720 μmol CO2 mol−1, the chlorenchyma was 20% thicker but contained 11% less chlorophyll and had a lower absorptance than under the current CO2 concentration (370μmol mol−1). Greater nocturnal acidity increases and 14C accumulation following exposure to 14CO2 at night occurred at the doubled CO2 concentration despite 29–39% reductions in the activities of the two carboxylating enzymes, the lower absorptance, and a 24% increase in the cladode reflectance from 400–700 nm.
Influence of different nutrient regimes on the regulation of carbon metabolism in Norway spruce[Picea abies(L.) Karst.] seedlings
Authors: WINGLER ASTRID , EINIG WERNER , SCHAEFFER CHRISTOPH , WALLENDA THOMAS , HAMPP RÜDIGER , WALLANDER HÅKAN , NYLUND JAN‐ERIK
Published: April 2006

summary

Phosphoenolpyruvate carboxylase (PEPC) activity, fructose 2, 6‐bisphosphate (F26BP), starch and soluble sugar contents were determined m needles and roots of Norway spruce seedlings grown in a semi‐hydroponic cultivation system under different nutrient regimes, tn needles, a surplus of nitrogen caused an increase in specific PEPC activity (up to six times control activity) and F26BP content (up to three times control level) while starch content was reduced. Sucrose contents were not affected. Basically, the responses in root samples were similar. Here, PEPC was highest at an imbalance in nutrition (+ N/ ‐P) F26BP, with root contents being 3‐ to 11 ‐times higher than those in needles, significantly exceeded control values at + N/+ P. The results show that alteration of nitrogen supply leads to marked changes in allocation of carbon between pathways, which is also influenced by P‐nutrition. Pool sizes of F26BP and activity of PEPC are indicators for these changes in leaf as well as in root tissues of Norway spruce.
Leaf age‐structure effects on plant water use and photosynthesis of two wheat cultivars
Authors: VENEKLAAS ERIK , VAN DEN BOOGAARD RIKI
Published: April 2006

summary

The wheat cultivars ‘Katya Al’ and ‘Mexipak 65’, grown in pots under field conditions in a Mediterranean climate, differed only slightly in growth and water use on a whole‐plant basis, although Mexipak had a smaller leaf area. When expressed on a leaf area basis, plant biomass increase and transpiration were significantly greater in Mexipak. However, previous gas exchange measurements on the youngest fully expanded leaf showed only minor differences between the two cultivars. The hypothesis that different patterns of leaf ageing contributed to the differences in plant growth and water use was tested by combining leaf demography and gas exchange measurements. Plants were subjected to two moisture treatments: ‘well‐watered’ (frequent, watering to initial soil water content) and ‘intermittent drought’ (five drying‐rewatering cycles). Mexipak had, on average, older leaves than Katya in both treatments because of fast early growth, which in turn was clue to a larger area of individual leaves rather than a faster leaf appearance rate. Stomatal conductance and net photosynthetic rate were nearly the same for the two cultivars, but were considerably reduced by drought and did not fully recover after rewatering. Stomatal conductance and photosynthesis tended to decrease with ape, but effects of age or treatment or their interactions were not significant and could not explain the discrepancy between whole plant and leaf observations. One possible explanation is that age effects‐do exist in leaves older than those investigated. Another explanation may be that changes in microclimatological conditions caused photosynthesis and transpiration to differ from rates measured under standard conditions.
The keel colour polymorphism in Lotus corniculatus L.: differences in internal flower temperatures
Authors: JEWELL JENNIFER , McKEE JUNO , RICHARDS A. J.
Published: April 2006

summary

In bright sunshine, temperatures within the apex of the keel of flowers of Lotus corniculatus were consistently higher in dark‐keeled than in light‐keeled individuals. Temperature differences may increase With higher ambient temperatures and averaged 5.7°C at 23.2°C ambient, In overcast conditions, no significant temperature differences between dark‐keeled and light‐keeled flowers Were observed, or light keel temperatures were slightly greater. In general, temperatures within keels were lower than ambient.

Within sites, dark‐keeled plants showed a tendency to inhabit colder microsites than did light‐keeled plants. Contrary to some earlier reports, we believe that most clinal variation for keel colour is temperature related.

We suggest that there may be an optimum Temperature far pollen germination and pollen rube growth. In cold microsites. dark‐keeled plants would be more fecund, but in warm microsites tight‐keeled plants would set. more seed, thus maintaining the polymorphism found in most sites.
Contribution of ectomycorrhiza to the potential nutrient‐absorbing surface of pine
Authors: ROUSSEAU J. V. D. , SYLVIA D. M. , FOX A. J.
Published: April 2006

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The increase in potential nutrient‐absorbing surface area of loblolly pine (Pinus taeda L.) seedlings as a result of ectomycorrhizal development was quantified. In one experimental. In one experiment, loblolly pine seedlings were inoculated with Pisolithus tinctorius Pers. Coker (Pt) after having first been grown from seed for 8 wk under a low phosphorus (P) nutrient regime. Eight weeks following inoculation, seedlings were harvested and ail components of the nutrient absorbing system (including the fungal mycelium) were quantified. External mycelium accounted for only 5% of the potential absorbing‐system dry weight, but this mycelium comprised 75% of the potential absorbing system area and over 99% of the absorbing length. In a second experiment, the P uptake and contribution to potential absorbing surface of Pt was compared to Cenococcum geophilum Fr. (Cg). Seedlings inoculated with Pt differed from those inoculated with Cg in that they (i) absorbed almost twice the P. (ii) had a higher frequency of fine‐root branching, (iii) developed an extensive network of rhizomorphs, and (iv) had over 1.5 times the mycelial absorbing surface area and over 3 times the mycelial length of Cg. We conclude that for both Pt and Cg inoculated plants, external mycelium made by far the greatest contribution to the overall potential absorbing surface area of the pine seedling. Differences in total mycelial surface area and mycelial length may account for differences in P uptake between seedlings inoculated with Pt and those inoculated with Cg.
The effects of slightly elevated ozone concentrations and mild drought stress on the physiology and growth of Norway spruce, Picea abies (L.) Karst. and beech, Fagus sylvatica L., in open‐top chambers
Authors: LE THIEC DIDIER , DIXON MARTIN , PIERRE GARREC JEAN
Published: April 2006

summary

Two clones of eight‐year old trees of Norway spruce and beech, planted directly into the soil and in open‐top chambers, were exposed to elevated ozone concentrations and subjected to mild soil drought. When ambient ozone was increased by 50 ppb, the shoot extension of both Norway spruce clones was significantly reduced. The mild drought stress was begun in July 1993 and following a soil‐drying associated with a spell of fine weather, the drought remained relatively constant for over a month. During this period, gas exchange parameters were regularly monitored between 7.00 and 9.00 GMT and on two occasions followed throughout the day. Both clones responded to the mild drought by reducing stomatal conductance and photosynthesis. There were no apparent interactions between drought and ozone. The reaction of beech was more complicated. Ozone caused a significant decrease in stomatal conductance and photosynthesis in well‐watered treatments. All the ozone‐drought stress treated trees had greater stomatal conductance than the non‐drought stressed equivalents in the morning, but the situation was reversed as the day went on. As peak ozone concentrations occur in the afternoon, it is hypothesized that over a period of time the drought stressed trees are less affected by ozone as they receive a lower cumulative dose. Coupled with the low values of vapour pressure deficit occurring in the morning, the ozone‐treated, drought‐stressed trees can support relatively higher rates of photosynthesis than the well‐watered equivalents. The chlorophyll contents of beech lent support to this hypothesis, as ozone associated reductions were less marked in drought stressed trees.
Interactions between exposure to O3 and nutrient status of trees: effects on nutrient content and uptake, growth, mycorrhiza and needle ultrastructure
Authors: RANTANEN L. , PALOMÄKI V. , HOLOPAINEN T.
Published: April 2006

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The responses of Norway spruce and Scots pine to the effects of increased O3 and Ca or Mg deficiency stress, singly and in combination, for two growing seasons, were investigated in this study. The combination of open‐air exposure to O3 concentrations of 1.3–1.6 times higher than ambient, and an inadequate supply of Ca or My, did not affect root uptake and leaching of minerals from the needles of 3‐yr‐old seedlings, indicating that the had not developed severe nutrient deficiency. However, concentration of N decreased in the 1‐yr‐old needles of seedlings exposed O3. The height of the new shoots was promoted without an increase in shoot dry weight, which together with stimulated mycorrhiza development and decreased shoot‐to‐root radio indicated allocation of carbon from shoots to roots as an early effect of level O3 exposure. Although the ultrastructural study did not reveal clear O3 related injuries in cells, starch accumulated in chloroplasts of the fumigated seedlings prown with adequate, but not with deficient nutrients. The outcome of this study suggests that in medium‐term exposure of conifer seedlings to low concentrations of O3 and nutrient deficiency, stress can be tolerated by activated defence metabolism and compensation reactions, but adverse effects may be apparent in long‐term continuous exposure.
Interactions between combined exposure to SO2 and NO2 and nutrient status of trees: effects on nutrient content and uptake, growth, needle ultrastructure and pigments
Authors: RANTANEN L. , PALOMÄKI V. , HARRISON A. F. , LUCAS P. W. , MANSFIELD T. A.
Published: April 2006

summary

Two‐year‐old seedlings of Norway spruce were exposed for 110 or 158 d in outdoor chambers to a combination of 30 nl 1−1 sulphur dioxide and 30 nl 1−1 nitrogen dioxide, and limited availability of K, Ca or Mg. Growth, nutrient content and changes in needle ultrastructure and pigments were determined, and nutrient demand for P, K and N was examined using root uptake methods. Exposure to pollutants did not clearly enhance any nutrient deficiencies. However, distinct ultrastructural effects of fumigation and Me and K deficiency stress, especially when applied together, were observed. Slight changes in total carotenoid concentration and the ratio of chlorophyll a/chlorophyll b contents were detected at 110 d but these disappeared as the experiment proceeded. Delayed growth of fumigated seedlings at 110 d was observed. The demand for P and N was almost unaffected by the treatments, but the demand for K increased in seedlings receiving both K deficient nutrient solution and exposure to pollutants. The results suggest that effects of simultaneous exposure to air pollutants and limited availability of nutrients were injuring cell ultrastructure and delaying growth, bur root responses and overall nutrient demand were unaffected by 158 d.
Physiological integration among tillers of Holcus lanatus: age‐dependence and responses to clipping and competition
Authors: BULLOCK J. M. , MORTIMER A. M. , BEGON M.
Published: April 2006

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The ecological consequences of physiological integration among tillers were examined in a glasshouse experiment on the clonal grass Holcus lanatus L. We measured the effects of severing the internode connection between a tiller and its parent on the growth and survival of this marked tiller. The effects of three factors on the response to Severing were determined using this procedure: competition with the parent plant, by comparing tillers repotted in isolation with tillers remaining in the neighborhood of the parent; dipping treatment, comprising no clipping, clipping only the marked tiller and its daughter tillers or clipping the whole parent plant, including the marked tiller; and the change in the response with tiller age at severing, using four tiller ages (1, 2, 4 and 8 wk). These age, clipping and severing treatments wt‐re applied factorially.

After 8 wk of growth the responses to severing of the marked tillers, were dependent on the age and clipping treatments. Severing always decreased survival and growth (tiller production, biomass and tiller extension) of the youngest tillers (ages 1 and 2wk), indicating that they were dependent on the parent to support their early growth. Age 4 tillers were able to support their own growth and grew hest in isolation; but when grown in the parent's neighbourhood competition with the parent reduced growth, although parental support ameliorated these effects. Some of the oldest tillers (age 8 wk) showed decreased growth when unsevered. This indicated an outflow of resources to the parent and suggested that integration allowed the control and coordination of tiller growth.

The pattern of the severing effects was similar in all clipping treatments, varying only in degree. There was little evidence of increased support for clipped tillers or for a change in the pattern of integration when the whole plant was clipped, except that age 8 tillers showed a continued benefit of the connection, in contrast to the positive effect of severing in the other two clipping treatments. The extension rate of the marked tiller showed complex responses to clipping and severing treatments, including effects of integration on regrowth after clipping. This experiment has shown that the growth of tillers in H. lanatus is highly integrated but that this integration is extremely plastic in response to tiller age and, to a lesser extent, clipping treatment.