bluuebunny/crossref_metadata_2025_split huggingface dataset:
ROOT AERATION IN UNSATURATED SOIL: A MULTI‐SHELLED MATHEMATICAL MODEL OF OXYGEN DIFFUSION AND DISTRIBUTION WITH AND WITHOUT SECTORAL WET‐SOIL BLOCKING OF THE DIFFUSION PATH
Authors: ARMSTRONG W. , BECKETT P. M. 
Published: May 2006

SummaryTreating the root as a homogeneous cylinder with respect to oxygen diffusivity and respiratory demand is a mathematically convenient assumption that has long been an inherent weakness and potential source of error in modelling the oxygen relations of soil‐aerated roots. The two models described here render such assumptions unnecessary: radial differences in oxygen diffusivity and respiratory demand between stele, cortex, wall layers and rhizosphere film have been accommodated by modelling the root: rhizosphere system as a multicylindrical unit. The models were designed to examine the influence of radial and circumferential cortical gas‐phase diffusion on oxygen concentrations and, also, to supplement recent theoretical studies into the effects of a sectoral blocking of the radial diffusion path for oxygen by circumferential contact between root and wet soil. Model I treats symmetrical surroundings assuming uniformity in the rhizosphere and accommodates the formation of an anoxic region within the root. Model II allows for the probability of partial blocking of the root's circumference, but only holds for fully aerobic roots.As expected the results reveal markedly contrasting oxygen profiles between those roots having significant cortical gas‐phase diffusion (porous roots) and those without such diffusion (non‐porous). A stepped oxygen profile, the result of a shallow gradient in the cortex, characterizes the porous roots; in non‐porous roots a smooth profile is predicted. It is also predicted that as a consequence of cortical gas‐phase diffusion the maximum oxygen deficit (MOD) in porous roots ought normally to be confined to the stele and, with a deterioration in the soil oxygen supply, the stele will be first to experience anoxia. More adverse conditions accompany a high level of circumferential blocking and a second anoxic zone (in a part of the wall) should arise prior to the development of more widespread anoxia. In the examples shown, extensive blocking was required to create some stelar anoxia in porous roots but the apparent resistance to diffusion in the wall layer(s) and rhizosphere film in the unblocked sector was greatly enhanced by the effects of blocking elsewhere. It is shown that in the partially blocked porous root oxygen should mostly move circumferentially in the cortex of the blocked sector; movement in the stele should be largely radial. In non‐porous roots, blocking quickly shifts the MOD to the wall layers adjoining the blockage centre and the examples chosen indicated a wedge of anoxia spreading from the wall into cortex and stele when blocking exceeded 20%. Wall thickness was however of no particular significance. Annular contours, which indicate radial transport, are quickly lost as blocking progresses around non‐porous roots and eventually transport is approximately unidirectional across most of the root.
RECOVERY OF COBALT‐DEFICIENT ROOT NODULES IN LUPINUS ANGUSTIFOLIUS L.
Authors: RILEY IAN T. , DILWORTH M. J. 
Published: May 2006

SummaryThe capacity of cobalt‐deficient nodules of Lupinus angustifolius L. cv. Uniharvest to respond to delayed addition of cobalt was examined in a glasshouse. Plant and nodule mass, bacteroid concentration and acetylene reduction activity were measured at each of three harvests. A favourable response to cobalt addition was evident in all parameters measured. However, the degree of this response declined with increasing age of the nodule tissue. The contribution of this recovery in nodule cobalt to the overall recovery of cobalt‐deficient L. angustifolius is discussed.
NUCLEAR DNA CONTENTS, SHOOT PHENOLOGY AND SPECIES CO‐EXISTENCE IN A LIMESTONE GRASSLAND COMMUNITY
Authors: GRIME J. P. , SHACKLOCK J. M. L. , BAND S. R. 
Published: May 2006

SummaryWithin a species‐rich limestone grassland community in Northern England a correlation has been established between nuclear DNA content and the timing and rate of leaf extension in the spring. The data support the hypothesis that natural selection has operated upon nuclear DNA content through the differential sensitivity of cell division and cell expansion to low temperature. It is suggested that measurements of nuclear DNA content may provide an index of temporal niche differentiation in plant communities.
EFFICACY OF ENDOMYCORRHIZAL‐FUNGUS ISOLATES AND INOCULUM QUANTITIES REQUIRED FOR GROWTH RESPONSE*
Authors: HAAS JERRY H. , KRIKUN J. 
Published: May 2006

SummaryIsolates of Glomus macroncarpum Tul. & Tul. grown in soil cultures from single spores were tested at known numbers of propagules ml−1 soil for their efficacy in promoting growth of bell pepper (Capsicum annuum L.) seedlings. The soil cultures, propagated under similar growth conditions, had from 0.02 to 25 propagules ml−1 as measured by the most probable number technique. Seven cultures with similar levels of inoculum density (a median of 7 propagules ml−1) were used undiluted, and at 10−1 and at 10−2 dilutions to test efficacy of the isolates. Also, cultures with originally dissimilar propagule levels (0.02 to 15 ml−1) were diluted to uniform inoculum density levels and tested for efficacy.Large intra‐species variation in efficacy occurred in isolates collected from different soils and in those isolated from the same soil. Differences in the growth enhancement ability of isolates were evident from four weeks after seeding until harvest. The best isolates were superior at all inoculum levels tested but the ranking of isolates differed with the inoculum density.A significant positive correlation was found between initial G. macrocarpum propagules ml−1 soil and all plant height and weight parameters measured. Growth of mycorrhizal plants was significantly greater than that of non‐mycorrhizal plants when more than 0.5 propagule ml−1 was present. With more than 5 ml−1, 70% of the isolates were effective. A minimum level of 1 propagule ml−1 is suggested for infestation of pepper seed beds; greater benefits can be expected from higher levels up to at least 10 to 15 propagules ml−1.
IRON TOXICITY TO PLANTS IN BASE‐RICH WETLANDS: COMPARATIVE EFFECTS ON THE DISTRIBUTION AND GROWTH OF EPILOBIUM HIRSUTUM L. AND JUNCUS SUBNODULOSUS SCHRANK
Authors: WHEELER B. D. , AL‐FARRAJ M. M. , COOK R. E. D. 
Published: May 2006

SummaryThe distribution of two common species of base‐rich wetlands, Epilobium hirsutum L. and funcus subnodulosus Schrank, as dominant species within a small, spring‐fed fen is correlated with high concentrations of iron present in the areas marked by superficial precipitated iron ochre. E. hirsutum was confined to the less iron‐rich parts. Other chemical variables (including P) showed little relationship to Epilobium distribution. In laboratory conditions, growth of E. hirsutum seedlings on waterlogged substrata from the same fen was much less on iron‐rich than lower‐iron soil, but J. subnodulosus seedlings showed no differential response. Growth of E. hirsutum on iron‐rich soil was slightly ameliorated by addition of P but remained low relative to that on low‐iron soil. Growth of J. subnodulosus was not increased by P addition.Growth of E. hirsutum was substantially increased by maintaining the iron‐rich soil at 80% field capacity (F.C) rather than in waterlogged condition, though on low‐iron soils greatest growth was found in waterlogged conditions. At 80% F.C. both iron and P were less available than when soil was waterlogged. Growth of J. subnodulosus seedlings was consistently greatest in waterlogged conditions. In solution culture, Epilobium hirsutum seedlings showed poor growth, ill health and death at high iron concentrations (> 50 mg l−1) whilst, although growth of J. subnodulosus seedlings was also reduced, they remained visually healthy. High iron concentrations caused rapid blackening and ultimate flaccidity and necrosis of E. hirsutum roots; such symptoms were absent from J. subnodulosus. These data suggest that high iron concentrations are detrimental to E. hirsutum, both in the field and laboratory, and that this is not just an indirect effect of iron upon other aspects of mineral nutrition. The significance of this to possible mechanisms of iron toxicity and waterlogging tolerance is discussed.
PRE‐LAST GLACIATION MAXIMUM VEGETATION HISTORY AT HENTY BRIDGE, WESTERN TASMANIA
Authors: COLHOUN ERIC A. 
Published: May 2006

SummaryLake sediments dated to between about 28000 and 20000 years B.P. in the temperate rainforests of western Tasmania show that subalpine to alpine shrub, wet heath and herb communities occurred within 115 m of present sea level before the maximum of the last glaciation (20000 to 18000 years B.P.). The high herb, especially grass, values and charcoal content after about 22000 years B.P. may be related to the advent of aborigines.
TANSLEY REVIEW No 1.
Authors: COCKBURN W. 
Published: May 2006

SummaryThe term, photosynthetic acid metabolism (PAM), encompasses processes which involve four‐carbon (C4) acids as carbon‐carrying intermediates between the carboxylations catalysed by phosphoenolpyruvate (PEP) carboxylase and ribulose biphosphate (RuBP) carboxylase. These carboxylations may be separated either spatially, as in C4 photosynthesis which is not covered here, or temporally. Separation in time is referred to as diel PAM (DPAM) and the variations on this particular theme are the subject of this review. DPAM includes stomatal and astomatal types. The former types, usually described as crassulacean acid metabolism (CAM), are referred to here as stomatal CAM (SCAM). Astomatal PAM includes both aquatic and terrestrial forms; aquatic acid metabolism (AAM) and terrestrial astomatal acid metabolism (TAAM). Physiological, biochemical, structural, ecological and evolutionary aspects of these mechanisms of acquisition of carbon dioxide are reviewed.

CONTENTS

Summary
3

I.
General Introduction to Photosynthetic Acid Metabolism (PAM)
4

II.
Stomatal Crassulacean (Diel Photosynthetic) Acid Metabolism (SCAM)
5

III.
Astomatal Photosynthetic Acid Metabolism
13

IV.
Idling
18

V.
Structural Variation in Plants Exhibiting Diel PAM (DPAM)
18

VI.
The Mechanism of the Switch between C3 Photosynthesis and DPAM
19

VII.
The Cost of DPAM
19

VIII.
The Evolution of DPAM
20

IX.
Concluding Comment
22

Acknowledgements
22

References
22
THE EFFECT OF WINTER FIELD CONDITIONS ON THE DISTRIBUTION OF TWO SPECIES OF UMBILICARIA
Authors: SCOTT MARTHA G. , LARSON DOUGLAS W. 
Published: May 2006

SummaryTwo lichen species of the genus Umbilicaria were transplanted into each other's habitat in order to determine the role of winter field conditions in regulating distribution patterns. U. vellea (L.) Ach., which normally grows in a steeply inclined, snow free habitat, was transplated into the level‐ground, snow‐covered habitat of U. deusta (L.) Baum. The opposite was done for U. deusta. Suitable controls to test the effect of transplanting were also run for both species. The reciprocal transplantation was done in each of two years, one of which had a normal snow load, the other which had almost no snow cover.The effect of reciprocal transplantation was to reduce significantly the carbon fixing ability in U. vellea in the year with the normal snow‐load. Transplantation had no effect on U. deusta. The effects on CO2 exchange were only slight for U. vellea in the year with the lesser snow‐load. It is therefore concluded that existing winter field conditions, and especially the nature of the snow cover, maintain the existing distribution pattern of the lichens in the field.
MYCORRHIZAL INFECTION OF BETULA PENDULA AND ACER PSEUDOPLATANUS: RELATIONSHIPS WITH SEEDLING GROWTH AND SOIL FACTORS
Authors: FRANKLAND JULIET C. , HARRISON A. F. 
Published: May 2006

SummaryMycorrhizal infection of two‐year‐old seedlings of Betula pendula Roth, and Acer pseudoplatanus L. was examined in a pot experiment, in relation to several soil variables (pH, organic matter, N, P, K, Ca, Fe, and phosphatase activity), host uptake of 32P, and plant performance (height and weight), in 25 Cumbrian soils from natural and semi‐natural habitats (such as woodland, carr and upland heath). Soils were used in a fresh state to maintain indigenous mycofloras and seedlings were raised from several seed‐lots to include possible ecotypic variation. Infection (incidence and intensity) of both ‘immature’ and ‘mature’ mycorrhizas was estimated.Most plants were mycorrhizal, ectomycorrhizas occuring on Betula and vesicular‐arbuscular (VA) endophytes in Acer. Differences in the degree of infection between soils, but not between seed‐lots, were highly significant. Infection of one or both species was highly correlated with several soil factors (pH, organic matter, phosphorus and iron), and with all the plant variables. In Betula, evidence for most of these relationships was obtained only from ‘immature’ mycorrhizas, suggesting early physiological activity. Mycorrhizas accounted for a small but significant proportion of the variation in growth of both hosts, and soil properties accounted for a high proportion of the variation in both the plant growth and mycorrhizal infection, as shown by multiple regression analyses. Growth of Acer appeared to have a greater influence than soil factors on the variation in VA infection. ‘Beading’ of Acer roots was negatively correlated with plant weight and soil phosphorus, suggesting a morphological response to P‐ deficiency. Possible causal relationships between hosts, fungal symbionts and soils are discussed.
CRITICAL LEAF CONCENTRATIONS FOR DEFICIENCIES OF NITROGEN, POTASSIUM, PHOSPHORUS, SULPHUR, AND MAGNESIUM IN PERENNIAL RYEGRASS
Authors: SMITH G. S. , CORNFORTH I. S. , HENDERSON H. V. 
Published: May 2006

SummaryCritical leaf concentrations for deficiency of nitrogen, potassium, phosphorus, sulphur, and magnesium were estimated for perennial ryegrass (Lolium perenne L.) grown in sand culture. The values associated with a 10% reduction in dry matter yield were as follows (all results expressed as g kg−1 DM except for the nitrate‐nitrogen value which appears as μg−1 DM): Kjeldahl‐nitrogen 32; nitrate‐nitrogen 500; potassium 28; phosphorus 2.1; sulphur 1.8; and magnesium 0.7. A major difference between the critical leaf concentrations estimated in this study and the tentative values published elsewhere was for potassium. Concentrations required in the shoot for near maximum growth were higher than previously reported. Differences in the nitrogen status of the plants probably account for this result. The depressing effect of potassium on the absorption of magnesium and calcium is discussed in relation to plant and animal nutrition. Sulphur was found to be inefficiently absorbed by phosphorus deficient plants despite non‐limiting amounts of sulphur applied in the nutrient solution. A possible explanation for this effect may be linked to the observation that the transport of sulphate into the chloroplast was coupled with that of phosphate. The concentration of macroelements required in the nutrient solution to produce maximum shoot growth of perennial ryegrass was very much greater than that generally applied to plants grown in sand culture.
PHENYLALANINE AMMONIA LYASE AND PEROXIDASE ACTIVITY IN MYCORRHIZAL AND NONMYCORRHIZAL SHORT ROOTS OF SCOTS PINE, PINUS SYLVESTRIS L.
Authors: RONALD PAMELA , SÖDERHÄLL KENNETH 
Published: May 2006

SummaryPhenylalanine ammonia lyase was characterized in roots of Pinus sylvestris L. The Km for the pine root enzyme with phenylalanine as a substrate was l.2 ± 0.4 X 10−4 M. The enzyme had a pH activity optimum of 9 and the subunit molecular weight was 70 to 72 kD as determined by Western blotting. Enzyme activity could be inhibited by D,L‐2‐aminooxy 3 phenylpropionic acid at 1 μ. Treatments with zymosan, pectinase, light or kinetin and naphthylacetic acid did not induce higher phenylalanine ammonia lyase or peroxidase activity in pine roots. No significant differences were observed in phenylalanine ammonia lyase or peroxidase activity in mycorrhizal and nonmycorrhizal short roots in the P. sylvestris‐L. laccata symbiosis 15 weeks after cultivation.
ULTRASTRUCTURE OF THE FUSION CELL IN GRACILARIA VERRUCOSA (HUDS.) PAPENFUSS (RHODOPHYTA, GIGARTINALES)
Authors: DELIVOPOULOS STYLIANOS G. , TSEKOS IOANNES 
Published: May 2006

SummaryThe fusion cell in Gracilaria verrucosa (Huds.) Papenfuss is large, multinucleate and irregularly shaped. It originates from cytoplasmic fusions of haploid and diploid cells, and expands continuously by incorporating adjacent vegetative cells. Plastids are arrested in their development remaining in a proplastid state. Mitochondria possess ring‐like structures. Dictyosome activity is limited to forming the first wall layer. Large mucilage sacs, formed from ER, discharge their contents, thereby contributing to the formation of a second wall layer. Copious amounts of floridean starch as well as crystalline inclusions and osmiophilic granules are present in the cytoplasm. Numerous cisternae of endoplasmic reticulum occur in concentric stacked aggregations. Dark‐staining, spherical masses in the cytoplasm may represent condensed, inactivated haploid chromatin. Ultrastructural features of the fusion cell indicate that it has a nutritive function.
THE EFFECT OF REMOVAL OF EXTRARADICAL HYPHAE ON WATER UPTAKE BY VESICULAR‐ARBUSCULAR MYCORRHIZAL PLANTS
Authors: HARDIE KAY 
Published: May 2006

SummaryResults from experiments on clover (Trifolium pratense L.) and leek (Allium porrum L.) revealed that removal of extraradical hyphae from vesicular‐arbuscular mycorrhizal (VAM) plants had a detrimental effect on transpiration flux. The advantage of comparisons between VAM plants with and without extraradical hyphae rather than between VAM and non‐mycorrhizal plants is discussed in relation to this type of investigation. It is suggested that extraradical hyphae increase the root absorptive‐surface area, independently of an enhanced nutrient status.
INFLUENCE OF AGE OF ROOTS ON THE PATTERN OF VESICULAR‐ARBUSCULAR MYCORRHIZAL INFECTION IN LEEK AND CLOVER
Authors: HEPPER CHRISTINE M. 
Published: May 2006

SummaryThe effect of the age of roots on their susceptibility to infection by a vesicular‐arbuscular mycorrhizal fungus was compared in leek (Allium porrum L.) and clover (Trifolium parviflorum Ehrh.). Plants were grown in soil lacking mycorrhizal fungi for up to 21 d (clover) or 32 d (leek) and then transplanted into soil infested with Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe. The pattern of infection which occurred was compared with that in plants grown continuously in infested soil.Leek roots up to 32 d old retained their susceptibility to infection whereas clover roots as young as 5 d old had become almost completely immune to penetration by G. mosseae and those which were 21 d old did not become infected at all. The most proximal part of the roots (9 mm in leek and 21 mm in the main root of clover) always remained uninvaded.A difference between leek and clover was also observed in the distance of the most distal entry point from the root tip (10 and 1 mm, respectively). Some examples of host resistance to infection are described. One clover plant was not colonized by G. mosseae despite the formation of many entry points.
THE CELL CYCLES OF CHLAMYDOMONAS AND CHLORELLA
Authors: DONNAN LORRAINE , CARVILL EILEEN P. , GILLILAND TREVOR J. , JOHN PETER C. L. 
Published: May 2006

SummaryIn Chlorella and Chlamydomonas two periods of relatively constant duration determine total cell cycle length and cell size is stabilised by control of whether 2, 4, 8 or 16 daughter cells are formed. A timer runs through G1 phase and leads to the attainment just before S phase of a commitment to divide without further requirement for growth. The commitment timer requires growth for its continuation, is stabilized against a raising or lowering of temperature between 20 and 30°C but it is only partly stabilized against slow growth due to low energy supply. In Chlamydomonas 137c, at 25°C when growth is limited by light energy, the period between the beginning of growth in fully formed daughter cells and the attainment of first commitment to divide approximates to 5 + 0.75 × doubling time (h), at protein doubling times between 5 and 25 h. Under the same conditions division processes occurring in the period after first commitment also confer time properties since they are completed in 6 h. Postcommitment events are extended in the first cycle following a temperature reduction but develop temperature compensation in the second cell cycle. The mean generation time of Chlamydomonas 137c approximates to 11 + 0.75 × mass doubling time (h).In both algae cell size is stabilized by an influence of mother cell mass on the number of successive further commitments that can occur following first commitment to divide. Each commitment is to perform a single further round of DNA replication and achieve a further doubling of cell number without further requirement for growth. Comparison of cells of different size when growing at the same rate shows that time, not size, controls the start of division events, and that size and not growth rate determines division number. In Chlamydomonas, division numbers provide a constant mean apportionment of 20 pg Lowry positive material to committed daughter cells at the time of final commitment. It is proposed that commitments continue until the mass available for further apportionment falls below a critical minimum of 27 pg, therefore, the minimum apportionment will be 13.5 pg and the maximum 27 pg per committed daughter ceDs. This predicted twofold range of cell sizes is confirmed by cell size frequency measurements made by microscopy and by fluorescence‐activated cell sorting. Size frequency measurements made after growth intermediate between 2, 4 or 8 in a cell cycle are consistent with increments of commitment under size control. Multiple fission cell cycles are compared with others.
FLUXES OF CARBON IN ROOTS OF BARLEY PLANTS
Authors: FARRAR J. F. 
Published: May 2006

SummarySucrose entering barley roots is unloaded symplastically from the phloem, as indicated by anatomical considerations, the unexchangeability of [14C]sucrose of shoot origin, and the characteristics of uptake of exogenous sucrose. It then enters a cytoplasmic sucrose pool which, together with an apoplastic pool exchanging rapidly with it, accounts for 40 to 50% of sucrose in the root. The remainder is in vacuoles, from which it is released with a half‐time of 8 h. Storage polysaccharides have a half‐time of about 17 h. About one‐quarter of all sucrose leaving the cytoplasmic plus apoplastic pool is temporarily stored as sucrose or polysaccharide. The net flux of carbon to growth of structure is about 55% of that entering the root; over 40% is lost in respiration. On root excision, the flux of sucrose out of the vacuole rose but the breakdown of storage carbohydrate did not.
SELF‐COMPATIBILITY IN DISTYLOUS CRYPTANTHA FLAVA (BORAGINACEAE)
Authors: CASPER BRENDA B. 
Published: May 2006

SummaryThe seed production of hand pollinated flowers indicates that distylous Cryptantha flava (A. Nels.) Payson is both intramorph and self‐compatible. In addition, there is no inhibition of pollen tube growth following either intramorph or self‐pollinations. Despite the potential for crosses between individuals of the same style length and thus the production of unequal morph ratios, pins and thrums occur in equal numbers in natural populations.