Abstract: The ability of a range of commonly occurring ectomycorrhizal fungi to utilize peptides and proteins as sole sources of nitrogen at a range of pH levels was examined by determining patterns of growth and nitrogen uptake in liquid cultures. Differences in patterns of utilization of the nitrogenous substrates were found. Some of the fungi had little ability to grow on peptides or proteins but grew well on ammonium and were termed 'non-protein fungi'. Others grew vigorously on peptide and protein, severely depleting N contents of the growth media. These were termed 'protein fungi'. An intermediate category was also recognized in which some growth occurred on protein at most of the pH levels though final yields were lower than those of the 'protein fungi'. The implications of the results are discussed in relation to the ability of the fungi to sustain a saprotrophic or mycorrhizal habit in soils differing qualitatively in their nitrogen status.

Abstract: SUMMARY The occurrence, structure and metabolism of fructose polymers in tissues of vascular plants are discussed in relation to the metabolism of sucrose. Distinctions are made between long-term and short-term storage of such polymers and the regulatory mechanisms which govern accumulation are examined. The roles of various fructosyltransferases in the synthesis of the different fructan structures from sucrose are outlined. The potential selective advantages of the possession of fructan metabolism in different species are assessed with reference to possible roles as cryoprotectants, in osmotic control and as storage carbohydrates whose metabolism can continue at low temperatures (O to 5 ?C). It is concluded that the complexity and variety of fructan structures and of the associated enzyme systems has resulted in an incomplete understanding of their physiology and biochemistry, but their significance as an alternative storage polysaccharide in both leaves and storage organs should not be underestimated.

Abstract: Summary The role of ectomycorrhizas in the metal tolerance of birch seedlings from Sudbury, Ontario was investigated. Betula papyrifera Marsh, is one of the few tree species able to survive in the copper- and nickel-polluted area near Sudbury. Two types of birch seedlings were tested; those inoculated with Laccaria proxima (Boud.) Pat., Lactarius hibbardae Peck, Lactarius rufus (Scop, ex Fr.) Fries, or Scleroderma flavidum E. & E. isolates originating from the Sudbury area, and those which were not inoculated. Once the seedlings were infected, they were grown in sand culture containing 34 or 85 μM Ni, 32 or 63 Cu, or a control solution. At the low nickel concentration, the mycorrhizal plants, especially those infected with S. flavidum, grew significantly better than did non-mycorrhizal plants. At the higher nickel concentration, S. flavidum-infected seedlings weighed 86% of controls without nickel, while the other seedlings weighed only 52 to 61 % of control. The good growth of S. flavidum-infected birch seedlings may have been due to retention of nickel in the mycorrhizas. These seedlings had the highest root nickel contents and the lowest stem nickel contents. At the high concentration of copper, growth of the mycorrhizal seedlings was significantly reduced compared with the non-mycorrhizal seedlings. This reduction in growth of infected seedlings did not relate to an increase in the uptake or translocation of copper. Under the low copper treatment, infection with mycorrhizal fungi did not affect seedling growth. The potential role of iron and phosphorus in affecting host metal tolerance was investigated. Changes in the tissue concentrations of these elements did not relate to the effect of the fungi on metal tolerance.

Abstract: The ability of four major species of trees of boreal forests, Betula pendula, Picea mariana, P. sitchensis and Pinus contorta, to utilize protein as a sole nitrogen source was compared when the plants were grown in mycorrhizal association with the fungus Hebeloma crustuliniforme and in the non-mycorrhizal condition. When mycorrhizal, all species used protein N readily, producing vigorous shoots with nitrogen contents ranging from 5 % in birch to around 3 % in the conifers, and consuming up to 53 % of the nitrogen provided in the culture vessels. In the absence of infection birch, black spruce and pine were completely unable to use protein as an N source and Sitka spruce had only a minimal ability to do so. It is suggested that early infection by fungi with proteolytic capability may be of particular importance for small seeded species germinating in soils of boreal and arctic regions where mineralization of nitrogen is inhibited by low temperatures.

Abstract: SUMMARY Atmospheric nitrate deposition varies across Northern Britain, and has increased approximately fourfold since the last century in the Manchester Region. Ombrotrophic mires depend on an atmospheric supply of elements, and some components of nitrogen deposition at two mire sites in northern Britain were investigated. The sites differed in proximity to major pollution sources. Growth of Sphagnum cuspidatum Hoffm, in bog pools was less in the polluted site and this was associated with a marked increase in tissue nitrogen concentration. Field experiments in which S. cuspidatum plants from unpolluted sites were exposed solely to atmospheric deposition in artificial bog pools showed that much of this large increase in nitrogen concentration could have resulted from atmospheric deposition alone. Concentrations of nitrate and ammonium within the range observed in bulk deposition at the polluted site reduced the growth of S. cuspidatum in a laboratory experiment. The results are discussed in relation to a general increase in atmospheric nitrogen deposition, and its potential importance to plant growth.

Abstract: SUMMARY Many data support the view that, when NH4+ [or N2, NH3, or CO(NH2)2] is the N source for plant cell growth, the excess H+ generated in the synthesis of core metabolites is excreted to the bathing medium (biophysical pH-stat). This paper explores the possibility that a ‘biochemical’ disposal of these excess H+ could occur, thus allowing net NHJ assimilation to take place in the shoot of land plants. A‘biochemical’ H+-neutralizing pH-stat requires that a non-toxic resource be taken into the plant in a form in which metabolism can convert into a non-toxic product with H+ consumption or OH− production. This possibility was explored for reductive metabolism of B(OH)3, Si (OH)4, H2PO4−, H2AsO4−, O2, SO42, SeO42− and HVO42; and for oxidative metabolism of Cr, Br−, I−, Fe2+ and Mn2+. For B(OH)3 and Si(OH)4, reductive metabolism (even if it were thermo-dynamically possible, granted the reductants available to plants) does not involve significant 11+ removal. H2PO4− reduction may be thermodynamically possible, but is quantitatively insignificant as an H+ sink in plants. H2AsO4− reduction is probably a detoxification mechanism, and it is not a significant H+ sink in plants for which quantitative data are available. O2 assimilation (reduction) into -OH, and thence ≡O+, occurs in anthocyanin synthesis, but not to an extent which disposes of much of the excess H+ produced in growth with NHJ as N source. SO42− reduction in excess of that required by primary, core metabolism (i.e. that leading to amino acids, thylakoid sulpholipid and cell wall esters) can generate OH−, but such ‘secondary’ SO42− metabolism is related to osmoregulation and to chemical defence rather than to H+ disposal per se. The quantity of S metabolism which is ‘negotiable’ is not, apparently, adequate to neutralize a substantial fraction of excess H+ formed during growth. SeO4−2 reduction and assimilation performs largely a detoxification and/or chemical defence role, and the quantities involved (even in Se-accumulators) do not generate enough OH− to offset much of the excess H+ formed during growth. Vanadate reduction is quantitatively insignificant as an H+ sink. Oxidation of Cl−, Br− and I− in incorporation into C-halide groups is, in land plants, a quantitatively insignificant process. H+ disposal via HCl volatalization from an aqueous phase of low pH which contains Cl− does not seem to be an important sink for H+ in terrestrial plants. Oxidation of F− to form ≡C-F usually produces CH2F.COO− with no net H+ consumption. Oxidation of Fe2+ and Mn2+ is H+-consuming as long as oxides or hydroxides of Fe3 and Mn4+ are not formed. However, the oxides and hydroxides are often formed so that the oxidation processes consume OH− rather than H+. These quantitative considerations, together with those of the availability of starting materials and the toxicity of end products suggest that the H+-consuming processes, even in combination, probably cannot dispose of all of the H+ generated in growth with NHJ as N source. In general, these H+-consuming reactions seem to be related to synthesis of osmoregulatory and chemical defence compounds, and to detoxification; the products appropriate to these functions generally have high molecular masses per mol H+ consumed in their synthesis, a feature which does not make them ideal parts of a ‘biochemical pH-stat’.

Abstract: The effect of the presence of an exogenous carbon source in the synthesis medium on compatible and incompatible interactions between Suillus grevillei (Klotzsch) Sing. and a number of ectomycorrhizal hosts has been studied at the ultrastructural level. Comparisons are made with the results of the previous study in which carbohydrate was omitted. Observations suggest that the availability of an external source of carbon to the fungus upsets the balance of the symbiosis in favour of the fungal partner, even in compatible interactions, causing changes in the host cell wall and at the host-fungus interface. The rate and degree of colonization of the root surface is also influenced by the presence of carbohydrate in the synthesis medium. These results suggest that any in vitro studies undertaken on compatibility and specificity in ectomycorrhizal associations should omit carbohydrate from the medium or use an aseptically synthesized donor host as the source of fungal inoculum.

Abstract: Summary Phosphate and the fungicide, benomyl, were applied to two alpine grasslands in the Kananaskis Valley, Alberta, Canada, to test the hypothesis that a reduction in leaf phosphorus concentration should result from reduction in vesicular-arbuscular mycorrhizal (VAM) infection if mycorrhizal hyphae are the main route of P uptake by roots. Benomyl successfully reduced infection in the roots of several species. At one site the result was an increase and not a decrease in leaf N and P concentrations, which was directly proportional to the original infection level, implying a benefit to the plant from the reduction in infection. At the other site, opposite trends were observed before and after a severe drought episode, implying that infection was initially deleterious and later beneficial. These results are adduced as evidence to support a hypothesis that VAM infection is only beneficial to plants under particular environmental conditions or at specific times in the year or life-cycle.

Abstract: The commonly quoted values of maximum photosynthetic efficiency have been those obtained by determining the oxygen yield from suspensions of resting algal cells in which growth was disregarded. The unpredictability of the metabolism of resting cells severely vitiates the reliability of measurements made on their energy metabolism. Also the validity of the measurements with resting cells is made doubtful by anomalous values for the photosynthetic quotient (-δCO2 /δO2 ). The measurements on resting cells fall into two categories: one in which the cells were suspended in acid media (pH 5) with a CO2 partial pressure (pCO2 ) of 5% atmospheric, and one in which the cells were suspended in alkaline media (about pH 9) with a pco2 of 0.25% atmospheric. In acid media with 5% CO2 , the most probable value of the minimum quantum demand is 5 to 6 hv/O2 . With pH 9 media, equilibrated with 0.25% CO2 , the minimum quantum demand found is about 10 hv/O2 . This low efficiency seems to be caused by a sub-optimal CO2 partial presure, since it has been observed that the value at alkaline pH agrees with that at acid pH provided the pCO2 is maintained at 2 % atmospheric. This pCQ2 effect has been neglected by many workers. To avoid the controversial methods using resting cells, it is essential to determine the photosynthetic efficiency of cells in a steady state of growth. The environmental conditions during growth of the cells have a strong influence on the efficiency of photosynthesis; for instance, the efficiency appears to be strongly dependent on the temperature during growth. Under light-limited conditions when the photosynthetic efficiency of growth is optimized the minimum quantum demand of algal cells is found to be 5 to 6 hv/O2 . The minimum quantum demand of CO2 fixation varies from 1.1 to 1.4 times the value for O2 depending on the nature of the nitrogen source for growth. Significant doubt must be attached to measurements of the maximum photosynthetic efficiency with isolated chloroplasts, on the grounds that in vitro conditions may impair their efficiency and that the efficiency may be affected by the growth conditions of the parent plant. Thus, a unified view of the experimental data indicates that the most probable value of the minimum quantum demand is 5 to 6 hv/O2 . The preference for the apparently sub-optimal value of about 10 hv/O2 found with alkaline media and a pco2 of 0.25 %, which is the prevailing view, is necessitated by the requirement of the Z-scheme paradigm of the mechanism of the electron transfer. Thus it appears that hypothesis rather than a unified view of the experimental data on the efficiency is dictating the view of the mechanism involved. A cell of Chlorella (strain 211/8k) fully charged with reducing equivalents and energy can continue to assimilate CO2 and grow at the maximum rate (doubling time 3 h) for 9 s. It is calculated that exposure to 20 W m-2 (daylight PAR) for 0.5 s is sufficient fully to charge such a cell with energy and reducing equivalents. This calculation predicts that, in the steady state of growth, cycles of exposure of each cell to 20 W m-2 for 0.5 s followed by 9 s in the dark will support growth at the maximum rate. The theoretical expressions used to express the maximum thermodynamic efficiency of conversion of radiation to chemical work (ηT ) are shown to be inconsistent. The correct value is taken to be given by Spanner's equation ηT = 1 -(T/Tr ), where T is the ambient temperature and Tr is the radiation temperature. Hence, the maximum value of ηT for conversion of the PAR in sunlight to chemical work varies from 0.93 for unscattered sunlight to 0.70 if it is isotropically scattered. It is deduced that under the usual ambient conditions the value of ηT for photosynthesis will decrease by 0.043 for each log decrease in the irradiance. Contents Summary 3 I. Introduction 4 II. The stoichiometry of photosynthesis 6 III. Thermodynamic limits to photosynthetic efficiency 7 IV. The theoretical quantum demands for production of NADPH and ATP 8 V. The dynamics and energetics of photosynthetic growth 10 VI. The physiology of cells at or near zero growth rate 12 VII. Manometric measurements of quantum demands of resting cells 13 VIII. Non-manometric measurements of quantum demands of resting cells 16 IX. Quantum demands of vascular plants and isolated chloroplasts 18 X. The quantum demands of growing cells 19 XI. The influence of wavelength of radiation on photosynthetic efficiency 22 XII. Conclusion 23 XIII. Appendices 24 References 34.

Abstract: Summary Variation in seed size is an ecological paradox. Seed size, an important determinant of ecological distribution, is subject to considerable selection pressure, yet intra-family variation in seed size in the Sheffield region of Central England is less than expected. Taxonomically-linked constraints of variation result from: number of ovules per carpel (solitary or numerous); placentation type (apical, basal or axile, parietal); presence or absence of endosperm in the ripe seed and the pattern of embryogenesis (Asterad, Chenopodiad or Caryophyllad, Onagrad, Solanad). These character states are not readily modified and tend to be conservatively expressed in families. The smaller- and larger-seeded families of the local flora are characterized by different combinations of these features. Larger-seeded families may be further subdivided into those from moist or relatively dry habitats. It is suggested that the presence of a starchy endosperm, an unusual feature in the dicotyledons, may allow the development of a high root/shoot ratio in the young seedling. From extrapolation, it is suggested that (a) optimization of ecologically important characteristics and (b) adaptive radiation of major taxa during the evolutionary history of the angiosperms may have been restricted by these relatively stable groups of characters.

Abstract: Summary The chromosome numbers of 114 populations of the Deschampsia cespitosa (L.) Beauv. complex, widely distributed in the British Isles, were determined from root-tip squash preparations. This revealed two widespread morphologically cryptic chromosomal races of seminiferous D. cespitosa (2n= 26, 52). The tetraploid is found throughout Britain; its range of habitats includes meadows, pastures, woodland, plantations, verges and waste ground. This is the first report of an extensive geographical distribution for tetraploid seminiferous D. cespitosa. The diploid appears to be mainly restricted to woodland, of mostly ancient, semi-natural origin. Populations with both chromosome numbers are rare. The tetraploid is usually found where invasive colonization has clearly occurred. The closely related proliferous taxon, D. alpina (L.) Roem. & Schult., was tetraploid, in agreement with published data. The prolifery itself induces changes in floret morphology. The floral morphology and cytological data together suggest that sub-specific rank is appropriate for this variant in British material.

Abstract: SUMMARY The effects of photon irradiance on the growth of young plants (up to three weeks old) of Trifolium subterraneum L. and on the development of mycorrhizal root systems were studied with plants grown in a soil/sand mixture inoculated with Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe. Total plant growth was lower when photon irradiance was 100 μmol m−2 s−1, compared with 450 μmol m−2 s−1. Fresh weight of shoots was unaffected, but the fresh weight/dry weight ratio was increased at the lower irradiance in shoots, but not in roots. The main effect of decreased irradiance on the growth of the root system was a reduction in the numbers of first- and second-order lateral roots initiated. The average rate of extension of axial and lateral roots was only slightly reduced. The fraction of the root length infected was lower at the lower irradiance, particularly in the first two weeks. Development of infection was analyzed in terms of the role of formation of mycorrhizal entry-points (A) and the average rate of growth of infection units (B). Reduction in the fraction of the root length infected was found to be due to a reduction in A. B was remarkably constant at the two irradiances and in the different root subsystems. Thus both roots and infection units respond by making fewer units of unaltered rate of growth.

Abstract: Summary Details are presented of ectomycorrhizas in seventeen genera of tropical angiospermous trees from six families. Mycorrhizas of Intsia, Melaleuca, Monotes, Neea, Tristania and Vateria are figured for the first time. Overall, the tropical mycorrhizas are of a smaller diameter than is typical for those of temperate angiosperm trees but the sheaths are thicker and the fungus can form up to about 80% by weight of the dual organ. Our observations do not support the notion of a higher degree of host/fungus specificity in the tropics than in the temperate zones.

Abstract: Summary Ammonia assimilation has been followed in ectomycorrhizal roots of Fagus sylvatica. The absorption of ammonium ions was associated with a rapid synthesis of free amino acids in mycorrhizal tissues, glutamine being the most prominent. In the presence of [15N]ammonium, glutamate, glutamine and alanine became the most strongly labelled metabolites of ectomycor-rhizas. Nitrogen-15 nuclear magnetic resonance spectroscopy demonstrated that the glutamine amide-N was the most highly enriched component of the extracts. Methionine sulphoximine and albizine, inhibitors of glutamine synthetase and glutamate synthase, almost completely blocked the incorporation of 15N label into amino acids and induced an accumulation of NH4+. These observations suggest that in the ammonia-fed beech ectomycorrhizas, ammonia assimilation occurs mainly via the glutamine synthetase/glutamate synthase pathway, and that glutamate dehydrogenase plays little, if any, part in this process. Alternative models for the nitrogen assimilation pathways in fungal and host tissues are presented.

Abstract: Summary Roots and rhizomes were sampled in a three-year-old grass ley during one year using a mesh bag method and soil coring. Samples, collected after different growth periods (1, 2, 3, 4, 5, 6 and 12 months) and at different times of the year, were analyzed for carbohydrates and Klason lignin. Throughout the year the rhizomes contained more non-structural carbohydrates (20 to 40% of the organic matter) than the roots (1 to 8%). The non-structural carbohydrate content varied over the year with a maximum in autumn and minimum in early spring and summer after the first grass cut. Fructan was the predominant constituent in this fraction. Structural carbohydrates and Klason lignin showed relatively small variations over the annual cycle. The ratio between structural carbohydrates and Klason lignin showed little variation with time but differed between roots (19) and rhizomes (2.5). The xylose content was higher in the roots than in the rhizomes. Only small changes occurred with time in the relative composition of the structural carbohydrates. This consistency in composition implies that there was a difference between subterranean and aerial parts. In the latter, ageing is characterized by increased lignification and systematic changes in structural carbohydrates owing to the formation of secondary cell walls.

Abstract: SUMMARY The pollen spectra obtained from 127 lake sediment surface samples from the western interior of Canada are examined. Principal components biplots and discriminant analysis are used to investigate the correspondence between modern pollen rain and major vegetation zones in the study area. It is demonstrated that the major vegetation zones in the western interior of Canada can be distinguished on the basis of their modern pollen rain. Principal components biplots and discriminant analysis are also used to compare late Quaternary fossil pollen assemblages from lakes located near the southern and northern periphery of the modern boreal forest with the modern pollen spectra. The results suggest that the late Pleistocene and early Holocene pollen spectra from the southern and northern periphery of the boreal forest lack modern analogues in the western interior of Canada. The northern and southern boundaries of the boreal forest were located north of their modern positions during the mid Holocene. Vegetation developed and responded to mid Holocene climatic change at different rates at the two sites. Modern vegetation conditions were established at both sites between 5000 B.P. to 3000 B.P. Vegetation has remained relatively stable during the last three thousand years.

Abstract: SUMMARY Growth and rates of uptake of nitrogen and phosphorus (inflow) in Allium cepa L. were measured in three experiments. Effects of mycorrhizal infection (Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe) and N and P fertilization were investigated. The experiments were carried out in a naturally-lit glasshouse, so that seasonal variations in solar radiation influenced experimental results. In all experiments, a large positive growth response to mycorrhizal infection was observed when soil P was low. However, at high soil P smaller growth responses to infection were observed, as expected. Infection was associated with increased inflow of P, at all levels of soil P, even when non-mycorrhizal plants grew as well as or better than mycorrhizal plants. Lower P inflow was observed when infection was low and also at low irradiance in both mycorrhizal and non-mycorrhizal plants. The results show that mycorrhizal fungi increase the rate at which P is absorbed from soil, even under conditions which precluded a positive growth response to infection. In plants grown in spring and summer (two experiments), mycorrhizal infection was also associated with increased N inflow. N inflows in both mycorrhizal and non-mycorrhizal plants were lower in a third experiment in late winter and mycorrhizal infection had little or no effect on N inflow in this experiment. Increased N supply increased the inflow of N, concentrations of N in plant tissues and plant growth except in plants that were severely P limited, and there was no evidence that mycorrhizal infection alleviated N stress in low N plants. The results are discussed in relation to the environmental factors limiting plant growth, in particular nutrient uptake via and carbohydrate use by the fungal symbiont.

Abstract: SUMMARY Oidiodendron griseum, O. cerealis, O. rhodogenum, O. tenuissimum and O. truncatum were tested for their endophytic ability on axenic seedlings of Vaccinium angustifolium grown on a synthetic nutrient medium. O. griseum, O. rhodogenum and O. cerealis produced typical intracellular hyphal coils characteristic of the ericoid infection. For these three species, the level of infection reached 9 to 21 % of the root cells after 60 d of incubation. O. truncation and O. tenuissimum did not infect the Vaccinium roots but the latter species stunted development of secondary roots and reduced the growth of the seedlings.

Abstract: Summary This paper reports the results of an experimental study of Cd tolerance in the grass Holcus lanatus L. The responses of plants from a site aerially contaminated with Cd have been compared with those of plants from metalliferous mine sites and uncontaminated sites, using a range of soil treatments and pretreatments to assess the extent to which Cd tolerance can be affected. Responses in H. lanatus have been compared with those for three other grasses, Agrostis capillaris L., Deschampsia cespitosa (L.) Beauv. and Festuca rubra L., collected from the same sites and propagated as clones on their original soil and uncontaminated soil for three years prior to tolerance testing. Overall, a 13% drop in mean tolerance index was observed; even non-tolerant clones showed a loss of tolerance when grown in John Innes Potting Compost. These results suggest that H. lanatus is capable of greater phenotypic adjustment than A. capillaris, D. cespitosa and F. rubra and that Cd tolerance in this species can also be partially induced de novo in clones from uncontaminated sites. In H. lanatus there is also an indication that the clones from mines are more stable in their Cd tolerance than that from the aerially polluted site. The possible evolutionary significance of these observations is discussed.

Abstract: Summary Spartina anglica Hubbard seedlings were grown in nutrient solutions containing various concentrations of sodium salts, as the chloride, sulphate and sulphide. Two levels of nitrate were supplied to plants growing on the sodium chloride and sodium sulphate series. At low sodium chloride concentrations, higher growth rates were found in plants grown on the high nitrate level. At higher salinities, growth was inhibited and the inhibition was similar for plants grown on either of the two nitrate levels. Shoot levels of β-3-dimethylsulphoniopropionate (DMSP) showed no significant increase with increasing sodium chloride concentrations, at both nitrate levels. This strongly indicates that DMSP does not act as a compatible solute in S. anglica, grown under salt stress. Contrary to DMSP, levels of proline and quaternary ammonium compounds (QAC's) increased significantly in response to sodium chloride, and were significantly higher in plants grown on the high nitrate concentration. The influence of nitrogen availability on the accumulation of N-containing compatible solutes and growth is discussed. Growth rates of plants grown in increasing sodium sulphate concentrations were not inhibited. DMSP levels in plants did not increase with a sulphate increase in the medium. A significant inhibition of plant growth by sodium sulphide was found. Sulphate in the plant increased with increasing sulphide levels in the nutrient solution and an increase of DMSP was found at the highest sulphide level. A possible function of DMSP as storage for excess sulphur is discussed.

Abstract: SUMMARY Sodium chloride tolerance and phosphorus content were examined in split-root Carrizo citrange seedlings [Poncirus trifoliata (L.) Raf. x Citrus sinensis (L.) Osbeck] colonized with a vesiculararbuscular mycorrhizal fungus (Glomus intraradices Schenck & Smith) on zero, one or two root halves. Plants were treated with NaCl at 0, 25, 50 or 100 mm, and the degree of stress was measured as reduction of dry matter accumulation and rise in level of leaf proline-betaine (stachydrine). Shoot and root dry weight production during this period decreased with increasing levels of salt. Absolute reductions were similar for plants inoculated on one vs two half-root systems, but percentage decreases were less in the latter due to greater overall growth in all treatments. Betaine levels in leaf tissues were positively related to soil salt levels for each mycorrhizal treatment. Significant differences in betaine levels were also detected in plants with and without mycorrhizal fungi, and mean levels tended to be higher for those colonized on one vs two halves of their root system. In contrast, a half-root system and its fungal symbiont supplied enough phosphorus to allow concentrations of leaf P to equal those of fully infected root systems, yet the two groups did not show equal growth under control conditions or percentage reductions with NaCl stress.

Abstract: Summary Selected NaCl-tolerant lines of Trifolium alexandrinum L., Medicago sativa L., and Trifolium protease L. produced significantly greater dry matter than unselected control lines after 4 weeks of growth in sand culture with different NaCl concentrations. Tolerant lines of all three species generally contained less Na+ but more Cl− in their shoots than normal lines, although these differences were not statistically significant. Selected lines also contained less K+ in their shoots than unselected lines. Ca2+1 distribution was similar in T. allexandrinum and M. sativa but not in T. pratense, in which the tolerant line had significantly higher Ca2+ in the shoot than the unselected line.

Abstract: SUMMARY The effects of four soil temperatures on growth of Stoneville 213 cotton (Gossypium hirsutum L.) and root colonization by three vesicular–arbuscular mycorrhizal fungi were tested in soil temperature tanks in the glasshouse. Growth responses in fresh and dry weights of shoots and plant height were linear for noninoculated plants, but nonlinear for plants mycorrhizal with Glomus intraradices Schenck & Smith, Glomus ambisporum Smith & Schenck, or Gigaspora margarita Becker & Hall at soil temperatures of 18, 24, 30 and 36 °C. Total length of root and length of mycorrhizal root were positively correlated and increased as soil temperatures increased. However, total root length was not significantly changed by soil temperature in nonmycorrhizal plants. At 18 °C, shoot and root growth were not improved by mycorrhizas and total root length was actually suppressed by the endophytes. At 24, 30, and 36 °C, mycorrhizas stimulated plant growth. Shoot dry weights were maximum at 30 °C on plants mycorrhizal with G. margarita and G. intraradicvs and at 36 °C on plants inoculated with G. ambisporutn. Percent root colonization by the endophytes was less than 10% at 18 °C and ranged from 57 to 80% at temperatures of 24 °C or higher. All mycorrhizal plants had increased leaf tissue concentrations of P, Cu, Zn, and Mn with concentrations of Cu, Zn, and Mn greatest in plants mycorrhizal with G. ambisporum. The three mycorrhizal fungi generally stimulated plant growth equally well at 24 and 30 °C and G. ambisporum was slightly more effective as a symbiont at 36 °C than either G. intraradices or G. margarita.

Abstract: The post-glacial pollen stratigraphies of two sequences of lake sediments (Hockham Mere and The Mere, Stow Bedon) are compared. Both suggest displacernent of existing taxa when new taxa arrive from their cold-stage refugia and expand their populations. Hockharn Mere is within an area of sandy soils, while The Mere at Stow Bedon is within an area of calcareous till soils. There have been differences in the forest vegetation around the two sites for most of the last 10000 years, and the competitive interactions between the forest trees differ also. A great body of literature has built up concerning the theoretical behaviour of plant and animal populations, while the collection of observational data on what actually happens in real communities is scarce. In particular, records of populations over long periods of time (> 50 years) are almost non-existent. Some organisms, such as trees, may live for 102 to 1 03 years, and little is known about how their populations develop, and how populations react when new species are added. The continuous records, over 104 years, of pollen from forest trees preserved in lake sediments are therefore of great significance. Typically, at the beginning of the post-glacial, 10000 years ago, there were few tree species present, but gradually over a period of thousands of years, new species arrived and expanded their populations, while the species already present became less abundant or even locally extinct. Forest trees, like other organisms, occur in characteristic segments or niches of their total physical and biotic environments. A useful distinction may be made between the fundamental niche, a multidimensional hypervolume, and the realized niche for each species (Hutchinson, 1978). Relationships of trees along such one-dimensional gradients as altitude, soil moisture, pH, and texture, have been worked out by, for example, Whittaker (1956, 1960), Curtis (1959) and Maycock (1963) in North America, and by Rackham (1980) in eastern England. These studies all deal with the relationships of species in modern forests. Earlier in the post-glacial, not all these species were present together: what were the relationships like then? What changes took place in the realized niche of each species as a new taxon appeared in the forests and began developing its own realized niche? We see these organisms today growing in one set of physical and biotic conditions, giving rise to a particular realized niche for each. If we are to have any understanding of the full potential of each species, any data which reveal how each

Abstract: Summary Acid rain-induced direct injury to forest tree seedlings was investigated in specially designed controlled-environment simulated-rainfall chambers. Seed germinative capacity, seedling survival, seedling growth and morphological responses to simulated rains of pH 5.6, 4.6, 3.6 and 2.6 were examined during the first growth cycle in 11 commercially important north temperate tree species. Germinative capacity was weakly responsive to rain pH, while seedling survival was more sensitive. No evidence of macroscopic foliar injury was observed at rain pH > 2.6. 1 reatment with pH 4.6 rain was sufficient to induce statistically significant growth reductions and morphological changes in coniferous seedlings. Response varied with species, treatment pH and parameter measured. No consistent growth stimulations were observed. Initiation of Primary needles, axillary meristems and shoot apex height were most affected by simulated pH. Deciduous species were considerably more resistant than coniferous species. Treatment with ram of pH 2.6 was generally required to induce significant growth reductions in deciduous seedlings.

Abstract: Summary After 7 weeks' growth in varying NaCl concentrations in sand culture, dry matter production and tiller number were compared for the progenies of NaCl–tolerant selection lines and the Progenies of unselected control lines of Holcus lanatus L., Lolium perenne L., Dactylis glomerata L. and Festuca rubra L. The tolerant lines had been produced by selection at the seedling stage. In each species, selected lines produced significantly more dry matter and had greater tiller numbers than unselected material, particularly at high levels of NaCl. Shoot/root ratios differed significantly only in L. perenne, unselected material having a higher shoot/root ratio. These data confirm that for these four species, selection based upon differences in seedling root growth is a valid means of selecting for improved NaCl tolerance in adult plants, and that this tolerance does not lead to any reduced performance in the absence of NaCl.

Abstract: Percentage and concentration pollen diagrams from the sediments of two adjacent inter-drumlin hollow lakes near Dungannon, and in two cores from Lough Catherine, suggest that only small reductions in the pollen frequencies of trees such as pine and, at some sites, birch and oak, accompanied reduced Ulmus at the elm decline in these parts of Co. Tyrone. They also confirm that Pteridium aquilinum could sporulate and many herbs were able to flower more freely owing to an opening of the tree canopy. Seventeen radiocarbon dates provide chronologies for the sites and date the elm decline to between 5050 and 5375 B.P., the subsequent start of increased elm pollen percentages to between 5010 and 4850 B.P., and the beginning of a second decline in elm pollen to between 4330 and 4260 B.P. The initial decline in elm pollen values may have been caused by disease and this reduction was superimposed upon a background of small-scale clearances which continued after a general elm regeneration. The question of a general similarity and causation of the second elm decline in Ireland and elsewhere is considered. Chemical, magnetic and pollen preservation data from the Co. Tyrone sites suggest episodes of erosion occurring at the first elm decline and others at the second elm decline.

Abstract: SUMMARY The importance of vesicular-arbuscular mycorrhiza (VAM) and P fertilizer for P nutrition and dry matter production in field peas (Pisum sativum L.) was studied in moderately P-deficient soil. Half of the experimental plots were fumigated to reduce the level of VAM infection. Shoots and 0 to 30 cm soil cores were sampled on three occasions. An extensive VAM infection was rapidly established in untreated soil, whereas infection levels were low in fumigated soil. Root growth responded to fumigation by increased root length and decreased root diameter. Fumigation reduced the P content in shoots considerably, and correspondingly the mean rates of P inflow per unit root length were 60% lower in fumigated than in untreated soil during flowering. These effects of fumigation were ascribed to the low levels of VAM infection in fumigated soil. The production of dry matter was not decreased accordingly in fumigated plots, although both it and P uptake were increased by adding P fertilizer. The possible reasons for this discrepancy are discussed. A supplementary survey on infection development at five other field sites showed that peas are extensively colonized by VAM fungi, even in soils where a standard procedure is being used. These results indicate that VAM is of major importance to P uptake by the field-grown pea.