New Phytologist welcomes this month, and introduces, its new Managing Editor, Jonathan Ingram. He comes to New Phytologist from Elsevier Science's Trends in Plant Science, where he has worked as Assistant Editor since the highly successful launch of that magazine in January 1996.

Jonathan's introduction to plant science, at Oxford over 10 years ago, was through the excellent tuition of Vernon Butt in a traditional botany degree. He then took a DPhil with Andrew Smith and Chris Leaver, learning biochemical and molecular research methods while studying malate decarboxylation associated with Crassulacean acid metabolism. He subsequently moved to the Max Planck Institute for Breeding Research in Cologne, Germany, where he did research with Dorothea Bartels into the molecular mechanism of drought tolerance in the resurrection plant Craterostigma plantagineum, specifically the role of sucrose-phosphate synthase.

These are challenging times in science publishing, particularly as technological advances force rapid change, but there are also many exciting new opportunities. Jonathan's experience and background will help New Phytologist remain in the vanguard of plant journals, while maintaining its traditions of scientific excellence and friendly service to authors and readers, traditions carefully nurtured by his predecessor David Stribley.

We wish David improved health and a happy retirement.

This review considers the reasons for, and research governing, the regulation and monitoring of genetically engineered micro-organisms and viruses (GEMs) released into the environment. The hazards associated with releasing GEMs into the environment are the creation and evolution of new pests and diseases, and damage to the ecosystem and non target species. The similarities and differences between GEMs and conventional micro-organisms are discussed in relation to risk assessment. Other issues covered include the persistence of micro-organisms in the environment, transgene dispersal to non-engineered microbes and other organisms, the effects of transgenes and transformation on fitness, and the evolution of pests and pathogens that are given or acquire transgenes. Areas requiring further research are identified and recommendations for risk assessment made.

Responses of leaf gas exchange and above-ground growth of beech (Fagus sylvatica L.) and Norway spruce (Picea abies Karst.) to atmospheric CO2 enrichment (374 μl l−1 vs. 590 μl l−1) and increased wet deposition of N (5 vs. 50 kg N ha−1 a−1) in combination with two natural forest soil types (‘acidic’ and ‘calcareous’) were studied in large open-top chambers. Eight juvenile beech and spruce trees from different provenances, together with a ground cover composed of five understorey species, were established in each of 32 model ecosystems. Both beech and spruce showed sustained enhancement of photosynthesis in response to atmospheric CO2 enrichment during the first 2 yr of treatment. Nevertheless, switching measurement CO2 concentrations revealed partial downward adjustment of photosynthesis in trees grown in elevated CO2, beech generally showing more pronounced downward adjustment than spruce. The responsiveness of photosynthesis to CO2 enrichment did not vary significantly among trees from different provenances. Stomatal conductance was reduced under elevated CO2 in both tree species. In spruce, the radial growth of the main stem and the annual production of wood (shoot-wood dry mass of current-year lateral shoots), needle dry mass, and assimilation area per tree were stimulated both by CO2 enrichment and increased N deposition, but were not significantly affected by soil type by year 2. In contrast, in beech, the radial growth of the stem and the total leaf number, foliage dry mass, and assimilation area per tree were all not significantly affected by elevated CO2 and increased N deposition when responses of the two soil types were pooled, but were greater on calcareous than on acidic soil by year 2. However, CO2 interacted with soil type in beech: irrespective of the N deposition rate, saplings showed growth stimulation on the calcareous soil but responded negatively to CO2 enrichment on the acidic soil (where growth was slower). Our results suggest that complex interactions between CO2, species and soil quality need to be accounted for when attempting to predict forest development in a future CO2-rich world.

We tested the extent to which growth responses to elevated carbon dioxide (CO2) are temperature-dependent and change through early seedling ontogeny among boreal tree species of contrasting relative growth rates (rgr). Populus tremuloides Michx, Betula papyrifera Marsh, Larix laricina (Du Roi) K. Koch, Pinus banksiana Lamb., and Picea mariana (Mill.) B.S.P. were grown from seeds for 3 months in controlled-environment chambers at two CO2 concentrations (370 and 580 μmol mol−1) and five temperature regimes of 18/12, 21/15, 24/18, 27/21 and 30/24°C (light/dark). Growth increases in response to CO2 enrichment were minimal at the lowest temperature and maximal at 21/15°C for the three conifers and at 24/18°C or higher for the two broadleaved species, corresponding with differences in optimal temperatures for growth. In both CO2 treatments, rgr among species and temperatures correlated positively with leaf area ratio (lar) (r[ges ]0·90, P<0·0001). However, at a given lar, rgr was higher in elevated CO2, owing to enhanced whole-plant net assimilation rate. On average in all species and temperatures at a common plant mass, CO2 enrichment increased rgr (9%) through higher whole-plant net assimilation rate (22%), despite declines in lar in high CO2 (11%). Reductions in lar are thus an important feedback mechanism reducing positive plant growth responses to CO2. Proportional allocation of dry mass to roots did not vary between CO2 treatments. Early in the experiment, proportional increases in plant dry mass in elevated CO2 were larger in faster-growing Populus tremuloides and B. papyrifera than in the slower-growing conifers. However, growth increases in response to CO2 enrichment fell with time for broadleaved species and increased for the conifers. With increasing plant size over time, compensatory adjustments to CO2 enrichment in the factors that determine rgr, such as lar, were much larger in broadleaves than in conifers. Thus, the hypothesis that faster-growing species are more responsive to elevated CO2 was not supported, given contrasting patterns of growth response to CO2 with increasing plant size and age.

Three stands of Phragmites australis (Cav.) Trin. ex Steudel were investigated regarding the relationship between the number of efflux culms and convective ventilation efficiency affecting the hypoxic status of roots and rhizomes. The lack of old (efflux) culms after mowing the preceding winter caused a significantly higher counterpressure within the rhizome, thereby diminishing air flushing rate, i.e. oxygen supply, of rhizomes. The levels of alanine and c-aminobutyric acid in basal culm internodes increased significantly. Both amino acids indicate the hypoxic status of the root and rhizome metabolism of P. australis. Amino acid patterns of the basal culm internodes are discussed with respect to the maintenance of aerobic root metabolism and nutrient availability.

Most natural and semi-natural communities are limited by major nutrients such as nitrogen (N) or phosphorus (P), but most experiments on the effects of ozone on wild plants have used nutrient-rich composts or soil. In order to investigate interactions between ozone and low nutrient supply, two artificially selected lines (ozone-resistant and ozone-sensitive) of two populations Plantago major ssp. major L. were grown on a sandy loam, with (HN) and without (LN) addition of fertilizer. The soil was from a semi-natural grassland that has never been fertilized. Plants were exposed to either charcoal/Purafil®-filtered air (CF=<5 nl O3 l−1) or 70 nl O3 l−1 7 h d−1 from the seedling stage to seed production.

Poor growth (c. 25% of that in HN) of the low-nutrient plants, and leaf concentrations of N and P showed that the LN plants were severely nutrient-limited. In addition to affecting the total dry mass of the plants, the nutrient supply altered seed production, reproductive effort (number of seeds per total mass) and root-to-shoot allocation. Exposure to ozone had significant effects on physiology, growth, and seed production that varied with population, selection line, time, and plant development. There also were significant interactions between ozone effects and nutrient regime. In the Lullington Heath population, ozone reduced plant dry weight at 4 wk only in the LN treatment, and in the sensitive line of the Bush population, seed production was reduced by ozone only in LN. Therefore, contrary to what was expected, in the present experiment, plants given the LN treatment were often more sensitive to ozone than those grown under the high-nutrient regime. This increase in sensitivity was despite the fact that the LN treatment reduced stomatal conductance and ozone flux. It is concluded that there are potentially important interactions between ozone and low nutrient supply that need further investigation, particularly under field conditions.

We tested whether plants allocate proportionately less biomass to roots in response to above-ground competition as predicted by optimal partitioning theory. Two population densities of Abutilon theophrasti were achieved by planting one individual per pot and varying spacing among pots so that plants in the two densities experienced the same soil volume but different degrees of canopy overlap. Density did not affect root[ratio ]shoot ratio, the partitioning of biomass between fine roots and storage roots, fine root length, or root specific length. Plants growing in high density exhibited typical above-ground responses to neighbours, having higher ratios of stem to leaf biomass and greater leaf specific area than those growing in low density. Total root biomass and shoot biomass were highly correlated. However, storage root biomass was more strongly correlated with shoot biomass than was fine-root biomass. Fine-root length was correlated with above-ground biomass only for the small subcanopy plants in crowded populations. Because leaf surface area increased with biomass, the ratio between absorptive root surface area and transpirational leaf surface area declined with plant size, a relationship that could make larger plants more susceptible to drought. We conclude that A. theophrasti does not reallocate biomass from roots to shoots in response to above-ground competition even though much root biomass is apparently involved in storage and not in resource acquisition.

Field-grown trees of Alnus incana (L.) Moench, Alnus glutinosa (L.) Geartner and Betula pendula Roth displayed pronounced differences in responses of light-saturated net photosynthesis (Asat) to herbivory by the alder beetle (Agelastica alni L., Galerucinae), a specialized insect which primarily defoliates alders. We found that photosynthetic rates of grazed leaves increased following herbivory in Alnus but not in Betula. Area- and mass-based Asat of grazed leaves declined linearly with increasing amount of leaf perforation in B. pendula, by as much as 57%. By contrast Alnus glutinosa and Alnus incana increased area-based rates of Asat by 10–50% at all levels of leaf grazing. Given increased Asat in the remaining portion of grazed leaves, a net reduction in photosynthesis per leaf occurred only when the proportion of leaf area grazed exceeded 40% for Alnus incana and 23% for Alnus glutinosa. Since vein perforation by Agelastica alni was observed much more frequently in leaves of Betula than in Alnus, we hypothesized that declining Asat in herbivorized Betula was related to this disruption of water transport. A field experiment with artificial leaf perforation demonstrated a greater decline in Asat in vein-perforated Betula leaves than perforated leaves with midrib veins intact. However, regardless of leaf perforation regime, birch never showed post-perforation increases in Asat. In all species, rates of transpiration of grazed leaves linearly increased and water-use efficiency decreased with increased amount of leaf perforation. In grazed Alnus incana leaves, increasing leaf area consumption by Agelastica alni resulted in an increase of total phenols, a reduction in starch content and no changes in nitrogen concentration in the remaining portion. The increase in photosynthesis in Alnus incana might be related to declining leaf starch concentration or increasing stomatal conductance, but was unrelated to leaf nitrogen concentration. These gas exchange and leaf chemistry measurements suggest that in contrast to B. pendula, Alnus incana and Alnus glutinosa, which are the major host species for Agelastica alni, possess leaf-level physiological adaptations and defence mechanisms which can attenuate negative effects of herbivory by the alder leaf-beetle.

We grew cuttings of two early (mid Oct.) and two late (early Nov.) leaf-fall Populus tremuloides Michx. genotypes (referred to as genotype pairs) for c. 150 d in open-top chambers to understand how twice-ambient (elevated) CO2 and soil N availability would affect growth and C allocation. For the study, we selected genotypes differing in leaf area duration to find out if late-season photosynthesis influenced C allocation to roots. Both elevated CO2 and high soil N availability significantly increased estimated whole-tree photosynthesis, but they did so in different ways. Elevated CO2 stimulated leaf-level photosynthesis rates, whereas high soil N availability resulted in greater total plant leaf area. The early leaf-fall genotype pair had significantly higher photosynthesis rates per unit leaf area than the late leaf-fall genotype pair and elevated CO2 enhanced this difference. The early leaf-fall genotype pair had less leaf area than the late leaf-fall genotype pair, and their rate of leaf area development decreased earlier in the season. Across both genotype pairs, high soil N availability significantly increased fine root length production and mortality by increasing both the amount of root length present, and by decreasing the life span of individual roots. Elevated CO2 resulted in significantly increased fine root production and mortality in high N but not low N soil and did not affect fine root life span. The early leaf-fall genotype pair had significantly greater fine root length production than the late leaf-fall genotype pair across all CO2 and N treatments. These differences in belowground C allocations are consistent with the hypothesis that belowground C and N cycling is strongly influenced by soil N availability and will increase under elevated atmospheric CO2. In addition, this study reinforces the need for better understanding of the variation in tree responses to elevated CO2, within and among species.

The transport of sugars and amino acids into the mycelium of Erysiphe pisi DC. was investigated using two different systems, intact leaf discs and mycelial suspensions. Of the sugars tested, glucose was preferentially taken up by both uninfected and mildew-infected leaf discs, whereas glutamine was taken up by both tissues at a higher rate than lysine or aspartic acid. Leaf discs from infected tissue had a greater uptake capacity than those from healthy tissue for both sugars and amino acids. The uptake of glucose was inhibited more markedly than that of sucrose and fructose by 10 μm carbonyl cyanide m-chlorophenylhydrazone (CCCP), 1 mmN-ethylmaleimide (NEM), 1 mm diethyl pyrocarbonate (DEPC) and 1 mm phenylglyoxal, whereas 1 mm PCMBS (p-chloro-mercuribenzenesulphonic acid) inhibited sucrose uptake to the greatest extent. Uptake of glutamine, lysine and aspartic acid was inhibited similarly by CCCP (80%), NEM (20%), DEPC (70%) and PCMBS (60%). Additionally, leaf discs were used to determine which solutes could be taken up from leaf tissue by the fungus. The uptake of sugars into the mycelium was greater than that of amino acids.

Suspensions of powdery mildew mycelium accumulated glucose at about three times the rate of sucrose or fructose, and the amino acid glutamine was taken up at three times the rate of lysine or aspartic acid. Spores separated from the suspension had a low uptake capacity.

When the reducing sugar concentration of leaf apoplastic fluid was estimated, leaves infected by powdery mildew had much higher amounts in the apoplast, whereas the activity of acid invertase also appeared to be higher in apoplastic fluids from infected leaves. When apoplastic fluid samples were run on SDS gels, an invertase antibody detected two bands in samples from infected tissues that were not found in the uninfected samples.

Wetting of the upper leaf surface of Juglans regia L. and of model surfaces colonized by epiphytic micro-organisms was investigated by measuring contact angles of aqueous solutions buffered at different pH values. During June to October 1995, contact angles of aqueous solutions on the leaf surface of J. regia decreased by angles ranging from 12° (low pH values) to 25° at high pH values. At the end of this vegetation period, wetting was strongly dependent on pH showing significantly lower contact angles with alkaline solutions (pH 9·0) than with acidic solutions (pH 3·0). Contact angle titration measured angles on the leaf surface as a function of the pH of buffered aqueous solutions, covering a pH range from 3·0 to 11·0. Titration curves revealed inflection points around 7·5, indicating the existence of ionizable carboxylic groups at the interface of the phylloplane. Altered leaf-surface wetting properties observed on the intact leaf surface could be simulated in model experiments by measuring contact angles on artificial surfaces colonized by Pseudomonas fluorescens and by epiphytic micro-organisms isolated from the phylloplane of J. regia. Strong evidence is provided that interfacial carboxylic groups derive from epiphytic micro-organisms present on the phylloplane. Results suggest that the age-dependent increase in, and pH dependence of, wetting as leaves mature are related to the presence of epiphytic micro-organisms on the phylloplane. Ecological consequences of increased leaf-surface wetting, concerning the structure of the leaf surface as a microhabitat for epiphytic micro-organisms, are discussed.

Mycelial cord systems, up to 50-cm diameter, of the basidiomycete Phanerochaete velutina (DC.: Pers.) Parmasto, a common woodland saprotroph, grown on non-sterile soil in model laboratory microcosms were baited, after 27 d, with pairs of fresh beech wood blocks (baits), placed at 10 d intervals behind the foraging colony margin. System development was quantified by image analysis. Mean radial extent and hyphal cover increased linearly with time until day 21, but declined before the mycelial systems reached the edges of the laboratory microcosms. The mass (DBM) and border (DBS) fractal dimensions of the mycelial systems changed with time but the ratio DBM[ratio ]DBS became constant after 14 d. A separate central compartment containing the inoculum was supplied with 32P orthophosphate and its translocation to wood baits monitored non-destructively for 73 d. Whilst total 32P acquisition by wood baits increased linearly with time, the proportion of total allocated to baits varied significantly both temporally and according to the length of time that baits had been in contact with the mycelium. Most recently supplied wood baits were not the main sink for supplied phosphorus; rather, the rate of 32P acquisition was initially greatest in baits from which egress of the fungus had already occurred. The rate of 32P acquisition by the most recently added baits increased with time, supported by efflux from other wood baits, which had initially been the main sinks for translocated phosphorus. The results raise important questions about the ecological and functional significance of nutrient partitioning in cord systems and imply that ‘observed’ translocation, rather than being an absolute measure, indicates the degree to which phosphorus is loaded from a translocation stream in regions where it is being actively utilized and/or stored.

Dark septate root endophytes (DSE) are conidial or sterile fungi (Deuteromycotina, Fungi Imperfecti) likely to be ascomycetous and colonizing plant roots. They have been reported for nearly 600 plant species representing about 320 genera and 100 families. DSE fungi occur from the tropics to arctic and alpine habitats and comprise a heterogeneous group that functionally and ecologically overlaps with soil fungi, saprotrophic rhizoplane-inhabiting fungi, obligately and facultatively pathogenic fungi and mycorrhizal fungi. Numerous species of undescribed sterile and anamorphic taxa may also await discovery. Although DSE are abundant in washed root and soil samples from various habitats, and are easily isolated from surface-sterilized roots of ecto-, ectendo-, endo- and non-mycorrhizal host species, their ecological functions are little understood. Studies of DSE thus far have yielded inconsistent results and only poorly illustrate the role of DSE in their natural habitats. These inconsistencies are largely due to the uncertain taxonomic affinities of the strains of DSE used. In addition, because different strains of a single anamorph taxon seem to vary greatly in function, no clear generalizations on their ecological role have been drawn. This paper reviews the current literature on DSE and the ecology and discusses the need for and direction of future research.

To clarify the role of the fungal nitrate assimilation pathway in nitrate reduction by mycorrhizal plants, nitrate reductase (NR)-deficient (NR−) mutants of the ectomycorrhizal basidiomycete Hebeloma cylindrosporum Romagnesi have been selected. These mutants were produced by u.v. mutagenesis on protoplasts originating from homokaryotic mycelia belonging to complementary mating types of this heterothallic tetrapolar species. Chlorate-resistant mutants were first selected in the presence of different nitrogen (N) sources in the culture medium. Among 1495 chlorate resistant mycelia, 30 failed to grow on nitrate and lacked a detectable NR activity. Growth tests on different N sources suggested that the NR activity of all the different mutants is specifically impaired as a result of mutations in either the gene coding for NR apoprotein or genes controlling the synthesis of the molybdenum cofactor. Furthermore, restoration of NR activity in some of the dikaryons obtained after crosses between the different mutant mycelia suggested that not all the selected mutations mapped in the same gene. Utilization of N on a NH415NO3 medium was studied for two mutant strains and their corresponding wild-type homokaryons. None of the mutants could use nitrate whereas 15N enrichment values indicated that 13–27% of N present in 13-d-old wild-type mycelia originated from nitrate. Apparently, the mutant mycelia do not compensate their inability to use nitrate by a more efficient use of ammonium. These different NR mutants still form mycorrhizas with the habitual host plant, Pinus pinaster (Ait.), making them suitable for study of the contribution of the fungal nitrate assimilation pathway to nitrate assimilation by mycorrhizal plants.

Beech nuts (Fagus sylvatica L.) were germinated and grown in soil inoculated with the ectomycorrhizal fungus Laccaria laccata or Paxillus involutus for 18–20 wk. The success of mycorrhizal infection was monitored by measuring the ergosterol contents of the mycorrhizas. Ergosterol levels ranged from 122±23 μg g−1 d. wt (Laccaria mycorrhizas) to 94±36 μg g−1 d. wt (Paxillus mycorrhizas), indicating that ectomycorrhizal symbiosis was established. In root incubation chambers, rates of sulphate uptake and the xylem loading of sulphate of excised mycorrhizas were investigated. Both types of mycorrhizas showed saturation kinetics in external sulphate concentrations from 2·5–1000 μmol l−1. Linearization of these kinetics revealed two phases with low apparent Km (Laccaria mycorrhizas: 15±3 μmol l−1; Paxillus mycorrhizas: 13±3 μmol l−1) and Vmax (Laccaria mycorrhizas: 19±3 nmol h−1 g−1 f. wt; Paxillus mycorrhizas: 25±4 nmol h−1 g−1 f. wt) at low external sulphate concentrations and significantly higher kinetic constants at higher sulphate supplies. Relative xylem loading, i.e. the portion of sulphate loaded into the xylem that was taken up, remained constant over the entire concentration range investigated (c. 4–7% of the sulphate taken up). If trees were supplied for 72 h with different N and sulphur concentrations, both uptake of sulphate and relative xylem loading were unaffected by sulphur availability, but modulated by N supply. Nitrogen depletion diminished the rates of sulphate uptake in Laccaria and Paxillus mycorrhizas. In response to higher N availability combined with sulphur depletion, sulphate uptake of Laccaria mycorrhizas, but not of Paxillus mycorrhizas, increased. Organic compounds considered to be possible signals for the regulation of sulphate uptake were fed to excised mycorrhizas. l-Cysteine but not l-methionine and glutathione (γ-Glu-Cys-Gly) inhibited sulphate uptake of the two mycorrhizas and xylem loading of sulphate was stimulated rather than inhibited by l-Cys in both types. In Paxillus mycorrhizas glutathione had a similar effect. O-Acetyl-l-serine (OAS), a precursor of l-cysteine, stimulated sulphate uptake, but did not affect xylem loading. Apparently, OAS, generated in N metabolism, and l-cysteine, a product of assimilatory sulphate reduction, act as antagonists, together mediating regulation of sulphate uptake.

The Paxillus involutus (Fries) Karsten–Betula pendula Roth association was studied during the early stages of formation. Cytological studies revealed fungal colonization behind the root cap and gradually around the entire root apex. Ultrastructural investigations were carried out and insoluble polysaccharide distribution was followed. The density of starch grains increased in plant cells especially after 4 d of contact between the two partners, but later on decreased strongly in the root cap. Large amounts of glycogen were revealed in the hyphae in certain mycorrhizal regions after 6 d of contact: in the Hartig net, in the inner sheath but only near the net, and all along the outer sheath surrounding the mycorrhiza. Thickenings of the epidermal cell walls were detected as early as 2 d after contact and then varied according to the distance from the root tip. Such polysaccharide distributions are assumed to show a transfer of carbohydrates from the root to the fungus and are discussed in terms of carbon requirements for both partners.

Whereas much is known of the short-term growth response to elevated atmospheric CO2 concentrations, [CO2]elev, there is relatively little information on how the response of native species is modified by temperature, despite the fact that an increase in global mean temperature is expected to accompany the rise in [CO2]. In this study, five functionally related annual native species were exposed to different combinations of ambient and elevated [CO2] and temperatures in order to assess their response in terms of growth and allometry. Fast-growing annuals were selected for the study because their growth responses could be assessed over a major portion of the plant's life cycle and in as short a period as 8 wk. Plants were grown in eight hemi-spherical glasshouses, programmed to track outside ambient conditions and provide a replicated experimental design. Treatments comprised (i) current ambient [CO2] and temperature, (ii) elevated [CO2] (ambient+34 kPa), and ambient temperature (iii) ambient [CO2] and elevated temperature (ambient+3°C) and (iv) elevated [CO2] and elevated temperature (T°Celev). All five species responded positively to [CO2]elev, although the response was statistically significant for only one, Poa annua L. Averaged over all five species, [CO2]elev increased total plant biomass by 25% (P=0·005) at 56 d, reflecting a proportionally greater increase in leaf and stem mass relative to root weight. Elevated [CO2] had no effect on leaf area, either at the individual species level or overall. Elevated T°C, by contrast, had little effect on shoot growth but increased root mass on average by 43% and leaf area by 22%. Few interactions between elevated [CO2] and T°C were observed, with the CO2 response generally greater at elevated than ambient T°C. Both [CO2]elev and T°Celev resulted in a transient increase in relative growth rate, (rgr), during the first 14 d exposure and a 3°C increase in temperature had no effect on the duration of the response. CO2 stimulation of growth operated through a sustained increase in net assimilation rate. (nar), although the potential benefit to rgr was offset by a concurrent decline in leaf area ratio (lar), as a result of a decrease in leaf area per unit leaf mass (sla). The response to T°Celev was generally opposite of that to [CO2]elev. For example, T°Celev increased lar through an increase in sla and this, rather than any effect on nar, was the major factor responsible for the stimulation of rgr. Allometric analysis of CO2 effects revealed that changes in allocation observed at individual harvests were due solely to changes associated with plant size. Elevated T°C, by contrast, had a direct effect on allocation patterns to leaves, with an increase in leaf area expansion relative to whole plant mass during the initial stages of growth and subsequent increased allocation of biomass away from leaves to other regions of the plant. No change in the allometric relation between roots and shoots were observed at either elevated [CO2] or T°C. We conclude, therefore, that allocation of biomass and morphological characteristics such as sla, are relatively insensitive to [CO2], at least when analysed at the whole-plant level, and where changes have been observed, these are the product of comparing plants of the same age but different size.

The sampler extracts uncompressed cores of 13·3 cm in diameter, up to 70 cm long, from the surface layers of peat. It has two close-fitting concentric cylindrical tubes, the outer one acting as a cutter and the inner one as a collector. As the outer tube is introduced by rotation into the peat, the cut core is collected in the inner tube which is maintained in a fixed position during the rotation phase and then pushed down stepwise. This limits friction between the peat core and the wall of the corer and prevents compression or distortion of the peat. These problems are also reduced by means of three skew cutters allowing the peat to be supported during the slicing action. Air can penetrate between the tubes to the lower end of the core, suppressing any suction effect during withdrawal. The sampler has been tested and has worked satisfactorily in many different peat types.