The presence of host plants was found to be a key determinant of soil infectivity for endophytes of epacrids growing in south-west Australian jarrah forest carrying a sparse epacrid understorey. A comparable Banksia woodland with higher density of epacrids showed more uniform levels of infective endophytes, presumably because of closer overlap of host-supported patches of endophyte. Disturbed sites in jarrah forest, in which topsoil had been recently returned following bauxite mining, initially showed extremely low endophyte infectivity, probably due to disruption of the hyphal network, absence of host plants and/or increased competition from soil micro-organisms antagonistic to the endophytes. As the system stabilized and epacrids recruited and grew, inoculum potential of the soil re-established and by 12 yr it equalled that of adjacent undisturbed native forest. At disturbed sites with sparsely distributed adult members of the Epacridaceae, endophyte inoculum proved to be adequate only directly adjacent to the epacrids and declined steeply to negligible levels at only 40 cm radially distant from a host plant. The significance of live epacrid root systems on survival of endophyte inoculum in Banksia woodland was examined following removal of shoots of adult plants of the endemic epacrid, Leucopogon conostephioides DC. Coincident with demise of roots of the detopped plants, endophyte inoculum potential of closely adjacent soil declined by 50% during the growing season. However, the effect was short lived and infectivity rose the following year to equal that of undisturbed adjacent woodland as mycelial matrices supported by neighbouring epacrids invaded the depleted study areas.

Cuticular hydrocarbon composition was determined for 18 populations of Avicennia germinans (Avicenniaceae) collected from West Africa, Florida, the Pacific coast of Mexico and French Guyana. Variation in covariance structure among the hydrocarbons was evaluated from correlations among the traits for each of the populations and from a hierarchical common principal components analysis. Principal components ordinations of populations based on the 171 z* transformed correlation coefficients, onto which a minimal spanning tree was superimposed, suggested a network in which French Guyanan populations formed a nexus from which African populations differentiated biochemically from Floridan and Mexican groups. Common principal components analysis provided further support for the differentiation in covariance structure among these biochemical traits of African populations. Pacific coast Mexican populations appeared to have diverged less in covariation among traits from Atlantic American sources than did the northern (Floridan) and southern (French Guyanan) Atlantic American populations from one another. The complete isolation of Pacific coast sources after emergence of the Central American isthmus during the Pliocene provides a reference for comparison of levels of differentiation among regions that suggests an underlying pattern of divergence in this species. Partial Mantel matrix tests revealed significant geographic effects, with no significant climatic effects. Our results provide support for recognition of a major differentiation between Old and New World sources within the taxon and indicate the need for a full revision of this species.

Soilborne pathogens, especially Fusarium oxysporum, are responsible for damping-off and root necrosis in Eucalyptus nurseries. New technologies are increasingly considering strategies for plant disease control other than chemical fungicides. Among these, natural fungal antagonists, which are colonizers of the root cortex, are potential biocontrol agents. An in vitro system was used: (1) to test the pathogenic effects of F. oxysporum strain Foeu1 which was recovered from a forest nursery soil; (2) to explore the potential of the nonpathogenic F. oxysporum strain Fo47, which is known for its efficiency in biological control, to suppress damping-off of Eucalyptus seedlings; (3) to compare the patterns of root colonization and host response to invasion by the two Fusarium strains inoculated separately in a time-course study. Root inoculation of E. viminalis with F. oxysporum strain Foeu1 caused damping-off in young seedlings in vitro, whilst disease symptoms were not visible in plants inoculated with F. oxysporum strain Fo47 or when both strains (Foeu1 + Fo47) were inoculated simultaneously. Each strain showed similarities in patterns of root tissue colonization, and in the processes of root penetration and initial colonization. Differential effects on root tissue were observed with fungal development within the cortex: ingress of strain Foeu1 was accompanied by severe host-cell alterations whilst no tissue damage occurred with development of strain Fo47.

The short-term polyamine response to inoculation, with tobacco mosaic virus (TMV), of TMV-inoculated NN (hypersensitive) and nn (susceptible) plants of Nicotiana tabacum (L.) cv. Samsun was investigated. Free and conjugated polyamine concentrations, putrescine biosynthesis, evaluated through arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) activities, and putrescine oxidation, via diamine oxidase (DAO) activity, were analysed during the first 24 h from inoculation. Results were compared with those of mock-inoculated control plants. In NN TMV-inoculated plants undergoing the hypersensitive response (HR), free putrescine and spermidine concentrations had increased after 5 h compared with controls; polyamine conjugates also tended to increase compared with controls. In both virus- and mock-inoculated plants, ADC and ODC activities generally increased whereas DAO activity, which was present in controls, was detectable only in traces in inoculated tissues.

In TMV-infected susceptible plants, free putrescine and spermidine concentrations were lower at 5 h relative to controls, as were polyamine conjugates. No differences were revealed in ADC and ODC activities whereas DAO activity was not detectable. These results further support the hypothesis that polyamines are involved in the response of tobacco to TMV and that, only a few hours after inoculation, the response of hypersensitive plants is distinct from that of susceptible ones.

A series of glasshouse experiments was used to determine mycorrhiza-specific isozymes (MSIs) produced by five species of Glomus colonizing roots of a desert shrub legume (Anthyllis cytisoides L.), Thymus vulgaris L. and Allium porrum L. over time. Extracts of colonized roots were electrophoresed on non-denaturing polyacrylamide gels (PAGE) and stained for 10 different enzymes. Staining protocols for esterase, glutamate oxaloacetate transaminase, alkaline phosphatase and malate dehydrogenase provided MSIs for the mycorrhizas formed by different arbuscular mycorrhizal (AM) fungi that had colonized roots of the three host plants. There was no apparent correlation between levels of colonization or arbuscular intensities, at or between each sampling, and the presence of MSIs. The development of colonization by the AM fungi differed little between the three plants when assessed with two methods of estimating fungal biomass. The variety of MSIs detected might reflect the diversity of metabolic activities of these Glomus species and, possibly, differing ecological functions. The high-level induction of two alkaline phosphatase MSIs in the mycorrhizas of Anthyllis cytisoides colonized by Glomus microaggregatum BEG56 was used to track the fate of this fungus when the same plant was inoculated and transplanted into a semi-arid site in south-east Spain. The probable fungal origin of the isozyme was indicated by detection of the same isozyme in the extraradical mycelium formed by Glomus microaggregatum BEG56 on Allium porrum. The use of MSIs to detect the mycorrhizas of species of Glomus in colonized roots is discussed.

A factorial analysis was conducted to investigate the effects of different levels of photosynthetic photon flux (PPF) and CO2 concentration on the interactions between the vesicular–arbuscular endomycorrhizal fungus Glomus intraradices and potato plantlets (Solanum tuberosum) cultured in an in vitro tripartite system. We observed that CO2 enrichment from 350 to 10000 ppm stimulated root colonization by the fungus, and that this stimulation was more pronounced under high PPF (300 μmol m−2 s−1) than low PPF (60 μmol m−2 s−1). Consistent with these observations, the effects of G. intraradices on dry matter production in potato plantlets were strongly dependent on the CO2 and PPF levels during cultivation. There was no significant effect of the mycorrhizal fungus on dry matter production at 350 ppm of CO2. However, under the high CO2 concentration, mycorrhiza had opposite effects on dry matter production depending on the PPF: a decrease (−21%) and a stimulation (+25%) of dry matter production after 2 wk of growth under low and high PPF, respectively, were observed in presence of G. intraradices relative to plantlets grown in its absence. Furthermore, in mycorrhizal plantlets grown under high levels of both PPF and CO2, the chlorophyll and carotenoid contents as well as the quantum yields of photosynthetic electron transport and the photochemical quenching qP of the chlorophyll-a fluorescence measured near the PPF during growth were all higher than in non-infected plantlets. Our results therefore indicate that mycorrhizal G. intraradices can alleviate the down regulation of photosynthesis related to sink limitation, and its effect on dry matter production is strongly dependent on the levels of CO2 and PPF during growth which determine the balance between the photosynthetic carbon uptake by the plantlets and the carbon cost by the fungus.

The aim of this work was to assess whether or not oxidative stress had developed in a dwarf shrub bilberry (Vaccinium myrtillus L.) under long-term exposure to enhanced levels of ultraviolet-B (u.v.-B) radiation. The bilberry plants were exposed to increased u.v.-B representing a 15% stratospheric ozone depletion for seven full growing seasons (1991–1997) at Abisko, Swedish Lapland (68°N). The oxidative stress was assessed on leaves and stems by analysing ascorbate and glutathione concentrations, and activities of the closely related enzymes ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2). The affects of autumnal leaf senescence and stem cold hardening on these variables were also considered. The results showed that the treatment caused scarcely any response in the studied variables, indicating that u.v.-B flux representing a 15% ozone depletion under clear sky conditions is not sufficient to cause oxidative stress in the bilberry. It is suggested that no strain was evoked since adaptation was possible under such u.v.-B increases. The studied variables did, however, respond significantly to leaf senescence and especially to stem cold hardening.

Sequential harvests of cotton seedlings grown in soil cores enabled the quantification of the density of arbuscular mycorrhizal fungi to detect the effects of time, cultivation and periodic wetting of the soil. Cotton seedlings grown in soil cores from three locations formed arbuscular mycorrhizas at similar rates when cores were stored dry for up to 18 months. Disturbance of dry cores followed by dry storage for 18 months did not reduce the rate of establishment of mycorrhizas. Periodic wetting and drying of the cores, especially if the cores had first been disturbed, significantly reduced the rate of establishment of mycorrhizas. We suggest that long fallow disorder is possibly caused by falls of rain in clay soils of eastern Australia used to grow cotton. The proportion of the root with mycorrhizas at 3 wk was strongly correlated with the infection at 8 wk. We also suggest that it might be possible to predict maximum levels of infection and early uptake of phosphate of seedlings by determining the proportion of roots that are mycorrhizal 3 wk after emergence of cotton seedlings.

Maternal-environmental effects on subsequent progeny life-history traits were evaluated in squash (Cucurbita pepo L.) in terms of the amount of time available for seed development, and the timing of fruit production. Progeny arising from three kinds of fruit were compared. Plants from which fruits were removed 3 d post-pollination throughout the growing season developed only ‘late’ fruits (during 10–15 d) at the end of the growing season; on control plants both ‘early’ and ‘late’ fruits developed (both types allowed to ripen fully). Seed from each type of fruit was weighed individually and categorized into three size classes, then germinated and raised to maturity, including regular harvesting of all fruits 3 d post-pollination. Maternal effects were evident for both vegetative and reproductive traits and carried over to later stages. In contrast, effects due simply to seed size disappeared by day 30 for leaf variables and day 60 for male flower production. Within a seed-size class, progeny arising from fruit of treated plants produced significantly more leaves, with greater size, and more male flowers than those arising from fruit of control plants, while the reverse was true for fruit number and fruit mass. This result is discussed in terms of possible gibberellic acid involvement. In control plants, progeny arising from seeds in the large, fully mature ‘early’ fruits produced significantly more, and larger leaves by day 30 than did those from late fruits (suggesting differential provisioning in seeds during development). Male flower production had a highly significant positive correlation with vegetative mass and a significant negative correlation with fruit production.

Ozone (O3)-sensitive and tolerant clones of aspen (Populus tremuloides) were exposed to O3 at 1.0, 1.7 and 3.0 times the concentration in ambient air at Ithaca, NY, USA (×1.0, ×1.7 and ×3.0) for 3 months. Visible foliar injury occurred within a few days of the initiation of treatments and developed continuously in ×1.7 and ×3.0 treatments. Leaf senescence began earlier in trees exposed to greater-than-ambient treatments. Gas-exchange variables were measured five times over the growing season. Net photosynthesis was progressively decreased and finally reduced by 40 and 70% on tolerant and sensitive clones, respectively, but stomatal conductance was not affected by the O3 treatments. As stomatal conductance (gs) values did not differ in the two types of aspen, we conclude that this is not the defense mechanism to O3 in aspen. At the end of the season, dry weight was reduced by up to 55 and 35% in sensitive and tolerant clones, respectively. Ozone effects were significant and linear on foliar injury, biomass and growth variables such as height, diameter of stem and total leaf area. The levels of two antioxidants, ascorbic acid and glutathione, were investigated to determine if a clonal difference occurred. Concentrations of the free-radical scavengers did not differ in the clones, nor did they seem to be induced by O3. A cumulative O3 index, SUM06 (the sum of the total μl l−1 of exposure when the O3 concentration exceeded 0.06 μl l−1), was highly correlated with most foliar injury variables and gas-exchange variables except gs in higher O3 treatments. The reduction of carbon gain due to O3 is discussed with regard to foliar damage and biomass decrease.

To analyse the effect of arbuscular mycorrhizal (AM) colonization on tomato gene expression, two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) patterns of crude extracts, soluble and membrane proteins of tomato roots, either mycorrhizal and the AM fungus Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe or non-mycorrhizal, have been compared. In the three fractions analysed, AM colonization induced up-regulation with down-regulation of the synthesis of polypeptides already present in tomato roots and induction of some new polypeptides. Separation of root extracts into soluble and membrane fractions allowed us to identify two soluble, and five membrane-bound, newly induced polypeptides in AM roots. Comparison of the protein patterns of AM roots with those of the external mycelium of G. mosseae showed that one of the newly induced polypeptides might correspond to a fungal polypeptide. By using this experimental approach, we have been able to detect 44 polypeptides that are differentially displayed in tomato roots as a consequence of the establishment of the AM symbiosis.

Few topics in ecology are as intriguing or bedeviling as comparative studies of different types of mycorrhizas formed in the same plant species. Attempts to determine the relative benefits from each fungal type to the host plant are fraught with difficulties (Jones et al., 1998), and for this reason plants that form tripartite associations with arbuscular and ectomycorrhizal fungi make ideal experimental systems. Just such a tripartite system is explored in a report in this issue by Chen et al. (pp. 545–556).

Why compare mycorrhizas? Although both ecto- and arbuscular mycorrhizas are generally known to increase the uptake of nutrients such as phosphorus and nitrogen in infertile soils, their functions and the benefits they provide to their host plants may not be equivalent (Jones et al., 1998). Hence the ecological benefits of the two types of symbiosis are of great interest to plant community ecologists and researchers studying nutrient cycling. Arbuscular mycorrhizas are formed as a symbiosis of plant roots with primitive fungi of the order Glomales (Zygomycetes), while ectomycorrhizas are formed with higher basidiomycetes and a few ascomycetes. Only a few plant genera and species are capable of forming both types of association, sometimes on the same root tip (Fig. 1), but it is these that are so useful in comparative studies.

A β-1,4-endoxylanase from the ericoid mycorrhizal fungus H. ericae has been purified to electrophoretic homogeneity using isoelectric focusing, ion exchange and gel permeation chromatography. The enzyme has an isoelectric point of 4·85–5·20 and a molecular weight of 58·4 kDa. The apparent S0·5 of the enzyme for soluble birchwood glucuronoxylan is 3·75 mg ml−1 and the Vmax 468·0 nkatal mg−1 protein. The pH optimum for activity is 4·5 and that for stability is 3·5–4·0; these values are discussed in the context of the pH of the mor humus. The role of wall-degrading activities in the establishment of the ericoid mycorrhizal symbiosis is considered.

This paper reports general patterns of relative growth rate and related traits in response to elevated atmospheric CO2 in eight woody species ranging widely in life form, leaf habit, taxonomy and ecology. Young plants of these species, all of comparable ontogenetic phases, were grown simultaneously in large containers with favourable nutrient and water availability in transparent outdoor chambers at 350 and 700 μl l−1 CO2 for one growing season. We found the following consistent responses. (1) All species grew faster at elevated CO2, whereas the following leaf and allocation traits were consistently lower in CO2-enriched environments: specific leaf area (quotient of leaf area and leaf weight), leaf area ratio (quotient of total leaf area and plant weight), weight-based foliar N concentration and, to a smaller extent, leaf weight fraction (quotient of leaf weight and plant weight). (2) There was important interspecific variation in the magnitude of the response of relative growth rate to CO2. Specific leaf area at ambient CO2 explained 88% of the variation in relative growth rate response to CO2 among the eight species. At ambient CO2, relative growth rate itself, was significantly correlated with the relative growth rate response to CO2 only if the leafless species Ulex gallii was excluded from analysis. (3) The four deciduous species had a significantly stronger relative growth rate response to CO2 than the four evergreens. This corresponded with their generally higher specific leaf area. (4) Specific leaf area and leaf habit might be useful for scaling up exercises, as easy-to-measure substitutes for growth responses of (woody) vegetation to elevated CO2. However, the usefulness of such traits in this context needs to be tested in realistic, longer-term manipulative experiments in real ecosystems.

In two open, flow-through systems 11 lichen species were fumigated with concentrations between 0·036 and 2·0 ppm (c. 94·3–5240 μg m−3) SO2. Sulphur dioxide uptake was monitored concurrently as a mass balance between incoming and outgoing SO2 concentrations. The rate of uptake ranged from 0·025 (±0·006) to 0·7 (±0·16) nmol SO2 g−1 d. wt s−1, for all species. After the first hour of fumigation the uptake rate was almost constant during the following 5 h for concentrations up to 1·0 ppm SO2. At higher concentrations the uptake declined over time continuously. Within the range of measured SO2 concentrations the uptake rate was linearly correlated with SO2 concentrations (r2=0·90). Thalli which were killed by heat treatment or in which respiration was inhibited by azide treatment did not show significantly different SO2 uptake from living thalli. No differences in uptake were found during fumigation in the light versus in the dark.

The post-cytokinetic guard cells of Asplenium nidus display a prominent perinuclear microtubule system and a few microtubules under the periclinal walls. Afterwards, microtubules appear on the whole surface of the ventral wall, whereas those below the periclinal walls proliferate and tend to become parallel with the ventral wall. The perinuclear microtubules gradually diminish but persist in later stages of guard cell differentiation. In post-cytokinetic guard cells, actin is found in the perinuclear cytoplasm and in the cortical cytoplasm lining all the walls. In differentiating guard cells, the following cortical microtubules and actin filament ‘systems’ appear in succession: (a) radial microtubule and actin filament arrays beneath the periclinal walls converging on the stomatal pore region, (b) anticlinal microtubule bundles, which are co-localized with actin filaments, along the ventral wall outlining the region of the stomatal pore, (c) periclinal microtubules and actin filaments on the polar ventral wall ends. These cytoskeletal systems, except for the radial actin filaments, persist in advanced stages of guard cell differentiation. Instead of the radial actin filaments, a prominent actin filament reticulum is organized under the margins of the developing wall thickenings of the stomatal pore. In addition, an extensive endoplasmic actin filament reticulum develops around the plastids. It seems likely that the successive microtubule systems in guard cells are formed by putative microtubule organizing centres operating in a definite spatial and temporal succession. Guard cell morphogenesis is the outcome of a definite process, in which the cortical microtubule cytoskeleton plays the primary role, implicated in the deposition of cellulose microfibrils and probably of the local wall thickenings. Callose or a callose-like glucan is deposited on the whole surface of the nascent ventral wall and in the wall regions where thickenings are deposited. Finally, the guard cells of Asplenium assume a kidney shape and display polar hypostomatic swellings. Particular structural features established in guard cell mother cells affect guard cell morphogenesis.

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.

The nodulation status and nodule morphology of 62 taxa of Leguminosae in a rain forest in French Guiana are reported according to the taxonomy of the family. The N2-fixing species are then fitted into ‘functional groups’ according to their behaviour towards illumination, in order to evaluate their importance in the global dynamics of the stand. The results showed that 67% of the observed species were nodulated (50, 71 and 77% of the Caesalpiniaceae, Mimosaceae and Papilionaceae, respectively). In the Caesalpiniaceae, nodule-like structures were reported in the genus Crudia and in the species Senna quinquangulata, although this needs to be confirmed. All the nodules studied in this subfamily were astragaloid and mucunoid. In the Mimosaceae, the ability of a new genus (Balizia) to form nodules was reported, as well as nodulation on aerial roots in Inga stipularis. The nodules studied were mainly mucunoid. In the Papilionaceae, nodulation on aerial roots in Poecilanthe hostmannii and on conventional roots of the genus Paramachaerium were reported for the first time. All types of nodular structures were found in this subfamily but the structures were quite uniform at the tribal level. These are consistent with suggestions that nodule morphology has a taxonomic value. Eight functional groups of N2-fixing species are proposed, ranging from light dependance to shade tolerance. These results indicate the important role played by N2-fixing species in the global dynamics of the stand and that N inputs by N2 fixation were continuous along the gradient of energetic resources that characterizes the silvigenetic process. The interactions between the photosynthetic capacities of the species and the ability to fix N2 in low light conditions are discussed.

Sporulation in the floating fern Azolla filiculoides Lam. is both frequent and widespread in Britain and might therefore play a greater part in the population dynamics of the species than has been suggested by earlier reports. In laboratory experiments, increasing plant density and/or phosphorus supply resulted in increased sporulation. It was estimated that a thick mat of 8 kg m2 fresh biomass can produce 380000 microsporocarps and 85000 megasporocarps per m2.

Light and temperatures >10°C were necessary for sporocarp germination. Sporocarps could survive exposure to both low temperatures (5°C for at least 3 months) and sub-zero temperatures (−10°C for at least 18 d). Sporocarps were found to survive storage in water for 3 yr and to germinate from mud samples collected in the field. In laboratory culture, sporeling growth and survival were optimal at 15°C.

There is some evidence that A. filiculoides might have adapted to the British climate since its introduction.

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.