The inter- and intracellular distribution of the elements calcium, potassium and sodium in non-mycorrhizal and mycorrhizal roots of Pinus sylvestris dependent on different external nutrient supply conditions was detected by energy-dispersive X-ray microanalysis after cryofixation, freeze-drying and pressure infiltration of the material. In non-mycorrhizal and mycorrhizal roots, calcium was mainly detectable in the apoplastic regions. The levels in vacuoles and cytoplasm were near the limits of detection by X-ray microanalysis. Incubation with high concentrations of potassium and sodium, or mycorrhizal infection with Suillus bovinus and Pisolithus tinctorius reduced the amounts of calcium detectable in the roots, especially in the apoplast of cortical cells. The studies revealed that: potassium is mainly localized in cytoplasm and cell walls; the cytoplasmic content is regulated over a wide range of external potassium concentrations; potassium levels in the inner parts of roots are higher than in the outer parts. Mycorrhizal infection with Suillus bovinus had no effect on the inter- and intracellular distribution of potassium in roots but, if the external supply was low, the potassium content in shoots was reduced. In non-mycorrhizal pine roots and those infected with Paxillus involutus an increase in the sodium content of all cell compartments was observed after treatment with high external concentrations of NaH2PO4. However, an increase in sodium content in mycorrhizas of S. bovinus was not detected. The X-ray microanalytical results are discussed in relation to the apoplastic movement of nutrients in non-mycorrhizal and mycorrhizal fine roots of pine and to the demand for these nutrients in different intracellular compartments.

Experiments were set up to assess the relative impacts of grass lamina fragment density, size and quality on the activity and growth of four fungi in a particulate soil-like matrix. The fungi studied were Cladosporium cladosporioides, Fusarium lateritium, Phoma exigua and Trichoderma viride, all of which are common inhabitants of UK upland grassland soils. Resource quality was varied by using three contrasting grasses as sources of lamina fragments: Lolium perenne, Agrostis capillaris and Nardus stricta. All the fungi were able to forage effectively through the soil-like matrix (at a rate of 1–2 ml matrix d−1) and colonize and partially decompose available lamina fragments (up to 40% d. wt loss). Foraging rates (ml matrix d−1) were affected by lamina fragment species but not by fragment density or size. In general, F. lateritium and T. viride foraged at a faster rate than the other species. Mycelial activity in the soil-like matrix was directly proportional to total lamina fragment availability and was unaffected by fragment size. Biomass production on solid media was also directly related to substrate (carbohydrate) availability. The results indicate that these fungi can adjust their growth patterns in response to fragment density so as to maximize foraging efficiency (energy acquired per unit exploratory biomass production). Differences in lamina fragment species were responsible for up to 50% reduction in mycelial activity.

To test the ability of plants to integrate small-scale imbalances in soil nitrate and phosphate patches, plant growth and acquisition of nitrate and phosphate were measured for the perennial grass Agropyron desertorum (Fisch. ex Link) Schult. and the shrub Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) Beetle in soil where the principal supply of nitrate and phosphate came from two enriched patches. The soil was calcareous loamy-skeletal Typic Haploxerolls. These patches were applied in two treatments: either nitrate and phosphate were applied in both patches (balanced treatment) or one patch contained only nitrate and the other only phosphate (unbalanced treatment). The same total quantity of nutrients was applied in both treatments and these included 15N and 32P tracers. The plants were in large pots in open field conditions. There were no significant differences in total biomass production and nitrogen concentration between the two treatments, indicating that both species had the physiological ability to integrate soil nutrient resources. Artemisia was able to acquire more phosphate in the unbalanced treatment, probably due to the high local solution phosphate concentration. Generally Artemisia acquired more N and P than did Agropyron.

We conducted two experiments to investigate the expression of shade avoidance in response to low ratios of red to far-red irradiation (R[ratio ]FR) in the C4 perennial grass Schizachyrium scoparium at two levels of above-ground (photosynthetic photon flux density (PFD) 400–700 nm) and below-ground (soil volume) resource availability and in plants of two ages. Young plants showed greater sheath and ramet height in response to low R[ratio ]FR and old plants showed reduced ramet initiation in experiments one and two, respectively, but both responses were not expressed simultaneously in either group. Growth of all ramet variables, including ramet initiation, was suppressed in small as opposed to large soil volumes. By contrast, architectural variables, but not ramet initiation, were greater for plants grown in low as opposed to ambient PFD. However, expression of shade avoidance to low R[ratio ]FR was not significantly affected by either level of PFD or soil volume. We must conclude that the levels of resource availability provided do not modulate shade avoidance in this perennial grass. These results demonstrate that S. scoparium is capable of expressing shade avoidance in response to low R[ratio ]FR, but inconsistent juvenile ramet initiation and architectural responses in plants of different ages and phenological stages of development indicate that the shade avoidance response might not be expressed consistently throughout the life of plants.

Gynodioecy is a dimorphic breeding system in which hermaphrodites coexist with male steriles in natural populations. Theoretical models predict that without any compensation in female fitness, male steriles will quickly disappear from a population. The amount of compensation required depends upon the mode of inheritance. In this study we investigated whether performance, during early vegetative growth, could play a role in the maintenance of male steriles in populations of gynodioecious self-incompatible Plantago lanceolata. This was accomplished by comparing the growth of the predominant male-sterile type from a natural population with two hermaphroditic types. One of the hermaphroditic types differed from the male sterile only in nuclear genome, having the same type of cytoplasm. The other type was nuclearly nearly isogenic, but had a different cytoplasm. Plants were grown under controlled conditions, either in near-optimal hydroponic solutions, or in a range of N- supplies on sand. A detailed growth analysis was carried out, and the relative growth rate (RGR) of each type was analysed into its underlying components, the net assimilation rate, the leaf mass ratio and the specific leaf area. No difference between the sex types in relative growth rate was found and, in the components underlying the RGR, only a few small differences were detected. In none of the growth parameters examined did the male steriles differ from either hermaphroditic type. Differences in plant growth related to N-supply, differences in growth on hydroponics compared with sand culture, as well as the maintenance of male sterility in populations of P. lanceolata are discussed.

Possible limitations of sink strength for fructan storage in tubers of Jerusalem artichoke (Helianthus tuberosus L. cv. Waldspindel) were studied in 2-yr field experiments. Treatments included the removing of side branches and the breaking of apical dominance in unbranched plants. Data from both treatments and the comparison of results obtained for 2 yr, which differed in temperature and total irradiance, indicated that fructan storage in tubers during the storage phase was not limited by supply of assimilate (sucrose). Moreover, fructan concentrations were very constant despite large variations in tuber yields and yield components (e.g. number of tubers per plant, tuber length). However, stimulation of cell expansion and diameter of tubers increased fructan concentrations, probably owing to a larger vacuolar volume in the storage cells. We concluded that fructan storage in tubers of Jerusalem artichoke is not source-limited as far as carbon import into tubers is concerned. However, a strong shoot control, most probably regulated via phytohormones, limits sink strength. Fructan concentrations in tubers might not only be increased by sink activity (fructan-synthesizing enzymes) but also by sink capacity (vacuolar volume). In this respect the shoot might play a decisive role not only as a temporary storage pool for carbohydrates but also as a source of native growth-regulators which control sink capacity.

The association between willow (Salix) and rust (Melampsora) is highly specific. Willows named Salix burjatica, S. dasyclados (S.×dasyclados) and S.×calodendron are important in renewable-energy plantations in the UK and western Europe. There has been much controversy over their origin, species status and nomenclature. It has been suggested that they have originated from hybridization between. S. caprea, S. viminalis and S. cinerea. In the present work, 59 willow clones were investigated through morphological examination and detached leaf inoculation using willow differentials, for their association, in southwest England, with M. capraearum and three pathotypes of Melampsora epitea (Me-A, B and C). M. capraearum was found on all clones of S. caprea and its hybrids with S. aurita; Me-A on all S. viminalis clones; Me-B on wild S. cinerea, S.×calodendron, S.×dasyclados ‘De Biardii 445’ and S. ‘Spaethii’; Me-C on all S. burjatica clones and most S.×dasyclados clones. Both M. caprearum and Me-A infected all S.×sericans (S. caprea×viminalis) clones and S.×dasyclados ‘LA041/03’. We suggest that S.×dasyclados ‘LA041/03’ should be treated as S.×sericans (S. caprea×S. viminalis); S. burjatica, S. dasyclados and S.×dasyclados as synonyms; S.×dasyclados ‘De Biardii 445’ as S.×calodendron ‘De Biardii 445’; and S. ‘Spaethii’ as S.×calodendron ‘Spaethii’.

Re-analysis of data from Salisbury (1974) shows no significant relationship between seed size and habitat conditions, a relationship for which this paper is frequently cited as support. The discrepancy between the results reported here and those found in the original paper is due to Salisbury's ‘evidence’ being a table of congeneric pairs collected specifically because they possessed the target relationship. This paper emphasizes particularly the need for an unbiased sampling of species pairs in comparisons attempting to define ecological relationships. The analysis presented here represents the fourth such instance in which previously assumed robust examples of the relationship between seed size and habitat type are shown not to be so when the appropriate methods are used to account for relatedness among species.

For a number of generations, we followed the frequency, performance and fecundity of an initial mixture (50[ratio ]50) of triazine resistant (R) and susceptible (S) but otherwise near-isogenic lines of Brassica rapa (for 3 yr) and of Chenopodium album (for 2 yr) in neighbouring experimental garden plots, which differed in aspect (north-facing versus south-facing), shading, and transparent cover from precipitation. Each of eight treatments was replicated four times per species. Seed from each plot was kept separate and sown back in its plot of origin to provide the next generation. For both Brassica and Chenopodium, R frequency changed between generations. In Brassica R frequency declined consistently from an initial 0.5 and, after 2 yr, R plants had disappeared in all replicates in two treatments and averaged <0.126 in the remaining treatments. However, R frequencies in the smaller second generation samples in each year were less consistent. In Chenopodium, R frequency increased consistently from an initial 0.5 in all treatments and replicates during 1995 to average 0.772 on south-facing sites and 0.675 on north-facing sites. However, in 1996 Chenopodium R frequency did not change significantly from that in 1995 for any treatment. Brassica S plants were more fecund that R plants, except in shaded conditions, and south-facing plots produced significantly more S seeds than north-facing plots. Both Brassica plants and plots were more productive in 1996 than in 1995. By contrast, Chenopodium was much less productive in 1996, a season with more climatic extremes between plots than 1995. In 1995, R plants were more fecund than S plants in south-facing plots and in covered conditions, but this difference was not detected in 1996. South-facing Chenopodium plots were more productive than north-facing plots in 1995, but the reverse was the case in 1996. Cover resulted in an increase in seed production in Chenopodium on south-facing plots in 1995, but a decline in 1996. We conclude that selection might act against triazine-resistant plants in B. rapa under the climatic conditions in the UK, but in C. album, which is more susceptible to extreme conditions of light and water stress, triazine-resistant phenotypes might predominate in low stress cool moist conditions. We suggest that a relationship might exist between the overall climatic tolerance of a species, and climate thresholds beyond which herbicide-resistant phenotypes might spread. Thus, in the absence of herbicide, it is not inevitable that the frequency of R phenotypes will decline in field conditions.

CH3Cl emissions by freshly harvested tubers of 61 potato cultivars ranged from less than 4 to 650 ng g−1 f. wt d−1. In experiments with Anna, the cultivar displaying the highest release rate, maximum emission of CH3Cl occurred at 20°C but the rate diminished after 48 h, a decrease due in part to inhibition of CH3Cl release by the accumulation of CH3Cl in the headspace. In 1995 and 1996, CH3Cl emission by tubers was first detectable 6 wk before the normal harvest date. If tubers were stored at 20°C immediately following harvest, release attained a maximum of 350 ng g−1 f. wt d−1 about 4 d after harvest, falling to less than 4 ng g−1 f. wt d−1 within 3 wk of harvest. On storage at 6°C post-harvest, maximum release of CH3Cl (c. 600 ng g−1) was delayed until 5 wk after harvest and release fell below 4 ng g−1 f. wt d−1 after 200 d. Release of CH3Cl was not significantly affected by cutting or bruising tuber tissue, and CH3Cl biosynthesis occurred in both core and superficial tissues of the tuber. The S-methyl group of either L- or D-methionine acted as a precursor of CH3Cl in sliced tubers, but the methylating system was specific for Cl−. An isotope dilution technique using C2H3Cl demonstrated that the amount of CH3Cl metabolized by the intact tuber was approximately 36% of the net release. However, investigations with 14CH3Cl showed that only a small proportion (7%) of the CH3Cl metabolized was fixed in involatile form in the tuber. In both skin and core tissues, fixed 14C was located primarily (80%) in the fraction soluble in phosphate buffer, but the specific activity of skin tissue was about twice that of core tissue. Autoradiography demonstrated that 14C fixation in the tuber was greatest within the lenticels, possibly indicating a microflora adapted to use the locally high concentrations of CH3Cl. Significant 14C fixation was also associated with the periderm but was not attributable to labelling of the O-methyl groups of the phenolic components of suberin. Within the core of the tuber, 14C fixation was located primarily in the phloem, pith and medullary rays.

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.

This study investigates the effects of the spatial arrangement of aerial stems and current-year shoots on patterns of herbivory, competition and on the requirements for mechanical support in Hydrangea hirta Sieb. et Zucc. growing in a light-limited environment. Stem demography was followed for three consecutive growing seasons. Stem mortality rates decreased with increasing stem age. Age-specific mortality rate was highest for new stems owing to the high incidence of herbivory. Mortality due to herbivory was low in older stems and was attributed to the dispersion of the risk of herbivore attack as a result of the increase in number of current-year shoots per stem. Clumping of stems led to intense intra-clonal competition as inferred from size-dependent mortality and density-dependent turnover of stems, and higher maximum stem length in clumps with higher stem density. Analysis of the spatial distribution of current-year shoots within the stem crown revealed a uniform, mono-layered crown architecture. The horizontal distribution of buds within the mono-layer was aggregated as a result of their opposite position, but as current-year shoots grew, their apices became uniformly distributed, resulting in efficient leaf display for light capture and shading out competing stems. However, limits on stem growth were observed in crown expansion, shoot production rate and current-year shoot size. Crown width increased with increasing basal diameter to reach a maximum. Both shoot production rate and current-year shoot size decreased with stem growth and a minimum current-year shoot size was defined. These limits on stem growth were attributed to suppression from intra-clonal competition and to the requirements for mechanical support of the mono-layered crown.

The effect of arbuscular mycorrhizas on fructan accumulation was studied in barley (Hordeum vulgare) infected with Glomus mosseae. Treatments with and without fertilizer were included in order to distinguish between mere fertilizer effects and the effects of the symbiosis, and plants were harvested at two different time points, 35 and 50 d after planting. Fructan was the major storage carboyhdrate in both leaves and roots. The amounts of fructan were markedly altered in the mycorrhizal plants. In roots of non-fertilized mycorrhizal plants, fructan pools were significantly greater than in the corresponding non-mycorrhizal plants. By contrast, fertilization caused a general decrease in amounts of fructan in roots. The increase of fructan in mycorrhizal roots was correlated with a decrease of invertase activity. In leaves, fructan pools decreased or remained unchanged upon mycorrhizal infection; fertilization had a similar effect. However, when individual leaves of a plant were compared, intriguing effects of the mycorrhizal symbiosis could be observed. Whereas in non-mycorrhizal plants, the youngest leaves had the highest fructan contents and the oldest leaves the lowest (as previously reported), this gradient was markedly altered in mycorrhizal plants, indicating systemic effects of mycorrhiza on assimilate partitioning in shoots.

Ectomycorrhiza formation is a complex developmental process that is still not well understood. To study this process, we identified genetic markers for mycorrhiza development by differential screening of a cDNA library obtained from fully developed Picea abies–Amanita muscaria mycorrhizas. Twenty-three cDNA clones were identified that showed significantly altered gene expression during the ectomycorrhizal interaction. A detailed analysis was performed for two fungal cDNA clones, SC13 and SC25, exhibiting the most pronounced differences. SC13 encodes a protein of 184 amino acid residues that shows no homology with any sequence in databases. It was highly expressed in non-mycorrhizal hyphae, whereas its expression was decreased at least 50-fold in mycorrhizas and fruit bodies. SC25 encodes a protein of 198 residues that shows weak sequence homology with extensin-like plant proteins. The expression of this gene was weak in non-mycorrhizal hyphae but approx. 30-fold higher in mycorrhizas and fruit bodies. Because the expression of both developmentally regulated fungal genes was identical for mycorrhizas and fruit bodies, a common regulation mechanism for both developmental processes is proposed.

The relative importance of some aspects of iron nutrition for the distribution of six Plantago species (P. maritima L., P. coronopus L., P. major ssp. major L., P. serpentina All., P. media L. and P. lanceolata L.) with different habitat requirements for soil pH and moisture was evaluated. Iron efficiency and Fe tolerance of hydroponically-grown plants were assessed by determining the decrease in relative growth rates caused by suboptimal and supra-optimal external Fe concentrations. Marked interspecific differences were observed in visual symptoms of Fe deficiency and Fe toxicity and in the external Fe concentrations leading to 50% inhibition of maximal relative growth rates (rgr50%). Whereas P. serpentina displayed a clear preference for low external Fe concentrations, growth rates of P. maritima and P. media were found to be increased at higher concentrations. Severe growth restriction at both low and high Fe concentrations was evident in P. lanceolata and P. major. A broad optimum was observed in P. coronopus exhibiting a low external Fe requirement and a high tolerance to supra-optimal Fe concentrations. Iron efficiency and Fe tolerance differed in a way which was only partly correlated with the expected Fe availability at the natural habitat of the species, suggesting that Fe concentrations are of minor importance for their distribution, or that some of the mechanisms that render Fe oxides available for uptake in situ are masked in solution experiments.

To gain insight into the impact of the physiological and morphological characteristics of the species on Fe efficiency, the effect of Fe status on shoot[ratio ]root ratio, relative root surface area, root Fe(III) reductase and proton extrusion capacity were investigated. Roots of all species showed increased Fe chelate reduction activity upon growth at suboptimal Fe concentrations; marked differences were observed with respect to the kinetic parameters of the reductase. Maximal velocity of the reduction was positively correlated with relative growth rate and was not related to the Fe efficiency of the species. By contrast, Km corresponded to Fe efficiency ranking and can therefore be regarded as an important parameter for the uptake of Fe at low availability. Enhanced ability to acidify the rhizosphere was only observed in P. major. From the morphological characteristics investigated, root surface area appears to be the most important parameter in the uptake of Fe at suboptimal external concentrations.

This Special Issue of New Phytologist contains the latest information and new ideas about how root dynamics might alter in the face of a globally changing environment. The importance of this topic is clear: changes in the production and turnover of roots in forests and grasslands in response to rising atmospheric CO2 concentrations, elevated temperatures, altered precipitation, or nitrogen deposition could be a key link between plant responses and longer-term changes in soil organic matter and ecosystem carbon balance.

The introductory review (Norby & Jackson, 2000), which draws together the different contributions to the volume, asks three central questions:

[bull ] Do elevated atmospheric CO2, nitrogen deposition, and climatic change alter the dynamics of root production and mortality?

[bull ] How do physiological responses of roots to global change factors impact whole-plant and ecosystem metabolism?

[bull ] What are the implications of root dynamics for soil microbial communities and the fate of carbon in soil?

Ecosystem-level observations of root production and mortality in response to global change factors are just starting to emerge. The challenge to root biologists is to overcome the profound methodological and analytical problems and assemble a more comprehensive data set from which ecosystem responses can be explained. The commissioned reviews and research papers in this volume attempt to meet that challenge. Following the introductory review, three papers provide a framework for subsequent analyses by presenting a global perspective on root turnover, a review of morphological and physiological attributes of roots, and a discussion of concepts of carbon allocation in plants. This is followed by a series of papers describing experimental studies on the effects of elevated CO2 and climatic change in various ecosystems. Three papers consider the physiological responses of roots to global change factors, followed by three papers reviewing mycorrhizal interactions and soil biology, and the implications for carbon sequestration in soil. The final paper returns to a global perspective with an analysis of how roots are handled in models of global change. Throughout these articles there is information on topics such as methodology for studying root dynamics, the major gaps in our knowledge, and the idea that leaves are a good analogy for roots.

The extent of vertical migration of 33P in thalli of the heathland lichen Cladonia portentosa was investigated under field conditions. 33P-labelled orthophosphate was introduced into the bottom 25 mm of podetia cut to a length of 50 mm from the apices. The distribution of label was scanned using a molecular imager immediately after incubation, and after growing for 8 wk and 6 months. Differences in the relative distribution of label between podetia harvested at the beginning and the end of the experiment showed that there had been a significant migration of 33P upwards out of the labelled 25 mm stratum towards the apex. This was confirmed by statistically significant changes in the median (md) and the 90 percentile of total relative distribution of 33P label. In a control treatment in which label was introduced into the apical 25 mm of podetia, which were then grown inverted (top down), no upward movement of label was detected. By contrast, a statistically significant reduction in the md of the distribution indicated migration downwards towards the thallus apex. The results are consistent with the hypothesis that P is recycled within podetia of mat-forming lichens, migrating from degrading basal regions upwards to the growing apices following a source–sink relationship.

Parameters of convective ventilation and also the content and composition of free amino acids and free carbohydrates in roots, basal culm internodes and leaves were investigated in five stands of Phragmites australis that were subjected to different growth conditions and salinity levels. Shoot length, stem diameter and productivity decreased with increasing salinity. These morphometric variations in turn affected parameters of convective ventilation and amino acid patterns. Phragmites populations growing at the highest salinity levels possessed the lowest rhizome conductivities, which was probably caused by their more pronounced xeromorphic growth. High counterpressures of the rhizome system and low stem diameters were limiting factors for convective flows. The Phragmites stand with lowest flow rate and ventilation efficiency had the highest percentage of alanine, serine and γ-aminobutyric acid (55% of total free amino acids) in its roots, indicating hypoxic stress in basal plant parts. Increasing salinity was connected with significantly higher fractions of glutamine (in basal culm internodes), glutamate (in roots) and proline (in both) as well as slightly increasing osmolality of plant sap. However, total contents of free amino acids and carbohydrates were low, and not related to either salinity level or osmolality of plant sap. This suggests that they might not have an important, direct role as an osmolyte in P. australis. Stand-specific variations in amino acid and carbohydrate patterns of leaves were negligible. Ratios of amino acids to carbohydrate were positively related to potential N supply. It is concluded that (1) salinity affects convective rhizome ventilation by varying the reed morphometry, and (2) the pattern of free amino acids responds characteristically to conditions of salinity and hypoxic growth.

The interactive influences of elevated carbon dioxide, water stress, and ontogeny on carbon assimilation and biomass production were investigated in northern red oak, a species having episodic shoot growth characteristics. Seedlings were grown from acorns through three shoot-growth flushes (8–11 wk) in controlled-environment chambers at 400, 530 or 700 μmol mol−1 CO2 and under well watered or water-stressed soil-moisture regimes. Increasing CO2 growth concentration from 400 to 700 μmol mol−1 resulted in a 34% increase in net assimilation rate (A), a 31% decrease in stomatal conductance to water vapour (gs) and a 141% increase in water use efficiency (WUE) in well watered seedlings. In contrast, water-stressed seedlings grown at 700 μmol mol−1 CO2 demonstrated a 69% increase in A, a 23% decrease in gs, and a 104% increase in WUE. However, physiological responses to increased CO2 and water stress were strongly modified by ontogeny. During active third-flush shoot growth, A in first-flush and second-flush foliage of water-stressed seedlings increased relative to the quiescent phase following cessation of second-flush growth by an average of 115%; gs increased by an average of 74%. In contrast, neither A nor gs in comparable foliage of well watered seedlings changed in response to active third-flush growth. Whereas seedling growth was continuous through three flushes in well watered seedlings, growth of water-stressed seedlings was minimal following the leaf-expansion stage of the third flush. Through three growth flushes total seedling biomass and biomass allocation to root, shoot and foliage components were very similar in water-stressed seedlings grown at 700 μmol mol CO2 and well watered seedlings grown at 400 μmol mol−1 CO2. Enhancement effects of elevated CO2 on seedling carbon (C) assimilation and biomass production may offset the negative impact of moderate water stress and are likely to be determined by ontogeny and stress impacts on carbon sink demand.

The first axenic synthesis of morphologically typical ericoid mycorrhizas of the Epacridaceae has been achieved in micropropagated Epacris impressa Labill. with eight fungi isolated from roots of two epacrid species, E. impressa and Astroloma pinifolium (R.Br.) Benth. Mycorrhizal synthesis has also been achieved between E. impressa and both Hymenoscyphus ericae (Read) Korf and Kernan and Oidiodendron griseum Robak, recognized endophytes of Ericaceae, suggesting that the endophytes of the Epacridaceae and Ericaceae are capable of cross-infection. Infection rate of epidermal cells on hair roots varied from 3–77% infection and the density of hyphal coils varied widely. This synthesis makes possible studies of the roles of these endophytes in the Epacridaceae and comparison with their roles in the Ericaceae.