Salinity stress inhibits Ca translocation to the shoot, leading to Ca deficiency. The objective of this study was to determine whether salt stress inhibits Ca translocation through effects on younger root regions, where radial Ca transport is largely apoplastic, or through effects on mature regions of the roots, where radial Ca transport is largely symplastic. Roots were excised from 4-d-old dark-grown barley seedlings. Calcium translocation was studied by application of 45Ca 3 or 6 cm from the root tip and measurement of its appearance in the root exudate. Calcium uptake along the axis of excised roots was studied with a vibrating Ca+2 microelectrode. Salt stress (60 mM NaCl) inhibited Ca translocation from the 6 cm region more than from the 3 cm region. Sodium sulphate treatments (30 and 36 mM) were more deleterious to Ca translocation than was NaCl in the 3 cm region, and 110 mM mannitol and 60 mM KCl affected Ca translocation similarly to Na2SO4. The salt and mannitol treatments were more deleterious to Ca translocation in the 6 cm region than in the 3 cm region, and mannitol and KCl inhibited Ca translocation more than the sodium treatments. Supplemental Ca could overcome the inhibition of Ca translocation by NaCl stress. Calcium uptake into the root at the 3 and 6 cm regions was not reduced by NaCl, but was retarded 0·05 cm from the apex. We conclude that symplastic Ca transport is more inhibited than apoplastic transport in salinized roots, and that the osmotic component of salt stress causes most of the inhibition. Since symplastic transport is inhibited, the possibility exists that research into the effects of salinity on the transport functions of endodermal cells will yield information that can be used to improve Ca translocation in salt-affected plants.

The genus Phillyrea includes woody shrub species of Mediterranean maquis which can be found occasionally in saline soils or areas exposed to salt aerosols. To test salinity tolerance in Phillyrea latifolia L., plants were grown in 1-l containers and exposed to different levels of salinity in a glasshouse over two growing seasons. Plants survived exposure to NaCl concentrations of up to 500 mM NaCl for 4 months. Analysis of the growth response to increasing salinity showed that shoot elongation was inhibited by 50% at 123 and 135 mM external NaCl after 31 and 123 d of salt treatment, respectively. Growth parameters were completely inhibited by treatment with 300 mM external NaCl for 64 d. High salt tolerance in Phillyrea plants was the result of both exclusion and secretion mechanisms. Secretion of ions occurred via salt glands present mainly on the abaxial surface of the leaf. Salt glands occurred alone or in pairs and were typically formed by a highly vacuolated collecting cell, a stalk cell and a group of 10–16 secretory cells. The mean diameter of the glands was 54 μm and the average density was 6·1 mM−2 (abaxial side). Peaks of Cl, K, Ca, Na, Si, Mg, Fe and Cu were detected in salt crystals near glands by X-ray microprobe analysis. This is the first report of salt glands in the Oleaceae family and of their role in salinity tolerance in Phillyrea species.

A recent re-analysis of the data of Salisbury (1974) claims his data do not support the hypothesis that seeds of species from shaded habitats are heavier than those from unshaded habitats, partly because the original analysis was inappropriate and partly because of bias in the dataset. We show first that the re-analysis itself contains errors, and second that the charge of bias is based largely on a misunderstanding. We also show that analysis of a larger dataset, drawn from Salisbury (1942) and from Salisbury (1974), provides convincing support for the hypothesis and suggests that the relationship is independent of life history.

Ion exchange chromatography of water extracts was used to classify the fructans in leaves of 40 temperate dicots and 110 temperate grass species. Of the 150 species studied, only Poa ampla (Merrill) contained a single β-2,6 linked fructan series. All other species grown at 10/5°C day/night temperatures (16 h day) contained some β-1,2 linked oligofructans, even when the major fructan series was β-2,6 linked. Leaves of P. ampla plants grown at 15/10°C day/night temperatures contained some β-1,2 linked fructans and raffinose in addition to the dominant β-2,6 series, but did not contain significant amounts of 1-kestose or bifurcose (1&6-kestotetraose). Leaves of Poa arctica R.Br. and Poa bulbosa L. contained significant amounts of raffinose and various β-1,2 linked oligomers but no 1-kestose. In vivo synthesis of 6-kestose in leaves of P. ampla grown at 10/5°C proceeds in the absence of significant amounts of either 1-kestose or bifurcose. Thus P. ampla probably has a specific 6-SST (6-sucrose-sucrosefructosyl transferase) and might provide a ready source of β-2,6 linked grass fructan.

Five species of white truffle were classified using PCR-based techniques. RAPD (random amplified polymorphic DNA) fingerprints and specific pairs of primers were used. A RAPD fragment was constant in Tuber borchii Vittad. isolates and polymorphic among the other species. Two molecular markers specific for T. borchii were developed from the sequence of the non-polymorphic RAPD fragment and from regions flanking the 5′-3′ ends of a truffle gene. These markers were applied in the identification of T. borchii fruit bodies, mycelia and mycorrhizas, allowing us to monitor the development of this fungus during its entire life cycle.

A study was carried out to determine whether expansion of marram-grass stands (Ammophila arenaria (L.) Link) on acidic inner Dutch coastal dunes was caused by suppressiveness of soils from these stands against three potential pathogenic fungi of marram grass, namely Fusarium culmorum (W. G. Sm.) Sacc., Phoma exigua Desm. and a Ulocladium sp. The suppressiveness of the acidic inner dune soils was compared with that of lime-rich dune soils from vigorous and declining marram-grass stands. Suppressiveness of the dune soils against the saprotrophic fungi Chaetomium globosum Kunze: Fr, Mucor hiemalis Wehmer and Trichoderma harzianum Rifai was also determined. All fungi had been isolated from marram-grass roots. Suppressiveness was determined by comparing the formation of hyphae from potato–dextrose agar discs into (layer method) or on top of (surface method) dune soils with that of controls consisting of sterile, acid-washed beach sand. The growth of the three root-infecting fungi was strongly inhibited in all soils regardless of the method used. Hence, there were no indications that the potential pathogenic fungi were selectively suppressed by the acidic dune soils and, consequently, the results did not give any indication for the involvement of a fungal component in the decline of marram grass. Growth of the saprotrophs C. globosum and M. hiemalis was much less inhibited than that of the root-infecting fungi. Growth of T. harzianum was strongly inhibited in alkaline soils but not in the acid ones. The suppression of fungal growth could be partly or completely eliminated by a microwave treatment, indicating that biological components of the soil were essential to suppressiveness. The suppression of the fungi by colonies of dune soil micro-organisms on water-agar differed considerably from soil alone. Yet, all methods indicated the occurrence of general suppressiveness against fungi by dune soils, irrespective of the origin of the soil samples. This suppressiveness was probably not due to direct competition with other soil micro-organisms for nutrients but to inhibiting compounds produced by the soil micro-organisms.

The purpose of this study was to describe morph-specific patterns of stigma–anther separation and style curling in the distylous Jasminum fruticans. We also examined whether variation in floral traits is correlated with variation in seed production. Stigma–anther separation is more variable in short-styled plants than in long-styled plants. In all populations studied, some plants bear flowers that lack any stigma–anther separation. These plants have the pollen characteristics (size and number) and compatibility relations of short-styled plants. Comparison with other distylous species illustrates that the variability of stigma–anther separation in short-styled plants is a novel finding for a distylous species. Long-styled plants have greater stigma–anther separation than short-styled plants, styles are often curled and protrude from the corolla, and anthers are placed well within the corolla tube. The frequency of long-styled plants with curled styles and the mean degree of style curling were significantly correlated with style length. Short-styled plants have larger corollas than long-styled plants and never have curled styles. Morph ratios are always 50[ratio ]50 in natural populations. Mean values of each floral trait in the two morphs were significantly correlated among populations. There were no consistent differences in fecundity of the two morphs nor any correlation between floral traits and seed set for each morph in natural populations. We discuss the potential causes and significance of the two morph-specific patterns we describe; reduced stigma–anther separation in short-styled plants and the presence of curled styles in long-styled plants.

Pathozone behaviour of soil-borne plant pathogenic fungi is characterized by curves for the change in probability of infection with distance of inoculum from a host. We identify three major components that give rise to the pathozone profile for infection efficiency: the germinability of inoculum, given that it occurs in the pathozone (P1), the growth of the resulting fungal colony outwards to make contact with the host (P2), and the infectivity of mycelium once contact is made (P3). The probability of infection (P) is then given by the product, P1 × P2 × P3. Using Raphanus sativus and two contrasting types of inoculum of Rhizoctonia solani as a model experimental system, we measured each of the three components by quantifying germinability, colony architecture (to determine the chance of contact by one or more hyphae) and the change in susceptibility over time as a measure of infectivity as mycelium arrives from different distances away. The germinability of inoculum is uniform across the pathozone whereas the probability of contact declines with distance, and the net effect of host susceptibility and infectivity increases. The characteristics of these components result in pathozone profiles that vary in shape. Infection efficiency can decline in an exponential or sigmoidal fashion with increasing distance from the host or follow a curve that rises close to the host and then falls asymptotically to zero with increasing distance. Colony architecture was summarized by the distribution of the furthest extent of hyphal growth amongst colonies growing out from single inoculum units (described, because of its asymmetrical pattern, by a gamma distribution) and by the radial density of hyphae on concentric circles at different distances from the centre of the colony (described by a negative binomial distribution with parameters changing with distance).

The mechanistic model for the components of pathozone behaviour is tested by comparing the magnitude and shape of pathozone profiles predicted by the model with independent estimates for P obtained by placing inoculum at fixed distances from the host, and measuring the proportion of successful infections. The shape depends on the relative magnitudes and change with distance of the three components, P1, P2 and P3, which differed between the two types of inoculum. The profiles could be reproduced accurately when the probability of contact was based on the distribution and density of hyphae reaching the host rather than on the furthest extent of hyphal growth amongst colonies. The model is used to analyse the effects of replication and stochastic variability in the components of pathozone behaviour on the comparison of treatments for disease control.

The identity of individual ectomycorrhizas, root colonization patterns and early growth responses of interconnected Scots pine (Pinus sylvestris L.) seedlings were investigated following interactions between local genets of Suillus bovinus (L. ex Fr.) O. Kuntze (SBK4b and SBK5b) and S. variegatus (Swartz ex Fr.) O. Kuntze (SVK3b) and different host–genotype combinations. Three equidistant 39-d-old seedlings, in pots that contained sterile N-limited nursery soil, were each inoculated with one of the three genets in the multiple inoculation treatment (MIT). Single inoculation treatments (SITs), involving inoculation of only one seedling in the triad with one of the three genets, and a similarly configured uninoculated treatment (UIT), were also prepared for comparative analysis. All seedling roots in the inoculated treatments, except for one SIT/SBK4b combination, hosted large numbers (>150) of Suillus-type ectomycorrhizas after 23–25 wk growth without additional fertilization. Esterase (EST) isozyme analysis of individual ectomycorrhizas from all SIT and MIT combinations enabled efficient interspecific and intraspecific typing of fungal (genet) colonization (89 and 72%, respectively) and identification of host genotype variation (Z locus polymorphism) at a lower rate (51%). Species, but not S. bovinus genet, typing within randomly sampled individual ectomycorrhizas from selected SITs was successful (50–70%) following PCR/RFLP analysis of diagnostic sequences of fungal rRNA genes. In the SITs, only the inoculated fungal genet was detected in ectomycorrhizas on all three seedlings. Roots were predominantly colonized by SBK4b in one, and SBK5b in three, of the MIT combinations, although ectomycorrhizas of the former genet were detected at low frequencies on nearly all seedlings. In the remaining MIT combination, both SBK4b and SVK3b were found to co-dominate as ectomycorrhizas on the seedling roots. Small numbers of the latter genet were detected in ectomycorrhizas of two SBK5b-dominated MIT combinations. However, no significant trends in host-mycorrhiza interactions were detected using a log–linear analysis. Compared with the UIT, significant positive mycorrhizal plant growth responses, particularly increased needle length, were recorded in all the heavily colonized seedlings in most SIT and all MIT combinations. Intermediate seedling growth was restricted to the one SIT/SBK4b combination where seedlings supported limited numbers of ectomycorrhizas. The general host-fungal colonization patterns observed provide further below-ground evidence supporting genet interactions previously detected through sporocarp population analyses in young Scots pine reforestation sites.

Numerous biochemical and physiological studies have demonstrated the importance of ascorbate (ASC) as a reducing agent and antioxidant in higher plant metabolism. Of special note is the capacity of ASC to eliminate damaging activated oxygen species (AOS) including O2−· and H2O2. N2-fixing legume nodules are especially vulnerable to oxidative damage because they contain large amounts of leghaemoglobin which produces AOS through spontaneous autoxidation; thus, ASC and other components of the ascorbate–reduced glutathione (ASC–GSH) pathway are critical antioxidants in nodules. In order to establish a meaningful correlation between concentrations of ASC and capacity for N2 fixation in legume root nodules, soybean (Glycine max) plants were treated with excess ASC via exogenous irrigation or continuous intravascular infusion through needles inserted directly into plant stems. Treatment with ASC led to striking increases in nitrogenase activity (acetylene reduction), nodule leghaemoglobin content, and activity of ASC peroxidase, a key antioxidant enzyme. The concentration of lipid peroxides, which are indicators of oxidative damage and onset of senescence, was decreased in ASC-treated nodules. These results support the conclusion that ASC is critical for N2 fixation and that elevated ASC allows nodules to maintain a greater capacity to fix N2 over longer periods.

We tested how nitrogen availability affects suitability of ectomycorrhizal (ECM) and non-mycorrhizal Pinus sylvestris (L.) for a polyphagous insect herbivore. Seedlings grown on sterile agar at two N levels, were infected or not with the ECM fungus Cenococcum geophilum (Sow.) Ferd. & Winge. Ultrastructural observations showed that C. geophilum formed well-developed ectomycorrhizas in pine roots. After mycorrhizal establishment, oviposition preference of the polyphagous tarnished plant bug (Lygus rugulipennis Popp.) was determined in three different experiments. The duration of these experiments and the amount of irradiance were different. Nitrogen level or mycorrhizal treatment did not have significant effects on oviposition preference. However, mycorrhizal seedlings were favoured as an oviposition site at the lower N level, but only in expt 1. Total or individual terpene, total resin acid and total or individual sugar concentrations in pine shoots were not altered by treatment. Total phenolics concentration in pine shoots and roots was also the same in different treatments. Of individual resin acids, the concentration of dehydroabietic acid was increased after mycorrhizal treatment. Total resin acid, abietic acid and sandaraco pimaric acid concentrations correlated negatively with the number of Lygus eggs, but the correlations were only marginally significant. Of individual terpenes, β-pinene and bornylacetate concentrations had a significant positive correlation with the number of Lygus eggs. Greater amounts of N predictably increased total N concentration in pine seedlings in expts 1 and 2, but mycorrhizal infection increased total nitrogen concentration only in expt 3. Total N concentration did not correlate with the number of Lygus eggs in expts 1 and 2. An early stage of mycorrhizal development did not provide mycorrhizal benefits to the host plant as a higher nutrient concentration or as increased growth. These results suggest that host–plant quality might be involved in selection of oviposition site by L. rugulipennis, but ectomycorrhizal infection at this level does not seem to be an important mediator.

The effects of three conditions likely to affect soluble carbohydrate pools, namely drought, expression of barley sucrose: fructan 6-fructosyl transferase (6-SFT, EC 2.4.1.10) and the establishment of the arbuscular mycorrhizal symbiosis with Glomus mosseae were studied in a multifactorial experiment using tobacco (Nicotiana tabacum). Tobacco, a plant naturally unable to form fructan, accumulated fructan in leaves, and to a larger extent in the roots, when transformed with 6-SFT. Under drought conditions, growth was considerably reduced, but neither expression of 6-SFT nor mycorrhiza formation had an effect on growth rate. However, in response to drought, carbon partitioning was significantly altered towards accumulation of soluble sugars. In plants exposed to drought, pools of sucrose were greater than those of unstressed plants, particularly in their roots. In the transgenic plants expressing 6-SFT, there were also increased contents of the products of 6-SFT, namely fructan, most probably because of the increased availability of the substrate, sucrose. These effects were the same in the presence or absence of mycorrhiza. Hexoses (glucose and fructose) also increased in response to drought, primarily in the leaves. This effect of drought was little affected by the expression of 6-SFT, except that it slightly enhanced drought-induced glucose accumulation in roots. However, the presence of mycorrhiza led to a considerable reduction in drought-induced accumulation of hexoses in the leaves. The content of the fungal disaccharide trehalose was greatly increased in the roots of all mycorrhizal plants upon exposure to drought, particularly in some of the transgenic plants expressing 6-SFT.

Gene-specific probes were used to assess the expression patterns of four different phenylalanine ammonia-lyase (pal) genes in infected or elicitor-treated leaves and suspension-cultured cells of barley. Genes corresponding to hpal2, hpal3, hpal4, and hpal6 were all induced by mercuric chloride and fungal infection by Bipolaris sorokiniana Sacc. (Shoem.) in barley (Hordeum vulgare L. cv. Pokko) leaves, but with considerable variation in their expression level and timing. The expression patterns of hpal2 and hpal6 were similar, both showing a rapid, strong induction after treatment with mercuric chloride and a slower induction after fungal inoculation, whereas the more divergent hpal3 was induced at a later time and at a lower level after both treatments. Hpal4 was expressed with timing like that of hpal2 and hpal6 in infected or mercuric chloride-treated leaves but its expression was much weaker. Hpal2 and hpal4 were induced in elicitor-treated, suspension-cultured barley cells, whereas the expression of hpal3 was nearly undetectable, and hpal6 was strongly and constitutively present. All pal genes except hpal4 were developmentally regulated, but differentially expressed in various barley tissues. The results suggest that the four pal genes studied here might be responsible for the activation of different branches in the phenylpropanoid biosynthesis of barley.

Elimination of calcium ions from the medium of undifferentiated cell cultures of Digitalis thapsi increased cardenolide production and induced extracellular H2O2 accumulation, as measured by the quenching of pyranine fluorescence. The addition of catalase reduced the response and the inclusion of superoxide dismutase enhanced the loss of fluorescence. This suggested that, besides H2O2, the superoxide anion was also formed before dismutating to H2O2. Additionally, exogenous H2O2 or superoxide dismutase stimulated cardenolide production whereas the addition of catalase markedly reduced it. These results point to a connection between H2O2 and cardenolide formation. The absence of calcium did not alter the levels of lipid peroxidation products; however, changes in the antioxidant system of D. thapsi cells were observed. Catalase activity was extremely low in control cultures and remained unaltered upon calcium elimination. Ascorbate peroxidase activity was not modified in calcium-free cultures. By contrast, calcium deprivation stimulated superoxide dismutase activity and strongly inhibited glutathione reductase activity. Also, a significant decrease in reduced glutathione was observed. These responses were emulated by treatment of the cultures with the glutathione biosynthesis inhibitor buthionine sulfoximine and by ethyleneglycol-bis-β-aminoethyl ether and LaCl3. All these results indicate that the depletion of extracellular calcium induces changes in the redox state of cells and suggest that this alteration stimulates cardenolide formation in D. thapsi cultures.

Genetic diversity, population genetic structure and gene flow in Calluna vulgaris (L.) Hull were assessed by means of seven allozyme loci scored in 18 populations from the South-Western area of the species' range. Genetic diversity was lower (HT=0·20) than reported for long-lived widespread species but was characterized by a high number of alleles per locus (5·60 at the species level) of which more than 70% were rare. More than 95% of genetic variation was found at the intrapopulation level (GST=0·047). High levels of past gene flow were inferred, based on the allozyme data (Nm=5·2 from GST, Nm=10·2 from the ‘private allele’ method). Calluna vulgaris exhibited several geographic patterns of genetic variation. Both cluster analysis, constructed with various genetic distances and principal components analysis showed that Spanish and Pyrenean populations were clearly different from those collected in the Massif Central and Belgium. Also, a trend for decreasing genetic diversity towards Northern populations was detected. These patterns might be related to the post-glacial history of Calluna. In addition, it is shown that isolation by distance has played a role in the geographic shaping of genetic variation in this species.

How appropriate that at the turn of a century that has overseen a second industrial revolution in agriculture, there is an increasing appreciation of the central role played by the mycorrhizal symbiosis, first described in the latter part of the nineteenth century (Frank, 1885). Simply stated, nearly all families of plants form root symbiotic organs, termed mycorrhizas, with soil fungi belonging to all the main phyla, namely Zygomycotina, Ascomycotina, Basidiomycotina and the Fungi Imperfecti (Harley & Harley, 1987). The importance of this symbiosis in controlling plant nutrient status and growth is well established (Smith & Read, 1997), but a report in this issue now provides, long awaited, nitrogen and phosphorus budgets for mycorrhizal trees (Perez-Moreno & Read, pp. 301–309).

The role of carbonic anhydrase in the carbon-concentrating-mechanism of bryophytes of the class Anthocerotae was investigated by comparing the gas-exchange characteristics of material which had been incubated in the membrane-permeable Carbonic Anhydrase inhibitor ethoxyzolamide, with those of untreated material and material which had been incubated in buffer solution. In Phaeoceros laevis (Anthocerotae), incubation in ethoxyzolamide caused a depression in the rate of gross assimilation and a decrease in CO2 affinity beyond that which could be attributed to increased diffusion limitation. A range of liverworts and mosses, in which a carbon-concentrating-mechanism is absent, were also investigated. These showed no depression of rates of gross assimilation after incubation in ethoxyzolamide relative to those of untreated material. The CO2 compensation point and CO2 uptake characteristics of Phaeoceros laevis were significantly affected by incubation in ethoxyzolamide. Values of CO2 compensation point for Phaeoceros laevis rose from 2.5 Pa, after incubation in buffer, to 20 Pa after incubation in ethoxyzolamide. The CO2 compensation point for the liverworts Pellia epiphylla and Marchantia polymorpha was not significantly affected by incubation in ethoxyzolamide. Measurements of the release of CO2 at the end of a short (15 min) period of illumination revealed that, after suppression of carbonic anhydrase activity, the rapid release of a CO2 pool occurred in Phaeoceros laevis but not in the liverworts. There were also significant differences between values for fractionation measured in units per mil (‰), measured instantaneously, for Phaeoceros laevis incubated in ethoxyzolamide, compared with fractionation values for this species after incubation in buffer. Incubation in ethoxyzolamide caused fractionation values to rise from 12.4–22.7‰, indicating that the carbon-concentrating-mechanism of this species had been inactivated. Incubation in ethoxyzolamide had no effect on fractionation values for the liverworts. The convexity of the light saturation curves of liverworts and Phaeoceros laevis was also investigated, but there were no differences between groups before or after the two treatments. The data indicate an important role for carbonic anhydrase in the functioning of the carbon-concentrating-mechanism in the Anthocerotae.

Foliage construction cost (glucose requirement for formation of a unit foliar biomass, G, kg glu kg−1), chemical composition and morphology were examined along a light gradient across the canopies in five deciduous species, which ranked according to increasing shade-tolerance as Populus tremula <Fraxinus excelsior <Tilia cordata = Corylus avellana <Fagus sylvatica. Light conditions in the canopy were estimated by a hemispheric photographic technique, allowing ranking of sample locations according to long-term light input incident to the sampled leaves (relative irradiance). G and foliage carbon concentration increased with increasing relative irradiance in F. excelsior, T. cordata and C. avellana, but wereindependent of irradiance in F. sylvatica and P. tremula. However, if G of non-structural-carbohydrate-free dry mass was considered, it also increased with increasing relative irradiance in P. tremula. A positive correlation between the concentration of carbon-rich lignin and irradiance, probably a result of the acclimation to greater water stress at higher light, was the major reason for the light-dependence of G. Lignin concentrations were highest in more shade-tolerant species, resulting in greatest carbon concentrations in these species. Since carbon concentration and G are directly linked, the leaves of shade-tolerant species were also more expensive to construct. As the result of these effects, G increased faster with increasing leaf dry mass per area which was mainly determined by relative irradiance, in shade-tolerators. Given that shade-tolerant species had lower leaf dry mass per area at common irradiance and that this saturated at lower relative irradiance than leaf dry mass per area in the intolerant species, it was concluded that enhanced energy requirements for foliage construction might constrain species morphological plasticity and the upper limit of leaf dry mass per area attainable at high light.

The treatment of wheat roots with 2,4-dichlorophenoxyacetic acid (2,4-D) led to the formation of tumour-like structures, para-nodules, which were readily colonized by cyanobacteria. The amount of cyanobacteria found on 2,4-D treated roots was 3.6 times higher than that found on untreated roots. Cyanobacteria penetrated the para- nodules by migrating in between loosely arranged cells that covered their surfaces or by penetrating the space at the junction of root and para-nodule. In plants treated with 2,4-D and co-cultivated with cyanobacteria in medium without combined nitrogen, the rate of acetylene reduction was three times that seen in untreated but colonized roots. Addition of 2,4-D itself did not change the rate of acetylene reduction in free-living culture of Nostoc sp. strain 2S9B. In plants treated with 2,4-D and co-cultivated with Nostoc sp. strain 2S9B in medium without combined nitrogen the nitrogen content of roots but not shoots was significantly increased.

Studies on the rhizomatous clonal sedge Carex bigelowii, at a fellfield site in subarctic Swedish Lapland examined the ecological potential of rhizomes as nitrogen uptake systems. Direct application of a solution of 15NH415NO3 to the rhizomes of C. bigelowii significantly enriched the 15N content of the plant tissue. The pattern of enrichment indicated movement of labelled nitrogen into rhizomes and adjoining tissue (including roots and shoots), showing both uptake and translocation via the rhizome system. There was a gradient of decreasing 15N enrichment with increasing distance from the point of labelling, and estimation of the total mass of nitrogen taken up via labelled rhizomes showed low levels and rates of uptake. Quantification of the size of rhizome and root systems of C. bigelowii at the study site indicates that 80% of the living biomass may be below ground, and that the surface area of the rhizome system of C. bigelowii is approx. two-thirds that of the roots. The rhizome system of C. bigelowii can therefore act as a route for nitrogen uptake, with the potential to exploit almost as great a volume of soil as the root system. This mechanism of nitrogen uptake may play an important role in the Arctic, where many species have a clonal, rhizomatous growth form. In addition, plant growth in many arctic ecosystems is limited by low soil nutrient availability, a result of low temperatures (leading to slow soil decomposition rates) and patchy resource distribution. Nitrogen uptake via rhizomes may provide plants with the capacity to take advantage of transient nutrient supplies, and may partly compensate for the cost of developing and maintaining persistent rhizome networks in ecosystems where nutrient resources are in short supply.