Three groups of species (21 herbaceous monocotyledons, 22 herbaceous dicotyledons and 16 woody dicotyledons), including representatives of a wide range of natural habitats and life forms in inland Britain, were grown in the seedling phase in a resource-rich controlled environment and assessed over a 14-day period (21 d in the case of woody species). Mean values of relative growth rate (RGR), unit leaf rate (ULR), leaf area ratio (LAR), leaf weight fraction (LWF), specific leaf area (SLA), and the root–shoot allometric coefficient were derived.

In herbaceous species, the grand mean RGR was 0·20 d−1, comparable to values previously recorded. For woody species, the mean was 0·09 d−1. An existing assumption linking high RGR to high allocation to photosynthetic biomass was upheld by comparisons made between groups. Within groups, however, no pattern of this kind could be demonstrated.

When photosynthetically active radiation was increased from 125 to 250 µmol m−2 s−1, ULR was increased almost pro rata. The parallel response in RGR was only slight, being offset by considerable reductions in LAR. The apparent mean quantum yield for photosynthesis in herbaceous species (whole-plant d. wt basis) was 0·60 g mol−1.

There was no significant dependence of RGR on ULR in any of the three groups of species, although the absolute magnitude of ULR declined in the order: herbaceous monocotyledons > herbaceous dicotyledons > woody dicotyledons. In all three groups, RGR was strongly dependent upon LAR but no differences emerged in absolute scale of LAR. The absolute scale of mean LWF decreased from herbaceous to woody species, but the dependence of LAR on LWF strengthened. Groups showed no systematic differences in magnitude of SLA, but the correlation of LAR with SLA was strong throughout.

Multiple regression showed that the leading determinants of RGR were ULR and SLA in herbaceous species and LWF in woody species. Principal components analyses (PCA) on each of the three groups explained at least 77% of variation and agreed closely with an optimal (non-hierarchical) classification. Only six cluster ‘types’ were recognized out of the 16 theoretically possible combinations of ‘high’ or ‘low’ values of the four growth parameters. Strong evidence of evolutionary trade-offs emerged, most strikingly in that high RGR was never seen in combination with low SLA. The morphological/physiological types identified by an all-groups PCA separated woody from the herbaceous species, but dicotyledons were almost congruent with the monocotyledons.

The non-growth-analytical attributes most strongly correlated with mean RGR were percentage yield at a low level of mineral nutrients, leaf nitrogen concentration, and seed weight. It was concluded that mean RGR plays a central role in the identification of pathways of evolutionary specialization in herbaceous species.

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.

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.

Leaf mineral concentration of Citrus aurantium (sour orange tree) was measured at bi-monthly intervals from 30 to 85 months of exposure in a long-term study on the effects of a 300 µmol mol−1 enrichment of atmospheric CO2, under conditions of high nutrient and water supply. There were clear seasonal trends in the concentrations of most of the elements studied. There were initial decreases in the leaf concentrations of N and the xylem-mobile, phloem-immobile elements Mn, Ca and Mg, as well as a significant and sustained increase in the leaf concentration of B, and no changes in the concentrations of K, Fe, Na, P, S, Zn and Cu. Interestingly, the initial reductions in the leaf concentrations of Mn, N, Ca and Mg gradually disappeared with time.

To gain detailed information on the structure and dynamics of the foliage within a canopy, the longevity of leaves of cacao trees (Theobroma cacao L.) growing under normal commercial planting shade in Bahia State, Brazil, was determined relative to their position within the canopy and the time of leaf emergence.

In the experimental stand, the relative light intensity above the cacao canopy ranged between 30 and 100% of full daylight, and 4–10% at ground level. The mean leaf area index for the canopy, and the extinction coefficient of the foliage were 3·9 and 0·61, respectively.

The longevity of leaves of adult trees of cacao with closely packed crowns varied with their position within the canopy, and/or the irradiance received, and the time of emergence. In particular longevity decreased greatly with the height of the leaf from ground level. The mean longevity for the upper foliage (more than 220 cm above the ground) within the canopy was 181 d; the mean longevity of the lower leaves (0–150 cm above the ground) was about twice that of the upper leaves.

Approximately 23% of emergent leaves fell within 60 d of emergence, following infection (about 14% of loss) or as a result of wind damage (about 5% of loss). Thereafter, in mature and senescent leaves, leaf fall followed normal physiological changes.

We investigated interactions between the effects of elevated atmospheric carbon dioxide concentrations ([CO2]) and soil water availability on root biomass, root length and nutrient uptake by spring wheat (Triticum aestivum cv. Tonic). We grew plants at 350 and 700 µmol mol−1 CO2 and with frequent and infrequent watering (‘wet’ and ‘dry’ treatments, respectively). Water use per plant was 1·25 times greater at 350 than at 700 µmol CO2 mol−1, and 1·4 times greater in the ‘wet’ than in the ‘dry’ treatment. Root biomass increased with [CO2] and with watering frequency. Elevated [CO2] changed the vertical distribution of the roots, with a greater stimulation of root growth in the top layers of the soil. These data were confirmed by the video data of root lengths in the ‘dry’ treatment, which showed a delayed root development at depth under elevated [CO2]. The apparent amount of N mineralized appeared to be equal for all treatments. Nutrient uptake was affected by [CO2] and by watering frequency, and there were interactions between these treatments. These interactions were different for N, K and P, which appeared to be related to differences in nutrient availability and mobility in the soil. Moreover, these interactions changed with time as the root system became larger with [CO2] and with watering frequency, and as fluctuations in soil moisture contents increased. Elevated [CO2] affected nutrient uptake in contrasting ways. Potassium uptake appeared to be reduced by the smaller mass flow of water reaching the root surface. However, this might be countered with time by the greater root biomass at elevated [CO2], by the greater soil moisture contents at elevated [CO2], enabling faster diffusion, or both. Phosphorus uptake appeared to be increased by the greater root biomass at elevated [CO2]. We conclude that plant nutrient uptake at elevated [CO2] is affected by interactions with water availability, though differences between nutrients preclude generalizations of the response.

The possible involvement of polyamines in the tobacco mosaic virus (TMV)-induced hypersensitive reaction (HR) in Nicotiana tabacum (L.) cv. Samsun NN, which bears the N resistance gene, was investigated. Concentrations of free and conjugated polyamines, as well as the activities of their biosynthetic enzymes ornithine decarboxylase (ODC) and arginine decarboxylase (ADC), were analysed in the necrotic area (I, internal zone) and in the two concentric zones surrounding it (M, middle zone; E, external zone) during the progression of the HR (1, 3 and 5 d from TMV inoculation). Results were compared with those obtained in control plants (mock-inoculated) and with the pattern in susceptible TMV-infected tobacco plants.

In the HR, concentration increased towards zone I for free putrescine and spermidine. Highest concentrations in zones M and I occurred on day 3. Conjugated polyamines similarly showed an increasing concentration gradient towards zone I, with maximum accumulation on day 5. ODC and ADC activities also showed an increasing gradient towards zone I that could be related to the increase in free and conjugated polyamines. By contrast, in control plants concentrations of free and conjugated polyamines decreased from day 1 to day 5, ODC activity increased slightly, whereas ADC activity did not show significant changes. In the TMV-infected susceptible tobacco plants, polyamines tended to remain in the free state instead of being conjugated as infection progressed. These results suggest that polyamines could play a role in mechanisms of resistance to biotic stress.

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.

Spring ephemerals have evolved specific growth strategies that take advantage of the high photon fluence rates of early spring. These strategies involve a sequential growth of different organs. Erythronium americanum (Ker-Gawl), a common spring ephemeral of northern maple forests, produces its roots in the autumn, although stems and leaves develop in the spring. Mycorrhizal infection of the root system occurs very rapidly and intensively. The fungi thus depend on carbohydrate reserves accumulated in the corm (underground reserve organ) for their growth and development through the winter. We found that the presence of mycorrhizas drastically decreases root growth during the cold period and is more costly of carbohydrate reserves than root growth alone. However, during the spring, the presence of mycorrhizas fully benefits the plant: we measured an annual growth rate of mycorrhizal plants twice that of fungicide-treated plants which were non-mycorrhizal. We suspect that E. americanum is highly susceptible to water stress during the growing season and might rely on its mycorrhizas for water supply to a greater extent than for nutrient supply. Nutrient uptake might occur mainly in the autumn when arbuscules are at their most abundant.

The response of epicuticular wax of Scots pine (Pinus sylvestris L.) needles to dry- and wet- deposited sulphur and heavy metals was investigated at six sites located 10–110 km from the Monchegorsk Cu-Ni smelter on the Kola Peninsula, North-West Russia, and in a long-term irrigation experiment where pines were exposed over four growing seasons (1991–1994) to either acid rain treatment at pH 3·1 (H2SO4), metal treatment at pH 5·7 (Cu and Ni) or a combination of these at pH 3·1. Needle wettability exhibited a closer relationship with epistomatal wax tube distribution (WTD) than with chemical composition of epicuticular wax. Water droplet contact angles (DCA) decreased towards the smelter, and significant differences due to site were noted for 26-month-old and 38-month-old needles. Significant differences due to site were determined for secondary alcohols, dehydroabietic acid and hydroxy fatty acids, the proportions of which ranged from 22·5 to 48·9%, 6·2 to 22·4% and 0·6 to 2·6% respectively, depending on site and needle age class. The proportion of dehydroabietic acid increased towards the smelter, but no gradient was observed in the proportion of secondary alcohols or hydroxy fatty acids. No major effect of experimentally applied pollutants on the chemical composition or structure of the epicuticular wax was observed. The effect of treatment on DCA was significant in 1993 and 1994 due to a 6·5–13·2 degree greater wettability of the 37–49-month-old acid-treated needles relative to the irrigated or dry controls. Sulphuric acid at pH 3·1 did not increase needle wettability when combined with copper and nickel sulphate in similar concentrations. These data indicate that S deposition, especially H2SO4, plays a more important role in needle surface deterioration than Cu and Ni. Pollutant-induced changes in epicuticular wax structure and needle wettability mimic natural wax ageing, but at an accelerated rate. Changes in wax chemical composition might also be caused by pollutant-induced metabolic changes in elongating needles.

This paper reports effects of molybdenum and vanadium on Anabaena variabilis Kutz. (ATCC 29413) and Anabaena cylindrica Lemm. (PCC 7122), previously grown in NH4+-containing medium deficient in Mo and V (−Mo −V) and then transferred to media lacking combined nitrogen. Diazotrophic growth of A. variabilis was dependent on the presence of Mo or V, with little growth occurring in their absence. Neither Mo nor V was required for heterocyst differentiation in either cyanobacterium, and the highest heterocyst frequencies occurred in cultures showing the lowest growth rates. Although A. cylindrica also showed Mo-dependent diazotrophic growth and a low rate of growth in the absence of added Mo, the latter was inhibited by addition of 1 μM V. The rate of acetylene reduction by A. variabilis increased rapidly following addition of V to −Mo−V cultures, and increased ethane formation was detected in the acetylene reduction assays. Addition of Mo resulted in a smaller initial increase in the rate of acetylene reduction, but this was also accompanied by increased ethane formation, followed by a slow and much more extensive increase in acetylene reduction with a decrease in ethane formation. These observations indicate that nitrogenase polypeptides, probably those of a V-nitrogenase, are synthesized in A. variabilis in the absence of added Mo or V, that added Mo can be incorporated into the V-nitrogenase, and that synthesis of Mo-nitrogenase is dependent on the presence of Mo. By contrast, A. cylindrica appears either to synthesize only a Mo-nitrogenase, even in the absence of Mo (though 1 μM V inhibits its synthesis) or to synthesize a Mo- and V-independent nitrogenase, but only in the absence of added Mo and V. Western blots using antisera against the Mo-Fe and Fe proteins of the Mo-nitrogenase of Rhodospirillum rubrum indicated the presence of Mo-nitrogenase polypeptides in both Mo-grown and −Mo−V grown A. cylindrica, providing evidence in support of the former possibility. Physiologically, the V-nitrogenase of A. variabilis showed several distinct similarities to the Mo-nitrogenase of A. cylindrica, including responses to metal concentrations as well as the above responses to addition of V and Mo, respectively.

Three successive emergent macrophytes (Typha latifolia L., Phragmites australis (Cav.) Steudel and Glyceria maxima (Hartman) Holmbly) were each grown in substrates collected from three different zones of shoreline vegetation development (non-vegetated sediment, the interface between T. latifolia and P. australis, and degenerating P. australis). The aim of the study was to assess whether accumulation of litter changes growth conditions of P. australis, and to determine its effects on pre- and post successional plant species. The study was carried out by means of pot experiments in a glasshouse. Seedlings of the three species were cultured in fertilized and unfertilized substrates under both waterlogged and drained conditions.

In its own litter, growth of P. australis was strongly reduced, compared with the productivity of plants in substrates from preceding successional stages, and could not be compensated for by fertilization or soil drainage. The redox potential of the substrate was not strongly reduced and the sediment density was well above the critical level. Soil sterilization by gamma-irradiation did not improve growth substantially, although there was some positive effect in unfertilized substrate. Phytotoxic compounds might have caused poor growth of P. australis in its own litter. T. latifolia and G. maxima were relatively less affected by the P. australis litter. The possible importance of litter accumulation on species replacement in shoreline vegetation is discussed. It is concluded that the accumulation of organic matter should be considered as a factor affecting spatio-temporal processes in littoral vegetation owing to its specific impact on the functioning of individual dominant plant species.

The biomass of Mycelis muralis (L.) Dumort plants increased with increases in growth irradiance and nitrate supply. Comparisons of the data from this study with published information indicate that biomass production and growth rate of M. muralis are comparable to that of a number of slow-growing species from resource-poor environments. Biomass allocation varied with growth irradiance and nitrate supply. At high irradiances and low nitrate supplies there was a significantly greater allocation of plant mass to roots, resulting in a lower leaf area ratio (LAR) and leaf mass ratio (LMR). In contrast to the findings of a number of other studies, light level and nitrate supply had interactive effects on leaf mass per unit area (LMA). Changes in LAR due to variations in irradiance were mainly a consequence of changes in LMR. Given the ability of M. muralis to grow in deep shade, this suggests that large changes to within-leaf allocation (LMA) are not an essential requirement for growth at low irradiances. Conversely, because M. muralis can also grow in fully exposed situations, these traits might not exclude some shade species from high irradiance habitats. However, a low growth rate, or traits which result in a low growth rate, might be advantageous in a number of resource-poor environments.

The lower part (460–650 cm) of a lacustrine sequence from Lac de Creno, Corsica (1310 m) is analysed on the basis of 68 pollen spectra and with the support of 10 14C dates (including nine A.M.S. dates). This sequence, which extends from the end of the Würm to the beginning of the Postglacial, reveals a complete late-glacial. The absence of forest dynamics during the late glacial Interstadial in Corsica is a real mystery. Pollen data clearly suggest that Pinus laricio ( = Pinus nigra Arnold ssp. laricio Maire) and perhaps other tree species did not exist in Corsica at that time.

Solution culture experiments were made using two subspecies of Cerastium fontanum and Cochlearia pyrenaica ssp. alpina (Bab.) Dalby and Festuca rubra L. of ultramafic and non-ultramafic origin to test: (1) whether Mg and Ni toxicities are likely to exclude non-ultramafic races of the three species; (2) whether tolerance to Mg and Ni toxicities by the ultramafic plants differed markedly among the species; and (3) to use (2) to generate a hypothesis about controlling factors of species distribution on the Meikle Kilrannoch (MK1) ultramafics. The solution cultures were based on soil solution extracts with experimentally varied concentrations of Mg, Ni and Na. The solution with high (7·5 mM) Mg and high (0·7 mg l−1) Ni concentrations simulated the ultramafic soil solution. Care was taken to use a Fe source which did not react with Ni and microelements. Of the non-ultramafic plants, the growth of Cerastium was reduced by high concentrations of Mg but not by Ni, whereas both the Cochlearia and the Festuca suffered severe reduction in biomass production in the presence of high Mg or Ni or both. Of the ultramafic plants, Festuca was tolerant of high Mg and Ni concentrations; Cerastium was less tolerant of high Mg; and Cochlearia had low shoot production in high Ni (although the effect was ameliorated by high Mg). The different interspecific responses of the ultramafic plants to Mg and Ni supported field observations that the three species might occupy microhabitats which differ in Mg and Ni.