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.

The incorporation of [35S]sulphur in thiophenes by Tagetes patula roots was used as a model to study the regulation of secondary metabolism with a limited supply of substrate. Growth and thiophene accumulation were measured in root cultures incubated at various sulphate concentrations in the medium. A 20-fold to 40-fold reduction in the sulphate concentration did not affect elongation growth, branching and biomass production within 14 d but decreased the thiophene level to 25–50% of the control in the same period. The reduction in thiophene content was found to result from a decline in biosynthetic capacity of 80–95% after 8 d. This capacity was restored when roots were transferred to standard medium. The restoration took more than 24 h and was suppressed by cordycepin, an inhibitor of mRNA processing. It is concluded that the rate of thiophene synthesis is regulated by a control mechanism that reacts to the availability of sulphate to the roots.

The aim of this paper is to review the present knowledge of the main aspects of differentiation of Acetabularia, a unicellular, eukaryotic organism, and to underline the multiple control pathways modulated by circadian rhythmicity. Growth and morphogenesis are sequentially programmed. Timing of cap differentiation is highly dependent on external conditions. The importance of the sequence of processes is shown by experimental disregulation.

The alga is a highly polarized cell, both in morphology and in the relative concentrations of a number of the molecules it contains. Apical cap differentiation is regulated at the post-transcriptional level and could also depend in part on polyamines and on proteolytic activity.

A great diversity of plants and fungi engage in mycorrhizal associations. In natural habitats, and in an ecologically meaningful time span, these associations have evolved to improve the fitness of both plant and fungal symbionts. In systems managed by humans, mycorrhizal associations often improve plant productivity, but this is not always the case. Mycorrhizal fungi might be considered to be parasitic on plants when net cost of the symbiosis exceeds net benefits. Parasitism can be developmentally induced, environmentally induced, or possibly genotypically induced. Morphological, phenological, and physiological characteristics of the symbionts influence the functioning of mycorrhizas at an individual scale. Biotic and abiotic factors at the rhizosphere, community, and ecosystem scales further mediate mycorrhizal functioning. Despite the complexity of mycorrhizal associations, it might be possible to construct predictive models of mycorrhizal functioning. These models will need to incorporate variables and parameters that account for differences in plant responses to, and control of, mycorrhizal fungi, and differences in fungal effects on, and responses to, the plant. Developing and testing quantitative models of mycorrhizal functioning in the real world requires creative experimental manipulations and measurements. This work will be facilitated by recent advances in molecular and biochemical techniques. A greater understanding of how mycorrhizas function in complex natural systems is a prerequisite to managing them in agriculture, forestry, and restoration.

To investigate the extent and size of root–soil air gaps that develop during soil drying, resin casts of roots of the desert succulent Agave deserti Engelm. were made in situ for container-grown plants and in the field. Plants that were droughted in containers for 7 and 14 d had 24 and 34% root shrinkage, respectively, leading to root–soil air gaps that would reduce the hydraulic conductivity at the root–soil interface by a factor of about 5. When containers were vibrated during drought, root–soil air gaps were greatly diminished, and the predicted conductivity at the interface was similar to that of the control (moist soil). For plants in the field (4 and 6 wk after the last rainfall), root shrinkage was greater than for container-grown plants, but root–soil contact on the root periphery was greater, which led to a higher predicted hydraulic conductivity at the root–soil interface. To test the hypothesis that root–soil air gaps would help to limit water efflux from roots in drying soil, the water potentials of the soil, root, and shoot of plants from vibrated containers (with gaps eliminated or reduced) and non-vibrated containers were compared. The soil water potential was lower for vibrated containers after 14 d of drought, suggesting more rapid depletion of soil water due to better root–soil contact, and the root water potential was lower as well, suggesting greater water loss by roots in the absence of root–soil air gaps. Thus, air gaps could benefit A. deserti by helping to maintain a higher root water potential in the early stages of drought and later by limiting root water loss at the root–soil interface when the water potential exceeds that of the soil.

The effects of potassium deficiency (KD) and all-macronutrient deficiency (MD) on elongation of tap and lateral roots were studied on maritime pine seedlings (Pinus pinaster Ait.) in hydroponic culture.

Tap root elongation was unaffected by either of the two deficiencies. By marked contrast, lateral root elongation was strongly reduced. The analyses of cell turgor pressure and relative elemental growth rate (REGR) profile in the growing zone allowed us to determine the effects of the nutrient stresses on cell-wall properties. For both deficiency treatments, elongation rate, REGR profile (measured only for control and KD) and turgor pressure in the fastest growing cells were unaffected in the tap root, suggesting that KD and MD did not modify cell-wall properties in the growing zone. In lateral roots, KD shortened the growing zone and significantly reduced REGR. However, turgor pressure remained unaffected in this region. The absence of turgor pressure change suggests that KD reduced elongation of lateral roots by tightening cell walls. In mature cells of the two types of roots, turgor and osmotic pressures tended to be reduced by the nutrient deficiencies, indicating that these parameters were better maintained in the growing cells.

Cell turgor and osmotic pressures of control plants were 0·1 MPa lower at 30 mm (mature cells) than at 2–4 mm (expanding cells) from the meristem. Moreover, these parameters were 0·1 MPa lower in expanding cells of lateral roots than in those of tap the root. Turgor and osmotic pressures were not homogeneous throughout the root system and were affected differently by the nutrient deficiencies depending on the location in the root system.

Plants of Chondrus crispus Stackhouse, collected from mid-littoral tidepools, were treated as follows. Some plants were kept for a few weeks under controlled starvation conditions in order to decrease their initial content of total tissue phosphorus, then incubated for up to 48 h in phosphorus (15 μM) and nitrogen (25 μM) enriched sea water. Other plants were directly incubated in enriched sea water. Chemical analyses showed that the total phosphorus content of fresh and starved plants remained stable, reflecting the nutritional status of the plants. The predominant acid-soluble phosphate fraction was larger in fresh than in starved plants. The content of acid-soluble polyphosphates, similar in both types of plants at the beginning of the experiment, doubled in starved plants, and increased by a factor of 2·7 in fresh plants, over 48 h. The content of acid-insoluble polyphosphates was lower than that of acid-soluble polyphosphates.

Transmission electron microscopy and energy dispersive X-ray microanalysis confirmed the presence, mostly in medullary cells, of acid-insoluble polyphosphates in the form of cytoplasmic granules and precipitates along the plasmalemma, particularly near pit plugs. This is the first report of such phosphorus storage structures in a red macroalgal 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.

Earlier work has shown that rice plants growing in reduced soil are able to solubilize P and thereby increase their P uptake by inducing an acidification in the rhizosphere; the acidification is caused by H+ produced in Fe2+ oxidation by root-released O2, and by the direct release of H+ from the roots to balance cation–anion intake. Here, we report rates of release of O2 and H+ from P-stressed and P-sufficient rice plants into sand cultures continuously perfused with deoxygenated nutrient solution. The P stress was sufficient to reduce plant dry mass by roughly half, but root dry mass increased roughly twofold and root surface area 2·5-fold. The proportion of fine roots increased from 11 to 21% of root length under P deficiency; root porosity, averaged over the whole root system, increased from 0·25 to 0·40. Apparent rates of O2 release were 0·8–3·3 μmol per plant d−1, or 22–87 μmol g−1 (root dry mass) d−1. Assuming that the bulk of the O2 was released from medium and fine roots, the fluxes of O2 were 0·02–0·13 nmol dm−2 (root surface) s−1, which is in the range found for soil-grown plants. The release per plant was twofold greater in the low P treatment, although rates of release per unit root mass were slightly lower. The increased release under P deficiency is consistent with the increased length of fine roots and increased porosity. Rates of H+ release were 0·7–1·2 mmol per plant−1 d−1, or 1·4–6·1 mmol g−1 (root dry mass) d−1. The H+ release per unit plant dry mass was 60% greater in the low P treatment, but the release per unit root mass was 2·5-fold lower. The increased H+ release under P deficiency was associated with increased NH4+ intake and decreased NO3− intake, and a tenfold increase in plant NO3-N. This suggests that P deficiency reduced NO3− assimilation, causing reduced NO3− influx and/or increased efflux.

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.

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.

Net CO2 assimilation rates and chlorophyll a fluorescence were measured on leaves of an ABA-unresponsive poplar (Populus trichocarpa × koreana cv. Peace) during a period of drought. Stomata of fully expanded leaves of ‘Peace’ partly closed during drought, while those of Populus euramericana cv. Robusta closed almost completely. The measured data were used to calculate total light-driven electron flows and to derive an estimate of a CO2 mole fraction in the chloroplasts. Two major results were obtained. (i) In well watered plants, photosynthesis operated at lower CO2 mole fractions in the chloroplasts of cv. Peace than in those of cv. Robusta, whereas CO2 mole fractions in the substomatal spaces were of the same order of magnitude. We concluded that a higher resistance to CO2 influx in the mesophyll contributed to the lower net assimilation rates in ‘Peace’. (ii) Drought induced an important decrease in CO2 availability in ‘Robusta’ but not in ‘Peace’. This suggested that reduced CO2 influx was a major cause of the limitation of net CO2 assimilation during drought in ‘Robusta’, but not in ‘Peace’, where drought probably reversibly reduced the apparent carboxylation efficiency of Rubisco. Measurements of O2 evolution under saturating CO2 supported this view, as photosynthesis decreased in droughted plants of ‘Peace’ but not of ‘Robusta’. Moreover, estimates of the 13C/12C isotope ratio in the leaves of both cultivars showed drought-related decreases in discrimination, which, in the case of ‘Peace’, could only be explained by changes in activity of the photosynthetic carbon reduction cycle.

Apparent Km and Vmax for net NO3− uptake and short-term translocation patterns of recently absorbed N were compared in a stay-green mutant and wild-type selection line of Lolium perenne L. by means of a series of depletion studies using 15NO3−, performed over 12 d under conditions of progressively increasing N deprivation. In view of the greater retention of N in senescent leaves of the stay-green phenotype, it was predicted that NO3− uptake would be up-regulated relative to the normal line, and that a proportionally higher fraction of recently absorbed N would be allocated to young leaves. It was shown that the stay-green trait had significant phenotypic consequences for plant N relations, with higher ‘sink strength’ of shoots for recently absorbed N, and higher Vmax for NO3− uptake compared with those of normal plants. The stay-green mutation had no effect on the Km of the nitrate uptake system. Although the N-use efficiency might be expected to be lower in stay-green than in normal plants, there were no differences in rates of dry matter production.

Bracken (Pteridium aquilinum (L.) Kuhn) and heather (Calluna vulgaris (L.) Hull) are important upland species which often grow in close proximity in the UK. The effects of factorial treatments of elevated atmospheric CO2 (539 μmol mol−1 as opposed to ambient atmospheric CO2 concentrations of 355 μmol mol−1), added N (50 kg N ha−1 as NH4NO3) and added P (20 kg P ha−1 as NaH2PO4) on the performance of these two species were studied under controlled environmental conditions using container-grown plants. Plants grown and measured at high CO2 had higher rates of net photosynthesis than those grown and measured in ambient CO2 . This increase was greater in heather than in bracken and resulted in a large stimulation of growth in the former. In bracken there was no significant change in plant size or phenology. The increase in biomass of heather in high CO2 was greatest in the absence of added nutrients and lowest when both N and P were supplied. The growth and photosynthesis of both plants responded positively to the supply of P alone or P with N (in both CO2 atmospheres), but there was little response to N alone. The implications of these findings for bracken and heather growing in the field under conditions of an elevated CO2 atmosphere and greater nutrient availability 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.

The potential role of sclerophylly (leaf hardness and rigidity) in the control of leaf dehydration and rehydration was investigated in two sclerophylls (Viburnum tinus and Ilex aquifolium) and two non-sclerophylls (Hedera helix ssp. helix and Sambucus nigra). After leaves were dehydrated in the pressure chamber, water transport from the apoplast (mainly consisting of xylem conduits and mechanical cells) to symplast was detected 15 min from pressure release, in terms of a spontaneous increase in leaf water potential (Ψ1). This Ψ1 increase was much larger in sclerophylls than in non-sclerophylls.

Positive pressures applied to leaves simulated the tensions developing in the leaf apoplast under water stress conditions, causing water to be expelled from leaf xylem conduits and mechanical cells and transferred to the leaf symplast, thus leading to symplast rehydration and to the consequent Ψ1 increase.

No correlation was found between the leaf modulus of elasticity at full turgor or the degree of sclerophylly (in terms of the ratio of leaf d. wt to surface area) and the characteristic rehydration time of the leaves, i.e. between the two main parameters expressing the rigidity of the leaf blade and the rate of leaf rehydration. However, when changes in Ψ1 were measured as a function of leaf water deficit (RWD), equal Ψ1s corresponded with larger RWDs during leaf rehydration than during leaf dehydration in the two non-sclerophylls. In particular, the two sclerophylls showed rehydration of their leaf apoplast and symplast completely and simultaneously. By contrast, the two non-sclerophylls showed a persisting water loss, localized, it is likely, in their xylem conduits and mechanical cells.

In other words, the two sclerophylls did not recover from water loss more rapidly than non-sclerophylls but they recovered from xylem cavitation more completely. The major elasticity of the cavitation strain shown by the two sclerophylls studied was interpreted as of advantage to plants subjected to diurnal large drops in Ψ1 followed by nocturnal recovery. This is the case in Mediterranean sclerophylls growing in areas characterized by high humidity of the air condensing on the soil at night. The same mechanism of cavitation recovery, however, would be useless in very xeric areas.

The hypothesis is advanced that sclerophylly of Mediterranean species may derive from similar anatomical structures developed in species formerly adapted to more humid environments which later migrated to more arid zones.

Cell division was examined during leaf initiation in the slow-to-green mutant of Lolium temulentum L. to test the hypothesis that the cell cycle in the leaf primordium is a key regulator of the well characterized reduction in final leaf length in the mutant compared with that of the wild type. The cell doubling time (cdt, by colchicine method) was substantially longer in the youngest leaf primordium (YLP) of the mutant (107 h) than in the wild type (43 h) although the duration of the most rapid cell cycle (cc, by percentage labelled mitoses method) was between 18–20 h in each. As a consequence, the proportion of rapidly proliferating cells was only 20% in the mutant compared with 47% in the wild type. The size of the shoot apical meristem and the plastochron were similar between genotypes which indicates that the shoot meristem was largely buffered from the effects of the mutation. Mitotic cell area was also similar in the YLP of both genotypes. However, as the leaf elongated, mitotic cell area and interphase cell size were significantly larger in the mutant compared with the wild type. This change was coupled with a reduced number of cells per unit length of leaf in the mutant. The data are consistent in showing that the proportion of rapidly proliferating cells in the YLP (but not the rate of cell division) is a key parameter which influences growth of the leaf.

A dry soil is generally a hard soil. Thus, the effects of water stress and mechanical impedance on plant growth are difficult to separate. To achieve this we have developed a growth cell that allows manipulation of the strength of growth media (i.e. mechanical impedance) without altering the availability of water or nutrients. We monitored leaf elongation rates of barley and wheat seedlings before and after the mechanical impedance to root growth was increased. Results show that a large and rapid reduction (within 10 min) of leaf elongation rates occurred after impedance to the roots was increased. The average reductions for barley and wheat, with associated standard errors, were 22·6% (4·84) and 36·2% (5·48), respectively. The data are consistent with the hypothesis that mechanical impedance of roots might have a direct negative effect on leaf growth even where nutrients and water are in plentiful supply to the plant. The implications of the rate of the response are examined with respect to the underlying mechanisms controlling root–shoot signalling.

Salt resistance was compared in populations of Armeria maritima (Mill.) Willd. from salt marshes and from inland sites to investigate which salt-resistance-related traits are present in all populations and which are derived traits of the salt-marsh ecotype. Plants were raised from seeds from six different populations and grown on a mixture of sand and ion-exchange resin at different salinity levels. Inland populations grew better at 40 mM NaCl than with salt-free treatment and survived several months at 200 mM NaCl, and were thus as salt-resistant as many species from brackish habitats. Salt-marsh populations were as salt-resistant as euhalophytes. Growth enhancement by NaCl was related to an increase in shoot [ratio ] root d. wt ratio, which was shown not to be the result of damage to the roots. Carbon allocation to roots seemed to be reduced as a consequence of a better nutrient supply at elevated NaCl concentrations. In plants from all populations, tissue tolerance of sodium and chloride (500–1000 mmol kg−1 d. wt) was higher than that in glycophytes. Na substituted for K and to some extent Ca and Mg without growth reduction. Betaines were accumulated as cytoplasmic compatible solutes by all populations, whereas proline accumulation was not involved in adjustment to long-term salt stress. The halophytic capacity to load the xylem with Na was found in all populations of A. maritima. However, the allocation of Na to the shoot started at higher salinities in inland populations than in salt-marsh populations. This was presumably due to the Na storage capacity of roots of inland populations being higher than that of coastal populations. Nevertheless, the inland populations of A. maritima were significantly salt-tolerant as a consequence of their capacity to accumulate betaines and allocate Na to the shoot; this might have facilitated the colonization of salt marshes by the species.

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.