Conditions Of Nutrient Supply Research Articles

Molecular cloning and cellular distribution of two 14-3-3 isoforms from Hydra: 14-3-3 proteins respond to starvation and bind to phosphorylated targets

In the simple metazoan Hydra a clear link between food supply and cell survival has been established. Whilst in plants 14-3-3 proteins are found to be involved in signalling cascades that regulate metabolism, in animals they have been shown to participate in cell survival pathways. In order to explore the possibility that 14-3-3 proteins in Hydra could be involved in regulating metabolism under different conditions of food supply, we have cloned two isoforms of 14-3-3 proteins. We show here that 14-3-3 proteins bind to phosphorylated targets in Hydra and form homo- and heterodimers in vitro. 14-3-3 proteins are localised in the cytoplasm of all cells and also in the nuclei of some epithelial cells. This nuclear localisation becomes more prominent during starvation. Moreover, 14-3-3 protein is present in large amounts in food granules and from this we conclude that it performs functions which are associated with metabolism and food storage in Hydra.

Early Interference Dynamics in Intercrops of Pea, Barley and Oilseed Rape

ABSTRACT Intercropping, a practical application of ecological principles such as diversity, interference, competition and coexistence in agriculture, is gaining increasing interest in organic farming. To be able to improve the management of intercrops, a more detailed knowledge is required on aspects of interference between crops. A bioassay and a pot experiment were conducted to assess both the mechanisms and the time of expression of processes involved in the early interference between pea (Pisum sativum L.), barley (Hordeum vulgare L.) and oilseed rape (Brassica napus L.) when grown as intercrops. Conditions of non-limiting nutrient and water supply were chosen to eliminate competition for these growth factors. The bioassay gave no indication of either competitive or allelopathic interactions, as none of the crops were growth depressed when intercropped compared with when grown as sole crops. The effect of barley interference, as a depression in pea dry matter production in the IC, was observed in the pot experiment as early as 2 weeks after emergence. Although competition was supposedly eliminated, there were indications of strong above-ground competition among sole cropped barley plants as well as among pea and oilseed rape plants intercropped with barley. Growth characteristics that allow for rapid establishment of barley plants are likely to be the determining factors leading to the dominance exerted by this species when intercropped.

Ten-year decomposition in a loblolly pine forest

A litter sandwich approach was used to examine the loss of mass, acidity, and nutrients through 10 years of decomposition in a stand of loblolly pine (Pinus taeda L.). Each year, a new layer of 3-mm mesh fiberglass was placed on the annual accumulation of litterfall. Ten years of decomposition led to a loss of about 80% of the litter organic matter (giving a decomposition constant of 0.1655), which predicted a steady-state mass of the forest floor within 10% of the observed value. The pH (in 0.1 M KCl) showed little variation over time, ranging just from 3.2 to 3.5. The decline in titratable acidity appeared related primarily to the loss of organic matter rather than to any change in the acid characteristics of the material. Nitrogen loss was slow; the 10-year-old cohort of material contained 70% as much nitrogen as the original material. The loss of other nutrients was rapid, exceeding 80% loss by 6 years for phosphorus, potassium, calcium, and magnesium. The litter-sandwich method for examining decomposition is an easy, long-term approach that appeared to provide reasonable representation of the dynamics of unconfined forest floor materials. Future work should test this method for examining the decomposition effects of litter quality, nutrient supply, and environmental conditions.

Phosphorus use efficiency in tall, semi-dwarf and dwarf near-isogenic lines of spring wheat

The impact of the Rht dwarfing genes on P utilization efficiency (PUTE = grain dry matter per kg P in above-ground biomass), total P uptake (Pt) and related traits was studied in the varietal backgrounds of two tall wheat cultivars, Maringa and Nainari 60. Four sets of near-isogenic lines carrying different combinations of the alleles Rht-B1b, Rht-D1b and Rht-B1c for gibberellin-insensitive dwarfism in the hexaploid wheat (Triticum aestivum L.) were compared with tall controls in two field trials under conditions of adequate nutrient supply and irrigation in Northwest Mexico. The yield-increasing effect of the dwarfing genes Rht-D1b and Rht-B1b led to improved PUTE in Maringa and total P uptake in both cultivars. Also, the double dwarf line of Maringa had larger grain yields and P uptake compared to the tall control. The Rht-B1c genotypes showed low PUTE, thick roots and high P concentration in vegetative biomass indicating a surplus of assimilates and P, which could not be translocated into the grains. A similar problem could be observed in Nainari 60 with Rht-B1b and Rht-D1b, which produced the largest grain dry matter with the lowest P concentrations in grains although they showed high P accumulation in straw. Most of the net P uptake occurred before anthesis. P absorption after anthesis was more critical for the dwarf genotypes. For double dwarfs and Rht-B1c, respectively, only 3% and 21% of the total accumulated P at maturity was absorbed at post-anthesis. The grain P of the dwarf lines came more from P accumulated at pre-anthesis and translocated from the vegetative biomass into the grain. The pre-anthesis P accumulation was positively correlated with spikes per m2 (r = 0.91), whereas post-anthesis P accumulation correlated better with grains per spike(r = 0.72), and thousand kernel weight (r = 0.51). P uptake efficiency played a secondary role under these non-P-limiting conditions, and differences in root length density were only slightly affected by Rht-genes.

Effects of zooplankton on nutrient availability and seston C : N : P stoichiometry in inshore waters of Lake Biwa, Japan

Forty-eight-hour experimental manipulations of zooplankton biomass were performed to examine the potential effects of zooplankton on nutrient availability and phytoplankton biomass (as measured by seston concentration) and C : N : P stoichiometry in eutrophic nearshore waters of Lake Biwa, Japan. Increasing zooplankton, both mixed-species communities and Daphnia alone, consistently reduced seston concentration, indicating that nearshore phytoplankton were generally edible. The zooplankton clearance rates of inshore phytoplankton were similar to rates measured previously for offshore phytoplankton. Increased zooplankton biomass led to increased concentrations of nutrients (NH4-N, soluble reactive phosphorus [SRP]). Net release rates were higher than those found in previous measurements made offshore, reflecting the nutrient-rich nature of inshore seston. Zooplankton nutrient recycling consistently decreased TIN : SRP ratios (TIN = NH4 + NO3 + NO2). This effect probably resulted from the low N : P ratios of nearshore seston, which were lower than those commonly found in crustacean zooplankton and thus resulted in low retention efficiency of P (relative to N) by the zooplankton. Thus, zooplankton grazing inshore may ameliorate algal blooms due to direct consumption but tends to create nutrient supply conditions with low N : P, potentially favoring cyanobacteria. In comparison with previous findings for offshore, it appears that potential zooplankton effects on phytoplankton and nutrient dynamics differ qualitatively in inshore and offshore regions of Lake Biwa.

Growth and Resource Use of Birch Seedlings Under Elevated Carbon Dioxide and Temperature

The effects of elevated CO2and temperature on the growth, resource acquisition and resource allocation of small birch seedlings (Betula pendula Roth.) were examined under conditions of non-limiting soil, water and nutrient supply. Seedlings were planted in pots and placed in controlled environment chambers either under normal ambient conditions (CON), or in the presence of elevated CO2(approx. 700μmolmol−1; Elev. C), elevated temperature (approx. 3°C above the outside ambient temperature; Elev. T) or a combination of elevated CO2and elevated temperature (Elev. C+T). Both Elev. C and Elev. T significantly increased biomass accumulation, but the extent of the increase depended greatly on the stage of development of the seedlings. Furthermore, the theoretically expected positive effect of the warmer temperature on the CO2-induced stimulation of growth was not observed. By analysing resource acquisition (i.e. CO2, nitrogen and water uptake), seedling development, leaf area production and the allocation pattern, it was deduced that the CO2-stimulated increase in biomass resulted mainly from the initial ‘fertilization’ effect of CO2while the temperature-induced increase in biomass stemmed from higher net carbon intake during the middle and latter parts of the growing season achieved by virtue of the increased leaf area and larger photosynthetic capacity. The lack of positive stimulation by temperature under Elev. C+T may be related in part to (1) CO2-induced acceleration of seedling development, which led to a small or no response to CO2enrichment and lower leaf area production during the latter part of the growth season, and (2) a cumulative delay in the response of growth to the warmer temperature, which did not increase net carbon intake when the seedlings were at a juvenile stage. Neither Elev. C nor Elev. T altered the root:shoot ratio during early growth, but Elev. C increased it during the latter part of the growth season while Elev. T decreased it, possibly on account of a change in leaf area retention. Finally, the nitrogen and water use efficiencies of seedlings at different stages of development are discussed.

Meta-analysis of the interaction between shade-tolerance,light environment and growth response of woody species to elevated CO2

Growth responses of different tree species to elevated CO2 vary enormously, even when grown under the same basic experimental conditions (such as nutrient supply and light conditions). A test of the hypothesis that this variation is associated with the species' shade-tolerance is presented. A meta-analysis of 74 logarithm-transformed response ratios RR (total biomass in -700 mu mol.mol(-1) CO2/biomass in current ambient CO2), grouped according to the species' relative tolerance to shade, revealed that RR differed widely and significantly between seedlings or saplings of woody species of different shade-tolerance. Only comparative studies were included in the meta-analysis, and interference from differences in basic experimental conditions between experiments was minimised. The mean RR of species with very high shade-tolerance was 1.51. This was significantly greater than the value of 1.18 for species intolerant of shade. Smaller differences in mean RR were found between groups of species that differed less widely in shade-tolerance. When responses were categorised according to two aspects of light environment in the experiments, daily integrated or peak photosynthetically active photon flux density (PFD), the differences in RR between different shade-tolerance classes disappeared at daily integrated PFD below similar to 20 mol.m(-2).ad(-1) or peak PFD below similar to 250 mu mol.m(-2).s(-1). Growth stimulation in juvenile trees is likely to cause increased survivorship in subsequent years. Even if the observed differences in RR were restricted to sites experiencing no or only moderate shading, it appears likely that they will affect species composition of naturally regenerating forests in the long term. (C) 2001 Editions scientifiques et medicales Elsevier SAS.

Biological stoichiometry from genes to ecosystems

Ecological stoichiometry is the study of the balance of multiple chemical elements in ecological interactions. This paper reviews recent findings in this area and seeks to broaden the stoichiometric concept for use in evolutionary studies, in integrating ecological dynamics with cellular and genetic mechanisms, and in developing a unified means for studying diverse organisms in diverse habitats. This broader approach would then be considered “biological stoichiometry”. Evidence supporting a hypothesised connection between the C:N:P stoichiometry of an organism and its growth rate (the “growth rate hypothesis”) is reviewed. Various data indicate that rapidly growing organisms commonly have low biomass C:P and N:P ratios. Evidence is then discussed suggesting that low C:P and N:P ratios in rapidly growing organisms reflect increased allocation to P‐rich ribosomal RNA (rRNA), as rapid protein synthesis by ribosomes is required to support fast growth. Indeed, diverse organisms (bacteria, copepods, fishes, others) exhibit increased RNA levels when growing actively. This implies that evolutionary processes that generate, directly or indirectly, variation in a major life history trait (specific growth rate) have consequences for ecological dynamics due to their effects on organismal elemental composition. Genetic mechanisms by which organisms generate high RNA, high growth rate phenotypes are discussed next, focusing on the structure and organisation of the ribosomal RNA genes (the “rDNA”). In particular, published studies of a variety of taxa suggest an association between growth rate and variation in the length and content of the intergenic spacer (IGS) region of the rDNA tandem repeat unit. In particular, under conditions favouring increased growth or yield, the number of repeat units (“enhancers”) increases (and the IGS increases in length), and transcription rates of rRNA increase. In addition, there is evidence in the literature that increased numbers of copies of rDNA genes are associated with increased growth and production. Thus, a combination of genetic mechanisms may be responsible for establishing the growth potential, and thus the RNA allocation and C:N:P composition, of an organism. Furthermore, various processes, during both sexual and asexual reproduction, can generate variation in the rDNA to provide the raw material for selection and to generate ecologically significant variation in C:N:P stoichiometry. This leads us to hypothesize that the continuous generation of such variation may also play a role in how species interactions develop in ecosystems under different conditions of energy input and nutrient supply.

Biological stoichiometry from genes to ecosystems

Ecological stoichiometry is the study of the balance of multiple chemical elements in ecological interactions. This paper reviews recent findings in this area and seeks to broaden the stoichiometric concept for use in evolutionary studies, in integrating ecological dynamics with cellular and genetic mechanisms, and in developing a unified means for studying diverse organisms in diverse habitats. This broader approach would then be considered “biological stoichiometry”. Evidence supporting a hypothesised connection between the C:N:P stoichiometry of an organism and its growth rate (the “growth rate hypothesis”) is reviewed. Various data indicate that rapidly growing organisms commonly have low biomass C:P and N:P ratios. Evidence is then discussed suggesting that low C:P and N:P ratios in rapidly growing organisms reflect increased allocation to P-rich ribosomal RNA (rRNA), as rapid protein synthesis by ribosomes is required to support fast growth. Indeed, diverse organisms (bacteria, copepods, fishes, others) exhibit increased RNA levels when growing actively. This implies that evolutionary processes that generate, directly or indirectly, variation in a major life history trait (specific growth rate) have consequences for ecological dynamics due to their effects on organismal elemental composition. Genetic mechanisms by which organisms generate high RNA, high growth rate phenotypes are discussed next, focusing on the structure and organisation of the ribosomal RNA genes (the “rDNA”). In particular, published studies of a variety of taxa suggest an association between growth rate and variation in the length and content of the intergenic spacer (IGS) region of the rDNA tandem repeat unit. In particular, under conditions favouring increased growth or yield, the number of repeat units (“enhancers”) increases (and the IGS increases in length), and transcription rates of rRNA increase. In addition, there is evidence in the literature that increased numbers of copies of rDNA genes are associated with increased growth and production. Thus, a combination of genetic mechanisms may be responsible for establishing the growth potential, and thus the RNA allocation and C:N:P composition, of an organism. Furthermore, various processes, during both sexual and asexual reproduction, can generate variation in the rDNA to provide the raw material for selection and to generate ecologically significant variation in C:N:P stoichiometry. This leads us to hypothesize that the continuous generation of such variation may also play a role in how species interactions develop in ecosystems under different conditions of energy input and nutrient supply.

Predicting broccoli development I. Development is predominantly determined by temperature rather than photoperiod

Predictive models of broccoli ( Brassica oleracea L. var. italica Plenck) ontogeny will aid farmers who need to forecast changes in crop maturity arising from variable climatic conditions so that their forward marketing arrangements can match their anticipated supply. The objective of this study was to quantify the temperature and photoperiod responses of development in a sub-tropical environment from emergence to floral initiation (EFI), and from floral initiation to harvest maturity (FIHM). Three cultivars, (‘Fiesta’, ‘Greenbelt’ and ‘Marathon’) were sown on eight dates from 11 March to 22 May 1997 and grown under natural and extended (16 h) photoperiods at Gatton College, south-east Queensland, under non-limiting conditions of water and nutrient supply. Climatic data, dates of emergence, floral initiation and harvest maturity were obtained. The estimated base ( T base) and optimum ( T opt) temperatures of 0 and 20 °C, respectively, were consistent across cultivars, but thermal time requirements were cultivar specific. Differences in thermal time between cultivars during FIHM were small and of little practical importance, but differences in thermal time during EFI were large. Sensitivity to photoperiod and solar radiation was low in the three cultivars used. When the thermal time models were tested on independent data for five cultivars (‘Fiesta’, ‘Greenbelt’, ‘Marathon’, ‘CMS Liberty’ and ‘Triathlon’) grown as commercial crops over two years, they adequately predicted floral initiation and harvest maturity.

Subcellular compartmentation of elements in non‐mycorrhizal and mycorrhizal roots of Pinus sylvestris: an X‐ray microanalytical study. II. The distribution of calcium, potassium and sodium

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.

A comparative study of feeding and growth in two coexisting species of carnivorous gastropods

The effects of variable food supply on growth rate and feeding behaviour in two coexisting intertidal gastropods were examined through field and laboratory experiments involving mark and recapture procedures, growth experiments under controlled food supply and video observations of feeding. All cohorts of both Japeuthria species grew most in summer, with the highest growth rate being achieved by the youngest cohort of both sexes. In contrast, almost all cohorts (except the youngest one) showed zero to negative growth in winter. The growth rates of Japeuthria species clearly varied depending on feeding frequencies and the initial size of individuals. Females of both species had a significantly higher growth rate than males, though the difference became less marked with decreasing food supply. The total time spent on feeding and the length of the first feeding bout generally increased as the duration of the interval between meals was increased across treatments. From both the field growth experiment and the observations of feeding behaviour it is clear that J. ferrea had a higher frequency of feeding than J. cingulata in the field; 1- to 3-d intervals of feeding frequency in the former and 3- to 6-d intervals in the latter. Most notably, the two species showed a reversal in growth rates with changing conditions of food supply. When food was relatively abundant J. ferrea achieved better growth than J. cingulata, but J. cingulata grew better than J. ferrea under low food supply. In view of the fact that J. ferrea seems to be competitively superior to J. cingulata under normal levels, the present observation that J. cingulata can perform better than J. ferrea when food availability is low gives an important advantage to the latter in terms of its coexistence with the former.

Source-sink relations affect growth but not the allocation pattern of birch (Betula pendula Roth) seedlings under elevated [CO2

ABSTRACT Birch (Betula pendula Roth.) seedlings were kept for two growing seasons under ambient (∼350 µmol mol-1) and elevated (∼700 µmol mol-1) [CO2]. The present study was designed to examine the effects of [CO2] and pot size on growth and carbon allocation under conditions of non-limiting water and nutrient supply, in order to separate the effects of source-sink interaction from the effects of nutrient deficiency. The manipulation of the source-sink relations had a strong influence on the growth response to elevated [CO2]. When the rooting volume was inadequate, it resulted in a source-sink imbalance which constrained growth under elevated [CO2]. When root exploration was unconstrained, total dry mass was significantly increased (by about 24%) under elevated [CO2]. However, the allometric relationships in allocation pattern and in morphogenetic development were not affected by either [CO2] or pot treatments when the saplings were of the same size. Thus, by constraining dry mass production, small sinks affected the magnitude of the growth responses to elevated [CO2], but did not affect the plant allocation pattern and allometric relationships when nutrient supply was non-limiting. However, by slowing down growth, sink restrictions counteract the speed-up of ontogeny which is the main effect of elevated [CO2] on tree growth.

Long-term effects of elevated carbon dioxide concentration and provenance on four clones of Sitka spruce (Picea sitchensis). I. Plant growth, allocation and ontogeny.

Four clones of Sitka spruce (Picea sitchensis (Bong.) Carr.) from two provenances, at 53.2 degrees N (Skidegate a and Skidegate b) and at 41.3 degrees N (North Bend a and North Bend b), were grown near Edinburgh (55.5 degrees N), U.K., for three growing seasons in ambient (~350 micromol per mol) and elevated (~700 micromol per mol) CO2 concentrations under conditions of non-limiting water and nutrient supply. Bud phenology was not affected by elevated [CO2] in the second growing season, but in the third year, the duration of shoot extension growth in three of the four clones (North Bend clones and Skidegate a) was significantly shortened, because of the suppression of lammas growth. Saplings in elevated [CO2] had significantly greater dry masses of all components than saplings in ambient [CO2]. However, comparison of relative component dry masses between plants of similar size showed no effect of [CO2] treatment on plant allometric relationships. This finding, and the observed suppression of lammas growth by high [CO2] during the third growing season suggests that the main effect of increasing [CO2] is to accelerate sapling development. Clonal provenance did not affect dry mass production in ambient [CO2]. However, in elevated [CO2] the more southerly clones significantly out-performed the more northerly clones when grown at a latitude close to the latitudinal provenance of the Skidegate clones. As atmospheric carbon dioxide concentration rises, such changes in the relative performance of genotypes may be exploited for economic gain through appropriate selection of provenances for forest plantings.

Interacting components of interspecific relative growth rate: constancy and change under differing conditions of light and nutrient supply

1. One thousand three hundred and twenty plants from 22 species of herbaceous angiosperms, typical of open sunny habitats, were grown from seed for 35 days under controlled conditions in four experimental environments: high (1100 μmol m–2 s–1 PAR) and low (200 μmol m–2 s–1 PAR) light, combined with high (full‐strength) and low (1/6 dilution) levels of hydroponic nutrient solution. Plants of each species were harvested at 15, 20, 25, 30 and 35 days post‐germination. 2. Relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA) and leaf mass ratio (LWR) were estimated for each species in each treatment combination. 3. Both light and nutrient levels affected RGR and each of the growth components. Average NAR increased, while SLA and LWR decreased, with increasing light. Increasing nutrient levels increased all three growth components. Light and nutrient levels interacted in their effects on NAR and SLA, but not in their effects on LWR. 4. Those species having the highest RGR in the most productive environment were most severely depressed in the less productive environments. This same pattern also occurred with NAR and SLA, but not with LWR. 5. The rank order of species with respect to SLA and LWR remained similar across the treatment environments; with respect to NAR the rank order remained similar in only four of the six treatment contrasts; with respect to RGR the rank order remained similar in only two of the six treatment contrasts and the rank order actually reversed in one treatment contrast. 6. RGR did not display strong bivariate correlations with any of the growth components in any of the treatment groups. It had positive, moderately strong correlations with NAR but only in the low‐nutrient treatments. It had positive, moderately strong correlations with LWR only in the high‐nutrient treatments. After controlling for the other growth components, each showed strong positive relationships with RGR. Furthermore, the effects of the treatments disappeared after controlling for the components, showing that the treatment effects were completely mediated through their effects on these underlying components. 7. There were also strong negative partial correlations between each of the growth components. These compensatory relationships buffered RGR from large changes in response to changing environments.

A Model of Phytoplankton Competition for Limiting and Nonlimiting Nutrients: Implications for Development of Estuarine and Nearshore Management Schemes

The global increase of noxious bloom occurrences has increased the need for phytoplankton management schemes. Such schemes require the ability to predict phytoplankton succession. Equilibrium Resource Competition theory, which is popular for predicting succession in lake systems, may not be useful in more dynamic environments, such as estuaries and coastal waters. We developed a mathematical model better suited to nonsteady state conditions. Our model incorporated luxury consumption of nonlimiting nutrients and cell starvation processes into a cell-quota-based nutrient-phytoplankton scheme. Nutrient pools described included nitrogen and phosphorus. Phytoplankton groups characterized in the model were a phosphorus-specialist, a nitrogen-specialist, and an intermediate group. We emphasized competition for nutrients under conditions of continuous and pulsing nutrient supply, as well as different nutrient loading ratios. Our results suggest that delivering nutrients in a pulsing fashion produces dramatic differences in phytoplankton community composition over a given period, that is, reduction of accumulated biomass of slower growing algae. Coastal managers may be able to inhibit initiation of slow-growing noxious blooms in estuaries and coastal waters by pulsing nutrients inputs from point sources, such as sewage treatment plants.

Parental investment and the management of an endangered penguin

The yellow-eyed penguin, Megadyptes antipodes, is considered one of the most threatened species of penguin in the world. Research has indicated that yellow-eyed penguin parents will reduce their overall investment in offspring to match the available food supply, but they rarely exhibit brood reduction. Increased adult mortality under adverse conditions has led to the suggestion that yellow-eyed penguins incur a cost of reproduction in `poor food' years and that such a cost could be avoided by managers relieving them of the burden of raising one of their two chicks. We examined the effects of artificially reducing brood size in yellow-eyed penguins to determine: (1) how reproductive costs may be expressed, and (2) whether brood reduction has the potential to relieve such costs. Our results indicate that yellow-eyed penguins adjust their level of parental effort according to brood size, at least under favourable conditions of food supply. Moreover, parents of single-chick broods were in better condition and guarded their offspring for longer periods than those raising twins. Nevertheless, we found no significant effects of reducing brood size on adult survival or the frequency with which juveniles were resighted. However, if adult condition is sensitive to the effects of brood size this outcome may have significant implications for their ability to survive post-breeding moult in years when food availability is low. Overall, the study emphasises the value of approaching conservation issues from within a theoretical framework.

A simple empirical model for predicting development and dry matter partitioning in cauliflower ( Brassica oleracea L. botrytis)

An empirical model derived from data of field experiments is presented that predicts development and dry matter partitioning in cauliflower under conditions of unrestricted nutrient and water supply. The model is a combination of an empirical relationship between temperature sum and leaf number, a vernalisation model, an allometric approach of dry matter partitioning between leaf and stem and an empirical logistic function describing the fraction of dry matter allocated to the curd depending on the temperature sum after the end of the vernalisation process. This model was incorporated in a simple dry matter production model which calculated dry matter production using the product of intercepted photosynthetic active radiation and light use efficiency. However, the parameter values light use efficiency and specific leaf area of the model had to be fitted to every experiment in order to get an acceptable description of cauliflower dry matter production. Applied to an independent data set the model was able to predict measurable parameters like leaf number ( r 2 = 0.73), the proportion of leaf, stem and curd on total dry matter ( r 2 = 0.55, 0.08 and 0.77) and the length of the growing season ( r 2 = 0.69).

The Effect of Nutrient and Water Availability on Nectar Secretion and Nectary Structure of the Dominant Labiatae Species of Phrygana

The effect of irrigation and artificial nutrient supply on nectar secretion and nectary structure of three of the main Labiatae species occurring in a phryganic community (viz. Satureja thymbra, Stachys cretica, and Thymus capitatus) was studied. Experiments were carried out on potted plants taken from the wild, along with control plants (untreated or/and naturally growing). Only T. capitatus clearly secreted a higher nectar volume and sugars after treatment, whereas the yield of S. thymbra did not increase significantly when plants were irrigated or artificially supplied with nutrients. The case of S. cretica was more complicated showing different trends depending on the time of the year. Conclusions are: (i) nutrient supply does not always enhance nectar secretion in the poor-soil phrygana; (ii) irrigation is more important in increasing per flower nectar secretion than fertilization; (iii) nutrient supply results in the presence of nectarless flowers; (iv) nectar analyses made on three plants show that neither of the treatments affects amino acid concentration of the nectar, but they result in either glucose excess in the nectar of woody species (viz. S. thymbra, T. capitatus) or in sucrose excess in the nectar of herbaceous species (S. cretica). Most of these results can be explained through a differential resource allocation of the water-stressed plants grown in the wild on the one hand, and the treated plants on the other. This difference stems from the fact that woody species clearly distinguish between growth and reproductive phases, whereas in herbaceous perennials the growing phase overlaps with reproductive phase and blooming. Under conditions of artificial nutrient supply, plants may continue to allocate to vegetative growth rather than to pollinator allurement; on the contrary, wild growing plants may invest exclusively in pollinator allurement. It is assumed that the approach of the summer is very critical and conclusive for a shorter life cycle of the species. Some intraspecific differences in nectary structure were found as a result of the treatments. However, because these differences were not consistent either with the treatment effects on nectar secretion or with the nectar characteristics studied, it is concluded that the observed differences may be mere intraspecific variations normally occurring in nature.

Detachment of biofilm bacteria due to variations in nutrient supply

Growth and detachment rates of an environmental isolate of Aeromonas hydrophila attached to a surface were determined under varying nutrient supply conditions in a complex medium. Growth and detachment of cells were observed in real time using phase contrast microscopy in glass parallel plate flow chambers. Surface shear stress was controlled in all experiments at 3 N m−2. Images were taken every 15 min. Digital image analysis was used to determine specific growth and detachment rates. An observable parameter proportional to the nutrient depletion at the surface due to transfer limitations was used to indicate nutrient limitations. Specific detachment rates increased as the depletion parameter increased, indicating that nutrient limitations cause this bacterium to detach at greater rates.