Blue, red and blue plus red light control of chlorophyll content and CO2 gas exchange in barley leaves: Quantitative description of the effects of light quality and fluence rate

The dependence of the Chl content and the rate of CO₂ gas exchange (RGE) on both blue and red quanta fluence rates have been studied in primary leaves of barley ( Hordeum vulgare L. cv. Viner). Empirical equations connecting the two photosynthetic indices with fluence rates of blue or red light were developed. These equations consist of 3 (Chl content) or 2 (RGE) terms, each reflecting the involvement of a specific reaction in the long-term light control of the development of the photosynthetic apparatus. On the basis of the equations the effects of mixed blue plus red light on both the Chl content and RGE were calculated. An additive mode of the co-action of blue and red light in the range of high PFDs (10–170 μmol m⁻² s⁻¹) becomes evident from the comparison of the experimental results and calculated data. The results indicate the involvement of phytochrome, cryptochrome and chlorophyll in the long-term regulation of the Chl content and RGE.     

Grazing Behavior of Heterotrophic NanoFlagellates Observed with a High Speed VTR System

The grazing patterns of heterotrophic nanoflagellates ( Cafeteria roenbergensis and Actinomonas mirabilis ) were recorded by high speed video micrography. Experiments were carried out at 10, 15 and 25° C at a salinity of 36 psu and at 20° C when the salinity was either 20 or 36 psu. Bacteria entrained in a stream of water generated by flagellar beating were propelled toward the cell body (phase 1). Each bacterium destined for ingestion made contact with the anterior end of the flagellum of Cafeteria or was captured with an actinopod of Actinomonas (phase 2). The captured bacterium was drawn close to the cell body (phase 3) and ingested (phase 4). Cafeteria was observed during 38 grazing events and appeared to have two different patterns of ingestion, "enclosing" and "pocket phagocytosis." The mean time for food capture was 0.10 s and the subsequent ingestion was complete on average in 1.59 s. No further bacteria were captured until ingestion was complete. Actinomonas was observed during 27 grazing events in which capture of panicles on an actinopod was followed by transport to the cell body and subsequent "enclosing phagocytosis." The mean time to complete grazing was 39.16 s, which is about 25 times longer than for Cafeteria ; the phase of transport to the cell body occupied most of this time. During the grazing cycle, Actinomonas captured other bacteria on the actinopodia, but sometimes released them. Grazing time in Cafeteria was positively correlated with temperature but not correlated with salinity. Grazing behavior in Actinomonas was correlated with neither temperature nor salinity.     

Calanoid copepod grazing on phytoplankton: seasonal experiments on natural communities

Calanoid copepods are major components of most lacustrine ecosystems and their grazing activities may influence both phytoplankton biomass and species composition. To assess this we conducted four seasonal, in situ, grazing experiments in eutrophic Lake Rotomanuka, New Zealand. Ambient concentrations of late stage copepodites and adults of calanoid copepods (predominantly Calamoecia lucasi, but with small numbers of Boeckella delicata) were allowed to feed for nine days on natural phytoplankton assemblages suspended in the lake within 1160 litre polyethylene enclosures. The copepods reduced the total phytoplankton biomass of the dominant species in all experiments but were most effective in summer (the time of highest grazer biomass) followed by spring and autumn. In response to grazing pressure the density of individual algal species showed either no change or a decline. There were no taxa which increased in density in the presence of the copepods. The calanoid copepods suppressed the smallest phytoplankton species (especially those with GALD (Greatest Axial Linear Dimension) < µm) and there appeared to be no selection of algae on the basis of biovolume. Algal taxa which showed strong declines in abundance in the presence of the copepods include Cyclotella stelligera, Coelastrum spp., Trachelomonas spp., Cryptomonas spp., and Mallomonas akrokomos. Calanoid copepods are considered important grazers of phytoplankton biomass in this lake. The study supports the view that high phytoplankton:zooplankton biomass ratios and large average algal sizes characteristic of New Zealand lake plankton may, at least partly, be caused by year round grazing pressure on small algae shifting the competitive balance in favour of larger algal species.     

Immobilized Coffea arabica cell culture using a bubble-column reactor with controlled light intensity

Coffea arabica cells immobilized by calcium alginate gel were photocultured using a bubble-column reactor under controlled light intensity. This process was carried out after their alkaloid productivity was improved by increasing the cell density in the initial gel matrix and preculturing the immobilized cells in the dark prior to light irradiation. The cells were grown in the form of a biofilm on gel beads, producing 100 mg/L of purine alkaloids in a 24-day batch culture. Alkaloid production was relatively constant with respect to light intensity changes, and also cell growth was not suppressed much at high light intensity, with these behaviors being different from those obtained using suspended cells. These phenomena are explained by estimating the light intensity gradient within the cell-immobilizing particles and by measuring the viable cell distribution within them. It subsequently suggests that the subsurface cells affect both the production and growth behaviors. (c) 1993 John Wiley & Sons, Inc.     

Shedding light on a hot topic: Tuberisation in potato

Growing small seedling tubers from true seed, comparable with mini tubers, in controlled conditions could be a method to multiply healthy starting material of potato. In indoor farming systems, the conditions can be optimised for high production. In field trials, it is impossible to investigate the effects of environmental factors such as temperature and light separately. In this study, we performed three climate room experiments in which the effects of light intensity, temperature and percentage of far-red light in the light spectrum on tuber production were assessed. We found that increasing the average temperature reduced tuber number and tuber weight. Increasing the diurnal temperature variation while keeping the average temperature equal resulted in increased tuber size. The light treatments on the other hand only affected the number of tubers per plant: increasing light intensity and increasing the percentage of far-red light in the spectrum enhanced the number of tubers. Moreover, interaction in tuber production between inbred lines and temperature was significant, with some inbred lines being relatively tolerant to high temperature. These findings will help breed for heat tolerant varieties and optimise growing conditions for tuber production in indoor farming systems.     

Some ecological relationships of larval ascaridoids from south-eastern Queensland marine fishes

Nine larval types within the genera Anisakis, Terranova, Thynnascaris and Contracaecum were recovered from south-eastern Queensland marine fishes. Data on (i) incidence, (ii) intensity of infection, (iii) host diet and (iv) habitat for each type suggest Anisakis is an open water type, Contracaecum an inshore, shallow water type and both Terranova and Thynnascaris have intermediate distributions. Host diets indicate Anisakis and Terranova are found in predators of nekton, Contracaecum and Thynnascaris in benthic feeders.     

Carbon (13C) uptake and allocation in pasture plants following field pulse-labelling

The allocation of carbon (C) to plant roots and conversion to soil organic matter is a major determinant of the size of the terrestrial C pool in pastoral ecosystems. The aim was to quantify C allocation to roots in contrasting pastoral ecosystems. Pastures on long-term research sites in Canterbury, New Zealand were pulse-labelled using ¹³CO₂ within portable gas-tight enclosures. Sites included Winchmore (with or without superphosphate fertiliser, and with or without irrigation) and Tara Hills (low, medium or high grazing intensity with continuous or alternating grazing). Separate micro-plots were labelled in late spring, summer and autumn at Winchmore and in spring at Tara Hills. Herbage label ¹³C recoveries were greatest one hour after pulse labelling and declined by 21 days, whereas in roots they were initially lower but generally continued to increase until 21 days. The greatest recoveries of ¹³C in roots, one hour and 21 days after labelling, were in summer and autumn respectively. The proportion of label ¹³C allocated to roots by 21 days was 0.50 in the absence of superphosphate and 0.41 in the superphosphate treatment, and was 0.39, 0.43 and 0.51 respectively in spring, summer and autumn. Irrigation had no significant effect on root allocation. The low stocking rate at Tara Hills, which had the greatest herbage biomass, also had greater total ¹³C, tussock herbage ¹³C and root ¹³C recoveries than the higher stocking rate treatments. Inter-tussock root recovery and allocation of ¹³C to roots increased with increasing stocking rate, whereas tussock root allocation was greatest in the high and least in the medium stocking rate treatment. By 21 days there was a greater inter-tussock and tussock root recovery and lower inter-tussock herbage recovery in the continuous than in the alternating grazing management treatment. The root allocation was generally greater in the continuous than in alternating grazed treatments, except for tussocks one hour after labelling where the reverse was the case. In conclusion the ¹³C pulse labelling showed pasture plants allocate more C to roots with low soil fertility, high grazing intensity, continuous grazing, and in autumn.     

Influence of Seiche-Generated Light Field Fluctuations on Phytoplankton Growth

Phytoplankton, owing to the periodic ascent and descent caused by internal seiches, is exposed to experiential fluctuations in light intensity. The increase in light intensity associated with its ascent towards the surface is greater than the decrease caused by its descent. A simple mathematical model is used to derive relationships showing that 1) the mean light intensity in an epilimnion influenced by internal waves is not more than 6.1% lower than in a stationary system and 2) in the meta- and hypolimnion of lakes of low transparency (i.e. with a high extinction coefficient) internal seiches of large amplitude increase the mean light intensity by several orders of magnitude. This can produce a many-fold increase in the depth of the euphotic zone. The mean rates of photosynthesis of phytoplankton in the meta- and hypolimnion increase particularly at the antinodes of the waves. Internal seiches evidently may play an important role in causing plankton patchiness and in the presence of photosynthetically active phytoplankton at depths far below the 1% light limit.