THE RELATIONSHIP OF LIGHT,TEMPERATURE, AND CURRENT TO THE SEASONAL DISTRIBUTION OF BATRACHOSERMUM (RHODOPHYTA)12

Observations of the 2 growth sites and the laboratory experiments performed on B. vagum and B. moniliforme indicate that B. moniliforme is better suited to higher intensity illumination than is B. vagutn. B. vagnm was found growing year-round in a dark-water stream protected from high intensity light by the filtering effect of the bog-dark water. B. moniliforme was found growing in a clear water stream. Without the protection of dark water, the B. moniliforme disintegrated under the high light intensities of summer. In the laboratory, B. moniliforme retained a healthy macroscopic condition over a full range of light-intensity treatments; above 250 ft-c B. vagum was increasingly distintegrated. Light intensity, however, was not the only factor regulating the growth, of Batrachospermum in the 2 growth sites. The pattern of growth of B. vagum in Sinking Creek varied with the depth of the water and, therefore, with the light intensity it received. However, it was found that where all Conditions were the same, the greatest percent cover of the algae was in the center of the stream where the current was the greatest. Thus it was found that within the limitations caused by water depth, current velocity can become limiting to the growth of B. vagum. Although the evidence for environmental factors affecting the growth of B. moniliforme in Smay's Run is less extensive, light intensity and current velocity in this site also appear to interact to control the growth pattern of the algae.     

PATTERNS OF GROWTH AND CELL COMPOSITION OF FRESHWATER ALGAE IN LIGHT-LIMITED CONTINUOUS CULTURES1

Selenastrum minutum (Näg.) Collins and three species of Scenedesmus were grown in light-limited continuous cultures. Comparative growth patterns were explained in terms of differences in the rates of light absorption and utilization. For all species, increasing light intensity or lowering temperature caused chl a/C to decrease and RNA/C to increase. Similar shifts in pigment composition have been widely reported. However, the RNA:light interaction has only been reported infrequently, and the RNA:temperature interaction is believed to be the first reported observation of its kind in algae. Distinct differences in RNA/C among the test algae may be size-dependent. Similar environmentally induced shifts in chl a/C and RNA/C among all test algae point to the existence of a common control mechanism which maximizes the specific growth rate through adjustments to cell composition.     

EFFECT OF LIGHT INTENSITY AND GLYCEROL ON THE GROWTH,PIGMENT COMPOSITION,AND ULTRASTRUCTURE OF CHROOMONAS SP.1,2,3

Growth of Chroomonas sp. increased with light intensity (100, 1800, and 2700 μW/cm²) with a fivefold increase from the lowest to the highest intensity. Chlorophyll and phycocyanin content per cell were greater in cells grown at low light intensity, but the ratio of chlorophyll a and c did not vary appreciably. Cells grown at low light intensity had 30% more phycocyanin than cells grown at high intensities of light. The chloroplast of cells with the higher phycocyanin content had average intrathyla-koidal widths of 300 Å, whereas those cells with the lower phycocyanin content had average intrathylakoidal widths of 200 Å. This result is compatible with the hypothesis that phycocyanin is located in the intrathylakoidal space in the cryptophyte algae. Of the various energy sources tested, only glycerol was able to support limited growth tinder nonphotosynthetic conditions. Under no condition was the chloroplast reduced to an elioplast or proplastid state. Starch accumulation was greatest in cells grown in continuous while light in glycerol. Eye-spots were commonest in cells grown in darkness and interrupted every 24 hr by a few seconds of white light. It was concluded that this organism is an obligate phototroph.     

THE EFFECT OF GROWTH IRRADIANCE ON THE COUPLING OF CARBON AND NITROGEN METABOLISM IN CHAETOMORPHA LINUM (CHLOROPHYTA)

The influence of growth irradiance on the non-steady-state relationship between photosynthesis and tissue carbon (C) and nitrogen (N) pools in Chaetomorpha linum (Muller) Kutzing in response to abrupt changes in external nitrogen (N) availability was determined in laboratory experiments. For a given thallus N content, algae acclimated to low irradiance consistently had a higher rate of light-saturated photosynthesis (P_max normalized to dry weight) than algae acclimated to saturating irradiance; for both treatments, P_max was correlated to thallus N. Both P_max and the photosynthetic efficiency (α_dw) were correlated in C. linum grown at either saturating or limiting irradiance over the range of experimental conditions, indicating that variations in electron transport were coupled to variations in C-fixation capacity despite the large range of tissue N content from 1.1% to 4.8%. Optimizing both α and P_max and thereby acclimating to an intermediate light level may be a general characteristic of thin-structured opportunistic algae that confers a competitive advantage in estuarine environments in which both light and nutrient conditions are highly variable. Nitrogen-saturated algae had the same photosynthesis–irradiance relationship regardless of light level. When deprived of an external N supply, photosynthetic rates did not change in C. linum acclimated to low irradiance despite a two-fold decrease in tissue N content, suggesting that the active pools of chlorophyll and Rubisco remained constant. Both α and P_max decreased immediately and continuously in algae acclimated to high irradiance on removal of the N supply even though tissue N content was relatively high during most of the N-starvation period, indicating a diversion of energy and reductant away from C fixation to support high growth rates. Carbon and nitrogen assimilation were equally balanced in algae in both light treatments throughout the N-saturation and -depletion phases, except when protein synthesis was limited by the depletion of internal N reserves in severely N-starved high-light algae and excess C accumulated as starch stores. This suggests that the ability for short-term adjustment of internal allocation to acquire N andC in almost constant proportions may be especially beneficial to macroalgae living in environments characterized by high variability in light levels and nutrient supply.     

DIFFERENTIAL IMPACTS OF PHOTOACCLIMATION AND THERMAL STRESS ON THE PHOTOBIOLOGY OF FOUR DIFFERENT PHYLOTYPES OF SYMBIODINIUM (PYRRHOPHYTA)1

The capacity for photoacclimation to light at 100 or 600 μmol photons·m^?2·s^?1 and the subsequent response to thermal stress was examined in four genetically distinct cultures of symbiotic dinoflagellates in the genus Symbiodinium with the ITS2 designations A1, A1.1, B1, and F2. While all algal types showed typical signs of photoacclimation to high light via a reduction in chl a, there was a differential response in cellular growth, photosystem II (PSII) activity, and the chl a‐specific absorption coefficient between cultures. When maintained at 32°C for up to 10 days, significant variation in the susceptibility to thermal stress was observed in the rate of loss in PSII activity and electron transport, PSII reaction center degradation, and cellular growth. The order of thermal tolerance did not change between the two light levels. However, as expected, loss in photosynthetic function was exacerbated in the thermally sensitive phylotypes (B1 and A1.1) when acclimated to the higher light intensity. There was no consistent relationship between thermal tolerance and changes in light energy dissipation via non‐photochemical pathways. Phylotypes F2 and A1 showed a high degree of thermal tolerance, yet the cellular responses to light and temperature were markedly different between these algae. The F2 isolate showed the greatest capacity for photoacclimation and growth at high light and temperature, while the A1 isolate appeared to adjust to thermal stress by a slight decline in PSII activity and a significant decline in growth, possibly at the expense of increased photosystem and cellular repair rates.     

THE EFFECT OF DAYLENGTH AND LIGHT INTENSITY ON THE GROWTH RATE OF THE MARINE DIATOM DETONULA CONFERVACEA (CLEVE) GRAN1

The influence of 40 combinations of temperature (2, 7 C), light intensity (50, 200, 600, 1200, 1800 ft-c), and photoperiod (24, 15:9, 12:12, and 8:16 LD) at 30% salinity on the rate of cell division of the Narragansett Bay clone of Detonula confervacea (Det-1) was examined following appropriate preconditioning. At 2 C Detonula is a long day species (24 L) and prefers low light intensities (200–600 ft-c); poorest growth occurred at 12:12 and 8:16 LD, and the compensation intensity was about 10 ft-c. Increasing temperature to 7 C increased the mean growth rate, reduced the optimal daylength (15:9 LD), even though Detonula remained a long day species and increased the optimal light intensity (600–800 ft-c). The compensation intensity varied with daylength and ranged from about 10–50 ft-c. Photoperiods of 12:12 and 8:16 LD were least favorable for growth at both temperatures; light limitation and inhibition were observed at 50 and 1800 ft-c. respectively; inhibition was less pronounced at 7 C. There is some indication that the conditions of growth that the stock cultures were exposed to prior to preconditioning for use in the experiments may have sometimes influenced response. Detonula produced resting spores without nutrient depletion at 2 and 7 C at all light intensities when the photoperiod was lengthened. Auxospore formation was also observed. Although short daylengths (9:15 LD) limit Detonula's growth during the early stages of the winter bloom, it competes successfully against Skeletonema costatum initially. This results from its higher rates of growth and of photosynthesis at the prevailing temperature and light conditions and a lower compensation intensity than reported for Skeletonema. The main causes of Detonula's growth inception and termination in Narragansett Bay differ.     

ACCLIMATION OF THE PHOTOSYNTHETIC APPARATUS OF PALMARIA PALMATA (RHODOPHYTA) TO LIGHT QUALITIES THAT PREFERENTIALLY EXCITE PHOTOSYSTEM I OR PHOTOSYSTEM II1

Acclimation of the photosynthetic apparatus to light absorbed primarily by phycobilisomes (which transfer energy predominantly to photosystem II) or absorbed by chlorophyll a (mainly present in the antenna of photosystem I) was studied in the macroalga Palmaria palmata L. In addition, the influence of blue and yellow light, exciting chlorophyll a and phycobilisomes, respectively, ivas investigated. All results were compared to a white light control. Complementary chromatic adaptation in terms of an enhanced ratio of phycoerythrin to phycocyanin under green light conditions was observed. Red light (mainly absorbed by chlorophyll a) and green light (mainly absorbed by phycobilisomes) caused an increase of the antenna system, which was not preferentially excited. Yellow and blue light led to intermediate states comparable to each other and white light. Growth was reduced under all light qualities in comparison to white light, especially under conditions preferably exciting phycobilisomes (green light-adapted algae had a 58% lower growth rate compared to white light-adapted algae). Red and blue light-adapted algae showed maximal photosynthetic capacity with white light excitation and significantly lower values with green light excitation. In contrast, green and yellow light-adapted algae exhibited comparable photosynthetic capacities at all excitation wavelengths. Low-temperature fluorescence emission analysis showed an increase of photosystem II emission in red light-adapted algae and a decrease in green light-adapted algae. A small increase of photosystem I emission teas also found in green light-adapted algae, but this was much less than the photosystem II emission increase observed in red light-adapted algae (both compared to phycobilisome emission). Efficiency of energy transfer from phycobilisomes to photosystem II was higher in red than in green light-adapted algae. The opposite was found for the energy transfer efficiency from phycobilisomes to photosystem I. Zeaxanthin content increased in green and blue light-adapted algae compared to red, white, and yellow light-adapted algae. Results are discussed in comparison to published data on unicellular red algae and cyanobacteria.     

FORECASTED CO2 MODIFIES THE INFLUENCE OF LIGHT IN SHAPING SUBTIDAL HABITAT1

Some abiotic conditions are well known to play disproportionately large roles in shaping contemporary assemblages, yet their roles may not continue to have similar magnitudes of effect into the future. We tested whether forecasted levels of CO₂ could alter the strength of influence of an abiotic factor (i.e., light intensity) well known for its strength of influence on the subtidal ecology of photosynthetic organisms. We investigated these dynamics in two subtidal algal species that form contrasting associations with kelp forests, one negatively associated with kelp canopies (turf‐forming brown algae, Feldmannia spp.) and the other positively associated with kelp as understory (calcifying red crustose algae, Lithophyllum sp.). Using an experimental approach, we assessed the independent and combined effects of [CO₂] (control and elevated) and light (shade, low ultraviolet B [UVB], full light) on growth, recruitment, and relative electron transport rate (rETR). Under control [CO₂], the effects of light corresponded to the relative light environments of the two groups of algae. The influence of light on the percentage cover and biomass of understory crusts was substantially reduced under elevated [CO₂], which caused crusts to grow less. While elevated [CO₂] had the opposite effect of positively influencing turf cover and biomass, it had the same effect of reducing the structuring effects of light and UVB. Hence, if we are to predict the ecological consequences of future CO₂ conditions, the role of contemporary processes cannot be assumed to produce similar effects relative to other processes, which will change with a changing climate.     

STUDIES ON THE AUTECOLOGY OF THE MARINE DIATOM THALASSIOSIRA NORDENSKIÖLDIICLEVE. 1. THE INFLUENCE OF DAYLENGTH,LIGHT INTENSITY,AND TEMPERATURE ON GROWTH1

The marine diatom Thalassiosira nordenskiöldii Clave was grown at 48 different combinations of daylength (9:15, 12:12, 15:9 LD), light intensity (0.011, 0.027, 0.066, 0.100 ly/min [g cal/cm²/min]), and temperature (0, 5, 10, 15 C). Growth occurred at all combinations of light and temperature except at 15 C at the highest light level. Maximum growth (K = 1.8 doublings/day) occurred at 10 C under the 15:9 LD cycle. At 15 C the maximum rate was 1.7 doublings/day but occurred at the shortest day-length (9:15 LD). The maxima at 5 and 0 C were 1.32 and 0.67 doubling/day, respectively. At 0 C growth was similar over a wide range of light intensities (K = 0.6–0.65), with, maximum growth being attained at a much lower light intensity than at 5 C. Above 5 C there was a decrease in the light intensity at which maximum growth occurred and excessive light became inhibitory to growth. At 15 C the light intensity at which maximum growth occurred was greater with shorter day-lengths. The temperature optimum was 10 C at 15:9 and 15 C at 9:15 LD. The chlorophyll a content of the cells was greatest under low light intensities and short daylengths, while temperature had a variable effect. The response of Thalassiosira in the laboratory contrasts with, its apparent preference for low temperatures in nature (0–5 C). The experiments suggest that the termination of the bloom of Thalassiosira in Narragansett Bay and elsewhere is not solely temperature dependent.     

THE WAVELENGTH DEPENDENCE OF MASSIVE CAROTENE SYNTHESIS IN DUNALIELLA BARDAWIL (CHLOROPHYCEAE)1

Dunaliella bardawil Ben-Amotz & Avron accumulates high concentrations of β-carotene when grown under high light intensity. The β-carotene is composed mainly of 9-cis and all-trans β-carotene. Accumulation of β-carotene and an increase in the ratio of the 9-cis to the all-trans isomer are strongly dependent on the light intensity under which the algae are cultivated but are independent of light quality within the photosynthetically active radiation range. Cells grown under continuous red (>645 nm) or white light of 500 W·m^?2 reach a value of about 32 pg β-carotene·cell^?1 and a ratio of 9-cis to all-trans β-carotene of around 2, whereas cells grown under low red or white light intensity of 25 W·m^?2 contain about 3 pg·cell^?1 and a ratio of isomers of around 0.3.     

THE SHORT‐TERM EFFECT OF IRRADIANCE ON THE PHOTOSYNTHETIC PROPERTIES OF ANTARCTIC FAST‐ICE MICROALGAL COMMUNITIES1

Although sea‐ice represents a harsh physicochemical environment with steep gradients in temperature, light, and salinity, diverse microbial communities are present within the ice matrix. We describe here the photosynthetic responses of sea‐ice microalgae to varying irradiances. Rapid light curves (RLCs) were generated using pulse amplitude fluorometry and used to derive photosynthetic yield (Φ_PSII), photosynthetic efficiency (α), and the irradiance (E_k) at which relative electron transport rate (rETR) saturates. Surface brine algae from near the surface and bottom‐ice algae were exposed to a range of irradiances from 7 to 262 μmol photons · m^?2 · s^?1. In surface brine algae, Φ_PSII and α remained constant at all irradiances, and rETR_max peaked at 151 μmol photons · m^?2 · s^?1, indicating these algae are well acclimated to the irradiances to which they are normally exposed. In contrast, Φ_PSII, α, and rETR_max in bottom‐ice algae reduced when exposed to irradiances >26 μmol photons · m^?2 · s^?1, indicating a high degree of shade acclimation. In addition, the previous light history had no significant effect on the photosynthetic capacity of bottom‐ice algae whether cells were gradually exposed to target irradiances over a 12 h period or were exposed immediately (light shocked). These findings indicate that bottom‐ice algae are photoinhibited in a dose‐dependent manner, while surface brine algae tolerate higher irradiances. Our study shows that sea‐ice algae are able to adjust to changes in irradiance rapidly, and this ability to acclimate may facilitate survival and subsequent long‐term acclimation to the postmelt light regime of the Southern Ocean.     

低平均光强下波动光对铜绿微囊藻生长的影响

为了研究波动光对藻类的影响, 以典型水华藻种铜绿微囊藻Microcystis aeruginos为研究对象, 运用了基于单片机系统的光强控制实验装置, 开展了不同光照条件下铜绿微囊藻的生长研究。共设置了四种光照条件, 分别为不同周期波动光强FL(Fluctuating Light)组(10min FL、1h FL和6h FL)和平均光强AL(Average Light)组。实验结果表明, 在低平均光强下, 6h FL、1h FL和10min FL组铜绿微囊藻藻密度相对于AL组分别增加了28.3%(P<0.05)、18.2%(P<0.05)和7.7(P>0.05)。三组波动光强下铜绿微囊藻的比增长速率、F_v/F_m和rETR均显著大于平均光强组(P<0.05), 且随着波动光周期的增大, 各指标也会显著增加(P<0.05), 而热耗散NPQ平均值、单个细胞类胡萝卜素含量等指标与上述指标呈相反的规律并且差异显著(P<0.05)。结果也表明在低平均光强下, 相比于恒定光照, 铜绿微囊藻在波动光下能更好地调节自身光合作用机制去利用光能, 且波动周期越大, 铜绿微囊藻对光能利用效率越高。这暗示了低强度波动光可以作为提高藻类产量的一种手段。     

群体和单细胞微囊藻对短期高光胁迫的生理响应

为了探讨不同形态的微囊藻（Microcystis）对光的耐受能力及其应对机制,研究比较了短期高光强条件下群体微囊藻和单细胞微囊藻的生理响应,结果表明,在高光强胁迫下,群体和单细胞微囊藻的叶绿素含量、最大电子传递速率（ETR_max）均降低,但与单细胞微囊藻相比,群体微囊藻的下降幅度较小;在高光强胁迫下,群体微囊藻的过氧化氢酶（CAT）与超氧化物歧化酶（SOD）的活性均显著增加,而单细胞微囊藻只有CAT活性增加;在短期高光胁迫下,群体微囊藻的死亡率没有显著变化。这些结果表明群体微囊藻比单细胞微囊藻能耐受更高的光强,也暗示了群体微囊藻在野外高光强条件下更具竞争优势。     

EFFECTS OF VARIATIONS IN LIGHT INTENSITY ON THE EFFICIENCY OF GROWTH OF SKELETONEMA COSTATUM (BACILLARIOPHYCEAE) IN A CYCLOSTAT1

The relative importance of respiration and organic carbon release to the efficiency of carbon specific growth of Skeletonema costatum (Grev.) Clave was evaluated over a light range from 1500–15 μE · m^?2· s^?1. Net growth efficiency ranged from 0.45–0.69 with a maximum at 130 μE · m^?2· s^?1. Respiration was 93% or more of the variations in growth efficiency. Organic carbon release ranged from 0–7% of gross production and increased with light intensity. Carbon specific particulate production was a hyperbolic function of incident light intensity and was related exponentially to particulate carbon production per unit chlorophyll a. Full sunlight conditions, 1500 μE · m^?2· s^?1, did not induce photoinhibition of gross production. Variations in the efficiency of growth of S. costatum were minimized over a wide range of light intensities mainly because of variations in cellular pigments which permitted the efficient utilization of available light energy, and a reduction in the losses of carbon which increases the growth rate, possibly as a consequence of the recycling of respired carbon within the cell.     

THE DEPENDENCE OF CELL DIVISION IN CHLORELLA ON TEMPERATURE AND LIGHT INTENSITY

The effects of temperature and light on cell division were studied in synchronized suspensions of the high-temperature strain Chlorella 7–11–05. It was found that the time for incipient cell division, the progress in the process after it started, and the number of cells produced are influenced by temperature and light intensity. Within limits, cell division is generally favored by the increase in temperature. The increase in light intensity first favors cell division then, after the optimal light intensity is attained, a further increase in light intensity inhibits cell division. Observations are discussed in connection with the findings of other investigators. The limitations of cell division by temperature and light intensity are considered to be separate from the effects of these factors on growth.     

CIRCADIAN REGULATION OF BIOLUMINESCENCE IN THE DINOFLAGELLATE PYROCYSTIS LUNULA1

In the unicellular algae Pyrocystis lunula Schütt and Gonyaulax polyedra Stein, bioluminescence and its circadian regulation are similar in several respects, but there are also several important differences. As in G. polyedra, P. lunula emits light both as bright flashes and as a low intensity glow. At 20° C, the individual flashes are considerably brighter than in G. polyedra, and their durations are typically less than 500 ms. Both species show a circadian rhythm in the frequency of spontaneous flashes, which peaks in the night-phase under light–dark cycles and continues in both continuous light and dark. However, compared to G. polyedra, the circadian system in P. lunula is more sensitive to light: 10 min exposures (500 μmol · m^–2· s^–1 white light) can shift the phase of the rhythm by more than 8 h, and rhythmicity is completely suppressed at an irradiance above 20 μmol · m^–2· s^–1, where the G. polyedra rhythym persists for weeks. Like G. polyedra, period length increases with increasing irradiance of continuous red light but decreases with increasing intensity of continuous blue light. The glow in P. lunula differs markedly from that in G. polyedra in that it occurs at about the same intensity at all times during the circadian cycle; thus, it is not under circadian control but may fluctuate 5–10-fold in intensity within a time frame of seconds. This suggests that the glow may differ in its physiological basis in the two organisms. The results also indicate that the circadian regulation of luciferase activity differs in the two species. In G. polyedra, the organelle responsible for bioluminescence and luciferase is lost and then reformed on a daily basis; in P. lunula, the luciferase is conserved and localized elsewhere during the nonbioluminescent phase of the cycle.     

EFFECT OF LIGHT ON THE DEVELOPMENT OF THE CIRCADIAN RHYTHM OF MOTOR ACTIVITY IN THE MOUSE

In previous experiments, we found that rats raised in constant light (LL) manifested a more robust circadian rhythm of motor activity in LL and showed longer phase shifts after a light pulse in constant darkness (DD) than those raised under constant darkness. In addition, we observed that the effects produced by constant light differed depending on the time of postnatal development in which it was given. These results suggest that both sensitivity to light and the functioning of the circadian pacemaker of the rat could be affected by the environmental conditions experienced during postembryonic development. Thus, the present experiment aimed to study whether postnatal exposure to light could also affect the circadian system of the mouse. Three groups of mice were formed: One group was raised under constant darkness during lactation (DD group), the second under constant light (LL group), and the third under light-dark cycles (LD group). After lactation, the three groups were submitted first to constant light of high intensity, then to LD cycles, and finally to constant darkness. In the DD stage, a light pulse was given. Finally, mice were submitted to constant light of low intensity. We observed that the circadian rhythm of the DD group was more disturbed under constant light than the rhythm of the LL group, and that, when light intensity increased, the period of the rhythm of the DD group lengthened more than that of the LL group. No significant differences among the groups were found in the phase shift induced by the light pulse. Therefore, it appears that DD mice are more sensitive to light than their LL counterparts. However, at present there is no evidence to affirm that the light environment experienced by the mouse during postnatal development affects the circadian pacemaker. (Chronobiology International, 18(4), 683–696, 2001)     

THE UPTAKE OF MANNITOL AND SORBITOL BY A SPECIES OF CHLORELLA (CHLOROPHYCEAE)1

Chlorella saccharophila (Krüger) Nadson takes up mannitol and sorbitol in the light and the dark. The rate of uptake is concentration dependent. is not affected by pH in the range pH 6.0 to 8.0 and ii not stimulated by light. Uptake is inhibited by the respiration inhibitor sodium azide (10^-2 M) but not by 3-(3,4-dichlorophenyl)-1,1-di-methyl urea (10^-6 M), an inhibitor of photosynthesis. Sorbitol. but not mannitol, stimulates the rate of dark respiration but both support the heterotrophic growth of the alga. Both compounds permeate the cells of C. miniata. and two strains of C. pyrenoidosa but do not support the heterotrophic growth of these algae. The cells of C. vulgaris are impermeable to both compounds.     

Far‐red dependent changes in the chemical composition of Spirulina platensis

The influence of far‐red light (FRL) was studied on the chemical composition of Spirulina platensis biomass. The following light compositions were used during the culture white light, blue‐red LED light (BRL) and BRL supplemented with FRL (BRFRL). Chlorophyll and phenol contents were measured by spectrophotometric methods, whereas presence of carotenoids, lipids, and phycobiliproteins were estimated by Fourier‐transform Raman spectrometry. Additionally, phenol content was investigated by fluorescence intensity of algae culture in the range of 430–650 nm. The content of chlorophyll and phenols in algae cells depended on the spectral composition of light and was the highest under BRL (16.7 ± 0.5 and 9.1 ± 0.6, respectively). It was shown that there is a positive linear correlation (R = 0.902 at p < 0.0000001) between the ratio of relative fluorescence intensity of S. platensis suspensions at 450 nm to the suspensions at 540 nm (F450/F540) and the content of phenolic compounds in the biomass. Changes in the F450/F540 ratio can explain approximately 80% changes of phenol contents in algae cells. Spirulina platensis Raman spectra demonstrated that the biomass of algae growing under white light and BRL had a significantly higher intensity of phycobiliprotein bands than the algae growing under BRFRL.     

Growth of shredders on leaf litter biofilms: the effect of light intensity

1. The effect of light intensity on the decomposition of poplar (Populus nigra) leaves and growth of the shredders, Asellus aquaticus and Gammarus pulex, was studied in a laboratory experiment. The response was studied along a gradient of six light intensities of 0, 5, 23, 54, 97 and 156 μmol m^?2 s^?1. It was hypothesised that an increase in light intensity would increase growth of shredders, because of an increase of algae (i.e. food quality) in the leaf‐biofilm. 2. Light intensity affected both leaf‐biofilm quality and consumer behaviour and affected several aspects of the decomposition‐consumer interaction. In the absence of invertebrates, leaf mass loss was lower in the dark, while light intensity had no significant effect on mass loss of poplar leaf in the presence of invertebrates. Light intensity affected algal biomass, density and composition, and had a significant positive effect on the growth of both shredders. 3. Our results suggest that algae can be an important component of the nutritional value of the leaf‐biofilm for benthic invertebrates, directly as an additional food source and indirectly through a link with bacteria and/or fungi. 4. The River Continuum Concept mainly emphasises allochthonous inputs to headwater streams and autochthonous production further downstream. Our results suggest that light, by its effect on the biofilms on leaf surfaces, might be a more important factor in headwaters than is usually assumed.