Light-Mediated Uptake of H-Glucose in a Small Hard-Water Lake

Abstract

This study examines the occurrence of photoheterotrophy, the light—mediated assimilation of organic compounds at or near natural substrate concentrations, in the phytoplankton of a lake. The pelagic zone of Lawrence Lake, an oligotrophic, dimictic, hard—water lake in southwestern Michigan, was selected as the study site because extensive information is already available on its carbon cycle. The uptake of glucose by the plankton was monitored in both light and dark bottles over an annual period. Uptake was measured during 3 sampling periods throughput the daylight hours (i.e., sunrise, midday, and sunset) and at 3 depths within the water column (i.e., 2, 6, and 10 metres). The patterns of dark heterotrophic activity, chemoheterotrophy, and light—mediated heterotrophic activity, photoheterotrophy, were significantly related to the variables of months, depths, and time of day. Chemoheterotrophic activity generally increased throughout the daylight period and with greater depth within the water column. Maximal values were generally observed during the sunset—incubation series and at 10 metres depth. Generally high and uniform activities with respect to depth were observed during periods of water circulation. Increasing activity at greater depth during the stratified summer period was also observed. Maximal values for photoheterotrophy were observed during spring circulation and late summer stratification. Activity was generally greatest below 2 metres and during morning and midday incubation periods. There was an apparent shift during the daylight period in the area of maximal uptake from 2 and 6 metres in the morning to 6 and 10 metres as the day progressed. Chemoheterotrophy and photoheterotrophy are both temporally and spatially separated with respect to activity within the water colum on a diurnal as well as a seasonal basis. The study revealed that dark bottle measurements of heterotrophic activity undrestimate total activity and can be justified as a means of assessing chemoheterotropich activity only. Light bottle uptake values averaged 146% of dark bottle estimates during the light period. Photocheterotrophy was shown to be quantitatively comparable to chemoheterotrophy within the pelagic zone. Photoassimilation averaged 67.6% of chemoheterotrophic activity based on individual comparisons (N = 360) over an annual period. Photoheterotrophy represents an important step in our further understanding of the cycling of carbon within aquatic systems and of biological interactions within the planktonic community.

Heterotrophic and photoheterotrophic utilization of lactate by the diatom,Cylindrotheca fusiformis

“…B. WIMPLE AND C. T. OHLMAN A number of studies have shown that light stimulates the use of organic compounds by algae, especially under situations of limiting light intensities or limiting concentrations of inorganic carbon (Neilson & Lewin, 1974;Hellebust & Lewin, 1977). Several recent reports have demonstrated the importance of this photoheterotrophy in field situations (McKinley, 1977;Vincent, 1980;Vincent & Goldman, 1980). Our study has shown that light markedly stimulated the incorporation rate of lactate carbon in induced cells, but has less of an effect on uptake rates.…”

“…The experiments were conducted under both light and dark conditions because of earlier reports (Cooksey, 1974;McKinley, 1977) …”

Photolithotrophy, photoheterotrophy and chemoheterotrophy during spring phytoplankton development (Lake Pavin)

“…It was also for a long time considered that algae were not competitive compared with bacteria in taking up organic substrates in the natural environment [14,21,25,43]. Thus, photoheterotrophy was attributed almost entirely to algae, and chemoheterotrophic activities were attributed to bacteria [22], Photosynthetic bacteria are, however, capable of displaying photoheterotrophy, but under anaerobic conditions (with the exception of cyanobacteria) [11,34], and phytoplankton species are capable of assimilating organic substrates by chemoheterotrophy at concentrations encountered in the natural environment [7, …”

Physiological studies of phototrophy and heterotrophy in two algae with contrasting nutritional characteristics, Pyrenomonas salina (Cryptophyceae) and Poterioochromonas malhamensis (Chrysophyceae)

“…The uptake kinetics of algae for dissolved organic substrates have been shown to be adequate in some cases for successful competition with bacteria (Hellebust 1970, Vincent and Goldman 1980 but inadequate in other cases (Hobbie and Wright 1965, Sloan and Strickland 1966, Bennett and Hobbie 1972, Platt et al 1983. Size-fractionation studies examining the incorporation of radiolabeled organic compounds by photosynthetic organisms have indicated that algal uptake of dissolved organic matter can range from 0% to greater than 50% of the total plankton community incorporation (Munro and Brock 1968, Williams 1970, Paerl and Goldman 1972, Maeda and Ichimura 1973, Berman 1975, Azam and Hodson 1977, McKinley 1977, Vincent 1980, Vincent and Goldman 1980, Moll 1984, Rivkin and Putt 1987. Given the newfound abundance of picophytoplankton in many aquatic environments (reviewed in Stockner 1988, Hargraves et al 1989, Sieburth and Johnson 1989, however, assumptions that uptake in the smallest size fractions is strictly due to bacteria must be viewed with caution.…”

“…salina in nature and their uptake affinities for these substrates, the effects of dissolved organic substrates on their physiology, as observed here, will remain phenomenological. However, a large volume of evidence exists that indicates that algal heterotrophy can occur in nature, including laboratory studies demonstrating that the uptake affinities of some photosynthetic plankton for organic compounds is comparable to that of bacteria (Bunt, 1969;Hellebust, 1970;Saunders, 1972;Berman et al, 1977;Taft et al, 1977;Ellis and Stanford, 1982;Currie and Kalff, 1984a;Flynn and Syrett, 1986;Feuillade and Feuillade, 1989;Palenik and Morel, 1990) and field studies showing that a significant proportion of labeled organic compounds introduced into aquatic environments can be taken up by photosynthetic plankton Saunders, 1972;Maeda and Ichimura, 1973;Lee et al, 1975;North, 1975;McKinley, 1977;Taft et al, 1977;Tilzer et al, 1977;Wheeler et al, 1977;Vincent, 1980;Vincent and Goldman, 1980;Currie and Kalff, 1984b;Moll, 1984;Li and Dickie, 1985;Palmisano et al, 1985;Rivkin and Putt, 1987;Feuillade et al, 1988;Bourdier et al, 1989). Exactly how phytoplankton coordinate different modes of carbon acquisition within the cell, however, is poorly understood.…”