Max M. Tilzer

Survival of Scenedesmus acuminatus (Chlorophyceae) in darkness

Survival of the green alga Scenedesmus acuminatus Lagerh. in complete darkness was studied in axenic batch cultures at 7°C and 22°C for three months. The decrease in cell numbers was insensitive to temperature and slower than the loss of dry weight. However, the lag phase before cells began to lyse was more than twice as long at 7° C than at 22°C. The decline in cellular carbohydrates and proteins occurred in two phases. During the first 3‐4 days, the decrease in cellular carbohydrate levels was significantly accelerated and temperature‐sensitive. Pyrenoids disappeared within 5 days of darkness. Proteins showed 20‐fold higher degradation rates at 22°C than at 7°C during the first 4 days. Thereafter, the rates of carbohydrate and protein decomposition were slow and temperature‐independent. By contrast, lipids degraded only little at virtually constant and temperature‐insensitive rates over the entire experimental period.

Importance of Mixing, Thermal Stratification and Light Adaptation for Phytoplankton Productivity in Lake Tahoe (California‐Nevada)

Lake Tahoe is highly transparent (Secchi readings 20—42 metres) and never freezes over. Deep mixing throughout its 500—metre water column occurred in March 1974 and 1975. Between June and October 1974, a distinct epilimnion of 15— to 30—metre thickness existed. Phytoplankton, which is dominated by diatoms, showed no significant vertical shifts in species composition. Chlorophyl α concentrations were highest at the bottom of the trophogenic zone (75—100m) during thermal stratification. Maximum photosynthetic rates were observed at greater depths during winter mixing of the lake than during thermal stratification. In situ experiments, in which incubations flasks containing phytoplankton from 3 discrete depths were distributed over the trophogenic zone, were conducted to study light adaptation. Results indicated that seasonal variation in the vertical distribution of photosynthesis was controlled to a greater extent by algal adaptation to prevailing subaquatic light conditions than by variations in solar irr...

CHLOROPHYLL A VERSUS ADENOSINE TRIPHOSPHATE AS ALGAL BIOMASS INDICATORS IN LAKES1

The relation between phyloplankton chlorophyll a and adenosine triphosphate (ATP) was investigated during a yearly cycle in Lake Tahoe, California–Nevada, and a variety of North American and New Zealand lakes of ranging trophic state. Since cellular concentrations of ATP have been shown as acceptable indicators of live biomass among natural microbial populations, the ratio of chlorophyll a to cellular ATP reveals the extent of pigment production per unit biomass under diverse environmental conditions.