Ecological Consequences of Long-Term Exposure of Anabaena variabilis (Cyanophyceae) to Shifts in Environmental Factors

Abstract

Cultures of Anabaena variabilis were exposed to different light intensities, and the time course of photoadaptation was measured by photosynthetic rate and changes in pigmentation. A shift down in intensity of 284 ,uEin * m-2 _ sec-1 caused a temporary decrease in the photosynthetic response followed by gradual adaptation to the new conditions. Final chlorophyll a and carotenoid concentrations were reached after 1 day, although other physiological indicators showed that adaptation required 4 days. The parameter Ik was shown to be the best indicator of photoadaptation. A shift up in light intensity of the same magnitude also required 4 days for complete photoadaptation by the culture, although chlorophyll and carotenoid concentrations stabilized within 1 day. A shift down in light intensity of 392 1xEin * m-2* sec-1 resulted in a temporary attempt to adapt followed by collapse of the population. This demonstrates an apparent threshold in the magnitude of the shift in light intensity which will permit successful adaptation. Simultaneous changes in light intensity and temperature also adversely affected culture populations. Our observations present a possible cause for the decline or prevention of an algal bloom under a fluctuating light regime and suggest that it may be possible to predict this decline as a result of synoptic weather patterns or hydrodynamic influences.

Acclimation of photosystem II in a cyanobacterium and a eukaryotic green alga to high and fluctuating photosynthetic photon flux densities, simulating light regimes induced by mixing in lakes

“…Increased myxoxanthophyll and zeaxanthin contents led to higher carotenoid/chlorophyll ratios at higher TDLD. This form of acclimation to higher Hght doses is generally found in cyanobacteria (Collins & Boylen, 1982;Nultsch & Angel, 1986;Garcia-Pichel & Castenholz, 1991). Individual caro- tenoids showed little variation, and acclimation to the diurnal variation in PPFD was not observed, in contrast to the patterns of lutein in Scenedesmus.…”

“…Artificially induced mixing of lakes has been applied to reduce nuisance populations of cyanobacteria (see Paerl, 1988). One of the causes of reduced growth under mixed conditions may be the reluctant acclimation of cyanobacteria to changes in PPFD as found by Ward & Wetzel (1980) and Collins & Boylen (1982). These studies examined acclimation to a single shift in PPFD, whereas the light field in lakes is highly variable.…”

Kinetics of nutrient-limited transport and microbial growth.

“…YXA Kt At higher concentration saturation restricts the specific affinity. At the Michaelis concentration it is restricted in this hypothetical system to aA0 aAK, (47) and K, (l=max/2) (48) Kp YXA where YXA is the cell yield at P,max/2. For a growing bacterium to achieve a IXmax = 0.1/h during growth on a sugar with a yield of YXA = 1.0 and K, = 0.1 mg of A per liter, the specific affinity required is 1,000 liters/g of cells per h (500 if the Michaelis concentration K,.…”