| Popis: |
Photosynthesis vs. irradiance relationships were determined for phytoplankton communities from seven lakes in the Canadian high Arctic, including ultraoligotrophic Char Lake, nutrient-enriched Meretta Lake, and two meromictic lakes. The derived photosynthetic parameters were low for all samples, with a mean (6SD) light-saturated photosynthetic rate (P ) of 0.46 (60.28) g C g 21 chlorophyll a (Chl a )h 21 and a mean a B (light-limitation parameter) B m of 1.23 (60.56) g C g 21 Chl a m 2 mol 21 . The saturation irradiance (Ek) ranged from 50 to 196 mmol quanta m 22 s 21 and was positively correlated with mean irradiance for the water column. Quantum yields for photosynthesis in the Arctic lake phytoplankton were also low (mostly ,10 mmol C mol 21 quanta). An intersystem comparison of a B and P values with literature data for algae from other cold environments showed that the photosynthetic B m parameters for phytoplankton in Arctic and Antarctic lakes are three- to sixfold lower than for marine algae, ice algae, and cultures over the same low-temperature range. This may be the result of more severe nutrient stress in high-latitude lakes relative to polar marine environments and to the persistence of nonactive pigments in cold freshwaters. |
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