No abstract

Natural algal populations in 4-, lo-, and 800-liter enclosures were fertilized to ascertain to what extent ammonium, nitrate, or phosphate enrichment changed phytoplankton abundance and physiology in an Amazon floodplain lake (Lake Calado). When water was rising and was between 8 and 11 m (March-May 1982), algal abundance ranged from 13-24 pg Chl a.liter-l and epilimnetic NH,+, N03-, and POa3-concentrations were usually ~0.3 HM. Chlorophyll increased over the control by 60-265% in the P treatment, 5-40% in the N treatments, and 75-270% in the N+P treatments after about 5 days. In three of the four experiments, increases in chlorophyll after addition of phosphate alone were significantly greater (P -=z 0.05) than after additions of nitrate or ammonium alone. Increases in net photosynthesis and in particulate C and N concentrations corroborated the chlorophyll data. Deficiency indices (ammonium-enhanced dark 14C fixation, N and P uptake rates, and sestonic N:P ratios) implied that the phytoplankton were impoverished with respect to nitrogen and phosphorus; nutrient enrichment relieved this condition but deficiency often returned after a few days. When water depth was falling and was between 7 and 2 m (September-November 1982) algal abundance ranged from 4 to 15 pg Chl a-liter-', turbidity increased, and epilimnetic inorganic N and P were usually ~0.3 PM. During September both N and P additions increased algal standing crop, whereas in early October enrichment with N increased abundance substantially (P < 0.05) above that after P addition. The physiological evidence indicated that the lake was N-deficient during September; in October neither N nor P deficiency was discernible except for slight alkaline phosphatase activity.Evaluation of the worldwide importance of nutrient supply to the productivity and abundance of phytoplankton is hindered by a paucity of information from the tropics (Schindler 1978). Tropical floodplain lakes are especially important because immense floodplains border most large tropical rivers; in South America and Africa about 320,000 and 250,000 km2 are inundated at peak flood (Welcomme 1979). Bordering the middle reaches of the Amazon River is a 60,000-km2 floodplain with thousands of lakes. As the Amazon River and its tributaries rise and fall each year, the floodplain lakes are filled by the rivers and local rain and then drain back to the river. Fisher and Parsley (1979) estimated that 5-l 0% of the Amazon's discharge may be stored in the lakes during rising water and suggested that the riverine inputs of nitrate and phosphate are of primary importance in the productivity of the lakes. We report here experiments to determine the relative importance to phytoplankton of nitrogen and phosphorus supply in Amazonian floodplain lakes, using two complementary approaches over the full range of conditions during a year. We enriched natural populations in enclosures and followed the responses for about 5 days. The added inorganic N and P simulated concentrations in Amazon river water. Chang...

No abstract

To examine the effects of exhaustive swimming in normal and myopathic hamsters on muscle mitochondrial Ca2+ metabolism, sedentary normal and BIO 14.6 dystrophic Syrian hamsters swam individually in 35 degree C water until exhaustion occurred. Although the normal hamsters swam three times longer than did the BIO 14.6 hamsters, both swimming groups had a comparable two-fold increase in blood lactate. Contrary to exhaustive running, exhaustive swimming did not significantly affect mitochondrial Ca2+ uptake in either cardiac or skeletal muscle, regardless of the disease state. However, in general, the coefficients of variation for mitochondrial Ca2+ metabolism increased as a function of exercise, with the BIO 14.6 swimmers more variable than the normal swimmers. This suggests that the mitochondrial Ca2+ uptake process may be affected in some manner by exhaustive swimming, so that deviations from the norm are more apparent. The results provide further evidence that mitochondrial Ca2+ metabolism adapts to the specific type of exercise utilized to produce exhaustion.

The effects of increasing salt stress on leaf senescence and salt regulation were investigated in the halophyte Jaumea carnosa in hydroponic culture experiments. The plants were grown in Hoagland's nutrient solution plus additional NaCl salt (0, 300,400, 500 mMNaCl). Decreases in nucleic acids, protein, and chlorophyll were used as indicators of leaf senescence. The results indicated no definitive pattern of acceleration in leaf senescence with increasing salt stress. Salt regulation was also unaffected as leaves aged under increasing NaCI concentrations. The results are consistent with those of previous studies of the halophyte which indicated that the species was very tolerant of high NaCI concentrations.