We collected data from 20 saline lakes (total dissolved solids from 1000 to 91 000 mg∙L−1) in southeastern Alberta to compare relationships between phosphorus, nitrogen, and phytoplankton standing crop with those in freshwater lakes. In 18 lakes, Na+, Mg2+, SO42−, and HCO3−-CO32− were the dominant ions. In these lakes there was a significant positive correlation between Ca2+ and chlorophyll a (Chl a), and there were significant negative correlations between Chl a and conductivity, pH, Na+, Mg2+, SO42−, HCO3−, and CO32−. When all 20 lakes were considered there were no significant relationships between Chl a and phosphorus or nitrogen. Empirical relationships for freshwater lakes, based on spring or summer total phosphorus (TP) or total nitrogen (TN), overestimated Chl a in all the study lakes. However, in saline lakes with similar ionic composition and TN to TP ratios greater than 12 (by weight), there was a significant positive relationship between TP and Chl a. For the saline lakes with TN to TP ratios greater than 12, the deviations between the Chl a levels predicted from models developed for freshwater lakes and the observed levels were positively correlated with conductivity, total dissolved solids, and Na+ (r2 = 0.78–0.82, P < 0.001). We developed the first empirical model that describes nutrient – Chl a relationships for inland saline lakes. The deviation of measured phytoplankton biomass from that predicted by models developed for freshwater lakes can be explained by conductivity or dominant ion concentration.
A study was made on the effect of light and temperature on net photosynthesis, growth and transpiration of Coffea arabica. Net photosynthesis was described as a diffusive process depending on a carbon dioxide gradient and an overall resistance. At a relative low temperature (24"C), the effect of light on net photosynthesis was comparable with that of most annual agricultural crops. Calculated internal concentration and overall resistance at 0.3 cal cm-' rnirr' were zero p.p.m. and 15 sec crrr'? respectively. Above this temperature each degree riseresulted in an increase of 20 p.p.m. in internal CO. concentration. This effect alone accounts already for a decrease in dry matter production of approximately 7 % per degree centigrade.The increase in internal CO. was accompanied with an increase of the overall resistance, reducing still more the dry matter production. Low rates of photosynthesis in coffee reported in literature could be explained. Increasing the external CO. content and thus the CO. gradient had only a minor effect on photosynthesis. The effect of temperature and light on growth confirmed the conclusions of net photosynthesis research. Since both factors increase transpiration substantially, the water use efficiency decreases strongly with an increase in light and in temperature above 24°C. The results may have importance for selecting optimum growth conditions for coffee. c e
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