Carbon dioxide compensation point

Tolbert N. E., Benker C., and Beck E. (1995) The oxygen and carbon dioxide compensation points of C3 plants possible role in regulating atmospheric oxygen. Proc. Natl. Acad. Sci. 92, 11230-11233. 

Why does exposing C3 plants to high temperatures raise the carbon dioxide compensation point ... 

Under conditions of high temperature, the carbon dioxide compensation point of C3 plants rises because the oxygenase activity of Rubisco increases more rapidly than the carboxylase activity. 

If a plant is illuminated in a closed container the carbon dioxide concentration inside the container eventually reaches a steady level which is known as the carbon dioxide compensation point. The final level represents the balance attained between carbon dioxide fixing and carbon dioxide releasing reactions. That carbon dioxide releasing reactions do occur is readily demonstrated if leaves which have previously been photosynthesising in labelled carbon dioxide are transferred to unlabelled carbon dioxide—labelled carbon dioxide can be detected in the atmosphere surrounding the leaves. This sort of experiment underlines the fact that when photosynthesis is measured as CO2 uptake or oxygen evolution the value obtained represents apparent photosynthesis—the balance between reactions resulting in... 

Figure 17.15 Carbon dioxide exchange rate (net photosynthetic rate) of a 20 potato stand at different CO2 concentrations. The photosynthetic rates saturated above 1200 ppm while the CO2 compensation point occurred at 97 ppm (source Wheeler et al., 2008a).

Supercritical fluid chromatographic pumps must have both a wide range of compensation and use dynamic compressibility compensation to produce accurate and reproducible flow and composition. Whereas water has a compressibility factor of 75 x 10 /bar, methanol is more compressible at 120 X 10 /bar. Carbon dioxide has widely varying compressibility from 95 to 395 X 10 /bar at 5°C, depending on the pump delivery pressure (column head pressure). The viscosity of pure carbon dioxide is 1 /20 the viscosity of pure methanol. During composition programming, the viscosity of the mixed fluid and the column head pressure increases as the modifier concentration increases. Without dynamic compensation, the actual delivery of the carbon dioxide would roll off. The total flow would be less than the set points and the modifier concentration would be more than the set points. 

All of the pumps must be both accurate and reproducible in flow and composition. Accuracy requires careful control of both the temperature of the fluid and the supply pressure, along with comparable dynamic compressibility compensation schemes. Without dynamic compressibility composition, pumps delivering carbon dioxide will deliver different fractions of their set points, depending on the pressure. Total flow and composition will probably deviate from the set points differently at the two different scales. Accurate compressibility compensation assures scalable pumping. 

Respiration is essentially the converse of the process of photosynthesis. If the two processes occur concurrently, then the rate of photosynthesis as actually observed (net photosynthesis) will be less than the total rate (gross photosynthesis) by an amount equal to the rate of consumption of the products of photosynthesis in respiration. At certain low light intensities or carbon dioxide concentrations the two processes balance so that there is no net gas exchange and the photosynthetic organism is then said to be at its compensation point. It has usually been assumed, according to Fogg... 

Earth is currently balanced on the hquid island east of water s triple point, but this balancing act was difficult to maintain. Any planet left out in the vacuum of space changes in temperature and pressure over time. Air pressure leaked away as hydrogen left the Earth and carbon dioxide was packed into limestone. Gravity and sunlight helped compensate for the loss, but stability can be elusive—just ask Venus and Mars. 

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