Carbon dioxide assimilation, rate

Fig. 5.1, Relationship of carbon dioxide concentration to the rate of carbon dioxide assimilation at various light intensities (shown against each curve in kerg/cm /sec). (Data for whole plants of Triticum sativa (wheat) after W. H. Hoover, E. S. Johnston and F. S. Brackett, Smithsonian Inst. Publ. Misc. Collections, 87 No. 16, 1933.) (From E. I. Rabinowitch, Photosynthesis, vol. 2, pt. 1, Interscience Pub. Inc., New York, 1951.)...

Significant differences in net photosynthetic assimilation of carbon dioxide are apparent between C, C, and CAM biomass species. One of the principal reasons for the generally lower yields of C biomass is its higher rate of photorespiration if the photorespiration rate could be reduced, the net yield of biomass would increase. Considerable research is in progress (ca 1992) to achieve this rate reduction by chemical and genetic methods, but as yet, only limited yield improvements have been made. Such an achievement with C biomass would be expected to be very beneficial for foodstuff production and biomass energy appHcations. 

The balance between animal and plant life cycles as affected by the solubiHty of carbon dioxide ia the earth s water results ia the carbon dioxide content ia the atmosphere of about 0.03 vol %. However, carbon dioxide content of the atmosphere seems to be increa sing as iacreased amounts of fossil fuels are burned. There is some evidence that the rate of release of carbon dioxide to the atmosphere may be greater than the earth s abiHty to assimilate it. Measurements from the U.S. Water Bureau show an iacrease of 1.36% ia the CO2 content of the atmosphere ia a five-year period and predictions iadicate that by the year 2000 the content may have iacreased by 25% (see Airpollution). 

CO can be oxidized to carbon dioxide by selected microbial groups including ammonia oxidizers and methylotrophs that have a broad substrate specificity and high affinity for CO. However, only the carbox-idotrophs obtain energy from this reaction, and these may be unable to assimilate CO efficiently at in situ concentrations. CO turnover times of 4 hours are typical for coastal waters, whereas this varies between 1 and 17 days in the open ocean. The lower oxidation rate in the open ocean may be due to light inhibition of CO oxidation. Extrapolation from laboratory... 

Photosynthesis is the process that provides energy to all anabolic and catabolic processes in ecosystems. The rate at which plants assimilate CO2 in the field may be quite different from optimal conditions in the test tube or in growth cabinets. The rate depends on the environmental conditions of the habitat which determine to what extent the genetic capability of a plant can actually be used for photosynthesis. The main factor restricting photosynthesis in the field is the availability of light. But, other factors my become just as rate 1imitating, such as atmospheric carbon dioxide concentration, air humidity and temperature, and water or nutrient supply from the soil. Time is an additional important factor which influences the carbon balance via plant age but also by deterimining the dose of stress. 

Mineralization (corrversion to carbon dioxide, water and biomass via microbial assimilation at the same rate as natural materials (leaves, paper, grass and food scraps))... 

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