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How Plants React to the Climate Change

Author:
[ Koocheki ] -

Abstract:

150000 years ago up to the present time, carbon dioxide concentration in the atmosphere has been fluctuating between 200 to 300 ppm and for the last 1000 years this has reached 280 ppm. From the beginning of industerial revolution in 1850 together with the inappropriate use of fossil fuels and deforestation C02 concentretion increased exponentially to a level of 325 ppm in 1990. In all of lower and higher plants in the dark phase of photosynthesis, C02 is reduced to carbohydrates through a similar mechanism called PCR. In C3 plants Rabisco which is not only involved in catalysing C02 reaction with RUBP but also acts as a catalyzor for reaction of RUBP with oqgen. In this case instead of C02 fixation and formation of 2 molecule of 3-phosphoglyceric acid, one molecules of 3-phophoylyceric acid and one molecule of phosphaoglyceric are formed. Reaction of RUBP with oxygen or photorespiration not only wastes one molecule of Rabisco but also evolves one molecule of C02 which was fined earlier. This causes lower efficiency in photosynthesis in C3 plants. Photorespiration causes C3 plants to reach compensation point at 35 to 45 ppM C02 and that of C4 plant at zero to 5 ppm. On the other hand C4 plants, reach saturation at 400ppm and some of them even at the present level of C02 while C3 plants even with doubling of C02 concentration do not reach saturation and therefore react to C02 elevation. Therefore since present level of C02 in lower than the optimum level for plants, generally an increase in C02 concentration will increase production in C3 and C4 and particularly in C3 plants. on the other hand C02 elevation will cause increase in temperature through greenhouse effects. Temperature increase will reduce oxygen and C02 solubility in water. This will also reduce lower reaction of Rabisco with C02 and therefore an increase in photorespiration. Positive effects of radiation on photosynthesis is more pronounced at , higher C02 wentration. It is believed that at lower C02 concentration C02 limited, and at higher C02 concentration regeneration of RUBP is a limiting factor for photosynthesis. One of the advantages of C4 plants at higher temperature and height is heigher W. At a given Stomata resistance, water entrance to the stomata is higher tha C02 export. With an increase in C02 concentration stomata in C3 is reduced and this will reduce evaporation of water relative to C02 enterance, therefore WUE is increased.

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