Model of Photosynthetic Light Response Curve of Rice …

 Photosynthetic light response curves for different bermudagrass cultivars

the result is a photosynthesis light response curve ..

The closed greenhouse is a new development in protected cultivation. As air is not ventilated to the outside environment, CO2-concentrations are higher than in conventional greenhouses, causing 15¿20% increased production. The question remained as to whether increased air flow rates in a closed greenhouse cause photosynthetic adaptation. This was evaluated in a tomato crop that was planted in the summer of 2005 in The Netherlands in regular greenhouse compartments, in which air tubes were placed low and high in the canopy. Photosynthesis light-response curves were established at these two heights at 400, 700 and 1000 ppm of air CO2. Increased CO2 concentration and a higher position in the canopy caused an increase of the maximum photosynthetic rate, confirming earlier knowledge. However, the pattern of air circulation did not change the photosynthesis light-response curve. This corresponded with the absence of differences in total dry matter production and cumulative fruit growth. The INTKAM tomato model adequately simulated growth and development. It is therefore concluded that the pattern of air circulation did not cause adaptation of the photosynthetic apparatus, and that yield increases are attributable to the instantaneous effects of elevated CO2-concentrations.

" Photosynthetic light response curves for different bermudagrass cultivars "

8 to an experimentally obtained net photosynthesis response curve ..

The balance between respiration and photosynthesis is critical to the exchange of carbon between the atmosphere and the terrestrial biosphere –. Instantaneous increases in foliar temperature (Tleaf) typically result in an increase in respiration/photosynthesis (R/A) ratio because the response of respiration to Tleaf normally follows an approximate exponential-type curve (at moderate temperatures) while the response of photosynthesis to Tleaf often bears a bell-shaped curve [i.e. the thermal optimum (Topt) of respiration is higher than that of photosynthesis] , . In contrast, long-term warming experiments have suggested that R/A ratio is often conservative to changes in growth temperature (Tgrowth) through acclimation, the metabolic adjustment for compensating changes in Tgrowth–. Acclimation could occur via suppression of respiration in response to changes in foliar carbohydrate supplies , . The thermal acclimation of respiration and photosynthesis is associated with multitudes of signal cascades and networks, which involves the reallocation of resources to achieve and maintain not only optimal R/A ratio but also protective strategies under sustained warming as projected by global climate models –. However, the mechanisms of thermal acclimation of respiration and photosynthesis to climate warming are far from clear, especially in natural ecosystems.

Plants capable of C4 photosynthesis carry on a more efficient form of photosynthesis. There are two crucial differences between the light response curve of C3 and C4 plants. For C4 plants, the light saturation point is higher and the light compensation point is lower than for C3 plants. Both of these characteristics relate to the ability of C4 plants possess to increase the amount of CO2 available to the Calvin-Benson cycle.


Deforestation and Carbon Emission

Light is a critical resource for plants that can limit growth and reproduction. When photosynthesis rates are plotted against light intensity, the result is a photosynthesis light response curve (Figure 8). In the dark, there is no photosynthetic carbon assimilation, and instead CO2 is given off by the plant because of mitochondrial respiration. By convention, CO2 assimilation is negative in this part of the light-response curve. As the photon flux increases, photosynthetic CO2 assimilation increases linearly until it equals CO2 release by mitochondrial respiration. The point at which photosynthetic CO2 uptake exactly balances CO2 release is called the light compensation point. Increasing light above the light compensation point proportionally increases photosynthesis, indicating that photosynthesis is limited by the rate of electron transport, which in turn is limited by the amount of available light. This portion of the curve is referred to as light-limited. Further increases in photosynthesis are eventually limited by the carboxylation capacity of RubisCO or the metabolism of triose phosphates. This part of the curve is referred to as CO2-limited.

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The acclimation of foliar respiration and photosynthesis is also reflected in R/A ratio which indicates the balance between carbon gain, loss and accumulation , . Our results show that the instantaneous (Rd/Ag ratio, indicating proportionally more carbon loss through Rd as Tleaf goes up (). However, the 6-year experimental warming has resulted in thermal acclimation of the grasses as evidenced by the decrease of the curvature of the response curve of Rd/Ag ratio to Tleaf (). It is important to note that though the balance between Rd and Ag was re-established through the thermal acclimation , , , , Rd/Ag ratio was still increasing with Tgrowth in a wet year (). This means that, at foliage level, acclimation can only partially compensate the negative impact from the global warming.