Carbon dioxide plant uptake

The respiratory quotient (RQ) (of evolution of carbon dioxide to uptake of oxygen) has been found to be near 1.0 for plant tissues and for metabolized carbohydrates. Fats evolve less carbon dioxide and have an RQ... 

FIGURE 22.30 Essential features of the coinpartinenCation and biochemistry of die Hatch-Slack padiway of carbon dioxide uptake in C4 plants. Carbon dioxide is fixed into organic linkage by PEP carboxylase of meso-phyll cells, forming OAA. Eidier malate (die reduced form of OAA) or aspartate (the ami-iiated form) serves as die carrier transpordiig CO9 to the bundle slieadi cells. Within die bundle slieadi cells, CO9 is liberated by decar-boxyladon of malate or aspartate die C-3 product is returned to die mesophyll cell. 

Alternatives to fossil fuels, such as hydrogen, are explored in Box 6.2 and Section 14.3. Coal, which is mostly carbon, can be converted into fuels with a lower proportion of carbon. Its conversion into methane, CH4, for instance, would reduce C02 emissions per unit of energy. We can also work with nature by accelerating the uptake of carbon by the natural processes of the carbon cycle. For example, one proposed solution is to pump C02 exhaust deep into the ocean, where it would dissolve to form carbonic acid and bicarbonate ions. Carbon dioxide can also be removed from power plant exhaust gases by passing the exhaust through an aqueous slurry of calcium silicate to produce harmless solid products ... 

Many estimates of total terrestrial net primary production are available, ranging between 45.5 Pg C/yr (Lieth, 1972) and 78 Pg/yr (Bazilevich et al., 1970). Ajtay ef oZ. (1979) have revised the various estimates and methods involved, they also reassess the classifications of ecosystem types and the extent of the ecosystem surface area using new data and arriving at a total NPP of 60 Pg C/yr. Gross primary production is estimated to be twice net primary production, i.e., 120 Pg C/yr. This implies that about 60 Pg C/yr are returned to the atmosphere during the respiratory phase of photosynthesis. It is well known that carbon dioxide uptake by plants follows daily cycles most plants take up CO2... 

Growth can be defined as the production of organic matter by increase in size or volume. This process involves the uptake of water, carbon dioxide and minerals. In plants, growth is made possible by the process of photosynthesis, which produces the sugars (as primary components) from which compounds such as starch, cellulose, amino acids and proteins are derived. 

These gas- and water-impermeable cell layers protect the plant from desiccation, but they also hamper the uptake of carbon dioxide necessary for photosynthesis and oxygen necessary for respiration. Specialized tissues have evolved to allow passive (lenticels) and active (guard cells) modification of the permeability of the external cuticle to gas exchange. 

The two main pathways for the uptake of toxic substances by plants are through their root systems and across their leaf cuticles. Stomata, the specialized openings in plant leaves that allow carbon dioxide required for photosynthesis to enter the leaves and oxygen and water vapor to exit, are also routes by which toxic substances may enter plants. The mechanisms by which plants take up systemic pesticides and herbicides, which become distributed within the plant, have been studied very intensvively. 

Biodiesel to Fuel a Large Power Plant. Researchers at ASU s Center for Bioenergy and Photosynthesis have calculated that a 25 x 25 km field of bioreactors using cyanobacteria to fix carbon could uptake all of the carbon dioxide produced by a 1.6 GW power plant and subsequently provide the biomass as lipid to fuel the power plant. The parameters necessary to achieve this goal are a seven percent power conversion efficiency for photosynthesis, 40 percent conversion efficiency of biomass to fuel, 50 percent conversion efficiency of fuel to electricity, and 80 percent conversion efficiency of land area covered by the bioreactors. This system would then be carbon neutral in operation and produce about 1.6 GW of electrical power. The key to making this feasible is to achieve a seven percent power conversion efficiency for cyanobacteria. Moore noted that the area required to produce a specified amount of energy scales directly with the energy conversion efficiency of the system or device. 

Fractionation and Contamination. The ratio 14C/12C in certain materials may be affected by isotopic fractionation. For example, the uptake of carbon dioxide and its incorporation into plant tissue may be accompanied by substantial fractionation that depends on the plant species. With marine organisms, fractionation may also be important, especially when inorganic carbonate and bicarbonate are involved. Corrections for fractionation must be made for precise radiocarbon dating. 

Farquhar, G.D., Schulze, E.-D., and Ktippers, M. 1980. Responses to humidity by stomata of Nicotiana glauca L. and Corylus avellana L. are consistent with the optimization of carbon dioxide uptake with respect to water loss. Aust. J. Plant Physiol. 7 315-327. 

The interplay of acid-base, solubility, and complex ion equilibria is often important in natural processes, such as the weathering of minerals, the uptake of nutrients by plants, and tooth decay. For example, limestone (CaCOj) will dissolve in water made acidic by dissolved carbon dioxide ... 

Another approach is to increase carbon dioxide uptake by forests to reverse the effects of severe deforestation of the last 150 years. It has been estimated that a rapidly growing rainforest can remove 4-7kg/m year of carbon dioxide from the atmosphere, as compared to a typical crop uptake of 0.8-1.6kg/m year. Thus, vigorous reforestation could assist in increasing the photosynthetic removal of carbon dioxide from the atmosphere [59]. Annual crops also perform photosynthetic uptake of carbon dioxide, but consumption and metabolism of the product(s) and prompt decomposition of the plant wastes promptly return the fixed carbon dioxide to the atmosphere [60]. 

The uptake and storage of carbon trees and plants, for example, absorb carbon dioxide, release the oxygen and store the carbon... 

It should be mentioned that only about the half of anthropogenic C02 remained airborne in the past decades.4 However, this does not necessarily mean that the fraction of man-made C02 stored in the atmosphere will always be the same in the future. For this reason it is essential to determine from past variations the factors governing the fate of anthropogenic carbon dioxide. It is also essential to include these factors in so-called reservoir or box models5 to calculate, on the one hand, the fraction absorbed by oceans and, on the other hand, the part of the emission used by the land biota. Since the uptake of carbon dioxide by ocean waters is governed by more or less known physical and chemical laws the response of land plants to the increase of C02 level, which is much more complicated, can be estimated by difference between total C02 input and oceanic absorption (e.g. Keeling, 1973). 

The interaction of bipyridyl herbicides (paraquat and diquat) with photosynthesis is different from that of the electron transport inhibitors. These compounds, with highly negative redox potentials (paraquat E 446mV diquat Eq -349mV), interact in the vicinity of ferredoxin causing a diversion of electron flow from the ultimate electron acceptor NADP. This was clearly seen in paraquat-treated plant material as a progressive inhibition of carbon dioxide uptake (25)... 

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