Maximum Assimilation Rate

Effect of Leaf Position on the Rate of Photosynthesis and Transpiration 

Leaf Height from Base Photosynthetic3 Rate Transpiration3 Rate 

Source Adapted from Soja, G. and Haunold, E., Field Crop Res., 26, 241-252, 1991. 

FIGURE 10.9 Seasonal pattern of dry matter allocation per plant and within the tubers for an early ( Columbia ) and late ( Violet de Renames ) cultivar. (After Spitters, C.J.T. et al., in Topinambour(JerusalemArtichoke), Report EUR 11855, Grassi, G. and Gosse, G., Eds., Commission of the European Communities, Luxembourg, 1988, pp. 37—43.) Arrows indicate the timing of the onset of dry matter recycling from the stems into the tubers. 

The effect of leaf position on the photosynthetic rate of Jerusalem artichoke (Soja and Haunold, 1991) is similar to that of the sunflower (English et al., 1979) in that leaf position becomes progressively more critical as the plant ages. When the plants reach their final height, only leaves in the upper 1/6 of the canopy display gas exchange rates greater than 50% of the most apical leaves (Table 10.3). 

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The absence of a close correlation between maximum C02 assimilation rate and yield indicates that one or more additional factors are critical in determining yield, and while a high photosynthetic rate may be an important component of yield potential, it does not at this time represent a rate-limiting step. 

CoUos, Y. (1983). Transient situations in nitrate assimilation by marine diatoms. IV. Non-hnear phenomena and the estimation of the maximum uptake rate. f. Plankton Res. 5, 677—691. 

Table III shows the average values of the coeflScients k and K for the three volatile acids at the temperatures studied. Values of k are given both as the maximum specific rate of assimilation of the primary volatile acid substrates (Equations 15, 16, and 18) expressed as equivalent amounts of acetic acid and as the maximum specific rate of conversion of the primary volatile acid substrate COD to methane. The fraction of...

Anaerobic Sulfide Oxidation. An alternative explanation is that sulfide is oxidized anaerobically in association with phototrophic reduction of C02 to organic carbon (46, 49). This hypothesis is supported by the discovery of considerable quantities of bacteriochlorophyll pigments within and below the suboxic zone (50). The integrated quantities of these pigments appear to exceed that of the chlorophyll a in the overlying oxygenated portion of the eu-photic zone. The light levels at the depth of the bacteriochlorophyll maximum, however, are very low (<<0.1% where Ia is the incident radiation) and the carbon assimilation rates necessary to verify the hypothesis are difficult to calculate or measure. 

Schulze, E.-D., Kelliher, F. M., Korner, Ch., Lloyd, )., and Leuning, R. (1994). Relationships between maximum stomatal conductance, ecosystem surface conductance, carbon assimilation rate and plant nutrition A global ecology scaling exercise. A inu. Rev. Ecol. Systciiuities 25,629-660. 

The radiological hazard of tritium to operating personnel and the general population is controlled by limiting the rates of exposure and release of material. Maximum permissible concentrations (MPC) of radionucHdes were specified in 1959 by the International Commission on Radiological Protection (79). For purposes of control all tritium is assumed to be tritiated water, the most readily assimilated form. The MPC of tritium ia breathing air (continuous exposure for 40 h/wk) is specified as 185 kBq/mL (5 p.Ci/mL) and the MPC for tritium in drinking water is set at 3.7 GBq/mL (0.1 Ci/mL) (79). The maximum permitted body burden is 37 MBq (one millicurie). Whenever bioassay indicates this value has been exceeded, the individual is withdrawn from further work with tritium until the level of tritium is reduced. 

At low irradiances, photosynthesis uses virtually 100% of the quanta, but in full sunlight, about 2000 imol quanta s , more quanta are available than can be used in photochemistry. Maximum rates of photosynthesis by Populus or Spinacia leaves of 15 and 70 jumol O2 m s , respectively, would require only 15 x 9 = 135 to 630 jumol quanta m s , or 10-40%. Leaves, therefore, need to be able to dissipate 60-90% of the quanta at high irradiance in an orderly manner such as non-radiative decay if they are to avoid the potentially damaging formation of oxygen radicals from reduced ferredoxin (Asada Takahashi, 1987). When plants are under a stress that restricts CO2 assimilation, excessive light will be reached at even lower irradiances. 

Of course, an accurate assessment of the fluxes of chemical elements in the atmosphere-vegetation-soil system is only possible with a detailed inventory of land covers. For instance, Fang et al. (2001) have undertaken such an inventory for seven time periods over the territory of China, including both planted and natural forests. It was shown that a maximum rate (0.035 PgCyr-1) of carbon assimilation from the atmosphere was observed between 1989 and 1993. Under this, different types of forest had various time periods for a maximum rate of carbon assimilation. This confirms... 

The total microbial community assimilation of NOs and NH4+, as well as total photoautotrophic N uptake all showed significant depth and time dependence, with maximum rates of N assimilation in the near-surface waters during summer (Figs.16.8A and 16.8B, Table 16.4). The f-ratio was consistently low (<0.1 in the... 

Chlorophyll a fluorescence induaion is a widespread method to evaluate the photosynthetic activity. This method is noninvasive, highly sensitive, fast, and easily measured. When chlorophyll molecules in photosystem II absorb light, that light may be assimilated into the hght reactions of photosynthesis or may be released as fluorescence or heat energy. In vivo fluorescence increases when photosynthesis declines or is inhibited. Numerous environmental f ors can affect the rate of electron transport between photosystem II and photosystem I due to interference with electron carriers between the two photosystems. For example, when the diuton is added in the measured sample, electron transport from photosystem II to photosystem I is blocked resulting in maximum fluorescence. This method was often employed to detect the photosynthetic activity of immobilized photosynthetic material. ... 

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