Fixation rates

Dinitrogen is fixed either by natural processes or by industrial ammonia (qv) production (1,8,9). The estimates for the aimual biological contribution range around 100-200 x 10 t. Industrial fixation contributes about 50 x 10 t/yr for fertilizer uses (see Fertilizers). Other processes, eg, lightning and combustion, are estimated to fix about 30 x 10 t/yr. Thus the biological process represents the majority (ca 65%) of the total aimual fixation rate, contributing about three times as much as the commercial production of fertilizer. 

P vs I Relationships. In our investigation we em-ployed a technique widely used by plant physiologists, namely, the study of rate of photosynthesis (P) as a function of irradiance (I). The results of one experiment in which phytoplankton were kept under the four experimental treatment conditions for 24 hours arc shown in Fig. 4. It is clear from this figure that phytoplankton exposed to visible light alone (i.e., when UV was excluded) had the highest photosynthctic rates, and these rates were maintained over a higher range of irradiance levels. On the other hand, the lowest carbon fixation rates occurred when the phytoplankton were exposed to ambient and enhanced levels of UV. 

Figure 12.19 Control of reactive dye fixation rate by Remazol automet (DyStar) alkali addition [151]...

Population genetics has produced a detailed theory of the relationship between frequency, drift, and selective value of genetic variation (Nei, 1975 Hard and Clark, 1989 Li, 1997). The problem with its straightforward application is that the main parameters, such as history of population size, fixation rate, and selective pressure, are difficult to establish. 

N2O contributes to the greenhouse effect with 4% (Schonwiese 1995). N2O emissions from agriculture come from mineral and organic N-fertilisers and from leguminous crops. The emission levels depend on the kind of fertiliser and on the application technique. The N2O emission factors for the most frequently applied forms of mineral N-fertilisers are < 0.5%, for organic manure 1.0 - 1.8% and for N from legumes, about 1% of the fixation rate. 

Further strategies being implemented to minimize dye and related chemical effluent include designing more environmentally friendly chemicals, more efficient (higher yielding) manufacturing processes, and more effective dyes, for example, reactive dyes with higher fixation rate. 

Vgp Carbon fixation rate per dry cell weight based on sucrose... 

Table 3 compares the values of Cchb apparent C02 fixation rate, RubisCO activity, and some other enzyme activities among the hairy roots of different types and different parts of the parent plants of pak-bung. The Cchl and AR values in the hairy roots cultivated photomixotrophically with 30 kg m 3 sucrose for 14 days were somewhat lower than those found in parent plant stems. Those values in the photoautotrophs were in excess of the values in the stems although even lower than those in parent plant leaves. Likewise, the C02 fixation rate of photoautotrophic hairy roots reached more than 3.0 times that of photo-mixotrophic ones. 

Table 3. Comparisons of the average Chi contents, apparent C02 fixation rates and some enzyme activities among the hairy roots of different types and different parts of the parent plants of pak-bung...

Table 4 summarizes properties of various plant cells with photosynthetic ability, indicating the Chi contents, RubisCO activities, and apparent C02 fixation rates of photoautotrophic cells derived from various plants [34,38,40]. The callus of G. max possessed the Chi content of 1.4-1.9 x 103 mg (kg-FW)-1, the value of which was about 28-fold over that in the callus of N. tabacum (58 mg (kg-FW)1). The photoautotrophic hairy roots of pak-bung exhibited relatively high Chi content of 6.1 x 102 mg (kg-FW)-1 though the value was lower than that of G. max callus. On the other hand, as shown in Table 4, the levels of RubisCO activity and Chl-based C02 fixation rate of the pak-bung hairy roots were comparable to those of the photoautotrophic plant cells reported in the literatures. These values, therefore, can be used as indicators for the potentials of photoautotrophic growth of plant cells. 

Table 4. Chi contents, RubisCO activities and apparent C02 fixation rates of photo autotrophic cells derived from various plants... 

Cells C02 and light conditions Chi content [mg (kg-FW) ] RubisCO activity [pmol-CO, (h mg-Chl)-1] Apparent C02 fixation rate [pmol-CO, (h mg-Chl) ] Ref. 

Provided that the average apparent C02 fixation rate is directly proportional to the Ar value, the following equation can be obtained ... 

B. If the CO2 fixation rate is 100 mmol (g chlorophyll)-1 hour-1, how long does it take to double the dry mass of the cell Assume that CO2 and H20 are the only substances entering the cell. 

Figure 2.6 Air-sea flux densities of N2 (bold lines) calculated as F = (0.39ujq ) (SRCair-Cair) (Scn2/660) (Wanninkhof, 1992). SR stands for the N2 saturation ratio and Um stands for the wind speed in a height of 10m. Water temperature and salinity were set to 25° C and 35, respectively. C ir is the equilibrium concentration of atmospheric N2 and was calculated with the equation given by Hamme and Emerson (2004). The dashed lines represent maximum (3110 pmol N m day ) and minimum (161 pmol N m day ) mean N2 fixation rates for the North Atlantic Ocean (Capone et a/., 2005).

Low, but measurable N2 fixation rates were recently reported by Needoba et al. (2007), from the inter-convergence zone, 200 km off the coast of Northern California, where sea surface temperatures were >19°C. In addition, they reported the temporal dynamics of mRNA abundance for nijH down to 80 m, where temperatures ranged 14-19°C, and expression was dominated by a unicellular Group A phylotype, and to a lesser extent by Group B. Similarly, HoU et al. (2007) reported N2 fixation in the upper water column of warm core and cold core eddies at temperatures at or below 19C in the Leeuwin Current off the west coast of Australia. 

A number of studies have speculated on diazotroph response to mineral dust Fe fertilization in the Atlantic (Mahaffey et al, 2003), and Pacific Oceans (Johnson et al, 2003). Circumstantial evidence for dust stimulation of marine diazotrophic biomass has recently been reported. A 1999 Saharan dust event coincided with increases in dissolved Fe concentrations on the west Florida shelf and a 100-fold increase in Trichodesmium biomass. N2 fixation rates were not measured, but DON concentrations doubled, presumably due to exudation by N2 fixers (Lenes et al, 2001). A recent Saharan dust addition experiment to surface water samples collected along a west African cruise transect (35°W-17°W), found a minimal increase in CO2 fixation and a large stimulation in N2 fixation, suggesting that diazotrophs were co-limited by both P and Fe (Mills et al, 2004). Note however, analysis of aerosol dust shows that while providing Fe, it also supplies P and combined N (Baker et al, 2003 Mills et al, 2004 Ridame and Guieu, 2002). 

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