Assimilation ratio

Data compiled by Hanks (1983) show that, contrary to earlier notions, the m coefficient in Equation 1 may be affected by the genotype. A relatively greater net gain of carbon for the same rate of transpiration under stress may be reflected in the m coefficient (Equation 1), in the ratio between assimilation and transpiration (assimilation ratio) or in the agronomic index, WUE (Equation 2). 

Williams, P. J. leB. (1995). Evidence for the seasonal accumulation of carbon-rich dissolved organic material, its scale in comparison with changes in particulate material and the consequential effect on net C/N assimilation ratios. Mar. Chem. 51, 17-29. 

At a station located in the North Pacific trades biome (18°N, 156°W), DiTuUio and Laws (1983) reported autotrophic N uptake rates of 7-11 pmol N m h for four samples coUectedin the euphotic zone. The integrated (0—120 m to the l%Ught level) rate of autotrophic N assimUation was 0.93 mmol N var h and the mean molar C N assimilation ratio (C assimilation was measured using " C) was 7.84 ( 0.23), compared... 

For the mussel, Thompson and Bayne have shown that assimilation efficiency and the total assimilated ratio is a function of cell concentration 115l If metal contaminated and uncontaminated algae are consumed at the same rate, then there may be no detectable difference in assimilation. On the other hand, when the animals... 

The cycles of carbon and the other main plant nutrients are coupled in a fundamental way by the involvement of these elements in photosynthetic assimilation and plant growth. Redfield (1934) and several others have shown that there are approximately constant proportions of C, N, S, and P in marine plankton and land plants ("Redfield ratios") see Chapter 10. This implies that the exchange flux of one of these elements between the biota reservoir and the atmosphere - or ocean - must be strongly influenced by the flux of the others. 

The amount of growth occurring when rainfall is limited depends on the ratio of assimilation rate to transpiration rate. In a leaf the instantaneous transpiration efficiency, A E, is given approximately by... 

Recently it has been recognised that the carbon isotope composition of small amounts of plant material may be used to assess differences inpi/pa and W (Farquhar et al., 1982). There are two stable isotopes of carbon, and C, which are in the molar ratio 1 89 in the atmosphere. During assimilation of atmospheric CO2 the plant fixes a smaller ratio... 

Jones, H.G. (1976). Crop characteristics and the ratio between assimilation and transpiration. Journal of Applied Ecology, 13, 605-22. 

Especially in dicotyledonous plant species such as tomato, chickpea, and white lupin (82,111), with a high cation/anion uptake ratio, PEPC-mediated biosynthesis of carboxylates may also be linked to excessive net uptake of cations due to inhibition of uptake and assimilation of nitrate under P-deficient conditions (Fig. 5) (17,111,115). Excess uptake of cations is balanced by enhanced net re-lea,se of protons (82,111,116), provided by increased bio.synthesis of organic acids via PEPC as a constituent of the intracellular pH-stat mechanism (117). In these plants, P deficiency-mediated proton extrusion leads to rhizosphere acidification, which can contribute to the. solubilization of acid soluble Ca phosphates in calcareous soils (Fig. 5) (34,118,119). In some species (e.g., chickpea, white lupin, oil-seed rape, buckwheat), the enhanced net release of protons is associated with increased exudation of carboxylates, whereas in tomato, carboxylate exudation was negligible despite intense proton extrusion (82,120). 

Most plant species are able to absorb and assimilate nitrate, ammonium, urea, and amino acids as nitrogen sources, but the response to a particular form of nitrogen varies from species to species (114). For example, optimal growth of tomato roots occurs in soil with a ratio of nitrate to ammonium of 3 1 and is inhibited if the ammonium concentration is too high (115). By contrast, white spruce has a strong preference for ammonium (116), whereas some arctic sedges prefer amino acids (117). 

Charette and Moran 1999 Charette et al. 1999 Amid et al. 2002). Such observations often coincide with the collection of significant quantities of large phytoplankton during the growth phase of a bloom such that the volume-to-surface area ratio of the cells is increasing and the POC/ Th ratio, representing the ratio of an assimilated element to an adsorbed one, follows. 

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