Assimilation efficiency models

The nitrogen flow model was tested for sensitivity to varying the "biological parameters" of filter-feeder electivity and assimilation efficiency. Results detailed in Wickens Field (1985) show that the model is not sensitive to varying biological parameters when the system is closed (i.e. no water transport through upwelling or... 

Efforts to model foodweb dynamics are hampered by calibration data, particularly the lower trophic levels, and by the large uncertainties associated with bioenergetic input parameters, such as PCB assimilation efficiencies for different organisms. Another major hindrance in aquatic foodweb models is a lack of understanding of the bioaccumulation of PCBs from water to the first trophic level, phytoplankton.61,62 Research in this laboratory has revealed that... 

Iron-containing proteins are essential for photosynthetic and respiratory electron transport. Chlorophyll synthesis is also dependent on iron, and chlorophyll content is diminished under iron limitation. Requirements for iron are also influenced by the nitrogen substrate used to support growth. Both nitrate and nitrite reductases contain iron in their catalytical centres. Iron efficiency models (Raven, 1988) and culture studies (Maldonado Price, 1999) show that cells using nitrate require 60-70% more cellular iron to support a given growth rate than those assimilating ammonia. 

The bioavailability of selenium to a benthic deposit-feeding bivalve, Macoma balthica from particulate and dissolved phases was determined from AE data. The selenium concentration in the animals collected from San Francisco Bay was very close to that predicted by a model based on the laboratory AE studies of radiolabelled selenium from both particulate and solute sources. Uptake was found to be largely derived from particulate material [93]. The selenium occurs as selenite in the dissolved phase, and is taken up linearly with concentration. However, the particle-associated selenium as organoselenium and even elemental selenium is accumulated at much higher levels. The efficiency of uptake from the sediment of particulate radiolabelled selenium was 22%. This contrasts with an absorption efficiency of ca. 86% of organoselenium when this was fed as diatoms - the major food source of the clam. The experiments demonstrated the importance of particles in the uptake of pollutants and their transfer through the food web to molluscs, but the mode of assimilation was not discussed. 

C02 assimilation. The amount of C02 available for photosynthesis decreases with decreasing C02 partial pressure at higher elevations, but this effect is offset by the increase in diffusion speed at lower air pressure (Gale 1972, 1973). The lower temperature at higher altitudes, however, decreases diffusion speed, and therefore the temperature lapse rate of the particular mountain determines whether C02 availability decreases (dry-moist lapse rate) or stays relatively constant (very wet lapse rate) (Smith and Donahue 1991). The lower air pressure at altitude does not just decrease C02 partial pressure but also 02 partial pressure, which results in lower photorespiration rates and more efficient photosynthesis. When all these effects are modeled, photosynthetic rates generally decrease with altitude, unless the temperature lapse rate is very low (which could occur in extremely wet mountain ranges), but the photosynthetic limitation is much less than expected based on just the partial pressure decrease (Terashima et al. 1995 Smith and lohnson 2007). 

Several laboratories have studied the assimilation of specific lysosomal enzymes using as model systems skin fibroblasts deficient in the enzyme under study. The underlying mechanism for the translocation of lysosomal enzymes was hypothesized to involve binding of carbohydrate-containing recognition markers to specific cell surface receptors (1 5). In support of this hypothesis Hickman, Shapiro, and Neufeld (16J found that treatment of N-acetyl-B-hexosaminidase with periodate under conditions that dTd not affect enzymatic activity prevented the efficient assimilation of this enzyme by Sandhoff fibroblasts. Additionally, Kresse and von Figura (1 7) found that treatment of f -acetyl-a-hexosaminidase with B-galactosidase reduced the assimilation of this enzyme by San-filippo B fibroblasts. 

The studies of the BSGC with the help of assimilation of shipborne and satellite altimeter data in the full hydrothermodynamic model [42] began simultaneously with the above-described adaptation calculations. In the course of the studies it was realized that the optimal variant of assimilation with respect to its efficiency and simplicity is the above-mentioned introduction of terms with relaxation to observations into the thermodynamic equations [43]. The main goals of the studies became the simulation of the detailed climatic annual cycle of the BSGC with the help of assimilation of climatic monthly temperature and salinity fields and the simulation of the synoptic variability of the BSGC with the use of the SLE acquired by the altimeter observations from the TOPEX/Poseidon and ERS-1,2 satellites. 

A number of models have been constructed to better understand the development physiology of Jerusalem artichoke. These models quantify the amount of solar radiation intercepted, the efficiency with which light is converted into dry matter, and the distribution of dry matter around the plant over time. Assimilated dry matter is used for structural growth or as storage reserves in different plant parts. 

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