Nutrient concentrations limitation

Silicic acid (H4Si04) is a necessary nutrient for diatoms, who build their shells from opal (Si02 H20). Whether silicic acid becomes limiting for diatoms in seawater depends on the availability of Si relative to N and P. Estimates of diatom uptake of Si relative to P range from 16 1 to 23 1. Dugdale and Wilkerson (1998) and Dunne et al. (1999) have shown that much of the variability in new production in the equatorial Pacific may be tied to variability in diatom production. Diatom control is most important at times of very high nutrient concentrations and during non-steady-state times, perhaps because more iron is available at those times. 

Frost, R. W. and Franzen, N. C. (1992). Grazing and iron limitation in the control of phytoplankton stock and nutrient concentration A chemostat analogue... 

Saponins and phenolics also have anti-microbial properties (Chung et ah, 1998) and have been associated with reduced rumen functions (Klita et al., 1996 Reed, 1995), thereby limiting the nutrient quality of forages. Also, carbohydrate complexes with hgnins and other compounds reduce carbohydrate utilization by rumen bacteria (Cornu et al., 1994). The influence of such anti-microbials on rumen functions can affect small intestine characteristics by altering nutrient concentrations (Barry and McNabb, 1999). 

Changes to the urinary tract in pregnant women predispose them to an increased incidence of bacteriuria, and subsequent urinary tract infections that may follow. These changes are not limited to amino acid and other nutrient concentrations in the urine, but extend to physiologic changes such as reduced bladder tone and dilation of the renal pelvis and ureters.22,23... 

The level of enzyme needed can influence the choice of preparation used for the study. Microsomal preparations from cell cultures allow the use of higher concentrations of active enzyme per unit volume than use of whole cells or cell lysates. The use of whole, viable cells allows the use of longer incubation times but at a lower enzyme concentration per unit volume. In addition, adequate oxygen transfer and nutrient concentrations are needed to maintain culture viability. These requirements impose limitations on cell concentration. In addition, microsomes cannot be efficiently prepared from all cultured cell types. We have found that standard microsome preparation procedures as used for human or rodent liver were unsuitable for isolating active enzymes from human lymphoblasts, and this appears to be a general property of cultured cell lines. Specific catalytic activities in microsomes were lower than for whole cell lysates. This loss of activity appears to happen in other mammalian cell systems which has led to the common use of whole cell lysates.With human lymphoblasts, shortening the length of... 

Despite generally high nutrient concentrations in rivers as compared to lakes, primary production in these systems appears to be in the same range as that of lakes due to the strong light limitation in these systems (Cole and Cloern, 1984 Roos and Pieterse, 1992). Annual production varies between 10 and 500 g C m 2yr 1 and averages about 100 g C m 2 yr-1 (Capblancq and Dauta, 1978 Bonnetto, 1983 Bonnetto et al., 1981 Saha et al., 1985 Lewis, 1988 Cole et al., 1989, 1992 Webster and Meyer, 1997). 

The carbon/nutrient balance hypothesis (CNBH) was originally proposed to explain resource allocation patterns in terrestrial vascular plants. It has also been used to examine defense allocation patterns in macroalgae. The CNBH predicts that when carbon is available but nutrients are limited, plants should increase concentrations of carbon-based defenses.135 When carbon is available but nutrients are abundant, plants should invest resources in growth. If carbon is limiting, such as when shading lowers photosynthetic rates, carbon should be allocated to growth and the production of carbon-based defenses should decrease. 

Adequate mineral nutrition is extremely important in determining the soil populations of bacteria that can utilize phenolic acids as a carbon source. Blum et al.3 observed that when Cecil A-horizon soil (initially nutrient limited) was supplied with 53 pg/mL (3.5 ml /h) of p-coumaric acid and a range of nutrient concentrations for 72 h, the populations of phenolic acid utilizing bacteria increased in a linear manner as nutrient concentration was increased. 

One key factor for tropical diazotrophs may be water temperature. For example, the distribution of Trkhodesmium spp. is roughly limited by the 20°C isotherm, and other planktonic cyanobacteria are likewise primarily tropical or subtropical in distribution. MetabolicaUy active populations of Trkhodesmium have been observed at 18.3°C in the North Atlantic (McCarthy and Carpenter, 1979), but activity was low, and substantial growth is typically not seen until water temperature exceeds 20°C (Carpenter, 1983a,b). Moreover, water temperature co-varies inversely with surface nutrient concentrations (Kamykowski and Zentara, 1986). Indeed, in previous studies we have used sea surface temperature as a proxy for oligotrophic waters in order to estimate the areal range of Trkhodesmium (Capone et al., 2005). 

Button, D. K. (1978). On the theory of control of microbial growth kinetics by limiting nutrient concentration. Deep-Sea Res. 25, 1163—1177. 

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