Preferential Substrate Utilization Research Articles

Rhizosphere feedbacks in elevated CO(2).

Understanding rhizosphere processes in relation to increasing atmospheric CO(2) concentrations is important for predicting the response of forest ecosystems to environmental changes, because rhizosphere processes are intimately linked with nutrient cycling and soil organic matter decomposition, both of which feedback to tree growth and soil carbon storage. Plants grown in elevated CO(2) substantially increase C input to the rhizosphere. Although it is known that elevated CO(2) enhances rhizosphere respiration more than it enhances root biomass, the fate and function of this extra carbon input to the rhizosphere in response to elevated CO(2) are not clear. Depending on specific plant and soil conditions, the increased carbon input to the rhizosphere can result in an increase, a decrease, or no effect on soil organic matter decomposition and nutrient mineralization. Three mechanisms may account for these inconsistent results: (1) the "preferential substrate utilization" hypothesis; (2) the "priming effect" hypothesis; and (3) the "competition" hypothesis, i.e., competition for mineral nutrients between plants and soil microorganisms. A microbial growth model is developed that quantitatively links the increased rhizosphere input in response to elevated CO(2) with soil organic matter decomposition. The model incorporates the three proposed mechanisms, and simulates the complexity of the rhizosphere processes. The model also illustrates mechanistically the interactions among nitrogen availability, substrate quality, and microbial dynamics when the system is exposed to elevated CO(2).

Genetic influences on human energy expenditure and substrate utilization.

Understanding the genetic factors of obesity requires consideration of the genetic basis of the underlying etiological factors including energy expenditure and substrate utilization. Genetic susceptibility studies suggest that altered energy expenditure and/or preferential substrate utilization are likely to be involved in the etiology of obesity. Twin and family studies suggest that there is a strongly heritable component to resting energy expenditure, substrate utilization, and the thermic response to feeding. Physical activity energy expenditure has been less well studied; new data are presented in young sib pairs that suggest moderate heritability of nonresting energy expenditure. Only a few candidate gene studies have been performed to examine the role of basic proteins involved in energy expenditure (the sodium-potassium ATPase and the uncoupling protein) or substrate utilization (fatty acid binding protein). The lack of information in this area warrants further investigation into genetic aspects of energy and substrate metabolism.