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• We used an inadvertent whole-ecosystem 14C label at a temperate forest in Oak Ridge, Tennessee, USA to develop a model ( Radix1.0) of fine-root dynamics. Radix simulates two live-root pools, two dead-root pools, non-normally distributed root mortality turnover times, a stored carbon (C) pool, and seasonal growth and respiration patterns. • We applied Radix to analyze measurements from two root size classes (< 0.5 and 0.5–2.0 mm diameter) and three soil-depth increments (O horizon, 0–15 cm and 30–60 cm). • Predicted live-root turnover times were < 1 yr and ∼10 yr for short- and long-lived pools, respectively. Dead-root pools had decomposition turnover times of ∼2 yr and ∼10 yr. Realistic characterization of C flows through fine roots requires a model with two live fine-root populations, two dead fine-root pools, and root respiration. These are the first fine-root turnover time estimates that take into account respiration, storage, seasonal growth patterns, and non-normal turnover time distributions. • The presence of a root population with decadal turnover times implies a lower amount of belowground net primary production used to grow fine-root tissue than is currently predicted by models with a single annual turnover pool. [ABSTRACT FROM AUTHOR]

From a stratified, random sampling of non-urban high schools in the Southeast, survey data were obtained from 5374 adolescent males. Over half reported trying smokeless tobacco, and approximately one third of these reported a regular, substantial level of use. The average age at initial use was 12.2 yr. and was negatively correlated with the level of use. Factor analysis of the psychosocial items resulted in four factors: substance use/deviant style, modeling, perceived negative consequences, and health behavior. Discriminant analysis of initial use indicated that substance use and modeling influences were the strongest predictors of trying smokeless tobacco. Regression analysis of level of smokeless tobacco use indicated that substance use, modeling, and perceived negative consequences were equivalent in their contribution. Separate analyses were performed for American Indian, Black, and White males. Although predictors of initial use were similar, level of smokeless tobacco use was most associated with the use of other substances in Blacks and with modeling influences in Whites.