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Introduction.
One of the most under-investigated carbon pools of woody plants is the fine root system. Herbaceous plants spend from 10- 50% of their daily assimilated carbon on root respiration (Lambers et al., 1997; Van der Werf et al., 1994). If this is also true of woody plants, it not only illustrates the sizable quantity of carbon needed for root function and growth, but also translates to a large amount of carbon being released below-ground into the soil. Additionally, fine roots provide a large carbon input to the ecosystem when they senesce. Fine roots can add as much or more organic matter to forest soils as leaf litter (Vogt et al., 1991).
The factors that control root senescence are very poorly understood. Fine root lifespan has been observed to be from 14 to 280 days (unpublished data on apple, Wells & Eissenstat; unpublished data on citrus, Bryla & Eissenstat). It is accepted that in most woody species, senescence and production occur simultaneously during the season. The extent that genetic factors control senescence, as opposed to environmental factors, is unclear. While there has been some examination of environmental effects on root senescence there has been virtually no examination of differences in root lifespans among contrasting species. In the study presented here, we show differences in fine root cost and nutrient uptake capacity between fast- and slow-growing species and begin to link these traits to mechanisms that may indicate inherent differences in fine root lifespan. The main purpose of this study was to examine the interactions of root attributes with fine root efficiency.
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