Christina Wells

MARKED DIFFERENCES IN SURVIVORSHIP AMONG APPLE ROOTS OF DIFFERENT DIAMETERS

Fine roots are responsible for a substantial fraction of terrestrial net primary productivity, and a better understanding of fine root production and turnover is crucial to improving global carbon and nutrient cycling models. In most studies, roots less than 1 or 2 mm in diameter (“fine roots”) have been treated as structurally and physiologically identical individuals. We used minirhizotron data from 16-yr-old apple (Malus domestica) trees to investigate differences in life span and life history among fine roots whose diameters differed by tenths of a millimeter. We also introduced the use of Cox proportional hazards regression models to assess the effects of multiple covariates on root mortality. Overwinter survivorship differed markedly among diameter classes in both years: 3–12% for roots 0.5 mm in diameter and brown, and these roots gave rise to new white laterals during the spring root flush. Based on the considerable differences in morphology and life history within the class of roots <1 mm in diameter, we advocate the use of a functional definition for the fine root whenever possible.