Plant and Soil 126, 144-148 (1990). (~ Kluwer Academic Publishers. Printed in the Netherlands. PLSO 8455 Seasonal nitrogen and carbon concentrations in white, brown and woody fine roots of sugar maple (Acer saccharum Marsh) DANIEL GOLDFARB, RON HENDRICK and KURT PREGITZER ~ Department of Forestry, Michigan State University, East Lansing, MI 48824, USA. IAddress for correspondence Received 9 October 1989. Revised March 1990 Key words: Acer saccharum, carbon concentration, fine roots, nitrogen concentration, translocation Abstract Small diameter (<l.0-mm) Acer saccharum Marsh roots were separated into white, brown and woody development state classes and analyzed for total N and C concentrations in April, July and October of 1988. White roots had greater concentrations of N and C than either brown or woody roots at each sampling date, and the N concentration of brown roots was consistently greater than that of woody roots. There were no temporal changes in N concentrations in any of the roots. C was slightly elevated in mid-summer in all three classes of roots. The data suggest the possible existence of an N translocation mechanism in ageing and developing fine roots. More research should be undertaken to establish the mechanisms of N loss in developing fine roots. Introduction Research has shown that fine root mortality and decomposition (turnover) can be a pathway of significant nutrient flux in forest ecosystems (Cox et al., 1978; Fahey et al., 1988; Joslin and Hen- derson, 1987). These and similar studies have also shown that concentrations of many nutrients decrease with increasing root diameter (e.g. Cox et al., 1978; Fahey et al., 1988 Fogel and Hunt, 1983; McClaugherty et al., 1982; Meier et al., 1985; Nambiar, 1987), and that the nutrient con- tent of small diameter root pools can be greater than that of larger roots (Cox et al., 1978; Joslin and Henderson, 1987; Vogt et al., 1983). Fine roots have traditionally been defined based largely upon their diameters, with fine root size maxima typically falling within the range of 2.0 to 5.0-mm. Size class differences in nutrient concentrations and contents, and the relationship between diameter and root longevi- ty, will determine the quantitative role of various sized roots in forest nutrient cycles. Nambiar (1987) has noted the need to pay close attention to root diameter-nutrient concentration relation- ships when establishing size classes in research on root turnover. However, it seems likely that there could be sizeable concentration differences in roots of different development states within the same diameter class, particularly among the smallest (and generally youngest) roots. Age or development state differences in nutrient con- centrations within a given root diameter class would not affect the contribution of root mortali- ty in that size class to soil nutrient inputs. How- ever, a better understanding of such differences could offer insight into the regulation of nutrient fluxes associated with root turnover. The data presented here result from a prelimi- nary effort in a larger study concerned with root dynamics in forests. The objectives were to de- termine total concentrations of carbon and nitro- gen in sugar maple (Acer saccharum Marsh.) roots <l.0-mm in diameter that were broadly age-classified by their development state (white, brown and woody), and to examine temporal variation in concentrations among and within the state classes.