Abstract

Fine roots are an important source and sink for nutrients in terrestrial biogeochemistry. We examined the following hypotheses for fine root nutrients by analyzing data from 56 published studies: 1) that there is a general, inverse relationship of fine root nutrient concentrations with root diameter, and 2) that retranslocation of nutrients out of fine roots is minimal. We analyzed nutrient concentrations of roots < 5 mm in diameter as a function of root diameter and root status (live, dead, and undifferentiated), including a comparison for coniferous and broad-leaved trees. For fine roots < 2 mm in diameter, average C:N and C:N:P ratios were 43:1 and 533:12:1, significantly narrower than for 2-5 mm roots (79:1 and 858:11:1). Live roots < 2 mm in diameter contained significantly more N, P, and Mg and less C than did roots 2-5 mm in diameter, but no significant differences were observed for K or Ca. Mean N and P concentrations were 11.0 g/kg and 0.9 g/kg, respectively, for live roots < 2 mm diameter compared to 6.5 and 5.0 g/kg in roots > 2 mm diameter. Mean N concentrations in live and dead fine roots were identical and may imply little retranslocation of root N with senescence, but conflicting evidence from Ca:N ratios highlights the need for further research. These results have practical implications for various ecological methods and for the representation of roots in biogeochemical models.