Root turnover and production by ¹⁴C dilution: implications of carbon partitioning in plants

Abstract

Estimates of belowground net primary production (BNP) obtained by using traditional soil core harvest data are subject to a variety of potentially serious errors. In a controlled growth chamber experiment, we examined the aboveground-belowground, labile to structural tissue, and plant to soil dynamics of carbon to formulate a ¹⁴C dilution technique for potential successful application in the field and to quantify sources of error in production estimates. Despite the fact that the majority of net ¹⁴C movement between above- and belowground plant parts occurred between the initial labeling and day 5, significant quantities of ¹⁴C were incorporated into cell-wall tissue throughout the growing period. The rate of this increase at late sampling dates was greater for roots than for shoots. Total loss of assimilated ¹⁴C was 47% in wheat and 28% in blue grama. Exudation and sloughing in wheat and blue grama, respectively, was 15 and 6% of total uptake and 22 and 8% of total plant production. When root production estimates by ¹⁴C dilution were corrected for the quantities of labile ¹⁴C incorporated into structural carbon between two sampling dates, good agreement with actual production was found. The error associated with these estimates was ± 2% compared with a range of −119 to −57% for the uncorrected estimates. Our results suggest that this technique has potential field application if sampling is performed the year after labelling. Sources of errors in harvest versus ¹⁴C dilution estimates of BNP are discussed.