Contribution of Root vs. Leaf Litter to Dissolved Organic Carbon Leaching through Soil

Very little is known about dissolved organic matter (DOM) originating from fine roots in forest soils in comparison to DOM originating from leaf litter. To compare the fate of root‐ vs. leaf‐derived dissolved organic carbon (DOC), we added 14 C‐labeled root litter at depths of 10 cm, a “shallow root treatment,” and 40 cm, a “deep root treatment,” and leaf litter to 50‐cm column soil microcosms. We analyzed the solution leached from the columns during a 47‐d simulated snowmelt treatment, trapped respired 14 CO 2 , and measured translocation of 14 C within the columns. In general, total C losses, as a percentage of 14 C added, were substantial and highest for the leaf treatment (8.2% leached as DOC, 13.4% translocated, and 14.8% respired), intermediate for the shallow root treatment (2.3, 5.2, and 3.9%, respectively) and lowest for the deep root treatment (2.4, 1.9, and 2.9%, respectively). The C lost to DOC leaching was similar, however, for the deep and shallow root treatments. As a percentage of total losses (i.e., the sum of DOC leaching, respiration, and translocation), 14 C lost as DOC leaching was significantly higher in the deep root treatment than other treatments. These observations suggest that leaf‐derived DOC may contribute to the formation of an A horizon and even to accumulation of soil organic carbon (SOC) in the B horizon during soil development, either by adsorption or microbial biomass incorporation. The 14 C data further showed that root‐derived DOC, especially from root litter at greater depths, may help explain both the presence of SOC at depth and a portion of the DOC draining from soil profiles.