Fernanda Santos, Life and Environmental Sciences, University of California-Merced, Merced, CA, Knute Nadelhoffer, Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI and Jeffrey A. Bird, School of Earth and Environmental Sciences, Queens College, City University of New York, Flushing, NY
Fine-roots (<2 mm diameter) are considered important sources of soil carbon (C) and nitrogen (N) in forest ecosystems, however the primary factors that control fine-root C and N mineralization rates in temperate forest soils are not well understood. In a two-year field study we examined the influence of long-term aboveground litter and N additions on fine-root decomposition and vertical transport of root-derived C and N. The fate of dual-labeled (13C/15N) red maple (Acer rubrum) fine roots was followed in soils within a long-term litter manipulation study (Detritus Input and Removal Treatments or DIRT), located in Pellston, MI, USA. In Fall 2010, labeled fine-roots were applied to soil mesocosm within DIRT treatments that (1) received high levels of N addition as fertilizer; (2) had no belowground litter inputs, (3) no aboveground and belowground litter inputs, or (4) no removal of litter or additional N added (control). Zero-tension lysimeters were installed underneath mesocosms to collect soil water. Mesocosms without added fine-roots served as experimental controls. After one and two years in situ, the recovery of 13C and 15N from fine-roots in bulk soil was determined within two depths (0-10 and 10-20cm). In addition, fine-root-13C in dissolved organic carbon leached below 20-cm soil depth was quantified. Root-derived C loss as 13CO2 was measured periodically during the 2-yr study. Initial results show that after 1 year in situ, the retention of root litter-derived C in soils was not significantly affected by either N additions or litter manipulation treatments. In contrast, treatments with no belowground litter additions had significantly lower retention of root-derived N than the control treatments.