Environmental Controls of Fine-Roots Decomposition Dynamics in a Northern Temperate Forest Soil.

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.