Liming suppresses fine root production and turnover in a northern hardwood forest

Fine roots and root-associated carbon (C) inputs contribute disproportionally to soil C stocks. Here, we quantified fine root dynamics in a mixed northern hardwood forest at the Woods Lake Watershed in the Adirondack Park, NY, USA, where an experimental lime application in 1989 led to the near-doubling of forest floor organic matter stocks two decades later. Prior work linked this organic matter accumulation with lower heterotrophic respiration and decreased abundances of major fungal saprotrophs and ectomycorrhizal fungi. We investigated whether liming-driven shifts in fine root dynamics and depth distribution also contributed to forest floor accumulation. Forest floor mass in limed plots again roughly doubled that in unlimed plots 32 years after liming, with persistently large accumulations in the Oa horizon. Liming decreased fine root production across all horizons measured (Oe, Oa, 0–10 cm mineral soil) and by 40% overall, with largest effects in the Oa horizon (−45%) where root turnover was also reduced (−59%). Thus, liming decreased, rather than increased, root detrital C inputs to the forest floor. These results suggest that liming must have suppressed decomposition even more than shown previously or increased some other C input to the forest floor to explain its substantial C accumulation.