Litter and root sources of soil organic matter in a temperate forest: Thirty years in the DIRT.

Managers increasingly seek to increase forest soil carbon but long‐term controls on soil organic matter (SOM) sources and stability are weakly understood. We used a 30‐year detrital input/removal treatment experiment in a deciduous forest to evaluate the importance of root and leaf litter to SOM. Inputs were assessed by excluding roots and leaves (litter) or by doubling litter inputs. In mineral soil, %SOM differed only at 0–10 cm (p = 0.11), with concentrations in the no litter and no roots treatments of 26% and 9%, respectively, lower than the controls. Cessation of litter inputs had a stronger effect on SOM than cessation of root inputs, but root litter inputs may contribute stable SOM. Doubled litter increased mineral SOM. Core Ideas: A long‐term (30 years) litter manipulation experiment examines sources of litter inputs to forest soil organic matter.The experiment contains five treatments: control, no litter, double litter, no roots, and no inputs.After 30 years, soil organic matter (SOM) has increased in the doubled‐litter treatment.The continued absence of leaf litter did not result in further loss of SOM since Year 20.The no roots plots have been unintentionally recolonized by roots, and SOM has increased since Year 20. [ABSTRACT FROM AUTHOR]