Standard Litterbags Underestimate Early-Stage Lower-Order Root Decomposition Rate in a Subtropical Forest, China

The standard litterbag method isolates soil or litter from decomposing roots by a dense nylon mesh that is likely to underestimate root decomposition rate. Thus, we evaluated the effect of direct contact between roots and soil or litter during root decomposition. Schima superba and Cleyera japonica order 1–3, 4–5, and 6 roots were decomposed using two types of litterbags at two soil horizons: standard litterbags (R_O, pure root in O horizon; R_A, pure root in A horizon) and mixed litterbags (R + L_O, mixed root with semi-decomposed litter in O horizon; and R + HS_A, mixed root with humus soil in A horizon). The mass and nutrient dynamics were measured in one year of decomposition. After one year of decomposition, litterbag types and soil horizons significantly affected root mass and nutrient dynamics. Litterbags mixed with humus soil and litter increased 1–3 order root decomposition rate by 139–143% and 42–89%, respectively. Furthermore, 1–3 order roots had a significantly different decomposition rate than higher-order roots, but standard and mixed litterbags showed the opposite effect. The decomposition rate of 1–3 order roots appears to be more sensitive to litterbag type than higher-order roots. Directly contact between root and soil or litter was important for root decomposition in corresponding soil layers. Standard litterbags significantly underestimate the decomposition rate of lower-order roots in the early stages of decomposition.