Slow decomposition of very fine roots and some factors controlling the process: a 4-year experiment in four temperate tree species

Background and aims Despite our growing appreciation of the large contribution made by fine roots to soil organic carbon pool and nutrient cycling, their decomposition dynamics still remain poorly quantified. Methods In a field experiment, we conducted a 4-year litterbag study on different root size classes (< 0.5 and 0.5-2.0 mm) in four temperate tree species. Results Very fine roots (< 0.5 mm) decomposed more slowly than 0.5-2.0 mm roots in the four species roots studied in both the initial and later phases of root decomposition. Of all the root tissue chemistry we measured, decomposition rates correlated best with acid-unhydrolyzable fraction concentrations. However, no correlation was found for any of the nutrient related root quality parameters and decomposition rates. In contrast to mass loss, root net N released declined more rapidly in very fine roots (< 0.5 mm) than in 0.5-2.0 mm roots. Additionally, much of nitrogen was released in the final stages of decomposition, during which the recalcitrant carbon compounds were decomposed. Conclusions We conclude that the quality of carbon in root detritus and not the concentration of initial nutrients control its decomposition dynamics in a relatively nutrient-rich soil in northeastern China. These patterns can be explained by lower easily accessible labile carbon and higher recalcitrant carbon fractions in very fine roots (< 0.5 mm) than in 0.5-2.0 mm roots, at least in the four species we studied.