Further evidence for slow decomposition of very fine roots using two methods: litterbags and intact cores

Root decomposition studies have rarely considered the heterogeneity within a fine-root system. Here, we investigated fine root (< 0.5 and 0.5-2 mm in diameter) decomposition and accompanying nutrient dynamics of two temperate tree species-Betula costata Trautv and Pinus koraiensis Sieb. et Zucc. Both litterbag and intact-core techniques were used to examine decomposition dynamic and nutrient release of the two size class roots over a 498-day period. Moreover, we examined differences between the two approaches. The very fine roots (< 0.5 mm) with an initially lower C:N ratio, decomposed more slowly than 0.5-2 mm roots of both tree species. The differences in mass loss between size classes were smaller when using the intact-core technique compared with litterbag technique. In contrast to root biomass loss, net N release was much higher in the fine roots (< 0.5 mm). All fine roots initially released N (0-75 days), but immobilized N to varying extent in the following days (75-498 days) during decomposition. Our results suggest that the slow decomposition rate of very fine roots (< 0.5 mm) may be determined by their high concentration of acid-unhydrolyzable structural components. Additionally, the heterogeneity within a bulk fine-root system could lead to differences in their contribution to soil in terms of carbon and nitrogen dynamics.