Tree species effects on fine root decomposition and nitrogen release in subtropical forests in southern China

Abstract

Background: Root decomposition is an important process that contributes to forest ecosystem carbon (C) flux and nutrient cycling. Aims: To determine how tree species affected fine root (≤ 2 mm) decomposition rates and nitrogen (N) release. Methods: Fine root samples of the coniferous Pinus massoniana, the deciduous Choerospondias axillaris and the broadleaved evergreen Cyclobalanopsis glauca tree species were collected from three secondary successional subtropical forests (P. massoniana–Lithocarpus glaber mixed forest, C. axillaris forest and C. glauca–L. glaber mixed forest) in southern China. Samples were incubated in situ, using the litterbag method for a period of 500 days to measure mass loss and changes in fine root C and N concentrations. Results: C. axillaris exhibited the fastest decomposition rate (k) during the 500 day decomposition period, followed by P. massoniana and C. glauca. Fine root mass loss was positively correlated with initial N concentrations and negatively correlated with initial C:N ratios. Initial fine root C concentrations had a significant effect on N release, but the effect varied over time. Annual fine root production released ca. 16.2–44.2 kg N ha−1 through decomposition. Conclusions: Fine root mass loss during decomposition differed considerably among tree species. The chemical quality of fine roots was a key driver in the rates of decomposition. Soil properties partly accounted for the differences in decomposition rates.