Effects of streams on lignin degradation during foliar litter decomposition in an alpine forest

Abstract

Aims Streams are widely distributed in alpine forests, and litter decomposition in which is an important component of material cycling across the forest landscape. The leaching and fragmenting effects as well as the unique environmental factors in streams may have significant impacts on lignin degradation during litter decomposition, but studies on this are lacking. Methods Using litterbag methods, we investigated the dynamics of lignin mass remaining and concentration (percent litter mass, %) during the decomposition of four foliar litters, which varied significantly in the initial litter chemical traits, from the dominant species of Salix paraplesia, Rhododendron lapponicum, Sabina saltuaria, and Larix mastersiana under different habitats (forest floor, stream, and riparian zone) in the upper reaches of the Minjiang River. Important findings After two year's incubation, litter lignin mass remaining for a specific litter species varied significantly (p < 0.05) among habitats, with an order of stream < riparian zone < forest floor. Lignin was degraded substantially in the early stage of litter decomposition process, and the lignin concentration first decreased and then increased with the proceeding of litter decomposition, but varied significantly (p < 0.05) among different litter species. Lignin mass showed a general trend of decrease across the 2-year decomposition course. In addition, habitat type, decomposition period and microenvironmental factors (e.g., temperature, pH value and nutrient availability) showed substantial influences on lignin degradation rate. These results suggest that the traditional view that lignin was relatively recalcitrant with an increase of concentration in the early stage of litter decomposition is challenged, but the loss of lignin in the early phrase is in line with recent findings about the fate of lignin during litter decomposition. Moreover, the significant differences of lignin degradation rates among different decomposition period and habitat types indicated that local-scale environmental factors can play a significant role in litter decomposition and lignin degradation processes.