Fine‐root decomposition characteristics of four typical shrubs in sandy areas of an arid and semiarid alpine region in western China

Background and aims: Research into the variability of fine-root decomposition and nutrient cycling processes in arid and semiarid ecosystems is highly significant not only for investigations of regional and global carbon and nitrogen cycling but also for offering a theoretical basis for vegetation restoration and reconstruction. In particular, information is limited on fine-root decomposition processes and nutrient releasing characteristics in the high-altitude Qinghai Gonghe basin, which has different tree species and variable fine-root diameters. Materials and methods: Four types of Salicaceae and Caragana shrubs were selected at the Qinghai Gonghe desert ecosystem research station. The litterbag method was adopted to measure decomposition rates of fine-roots with three diameter classes (1-2 mm, 0.5-1 mm, and 0-0.5 mm). Chemical analysis was performed to determine nutrient (C, N, P, and K) concentrations of fine-root, and nutrient release rates were compared among fine-roots with different diameters during different decomposition periods. The differences in mass residual ratio and nutrient release rate among different diameter classes were studied with one-way ANOVA. Results: Fine-root decomposition rates were in the order Caragana intermedia > Caragana korshinskii > Salix psammophila > Salix cheilophila. Fine-root decomposition showed a trend of "fast-slow-fast" variation, and decomposition rate increased as the diameter of fine-roots increased, irrespective of tree species. During the decomposition process, the nutrients C, N, and P of fine-root were in a release state for the four shrubs with different fine-root diameters, and the corresponding release rates of Caragana shrubs were higher than those of Salicaceae shrubs. Release rates of nutrients C and N accelerated as fine-root diameter increased, whereas release rates of nutrients P and K had no observed relation with fine-root diameter. Fine-root decomposition ratio was significantly correlated with initial values of N, P, C/N, C/P, and N/P of fine-root. Fine-root mass loss ratio was significantly correlated with initial concentration of soil nutrient K, and the correlation was positive for fine-roots with diameters of 0-0.5 mm and 0.5-1 mm; however, no other significant correlation was observed between fine-root mass loss ratio and initial soil environmental factors within this study. Conclusions: Our study showed that tree species and fine-root diameter strongly affected decomposition rates, whereas diameter class exerted little effect on nutrient release rates.