Decomposition trajectories in mixed-species leaf litter in cool-temperate deciduous forest with understory dwarf bamboo
Litter decomposition plays a central role in nutrient cycling in forest ecosystems, but the effects of species mixing on decomposition of individual litter species remain poorly understood. We conducted a two-year litterbag experiment in a cool-temperate deciduous forest in northern Japan using litter from two dominant canopy tree species (oak and birch) and the dominant understory bamboo (Sasa). Single-species and mixed-species litterbags were used to examine litter mass loss, litter chemistry (carbon, nitrogen, and lignin), and microbial communities assessed by phospholipid fatty acid (PLFA) analysis. Oak and birch litter decomposed significantly faster than Sasa litter, whereas decomposition rate constants did not differ between the two deciduous tree species. Changes in litter chemistry relative to mass loss were similar between oak and birch but differed markedly in Sasa, indicating a distinct decomposition trajectory of Sasa. Total microbial biomass increased rapidly during the early stage of decomposition in all litter types owing to fungal colonization, whereas the fungal-to-bacterial PLFA ratio was substantially lower in Sasa litter than in deciduous tree litter. Species mixing had no significant overall non-additive effect on decomposition, although mixtures of oak and birch tended to accelerate decomposition, whereas mixtures including Sasa tended to suppress it. These changes in decomposition rate were accompanied by corresponding changes in microbial biomass, while decomposition trajectories remained largely unchanged within each litter species. Our results suggest that Sasa contributes a distinct decomposition process in cool-temperate forests and that species mixing primarily modifies decomposition rates rather than the sequence of chemical transformations during decomposition.