One plus one is greater than two: mixing litter types accelerates decomposition of low-quality alpine dwarf shrub litter

Abstract

Aims Litter decomposition patterns, non-additive effects, and spectral data of abundant alpine leaf litters were assessed in litterbag experiments containing single species and mixtures. We tested if low-quality shrub litter decomposes faster in mixtures with high-quality litter and if predictions on decomposed litter using spectral data are feasible. Methods Chemical and physical traits and near-infrared reflectance (NIR) spectra of six alpine freshly fallen litter types were measured. A litterbag experiment (0.1 mm mesh size) with single and 2- and 3-species mixtures was conducted with three species from three functional groups (shrub, grass, forb). Decomposition rates, litter mass loss, non-additive effects, and NIR spectra were recorded after 6, 12, and 24 months. Results The six freshly fallen litter types differed significantly in leaf litter traits and NIR spectra. Decomposition rates steadily slowed during the 24 months, with shrub litter having the lowest on all sampling dates. In litter mixtures, shrub and grass litter showed higher decomposition rates after 12 and 24 months compared with the single-species treatments. Discussion The accelerated decomposition in litter mixtures indicates stimulating interactions between low- and high-quality litter types, most probably mediated by their associated microbiomes. By using NIR spectra, we successfully predicted all initial litter traits, but only total carbon content along the entire decomposition period.