Precipitation and Species Composition Mediate Litter Mixing Decomposition Effects in Arid Desert Regions

Mixed-species litters exhibit decomposition characteristics distinct from those of monospecific litters and are highly sensitive to precipitation changes in arid desert regions. However, the effects of altered precipitation on mixed-litter decomposition in these ecosystems remain poorly understood. Fresh leaf litter of Reaumuria soongarica, Salsola passerina and Nitraria sphaerocarpa was collected from arid desert habitats. We investigated decomposition differences among three monospecific litters and four mixed-species litters under different precipitation treatments. For both monospecific and mixed litters, increased precipitation significantly accelerated mass loss and nitrogen release through the entire experimental period. Compared with the natural precipitation treatment (CK), litter mass loss increased by 10.97-18.07%, while nitrogen (N) release increased by 4.64-7.96% after 12 months of decomposition. By contrast, decreased precipitation only significantly reduced carbon release. Increased precipitation did not shift the non-additive effects on mass loss from antagonistic to synergistic; it only weakened the antagonistic effects. Mixing effects on nutrient release varied among litter mixtures. Two-species mixtures exhibited stronger antagonistic effects than three-species mixtures, and increased precipitation moderately enhanced the synergistic effects in two-species mixtures. In conclusion, precipitation change altered litter decomposition in desert plants but had limited effects on litter-mixture interactions.