Millipede (Spirobolus walker) prefers feeding on a high-quality litter from a companion species when combined with Masson pine litter

Monoculture plantations, particularly the coniferous species (Pinus massoniana), often impede nutrient cycling, leading to declines in biodiversity and soil fertility. Selection of suitable companion tree species, especially a native broadleaf species is thus essential for improving forest ecosystem functions. Millipedes (Spirobolus walker), a widely distributed large arthropod to primarily consume litter, play a pivotal role in organic matter decomposition and nutrient cycling in terrestrial ecosystems. Addressing the feeding preferences of millipedes in relation to litter quality could provide insights into selection of appropriate mixed tree species, thereby facilitating the sustainable management of Masson pine plantations. Millipede feeding experiments on leaf litter from three typical subtropical broadleaf species – Camptotheca acuminata (high-quality litter), Quercus variabilis (intermediate-quality), and Michelia wilsonii (low-quality), were conducted in combination with Masson litter. We found that millipedes responded more to litter morphology rather than chemical characteristics. Acid insoluble components, consisting mainly of condensed tannins and lignin in litter had almost no effects on millipede feeding preferences. Despite C. acuminata containing high levels of tannins and phenols, millipedes exhibited the highest consumption rate (44 mg·g⁻¹·d⁻¹) on it, due to its higher tubularity and nitrogen concentration. Additionally, when multiple litter sources were available, millipedes showed greater preference for consuming high-quality litter, an indication of the better suitability of C. acuminata for mixture with Masson pine. A transformation of mono-species into a multiple-species based plantation forest would therefore enhance circulation of materials, particularly carbon and nitrogen, through millipedes’ preferential feeding activity.