Tardigrade is associated with ecosystem multifunctionality in subtropical forest soils of China

Soil tardigrades (water bears) are widespread microfauna and important members of soil food webs, yet their role in linking community attributes to ecosystem multifunctionality (EMF) remains poorly understood. Environmental heterogeneity across soil layers and resource shifts during stand development may jointly shape tardigrade communities and soil functioning. Here, we investigated tardigrade diversity, extraction- and counting-based absolute abundance, sequencing-based relative abundance, and their contribution to EMF across soil layers and stand ages in soils from subtropical plantations in China. Tardigrade communities were quantified using microscopic counting and high-throughput 18S rRNA amplicon sequencing. Tardigrade richness decreased significantly from the litter layer to deeper mineral soil layers, with the highest values observed in the litter layer, whereas stand age had no significant effect. Soil pH and nutrient availability were significant predictors of tardigrade richness and relative abundance, while soil water content was negatively associated with richness and abundance. Both absolute and relative abundances of tardigrades were positively correlated with soil available phosphorus (AP), acid phosphatase (ACP) and β-1,4-glucosidase (BG), indicating close associations with phosphorus availability and ecosystem functions related to carbon decomposition and phosphorus mineralization. The EMF declined with soil depth and was positively associated with tardigrade abundance. Structural equation models (SEMs) further identified tardigrade relative abundance as a key contributor to EMF. Together, these results suggest that soil layer and soil physicochemical properties shape tardigrade community attributes in subtropical forest soils, and highlight the potential contribution of soil tardigrades to EMF, particularly in carbon and phosphorus cycling.