Seasonal difference in soil health indicators mediating multidiversity-multifunctionality relationship depends on body size of soil organisms: Evidence from rubber plantation agroforestry system

Soil health is the foundation for the maintenance of ecosystem stability and multifunctionality. It is necessary to identify the key indicators of soil health that indicate ecosystem multifunctionality against anthropogenic disturbances such as land use change. Many studies have shown the pivotal role of soil biodiversity in maintaining ecosystem multifunctionality. However, the key role of soil multidiversity (including different body size soil organisms across multitrophic levels) in affecting ecosystem functions is poorly understood. We have implemented a multitrophic perspective to study soil multidiversity by including bacteria, fungi, nematodes (5 feeding types), and arthropods (thripidae, poduridae, and others). Here we show that a multitrophic approach for soil biodiversity assessment is important to highlight trophic interactions and their subsequent effects on the soil multidiversity-ecosystem multifunctionality (MEF) relationship. We postulate that soil multidiversity promotes soil health and thus drives the MEF relationship. We assessed soil multidiversity, 11 variables for ecosystem functions, and ecological network stability (reflected by co-occurrence network patterns) in rubber plantations differing in land-use intensity represented by monoculture (MRP), high (RHD) and low (RLD) diversity of other plant species. We also included tropical rainforest (TRF) as a reference system to compare our results. Results showed that soil multidiversity, multifunctionality, and soil network stability significantly improved in RHD as compared to MRP. Soil multidiversity rather than single diversity component had strong positive effects on multifunctionality. More specifically, we found that the relationship between soil multidiversity and multifunctionality was seasonally dependent on the soil attributes and the body size of soil organisms. We observed a negative correlation between large body size organisms and soil nutrients content in the dry season while a positive correlation between small body size soil organisms and enzymatic activities in the rain season. Particularly, we emphasized the role of soil multidiversity in enhancing ecosystem multifunctionality and stability via its prominent impacts on soil health. Our study elucidates that accurate identification of soil health indicators is an important approach to imply remedial management strategies to maintain soil health and MEF relationship in managed ecosystems such as rubber plantations.