This work was lead by Jingyi Ding and David J Eldridge from UNSW, Australia together with Manuel Delgado-Baquerizo from Universidad Pablo de Olavide, Spain and Jun-Tao Wang from Western Sydney Uni, Australia. 150 sites in NSW from Sydney coasts to Tibooburra arid area were surveyed. tested 16S for bacteria and 18S for fungi, protists, invertebrates. Millions of trees are expected to be planted in forested and non-forested ecosystems during the United Nations Decade of Restoration. Trees and soil organisms are known to interact and are both crucial for maintaining multiple ecosystem functions. However, little is known about how the two-way relationships among above- and belowground diversity and ecosystem functions differ across forested and non-forested ecosystems.2. We collected data from 126 sites from humid to arid areas in eastern Australia to explore the two-way relationships among aboveground (richness of trees and other plants) and belowground (richness of bacteria, fungi, invertebrate, protist) diversity and multiple ecosystem functions (multifunctionality, litter and labile carbon storage, nutrient pools, decomposition, groundstorey plant biomass production, soil stability) in forested (tree cover > 10%) and non-forested (tree cover = 10%, open woodland, shrubland) systems.3. We found that the relative importance of above- and belowground diversity differed among forested and non-forested systems. Ecosystem functions, such as litter and labile carbon storage and soil stability, were associated mainly with tree richness in forested systems. By comparison, ecosystem functions of non-forests was related to the richness of soil organisms. Such bidirectional biodiversity-ecosystem function relationships varied with the target function, and the relationship between ecosystem functions and the relative abundance of species varied with tree and soil taxa. The richness of other plants (i.e., plants except trees) and soil organisms was positively coupled in forests only, but there were no linkages among above- and belowground diversity and ecosystem functions in non-forests for groundstorey plant biomassproduction. Furthermore, increases in aridity and soil pH further weakened the biodiversity-ecosystem function relationships in forested and non-forested systems, by suppressing plant diversity and bacterial richness respectively.4. Synthesis. Our study provides strong empirical evidence that the two-way relationships among above- and belowground diversity and ecosystem functions are highly variable across ecosystem and function types. Moreover, our study demonstrates that soil biodiversity is relatively more important than tree diversity in supporting ecosystem functions in non-forested systems. This suggests that conservation of soil biodiversity is critical for maintaining the functioning of non-forested woodland and shrubland systems.