Study design and field sampling
We selected two plots with the same species mixture of the deciduous tree species Liquidambar formosana and Sapindus saponaria . The selected tree species have significant and dissimilar effects on soil microbial properties (Beugnon et al. 2021). In each plot, we selected five replicates of both monospecific pairs (L. formosana – L. formosana , S. saponariaS. saponaria ) and of the heterospecific pair (L. formosanaS. saponaria ). The litter layer was removed prior to sampling. To measure the spatial distribution of soil microbial biomass and respiration, we took five soil-cores on the transect line between each pair using 5 cm diameter soil-cores. To test for the effect of soil depth on soil microbial biomass and respiration, each soil-core was split into the depths of 0-5 cm and 5-10 cm and sieved through a 2 mm mesh. The soil samples were stored at -20°C. Altogether, 300 soil samples were collected from two plots, three combinations of trees replicated five times, five positions, and two depths (Fig. 1). Additionally, the tree diameter at breast height (DBH) was measured for each tree pair to calculate tree biomass, following (Beugnon, Bu, et al. 2023).