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. saponaria – S. saponaria ) and of the
heterospecific pair (L. formosana – S. 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).