Field sampling
The field samplings were conducted in an elevational gradients, including nine permanent plots (40 × 40 m) and ranging from 300 to 1100 m asl. To reduce the influence of aspect, all plots were located on the south side. All trees with a diameter at breast height above 1 cm in each plot were surveyed.
The field soil sampling was conducted in October 2018. In each plot, five subplots (10 × 10 m) were randomly selected. In each subplot, five litter samples were randomly collected in five 1 m × 1 m squares. After that, five soil cores (3.5 cm in diameter and 20 cm in depth) were collected and mixed as one sample. In total, we have 45 soil samples from the elevational gradients (9 gradients * 5 soil samples each gradient). All soil samples were seized by a 2-mm mesh to remove the stone, visible roots were collected as the root samples and the rest soil was collected as soil samples. The living roots were separated into coarse root and fine root (with diameter < 2 mm) by the root diameter. The litter and fine root samples were oven-dry at 65oC for 48 h, to determine the litter biomass and fine root biomass in each subplot. Meanwhile, soil water holding capacity (WHC) was measured using the ring knife method.