2.4. Fine root data
A portable hand auger (Φ=90mm) was employed to collect fine roots from two different jujube trees outside the 16 plots. Samples were collected down to 500 cm vertically, at 20 cm intervals. To reduce sampling uncertainty caused by spatial variability, for each jujube tree, root samples were collected at four locations: two of them along the contour line and the other two downslope from the stem (Figure S2). As shown in the figure, the distance of A and C locations was 0.5 m to the trunk of jujube tree and it was 1.0 m for the B and D locations. Mixed root samples were sealed in bags and stored immediately in a refrigerator at 4 °C. In the lab, root samples were gently washed in a 2-mm sieve, and the roots retained on the sieve were removed with tweezers. A Vernier caliper with a precision of 1×10-2 mm was used to separate fine roots (≤2 mm) from coarse roots (> 2 mm). The determination of fine roots and the calculations of fine root length density (FRLD) are given in Li et al. (2017).