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).