Pot Experiments

A greenhouse pot experiment was performed in a greenhouse (30°63′N, 104°07′E) at Chengdu Institute of Biology, Chinese Academy of Sciences. A strain of sweetpotato [Ipomoea batatas (L.) Lam.] cultivar Nanshu 88 was planted in a pot (high, 26.5 cm; diameter 24.0 cm) containing 6.5 kg of barren rocky soil. In the BP group, 75 ml of mixed PSB (approximately 10⁹ CFU/ml) was applied to each pot; in the CK group, 75 ml of sterile water without PSB was applied. Each group had eight pots. The greenhouse temperature was 25°C.

The field pot experiment was performed at the Yingxi experimental base (30°52′N, 106°02′E), and designed same as in the greenhouse pot experiment. During the experiment, the local monthly precipitation was 64–180 mm, and the mean temperature was 18.5–28.4°C.

At 100 days, the sweetpotato and soil in the greenhouse and field pot experiments were weighed and sampled. The P and potassium (K) content of sweetpotato roots and vines were measured using an elemental content analyzer with inductively coupled plasma optical emission spectrometry (ICP-OES; Optima 8300, PerkinElmer, United States). The nitrogen (N) content of sweetpotato roots and vines, as well as the pH, total carbon (TC), total nitrogen (TN), and AP of soil were measured using the methods described in a previous study (Ding et al., 2020).