Abstract: A pot experiment was conducted with a multilevel soil water content gradient, to examine the relationship between soil relative water content (RWC) and photosynthetic physiological indices of three-year-old Moso bamboo (Phyllostachys edulis) seedlings. With photosynthetic physiological parameters as judging criteria, soil water availability and productivity in the course of cultivation and management of P. edulis seedlings were graded and evaluated. The results showed that maximum net photosynthetic rate (P_max) of P. edulis peaked (9.56 μmol·m^-2·s^-1) at the RWC of 77.01%. At the photosynthetically active radiation intensity (PAR) of 1000 μmol·m^-2·s^-1, the P_n compensation water point (RWC_Pn=0) was 17.41%, and the maximum net photosynthetic rate (P_n-max=9.36 μmol·m^-2·s^-1) occurred at RWC_Pn-max=78.19%. The maximum water use efficiency (WUE_max =4.55 mmol·mol^-1) corresponded to a RWC of 64.28%. The average water use efficiency (WUE_ave=2.62 mmol·mol^-1) appeared at RWC=34.25% and 94.32%, respectively. The positive and negative turning point of water use efficiency (WUE) was at RWC=18.17%. P_n and WUE values of P. edulis under different soil moisture were used as the basis to evaluate “yield” and “efficiency”. The results showed that, when the RWC ranged from 44.69% to 94.32%, the productivity level of three-year-old seedlings of P. edulis was high-yield and high-efficiency. The productivity level was intermediateyield and high-efficiency when the RWC was 34.25%-44.69%. Meanwhile, RWC=17.41%-29.11% meant low-yield and low-efficiency productivity level. RWC >94.32% meant that the productivity level was high-yield and intermediate-efficiency, while RWC <17.41% made the production level non-productive and ineffective. This study puts forward the soil water utilization parameters for the cultivation of P. edulis seedlings, which provides a reference for efficient water management in the cultivation of P. edulis seedlings.

Key words: Moso bamboo (Phyllostachys edulis), soil relative water content, photosynthetic characteristics, classification and evaluation.