Objective To study the tolerance mechanism of Phyllostachys edulis to drought stress during seed germination by comparing the effects of different drought stress on seed germination, growth physiological characteristics of Ph. edulis so as to provide reference for Ph. edulis water management.

Method The effects of different concentrations (0%, 5%, 10%, 15%, 20%, 25%)of PEG stress on seed germination, growth, organic osmoregulation substances were measured with choosing Ph. edulis seeds and using Petri dish and filter paper germination method. The regression analysis were done between growth of radicle and embryo, seed germination and PEG stress.

Result (1) The control group (CK) and 5% test group began to germinate on the 4^th day. The initiation time of the other test groups was gradually delayed with the increase of treatment concentration, and 25% of the test group did not germinate. (2) The final germination percentage, germination energy, germination index, vigor index, radicle length and embryonic bud length increased at first and then decreased with the increase of PEG-6000 concentration, and reached the maximum value at the concentration of 5%. There was a unique cross between the control group and the 5% test group in the diurnal variation curve of Ph. edulis germination rate under drought stress. The critical and the maximum value of the seed germination of Ph. edulis were 14.49% and 19.27% under the PEG stress. (3) The final length of radicle and embryo reached the maximum at 5% concentration, and then decreased with the increase of concentration, and the difference was significant (P < 0.05). There was a unique cross between the diurnal variation curve of the radicle length of the control group and the 5% test group. The critical and the maximum value of growth of radicle of Ph. edulis were 14.49% and 19.27% under the PEG stress. (4) The activities of SOD, POD and CAT in the radicle increased with the increase of PEG concentration. And reached a maximum at concentrations of 5%, 10%, and 10%, respectively. (5) MDA and soluble protein content increased with the increase of PEG concentration, but the difference of MDA was not significant at low concentration (0%-10%).

Conclusion Low concentration drought stress can inhibit the seed germination and radicle formation of Ph. edulis at the early stage of germination, but can significantly improve the final germination rate of Ph. edulis seed and promote the growth of radicle in the late period of germination. The high concentration of PEG drought stress will delay the germination of Ph. edulis and inhibit the germination rate and growth of the whole germination period. Drought stress above 15% could cause the antioxidant enzyme system of Ph. edulis to be disturbed and cause significant damage to cell membrane system.