Background Gymnocarpos przewalskii is the rare relic of tertiary and endangered species of desert area in central Asia, and one of the oldest groups in saline environment. It is mainly distributed in the desert area in our country being one of the main constructive species in stony desert area where rainfall is small but evaporation is strong, which results in the salt accumulation in soil, subsequently drought and soil salt affect its seed germination and further its population establishment and regeneration. To protect G. przewalskii, salt and drought stress was respectively stimulated to research salt and drought resistance mechanism in seed germination.

Methods Seeds of G. przewalskii were collected from botanic garden of Anxi Extra-arid Desert National Nature Reserve with the mean annual rainfall of 45.3 mm and the salt content more than 2% in the soil depth of 30 cm. Using the different concentration of NaCl (50, 100, 150, 200, 250, and 300 mmol/L) and the different potential of PEG-6000(-0.1, -0.3, -0.5, -0.7, and -0.9 MPa) to stimulate salt stress and drought stress respectively, taking the distilled water as the control to measure the germinated seeds and time, germination rate, germination energy, germination index vigor index and average germination days were calculated and the germination characteristics and the response to salt stress and drought stress were analyzed.

Results The results showed that the germination rate and the vigor index increased at low concentration of NaCl (50 mmol/L) compared with the control. The germination rate, germination energy and average germination days were not significantly affected at the concentration of 100 and 150 mmol/L NaCl, and the germination rate, germination energy and vigor index decreased insignificantly at the osmotic potential of -0.3 MPa, which indicated that germination ability and uniformity was not significantly affected by relatively low concentration of NaCl (100 and 150 mmol/L) or relatively high osmotic potential of PEG (≥ -0.3 MPa). At high concentration of NaCl (≥ 250 mmol/L) or low osmotic potential of PEG (≤ -0.7 MPa), the germination rate, germination energy, germination index and vigor index extremely significantly decreased and the germination process was markedly prolonged, the seed germination of G. przewalskii was significantly inhibited and delayed due to the intensified osmosis and toxic action. Regression analysis indicated that the critical and limited value of NaCl stress on seed germination was 337.4 mmol/L and 628.6 mmol/L, respectively and the critical and limited value of PEG stress on seed germination was -0.70 MPa and -1.01 MPa, respectively.

Conculsions The seed germination of G. przewalskii was improved at the concentration of 50 mmol/L NaCl and showed some tolerance to salt and drought stress, beyond the range (more than NaCl concentration of 250 mmol/L or less than PEG osmotic potential of -0.7 MPa), its seed germination was significantly inhibited. Researching the seed germination characteristics of G. przewalskii can provide some basis for the cultivation of G. przewalskii and combating desertification in desert area.