关键词: 有效积温, 抽薹, 叶用莴苣, 花芽分化, 春化

Abstract: In order to study the diversity and function of endophytic bacteria, the roots of Stipa sp. were collected from six types of steppes (subalpine meadow, alpine meadow, Gobi desert, desert steppe, typical steppe, and meadow steppe in northern China) across Xinjiang, Gansu and Inner Mongolia. By strict surface disinfection and streak plate method, 200 endophytic bacteria that belonged to 28 genera, 7 classes, 4 phyla were isolated from the roots of Stipa sp. Half of the isolates were identified as Bacillus, which was the most dominant genus in the roots of Stipa sp. Pseudomonas and Bacillus were the most dominant genera in the samples of Gobi desert and the other five steppes, respectively. Subalpine meadow had the highest Shannon index, and typical steppe and meadow steppe had relatively higher Margalef index and evenness index. Alpine meadow which contained the lowest genus number showed the lowest Shannon index, Margalef index and evenness index. The similarity coefficients varied from 0.25-0.61 between the six steppes. Alpine meadow had relatively lower similarity coefficients (0.25-0.33) with the other steppes, followed by the similarity coefficients between Gobi desert and desert steppe. Furthermore, out of 200 isolates, 73 strains showed IAA-producing activity, 35 isolates turned out to have phosphatesolubilizing activity, 23 isolates were confirmed to have antifungal activity, 20 strains were proved to be diazotrophic bacteria, and 6 strains showed potassiumsolubilizing activity. Isolates producing IAA all ranked the first in abundance in each of the six steppes, especially in alpine meadow, subalpine meadows and desert steppe. Isolates with phosphatesolubilizing activity had a relatively larger proportion in alpine meadow, and the same to the isolates with antagonistic activity strains in subalpine meadow and nitrogenfixing bacteria in the desert steppe. However, the isolates with potassiumsolubilizing activity were in relatively lower abundance in all six steppes. The functional endophytic bacteria belonged to 25 genera, so their diversity was high. In addition, the isolates from Bacillus and Pseudomonas had more detected functions and high abundance, suggesting that endophytic bacteria belonging to Bacillus and Pseudomonas were important in the roots of Stipa. The study also collected 14 bacteria with high activity for detected function, which had great applied potential.

Key words: leaf lettuce, vernalization, bolting, effective accumulated temperature, flower bud differentiation