Seed dormancy and germination characteristics of Astragalus arpilobus (Fabaceae, subfamily Papilionoideae), a central Asian desert annual ephemeral

Although Astragalus is the largest genus of seed plants, it contains only a relatively few annual species, about which little is known with regard to seed dormancy and germination. Thus, seed dormancy-break and germination were investigated in the cold-desert annual Astragalus arpilobus Kar. et Kir. Most of the seeds had a water-impermeable seed coat that became permeable after mechanical or acid scarification, i.e. physical dormancy. Both wet heat and alternate wet heat and cold (ice water) made only a small portion of the seeds permeable, and neither exposure to high nor to low temperatures was effective in breaking dormancy. Scarified seeds germinated at temperatures ranging from 5/2 to 30/15. °C, with 20/10. °C and 25/15. °C being optimal. Non-dormant seeds germinated to high percentages in light and in darkness across the range of temperatures. Germination percentages did not increase with duration of dry storage at room temperature. Scarified seeds germinated to nearly 100% at water potentials between 0 and - 0.30. MPa but to 0% at - 0.77. MPa. Seedling emergence was higher for seeds buried at soil depths of 1 and 2. cm than at 0 or > 2. cm. Forty-three percent of the scarified seeds sown in July in an experimental garden under natural conditions germinated in autumn, and an additional 5% germinated in spring. In contrast, no non-scarified seeds germinated in autumn, and only 5.3% of them germinated in spring. Most of the non-scarified seeds that did not germinate became part of the persistent seed bank. Our results indicate that the high intensity of hard-seed dormancy in the annual A. arpilobus is similar to that reported for the perennial species of Astragalus.