| Astragalus arpilobus Kar.et Kir. is an annual ephemeral species in the family Fabaceae. In China, A. arpilobus is found only in Xinjiang, where it occurs only in the Junggar Basin in areas in which the vegetation cover is typically sparse. Flowering of this species occurs from May to June, and seeds mature in late June to early July, with fruits dehiscing as the seeds mature.Seed dormancy and germination characteristics and life-history traits of this species were studied both in field and laboratory in order to assess adaptive strategies of this species in the harsh environment of Jungaer desert. The main results are as follows:(1)Most seeds had a water-impermeable seed coat that became permeable after mechanical or acid scarification, i.e. they exhibited physical dormancy. Both wet heat and alternate wet heat and cold (ice water) caused only a small portion of the seeds to become permeable, and neither exposure to high nor to low temperatures was effective in breaking dormancy. Scarified seeds germinated at temperatures ranging from5/2to30/15℃, with20/10℃and25/15℃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.(2)Scarified seeds germinated to nearly100%at water potentials between0and-0.30MPa but to0%at-0.77MPa. Seedling emergence was in higher for seeds buried at soil depths of1and2cm than at0or>2cm. In July forty-three percent of scarified seeds sown in an experimental garden under natural conditions germinated in autumn, and an additional5%germinated in spring. In contrast, no non-scarified seeds germinated in autumn, and only5.3%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 perennial species of Astragalus.(3)If rainfall is high in autumn, the scarified seeds can germinate in autumn. If rainfall in autumn is limited, seeds do not germinate until spring. Germination timing and water influenced on life-history traits. A high percentage of the SW (germinated in spring and watered) plants survived than the AW (germinated in autumn and watered) plants. All the plants had high production. Plants height, biomass, and number of seeds increased with plant size [AW>SW, ANW (germinated in autumn and growed in natural)>SNW (germinated in spring and growed in natural), AW>ANW or SW>SNW]. The dry mass of SW, SNW, AW, ANW plants were0.835,0.596,3.013å'Œ1.568g, respectively, and differed significantfrom each other. The reproductive allocation rate for SNW, SW, ANW and AW were60.1%,55.5%,54.2%and50.5%, respectively. Plants that germinated in the spring were smaller and their reproductive allocation rate larger than those had germinated in the autumn. The reproductive allocation rate of plants that were not watered larger than those that were watered.Seed dormancy/germination characteristics influence germination timeing and subsegvent life history. Water affects germination and post-germination life history traits. Varialbe water supply therefore is expected to strong influence the performance of this species in the Junggar desert. |
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