Labour markets and flexibility in the 1990s Bettio, Francesca; Rosenberg, Samuel; Simonazzi, Annamaria ...
International review of applied economics,
09/1999, Letnik:
13, Številka:
3
Journal Article
Solidago shortii T. & G. is a hemicryptophyte perennial that reproduces by sexual and vegetative means. Flower bud formation begins in June, and anthesis occurs from early August to mid-October. ...Seeds ripen in October and November, are dispersed until March, and germinate from late February to April. A persistent seed bank is not formed. Twenty-two percent of 1344 first-year juveniles marked in the field in May 1989 were alive in mid-September 1990. Although plants can flower in their first year in cultivation, it takes more than 2 years for them to reach reproductive maturity in the field. Buds formed belowground at the base of current-year shoots in summer produce rhizomes and aerial stems, which emerge in autumn or in early spring. Elongation of aerial stems begins in early spring and continues until June or July (nonflowering stems) or late August (flowering stems). The life cycle characteristics of S. shortii are similar to those of some weedy and/or geographically widespread members of the genus.
Seeds of Solidago shortii are conditionally dormant at maturity in October and November and thus require high temperatures (25/15, 30/15, 35/20⚬C) and light to germinate to 50% or more. Seeds ...stratified at 5⚬C for 12 weeks, as well as those that remained on plants in the field during winter became nondormant. During cold stratification, seeds gained the ability to germinate at low temperatures (15/6, 20/10⚬C) and lost the light requirement. Thus, in spring high percentages of the seeds can germinate over a wide range of thermoperiods (15/6-35/20⚬C) in both light and darkness. The seed dormancy/germination characteristics of S. shortii are similar to those of the geographically widespread species S. canadensis and S. nemoralis, and thus they do not help to explain the rarity of the species.
Solidago shortii T. & G. (Asteraceae) is endemic to a 12.2-km2area in the Eden Shale Belt in Fleming, Nicholas, and Robertson counties, Kentucky. It was extirpated from the type locality on Rock ...Island at the Falls of the Ohio River in Louisville, Jefferson County, Kentucky, apparently over 100 years ago. Approximately 73,000 stems occur at 13 population sites, which are in various stages of succession from open glades and glade-like areas to fairly dense redcedar and hardwood thickets or woodlands. Some of the sites have remained relatively stable for at least 50 years, while others have undergone marked successional changes. Solidago shortii grows in a range of light environments from full sun to fairly dense shade, and on several geologic formation and soil series. The soils are not atypical in amounts of major nutrients and organic matter, pH, or texture. Sixty-two percent of 934 soil depth measurements taken at the 13 sites were 25 cm or less, but 17% were greater than 50 cm. Although moisture content at the 5-10-cm soil depth zone, where most of the roots of S. shortii occur, frequently drops below the permanent wilting percentage in summer, established plants do not wilt because some roots extend 50 cm or more into cracks in the rocky soil. A conceptual model of the successional relationships of S. shortii was developed based on extensive field observations and on examination of USDA aerial photographs taken in 1937, 1949, 1973, and 1985.
