Academic journal article The American Midland Naturalist

The Lazarus Effect: Rejuvenation of Leaf-Senescent Seedlings in a Rare Grassland Perennial

Academic journal article The American Midland Naturalist

The Lazarus Effect: Rejuvenation of Leaf-Senescent Seedlings in a Rare Grassland Perennial

Article excerpt

ABSTRACT.-Over 75% of the seedlings of the endemic sandplain grassland perennial, northern blazing star (Liatris scariosa var novae-ang/iae), die within their first growing season. During a study of the reproductive ecology of this rare plant, we found 17 seedlings whose leaves had become completely desiccated and brown and were classified as dead. Upon subsequent inspection, we discovered that these seedlings had developed a new shoot with green leaves. We have called this rejuvenation "the Lazarus effect." These seedlings became dormant by late June, which coincided with extended periods of drought, and were senescent for periods of 410+ wk. Rejuvenation of leaf-senescent seedlings occurred in late July and August, coincident with periods of increased precipitation. Surivorship of "Lazarus" seedlings to their second summer (9 of 17, 53%) was similar to survivorship of "normal" seedlings (=58%) which did not senesce. Thus, becoming senescent did not have undue costs to survivorship.

INTRODUCTION There are at least three forms of dormancy in plants: seed dormancy, bud dormancy, bud dormanqr and stressinduced dormancy (Jensen and Salisbury, 1972; Raven et al., 1992). Seed dormancy is a condition where a seed does not germinate for a period of time, usually years, rarely as long as 50 y. Bud dormancy refers to the period before a leaf or flower bud develops into a leaf or flower (Jensen and Salisbury 1972). Stress-induced dormancy is frequently the result of harsh environmental conditions, such as drought, and in deciduous plants often involves premature leaf-senescence (Raven et al., 1992). This condition may be short-term, i.e., a matter of weeks or several months in response to drought or periodic dry seasons (Janzen, 1983). However, after improved environmental conditions, a second set of leaves can appear in the same growing season in temperate regions (e.g., Baskin et al., 1981). Conversely, dormancy may persist for several years, as with some orchids, although it is unclear whether this dormancy is stress-induced (Arditti, 1992).

We report observations of seedlings of an herbaceous grassland perennial becoming dormant as a result of premature leaf-senescence, apparently in response to severe drought, and then breaking dormancy and growing new leaves in the same season. We have termed this response "the Lazarus effect," because in the New Testament, Lazarus, dead for four days, was restored to life (Johnll). To our knowledge, rejuvenation of stress-induced dormant seedlings has not been previously reported, although it probably occurs in a number of plant species adapted to stressful, especially xeric, habitats. METHODS Study site and plant biology.-The study site, located on a 210 ha sandplain grassland in Kennebunk, York County, ME, supports a rare assemblage of plants and animals, including the largest known population of northern blazing star (Liatris seosa var novae-angliae = Liatris borealis) in New England (see Vickery et al., 1992). For the past 3 y we have been studying the effects of fire on the reproductive ecology of northern blazing star at this site. Northern blazing star, a rare grassland perennial in the family Asteraceae, is usually found in early successional habitats such as sandplain grasslands, xeric heathland and pitch pine (Pinus rigida) openings in the northeastern United States (Hamilton, 1991). In 1994-96, we individually marked 856 northern blazing star seedlings to determine seedling survivorship and recruitment. Seedlings were marked in early June and were checked approximately every two weeks.

In southern Maine, northern blazing star seeds germinate in May Seedlings quickly develop 1-2 thin (<5 mm) leaves <3-cm-long. By June, the cotyledons are no longer green, but are still readily apparent. By late August, >80% of the surviving seedlings have two leaves, a few individuals have three. Surviving seedlings normally senesce for the winter by late September.


The Lazarus effect. …

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