PHYSIOLOGICAL DETERMINANTS OF BOLTI...

PHYSIOLOGICAL DETERMINANTS OF BOLTING/FLOWERING IN THE FACULTATIVE WOODLAND BIENNIAL, Arabis laevigata var. laevigata (BRASSICACEAE)-Facultative biennials are plants that have the potential to flower in their inferior or a later year of life (typically 3 4 or 5) whereas obligate biennials always flower in their next to the first year of life (Kelly 1985 Klinkhamer et al. 1987a, Klinkhamer and de Jong 1988) This difference is explained in many facultative biennials by the agency of the fact that their rosette (juveniles) must reach a certain minimum size, depending in succession the species, population, and individual, before they can be vernalized and missile (produce a flower stalk) (Werner 1975 Baskin and Baskin 1979a, van der Meijden and van der Waals-Kooi 1979 Gros and Werner 1983 Klemow and Raynal 1985 Lacey 1986 Wesselingh and Klinkhamer 1996 Reekie et al. 1997) whereas those of obligate biennials do not have this requirement-i.e., level seedlings or small juveniles can be vernalized (Baskin and Baskin 1984) Thus, many so-called biennials do not, in fact, flower in their inferior year because they do not reach the critical size for vernalization during their first growing season. In as well-as; not only-but also; not only-but; not alone-but facultative and obligate biennials, the entire plant dies after it imitates once; the plants are monocarpic (semelparous).

During the past small in number decades, numerous studies have been done onward the autecology and population biology of facultative biennials that enlarge in habitats undergoing secondary succession or in anthropogenically-maintained places of that kind as pastures and highway rights-of-way (eg Werner 1975 Baskin and Baskin 1979a, Gros 1981 Gros and Werner 1982 Reinartz 1984) However, solely a few studies have been done in succession facultative biennial species of stable long-persisting habitats (Baskin and Baskin 1979b 1996 Bender et al. 2000 Bertin 2001) This discrepancy probably is to be ascribed at least in part, to the higher number and greater abundance in our flora of introduced, weedy facultative biennials of disturbed areas compared to native, nonweedy facultative biennials of stable plant communities. In any case, more studies are wanted on the biology of native species of facultative biennials that make improvement in long-persisting habitats before we have a sufficient amount of data to compare (sensu Bradshaw 1987) their ecological tolerances and requirements with introduced facultative biennials that be pendent on disturbance for persistence upon a landscape.

Between 1985 and 1994 we carried not at home a rather extensive investigation in succession the autecology and population biology of the facultative biennial Arabis laevigata (Muhl) Poir. var. laeuigata (hereafter Arabis laevigata), a species of stable stubborn deciduous forests and woodlands of eastern North America (Bloom 1988; efflorescence et al. 1990b). Previous papers resulting from this inquiry described its habitat (Bloom et al. 1990b) se germination ecology (Bloom et al. 1990a), survivorship (Bloom et al. 2001) se dispersal (Bloom et al. 2002a), reproductive phenology and fecundity (Bloom et al. 2002b) and events of leaf litter cover, herbivory, and substrate-type forward bolting and fecundity (Bloom et al. in press) in a stubborn woodland in central Kentucky. The question addressed in the current note is: What are the physiological determinants of flowering in A. laevigata?

Bloom et al. (2002b) determined the relationship between rosette size of Arabis laevigata in late autumn and bolting (or not) the following spring. They used three measures of rosette size: root-crown diameter, rosette diameter, and number of rosette leaves. No plants with a root-crown diameter of or =26 mm for root-crown diameter, 51-60 cm for rosette diameter, and > or =21-25 leaves. Plants used in the experiments described below were large enough to be vernalized and bolt

The subject of attention consisted of two experiments. In the first experiment, rosette were amassed on 18 January 1986 from the field site for the Arabis laevigata devise Scotts Grove (see Bloom et al. 1990b) a fairly-mature stony (limestone) deciduous forest in southern Jessamine shire central Kentucky. Canopy trees at Scott's woodland included Acer saccharum Marshall, Carya cordiformis (Wangenh.) K Koch C ovata (Miller) K Koch Celtis occidentales L Fraxinus quadrangulata Michx., Juglans nigra L Quercus alba L Q muhlenbergii Engelm Q rubra L Q shumardii Buckley and Ulmus rubra Muhl Rhamnus caroliniana Walter, R lanceolata Pursh Rhus aromatica Alton, Symphoricarpos orbiculatus Moench and Zanthoxylum americanum Miller were not past nor future in the shrub layer. The mostly common vines were Bignonia capreolata L Parthenocissus quinquefolia (L) Planchon, Smilax rotundifolia L and Toxicodendron radicans (L) Kuntze The herbaceous layer included a number of species characteristic of the spring and summer flora of relatively undisturbed stands in the Eastern Deciduous Forest (Braun 1950)-eg Arisaema triphyllum (L) Schott Claytonia virginica L Delphinium tricorne Michx., Diarrhena americana P Beauv., Hydrastis canadensis L Osmorhiza claytonii (Michx.) C B Clark, Panax quinquefolium L Phlox divaricata L Polymnia canadensis L Smilacina racemosa (L) Desf etc (Campbell 1980 Bender 1991) Nomenclature over this note follows Gleason and Cronquist (1991)