Pennsylvania sedge is commonly used for forest restoration (Mottl et al., 2006) and has horticultural potential as a shade-tolerant groundcover and low-maintenance lawn species (Darke, 2007). This herbaceous perennial is native to dry deciduous forests of the eastern half of temperate North America (Gleason and Cronquist, 1991). It produces attractive slender leaves that form a 12-inch mound of foliage that expands through long and short rhizomes (Bernard, 1990) to form mats of 3 m2 (Mottl et al., 2006). Unlike most lawn species, it thrives in dry partial shade and is uniquely suited to the competitive environment under large trees. Pennsylvania sedge also provides spring interest because it blooms in mid-April to mid-May in southern Ontario and in the northern United States (Crins and Ball, 1983). Achenes ripen and dehisce in June in Minnesota (Table 1). Difficulties in achene germination limit the use of pennsylvania sedge for large horticultural and restoration projects. No germination protocol has been published, and native plant nurseries propagate plants by division. Overcoming dormancy and understanding germination requirements are essential for economically propagating pennsylvania sedge on a commercial basis.
Origin and collection month of ripe pennsylvania sedge achenes used in University of Minnesota germination experiments, 2005 and 2006.
Few Carex species exhibit physical dormancy or other germination barriers as a result of their unique morphology. Carex are distinguished from other genera within the Cyperaceae by a bladder-like sac called the perigynium (perigynia, plural) that tightly adheres to the hard pericarp of the achene (Amen and Bonde, 1964). The perigynium prevents germination in nebraska sedge (Carex nebrascensis) and northwest territory sedge (Carex utriculata) (Hoag et al., 2001; Jones et al., 2004). In other cases, Carex species respond to traditional physical dormancy treatments such as acidic scarification (Ishikawa et al., 1993) or pericarp nicking (Amen and Bonde, 1964). It is unknown whether pennsylvania sedge exhibits physical dormancy or other germination barriers.
Physiological dormancy is common in the Cyperaceae and may be overcome or reduced by one or more of the following treatments: 1) after-ripening (dry storage of seeds under ambient temperatures before sowing), 2) GA3, and 3) cold stratification (Baskin and Baskin, 1998, 2004). Broom sedge (Carex scoparia) germination was enhanced by up to 2 years of after-ripening (Larson and Stearns, 1990). Elongated sedge (Carex elongata) and remote sedge (Carex remota) increased germination following after-ripening in comparison with fresh achenes (Schutz, 1997b). However, some wetland Carex species had higher germination percentages when stored cold and moist (Budelsky and Galatowitsch, 1999).
Although GA3 failed to stimulate germination in black and white sedge (Carex albonigra), ebony sedge [Carex ebenea (Amen and Bonde, 1964)], and hood's sedge [Carex hoodii (McDonough, 1969)], it has been shown to increase germination for other monocots such as sand ryegrass [Leymus arenarius (Greipsson, 2001)], green needlegrass [Stipa viridula (Fulbright et al., 1983)], eastern gamagrass [Tripsacum dactyloides (Rogis et al., 2004)], and four Australian grass species (Hagon, 1976). In contrast to GA3 pretreatment, cold stratification has been shown to successfully alleviate physiological dormancy in many Carex species (Hoag et al., 2001; Kettenring and Galatowitsch, 2007a, b; Schutz and Rave, 1999). Although the most effective stratification temperatures for Carex species can vary, temperatures below 12 °C are most effective (Brandel and Schutz, 2005). Optimum stratification duration may range from 0.5 to 6 months for Carex species (Kettenring and Galatowitsch, 2007a).
Pennsylvania sedge may have additional germination requirements. A light requirement enables woodland Carex species to take advantage of gaps in leaf litter on the forest floor or in the deciduous forest canopy (Vellend et al., 2000). Germination of Carex species increased when imbibed achenes were exposed to white fluorescent light (Kettenring et al., 2006; Schutz and Rave, 1999). In a groundcover study, the frequency of pennsylvania sedge decreased under tree canopy compared with clearings (Collins and Good, 1987). Optimum germination temperature has not been identified for pennsylvania sedge. European temperate sedges typically require warm temperatures (>28 °C) for germination (Grimes et al., 1981). Schutz and Rave (1999) reported that a diurnally fluctuating temperature regime also enhances germination of some Carex species because this mimics spring temperatures. Alternating day and night temperatures of 27 and 15 °C increased germination for unstratified achenes for the majority of 12 temperate North American wetland Carex species (Kettenring and Galatowitsch, 2007a).
The objectives of this project were to test whether pennsylvania sedge germination is enhanced by treatments designed to overcome germination barriers posed by the perigynia and by the physiological dormancy. In addition, we sought to determine optimum light and sowing temperatures. We hypothesized that achene germination would be improved by 1) perigynia removal, 2) presence of white light, 3) after-ripening, 4) GA3 pretreatment, 5) cold stratification, and 6) diurnally fluctuating temperatures.
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