The Germination Ecology of Helonias Bullata L. (Swamp Pink) with Respect
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Aquatic Botany 133 (2016) 17–23 Contents lists available at ScienceDirect Aquatic Botany jou rnal homepage: www.elsevier.com/locate/aquabot The germination ecology of Helonias bullata L. (swamp pink) with respect to dry, saturated, and flooded conditions ∗,1 April P. Punsalan , Beverly Collins, Laura E. DeWald Department of Biology, Western Carolina University, 132 Natural Science Building, Cullowhee, NC, 28723, United States a r t i c l e i n f o a b s t r a c t Article history: Poor sexual recruitment is a major conservation concern for the rare obligate wetland plant Helonias Received 8 October 2015 bullata L. (swamp pink). Helonias predominately occurs in forested wetlands amongst hummock-hollow Received in revised form 12 May 2016 topography where water levels fluctuate spatially and temporally, creating a wide variety of moisture Accepted 13 May 2016 microsite conditions for germination. To determine how moisture conditions affect the germination Available online 13 May 2016 response of Helonias seeds, germination percentages and rates were compared after seeds were exposed to dry, saturated (stream margin), and flooded (floating and submerged) conditions in a growth chamber Keywords: and field for 1–35 days. Helonias final germination percentages were greater than 50% after exposure of Dispersal Buoyancy all conditions, except dry conditions in the growth chamber. Moisture availability at the time of seed arrival was the main factor that influenced the germination of Helonias. Helonias seeds exposed to satu- Germination ecology Hydrochory rated and flooded conditions germinated within a short time frame (10-30 days). Rapid germination may Forested wetland be important for Helonias plants in forested wetlands where variable moisture conditions can create a Rare plant narrow window for regeneration. For both the growth chamber and field experiment, final germination Southern appalachian region percentages were significantly higher (p < 0.05) for floating seeds compared to those kept dry. Water Helonias bullata likely serves as an important dispersal mechanism for Helonias seeds since they exhibit high floating capability and germinability relative to the length of time spent in the water. Published by Elsevier B.V. 1. Introduction of seed germination and seedling establishment (Scarano et al., 1997; Vivian-Smith 1997; Middleton 2000). In addition, the “ger- In forested wetlands, variations in topography create a mosaic mination window of opportunity” (Eriksson and Froborg 1996) of microhabitats (Huenneke and Sharitz 1986; Vivian-Smith 1997; for wetland plants can be narrow or wide across both space and Duberstein and Conner 2009; Rossell et al., 2009). Elevation, sub- time (Middleton 2000). At the narrow end, seedling recruitment for strate variability created by accumulation of woody debris and many wetland plant species appears limited to hummocks or other peat interwoven with tree roots, and hummock-hollow micro- emergent substrates, due to restricted germination in hypoxic con- relief contribute to microsite diversity in these systems where the ditions in flooded hollows (Huenneke and Sharitz 1986; Huenneke water table typically is at or above the soil surface (Ehrenfeld 1995; and Sharitz 1990; Jordan and Hartman 1995). Although many wet- Duberstein and Conner 2009). Seasonal differences in precipitation land plants reproduce vegetatively, seed dispersal, germination, also contribute to variability in moisture conditions (Ehrenfeld and and recruitment from seeds can aid in establishment of new pop- Schneider 1991). ulations and maintenance of genetic diversity within populations The spatial and temporal interactions of microtopography com- (Hawkins et al., 2011). bined with seasonal fluctuations in hydrology produce a wide Helonias bullata L. (swamp pink) (hereafter called Helonias) variety of moisture microsites and contribute to unpredictability is a rare obligate wetland species that occurs in forested wet- lands from the coast of New Jersey south to Virginia and into the mountainous regions of Virginia, North Carolina, South Car- olina, and Georgia, USA (Sutter 1984). These forested wetlands, ∗ Corresponding Author. including swamps, inland stream corridors, spring seepage areas, E-mail addresses: [email protected], april [email protected] fens, and swamp forest-bog complexes (Murdock 1994; Dodds (A.P. Punsalan), [email protected] (B. Collins), [email protected] 1996), typically occur at or near the beginning of streams (head- (L.E. DeWald). 1 water streams) and are perennially wet with a water table at or Present address: U.S. Fish and Wildlife Service, 176 Croghan Spur Road, Suite 200, Charleston, South Carolina, 29407, United States. near the surface (U.S. Fish and Wildlife Service, 1991). Helonias http://dx.doi.org/10.1016/j.aquabot.2016.05.005 0304-3770/Published by Elsevier B.V. 18 A.P. Punsalan et al. / Aquatic Botany 133 (2016) 17–23 grows along Sphagnum moss-covered stream banks and occurs the site’s sensitivity. The Pink Beds contains the largest Helonias amongst hummock-hollow topography. Population decline and population (approximately 10,000 individuals) in North Carolina loss of suitable habitat prompted the U.S. Fish and Wildlife Service (Sutter 1984). Helonias rosettes occur in swamp forest-bog com- to designate Helonias as a federally threatened species under the plexes (Schafale and Weakley, 1990) located along the headwaters Endangered Species Act in September 1988 (U.S. Fish and Wildlife of the South Fork Mills River and associated streams, small tribu- Service, 1991). Helonias has several life history traits, including taries, and seepage areas. Rosettes typically occur on hummocks limited inflorescence production, low seedling recruitment, and and stream banks covered with Sphagnum moss, and occasionally restricted long distance dispersal, which contribute to the species’ in hollows or seepage areas (April Punsalan, personal observation) vulnerability to extinction (U.S. Fish and Wildlife Service, 1991; with decomposed organic matter with silt loam underneath (Tox- Godt et al., 1995). Although the self-compatible flowers produce oway and Hatboro soil series) (Murdock 1994). During the 2012 copious viable seeds (U.S. Fish and Wildlife Service, 1991), the seeds field study (May 30th–June 29th), the water depth in the small trib- lose viability rapidly after several weeks (i.e., are short-lived and utary ranged from 4 to 8 cm and the average water temperature was ◦ do not appear to form a seedbank), and dispersal is limited within 16.6 C. populations (U.S. Fish and Wildlife Service, 1991; Godt et al., 1995). Given the high microsite heterogeneity in forested wetlands, 2.3. Seed collection Helonias seeds could encounter a variety of moisture conditions during their viable period. Seeds could remain dry in dehiscent We collected Helonias seeds from the Pink Beds population in capsules or disperse along the upper, emergent portions of litter- May 2011 and 2012. We randomly selected fifteen inflorescences, covered hummocks where drier conditions can occur (Ehrenfeld five per subpopulation, from three subpopulations approximately 1995; Vivian-Smith 1997). Alternatively, they might fall into the 0.8–1.6 km apart. Subpopulations were selected based on the high stream channel where they could float and disperse by water and/or number of individuals and the likelihood that individuals would sink and become submerged. Before germination, seed viability flower in 2011 and 2012. Collected seeds were mixed together to could be jeopardized by variable periods of saturation and hypoxia produce a homogeneous seed lot and stored in the lab at room tem- (Baskin and Baskin 1998; Lucas et al., 2012). The objective of our perature. Experiments commenced within 48 h of seed collection. research was to determine how variable periods of dry, saturated (stream margin), and flooded (floating or submerged) conditions 2.4. Growth chamber experiment affect the germination response (percentages and rates) of Helo- nias. In a growth chamber experiment, seeds were subjected to To determine the germination response of Helonias seeds after dry, floating, and submerged conditions for 1–35 days. In addition, exposure to different moisture conditions, seeds were (1) kept dry a field experiment was conducted in a small headwater stream to (dry), (2) placed floating in water (floating), or (3) submerged in test the germination response of seeds placed in dry (out of water), water (submerged). For each moisture condition, six replicates of saturated (stream margin) and flooded (floating or submerged in 200 seeds were used. For dry conditions, seeds were placed in cylin- stream) conditions for 1–30 days. We compared the germination drical 88 ml glass containers with no water. Floating seeds were response (germination percentages) and the breadth of the ‘germi- placed in 946 ml round glass containers (14 cm diameter) filled nation window’ over time (germination rates) among the moisture with distilled water, which was maintained at 6 cm water depth. conditions in each experiment. In addition, we examined the length Submerged seeds were placed in nylon mesh bags weighted with of time seeds float and maintain germinability when submersed or marbles and submerged beneath 5 cm of distilled water in 946 ml floating in order to assess the potential for water dispersal. glass containers (12 cm x 12 cm x 6 cm high). Containers were repo- sitioned daily in growth chambers to exclude position effects and water was added daily to maintain water depths. The