Germination niche of the permanent wetland specialist, Parnassia grandifolia DC
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Temperate wetland species often require light and warm temperatures for seed germination. However, recent studies indicate that species which specialize on permanently saturated wetlands that are maintained by groundwater discharge (fens, seeps and mountain springs), rather than wetlands with surface-water-driven hydrologic regimes, diverge from the typical wetland germination niche by germinating at cool temperatures and lacking photoblastic seeds. We conducted laboratory experiments that manipulated stratification conditions (non-stratified versus cold stratification in light and darkness), thermal regime (15/6, 25/15 and 35/20°C), and light (14 h photoperiod versus continuous darkness) to test whether seeds of the North American calcareous fen specialist Parnassia grandifolia diverged from the typical temperate wetland germination niche. After 30 d, fresh seeds were conditionally dormant and could only germinate to high percentages in light at 25/15°C. During 16 weeks of incubation, non-stratified seeds germinated to low percentages ( < 40%) at all thermal regimes in darkness. In contrast, cold-stratified seeds germinated to high percentages in both light and darkness at all thermal regimes, although germination was incomplete (no cotyledon emergence) at 35/20°C. Further, seeds did not require light during cold stratification to germinate to high percentages when incubated in light or darkness. Thus, seeds diverged from the typical temperate wetland germination syndrome in lacking a light and warm temperature requirement for germination. Our results reinforce previous work from European fens and Mediterranean wetlands. This indicates that multiple germination strategies are found in fen wetlands that are maintained by the continuous or near-continuous discharge of cool groundwater. © 2014 Cambridge University Press.
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