Germination Ecology of the Boreal-Alpine Terrestrial OrchidDactylorhiza lapponica(Orchidaceae)

Abstract

In order to reveal some of the germination requirements of the boreal-alpine terrestrial orchid Dactylorhiza lapponica, several experiments were carried out on seeds collected from the Sølendet nature reserve, central Norway. Seeds were sown in seed packets made of nylon cloth and deployed in situ vertically in the peat in order to study the temporal pattern of seed germination and determine if the seeds became part of the soil seed bank. In vitro germination experiments were carried out varying the growth media, fungal partner and chilling treatment, in order to study the effect of a fungal symbiont on germination and early protocorm development, and the possibility of a physiological seed dormancy. A high rate of germination a short time after sowing in the in vitro experiments together with a very low survival after deployment in the in situ experiments (0.2% after three years) indicate that D. lapponica seeds are not part of a long-lived soil seed bank. In vitro experiments also demonstrated that a fungal symbiont was not required for germination. Seeds sown in situ had very low germination rate (11%-12%) and lack of available nutrients is suggested as a possible explanation. Presence of a fungal symbiont clearly enhanced the early development of protocorms in vitro, and is probably necessary for the seedling to grow beyond the earliest protocorm stages under natural conditions. The results indicate that recruitment is highly variable and very low relative to population size, indicating that survival of established plants is crucial to the fate of a population.

Comparative in vitro germination ecology of Calopogon tuberosus var. tuberosus (Orchidaceae) across its geographic range

“…Chilling increased germination significantly compared to the control among all C. tuberosus seed populations. This is not surprising because chilling has been reported to increase germination in seeds of numerous orchid species (De Pauw and Remphrey 1993;Chu and Mudge 1994;Tomita and Tomita 1997;Miyoshi and Mii 1998;Koda 2004, 2005;Øien et al 2008). The results from this study indicate that physiological dormancy is present in seeds from several C. tuberosus populations.…”

“…Although the exact mechanism of chilling in orchid seeds is not well understood, chilling likely breaks physiological dormancy (Baskin and Baskin 2001;Øien et al 2008). A chilling requirement would prevent germination immediately after capsule dehiscence when environmental conditions are not adequate and mycorrhizal fungi needed for germination are not active (Rasmussen 1995;Baskin and Baskin 2001).…”

“…However, cold stratification has been reported to increase germination of many terrestrial orchid species (van Waes and Debergh 1986;Rasmussen 1992;De Pauw and Remphrey 1993;Chu and Mudge 1994;Tomita and Tomita 1997;Miyoshi and Mii 1998;Zettler et al 2001;Koda 2004, 2005;Øien et al 2008). In non-orchids, cold stratification has been reported to decrease enzymatic reactions, slow metabolic processes that inhibit germination and change enzyme production and concentrations (Bewley and Black 1994).…”

“…While examining in situ germination is ideal, studying the germination ecology of orchid seeds in situ is difficult and time consuming because orchid seeds are minute and germination is often low (Brundrett et al 2003;Zettler et al 2005;Diez 2007;Øien et al 2008). Alternative to in situ germination, asymbiotic in vitro techniques have been developed to successfully germinate orchid seeds (Kauth et al 2008a).…”

Examining the interaction of light, nutrients and carbohydrates on seed germination and early seedling development of Bletia purpurea (Orchidaceae)

“…Scientists using symbiotic approaches have recognized this dichotomy and many have focused on studying the biology of symbiosis. These in situ and in vitro studies of how symbiosis is affected by light quality, quantity and photoperiod (McKinley and Camper 1997;Rasmussen et al 1990a;Rasmussen and Rasmussen 1991;Zettler and McInnis 1994), substrate (Brundrett et al 2003;Diez 2007;Rasmussen and Whigham 1998), nutrients (Tsutsui and Tomita 1990;Zettler et al 2005), temperature (Øien et al 2008) and fungal species (Chou and Chang 2004;Øien et al 2008;Stewart and Kane 2007;Stewart and Zettler 2002) can guide future efforts to unravel orchid seed physiology using asymbiotic techniques as well.…”