Limbird, Eric James , Walck, JL , Phillips, NC , Hidayati, Siti .
Freeze-thaw effects on seed viability, seed germination and seedling survivorship vary among exotic and native woody plants.
During the cold-moist conditions of winter, stratification occurs that alleviates seed dormancy in many species enabling spring germination. However, winters in middle Tennessee, and throughout most of southeastern United States, are mild with warm spells lasting a few days that are interrupted by cold snaps when soils freeze. Temperatures during these warm or cold spells are usually above or below, respectively, those required for stratification. In this study, the effects of a freeze during stratification and following a warm spell on seeds and seedlings of locally common trees, shrubs, and vines were determined. We selected exotic species (Euonymus fortunei, Ligustrum sinense, Lonicera japonica, L. maackii) and native species (Celtis laevigata, Juniperus virginiana, Parthenocissus quinquefolia) that disperse fruits during autumn. In the laboratory, seeds were subjected to a simulated mid-winter freeze after (1) a 6 week non-freeze winter condition (stratification at 5°C) and (2) a warm spell (6-week stratification + 1 week at 20/10°C). After acclimation at 1°C, sets of seeds were sequentially moved from 0°C to -5°C to -10°C for 2 hours each, before staying overnight at -10°C and then warming by the same increments the following day. A set of seeds was removed following each temperature treatment and placed at 20/10°C for 2 weeks to examine germination and viability. In the field, acclimated seedlings (with emerged roots and/or cotyledons) were randomly planted [24/treatment (covered or not covered with leaves)] during a warm spell (up to 18°C) in late winter before a 3-day freeze (down to -13°C) associated with 2.5 cm snow. Freezing at both -10°C and overnight reduced seed viability in Euonymus, Juniperus, L. japonica, and L. maackii by 12-40%; it did not affect viability in the other species. Germination was reduced 30-66% in Euonymus and L. japonica when seeds were frozen at -10°C and overnight. Only seeds of L. japonica and L. maackii germinated during the simulated warm spell. These seedlings survived temperatures down to -5°C, but none survived overnight at -10°C. In the field experiment, Celtis, L. japonica and L. maackii had cotyledons before the freeze; seeds of the other species only had roots. Seedlings of L. japonica and L. maackii had moderate to high survivorship, whereas those of Celtis had low survivorship, regardless of being covered with leaf litter. Thus, freezing may differentially affect seed viability and germination and seedling survivorship of exotic vs. native species and potentially influence competitive interactions between them.
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1 - Middle Tennessee State University, Biology, 67 Whitsett Rd., Nashville, Tn, 37210, USA
2 - Middle Tennessee State University, Biology, 1500 Greenland Ave., Murfreesboro, Tn, 37132, USA
3 - Middle Tennessee State University, Agriscience and Agribusiness, 1500 Greenland Ave., Murfreesboro, Tn, 37132, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Salon 6/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 4:30 PM
Candidate for Awards:Ecological Section Best Graduate Student Paper