Tools for Carex revegetation in freshwater wetlands: understanding dormancy loss and germination temperature requirements

Abstract

Carex is a globally distributed genus with more than 2000 species worldwide and Carex species are the characteristic vegetation of sedge meadow wetlands. In the mid-continental United States, Carex species are dominant in natural freshwater wetlands yet are slow to recolonize hydrologically restored wetlands. To aid in Carex revegetation efforts, we determined the dormancy breaking and temperature germination requirements of 12 Carex species. Seeds were cold stratified at 5/1°C for 0-6 months and then incubated in light at 5/1°C, 14/1°C, 22/8°C, 27/15°C, or 35/30°C. We found that all Carex species produced conditionally dormant seeds. The optimal temperature for germination for all but three species was 27/15°C. As is the case in other species with physiological dormancy, cold stratification increased germination percentages, broadened the temperature range suitable for germination, and increased germination rates for most species, but the magnitude of the effects varied among species. Many species germinated to 80% at 27/ 15°C without cold stratification and at 22/8°C with £1 month of stratification but required much longer stratification (up to 6 months depending on the species) to germinate to 80% at 14/1°C and 35/30°C. Our findings illustrate how a stratification pretreatment can greatly benefit Carex seed sowing efforts by triggering rapid germination to higher percentages. We recommend that cold stratification be targeted towards species with strong dormancy or used across a wider range of species when seed supplies for restoration are limiting. For Carex revegetation, establishing Carex canopies rapidly may help to prevent the invasion of undesirable species such as Phalaris arundinacea.

Temperature requirements for dormancy break and seed germination vary greatly among 14 wetland Carex species

“…A Seed Regeneration Index (SRI; range 0-1) for each species was calculated as a means of comparing all species with respect to their seed viability, dormancy, and germination based on the results of the initial seed viability estimates, the move-along experiment, and a previously published Carex seed stratification experiment (Kettenring and Galatowitsch, 2007) (Fig. 1).…”

“…In the seed stratification experiment, Carex seeds were stratified at 5/1 8C for 0 weeks (control), 2 weeks, or 1, 2, 3, 4, 5, or 6 months and then germinated at one of five diel temperature regimes: 5/1 8C, 14/1 8C, 22/8 8C, 27/15 8C, or 35/30 8C (see Kettenring and Galatowitsch, 2007 for a more detailed description of the methods). Differences in germination for each species were qualitatively compared across the stratification lengths and temperature regimes and the data are summarized in Fig.…”

“…From a restoration perspective, breaking seed dormancy and providing suitable germination microsites can be relatively straightforward or very complicated depending on the species and its class of seed dormancy (i.e., physiological, morphological, morphophysiological, physical, or combinational) (Lippitt et al, 1994;Diboll, 1997;Baskin and Baskin, 1998;Cochrane et al, 2002). Seed dormancy and germination ecology can be quite different even for congeneric species (Grime et al, 1981;Shipley and Parent, 1991;Meyer et al, 1995;Schütz and Rave, 1999;Brändel, www.elsevier.com/locate/aquabot Aquatic Botany 87 (2007) [209][210][211][212][213][214][215][216][217][218][219][220] 2004; Hölzel and Otte, 2004;Kettenring and Galatowitsch, 2007). These variations in seed dormancy break and germination requirements influence plant emergence patterns that can drive plant population persistence and plant community diversity (Harper, 1977;Thompson and Grime, 1979;Hutchings, 1997).…”

“…While there have been numerous studies on seed dormancy and germination of many European Carex species (see Schütz, 2000 for a review), only a few studies have focused on the Carex species common in wetlands in mid-continental North America (Larson and Stearns, 1990;Baskin et al, 1996;Budelsky and Galatowitsch, 1999;van der Valk et al, 1999;Kettenring and Galatowitsch, 2007). For many species, it is not known whether freshly matured seeds are physiologically dormant and how this dormancy affects seed germination at different temperatures.…”

“…By contrasting the performance of seeds incubated at a constant diel regime with seeds that transition through a winter stratification period, we can determine: (1) whether seeds are totally dormant or conditionally dormant at maturity and (2) whether dormancy breaks down with stratification (in seasonal regime) or under growing season temperatures (in diel regimes). We combined the results of our study with those of a previously published paper on Carex seed dormancy (Kettenring and Galatowitsch, 2007) in a Seed Regeneration Index (SRI) that predicts how readily seeds of these Carex species are likely to germinate in the field under diverse temperature conditions.…”