Seed germination and propagation of Xyris tennesseensis, a federal endangered wetland species

Abstract

The recovery plan for the U.S. federally endangered Xyris tennesseensis calls for increasing the size of some existing populations and establishing new ones in suitable sites. As a contribution to this goal, we investigated seed dormancy and germination and attempted to propagate the species in non-native soil. Freshly matured seeds were conditionally dormant and germinated to 0, 0, 92, 91, and 74% in light after two weeks at 15/6, 20/10, 25/15, 30/15, and 35/20°C, respectively. Seeds retained the ability to germinate to 80–100% in light at 25/15 and at 30/15°C throughout a 39.5-month period of burial in an unheated greenhouse. Following the first year of burial, however, germination at 20/10°C showed an annual cycle, with 79–86% of the seeds germinating in spring but only 0–1% in autumn Under natural temperature regimes, seeds sown on native soil germinated from mid-May to early August. Seeds had an absolute light requirement for germination, and those incubated at 30/15°C required six days of light (14-hour daily photoperiod) to subsequently germinate in darkness. The species has a small persistent soil seed bank. Although no dormancy-breaking treatments are required for seeds to germinate to high percentages in light at high temperatures, growing seedlings/juveniles in non-native soil is very difficult. Seeds germinated during summer when sown on both inorganic and black organic soils, with and without the addition of lime, but few seedlings lived for more than one month. Only two of 125 juveniles lived for two months after they were transplanted from native soil into black organic soil. One strategy to increase the number of plants at a site may be to remove litter and sow seeds on the surface of undisturbed soil in late spring-summer.