The Effects of Temperature and Seasonal Change on the Germination of Two Salt Marsh Species, Atriplex prostrata and Salicornia europaea, along a Salinity Gradient.

Abstract

The purpose of this study was to determine whether seasonal temperature changes interact with salinity concentration to inhibit germination. Flooding of a marsh may also influence the size of the seed bank. Soil cores (6.0 cm diameterx7.5 cm deep) were collected from four salt marsh zones in Rittman, Ohio. Salt was most concentrated at the innermost zone, which contained almost exclusively Salicornia europaea, and least concentrated at the outermost zone, which contained mainly Hordeum jubatum and Atriplex prostrata. Soil cores were collected during April, June, and October 1996 and were placed in temperature treatments of 5 degrees /15 degrees C, 5 degrees /25 degrees C, 15 degrees /25 degrees C, and 25 degrees /35 degrees C (dark/light). Seeds were germinated for 8-10 wk, and the seeds that did not germinate were counted from a 2.2-cm-diameter subsample. Results demonstrated that for both S. europaea and A. prostrata, the total number of seeds that germinated decreased throughout the growing season. The number of ungerminated seeds decreased throughout the year for A. prostrata, but for S. europaea, the number of ungerminated seeds increased from April to June and then decreased from June to October. For both species, the ratio of germinated to total seeds decreased from April to June and increased from June to October. Over the growing season and in all salinity zones, the 5 degrees /25 degrees C temperature treatment was the most stimulatory to seed germination. We suspect that a flooding event in June that killed the standing vegetation may have reduced soil salinity and allowed more seeds than usual to germinate, thus effectively eliminating the S. europaea seed bank. Thus, seed banks play a significant role in these salt marsh habitats by providing a new source of seeds for the establishment of later cohorts after flooding or salt stress eliminates an early cohort of seedlings.