Germination Timing and Seedling Growth of Poa secunda and the Invasive Grass, Bromus tectorum, in Response to Temperature: Evaluating Biotypes for Seedling Traits that Improve Establishment

Abstract

Cold temperature seed germination and rapid root growth influence the ability of native plants to establish in the presence of invasive winter annuals. This represents a potential problem for plant material selection in the face of climate change. If seeds sourced from cold winter climates germinate and grow rapidly early in the season, managers that select materials from warmer winter climates could miss populations with traits that promote competitive establishment at restoration sites. We examined seed germination timing and seedling growth rates of the exotic grass, Bromus tectorum, two wild-collected Poa secunda accessions, and four commercial P. secunda accessions under two temperature regimes (20°C day/15°C night and 10°C day/5°C night) to examine the mechanisms responsible for differences in establishment and survivorship between P. secunda accessions observed in a previous field study. Our results show that B. tectorum had earlier germination, faster root elongation, and greater total root growth than all P. secunda accessions in both temperature regimes. Wild-collected P. secunda accessions germinated later and had slower cold temperature growth rates than most commercial accessions. Poa secunda accessions sourced from areas with colder winter climates germinated earlier and had greater total root length in the cold temperature treatment, suggesting that source location climate can be used to select plant materials with traits beneficial for seedling establishment and tolerance of invasive winter annuals.