Freezing resistance, safety margins, and survival vary among big sagebrush populations across the western United States

Abstract

Premise Physiological responses to temperature extremes are considered strong drivers of species’ demographic responses to climate variability. Plants are typically classified as either avoiders or tolerators in their freezing‐resistance mechanism, but a gradient of physiological‐threshold freezing responses may exist among individuals of a species. Moreover, adaptive significance of physiological freezing responses is poorly characterized, particularly under warming conditions that relax selection on cold hardiness. Methods Freezing responses were measured in winter and again for new foliage in spring for 14 populations of Artemisia tridentata collected throughout its range and planted in a warm common garden. The relationships of the freezing responses to survival were evaluated in the warm garden and in two colder gardens. Results Winter and spring freezing resistance were not correlated and appeared to be under differing selection regimes, as evident in correlations with different population climate of origin variables. All populations resisted considerably lower temperatures in winter than in spring, with populations from more continental climates showing narrower freezing safety margins (difference in temperatures at which ice‐nucleation occurs and 50% reduction in chlorophyll fluorescence occurs) in spring. Populations with greater winter freezing resistance had lower survivorship in the warmest garden, while populations with greater spring freezing resistance had lower survivorship in a colder garden. Conclusions These survivorship patterns relative to physiological thresholds suggest excess freezing resistance may incur a survival cost that likely relates to a trade‐off between carbon gain and freezing resistance during critical periods of moisture availability. This cost has implications for seed moved from cooler to warmer environments and for plants growing in warming environments.

Spatial grain of adaptation is much finer than ecoregional‐scale common gardens reveal

“…Differences in subspecies and population tolerances and/or resistance to drought (Kolb & Sperry, 1999; McArthur et al., 1998) and cold temperature (Brabec et al., 2017; Chaney et al., 2017; Lambrecht, Shattuck, & Loik, 2007; Lazarus, Germino, & Richardson, 2019) have been linked to differences in survival of big sagebrush populations in common gardens. Soil properties, such as restrictive subsurface layers, affected survival of outplanted seedlings of big sagebrush (Davidson et al., 2019) and were important factors affecting adaptive variation of another widespread perennial of the western US (Gibson, Nelson, Rinehart, Archer, & Eramian, 2019).…”

Weather affects post‐fire recovery of sagebrush‐steppe communities and model transferability among sites

“…However contrary to Brabec et al (2017), we observed an increase in sagebrush density in relation with lower mean temperature of the coldest month and higher mean temperatures in the hottest month in the first four years after fire. The OCTC has a relatively warm climate for sagebrush and low winter temperatures may be less of a selective factor here than in colder climates (Lazarus et al 2019). The lack of an effect of mean monthly temperature (from the five‐year weather model) on sagebrush density is consistent with the findings of Brabec et al (2017) and Kleinhesselink and Adler (2018), who suggest that temperature extremes are more often the limiting factor for establishment.…”

Plant functional groups and species contribute to ecological resilience a decade after woodland expansion treatments

“…We also analyzed the top three dominant shrub species and top three dominant perennial graminoid species (by mean cover) for the respective soil temperature and moisture regime. We did not separate A. tridentata into subspecies because of uncertainty of field identification to this taxonomic level; evidence suggests local adaptation of populations to site conditions may be more important than subspecies in explaining variation in A. tridentata performance (Lazarus et al 2019). Dominant species that were not shared by both of the soil temperature and moisture regimes were not included in the models that tested for an interaction of soil temperature and moisture regime with treatment and TDI.…”