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

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.

Online induction heating for determination of isotope composition of woody stem water with laser spectrometry: a methods assessment.

Application of stable isotopes of water to studies of plant-soil interactions often requires a substantial preparatory step of extracting water from samples without fractionating isotopes. Online heating is an emerging approach for this need, but is relatively untested and major questions of how to best deliver standards and assess interference by organics have not been evaluated. We examined these issues in our application of measuring woody stem xylem of sagebrush using a Picarro laser spectrometer with online induction heating. We determined (1) effects of cryogenic compared to induction-heating extraction, (2) effects of delivery of standards on filter media compared to on woody stem sections, and (3) spectral interference from organic compounds for these approaches (and developed a technique to do so). Our results suggest that matching sample and standard media improves accuracy, but that isotopic values differ with the extraction method in ways that are not due to spectral interference from organics.

Plasticity tradeoffs in salt tolerance mechanisms among desert Distichlis spicata genotypes.

We investigated genetic differences in salinity tolerance among 20 saltgrass (Distichlis spicata (L.) Greene) genotypes, including constitutive, gender-based and phenotypic plasticity traits, to better understand the basis of adaptation and acclimation by saltgrass in diverse environments. On average, the plants survived NaCl treatments up to ~1M, with reductions in growth and health that varied with genotype. For these 20 genotypes in a greenhouse study, we showed that greater plasticity in one salt tolerance mechanism was physiologically linked to lesser plasticity in another. Under various levels of constant salinity stress, genotypes employing a strategy of greater plasticity in foliar Na and lesser plasticity in both foliar K:Na and Na turnover rate were better able to substitute Na for K in some cellular functions, especially osmotic adjustment, leading to increased salinity tolerance. Although we observed gender segregation with salinity in the Owens (Dry) Lake Playa (Inyo County, CA, USA) population planted for dust control, from which the genotypes were collected, we did not observe gender differences in salinity tolerance in the greenhouse. Significant physiological plasticity tradeoffs among genotypes, however, did affect overall salinity tolerance and may be important for this species survival in diverse managed and natural habitats.