Biology ETDs

Publication Date



A basic understanding of vegetation responses to temperature and precipitation variability is paramount to the understanding of ecological adaptation, and comparisons across warm deserts are needed to increase our understanding of the controls on establishment in warm desert ecosystems. At the high latitude edges of warm deserts drought and freezing lower plant performance due to xylem dysfunction, as freeze-thaw embolism reduces stomatal conductance, or damage to leaf photosynthetic apparatus, as tissue desiccation reduces photosynthetic efficiency. Variation in these physiological responses can be observed across life-history stages, genetic background, climate gradients, and species, and this variation may be acted on by selection to produce adaptation to local climate conditions. The primary goal of our research was to determine the interactive effects of freezing and drought on the performance and survival of high latitude plants and to determine if physiological and morphological adaptations to freezing exist in populations which experience freezing. Data were collected from greenhouse and field grown plants from high and low latitude populations in North and South America. We observed differences in physiological and morphological characters across latitude for both L. tridentata and L. divaricata, in the absence of differences in ploidy, indicating that local adaptation to freezing has occurred in the warm desert shrub genus Larrea. We observed correlations between freezing tolerance and minimum temperatures accompanied by higher freezing tolerance in high latitude populations, suggesting that the evolution of increased freezing tolerance could have facilitated recent high latitude expansions of Larrea populations. Heritable variation is present in both high latitude L. tridentata and low latitude L. divaricata populations, allowing the potential for these populations to respond to climate change. The high latitude L. divaricata population exhibited low levels of variation, which may have resulted from prior selection for increased freezing tolerance and reduces the rate of evolution of freezing tolerance. Finally, fluctuating selection may maintain variability in seedling traits in the high latitude L. tridentata population. In the presence of mild drought, survival and performance following freezing events may by enhanced, and establishment of seedlings could be expected to occur in either warm, wet or cold, dry winters.

Project Sponsors

Funding agencies which provided support include the UNM Department of Biology which provided me with Teaching Assistantships; UNM Latin American Iberian Institute which awarded me a travel grant; the UNM Graduate and Professional Student Association which awarded me SRAC, RAC and GRD funding; the UNM Biology Graduate Student Association from which I received travel and supply funding through the GRAC grant; the Sevilleta LTER which provided summer support and the NSF GK12 program which provided my salary and summer support for two years




plant ecology, physiological ecology

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Degree Name


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Department Name

UNM Biology Department

First Committee Member (Chair)

Hanson, David

Second Committee Member

Marshall, Diane

Third Committee Member

Collins, Scott

Fourth Committee Member

Logan, Barry