I completed my master’s thesis project in November 2017 and have since worked at the Tejon Ranch Conservancy. I am in the process of applying to PhD programs.
My master’s thesis project yielded several intriguing questions and I would like to explore these, in part, in Ph.D. research. My current idea is as follows:
Project Purpose and Objectives:
Woody Atriplex (saltbush) species are dominant perennial elements of the native plant communities of the San Joaquin Desert and Mojave Desert of California. While saltbush-dominated communities were previously extensive, today they largely exist as fragmented populations, especially in the San Joaquin. These remaining fragments occur across a range of microhabitats that vary in their soil moisture, salinity, and degree of annual grass invasion. In the context of climate change, many regions of the American West are likely to become drier and more saline (Sankary and Barbour 1972, Mikhiel et al. 1992, Dodd and Donovan 1999). Therefore, I hypothesize that the ecological niche of saltbush shrublands may be impacted in the coming decades. There remain numerous unstudied aspects of saltbushes, in both basic and applied science. I would like to explore these unknowns, especially those that emerged from my master’s thesis (Coleman and Pratt 2019).
The proposed project would examine various ecophysiological traits of Atriplex spp. I am interested in examining whether Atriplex shrubs from different microsites, that vary in salt and available water, also vary in their physiological traits. Measures may include aspects of xylem traits, leaf-stem coordination, water status (water potentials), hydraulic flow, cavitation, photosynthesis (gas exchange), foliar isotope chemistry, stem biomechanics, and soil characteristics from samples collected at various sites. At present, I envision studying five widely dispersed species: Atriplex polycarpa (Torr.) S. Watson, A. lentiformis (Torr.) S. Watson, A. spinifera J.F. Macbr, A. canescens (Pursh) Nutt., and A. confertifolia (Torr. & Frém) S. Watson. At least six individuals per species would be measured across thirty sites (Fig. 1, Table 1). The proposed sites span the geographic range of saltbush in the San Joaquin Desert, and the western part of the range in the Mojave. The sites occur along a precipitation, temperature, and edaphic gradient, and thus provide a metric of site differences.
Benefit to Land Management in the San Joaquin and Mojave Deserts:
Saltbush shrublands are important communities that provide critical habitat for native wildlife. The shrubs also compact the soil and prevent erosion and dry dust events, an ecosystem service which is especially needed in the San Joaquin as the region has the worst air quality in the United States. Moreover, as C4-photosynthetic halophytes, these shrubs are some of the only perennial plants capable of thriving in highly xeric and saline sites. Saltbush communities have already been extensively threatened and have experienced extensive loss across their former range. Disturbance and climate change may lead to further threats. The proposed work will help to identify the range of ecological and physiological conditions saltbushes tolerate, and how they respond to rapidly changing conditions. Differences in the traits of plants in different sites may useful in identification of populations at risk, populations that could expand, and populations that could be good sources of seed for restoration.
References
Coleman, M. L., and R. B. Pratt (2019). The effects of invasive grass on seedling recruitment of native Atriplex polycarpa (Torr.) S. Watson (Chenopodiaceae) shrubs in the San Joaquin Valley of California. Biological Invasions 21 (6): 1871-1876.
Dodd, G. L., and L. A. Donovan. 1999. Water potential and ionic effects on germination and seedling growth of two cold desert shrubs. American Journal of Botany 86:1146-1153.
Mikhiel, G. S., S. E. Meyer, and R. L. Pendleton. 1992. Variation in germination response to temperature and salinity in shrubby Atriplex species. Journal of Arid Environments 22:39-49.
Sankary, M. N., and M. G. Barbour. 1972. Autecology of Atriplex polycarpa from California. Ecology 53:1155-1162.
Mitchell Coleman 