Biological Sciences Department
Our research is on the structure, function and ecophysiology of plants. This includes especially the biology of chaparral shrubs of California, mangrove trees of Mexico, and temperate and tropical climbing plants. At Cal Poly Pomona the central focus to our research program will be on native and invasive plants of the Voorhis Ecological Reserve. We will explore the wood structure/function/ecology/evolution at the tissue, organ, whole plant, community and landscape levels. A central theme will be the functioning of native versus exotic species and examination of the conditions that result in invasions of the native plant community. Wood (xylem) has functions of mechanical support, storage, and the transport of water and minerals. Much of our work concerns the ecology/evolution of tradeoffs between these functions. The water in plants is transported under negative pressures and thus the xylem is structured to resist implosion as well as air entry. Wide xylem vessels are more efficient in water transport, but they can also be more vulnerable to dysfunction via embolism (air blockage) than narrow vessels. The optimal wood structure can vary with the plant organ. For instance, in woody roots the storage and transport functions may be selected for, whereas in stems there is greater natural selection for mechanical strength. The optimal hydraulic/mechanical architecture can also vary with the ecosystem as well as the life history patterns of the species. For instance, exposure to drought, high salinity, and freezing temperatures all tend to select for species with narrower vessels, which are more resistant to environmentally induced embolism. Within an ecosystem, stems of climbing plants have little selection for mechanical strength. Instead they are optimized for water transport, flexibility and storage. In the coastal sage scub community, severe drought and occasional winter freezes should select for dense wood with narrow vessels. However, these plants may avoid the worst of the drought and freezing stress by dropping many of their leaves, by having very deep roots, or by going dormant until conditions allow for the production of new xylem in the spring. Examining the varying strategies of invasive versus native species should not only be of basic biological interest but it should be insightful as to the best management strategies for maintaining natural ecosystems. 200- Pratt R.B, Jacobsen A.L., Golgotiu K.A., Sperry J.S., Ewers F.W., Davis S.D. Life history type coupled to water stress tolerance in nine Rhamnaceae species of the California chaparral. Ecological Monographs (in press). 2007 Ewers F.W., Ewers J.M., Jacobsen A.L., López-Portillo, J. Vessel redundancy: modeling safety in numbers. International Association of Wood Anatomists Journal. (in press). 2007 Pratt R.B., Jacobsen A.L., Ewers F.W., Davis S.D. Relationships among xylem transport, biomechanics, and storage in stems and roots of nine Rhamnaceae species of the California chaparral. New Phytologist. (in press). 2007 Jacobsen A.L., Ewers F.W., Pratt R.B., Davis S.D. Cavitation resistance among twenty-six chaparral species of southern California. Ecological Monographs 71: 99-115. 2007 Jacobsen A.L., Agenbag L., Esler K.J., Pratt R.B., Ewers F.W. & Davis S.D. Xylem density, biomechanics, and anatomical traits correlate with water stress in 17 evergreen shrub species of the Mediterranean-type climate region of South Africa. Journal of Ecology 95: 171-183. 2005 Jacobsen A.L., Ewers F.W., Pratt R.B., Paddock W.A. III, Davis S.D. Do xylem fibers affect vessel cavitation resistance? Plant Physiology 139: 546-556. 2005 López-Portillo, Ewers F.W., Angeles G. Sap salinity effects on xylem conductivity in two mangrove species. Plant, Cell and Environment 28: 1285- 1292. 2005 Pratt R.A., Ewers F.W., Lawson M.C, Jacobsen A.L., Brediger M., Davis S.D. Mechanisms for tolerating freeze-thaw stress of two evergreen chaparral species: Rhus ovata and Malosma laurina (Anacardiaceae). American Journal of Botany 92: 1102-1113. 2004 Ewers F.W., López-Portillo J., Angeles G., Fisher J.B. Hydraulic conductivity and embolism in the mangrove tree Laguncularia racemosa. Tree Physiology 24: 1057-1062. 2004 Angeles G., Owens S.A., Ewers, F.W. Fluorescent shell: a novel view of sclereid morphology with the confocal laser scanning microscope. Microscopy Research and Technique 63: 282-288. Collaborators Anna Jacobsen, Graduate Student Michigan State University, East Lansing, MI Graduate Student alumni from lab William Paddock III (M.S. 2006) |
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