California State University Bakersfield
Welcome to the Webpage of
Dr. Anna L. Jacobsen
Plant Ecology and Evolutionary Biology
Dr. Jacobsen's Homepage Research Methods Page
If you are a current or prospective CSUB student interested in working in Dr. Jacobsen's lab, please stop by her office or email to set up an appointment to discuss your research interests. There are opportunities for both undergraduate and graduate students to participate in research!
Marta Percolla (undergraduate) (CSUB Student Research Scholars Program 2012-2013)
Hayden Toschi (undergraduate)
F. Daniela Rodriguez-Zaccaro (undergraduate)
Jessica Valdovinos (undergraduate)
Justin Martinez (graduate) (CSUB Student Research Scholars Program 2013-2014, CSUB Graduate Student Research and Scholarship Initiative 2013-2014)
Evan MacKinnon (post-grad)
Martin Venturas (post-doc)
The combined Jacobsen and Pratt labs in January 2014:
Daniela, Marta, Justin, Courtney, Sam, Dr. Pratt, Dr. Jacobsen, Dr. Venturas, Evan, Hayden, Jessica
Mark Bersentes (Student Research Scholars Program 2011-2012)
Mark De Guzman
Robert Atwood (committee)
Genetic variation among populations of the Bakersfield cactus Opuntia basilaris var. treleasei, based on amplified fragment length polymorphisms.
Heather Keldgord (committee)
The distribution of sexes across a rainfall gradient in a subdioecious southern Californa chaparral shrub Rhus ovata S. Watson (Anacardiaceae).
Evan MacKinnon (co-advisor)
(CSUB School of Natural Sciences, Mathematics, & Engineering Outstanding Graduate Thesis 2013)
A trait-based approach to restoring southern California habitats invaded by the Mediterranean grass Bromus madritensis ssp. rubens (Poaceae).
Courtney Traugh (committee)
Stem and root xylem trade-offs in carbohydrate storage, water stress tolerance, and biomechanics or sprouting and non-sprouting chaparral species.
Some of our current lab research topics/projects include:
Examining xylem vessel network structure and function in woody plants using developmental and intra-organismal systems (NSF IOS-1252232)
Plant hydraulic structure and function
Fire ecology of Mediterranean-type climate region shrubs
Community convergence among arid and semi-arid shrublands in Mediterranean-type climate regions
Plants transport water through specialized water transport cells. In flowering plants, these cells, called vessel elements, combine to form long multi-cellular jointed tubes termed xylem vessels. In the Jacobsen lab, we are working to understand the structure of these vessels at the cellular-level and at the tissue-level. We are particularly interested in examining the structure of the three-dimensional vessel network of woody plants (i.e. how vessels develop and connect with one another throughout the tissues of a plant). Additionally, we are examining how vessel structure relates to the hydraulic function of plants.
Vessels have three-dimensional structure, including significant curvature of vessels and significant changes in diameter of vessels (even along the length of a single vessel). Additionally, species can vary greatly in the interconnectedness of the vessel network and the density and structure of pitting between adjacent vessels. In the past year, work in the lab to examine inter- and intra-specific patterns in vessel length has yielded particularly interesting and exciting results, especially since this trait has sometimes been called the "neglected dimension" of vessel structure!
Many students in the lab have conducted research or are continuing to conduct research examining vessel structural traits, including measuring vessel pit traits, vessel diameter, vessel length, and connectivity of the vessel network. As a lab, we are working to combine data from different levels of xylem organization (cellular to tissue) to develop a model of the vessel network. We are also working to quantify other elements of xylem structure, such as fiber and parenchyma cell structure and abundance.
Nearly all of the research projects in the lab are based on the broad idea of how plants use and move water, especially in response to stress. Thus, all of the research projects in the lab are measuring plant hydraulic function in some way. The most common measures of plant hydraulic function that are completed in the lab include measures of xylem resistance to water stress induced cavitation and measures of hydraulic conductivity (transport efficiency). Additional information about our methods for these measures may be found here.
Fire Ecology and Community Convergence of Mediterranean-type Climate Region Shrublands
Much of the research conducted in the Jacobsen lab has focused on investigation of shrub communities from Mediterranean-type climate regions. There are five Mediterranean-type climate regions globally that are dominated by evergreen, tough-leaved shrub species.
The evergreen shrubs in these regions respond to fire by resprouting from modified root structures, recruiting through fire-cued seed germination, or through a combination of these strategies. We are currently investigating hypotheses related to how the xylem structure of resprouting plants relates to differential recovery of species post-fire, including why some species tend to suffer massive mortality during the first few years of post-fire recovery while other species are more resilient.
Additionally, fire can have a profound effect on community composition of Mediterranean-type shrub communities. I am currently involved in several long-term collaborative research projects investigating plant species and community response to fire, particularly in response to additional stresses such as heavy browse or drought. This work is being conducted at field sites in several locations throughout southern California, including the San Gabriel and Santa Monica Mountains, as well as on Santa Catalina Island off the coast of Los Angeles, California, and in the Western Cape Region of South Africa. This work involves collaboration with many other researchers and several undergraduate and graduate students.
Much of my work investigating plant hydraulic function has been completed in close collaboration with Dr. R. Brandon Pratt, who is also a member of the CSUB Department of Biology. Dr. Pratt has additional information about these research projects on his website. Additionally, I am pleased that the lab has recently collaborated with or continues to collaborate with the following individuals and labs in our investigations of plant hydraulic structure and function: Dr. Uwe Hacke of the University of Alberta, Dr. Frank Ewers of California State Polytechnic University, Pomona, Dr. Stephen Davis of Pepperdine University, and Dr. Karen Esler of Stellenbosch University.
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