California State University Bakersfield
Welcome to the Webpage of
Dr. Anna L. Jacobsen
Assistant Professor
Plant Ecology and Evolutionary Biology
Plant Structure-Function
Research
Dr. Jacobsen's Homepage Research Methods page
If you are a 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!
Also, CSUB students can find information about research related scholarships in Biology here.
Current students:
Mark Bersentes (undergraduate)
Tamani Gause (undergraduate)
Marta Percolla (undergraduate)
Evan MacKinnon (graduate)
Justin Martinez (graduate)
Former students:
Mark De Guzman (currently in a doctoral program at UC Riverside)
Raeanne Quaresma (currently in a doctoral program in Kansas)
Aaron Ramirez (currently in a doctoral program at UC Berkeley)
Gilberto Uribe (currently in a doctoral program at UC Riverside)
Alanisha Woods (currently in pharmacy school in Arkansas)
Some (but not all) of the current lab research topics/projects are described below:
Plant hydraulic structure and function
Plant xylem structure
Vessel connectivity and 3D structure
Plant development and structure
Plant hydraulic function
Fire ecology of Mediterranean-type climate region shrubs
Community convergence among arid and semi-arid shrublands in Mediterranean-type climate regions
Plant hydraulic structure and function
Plant xylem structure
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. The structure of these vessels, both at the cellular-level and at the tissue-level, where vessels form into an interconnected network, is a major theme of the research in my lab. 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.
Some micrographs describing lab research on vessel length and vessel network traits are shown below. 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!
Several students in the lab are currently working to measure 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.
As a lab, we are also working to quantify other elements of xylem structure, such as fiber and parenchyma cell structure and abundance. Alanisha Woods is currently working to measure the amount of parenchyma, fiber, and vessels in the xylem of many chaparral shrubs, including both evergreen and deciduous shrubs. The goal of this project is to determine if xylem tradeoffs between storage, structure, and transport functions are altered by leaf habit.
Vessel connectivity and 3D structure.
We are currently working to develop 3D models of xylem vessels through the use of serial sections and 3D imaging software. An undergraduate student, Tamani Gause, is assisting with these measures. One of the main features of the xylem network that we are examining is the contribution of small versus large vessels to overall connectivity. Thus far, we are finding that the majority of vessel connectivity in grape stems comes from the connections of small vessels to each other and to large vessels. For instance, in the images shown below on the left, the two large vessels highlighted in the red box are connected at several points along their length and these connections always occur through a "bridge" of small vessels as can be seen in the lower micrograph.
Tamani Gause is currently working in the lab to assist in 3D reconstructions of xylem vessel networks in grapevine.
Plant development and structure
Xylem vessel structure changes over the course of woody plant development, although many of these changes have not been described in detail nor at the level of the vessel network. We are currently initiating projects to look at changes in vessel structure over the course of plant development using two different experimental systems.
System 1: Poplar Tree Development
Undergraduate student Mark Bersentes is currently funded on an internal grant and is studying the structure of xylem vessels in 1, 2, and 3 year old Populus trichocarpa (Poplar). Mark is examining changes in the structure of inter-vessel pits, including pit density, pit aperture, and pit membrane area. Additionally, we have plans to include measures of vessel length, connectivity, diameter, etc. to examine how these changes in structure affect the hydraulic function of developing plants.
System 1: Resprouting Chaparral Shrub Development
Post-fire chaparral shrub resprouts have stems that are generally more vulnerable to water stress induced xylem cavitation when compared to co-occurring unburned plants. Resprouts also have lower xylem density and increased hydraulic efficiency. The structural changes that drive these functional shifts are unknown. The purpose of a second study is to examine xylem structural changes that may be linked to the observed shift in cavitation resistance and hydraulic efficiency of resprouting plants as compared to unburned plants of the same species. Vessel structural traits are being measured by undergraduate students Raeanne Quaresma and Mark Bersentes in one year old resprouting stems and in same-sized stems from unburned, approximately 30 year old plants, in 8 chaparral shrub species.
Plant hydraulic function
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 is included here.
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 Drs. Karen Esler and Shayne Jacobs or Stellenbosch University.
Selected related publications:
Ewers FW, Ewers JM, Jacobsen AL, López-Portillo J. 2007. Vessel redundancy: modeling safety in numbers. IAWA Journal 28: 373-388.
Pratt RB, Jacobsen AL, Ewers FW, Davis SD. 2007. Relationships among xylem transport, biomechanics, and storage in stems and roots of nine Rhamnaceae species of the California chaparral. New Phytologist 174: 787-798.
Jacobsen AL, Pratt RB, Ewers FW, Davis SD. 2007. Cavitation resistance among twenty-six chaparral species of southern California. Ecological Monographs 77: 99-115.
Jacobsen AL, Agenbag L, Esler KJ, Pratt RB, Ewers FW, Davis SD. 2007. Xylem density, biomechanics, and anatomical traits correlate with water stress in seventeen evergreen shrub species of the Mediterranean-type climate region of South Africa. Journal of Ecology 95: 171-183.
Jacobsen AL, Ewers FW, Pratt RB, Paddock WA III, Davis SD. 2005. Do xylem fibers affect vessel cavitation resistance? Plant Physiology 139: 546-556.
Fire ecology of Mediterranean-type climate region shrubs
Post-fire recovery of native shrubs
The chaparral community of southern California is a shrub community that is adapted to periodic wildfire. The evergreen shrubs in this community 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 has been funded by research grants awarded to Dr. Brandon Pratt and involves collaboration with many other researchers and several undergraduate and graduate students.
Below is a picture of students (Aaron Ramirez and Gilbert Uribe) sampling resprouts 1 year after a fire in the Santa Monica Mountains, California.
Selected related publications:
Pratt RB, Jacobsen AL, Mohla R, Ewers FW, Davis SD. 2008. Linkage between water stress tolerance and life history type in seedlings of nine chaparral species (Rhamnaceae). Journal of Ecology 96: 1252-1265.
Pratt RB, Jacobsen AL, Golgotiu KA, Sperry JS, Ewers FW, Davis SD. 2007. Life history type coupled to water stress tolerance in nine Rhamnaceae species of the California chaparral. Ecological Monographs 77: 239-253.
Jacobsen AL, Fabritius SL and Davis SD. 2004. Fire frequency impacts non-sprouting chaparral shrubs in the Santa Monica Mountains of southern California. (In Ecology, Conservation and Management of Mediterranean Climate Ecosystems. Eds. Arianoutsou M and Papanastasis VP. Millpress, Rotterdam, Netherlands).
Community convergence among arid and semi-arid shrublands in Mediterranean-type climate regions
I am interested in examining xylem structural and functional adaptations among shrubs occurring in arid and semi-arid plant communities from around the world and, particularly, in the relationship between community, whole plant traits, and plant cellular traits as they relate to abiotic stresses such as water stress. My interest in this topic has focused mainly on the 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. Do plants and plant communities in these different regions use similar strategies in response to the prolonged period of summer water stress that typifies these regions?
Chaparral and fynbos communities, which are morphologically similar appear to converge in their water use strategies, but differ from other communities that occur in these regions, such as coastal sage scrub and desert communities.
Although this is not a research question that is being actively addressed through current lab projects, I continue to find Mediterranean-type region communities to be particularly intriguing and I look forward to continuing this research in the future.
Selected related publications:
Jacobsen AL, Esler KJ, Pratt RB, Ewers FW. 2009. Water stress tolerance of shrubs in Mediterranean-type climate regions: Convergence of fynbos and succulent karoo communities with California shrub communities. American Journal of Botany 96: 1445-1453.
Hacke UG, Jacobsen AL, Pratt RB. 2009. Xylem function of arid-land shrubs from California, USA: an ecological and evolutionary analysis. Plant, Cell & Environment 32: 1324-1333.
Jacobsen AL, Pratt RB, Moe LM, Ewer FW. 2009 Plant community water use and invasibility of semi-arid shrublands by woody species in southern California. Madroño 56: 213-220.
Jacobsen AL, Pratt RB, Davis SD, Ewers FW. 2008. Comparative community physiology: non-convergence in water relations among three semi-arid shrub communities. New Phytologist 180: 100-113.
Jacobsen AL, Pratt RB, Davis SD, Ewers FW. 2007. Cavitation resistance and seasonal hydraulics differ among three arid Californian plant communities. Plant, Cell and Environment 30: 1599-1609.
At a global level, I am intrigued by the diversity of plant structural and functional traits and I hope that all of the research projects described above will contribute to increased understanding of plant structure, plant function, and the interesting ways that plants shape and are shaped by their environment.