Rhamnus ilicifolia xylem.

                                                                                                                                                                                                                                                                                                                 02/09/09

Research projects:

I. Tradeoffs in xylem function

In plants, the xylem transport system has three basic functions, namely long distance water transport, mechanical support of the plant body, and storage of water and nutrients. These functions are linked to xylem structure and largely interdependent such that xylem that is proficient at one function may necessarily be poor at another function giving rise to tradeoffs in xylem function. Understanding these tradeoffs and their structural underpinning is critical for understanding the diversity in physiological, structural, and life history types found among woody plant species. Although storage is an important xylem function, research into xylem functional tradeoffs has more often focused on xylem transport and mechanics. Thus, we currently lack information on how xylem storage integrates with the water transport and mechanical support functions of xylem.  My lab is currently examining xylem storage characteristics as they relate to xylem transport and mechanics in evergreen and deciduous species that occur in California's Mediterranean-type climate region.  This project is funded by an NSF CAREER grant for the next five years.

Gas bubbles (emboli) in the xylem vessels (left) and a Ceanothus leucodermis stem (right) stained

with IKI for starch (note the dark purple parenchyma).

II. Post-fire regeneration of chaparral and fynbos shrubs

Fire is a natural part of ecology of many biotic communities across the globe.  This is certainly true of the fire-prone Mediterranean-type climate regions in southern California, South Africa, Soutwestern Australia, and the Mediterranean Basin.  The shrubs that dominate these regions are able to regenerate following fire by fire stimulated seed germination or resprouting from stems or roots.  My students and I are currently examining the traits that facilitate vigorous resprouting following fire California chaparral and South African fynbos.  We are especially interested in the interaction between drought and post-fire resprout recovery.  We are collaborating with Drs. Karen Esler and Shayne Jacobs at the University of Stellenbosch in South Africa.  This work is funded by the Andrew Mellon Foundation for the next three years.

Chamise (Adenostom fasciculatum) resprout mortality

(left) next to a successful resprout (right).

III. Life history and stress tolerance among chaparral species.

This project is ongoing and in collaboration with Stephen D. Davis (Pepperdine University), and Frank Ewers at Cal Poly Pomona, Anna Jacobsen at California State University, Bakersfield and Gretchen North at Occidental College.

Life History Strategy of Chaparral Species

 

The modes of regeneration after wildfire: non-sprouting (NS), facultative sprouting (FS), and obligate sprouting (OS).  Non-sprouters exclusively rely on seed germination for establishment post-fire (A), facultative sprouters rely on a combination of both recruitment from seeds and vegetative sprouting (B), and obligate-sprouters exclusively rely on vegetative sprouting (C).  For obligate-sprouters, seedling recruitment only occurs during fire free intervals where seedlings establish in deep shade (C).  The spatial (deep shade vs. open exposure) and temporal (pre-fire vs. post-fire) differences experienced by recruiting seedlings may affect traits that are related to tolerance of water-stress.

IV. Ecophysiology of alien invasive species.

What functional traits help to explain the invasive nature of some alien species? Undergraduate student Haley O'Mara is studying functional

traits of alien invasive, weedy native, and non-weedy native species in the southern end of the Central Valley of California in an effort to

understand what traits contribute to the invasive nature of some species.  This work is in collaboration with Drs. Maynard Moe and Anna

Jacobsen at CSUB.

Student Haley O'Mara (on the left) and Dr. Anna Jacobsen examining

alien plants at Windwolves Researve in the Central Valley.

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