PARENT SESSION
Oral Session #31: Plant Ecology: Gas Exchange.
Presiding: R. Montgomery
Tuesday, August 6. 8:00 AM to 11:30 AM. Cochise Meeting Room, TCC.

Species living on the edge: ecophysiological adaptation to episodic events, climate change, and biodiversity in barrier beach plants .

Hancock, Thomas^*,1, Smith, William¹, ¹ Wake Forest University, Winston-Salem, NC

ABSTRACT- The barrier beach environment of the East Coast (US) has been characterized as dynamic, harsh, and physically limiting for organisms. Plants that inhabit this region must avoid or tolerate salt spray, sand movement, low soil moisture, low soil nutrients, high incident sunlight on both leaf surfaces and saltwater inundation. These stresses are present on a daily to annual basis. In addition, plants must cope with severe episodic events such as hurricanes that generate damage and mortality due to saltwater inundation, excavation and burial. Yet, few studies have addressed possible ecophysiological adaptations in sand dune species, or episodic stress. Photosynthetic light response curves and diurnal net photosynthesis for Amaranthus pumilus (a designated threatened species), Cakile edentula, and Hydrocotyle bonariensis demonstrated classic C4, C3 , and C3 photosynthetic responses, respectively. However, daily maximum photosynthesis in A. pumilus and C. edentula was similar, approximately 23 mol m-2 s-1 throughout the summer with a decrease to 5 mol m-2 s-1 just before senescence in October. In contrast, maximum photosynthesis for H. bonariensis was consistently between 10 and 12 mol m-2 s-1 during summer, and continued into October. Both A. pumilus and C. edentula had relatively high daily carbon gain during the summer (0.75 mol m-2 day-1 and 0.68 mol m-2 day-1, respectively) decreasing to 0.09 mol m-2 day-1 and 0.26 mol m-2 day-1, respectively, during October. In contrast, H. bonariensis levels remained almost constant at 0.27 mol m-2 day-1 throughout the summer and fall. The lowest xylem water potentials of the growing season occurred during afternoon periods for all species, and least for H. bonariensis (-0.7, -0.9, and -0.4 MPa, respectively). Daily and seasonal carbon gain may be significant in conferring stress resistance to episodic events in these barrier beach plants. Due to apparent differences in adaptive strategy and life history, coupled with proximity to the mean high tide line, these foredune species may be excellent candidates for assessing future global change impacts on biodiversity, with a focus on episodic events.

KEY WORDS: Sand Dunes, Foredunes, Barrier Beach, Episodic