Physiological Profiles as Indicators of Response to Hurricane Disturbance for Three Coastal Wetland Species

© Coastal Education & Research Foundation 2015. Hurricanes alter light and water availability via canopy damage and storm surge delivery and are expected to intensify with climate change. Plant species respond to environmental changes by making physiological adjustments in situ or through distribution changes. Three years after Hurricane Katrina, we compared functional traits and water relations among three species along the coenocline at Weeks Bay National Estuarine Research Reserve, Fairhope, Alabama, U.S.A. Based on posthurricane distribution changes for these species, we hypothesized that (1) Cladium mariscus, whose distribution expanded slightly, is responsive to increased light availability in the disturbed forest at the landward end but is strongly limited by water stress at its seaward edge; (2) Baccharis halimifolia, whose distribution shifted and abundance increased posthurricane, is responsive to increased light availability, cannot tolerate very low light levels or water logged soils, but can tolerate moderate salinity; and (3) Morella cerifera, whose distribution remained unchanged, would show little or no difference in measured functional traits and water relations at its landward vs. seaward edges. Cladium mariscus showed decreased water potential (Ψ) at its seaward edge, but leaf mass per area (LMA) did not vary as forest cover increased landward. Baccharis halimifolia exhibited lowest LMA and highest Ψ in the middle of its distribution, but was least vulnerable to cavitation (Ψ50) with increased forest cover. Morella cerifera exhibited no difference in water stress, wood density, or Ψ50 across its distribution. Our results suggest differences in physiological response to light availability and water stress may affect the postdisturbance distribution of plant species and influence changes in distribution of species exposed to chronic sea level rise

Examining California Chaparral and Coastal Sage Scrub Responses to Environmental Change: A Hydraulics Approach

Environmental change is occurring at an unprecedented rate. Being sessile and unable to escape rapidly changing conditions, many plant species will be unable to cope with the increased abiotic stress. This may lead to decreased physiological functioning and/or mortality. Drought and nitrogen deposition are two major disturbances that affect vegetation in California’s Mediterranean-type climate region. This region is a biodiversity hotspot and conservation priority. This research examined: 1) How water movement is coordinated among plant organs and the role this plays in drought adaptation; 2) The effects of long-term nitrogen deposition on plant hydraulic and drought adaptation traits; and 3) The mechanism underlying the open-vessel artifact when determining xylem vulnerability to cavitation using the centrifuge-based Cavitron. These results demonstrated that leaves act as hydraulic bottlenecks for vulnerable species, supporting the hydraulic segmentation hypothesis. In addition, Artemisia californica was highly responsive to alleviation of nitrogen limitation, displaying increasing gas exchange and stem water transport, and altered functional traits. Finally, the Champagne effect was confirmed as a culprit behind the early loss of conductance in ‘r’ shaped vulnerability curves measured using the Cavitron. Xylem water extraction curves compared with vulnerability curves showed when true cavitation was occurring. Overall, this research shows different species have different suites of traits that result in drought adaptation, indicating that not all species will respond equally to disturbance. Additionally, proper techniques and equipment are essential to correctly quantifying these traits

Physiological Profiles as Indicators of Response to Hurricane Disturbance for Three Coastal Wetland Species

© Coastal Education & Research Foundation 2015. Hurricanes alter light and water availability via canopy damage and storm surge delivery and are expected to intensify with climate change. Plant species respond to environmental changes by making physiological adjustments in situ or through distribution changes. Three years after Hurricane Katrina, we compared functional traits and water relations among three species along the coenocline at Weeks Bay National Estuarine Research Reserve, Fairhope, Alabama, U.S.A. Based on posthurricane distribution changes for these species, we hypothesized that (1) Cladium mariscus, whose distribution expanded slightly, is responsive to increased light availability in the disturbed forest at the landward end but is strongly limited by water stress at its seaward edge; (2) Baccharis halimifolia, whose distribution shifted and abundance increased posthurricane, is responsive to increased light availability, cannot tolerate very low light levels or water logged soils, but can tolerate moderate salinity; and (3) Morella cerifera, whose distribution remained unchanged, would show little or no difference in measured functional traits and water relations at its landward vs. seaward edges. Cladium mariscus showed decreased water potential (Ψ) at its seaward edge, but leaf mass per area (LMA) did not vary as forest cover increased landward. Baccharis halimifolia exhibited lowest LMA and highest Ψ in the middle of its distribution, but was least vulnerable to cavitation (Ψ50) with increased forest cover. Morella cerifera exhibited no difference in water stress, wood density, or Ψ50 across its distribution. Our results suggest differences in physiological response to light availability and water stress may affect the postdisturbance distribution of plant species and influence changes in distribution of species exposed to chronic sea level rise