PS 57-112
Individual hydraulic response strategies of four Mediterranean-type shrubs to long-term dry season nitrogen deposition

Thursday, August 14, 2014
Exhibit Hall, Sacramento Convention Center
Alexandria Pivovaroff, Botany & Plant Sciences, UC Riverside, Riverside, CA
George L. Vourlitis, Department of Biological Sciences, California State University, San Marcos, CA
Michael F. Allen, Center for Conservation Biology, University of California, Riverside, CA
David A. Grantz, Botany and Plant Sciences, University of California Riverside, Parlier
Louis S. Santiago, Department of Botany and Plant Sciences, University of California-Riverside, Riverside, CA
Background/Question/Methods

Anthropogenic nitrogen (N) deposition represents a significant N input for many semi-arid ecosystems, including southern California.  N deposition can alter plant communities, resulting in species composition shifts and reduced diversity.  On a smaller scale, increased N availability can strongly affect photosynthesis.  Few studies have investigated how changes in N availability affect plant hydraulic properties, including hydraulic conductivity and vulnerability to cavitation.

Experimental plots were established in a completely randomized design at Santa Margarita Ecological Reserve (SMER) and at Sky Oaks Field Station (SOFS) in southern California, USA, in 2003.  Each site has eight 10 x 10 m plots, four of which are fertilized with 50 kg N ha-1 yr-1 in a single application during the dry season and four of which are un-manipulated control plots.  The dominant species at SMER are Artemisia californica and Salvia mellifera, and at SOFS are Adenostoma fasciculatum and Ceanothus greggii.  In 2013-14, we measured stem hydraulic conductivity (Kh), xylem vulnerability to cavitation (P50), wood density, specific leaf area (SLA), predawn and midday water potentials (Ψpredawn and Ψmidday), leaf hydraulic conductance (Kleaf), and gas exchange including light saturated photosynthetic rate per area and mass (Aarea and Amass) and transpiration (E).

Results/Conclusions

Each species had an individual response strategy to long-term N addition.  Of the four study species, Artemisia californica was particularly responsive, as N addition increased stem hydraulic conductivity and transpiration, and decreased wood density and specific leaf area.  N addition also increased transpiration in C. greggiiAdenostoma fasciculatum was more vulnerable to xylem cavitation in N plots than in control plots.  July predawn xylem water potentials were less negative in N plots for all species except A. fasciculatum, but there was no difference in water potentials between N and control plots at midday, February predawn, nor February midday.  There were no differences in leaf hydraulic conductance, light saturated photosynthetic rate per area or mass between N and control plots for any species.  This Mediterranean-type ecosystem receives most precipitation during the winter months and is subject to an annual seasonal water deficit, which may limit the range of plant responses to increased N availability.