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Doctoral Student Alexandria Pivovaroff Publishes Article based on Research at SMER

Alex standing in foliage collecting stem sample

Alex Pivovaroff in the field at SMER

Coordination of stem and leaf hydraulic conductance in southern California shrubs: a test of the hydraulic segmentation hypothesis

Alexandria L. Pivovaroff1, Lawren Sack2 and Louis S. Santiago1

1Department of Botany and Plant Sciences, University of California, 2150 Batchelor Hall, Riverside, CA 92521, USA; 2Department of Ecology and Evolutionary Biology, University of California, 621 Charles E. Young Drive South, Los Angeles, CA 90095-1606, USA


 Coordination of water movement among plant organs is important for understanding plant water use strategies. The hydraulic segmentation hypothesis (HSH) proposes that hydraulic conductance in shorter lived, ‘expendable’ organs such as leaves and longer lived, more ‘expensive’ organs such as stems may be decoupled, with resistance in leaves acting as a bottleneck or ‘safety valve’.

 We tested the HSH in woody species from a Mediterranean-type ecosystem by measuring leaf hydraulic conductance (Kleaf) and stem hydraulic conductivity (KS). We also investigated whether leaves function as safety valves by relating Kleaf and the hydraulic safety margin (stem water potential minus the water potential at which 50% of conductivity is lost (Ψstem  Ψ50)). We also examined related plant traits including the operating range of water potentials, wood density, leaf mass per area, and leaf area to sapwood area ratio to provide insight into whole-plant water use strategies.

 For hydrated shoots, Kleaf was negatively correlated with KS, supporting the HSH. Addition- ally, Kleaf was positively correlated with the hydraulic safety margin and negatively correlated with the leaf area to sapwood area ratio.
 Consistent with the HSH, our data indicate that leaves may act as control valves for species with high KS, or a low safety margin. This critical role of leaves appears to contribute impor- tantly to plant ecological specialization in a drought-prone environment.

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Some images of the Santa Margarita River, taken 2/28/2014.  After receiving ~1.5″ of rain in a 24 hr period.  USGS gauging station just below the confluence reported 1,310 cu f/s @ 1300 hrs, 2000 cu f/s @1400 hrs.

Web cam images:


Aerial Shot of River Gorge, courtesy of Douglas McCulloh

SMER Dragonflies

Pictures courtesy of SDSU alumni Gary Suttle

Grossmont College Earth Science Class Final taken at SMER

SMER Spring Hike 2013


Photos courtesy of Mr. Bill Atkinson. Hike lead by Superstar Docent Ms. Beth Cobb.

Snow at Sky Oaks

Pechanga Band of Luiseño Indians Announce Acquisition of Liberty Quarry

Pechanga and Granite Construction Reach Historic Accord to Transfer and Preserve Site of Proposed Liberty Quarry, Nov. 15, 12

Watershed Clean Up

Fire Watch Cameras Installed at Sky Oaks

Remote fire watch system installed at SDSU’s Sky Oaks Field Station. Powered by photovoltaic panels and tied into the HPWREN network, four cameras provide a 360 degree view of the surrounding landscape. Part of a collaborative project involving UCSD, SDG&E and SDSU. 

Online images can viewed here: