Tobin, M. F. , Jacobsen, A. L. , Pratt, R. B. .
Stem cavitation resistance is reduced in post-fire resprouts of chaparral shrub species with divergent life history types.
In California, chaparral shrub species suffer fire-induced crown death during periodic wildfires. Chaparral shrubs reestablish in burned areas either by recruiting seedlings from a fire-cued seed bank or sprouting from a lignotuber (root crown). Some species exhibit only one of these strategies, while others are able to do both. Among species that sprout from lignotubers after fire, obligate sprouter (OS) species do not recruit seedlings in the burned areas, whereas facultative sprouters (FS) do recruit into these areas. Previous research has documented greater resprout mortality for FS species than OS species during the hot, dry summers characteristic of this region. We investigated the role of plant water stress in the mortality differences between co-occurring OS and FS species. The vulnerability of stems to water stress-induced xylem cavitation was measured for resprouting shoots of plants burned about 8 months prior to sampling and of adjacent unburned plants for four OS and four FS species. We also measured predawn and midday water potentials throughout the dry season to assess plant water status in the field. The water potential at 50% loss of hydraulic conductivity (P50) did not differ between OS and FS species. But for both OS and FS species, stems of burned plants were more vulnerable to cavitation (had less negative P50) than stems of unburned plants, suggesting reduced water stress resistance for resprouts. However, these differences did not necessarily equate to greater embolism during the dry season in burned plants because predawn and midday water potentials remained higher in burned plants relative to unburned plants. Higher water potentials of burned plants likely resulted from the lower leaf area index and associated reduced transpirational draw down of soil moisture found in recently burned areas. The reduced water stress resistance of resprouts is a potential mechanism by which fire and drought may interact to alter chaparral community regeneration.
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1 - California State University, Bakersfield, Department of Biology, 9001 Stockdale Hwy., Bakersfield, CA, 93311, USA
Presentation Type: Oral Paper:Papers for Topics
Location: 551B/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 1:45 PM