Preston, Katherine , Bhaskar, Radika .
Does fire level the hydraulic playing field for resprouting shrubs?.
Many fire-adapted shrub species can replace burned canopies by resprouting from their roots. The resulting high root-to-leaf-area ratio should relax soil water limitation for all resprouts, but species may still differ in leaf water supply when features of the plant itself are limiting. Xylem anatomy and leaf-to-sapwood-area ratio affect hydraulic supply, and interspecific variation in these traits reflects water use strategies of full-canopy plants. Shoot plasticity and variation in rooting depth may also modulate the hydraulic benefits of resprouting.
We compared water relations in six chaparral shrub species resprouting after a fire near Santa Barbara, CA. Species varied in leaf-to-sapwood-area ratio, SLA, vessel diameter, and wood density. In June, predawn and midday leaf water potentials showed that all species had equal access to soil water and similar leaf water status during peak photosynthesis. As predicted for these conditions, the rate of water transport to leaves (leaf-specific conductance) primarily reflected morphological traits (wood density, leaf-to-sapwood area).
By September water potentials varied widely as drying soil affected species differentially, largely due to differences in rooting depth. Resprouting plants nevertheless had more favorable water potentials than full-canopy individuals nearby, and the difference was most pronounced in species with the most negative water potentials (Arctostaphylos and Garrya). In September leaf-specific conductance declined with increasing tension in the xylem (leaf-to-soil water potential gradient). This pattern was evident across species and individuals and suggests that plants were losing conductance due to cavitation in the xylem. Thus, despite their highly favorable root-to-leaf-area, resprouting species had equal access to soil water for only part of the season, and we found evidence for cavitation-induced loss of conductance as soils dried.
1 - Stanford University, Biological Sciences, 371 Serra Mall, Stanford University, Stanford, California, 94305-5020, USA
Presentation Type: Paper
Location: Wasatch (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 9:00 AM