© 1996 Heron Publishing—Victoria, Canada
Effects of soil and stem base heating on survival, resprouting and gas exchange of Acer and Quercus seedlings
Julie A. Huddle (1, 2) and Stephen G. Pallardy (1)
1. School of Natural Resources, University of Missouri, Columbia, MO 65211, USA / 2. Department of Rangeland Ecology and Management, Texas A&M University, College Station, TX 77843, USA / Received June 6, 1995
Summary
Acer rubrum L., A. saccharum Marsh., Quercus alba L. and Q. rubra L. seedlings subjected to soil and stem base heat treatments showed rapid declines in rates of transpiration and photosynthesis.
Reductions in photosynthetic rate were partly attributable to mesophyll inhibition. Quercus seedlings were less able to maintain transpiration and photosynthesis after heat treatment than Acer seedlings. Declines in rates of transpiration and photosynthesis of Quercus seedlings were observed 1 h after heat treatment and became more pronounced over time. In contrast, rates of transpiration
and photosynthesis of Acer seedlings initially declined in response to heat treatment, partially recovered after one or two days, but then declined
again six to eight days after the heat treatment. Observed changes in leaf water potential after heating were small, suggesting
that hydraulic factors were not the primary signal eliciting the gas exchange response to soil and stem heating.
Ultimately, the heat treatments caused stem die-back of most seedlings. For all species, seedlings that resprouted had a greater
chance of surviving heat stress than seedlings that did not resprout. Despite the rapid loss of photosynthetic capacity in
response to heat treatment in Quercus seedlings, survival was higher in Quercus seedlings than in Acer seedlings, and was associated with a greater capacity for resprouting. We suggest that the reduced allocation of resources
toward recovery of photosynthesis in existing Quercus stems after heat stress is a physiological mechanism that facilitates resprouting and hence survival of Quercus seedlings after fire.
Keywords:
Acer saccharum, Acer rubrum, fire, photosynthesis, Quercus alba, Quercus rubra, resprouting, survival, thermotolerance, transpiration.
