Plant and Soil
206 (1): 85-97, September 1998
All rights reserved
Nelson T. Edwards
Oak Ridge National Laboratory, Oak Ridge, TN 37831-6422,
USA
Richard J. Norby
Oak Ridge National Laboratory, Oak Ridge, TN 37831-6422,
USA
Abstract
The research described in this paper represents a part of a
much broader research project with the general objective of describing the
effects of elevated [CO2] and temperature on tree growth, physiological
processes, and ecosystem-level processes. The specific objective of this
research was to examine the below-ground respiratory responses of sugar maple
(Acer saccharum Marsh.) and red maple (Acer rubrum L.) seedlings to elevated
atmospheric [CO2] and temperature. Red maple and sugar maple seedlings were
planted in the ground in each of 12 open-top chambers and exposed from 1994
through 1997 to ambient air or air enriched with 30 Pa CO2, in combination with
ambient or elevated (+4 °C) air temperatures.
Carbon dioxide efflux was measured around the base of the seedlings and from
root-exclusion zones at intervals during 1995 and 1996 and early 1997. The CO2
efflux rates averaged 0.4 μmol CO2 m-2 s-1 in
the root-exclusion zones and 0.75 μmol CO2
m-2 s-1 around the base of the seedlings. Mineral soil respiration in
root-exclusion zones averaged 12% higher in the high temperature treatments
than at ambient temperature, but was not affected by CO2 treatments. The
fraction of total efflux attributable to root + rhizosphere respiration ranged
from 14 to 61% in measurements made around red maple plants, and from 35 to 62%
around sugar maple plants. Root respiration rates ranged from 0 to 0.94 μmol CO2 s-1 m-2 of soil surface in red maple and
from 0 to 1.02 in sugar maple. In both 1995 and 1996 root respiration rates of
red maple were highest in high-CO2 treatments and lowest in high temperature
treatments. Specific red maple root respiration rates of excised roots from
near the soil surface in 1996 were also highest under CO2 enrichment and lowest
in high temperature treatments. In sugar maple the highest rates of CO2 efflux
were from around the base of plants exposed to both high temperature and
high-CO2, even though specific respiration rates were lowest for this species
under the high temperature and CO2 enrichment regime. In both species, patterns
of response to treatments were similar in root respiration and root mass,
indicating that the root respiration responses were due in part to differences
in root mass. The results underscore the need for separating the processes
occurring in the roots from those in the forest floor and mineral soil in order
to increase our understanding of the effects of global climate change on carbon
sequestration and cycling in the below-ground systems of forests.
Keywords
Acer rubrum, Acer saccharum, CO2 ×
temperature interactions, open-top chamber, root respiration