Below-ground respiratory responses of sugar maple and red maple saplings to atmospheric CO2 enrichment and elevated air temperature.

摘要

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 concentration and temperature on tree growth, physiological processes, and ecosystem-levelprocesses. The specific objective of this research was to examine the below-ground respiratory responses of sugar maple (Acer saccharum) and red maple (A. rubrum) seedlings to elevated atmospheric CO2 concentration and temperature. Red maple and sugar maple seedlings were planted in the ground in each of 12 open-top chambers and exposed from 1994 to 1997 to ambient air or air enriched with 30 Pa CO2, in combination with ambient or elevated (+4鳦) air temperatures. Carbon dioxide efflux was measured around the base of the seedlings and from root-exclusion zones at intervals during 1995, 1996 and early 1997. The CO2 efflux rates averaged 0.4 鎚ol CO2 m-2 s-1 in the root-exclusion zones and 0.75 鎚ol CO2 m-2 s-1 around the base of the seedlings. Mineralsoil 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 鎚ol CO2 m-2 s-1 of soil surface in red maple and from 0 to 1.02 in sugar maple. In both 1995 and 1996 rootrespiration 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 lowestin 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. It was suggested that 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 understanding of the effects of global climate change on carbon sequestration and cycling in the below-groundsystems of forests.