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Effect of measurement CO₂ concentration on sugar maple root respiration

Andrew J. Burton (1), Gregory P. Zogg (2), Kurt S. Pregitzer (1) and Donald R. Zak (2)

1. School of Forestry and Wood Products, Michigan Technological University, Houghton, MI 49931, USA / 2. School of Natural Resources and Environment, University of Michigan, Ann Arbor, MI 48109-1115, USA / Received November 19, 1996

Summary

Accurate estimates of root respiration are crucial to predicting belowground C cycling in forest ecosystems. Inhibition of respiration has been reported as a short-term response of plant tissue to elevated measurement [CO₂]. We sought to determine if measurement [CO₂] affected root respiration in samples from mature sugar maple (Acer saccharum Marsh.) forests and to assess possible errors associated with root respiration measurements made at [CO₂]s lower than that typical of the soil atmosphere. Root respiration was measured as both CO₂ production and O₂ consumption on excised fine roots (≤ 1.0 mm) at [CO₂]s ranging from 350 to > 20,000 µl l^–1. Root respiration was significantly affected by the [CO₂] at which measurements were made for both CO₂ production and O₂ consumption. Root respiration was most sensitive to [CO₂] near and below normal soil concentrations (< 1500 µl l^–1). Respiration rates changed little at [CO₂]s above 3000 µl l^–1 and were essentially constant above 6000 µl l^–1 CO₂. These findings call into question estimates of root respiration made at or near atmospheric [CO₂], suggesting that they overestimate actual rates in the soil. Our results indicate that sugar maple root respiration at atmospheric [CO₂] (350 µl l^–1) is about 139% of that at soil [CO₂]. Although the causal mechanism remains unknown, the increase in root respiration at low measurement [CO₂] is significant and should be accounted for when estimating or modeling root respiration. Until the direct effect of [CO₂] on root respiration is fully understood, we recommend making measurements at a [CO₂] representative of, or higher than, soil [CO₂]. In all cases, the [CO₂] at which measurements are made and the [CO₂] typical of the soil atmosphere should be reported.

Keywords: Acer saccharum, CO₂ production, direct effect of CO₂, oxygen consumption, root respiration.

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