Document: JOH-3-34-47

Response of growth and nitrate reductase activity in trees to elevated CO₂ varies with mycorrhizal status.

CONSTABLE, J.V.H.* and H.BASSIRIRAD

University of Illinois at Chicago, Chicago IL 60607 USA ¹

Abstract:
Plant responses to increased atmospheric CO₂ partial pressure may depend on the ability to acquire nutrients including nitrogen (N). Mycorrhizae facilitate N acquisition and alter N assimilation, therefore, mycorrhizae may modulate plant response to elevated CO₂. In this study we assessed how inoculation with the endomycorrhizae Glomus intraradices affected seedling growth and nitrate reductase activity (NRA) in Acer saccharinum (Acsa), Fraxinus pennsylvanica (Frpe), and Ulmus americana (Ulam) grown at either ambient (~38 Pa) or elevated (~70 Pa) CO₂. Total seedling growth was stimulated ~25% by elevated CO₂ in Acsa and Ulam regardless of mycorrhizal status. However, in Ulam the magnitude of the growth enhancement was less in mycorrhizal than non-mycorrhizal plants, a similar pattern was not observed in Acsa. Below-ground growth was stimulated by elevated CO₂ in both mycorrhizal and non-mycorrhizal seedlings of Acsa and Ulam. Total and below-ground growth of Frpe was unchanged by any treatment. Foliar NRA exceeded fine root NRA in all species regardless of experimental treatment. Elevated CO₂ depressed foliar NRA in Acsa (~-50%) and Ulam (~-30%). In Ulam, the negative effect of CO₂ was reversed by a mycorrhizal stimulation of foliar NRA (~+40%). A similar response was not observed in Acsa where mycorrhizae reduced foliar NRA at ambient (-30%), but not at elevated CO₂. Fine root NRA was enhanced ~25% by elevated CO₂ in both mycorrhizal treatments in Acsa. In Ulam, elevated CO₂ increased fine root NRA (+46%) in non-mycorrhizal seedlings, but depressed it (-38%) in mycorrhizal seedlings. Neither foliar or fine root NRA were affected by the treatments in Frpe. The results suggest that elevated CO₂ stimulated growth, but depending on plant species, mycorrhizae may determine the magnitude of this stimulation. Similarly, elevated CO₂ may have opposing effects on foliar and fine root NRA depending on mycorrhizal status. Mycorrhizae may affect plant growth response to elevated CO₂ through a variety of mechanisms including changes in N acquisition and assimilation.

Keywords: CO₂, nitrate reductase, climate change

This abstract is being presented at: 8:15 AM in session:
Oral Session #40: Elevated CO₂ In Forest Systems.