Constable, John .
Impacts of free-air CO2 enrichment (FACE) on assimilatory nitrate reduction.
THIS study examined how growth at elevated CO2 influenced the activity of nitrate reductase (NR), the first step in the assimilation of nitrate (NO3-), tissue nitrogen (N) concentration, and tissue carbohydrate concentration. Measurements were performed on four target species: Liquidambar styraciflua (Oak Ridge National Laboratory), Pinus taeda (Duke University), and C3 (Agropyron repens) and C4 (Bouteloua gracilis) grasses (University of Minnesota) grown under Free Atmosphere CO2 Enrichment (FACE). It was hypothesized that elevated CO2 would (a) increase NR activity; (b) stimulate root NR activity preferentially over foliar NR activity; and (c) enhance tissue carbohydrate concentration. Tissue NR activity was determined using an in vivo assay and carbohydrate concentration (soluble sugars and starch) in foliar and fine root tissue was assayed enzymatically. In Liquidambar growth CO2 did not affect NR activity in either tissue, but foliar activity exceeded that in root tissue. Activity of NR in Pinus was unaffected by either growth CO2 or tissue type. Similarly, in Agropyron and Bouteloua, NR activity in either tissue was not affected by growth CO2 and tissue types did not differ in NR activity. Although NR activity was unchanged at elevated CO2 this was not reflected as a decline in tissue N concentration. The lack of an effect of elevated CO2 on NR activity in either foliage or fine roots resulted in no change in the balance between above and belowground NR activity. In all species examined foliar carbohydrates (especially soluble sugars) exceeded those in the fine roots, but the effect of growth at elevated CO2 on carbohydrate concentration in either foliar or fine root compartments was not significant. Although laboratory studies frequently illustrate enhanced NR activity under elevated CO2, a similar enhancement in field grown species was not observed although several species examined here exhibit sustained growth increases under elevated CO2 conditions.[c.e.:srb]
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1 - California State University, Department of Biology, 2555 East San Ramon Ave. M/S SB73, Fresno, California, 93740-8034, USA
Presentation Type: Poster:Posters for Sections
Location: Auditorium/Bell Memorial Union
Date: Tuesday, August 1st, 2006
Time: 12:30 PM