title: Effect of elevated [CO(2)] and varying nutrient application rates on physiology and biomass accumulation of Sitka spruce (Picea sitchensis).
abstract: Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings were supplied with solutions containing nitrogen (N) at 0.1 x or 2 x the optimum rate (low-N and high-N supply, respectively) and grown either outside in a control plot or inside open-top chambers and exposed to ambient (355 &mgr;mol mol(-1)) or elevated (700 &mgr;mol mol(-1)) CO(2) concentration ([CO(2)]). Gas exchange measurements, chlorophyll determinations and nutrient analysis were made on current-year (< 1-year-old) shoots of the upper whorl after the seedlings had been growing in the [CO(2)] treatments for 17 months and the nutrient treatments for 6 months. Total seedling biomass and biomass allocation were assessed at the end of the experiment. Nutrient treatment had a significant effect on the light response curves, irrespective of [CO(2)] or chamber treatment; seedlings supplied with high-N rates had higher net photosynthetic rates than seedlings supplied with low-N rates. The degree of photosynthetic stimulation in response to elevated [CO(2)] was larger in seedlings receiving high-N rates than in seedlings receiving low-N rates. Light-saturated net photosynthesis of seedlings grown and measured in elevated [CO(2)] was 26% higher than that of seedlings grown and measured in ambient [CO(2)]. There was no significant effect of [CO(2)] or chamber treatment on the CO(2) response curves of seedlings receiving High-N supply rates. In contrast, analysis of the CO(2) response curves of seedlings receiving Low-N supply rates showed acclimation to elevated [CO(2)]. Both maximum rate of carboxylation (V(cmax)) and maximum electron transport capacity (J(max)) were lower and J(max)/V(cmax) higher in seedlings in the elevated [CO(2)] treatment. There was no effect of elevated [CO(2)] on stomatal conductance, although it was highly dependent on foliar [N], ranging from ~60 mmol m(-2) s(-1) at ~1.5 g N m(-2) to 200 mmol m(-2) s(-1) at ~5 g N m(-2). In the high-N and low-N treatments, foliar N concentration was 10 and 28% lower in seedlings grown in elevated [CO(2)] than in seedlings grown in ambient [CO(2)], respectively. There was no [CO(2)] effect on foliar phosphorus concentration ([P]). Chlorophyll concentration increased with increasing N supply in all treatments. There was no significant effect of elevated [CO(2)] on specific leaf area. Chlorophyll concentration expressed either on an area or dry mass basis for a given foliar [N] was higher in seedlings grown in elevated [CO(2)] than in seedings grown in ambient [CO(2)]. Elevated [CO(2)] increased total biomass accumulation by 37% in seedlings in the high-N treatment but had no effect in seedlings in the low-N treatment. There was a proportionally bigger allocation of biomass to roots of seedlings in the elevated [CO(2)] + low-N supply rate treatment compared with seedlings in other treatments. This resulted in a reduction in aboveground biomass compared with corresponding seedlings grown in ambient [CO(2)].
authors.affiliation: ITE, Bush Estate, Penicuik, Midlothian EH26 0QB, U.K.
authors.forename: M. B.
authors.initials: MB
authors.lastname: Murray
authors.forename: R. I.
authors.initials: RI
authors.lastname: Smith
authors.forename: A.
authors.initials: A
authors.lastname: Friend
authors.forename: P. G.
authors.initials: PG
authors.lastname: Jarvis