Effect of elevated CO2 and varying nutrient application rates on physiology and biomass accumulation of Sitka spruce (Picea sitchensis)

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 mol mol(-1)) or elevated (700 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).