Nutrient and [CO2] elevation had synergistic effects on biomass production but not on biomass allocation of white birch seedlings

This study investigated the interactive effects of nutrient supply and [CO2] elevation on the growth and biomass of white birch seedlings (Betula papyrifera Mash.). The seedlings were grown under two nutrient regimes (100 ppm N, 44 ppm P, 83 ppm K and 1/10 the strength of these levels) and two [CO2] levels (360 and 720 ppm) for 3.5 months. The [CO2] elevation had no significant effect on either height (H) or root collar diameter (RCD), but significantly reduced specific leaf area. The high nutrient treatment increased both H and RCD. High nutrient significantly increased total, stem and leaf biomass under both [CO2] treatments but the effect was greater under elevated [CO2], and it increased root biomass only under elevated [CO2], while [CO2] elevation increased total, stem, leaf and root biomass under high nutrient only. The high nutrient increased stem mass ratio (SMR) and decreased root mass ratio (RMR) under both [CO2] while [CO2] elevation reduced SMR under both nutrient treatments. [CO2], nutrient and their interactions had no significant effects on leaf mass ratio, or leaf to root ratio. [CO2] elevation reduced the leaf total N concentration and the effect was greater under low nutrient. [CO2] elevation had no significant effect on leaf phosphorus (P) and potassium (K) concentration while the high nutrient treatment generally increased them.