Search

Abstract: To investigate the interactive effects of CO2 concentration ([CO2]) and nitrogen supply on the growth and biomass of boreal trees, white birch seedlings (Betula papyrifera) were grown under ambient (360μmolmol−1) and elevated [CO2] (720μmolmol−1) with five nitrogen supply regimes (10, 80, 150, 220, and 290μmolmol−1) in greenhouses. After 90 days of treatment, seedling height, root-collar diameter, biomass of different organs, leaf N concentration, and specific leaf area (SLA) were measured. Significant interactive effects of [CO2] and N supply were found on height, root-collar diameter, leaf biomass, stem biomass and total biomass, stem mass ratio (SMR), and root mass ratio (RMR), but not on root mass, leaf mass ratio (LMR), leaf to root ratio (LRR), or leaf N concentration. The CO2 elevation generally increased all the growth and biomass parameters and the increases were generally greater at higher levels of N supply or higher leaf N concentration. However, the CO2 elevation significantly reduced SLA (13.4%) and mass-based leaf N concentration but did not affect area-based leaf N concentration. Increases in N supply generally increased the growth and biomass parameters, but the relationships were generally curvilinear. Based on a second order polynomial model, the optimal leaf N concentration was 1.33gm−2 for height growth under ambient [CO2] and 1.52gm−2 under doubled [CO2]; 1.48gm−2 for diameter under ambient [CO2] and 1.64gm−2 under doubled [CO2]; 1.29gm−2 for stem biomass under ambient [CO2] and 1.43gm−2 under doubled [CO2]. The general trend is that the optimal leaf N was higher at doubled than ambient [CO2]. However, [CO2] did not affect the optimal leaf N for leaf and total biomass. The CO2 elevation significantly increased RMR and SMR but decreased LMR and LRR. LMR increased and RMR decreased with the increasing N supply. SMR increased with increase N supply up to 80μmolmol−1 and then leveled off (under elevated [CO2]) or stated to decline (under ambient [CO2]) with further increases in N supply. The results suggest that the CO2 elevation increased biomass accumulation, particularly stem biomass and at higher N supply. The results also suggest that while modest N fertilization will increase seedling growth and biomass accumulation, excessive application of N may not stimulate further growth or even result in growth decline. [Copyright &y& Elsevier]

Abstract: 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 (100ppm N, 44ppm P, 83ppm K and 1/10 the strength of these levels) and two [CO2] levels (360 and 720ppm) 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. [Copyright &y& Elsevier]