Elevated ozone prevents acquisition of available nitrogen due to smaller root surface area in poplar

Aims Poplars are ecologically and economically important tree genus, sensitive to ozone (O-3). This study aimed to investigate modifying effects of elevated O-3 on poplar root response to nutrient addition. Methods In pot experiment, young trees of an O-3-sensitive Oxford poplar clone (Populus maximoviczii Henry x berolinensis Dippel) growing in soil with three levels of P (0, 40 and 80 kg ha(-1)) and two levels of N (0 and 80 kg ha(-1)) were exposed to three levels of O-3 (ambient - AA, 1.5 x AA, 2.0 x AA) at a free air exposure facility. After one growing season, root biomass, fine root (<2 mm) nutrient concentrations and ratios, and fine root morphology were assessed. Results Nitrogen addition resulted in an up to +100.5% increase in coarse and fine root biomass under AA, and only up to +46.3% increase under 2.0 x AA. Elevated O-3 and P addition had a positive effect, while N had a negative effect on P concentrations in fine roots. Nitrogen limitation for root growth expressed as a N:P ratio was more pronounced at elevated O-3. Nitrogen addition increased root surface area per soil volume by +78.3% at AA and only by +9.9% at 2.0 x AA. Conclusions Smaller root surface area per soil volume at elevated O-3 prevented acquisition of available N, rendering N fertilization of young poplar plantations in such conditions economically and environmentally questionable.