Chn 200

Leaves were freeze‐dried, then ground to a powder. Foliar N was measured by a Leco CHN‐200 auto‐analyser (Leco Corp., St Joseph, MI) and P by the molybdenum‐blue colorimetric method (Grimshaw et al. 1989) after digestion by the sulfuric‐peroxide procedure (Grimshaw 1987). N and P were expressed per unit dry mass (N_mass, P_mass) and per unit mass of water (N_water, P_water), the latter allowing an estimate of protoplasmic concentration. “Total phenolics” were extracted in acetone (Cork and Krockenberger 1991) and assayed by the Prussian blue method (Price and Butler 1977) with concentration expressed as GAE (gallic acid equivalents) per leaf dry mass. Tannin activity was estimated as the amount of bovine serum albumen bound by the phenolic extract (Asquith and Butler 1985), expressed as mass of protein precipitated per unit leaf dry mass. Total cell wall, measured as NDF (neutral detergent fiber), and ADL (acid detergent lignin) were quantified following Van Soest et al. (1991). The Loveless sclerophylly index (SI) was calculated as NDF per unit protein (N_mass × 6.25).

The height of the harvested poplar plants was measured and phytopathological symptoms of each specimen were recorded. The plants were then separated into root and shoots. The plant material was washed, dried at 40°C and weighed. Finally, the leaves (with petiole) were also separated and weighed, and the roots, leaves and stems were ground and analyzed separately.
Plant material (about 500 mg) was digested in acid (HNO₃ 65%: ratio 20:1) in a PerkinElmer® SPB 50–48 block digester, with progressive heating up to 90°C. The concentration of P, K, Ca, Mg, Co, Fe, Mn, Zn, Cu, Ni, Pb and Cd was determined in the digestate obtained by inductively coupled plasma optical emission spectrometry (ICP-OES, model Vista-PRO). Total carbon and nitrogen were determined by combustion of the ground samples in a LECO CHN-200.