Steady‐state nutrition and growth responses of Betula pendula to different relative supply rates of copper

Abstract

In a series of experiments on the growth and nutrition of copper‐limited birch (Betula pendula Roth) plants, growth was controlled by the relative addition rate of copper, RCu (d–1). This was 0·05, 0·10, 0·15 or 0·20 d–1 with free access to all other nutrients. An additional treatment provided free access to all nutrients. The pH in the nutrient solution was ≈ 4·5 and conductivity was 100 μS cm–1. At steady‐state growth, there was a linear relationship between the relative growth rate, RG, and RCu. The [Cu] of the plants ranged from 2·4 to 2·7 μg g–1 dry mass (DM) in all treatments with limiting RCu and was ≈ 28 μg g–1 in the free access treatment. The plants showed specific copper deficiency symptoms at limitation. Total non‐structural carbohydrate concentrations and the fraction of plant DM partitioned to roots was much less at copper limitation than at free access. The uptake rate of copper per unit root growth rate, dCu/dWr (μmol g–1 root DM) was unaffected by the copper supply. Low rates of plant growth at copper limitation were associated with high values of specific leaf area (SLA; 47 m2 kg–1) and leaf area ratio (LAR; 28 m2 kg–1 plant DM) but lower values of net assimilation rate (NAR; 2·5 kg m–2 leaf DM d–1) than were found at free access, 28 m2 kg–1 (SLA), 17 m2 kg–1 DM (LAR) and 14 kg m–2 leaf DM d–1 (NAR), respectively. It is not obvious from the present data how the growth response can help alleviate copper limitation in the field.