Abstract: Plants need certain proportions between elements for proper growth and functioning. These proportions vary with growth conditions and it has generally been found that with increasing relative growth rates P:N should increase (the growth rate hypothesis). However, the proportions between N and other elements change with growth rates, and how this determines which element is limiting growth is not well studied, but it is possible that limitations of other elements could restrain plant growth more than N. Using results from nine studies with birch plants (Betula pendula) with different limiting elements (N, P, K, S, Mg, Zn, Mn, Fe and Cu) under steady-state growth, I have investigated how the switch, defined as the ideal proportion, between which element is limiting growth varies with relative growth rate. The ideal proportion of element:N increases with increasing relative growth rate for K, P, Zn and Mn but a slight decline for Mg and S. The changes in element:N ratios are strongest at low relative growth rates. The consequences of these results for plant properties under global change are discussed.

Key words: ecological stoichiometry, relative growth rate, Betula pendula, nitrogen, ideal nutrient proportions, stoichiometric plasticity