2.4 Plant tissue nutrient analysis
Dried leaves were milled (Retsch MM 400, Retsch GmbH and Co. KG, Haan, Germany) and passed through a 1 mm sieve. Leaf P concentration was measured using the molybdate/stannous chloride method (John, 1970; Bao, 2000) after digesting a ~0.1 g sample in H2SO4-H2O2. Leaf N and carbon concentrations were determined using an elemental analyzer NA1500 (Carlo Erba, Thermo Fisher Scientific, Waltham, MA, USA) and leaf K concentration was determined by the atomic absorption method (Bao, 2000). All concentrations were calculated on a dry mass basis.