2.4 Root and foliar chemical analysis
The oven-dried leaves and roots were analyzed for N and P concentrations on composite sampling by the central point. N concentration was measured by the elemental analyzer (vario EL III, CHNOS Elemental Analyzer, Elementar Analysensysteme GmbH, Germany). P concentration was measured by ICP (ICAP6300). The ratios of N to P in leaves and roots were calculated.