Dynamics of nitrogen and phosphorus partition in four olive tree cultivars during bud differentiation

Variations of nitrogen and phosphorus levels in reproductive shoots and their leaves of self-rooting olive (Olea europaea) cultivars 'Amfissis' (A), 'Kalamon' (K), 'Manzanillo' (M), and 'Chalkidikis' (C) were monitored from the end of harvest until the emergence of the inflorescences. This 90-days period was divided into three sub-periods: before (pre-BD), during (BD), and after (post-BD) bud differentiation. The nitrogen (N)-content in leaves of the reproductive shoots varied between 10-20 mg g(-1) and among cultivars the order of decreasing concentration levels was C > K > A > M. The N-content in reproductive shoots varied between 6-14 mg g(-1) (K > A > C > M). Patterns of time-course variations are presented. Partitioning of N between leaves and shoots (N(L):N(S)) varied with time, with a ratio between 1.5-2. The fluctuations in the N(L):N(S) ratio over the 90 days showed two distinct phases: during pre-BD either increased ('Amfissis' and 'Chalkidikis') or remained relatively constant ('Kalamon' and 'Manzanillo'), while during BD and post-BD decreased in all cultivars. The order of decreasing N(L):N(S) ratio among cultivars was K > C > M > A. Phosphorus (P) content in leaves of the reproductive shoots varied between 0.1-2.5 mg g(-1), (A > C > K > M). Phosphorus content in reproductive shoots varied between 0.2-1.6 mg g(-1), with the highest levels in 'Amfissis' compared to the other cultivars. Patterns of P partitioning between leaves and shoots were similar in all cultivars. The P(L):P(S) ratio varied between 0.9-2 (A > C > K > M). The N:P ratio varied between 5:1-20:1 in reproductive shoots and 10:1-35:1 in their leaves, increasing over the examined period. The increase rate of the N:P ratio varied between the three sub-periods, the lowest rate being during BD. The pattern of changes in the N:P ratio was similar in both leaves and shoots and an increase of N:P ratio in leaves was highly correlated with the corresponding increase of N:P in shoots.