Cláudia Neto

ASSESSING THE NITROGEN NUTRITIONAL STATUS OF YOUNG NON-BEARING ‘ROCHA’ PEAR TREES GROWN IN A MEDITERRANEAN REGION BY USING A CHLOROPHYLL METER

To find an alternative tool to chemical analysis for assessing the nitrogen (N) nutritional status, the SPAD-Minolta-502 portable chlorophyll meter was tested in one- to three-years-old ‘Rocha’ pear trees fertilized with 0, 10, 20 and 40 kg N ha−1 year−1. SPAD readings in the third and fourth fully expanded leaves were as responsive to N fertilization as leaves sampled for foliar chemical analysis (medium third of one-year-old shoots), but individual leaves showed heterogeneous chlorophyll patterns. SPAD readings in leaves sampled at 60 and 110 days after full bloom (DAFB) related linearly with leaf N concentration but significant relationships could also be obtained later. Assuming an optimum leaf N concentration of ≥20 g kg−1 dry weight, SPAD readings ≥33 in leaves sampled at 60–110 DAFB corresponded to a good nutritional N status of young pear trees, making this diagnostic technique more practical, non-destructive and inexpensive, compared with chemical leaf analysis.

PREFERENTIAL AMMONIUM UPTAKE DURING GROWTH CYCLE AND IDENTIFICATION OF AMMONIUM TRANSPORTER GENES IN YOUNG PEAR TREES

Five sequences showing homology with gene coding for ammonium (NH+ 4 ) transporters of the subfamily AMT1 (AMT1 genes) involved in the nitrogen (N) uptake process were identified in 2-year-old ‘Rocha’ pear/BA29 through reverse transcription polymerase chain reaction (RT-PCR) analysis. Multiple AMT1 genes were expressed in each phase of the growth cycle and results suggest that ammonium uptake is conducted by several transporters expressed simultaneously. Trees grown in pots received 2 g N tree−1, at dates corresponding to active shoot vegetative growth, shoot growth cessation and beginning of leaf fall, in the form of either ammonium nitrate (NH 15 4 NO3) or 15NH4NO3. N was preferentially absorbed as NH+ 4 at all sampling dates, ranging from 62% to 66% of the total labelled N recovered in the trees. The fertilizer N use efficiency was also higher for ammonium treatment than for nitrate treatment at all sampling dates. N uptake rate and preferential NH+ 4-N absorption were not altered in response to root pruning and gibberellic acid (GA3) treatments.