|Authors: ||M.C. Müller, J.P. Smith, A.C. Clark, B.P. Holzapfel|
|Keywords: ||grapevine, nitrogen, xylem sap, amino acids, nitrate|
The nitrogen (N) uptake is influenced by the amount of water and N applied to a vineyard, influencing considerably the development of the vines.
The timing of N application is also critical for altering vine growth, the N directed to the berries and to the N reserves.
The amount and the proportion of nitrate and glutamine N in the xylem depends on N supply.
The aim of the study was to determine the influence of N and water supply on N uptake and translocation by assessing xylem nitrogenous compounds around veraison.
Three-year-old 'Semillon' and 'Riesling' vines were grown in pots (26 L) that were designed to fit into a large root pressure chamber.
Two levels of N fertiliser (3 and 7 g plant-1) were applied in five monthly applications from the four leaf stage; water supply was adjusted to either 50 or 100% evapotranspiration.
Xylem sap samples were taken at the transpiration rate from a petiole connected to a sample vial two to three weeks before and after veraison.
The collected xylem samples were stored at -80°C and analysed for amino acid and nitrate concentrations by HPLC. Generally, nitrate and amino acid concentrations were higher in the xylem sap before veraison in both cultivars.
The high N treatment resulted in significantly elevated sap N concentration before veraison in 'Semillon'. In contrast xylem sap samples taken after veraison from the high N treatment resulted in slightly lower N levels.
Nitrate levels in 'Riesling' xylem sap increased throughout the collection period. 'Semillon' tended to have higher glutamine levels under low water supply at both sampling dates.
In contrast 'Riesling' showed an opposite trend under water restriction after veraison.
Glutamine levels were slightly reduced of limited watered plants while nitrate concentrations significantly increased.
The lower N xylem sap concentration after veraison suggests that N was translocated to the berries from other vine organs rather than provided by uptake.
The work also indicates that cultivars can respond differently in their N uptake under restricted water supply.
N distribution might vary between grapevine cultivars under low water supply indicated by the different responses of 'Riesling' and 'Semillon'.
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