Diurnal and seasonal changes in nitrate reductase activity and nitrogen content of grapevines: Effect of canopy management

Abstract

Diurnal and seasonal in viva nitrate reductase activity (NRA) and nitrogen (N) contents in leaves, berries, and roots and the effect of canopy management were investigated in Vitis vinifera L. cv. Cabernet Sauvignon/99 Richter grapevines. Peak NRA in leaves occurred from mid-morning to mid-day. Young leaves had almost the same NRA as mature leaves before berries reached pea size stage, but subsequent to that displayed higher activity. Leaf NRA increased during the post-harvest period. Differences in NRA patterns between leaves conformed with classic source:sink behaviour. Canopy management stimulated nitrate reduction in basal source leaves, most likely through its favourable effect on canopy Light microclimate and photosynthetic activity. The NRA in the berries generally increased towards ripeness; treatments affected NRA only slightly. Peak root NRA corresponded to seasonal root growth patterns. In contrast to leaves and berries, NRA in roots increased from the morning to the afternoon. Effect of treatment on root NRA was minor. Leaf and berry N contents declined during the season, whereas reasonably stable concentrations were maintained in the roots. An involvement of NR in the N assimilation and in the energy supply pathways of the grapevine was substantiated. NRA proved to be a good indicator of fluctuations in N assimilation during growth, suggesting its determination to be instrumental in defining the N status and fertilization needs of the grapevine.