DIURNAL AND SPATIAL VARIATIONS OF NO3- UP TAKE IN PEACH-TREES

NO3- uptake was studied in natural climatic conditions on 3-to-5-year- old non-bearing peach trees (Prunus persica (L Batsch) cv 'Maycrest', grafted on Prunus 'Damas 1869'). Each root system was split in half an d put into two nutrient solution containers. The whole root system was maintained at 1 or 5 mM of NO3- by suitable additions of KNO3. Hourly NO3- uptake rates of each root subsystem were measured on 14 trees du ring 1992, 1993 and 1994. The NO3- uptake rate was subject to large di urnal variations, the maximal rate occurring during the afternoon. The NO3- uptake rate remained high during the night phase, accounting for up to 30 to 45% of the total daily NO3- uptake. About half of the tre es presented a heterogeneous uptake capacity within their root system despite a homogeneous nitrogen supply. The expression of a heterogeneo us capacity of NO3- root uptake was observed during several days. This was therefore not a punctual phenomenon. The existence of diurnal var iations of the NO3- uptake in woody species is discussed, as well as p ossible origins of the heterogeneity of the observed capacity of NO3- uptake.