Variations nycthémérales et spatiales de la capacité d'absorption de NO 3 - chez le pêcher

Abstract

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 and 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 during 1992, 1993 and 1994. The NO3- uptake rate was subject to large diurnal 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 trees presented a heterogeneous uptake capacity within their root system despite a homogeneous nitrogen supply. The expression of a heterogeneous capacity of NO3- root uptake was observed during several days. This was therefore not a punctual phenomenon. The existence of diurnal variations of the NO3- uptake in woody species is discussed, as well as possible origins of the heterogeneity of the observed capacity of NO3- uptake.