Autumnal N storage determines the spring growth, N uptake and N internal cycling of young peach trees

Although N storage determines early spring growth in trees, the usefulness of autumn N supply remains unclear as N uptake decreases in autumn, but could be restored earlier in spring to compensate for low N cycling. We intended here to evaluate the effects of autumn N supply on N uptake, storage and cycling, and spring growth. Four levels of N fertilisation were applied to 1-year-old peach trees, between the end of shoot growth and leaf fall. In spring, N supply was N-15 labelled. Organ dry weights and concentrations of N-14, N-15, starch and soluble sugars were evaluated after the first growth flush. Bud development had previously been described in the same trees by Jordan et al. (Trees-Struct Func 23:235-245, 2009). Fertilisation promoted autumn N uptake, spring N uptake and growth up to a threshold level, since no differences were evidenced between the three highest N treatments. The variability in tree N-14 contents was related to the number of phytomers per tree in autumn, i.e. to tree size. In spring, the depletion of the perennial structures was independent of treatment, indicating a complete mobilisation of the N stores. Spring growth was related to the amounts of cycling N, and spring N uptake was in turn proportioned to shoot and fruit growth. The lower N uptake of the N limited trees was not due to a C shortage since these trees displayed the highest starch concentrations. We conclude that a moderate autumn fertilisation improved spring growth and fruit production (Jordan et al. in Trees-Struct Func 23:235-245, 2009) and that a deficit of N storage could not be compensated for by an increase in spring N uptake.