Season-Dependent Fruit Loading: Effect on Nutrient Homeostasis of Tomato Plants

ABSTRACT Greenhouse tomato plants were grown hydroponically during the period of lower temperatures of winter (LT) versus the period of higher temperatures of summer (HT). In these plants, the effect of season on fruit load was dramatic. In order to study the alterations season introduces to the developmental allocation of nutrients within the various organs, concentrations of total nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) were determined during each season at weekly intervals in the dry mass of leaves and roots and in the extract of upper, middle, and lower parts of the stem. The level of N/P ratio was always higher in the leaves than in the roots, and these differences were more intense during HT. The short-term changes of ratio in the leaves during HT and LT were positively related with the changes in temperature (r = 0.59 and 0.51 for HT and LT, respectively). In contrast, such correlations in the root were negativ...