RELATIONSHIPS BETWEEN NITROGEN SUPPLY AND DIFFERENT PHOSPHORUS AND CALCIUM FRACTIONS IN LEAVES OF TOMATO AND CUCUMBER PLANTS

Tomato and cucumber plants were grown in a greenhouse with different N treatments (N1: 7.5; N2: 10; N3: 20; N4: 30 g/m2). Leaves were sampled every two weeks throughout the period of maximum fruit production to determine the different P fractions (inorganic P, organic P, lipidic P, RNA P, DNA P, and proteic P) and Ca fractions (soluble Ca, bound Ca, inorganic insoluble Ca, and organic insoluble Ca), obtained by extraction with different solvents. Inorganic and organic P were the largest fractions, representing 70% of total P in tomato (vs 10% RNA P; 8% of lipidic P; 7% of DNA P, and 5% of proteic P) and 55% in cucumber (vs. 15% of RNA P; 13% of lipidic P; 10% of DNA P, and 7% of proteic P). The highest concentration of lipid P was found with treatment N2 in both crop species. The organic insoluble Ca fractions together with the inorganic insoluble fraction made up 50% (tomato) and 80% (cucumber) of total Ca. Relationships between P and Ca fractions and macro-micronutrients were also studied. A positive correlation was found between Ca and Mn, and between Zn and Cu in tomato; whereas in cucumber, N, S, and Fe were inversely proportional to the concentration of inorganic P. The relationship between soluble P and total nutrients was similar to that between inorganic P and total nutrients in both species. Positive correlations were found between total Fe and soluble Ca and organic insoluble Ca in cucumber; bound Ca and Fe were highly correlated in tomato.