Diagnostic tools for nutrition status in Eucalyptus globulus: changes in leaves, xylem and phloem sap compounds according to N-, P-, and K-withdrawal or salt application

Abstract

The results presented here demonstrate the capacity for phloem sap as a diagnostic tool for monitoring the nutritional status of plants and highlight the processes of remobilisation and source–sink dynamics. It is essential to develop methods that accurately reflect plant nutritional status for growth. In a greenhouse experiment with potted eucalyptus, we studied the effects of withdrawing single macronutrients N, P, or K, or salt application on the abundance of components in phloem, xylem and leaves to identify and refine methods to rapidly and effectively assess the nutrient status of Eucalyptus globulus trees. Clear effects on growth (and photosynthesis) were found for “−N” treatment and NaCl application. Effects of nutrient withdrawal were detected indicating our methodologies are useful for nutrient availabilities below the threshold of growth responses. While “−P” resulted in significantly lower P in xylem sap, the corresponding effect for “−K” on K in xylem sap was not found, although Ca and Na increased. Salt application increased Na in xylem sap sixfold. In leaf material “−N” reduced N. Surprisingly, “+NaCl”, “−P” and “−K” did not change the corresponding elements in leaves. Additionally, “−P”-treatment had the tendency to affect C-, N-, K- and particularly P-increment (n.s.). In phloem sap, “+NaCl” resulted in several effects, most prominently doubling Na concentration. Importantly, “−N” increased amino acids in phloem sap (n.s.). Statistically significant relationships between concentrations in leaves and phloem sap were found for δ13C and amino acids. Within the results obtained from phloem sap, sugars and bivalent cations (Ca and Mg) are correlated with that obtained from the leaves as well as Na and P. The role and comparative advantages of phloem sap as a diagnostic tool for nutritional status are discussed.