Influence of foliar nutrients on phenol levels in leaves of Eugenia uniflora

Eugenia uniflora L., Myrtaceae, leaves contain high amounts of phenolic compounds which are responsible for several pharmacological activities. In order to evaluate the phenolics seasonal variation leaves were analysed on a monthly basis during the period of two years for the contents of hydrolysable tannins, total phenols, flavonoids, and nutrients (N, P, K, S, Ca, Mg, Mn, Zn, Cu, and Fe). Results were correlated with climate conditions (rainfall, humidity, and mean temperature) by Principal Component and ClusterAnalysis which allowed four groups to be distinguished with respect to the age of the leaves and the content of some metals. Young leaves were characterised by high levels of Zn and nitrogen whereas old leaves contained high levels of Fe and calcium, and both groups had moderate amounts of phenolics. Adult leaves were divided in two groups and results revealed that while one group had the highest levels of all phenols and lowest amounts of Mn and Cu, the other showed opposite quantities. The Canonical Correlation Analysis confirmed a highly significant negative correlation between phenol contents and Mn and Cu. These facts suggested that flavonoids and tannins production depends of the amounts of foliar nutrients, Cu and Mn in particular, which are cofactors of enzymes involved in phenol degradation and lignin biosynthesis. This knowledge can improve this specie cultivation in order to enhance the phenolic compounds concentration