Nutrient Ratios in the Leaves and Stems of Eucalyptus and Corymbia Species Under High Soil Phosphate

Eucalypts are a diverse group of Myrtaceae native to Australia and adapted to a wide range of edaphoclimatic conditions, including variation in phosphorus (P) soil availability. While Corymbia and Eucalyptus species have evolved in P-poor soils, they still respond to P additions. Nutrient ratios have been used to study nutritional imbalances in plants, as they relate to nutrient homeostasis within cells and ultimately productivity. This study investigated the effects of providing adequate (normal) and high doses of phosphorus (P) on nutrient ratios in leaves and stems of Eucalyptus and Corymbia species. High soil P may happen due to high natural soil concentration and over-fertilization. These species were pre-selected from a 22-eucalypt species screening, based on their responses—either positive, negative, or neutral—to increased dry mass at high soil P compared to normal P. Two species, Corymbia citriodora and C. maculata, which showed increased dry mass under high P levels, exhibited enhanced shoot growth and improvements in parameters related to photosystem efficiency. Except for Zn, which has an antagonistic relationship with P, the concentrations of other nutrients known to exhibit either antagonism or synergism with P were not significantly altered in the leaves and stems. As a result, there were no notable changes in the ratios with high P data compared to those with normal P data. Ratios calculated among K, Ca, Mg, Fe, and Mn data also remained unchanged. However, a principal component analysis, which was performed with all nutrient ratios, effectively separated the normal P and high P treatments and distinguished between species belonging to the genera Corymbia and Eucalyptus. The validity of such nutrient ratios is discussed, and it is suggested that they may not be applicable in studies involving high nutrient doses, which may also be true for other nutrients. Additionally, using ratios under unbalanced field fertilization may lead to an incorrect nutritional interpretation.