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Foliar macronutrient (N, P, K, Ca, Mg) concentration, content, retranslocation, internal balance, and variation with crown location and foliage age were quantified in 11-year-old loblolly pine (Pinustaeda L.) trees grown in two soil nitrogen regimes. Concentrations of N, P, and K decreased with foliage age, while the concentration of Ca increased. Nutrient content of new foliage increased with the elongation of foliage. Estimates of retranslocation were 75%, 73%, 83%, 28%, and less than 5% for N, P, K, Mg, and Ca, respectively. Increases in nutrient content of new foliage were associated with decreases in nutrient content of old foliage, suggesting transfer of nutrients to developing foliage. Concentrations and contents of P and K were greatest in the upper crown. Differences in N concentration among crown locations were small, although N content increased in the upper portion of the crown. Calcium and Mg concentrations decreased with crown height, but their contents generally did not differ among crown locations. Nitrogen fertilization increased N and Ca concentrations and fascicle weight, decreased P and Mg concentrations, and had no significant effect on K concentration. For the purposes of determining nutrient deficiency, our results suggest that foliar samples should be collected from 1-year-old foliage in the midcrown position during the rapid growth period for new shoots.
Zhang et al. (Thu,) studied this question.