Analysis of nutrient use efficiency (NUE) in Eucalyptus pilularis forests

Abstract

Alternative indices to use for nutrient use efficiency (NUE) were analysed for nitrogen, phosphorus, potassium, calcium, magnesium and sulfur, using 17 Eucalyptus pilularis forest sites to test the hypothesis that NUE increases with decreasing nutrient availability. Reported indices represent different measures of nutrient use, including (1) efficiency of acquisition from soil, (2) quantities required for organic matter production, (3) organic matter production related to uptake, (4) ability to internally retranslocate nutrients and (5) physiological requirement of nutrients. Some indices are highly correlated but the highest correlations were according to age. Phosphorus, the main growth-limiting nutrient, on average, produced 6.5 and 10.9 t of organic matter per kilogram of phosphorus required and taken up from soil, respectively. Comparable estimates were made for other nutrients. NUEs of mobile nutrients increased with decreases in nutrient availability and this supported the hypotheses when age was taken into account. The NUEs of one nutrient are not independent of other nutrients. The inverse of foliage nutrient concentration is a valuable low-cost index of nutrient utilisation and correlates with net primary production/nutrient requirement, and is related to age. Resorption of nutrients, comparing new and abscised tissue, was of low value, but abscised-tissue nutrient correlations are related to a lower benchmark and are of value. The use of selected NUE indices for species comparison was discussed.