PRE:NRE as a Sensitive Indicator of Phosphorus Limitation in Tropical Trees: A Comparative Analysis with Leaf N:P

The results obtained from fast-growing, slow-growing, and N-fixing trees indicate a widespread trend of exacerbated plant phosphorus (P) limitation with increasing tree age in tropical forests. However, leaf nitrogen to phosphorus ratio (N:P) remained unchanged with tree age, suggesting that leaf P resorption efficiency to nutrient resorption efficiency ratio (PRE:NRE) may be a more sensitive indicator than leaf N:P in reflecting changes in plant P limitation. Indeed, previous studies have suggested that leaf N:P ratio may not be as suitable as PRE:NRE for indicating plant P cycling (Gsewell & Koerselman, 2002; Du et al., 2020). The leaf N:P ratio might not accurately reflect P limitations when leaf P content is insufficient (Yan et al., 2017), which can hinder the estimation of plant P limitation levels. In some studies, discrepancies have been observed between nutrient limitation types estimated using leaf N:P and growth responses observed under N and P additions. Moreover, these discrepancies tend to increase as leaf nutrient concentrations decrease. Conversely, PRE:NRE has been found to be more responsive to variations in external soil P content (Shane & Lambers, 2006), rendering it a robust indicator of P limitation levels.