Increasing phosphorus limitation with tree age in tropical forests

The growth of tropical plants is commonly limited by the availability of phosphorus (P). Nevertheless, it remains uncertain whether this P limitation changes with the age of plants. Here we explored the effect of tree age on plant P limitation in a tropical forest by examining three functional plant groups: fast-growing, slow-growing, and nitrogen (N)-fixing trees. Leaf N and P resorption efficiency (NRE and PRE) were measured, and the PRE:NRE was employed to indicate the intensity of P limitation. Results showed no significant change in NRE across all plant types along with tree age. However, PRE and PRE:NRE significantly increased with tree age across all plant types, indicating a widespread increase in plant P limitation with tree age in tropical forests. Furthermore, the age-intensified P limitation in slow-growing and N-fixing trees was significantly higher than fast-growing trees. Overall, our results underscore the non-negligible influence of tree age on plant P limitation. These findings are vital for improving terrestrial biogeochemical model predictions as previous models have drastically overlooked the impact of tree age.