The effects of stand age on leaf N:P cannot be neglected: A global synthesis

Abstract Background Plant stoichiometry displayed flexible over age sequences in previous studies, but effect of stand age on stoichiometry showed large uncertainties for different plantations at the global scale. In this study, we want to obtain the general pattern of leaf N:P ratio for global plantations across age gradients through the compilation and analysis of published data from the individual studies. Results Stand age, together with life forms, and climatic variables strongly affected leaf N:P ratio. This result indicates that the stand age is an indispensable underlying mechanism on stoichiometry. Leaf N:P ratio increased with stand age for all plantations pooled together, revealing the existence of the general pattern in leaf stoichiometry for plantations across age gradients. Leaf N:P ratio exhibited no trend in evergreen trees, but an increasing trend was obtained in deciduous trees along age sequences. Meanwhile, leaf N:P ratio rose with stand age for plantations in humid subtropical regions, but it did not vary in dry temperate regions. Conclusions Our results reveal the effects of age on tree stoichiometry cannot be neglected. These age-related patterns of stoichiometry verified that global plantations changed from N limitation to P limitation with increasing stand age, particularly for deciduous plantations and in plantations in humid regions. The study highlights the importance of considering stand age when exploring nutrient patterns in plantations, which contributes to improving the plant stoichiometry theory and offers a guidance for the nutrient management of plantations at regional to global scales.