Abstract: Nitrogen deposition has increased rapidly in eastern China, which can affect the stoichiometric characteristics of plants. However, the effects of N addition on the nitrogen (N) and phosphorous (P) allocation strategies for various plant life forms (e.g. trees, shrubs and herbs) have rarely been studied. In this study, we evaluated the effects of N addition on N and P stoichiometry and their scaling exponents in the leaves and fine roots of the different life form groups. N and P concentrations in the leaves of shrubs and herbs increased under N addition treatments, whereas tree leaves exhibited a more stable response. In contrast, N addition had no significant effect on N and P concentrations in the fine roots of the three plant life forms. N addition enhanced the allocation of more N and P to the leaves than to the fine roots in all three life forms. Furthermore, the N-P allocation scaling exponents of the leaves and fine roots of the trees were equal to 1.0, indicating an isometric pattern. In contrast, the N-P allocation scaling exponents of shrubs and herbs were less than 1.0, indicating an allometric pattern. Although high N availability promoted shrubs and herbs to distribute P to leaves at a higher proportion than N, only slight effects were detected in tree leaves. These changes in N-P allocation patterns indicate that life forms and N addition levels work together to modulate plants allocation strategies. These results suggest the importance of life form categories when evaluating N-P allocation strategies in forest plants.

Key words: nitrogen addition, natural Pinus tabulaeformis forest, fine roots, leaves, N and P stoichiometry, N-P allocation scaling exponent