Leaf N and P resorption and stoichiometry characteristics of main tree species in the plain afforestation area of Beijing

  Objective  Based on the analysis of leaf nitrogen (N) and phosphorus (P) reabsorption and ecological stoichiometry characteristics of the main tree species in the plain afforestation area of Beijing, the ecological adaptation and nutrient utilization mechanism of different tree species were investigated.

  Method  Six tree species (Robinia pseudoacacia, Ailanthus altissima, Salix matsudana, Populus tomentosa, Fraxinus chinensis and Pinus tabuliformis) were taken as the research objects, the contents of N and P in fresh leaves and leaf litter were determined, the N and P reabsorption efficiency was calculated and also their relationships with leaf and soil nutrient indices were analyzed.

  Result  The leaf N content of Robinia pseudoacacia and P content of Salix matsudana were the highest; the leaf N∶P ratio of Fraxinus chinensis was significantly higher than that of other tree species (P < 0.05), while the leaf N∶P ratio of Populus tomentosa was the lowest. There was no significant difference among Robinia pseudoacacia, Ailanthus altissima, Salix matsudana and Pinus tabuliformis. The contents of N and P, and N∶P ratio in leaf litter of different tree species were significantly different from fresh leaves. The N reabsorption of Robinia pseudoacacia leaves and the P reabsorption of Ailanthus altissima leaves were significantly higher than those of other tree species. For most tree species, there was a significant negative correlation between nutrient content of leaf litter and N or P resorption.

  Conclusion  The study shows that the growth of Robinia pseudoacacia, Salix matsudana, Fraxinus chinensis and Pinus tabuliformis was restricted by P content, the growth of Ailanthus altissima and Populus tomentosa was restricted by N content. Therefore, the main afforestation tree species can adapt to nutrient restriction environment through leaf N and P resorption. These findings suggest that measures such as forest structure adjustment, leaf litter returning to woodland, artificial supplementary planting and fertilization should be taken to improve the nutrient limitation in plain forests.