| 摘 要： |
Forests are the largest carbon sink in terrestrial ecosystems, and the impact of nitrogen (N) deposition on this carbon sink depends on the fate of external N inputs. However, the patterns and driving factors of N retention in different forest compartments remain elusive. In this study, we synthesized 408 observations from global forest N-15 tracer experiments to reveal the variation and underlying mechanisms of N-15 retention in plants and soils. The results showed that the average total ecosystem N-15 retention in global forests was 63.04 +/- 1.23%, with the soil pool being the main N sink (45.76 +/- 1.29%). Plants absorbed 17.28 +/- 0.83% of N-15, with more allocated to leaves (5.83 +/- 0.63%) and roots (5.84 +/- 0.44%). In subtropical and tropical forests, N-15 was mainly absorbed by plants and mineral soils, while the organic soil layer in temperate forests retained more N-15. Additionally, forests retained more (NH4+)-N-15 than (NO3-)-N-15 , primarily due to the stronger capacity of the organic soil layer to retain (NH4+)-N-15. The mechanisms of N-15 retention varied among ecosystem compartments, with total ecosystem N-15 retention affected by N deposition. Plant N-15 retention was influenced by vegetative and microbial nutrient demands, while soil N-15 retention was regulated by climate factors and soil nutrient supply. Overall, this study emphasizes the importance of climate and nutrient supply and demand in regulating forest N retention and provides data to further explore the impacts of N deposition on forest carbon sequestration. |
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