Abstract：
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 15N tracer experiments to reveal the variation and underlying mechanisms of 15N retention in plants and soils. The results showed that the average total ecosystem 15N 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 15N, with more allocated to leaves (5.83 ± 0.63%) and roots (5.84 ± 0.44%). In subtropical and tropical forests, 15N was mainly absorbed by plants and mineral soils, while the organic soil layer in temperate forests retained more 15N. Additionally, forests retained more N 15 H 4 + $$ {}^{15}\\mathrm{N}{\\mathrm{H}}_4^{+} $$ than N 15 O 3 - $$ {}^{15}\\mathrm{N}{\\mathrm{O}}_3^{-} $$ , primarily due to the stronger capacity of the organic soil layer to retain N 15 H 4 + $$ {}^{15}\\mathrm{N}{\\mathrm{H}}_4^{+} $$ . The mechanisms of 15N retention varied among ecosystem compartments, with total ecosystem 15N retention affected by N deposition. Plant 15N retention was influenced by vegetative and microbial nutrient demands, while soil 15N 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.
摘要：
森林是陆地生态系统中最大的碳汇，氮（N）沉积对该碳汇的影响取决于外部N输入的命运。然而,不同林区氮素滞留的模式和驱动因素仍然难以捉摸。在这项研究中,我们从全球森林15N示踪实验中合成了408个观测值，以揭示15N在植物和土壤中滞留的变化和潜在机制。结果表明,全球森林生态系统15N总滞留量平均为63.04±1.23%,土壤池是主要的氮汇(45.76±1.29%)。植物吸收了17.28±0.83%的15N，更多的分配给叶(5.83±0.63%)和根(5.84±0.44%)。在亚热带和热带森林中，15N主要被植物和矿物土壤吸收，而温带森林的有机土壤层保留了更多的15N。此外,森林保留的N15H4+$${}^{15}\\mathrm{N}{\\mathrm{N}{\\mathrm{H}}_4^{}$$比N15O3-$$${}^{15}\\mathrm{N}{\\\mathrm{O}}}_3^{-$，主要是由于有机土壤层保留N15H4+$${}^{15}\\mathrm{N}{\\mathrm{H}}_4^{+}$的能力更强。15N滞留的机制在生态系统隔室之间有所不同，生态系统总保留15N受N沉积影响。植物15N的保留受营养和微生物营养需求的影响，而土壤15N的保留受气候因素和土壤养分供应的调节。总的来说,这项研究强调了气候和养分供需在调节森林氮素保留中的重要性，并提供数据进一步探讨氮沉降对森林碳固存的影响。
