Data from: Patterns and drivers of atmospheric nitrogen deposition retention in global forests

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 15NH4+ than 15NO3−,
primarily due to the stronger capacity of the organic soil layer to retain
15NH4+. 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.

森林是陆地生态系统中最大的碳汇（carbon sink）。氮（N）沉降（nitrogen deposition）对该碳汇的影响取决于外源氮输入的归趋。然而，不同森林组分（compartments）中的氮固持模式与驱动因子仍尚不明确。本研究整合了全球森林15N示踪试验的408组观测数据，以揭示植物与土壤库中15N固持的变异规律及其潜在机制。结果显示，全球森林生态系统总15N固持率均值为63.04 ± 1.23%，其中土壤库为主要氮汇（占比45.76 ± 1.29%）。植物吸收了17.28 ± 0.83%的15N，其中更多分配至叶片（5.83 ± 0.63%）与根系（5.84 ± 0.44%）。在亚热带与热带森林中，15N主要被植物与矿质土壤（mineral soils）吸收，而温带森林的有机土层（organic soil layer）固持的15N更多。此外，森林对15NH4+的固持量高于15NO3−，这主要源于有机土层对15NH4+更强的固持能力。生态系统各组分的15N固持机制存在差异，生态系统总15N固持率受氮沉降调控。植物15N固持受植被与微生物的养分需求影响，而土壤15N固持则受气候因子（climate factors）与土壤养分供给调控。综上，本研究强调了气候与养分供需在调控森林氮固持中的重要性，并为进一步探究氮沉降对森林碳固存（carbon sequestration）的影响提供了数据支撑。