森林土壌の窒素ガス損失と温暖化の関係を定量化（New Study Quantifies Warming Response of Soil Gaseous Nitrogen Losses in Temperate Forest）

2025-11-27 中国科学院（CAS）

＜関連情報＞

• https://english.cas.cn/newsroom/research_news/earth/202511/t20251127_1134064.shtml
• https://www.pnas.org/doi/10.1073/pnas.2513401122

気候温暖化により温帯林の土壌ガス窒素損失が減少 Climate warming reduces soil gaseous nitrogen losses in a temperate forest

Kai Huang, Di Wu, Dongwei Liu, +19 , and Yunting Fang
Proceedings of the National Academy of Sciences  Published:November 24, 2025
DOI:https://doi.org/10.1073/pnas.2513401122

Significance

Climate models project that under future warming scenarios, ecosystems will lose nitrogen (N) because of accelerated cycling and increased gaseous N losses. However, these projections are predominantly derived from laboratory experiments that may not accurately represent field conditions. Opposite to these projections, our 6-y field warming experiment revealed soil N emissions were suppressed under warming, an observation shared across other warming experiments receiving less than 1,000 mm of yearly precipitation. This reduction in soil N emissions was mechanistically linked to lower microbial processing of N as soil moisture decreased under warming. Our results underscore how warming-induced losses in soil moisture can offset expected temperature effects on soil N cycling as the planet warms.

Abstract

Global warming is projected to accelerate ecosystem nitrogen (N) loss via gaseous pathways, thereby decreasing N availability, a critical nutrient for primary productivity and carbon sequestration. However, the models forecasting this ecosystem N loss are based on laboratory experiments that are inherently uncertain and have had few in situ validations. Over 6 y, we measured ~200,000 soil nitric oxide (NO; an air pollutant) and nitrous oxide (N₂O; a powerful greenhouse gas) fluxes and used an upscaling approach to estimate N₂ fluxes after warming a temperate forest by 2 °C. Against thermodynamic theoretical predictions, warming unequivocally lowered emissions of NO by 19% and of N₂O by 16%. These lower gaseous N losses were not explained by complete reduction of NO and N₂O to N₂, leaching, nor plant uptake, but rather by the warming-induced drying of soils that constrained microbial activity, consistent with other warming experiments where precipitation was less than 1,000 mm y⁻¹. Our findings challenge ecosystem model assumptions where warming, alone, accelerates N emissions and underscores how warming-induced losses in soil moisture and shortened freeze-thaw periods can offset temperature effects. Our data underscore the need for explicit consideration of in situ soil moisture when predicting changes on the terrestrial N cycle as the planet warms.