Moss-associated nitrogen fixation, a previously underappreciated pathway of ecosystem nitrogen supply, plays a critical role in sustaining supporting plant growth in permafrost ecosystems under warming. This finding comes from a new study led by Prof. YANG Yuanhe at the Institute of Botany, Chinese Academy of Sciences (IBCAS).

Published inPNAS on February 18, the study provides in-situ evidence that moss-associated biological nitrogen fixation responds more sensitively to climate warming than conventional soil nitrogen transformation processes. The researchers further elucidate the mechanisms underlying the enhanced response.

Nitrogen availability fundamentally constrains plant productivity in permafrost regions. Whether nitrogen supply can keep pace with rising plant nitrogen demand under warming largely determines the capacity of vegetation to offset carbon release upon permafrost thaw. However, experimental evidence addressing this supply–demand balance has remained limited.

To address this gap, relied on a unique whole-ecosystem warming experiment established in the permafrost region of the Tibetan Plateau, the research team quantified 43 indicators related to plant nitrogen demand, nitrogen-use strategies, and soil nitrogen supply. This comprehensive assessment allowed them to disentangle how nitrogen supply-demand dynamics shift under climate warming scenarios and to identify their key drivers.

Experimental warming significantly increased plant nitrogen demand but did not alter leaf nitrogen resorption efficiency, indicating that plants primarily rely on soil nitrogen uptake to satisfy their elevated requirements under warming. Using ¹⁵N isotope tracing techniques, the researchers found that soil nitrogen transformation remained largely unchanged, whereas moss-associated biological nitrogen fixation significantly increased. Notably, the warming-induced enhancement in moss-associated nitrogen fixation accounted for ~48% of the additional nitrogen required by vegetation. This result highlights the pivotal role of moss-associated nitrogen fixation in sustaining plant growth under climate warming.

Further analyses using quantitative stable isotope probing (qSIP) revealed significant increases in both the richness and nitrogen assimilate capacity of active diazotrophic microorganisms under warming. These microbial changes are closely linked to warming-induced changes in moss functional traits, suggesting a coordinated plant-microbe response.

Collectively, these findings reveal how nitrogen supply and demand are restructured in permafrost ecosystems under climate warming, and provide critical experimental evidence for better understanding carbon-nitrogen interactions in these climate-sensitive regions.