Nitrogen Cycling in Terrestrial Ecosystems

Nitrogen shapes terrestrial productivity and ecosystem resilience through a complex network of transformations and transfers. Atmospheric N₂ enters ecosystems via biological fixation by specialised bacteria and archaea, converting inert gas into reactive forms. In soils, organic matter undergoes mineralisation to release ammonium, which is oxidised by nitrifying microorganisms to form nitrate. Plant roots take up ammonium and nitrate, supporting growth and influencing species composition. Excess reactive nitrogen may leach to aquatic systems or be lost as gases through denitrification, which reduces nitrate to N₂O and N₂ under anaerobic conditions. Microbial interactions, mycorrhizal associations and plant–soil feedbacks modulate the balance of these pathways, while climate, soil texture and land use drive spatial and temporal variability. Rising temperatures accelerate enzymatic rates, altering nitrification and denitrification fluxes, whereas changing precipitation patterns influence the mobility and retention of nitrate. Human activities have doubled the global supply of reactive nitrogen, exacerbating eutrophication, biodiversity loss and greenhouse-gas emissions. Conversely, ecosystem restoration and precision fertilisation aim to optimise nitrogen use efficiency and reduce off-site losses. A global synthesis of natural isotope data reveals that temperature more than precipitation or deposition governs plant reliance on soil nitrate, ammonium and organic nitrogen, underscoring the sensitivity of N-cycling to warming climates. In high-latitude permafrost regions, shifts in thaw dynamics intensify nitrogen losses by altering microbial turnover and plant demand, reinforcing nitrogen limitation despite enhanced mineral production. Understanding these interlinked processes is crucial for predicting ecosystem responses to environmental change and for guiding sustainable management across diverse terrestrial biomes.

Research from Nature Portfolio

Global analyses of plant and soil nitrogen isotopes have established that mean annual temperature, rather than precipitation or anthropogenic deposition, dictates the relative uptake of nitrate, ammonium and organic nitrogen by vegetation across biomes. This framework quantifies fractional contributions and demonstrates systematic shifts in plant nitrogen-use patterns along warming gradients.

Studies in alpine permafrost ecosystems reveal that vegetation nitrogen limitation has strengthened over the past decade despite rising nitrogen availability. Combined isotopic observations and biogeochemical modelling attribute this trend to heightened plant demand and increased gaseous nitrogen losses during thaw, indicating that nitrogen scarcity will constrain carbon sequestration in thawing terrains.

Nitrogen Cycling in Terrestrial Ecosystems publication trend

The graph below shows the total number of articles in nitrogen cycling in terrestrial ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Biological fixation: Conversion of atmospheric nitrogen gas into reactive forms by specialised organisms.

Mineralisation: Microbial decomposition of organic matter to release inorganic ammonium.

Nitrification: Microbial oxidation of ammonium to nitrate.

Denitrification: Anaerobic microbial reduction of nitrate to gaseous nitrogen species.

Stable isotope fractionation: Differential partitioning of isotopes during physical or biochemical processes.

Mycorrhizal symbiosis: Mutualistic association between plant roots and fungi that enhances nutrient exchange.

References

1. Global distribution and drivers of relative contributions among soil nitrogen sources to terrestrial plants. Nature Communications (2024).
2. Progressive nitrogen limitation across the Tibetan alpine permafrost region. Nature Communications (2020).
3. Plant–soil interactions alter nitrogen and phosphorus dynamics in an advancing subarctic treeline. Global Change Biology (2024).
4. Herbarium specimens reveal that mycorrhizal type does not mediate declining temperate tree nitrogen status over a century of environmental change. New Phytologist (2023).
5. Comparative C, N, and S cycling along a Californian grassland chronosequence. Geoderma (2023).