Biological Nitrogen Fixation in Tropical Forest Ecosystems

Biological nitrogen fixation (BNF) underpins the fertility and resilience of tropical forests by converting atmospheric N₂ into plant-available forms. In these ecosystems, both symbiotic associations with leguminous trees and free-living microbial communities drive new nitrogen inputs. Symbiotic fixers often dominate early successional stages, enhancing nitrogen pools and accelerating carbon accumulation, while asymbiotic bacteria and archaea contribute to background nitrogen supply throughout the forest floor. The dynamics of BNF are governed by interactions among nutrient availability—particularly phosphorus and molybdenum—soil characteristics, and forest age. Tropical forests exhibit high species diversity of nitrogen-fixing trees, each with distinct fixation strategies and responses to nutrient status. These fixation processes play a pivotal role in maintaining productivity, supporting the global carbon sink, and influencing feedbacks in climate models. Understanding the biogeochemical controls and ecological consequences of BNF informs reforestation efforts, carbon sequestration strategies and the management of nutrient limitations under changing environmental conditions.

Research from Nature Portfolio

Recent studies have demonstrated that symbiotic dinitrogen fixation substantially enhances carbon sequestration across tropical successional gradients. Field observations combined with individual-tree models reveal that nitrogen-fixing trees double early-successional carbon accumulation and boost mature forest carbon stocks by about ten per cent through both direct growth stimulation and altered competition among non-fixers. In the Atlantic Forest of Brazil, measurements of nitrogen fluxes across a 20–50-year chronosequence indicate that nitrogen cycling stabilises rapidly post-disturbance, with fixation rates remaining consistent across stand ages. Complementary work in legume-rich Trinidadian forests shows that symbiotic fixation alone meets most above-ground nitrogen demands, supporting sustained biomass gains through fertilisation of non-fixing species even after selective harvests. Together, these findings confirm that symbiotic BNF is sufficient to underpin long-term carbon sinks in humid tropical forests.

Biological Nitrogen Fixation in Tropical Forest Ecosystems publication trend

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

Technical terms

Biological nitrogen fixation (BNF): The microbial conversion of atmospheric nitrogen gas (N₂) into ammonia, making nitrogen available for plant uptake.

Symbiotic fixation: Nitrogen fixation carried out by bacteria within root nodules of certain plants, especially legumes, providing mutual benefits.

Asymbiotic fixation: Nitrogen fixation by free-living microbes in soil or litter without direct plant association.

Nitrogenase: The enzyme complex that catalyses the conversion of N₂ to ammonia, requiring molybdenum as a cofactor.

Tropical secondary succession: The natural regeneration of forest vegetation following disturbance, marked by changes in species composition and ecosystem processes.

References

1. Tropical carbon sink accelerated by symbiotic dinitrogen fixation. Nature Communications (2019).
2. Nitrogen cycling during secondary succession in Atlantic Forest of Bahia, Brazil. Scientific Reports (2018).
3. Symbiotic N fixation is sufficient to support net aboveground biomass accumulation in a humid tropical forest. Scientific Reports (2019).
4. Molybdenum and Phosphorus Interact to Constrain Asymbiotic Nitrogen Fixation in Tropical Forests. PLOS ONE (2012).
5. Phosphatase activity and nitrogen fixation reflect species differences, not nutrient trading or nutrient balance, across tropical rainforest trees. Ecology Letters (2018).