A roadmap for sampling and scaling biological nitrogen fixation in terrestrial ecosystems

Nitrogen is the primary limiting nutrient in high latitude ecosystems. Biological nitrogen fixation (BNF) by microorganisms associated with cryptogamic covers, such as cyanolichens and bryophytes, is an important source of new reactive nitrogen in pristine, high-latitude ecosystems. BNF is catalyzed by the enzyme nitrogenase, for which three isoforms have been described; the canonical molybdenum (Mo) nitrogenase which requires Mo in its active site and two alternative nitrogenases, the vanadium and iron-only nitrogenases. The low availability of Mo on land has been shown to limit BNF in many ecosystems from the tropical forest to the arctic tundra. Alternative nitrogenases have been suggested as viable alternatives to cope with Mo limitation of BNF, however, field data supporting this long-standing hypothesis have been lacking.Here, we elucidated the contribution of the vanadium nitrogenase to BNF by cyanolichens across a 600 km latitudinal transect in eastern Canadian boreal forests. We report a widespread activity of the vanadium nitrogenase which contributed between 15 to 50% of total BNF rates on all sites. Vanadium nitrogenase contribution to BNF was more robust in the northern part of the transect. Vanadium nitrogenase contribution to BNF also changed during the growing season, with a three-fold increase between the early (May) and late (September) growing season. By including the contribution of the vanadium nitrogenase to BNF, estimates of new N input by cyanolichens increase by up to 30%, a significant change in these low N input ecosystems. Finally, we found that Mo availability was the primary driver for the contribution of the vanadium nitrogenase to BNF with a Mo threshold of ~ 250 ng.glichen-1 for the onset of vanadium based BNF.This study on N2-fixing cyanolichens provides extensive field evidence, at an ecosystem scale, that vanadium-based nitrogenase greatly contributes to BNF when Mo availability is limited. The results showcase the resilience of BNF to micronutrient limitation and reveal a strong link between the biogeochemical cycle of macro- and micronutrients in terrestrial ecosystems. Given widespread findings of Mo limitation of BNF in terrestrial ecosystems, additional consideration of vanadium-based BNF is required in experimental and modeling studies of terrestrial biogeochemistry.

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Impacts of biological nitrogen fixation on N2O emissions from global natural terrestrial ecosystem soils: An Analysis with a process-based biogeochemistry model

10.5194/bg-2019-278 ◽

2019 ◽

Author(s):

Tong Yu ◽

Qianlai Zhuang

Keyword(s):

Nitrogen Fixation ◽

Biological Nitrogen Fixation ◽

Terrestrial Ecosystem ◽

Terrestrial Ecosystems ◽

Climatic Conditions ◽

N2o Emissions ◽

Emission Model ◽

Fixation Rate ◽

Observational Site ◽

Biological Nitrogen

Abstract. Biological nitrogen fixation plays an important role in the global nitrogen cycle. However, the fixation rate has been usually measured or estimated at a particular observational site. To quantify the fixation amount at the global scale, a process-based model is needed. This study develops a biological nitrogen fixation model and couples it with an extant biogeochemistry model of N2O emissions to examine the fixation rate and its effects on N2O emissions. The revised N2O emission model better matches the observed data in comparison with our previous model that has not considered the fixation effects. The new model estimates that tropical forests have the highest fixation rate among all ecosystem types, and decrease from the equator to the polar region. The estimated nitrogen fixation in global terrestrial ecosystems is 61.5 Tg N yr−1 with a range of 19.8–107.9 Tg N yr−1 in the 1990s. Our estimates are relatively low compared to some early estimates using empirical approaches, but comparable to more recent estimates that involve more detailed processes in their modeling. Furthermore, we estimate that the fixation contributes to −5 % to 20 % changes in N2O emissions compared to our previous estimates, depending on ecosystem types and climatic conditions. This study highlights that there are relatively large effects of the biological nitrogen fixation on ecosystem nitrogen cycling and soil N2O emissions and calls for more comprehensive understanding of biological nitrogen fixation and more observational data for different ecosystems to improve future quantification of the fixation and its impacts.

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Biological nitrogen fixation by alternative nitrogenases in terrestrial ecosystems: a review

Biogeochemistry ◽

10.1007/s10533-020-00666-7 ◽

2020 ◽

Vol 149 (1) ◽

pp. 53-73 ◽

Cited By ~ 3

Author(s):

J. P. Bellenger ◽

R. Darnajoux ◽

X. Zhang ◽

A. M. L. Kraepiel

Keyword(s):

Nitrogen Fixation ◽

Biological Nitrogen Fixation ◽

Terrestrial Ecosystems ◽

Biological Nitrogen

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Modeling biological nitrogen fixation in global natural terrestrial ecosystems

Biogeosciences ◽

10.5194/bg-17-3643-2020 ◽

2020 ◽

Vol 17 (13) ◽

pp. 3643-3657

Author(s):

Tong Yu ◽

Qianlai Zhuang

Keyword(s):

Nitrogen Fixation ◽

Nitrogen Cycle ◽

Biological Nitrogen Fixation ◽

Terrestrial Ecosystems ◽

Global Scale ◽

Climatic Conditions ◽

Fixation Rate ◽

Observational Site ◽

Biological Nitrogen ◽

Global Nitrogen Cycle

Abstract. Biological nitrogen fixation plays an important role in the global nitrogen cycle. However, the fixation rate has been usually measured or estimated at a particular observational site. To quantify the fixation amount at the global scale, process-based models are needed. This study develops a biological nitrogen fixation model to quantitatively estimate the nitrogen fixation rate by plants in a natural environment. The revised nitrogen module better simulates the nitrogen cycle in comparison with our previous model that has not considered the fixation effects. The new model estimates that tropical forests have the highest fixation rate among all ecosystem types, which decreases from the Equator to the polar region. The estimated nitrogen fixation in global terrestrial ecosystems is 61.5 Tg N yr−1 with a range of 19.8–107.9 Tg N yr−1 in the 1990s. Our estimates are relatively low compared to some early estimates using empirical approaches but comparable to more recent estimates that involve more detailed processes in their modeling. Furthermore, the contribution of nitrogen made by biological nitrogen fixation depends on ecosystem type and climatic conditions. This study highlights that there are relatively large effects of biological nitrogen fixation on ecosystem nitrogen cycling. and the large uncertainty of the estimation calls for more comprehensive understanding of biological nitrogen fixation. More direct observational data for different ecosystems are in need to improve future quantification of fixation and its impacts.

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Ecosystem scale evidence for the contribution of vanadium-based nitrogenase to biological nitrogen fixation.

10.5194/egusphere-egu21-7892 ◽

2021 ◽

Author(s):

Jean-Philippe Bellenger ◽

Romain Darnajoux ◽

Nicolas Magain ◽

Marie Renaudin ◽

Francois Lutzoni ◽

...

Keyword(s):

Nitrogen Fixation ◽

High Latitude ◽

Biological Nitrogen Fixation ◽

Terrestrial Ecosystems ◽

Growing Season ◽

The Arctic ◽

Field Evidence ◽

N Input ◽

Vanadium Nitrogenase ◽

Biological Nitrogen

Nitrogen is the primary limiting nutrient in high latitude ecosystems. Biological nitrogen fixation (BNF) by microorganisms associated with cryptogamic covers, such as cyanolichens and bryophytes, is an important source of new reactive nitrogen in pristine, high-latitude ecosystems. BNF is catalyzed by the enzyme nitrogenase, for which three isoforms have been described; the canonical molybdenum (Mo) nitrogenase which requires Mo in its active site and two alternative nitrogenases, the vanadium and iron-only nitrogenases. The low availability of Mo on land has been shown to limit BNF in many ecosystems from the tropical forest to the arctic tundra. Alternative nitrogenases have been suggested as viable alternatives to cope with Mo limitation of BNF, however, field data supporting this long-standing hypothesis have been lacking.Here, we elucidated the contribution of the vanadium nitrogenase to BNF by cyanolichens across a 600 km latitudinal transect in eastern Canadian boreal forests. We report a widespread activity of the vanadium nitrogenase which contributed between 15 to 50% of total BNF rates on all sites. Vanadium nitrogenase contribution to BNF was more robust in the northern part of the transect. Vanadium nitrogenase contribution to BNF also changed during the growing season, with a three-fold increase between the early (May) and late (September) growing season. By including the contribution of the vanadium nitrogenase to BNF, estimates of new N input by cyanolichens increase by up to 30%, a significant change in these low N input ecosystems. Finally, we found that Mo availability was the primary driver for the contribution of the vanadium nitrogenase to BNF with a Mo threshold of ~ 250 ng.glichen-1 for the onset of vanadium based BNF.This study on N2-fixing cyanolichens provides extensive field evidence, at an ecosystem scale, that vanadium-based nitrogenase greatly contributes to BNF when Mo availability is limited. The results showcase the resilience of BNF to micronutrient limitation and reveal a strong link between the biogeochemical cycle of macro- and micronutrients in terrestrial ecosystems. Given widespread findings of Mo limitation of BNF in terrestrial ecosystems, additional consideration of vanadium-based BNF is required in experimental and modeling studies of terrestrial biogeochemistry.

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Biological nitrogen fixation: rates, patterns and ecological controls in terrestrial ecosystems

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2013.0119 ◽

2013 ◽

Vol 368 (1621) ◽

pp. 20130119 ◽

Cited By ~ 320

Author(s):

Peter M. Vitousek ◽

Duncan N. L. Menge ◽

Sasha C. Reed ◽

Cory C. Cleveland

Keyword(s):

Nitrogen Fixation ◽

Biological Nitrogen Fixation ◽

Global Environmental Change ◽

Terrestrial Ecosystems ◽

N Fixation ◽

New Techniques ◽

N Cycle ◽

Global Environmental ◽

Wide Range ◽

Biological Nitrogen

New techniques have identified a wide range of organisms with the capacity to carry out biological nitrogen fixation (BNF)—greatly expanding our appreciation of the diversity and ubiquity of N fixers—but our understanding of the rates and controls of BNF at ecosystem and global scales has not advanced at the same pace. Nevertheless, determining rates and controls of BNF is crucial to placing anthropogenic changes to the N cycle in context, and to understanding, predicting and managing many aspects of global environmental change. Here, we estimate terrestrial BNF for a pre-industrial world by combining information on N fluxes with 15 N relative abundance data for terrestrial ecosystems. Our estimate is that pre-industrial N fixation was 58 (range of 40–100) Tg N fixed yr −1 ; adding conservative assumptions for geological N reduces our best estimate to 44 Tg N yr −1 . This approach yields substantially lower estimates than most recent calculations; it suggests that the magnitude of human alternation of the N cycle is substantially larger than has been assumed.

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