Terrestrial Biological Nitrogen Fixation in CMIP6 Models

2020 ◽  
Author(s):  
Taraka Davies-Barnard ◽  
Johannes Meyerholt ◽  
Sönke Zaehle ◽  
Pierre Friedlingstein ◽  
Victor Brovkin ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Nitrogen Fixation ◽  
Land Surface ◽  
Biological Nitrogen Fixation ◽  
Atmospheric Carbon Dioxide ◽  
Meta Analysis ◽  
Field Measurements ◽  
Carbon Dioxide Concentrations ◽  
Wide Range ◽  
Biological Nitrogen

<p>Biological nitrogen fixation (BNF) is a key contributor to sustaining the terrestrial carbon cycle, providing nitrogen input that plants require. This is particularly salient for projections of carbon uptake under increased atmospheric carbon dioxide concentrations, which may allow for so-called ‘carbon dioxide fertilisation’ if other plant requirements, such as nitrogen, do not prevent increases in productivity. The amount, processes, and global distribution of BNF is highly disputed and consequently land surface models represent it in varying ways. Looking at the latest generation of CMIP6 earth system models with terrestrial nitrogen cycles, we consider their performance with regard to BNF. We assess models against a new comprehensive meta-analysis of BNF field measurements that gives a global range and site-specific values. We find that compared to the wide range of upscaled observations, the models still have a larger range, with under and overestimates.</p>

Global pattern and controls of biological nitrogen fixation under nutrient enrichment: A meta‐analysis

2019 ◽  
Vol 25 (9) ◽  
pp. 3018-3030 ◽  
Author(s):  
Mianhai Zheng ◽  
Zhenghu Zhou ◽  
Yiqi Luo ◽  
Ping Zhao ◽  
Jiangming Mo
Keyword(s):  
Nitrogen Fixation ◽  
Nutrient Enrichment ◽  
Biological Nitrogen Fixation ◽  
Meta Analysis ◽  
Global Pattern ◽  
Biological Nitrogen

Early response of biological nitrogen fixation in a mature oak dominated forest to elevated atmospheric CO2 fumigation at BIFoR-FACE

2020 ◽  
Author(s):  
Sami Ullah ◽  
Ernesto Saiz Val ◽  
Fotis Sgouridis ◽  
Falko Drijfhout
Keyword(s):  
Carbon Dioxide ◽  
Nitrogen Fixation ◽  
Biological Nitrogen Fixation ◽  
Early Years ◽  
Available Nitrogen ◽  
Preliminary Results ◽  
Hypnum Cupressiforme ◽  
Feather Moss ◽  
Feather Mosses ◽  
Biological Nitrogen

<p>Elevated atmospheric carbon dioxide concentrations are stimulating photosynthesis and carbon sequestration. However, the extent of photosynthetic stimulation in forests under future climates is highly uncertain given that nutrient limitation in soils may constrain the CO<sub>2</sub> fertilization effect. The Birmingham Institute of Forest Research (BIFoR), University of Birmingham established the only global mature temperate deciduous forests Free Air Carbon Dioxide Enrichment (FACE) experiment to study the response of forests to future climates. Fumigation of the forest with ~550 ppm CO<sub>2</sub> started in 2017 and will continue until at least 2026. Soil nutrients cycling including nitrogen transformation in response to elevated atmospheric CO<sub>2</sub> (eCO<sub>2</sub>) fumigation is currently investigated to determine the role of nutrient availability in carbon capture by forests. In this paper, we show preliminary results of the response of asymbiotic biological nitrogen fixation (BNF) in soils and epiphytic bryophytes at BIFoR-FACE following a year of eCO<sub>2</sub> fumigation. It is hypothesized that the demand for available nitrogen by trees will increase under eCO<sub>2</sub> and that competition of roots and soil microbes for available nitrogen will enhance asymbiotic BNF to at least meet microbial metabolic nitrogen demands in the long run. Surface soils (0-5 cm) and epiphytic feather moss (Hypnum cupressiforme) growing on oak tree stems in the FACE site were  collected during the second year of eCO<sub>2</sub> fumigation for the quantification of BNF activity using the <sup>15</sup>N<sub>2</sub> assimilation methods (Saiz et al. 2019). Samples were incubated in 50 mL serum bottles under in situ conditions, followed by the analysis of soil and tissue samples for <sup>15</sup>N signature on an Isotope Ratio Mass Spectrometer for the quantification of BNF activity.</p><p>The BNF activity under eCO<sub>2</sub> were 369% higher than in soils under ambient atmospheric CO<sub>2</sub>. BNF rates associated with feather mosses (Hypnum cupressiforme) did not differ between the eCO<sub>2</sub> and control plots; however, rates under eCO<sub>2</sub> on average were 60% lower than in the control plots. Unlike soils, the moisture of feather mosses correlated significantly (R<sup>2</sup> = 51%) with BNF activity. Among nutrients in soil with implications for BNF activity, the concentrations of Mg, K, Co and Ni were significantly lower in soils under eCO<sub>2</sub> than in the control plots, while in feather moss tissues no differences were observed.  Our preliminary results show that eCO<sub>2</sub> fumigation primed asymbiotic BNF activity in soils. An enhancement of BNF together with the observation of a relatively low nutrient content under eCO<sub>2</sub> points to important changes in nitrogen cycling processes in the early years of CO<sub>2</sub> fumigation. Further detailed studies are underway to fully disentangle controls on nitrogen availability to trees under future climates.</p><p><strong> </strong></p><p><strong>Reference</strong></p><p>Saiz, E, Sgouridis, F, Drifjhout, F & Ullah, S. 2019. Biological nitrogen fixation in peatlands: comparison between acetylene reduction assay and <sup>15</sup>N<sub>2</sub> assimilation methods. Soil Biol. Biochem:131:157-165</p>

scholarly journals Nitrogen Cycling in CMIP6 Land Surface Models: Progress and Limitations

2020 ◽  
Author(s):  
Taraka Davies-Barnard ◽  
Johannes Meyerholt ◽  
Sönke Zaehle ◽  
Pierre Friedlingstein ◽  
Victor Brovkin ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Nitrogen Cycle ◽  
Land Surface ◽  
Atmospheric Carbon Dioxide ◽  
Carbon Uptake ◽  
Earth System ◽  
Global Trends ◽  
System Models ◽  
Biological Nitrogen ◽  
Earth System Models

Abstract. The nitrogen cycle and its effect on carbon uptake in the terrestrial biosphere is a recent progression in earth system models. As with any new component of a model, it is important to understand the behaviour, strengths, and limitations of the various process representations. Here we assess and compare five models with nitrogen cycles that will be used as the terrestrial components of some of the earth system models in CMIP6. We use a historical control simulation and two perturbations to assess the models' nitrogen-related performance: a simulation with atmospheric carbon dioxide 200 ppm higher, and one with nitrogen deposition increased by 50 kg N ha−1 yr−1. We find that, despite differing nitrogen cycle representations, all models simulate recent global trends in terrestrial productivity and net carbon uptake commensurate with observations. The between-model variation is likely more influenced by other, non-nitrogen parts of the models. Globally, the productivity response to increased carbon dioxide is commensurate with observations for four of the five models, but highly spatially variable within and between models. The productivity response to increased nitrogen is significantly lower than observed in two of the five models. The global and tropical values are generally better represented than boreal, tundra, or other high latitude areas. These results are due to divergent though valid choices in the representation of key processes. They show the need for better understanding and more provision of observational constraints of nitrogen processes, especially nitrogen-use efficiency and biological nitrogen fixation.

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

2013 ◽  
Vol 368 (1621) ◽  
pp. 20130119 ◽  
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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