Distribution of soil nitrogen and nitrogenase activity in the forefield of a High Arctic receding glacier

ABSTRACTGlaciers retreating in response to climate warming are progressively exposing primary mineral substrates to surface conditions. As primary production is constrained by nitrogen (N) availability in these emerging ecosystems, improving our understanding of how N accumulates with soil formation is of critical concern. In this study, we quantified how the distribution and speciation of N, as well as rates of free-living biological N fixation (BNF), change along a 2000-year chronosequence of soil development in a High Arctic glacier forefield. Our results show the soil N pool increases with time since exposure and that the rate at which it accumulates is influenced by soil texture. Further, all N increases were organically bound in soils which had been ice-free for 0–50 years. This is indicative of N limitation and should promote BNF. Using the acetylene reduction assay technique, we demonstrated that microbially mediated inputs of N only occurred in soils which had been ice-free for 0 and 3 years, and that potential rates of BNF declined with increased N availability. Thus, BNF only supports N accumulation in young soils. When considering that glacier forefields are projected to become more expansive, this study has implications for understanding how ice-free ecosystems will become productive over time.

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Accumulation and Distribution of Fertilizer Nitrogen and Nodule-Fixed Nitrogen in Soybeans with Dual Root Systems

Agronomy ◽

10.3390/agronomy10030397 ◽

2020 ◽

Vol 10 (3) ◽

pp. 397 ◽

Cited By ~ 3

Author(s):

Rui Zhang ◽

Cong Wang ◽

Wenzhi Teng ◽

Jing Wang ◽

Xiaochen Lyu ◽

...

Keyword(s):

Root System ◽

Root Nodules ◽

Culture Conditions ◽

Sand Culture ◽

Nodule Formation ◽

N Fixation ◽

Fertilizer N ◽

N Accumulation ◽

Biological N Fixation ◽

Nodule Growth

The soybean (Glycine max L. Merr.) is a crop with a high demand for nitrogen (N). The root nodules that form in soybeans can fix atmospheric N effectively, yet the goal of achieving high yields cannot be met by relying solely on nodule-fixed N. Nonetheless, the application of N fertilizer may inhibit nodule formation and biological N fixation (BNF), but the underpinning mechanisms are still unclear. In this study, we grafted the roots of non-nodulated soybeans onto nodulated soybeans to generate plants with dual root system. The experiment included three treatments conducted under sand culture conditions with NO 3 − and NH 4 + as N sources. Treatment I: The non-nodulated roots on one side received 50 mg·L−1 15 NO 3 − or 15NH4+, and the nodulated roots on the other side were not treated. Treatment II: The non-nodulated roots received 50 mg·L−1 15 NO 3 − or 15 NH 4 + , and the nodulated roots received 50 mg·L−1 14 NO 3 − or 14 NH 4 + . Treatment III: Both non-nodulated and nodulated roots received 50 mg·L−1 15 NO 3 − or 15 NH 4 + . The results showed the following: (1) Up to 81.5%–87.1% of the N absorbed by the soybean roots and fixed by the root nodules was allocated to shoot growth, leaving 12.9%–18.5% for root and nodule growth. Soybeans preferentially used fertilizer N in the presence of a NO 3 − or NH 4 + supply. After the absorbed fertilizer N and nodule-fixed N was transported to the shoots, a portion of it was redistributed to the roots and nodules. The N required for root growth was primarily derived from the NO 3 − or NH 4 + assimilated by the roots and the N fixed by the nodules, with a small portion translocated from the shoots. The N required for nodule growth was primarily contributed by nodule-fixed N with a small portion translocated from the shoots, whereas the NO 3 − or NH 4 + that was assimilated by the roots was not directly supplied to the nodules. (2) Based on observations of the shoots and one side of the roots and nodules in the dual root system as an N translocation system, we proposed a method for calculating the N translocation from soybean shoots to roots and nodules during the R1–R5 stages based on the difference in the 15N abundance. Our calculations showed that when adding N at a concentration of 50 mg·L−1, the N translocated from the shoots during the R1–R5 stages accounts for 29.6%–52.3% of the N accumulation in nodulated roots (Rootn) and 9.4%–16.6% of the N accumulation in Nodulen of soybeans. Through the study of this experiment, the absorption, distribution and redistribution characteristics of fertilizer N and root nodule N fixation in soybean can be clarified, providing a theoretical reference for analyzing the mechanisms of the interaction between fertilizer N and nodule-fixed N.

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Supplementary material to "Microbial dynamics in a High-Arctic glacier forefield: a combined field, laboratory, and modelling approach"

10.5194/bg-2016-52-supplement ◽

2016 ◽

Author(s):

James A. Bradley ◽

Sandra Arndt ◽

Marie Šabacká ◽

Liane G. Benning ◽

Gary L. Barker ◽

...

Keyword(s):

High Arctic ◽

Microbial Dynamics ◽

Glacier Forefield ◽

Field Laboratory ◽

Supplementary Material ◽

Arctic Glacier ◽

Modelling Approach

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Consumption of CH3Cl, CH3Br, and CH3I and emission of CHCl3, CHBr3, and CH2Br2 from the forefield of a retreating Arctic glacier

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-7243-2020 ◽

2020 ◽

Vol 20 (12) ◽

pp. 7243-7258 ◽

Cited By ~ 1

Author(s):

Moya L. Macdonald ◽

Jemma L. Wadham ◽

Dickon Young ◽

Chris R. Lunder ◽

Ove Hermansen ◽

...

Keyword(s):

Methyl Chloride ◽

High Arctic ◽

The Arctic ◽

Emission Rates ◽

Cyanobacterial Mats ◽

Small Surface ◽

Glacier Forefield ◽

Land Surfaces ◽

Arctic Glacier ◽

The Impact

Abstract. The Arctic is one of the most rapidly warming regions of the Earth, with predicted temperature increases of 5–7 ∘C and the accompanying extensive retreat of Arctic glacial systems by 2100. Retreating glaciers will reveal new land surfaces for microbial colonisation, ultimately succeeding to tundra over decades to centuries. An unexplored dimension to these changes is the impact upon the emission and consumption of halogenated organic compounds (halocarbons). Halocarbons are involved in several important atmospheric processes, including ozone destruction, and despite considerable research, uncertainties remain in the natural cycles of some of these compounds. Using flux chambers, we measured halocarbon fluxes across the glacier forefield (the area between the present-day position of a glacier's ice-front and that at the last glacial maximum) of a high-Arctic glacier in Svalbard, spanning recently exposed sediments (<10 years) to approximately 1950-year-old tundra. Forefield land surfaces were found to consume methyl chloride (CH3Cl) and methyl bromide (CH3Br), with both consumption and emission of methyl iodide (CH3I) observed. Bromoform (CHBr3) and dibromomethane (CH2Br2) have rarely been measured from terrestrial sources but were here found to be emitted across the forefield. Novel measurements conducted on terrestrial cyanobacterial mats covering relatively young surfaces showed similar measured fluxes to the oldest, vegetated tundra sites for CH3Cl, CH3Br, and CH3I (which were consumed) and for CHCl3 and CHBr3 (which were emitted). Consumption rates of CH3Cl and CH3Br and emission rates of CHCl3 from tundra and cyanobacterial mat sites were within the ranges reported from older and more established Arctic tundra elsewhere. Rough calculations showed total emissions and consumptions of these gases across the Arctic were small relative to other sources and sinks due to the small surface area represented by glacier forefields. We have demonstrated that glacier forefields can consume and emit halocarbons despite their young age and low soil development, particularly when cyanobacterial mats are present.

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Global soil nitrous oxide emissions in a dynamic carbon-nitrogen model

Biogeosciences ◽

10.5194/bg-12-6405-2015 ◽

2015 ◽

Vol 12 (21) ◽

pp. 6405-6427 ◽

Cited By ~ 15

Author(s):

Y. Huang ◽

S. Gerber

Keyword(s):

Nitrous Oxide ◽

Elevated Co2 ◽

N Uptake ◽

N2o Emission ◽

Nitrous Oxide Emissions ◽

N Fixation ◽

N Availability ◽

Plant N Uptake ◽

Biological N Fixation ◽

N2o Fluxes

Abstract. Nitrous oxide (N2O) is an important greenhouse gas that also contributes to the depletion of stratospheric ozone. Due to its high temporal and spatial heterogeneity, a quantitative understanding of terrestrial N2O emission and its variabilities and responses to climate change are challenging. We added a soil N2O emission module to the dynamic global land model LM3V-N, and tested its sensitivity to mechanisms that affect the level of mineral nitrogen (N) in soil such as plant N uptake, biological N fixation, amount of volatilized N redeposited after fire, and nitrification-denitrification. We further tested the relationship between N2O emission and soil moisture, and assessed responses to elevated CO2 and temperature. Results extracted from the corresponding gridcell (without site-specific forcing data) were comparable with the average of cross-site observed annual mean emissions, although differences remained across individual sites if stand-level measurements were representative of gridcell emissions. Processes, such as plant N uptake and N loss through fire volatilization that regulate N availability for nitrification-denitrification have strong controls on N2O fluxes in addition to the parameterization of N2O loss through nitrification and denitrification. Modelled N2O fluxes were highly sensitive to water-filled pore space (WFPS), with a global sensitivity of approximately 0.25 TgN per year per 0.01 change in WFPS. We found that the global response of N2O emission to CO2 fertilization was largely determined by the response of tropical emissions with reduced N2O fluxes in the first few decades and increases afterwards. The initial reduction was linked to N limitation under higher CO2 level, and was alleviated through feedbacks such as biological N fixation. The extratropical response was weaker and generally positive, highlighting the need to expand field studies in tropical ecosystems. We did not find synergistic effects between warming and CO2 increase as reported in analyses with different models. Warming generally enhanced N2O efflux and the enhancement was greatly dampened when combined with elevated CO2, although CO2 alone had a small effect. The differential response in the tropics compared to extratropics with respect to magnitude and sign suggests caution when extrapolating from current field CO2 enrichment and warming studies to the globe.

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A Research Road Map for Responsible Use of Agricultural Nitrogen

Frontiers in Sustainable Food Systems ◽

10.3389/fsufs.2021.660155 ◽

2021 ◽

Vol 5 ◽

Author(s):

Michael Udvardi ◽

Frederick E. Below ◽

Michael J. Castellano ◽

Alison J. Eagle ◽

Ken E. Giller ◽

...

Keyword(s):

Current Knowledge ◽

N Uptake ◽

Green Revolution ◽

Sustainable Use ◽

Industrial Process ◽

Agricultural Practices ◽

N Fixation ◽

N Availability ◽

Soil N ◽

Biological N Fixation

Nitrogen (N) is an essential but generally limiting nutrient for biological systems. Development of the Haber-Bosch industrial process for ammonia synthesis helped to relieve N limitation of agricultural production, fueling the Green Revolution and reducing hunger. However, the massive use of industrial N fertilizer has doubled the N moving through the global N cycle with dramatic environmental consequences that threaten planetary health. Thus, there is an urgent need to reduce losses of reactive N from agriculture, while ensuring sufficient N inputs for food security. Here we review current knowledge related to N use efficiency (NUE) in agriculture and identify research opportunities in the areas of agronomy, plant breeding, biological N fixation (BNF), soil N cycling, and modeling to achieve responsible, sustainable use of N in agriculture. Amongst these opportunities, improved agricultural practices that synchronize crop N demand with soil N availability are low-hanging fruit. Crop breeding that targets root and shoot physiological processes will likely increase N uptake and utilization of soil N, while breeding for BNF effectiveness in legumes will enhance overall system NUE. Likewise, engineering of novel N-fixing symbioses in non-legumes could reduce the need for chemical fertilizers in agroecosystems but is a much longer-term goal. The use of simulation modeling to conceptualize the complex, interwoven processes that affect agroecosystem NUE, along with multi-objective optimization, will also accelerate NUE gains.

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review: Microbial dynamics in a High-Arctic glacier forefield: a combined field, laboratory, and modelling approach.

10.5194/bg-2016-52-rc1 ◽

2016 ◽

Author(s):

Anonymous

Keyword(s):

High Arctic ◽

Microbial Dynamics ◽

Glacier Forefield ◽

Field Laboratory ◽

Arctic Glacier ◽

Modelling Approach

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Biological N Fixation in Forage-Livestock Systems

10.2134/asaspecpub28 ◽

1976 ◽

Keyword(s):

N Fixation ◽

Biological N Fixation ◽

Livestock Systems

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Solute in high arctic glacier snow cover and its impact on runoff chemistry

Annals of Glaciology ◽

10.3189/1998aog26-1-156-160 ◽

1998 ◽

Vol 26 ◽

pp. 156-160 ◽

Cited By ~ 3

Author(s):

Richard Hodgkins ◽

Martyn Tranter

Keyword(s):

Chemical Composition ◽

Atmospheric Transport ◽

Total Concentration ◽

High Arctic ◽

Sea Salt ◽

Acidic Ph ◽

Sea Salt Aerosol ◽

Wet Snow ◽

Potential Contributor ◽

Arctic Glacier

The chemical composition of snow and meltwater in the 13 km2 catchment of Scott Turnerbreen, Svalbard, was investigated during the spring and summer of 1993. This paper assesses the provenance of solute in the snowpack and its impact on runoff chemistry. Dry snow contains 420μeql-1 of solute, is slightly acidic (pH 5.4) and is dominated by Na+ and Cl-. Wet snow is more dilute (total concentration 340μeql-1), and less acidic (pH 5.9). This is consistent with the elution of ions from the snowpack by meltwater. Snowpack solute can be partitioned into the following fractions: sea-salt aerosol, acid aerosol and crustal. About 98% of snowpack solute is sea salt, yielding 22000 kg km-2a-1. The behaviour of snowpack-derived Cl- in runoff is distinctive, peaking at over 800 μeql-1 early in the melt season as runoff picks up, before declining quasi-exponentially. This represents the discharge of snowmelt concentrated by elution within the snowpack which subsequently becomes relatively dilute. A solute yield of 140 kg km-2 a-1 can be attributed to anthropogenically generated acid aerosols, representing long-range atmospheric transport of pollutants, a potential contributor to Arctic runoff acidification.

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