JULES-CN: a coupled terrestrial carbon–nitrogen scheme (JULES vn5.1)

Abstract. Understanding future changes in the terrestrial carbon cycle is important for reliable projections of climate change and impacts on ecosystems. It is well known that nitrogen (N) could limit plants' response to increased atmospheric carbon dioxide and it is therefore important to include a representation of the N cycle in Earth system models. Here we present the implementation of the terrestrial nitrogen cycle in the Joint UK Land Environment Simulator (JULES) – the land surface scheme of the UK Earth System Model (UKESM). Two configurations are discussed – the first one (JULES-CN) has a bulk soil biogeochemical model and the second one is a development configuration that resolves the soil biogeochemistry with depth (JULES-CNlayer). In JULES the nitrogen (N) cycle is based on the existing carbon (C) cycle and represents all the key terrestrial N processes in a parsimonious way. Biological N fixation is dependent on net primary productivity, and N deposition is specified as an external input. Nitrogen leaves the vegetation and soil system via leaching and a bulk gas loss term. Nutrient limitation reduces carbon-use efficiency (CUE – ratio of net to gross primary productivity) and can slow soil decomposition. We show that ecosystem level N limitation of net primary productivity (quantified in the model by the ratio of the potential amount of C that can be allocated to growth and spreading of the vegetation compared with the actual amount achieved in its natural state) falls at the lower end of the observational estimates in forests (approximately 1.0 in the model compared with 1.01 to 1.38 in the observations). The model shows more N limitation in the tropical savanna and tundra biomes, consistent with the available observations. Simulated C and N pools and fluxes are comparable to the limited available observations and model-derived estimates. The introduction of an N cycle improves the representation of interannual variability of global net ecosystem exchange, which was more pronounced in the C-cycle-only versions of JULES (JULES-C) than shown in estimates from the Global Carbon Project. It also reduces the present-day CUE from a global mean value of 0.45 for JULES-C to 0.41 for JULES-CN and 0.40 for JULES-CNlayer, all of which fall within the observational range. The N cycle also alters the response of the C fluxes over the 20th century and limits the CO2 fertilisation effect, such that the simulated current-day land C sink is reduced by about 0.5 Pg C yr−1 compared to the version with no N limitation. JULES-CNlayer additionally improves the representation of soil biogeochemistry, including turnover times in the northern high latitudes. The inclusion of a prognostic land N scheme marks a step forward in functionality and realism for the JULES and UKESM models.

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JULES-CN: a coupled terrestrial Carbon-Nitrogen Scheme (JULES vn5.1)

10.5194/gmd-2020-205 ◽

2020 ◽

Cited By ~ 2

Author(s):

Andrew J. Wiltshire ◽

Eleanor J. Burke ◽

Sarah E. Chadburn ◽

Chris D. Jones ◽

Peter M. Cox ◽

...

Keyword(s):

Carbon Cycle ◽

Nitrogen Cycle ◽

Primary Productivity ◽

Land Surface ◽

Net Primary Productivity ◽

Biogeochemical Model ◽

Surface Model ◽

Earth System ◽

Terrestrial Carbon ◽

The Impact

Abstract. Understanding future changes in the terrestrial carbon cycle is important for reliable projections of climate change and impacts on ecosystems. It is known that nitrogen could limit plants' response to increased atmospheric carbon dioxide and is therefore important to include in Earth System Models. Here we present the implementation of the terrestrial nitrogen cycle in the JULES land surface model (JULES-CN). Two versions are discussed – the one implemented within the UK Earth System Model (UKESM1) which has a bulk soil biogeochemical model and a development version which resolves the soil biogeochemistry with depth. The nitrogen cycle is based on the existing carbon cycle in the model. It represents all the key terrestrial nitrogen processes in an efficient way. Biological fixation and nitrogen deposition are external inputs, and loss occurs via leaching and a bulk gas loss parameterisation. Nutrient limitation reduces carbon-use efficiency (CUE – ratio of net to gross primary productivity) and can slow soil decomposition. We show that ecosystem level limitation of net primary productivity by nitrogen is consistent with observational estimates and that simulated carbon and nitrogen pools and fluxes are comparable to the limited available observations. The impact of N limitation is most pronounced in northern mid-latitudes. The introduction of a nitrogen cycle improves the representation of interannual variability of global net ecosystem exchange which was much too pronounced in the carbon cycle only versions of JULES (JULES-C). It also reduces the CUE and alters its response over the twentieth century and limits the CO2-fertilisation effect, such that the simulated current day land carbon sink is reduced by about 0.5 Pg C yr−1. The inclusion of a prognostic land nitrogen scheme marks a step forward in functionality and realism for the JULES and UKESM models.

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Fire intensity impacts on post-fire temperate coniferous forest net primary productivity

Biogeosciences ◽

10.5194/bg-15-1173-2018 ◽

2018 ◽

Vol 15 (4) ◽

pp. 1173-1183 ◽

Cited By ~ 9

Author(s):

Aaron M. Sparks ◽

Crystal A. Kolden ◽

Alistair M. S. Smith ◽

Luigi Boschetti ◽

Daniel M. Johnson ◽

...

Keyword(s):

Primary Productivity ◽

Tree Mortality ◽

Net Primary Productivity ◽

Coniferous Forest ◽

Radiative Energy ◽

Fire Intensity ◽

Wildland Fires ◽

Resistant Species ◽

Legacy Effect ◽

C Cycle

Abstract. Fire is a dynamic ecological process in forests and impacts the carbon (C) cycle through direct combustion emissions, tree mortality, and by impairing the ability of surviving trees to sequester carbon. While studies on young trees have demonstrated that fire intensity is a determinant of post-fire net primary productivity, wildland fires on landscape to regional scales have largely been assumed to either cause tree mortality, or conversely, cause no physiological impact, ignoring the impacted but surviving trees. Our objective was to understand how fire intensity affects post-fire net primary productivity in conifer-dominated forested ecosystems on the spatial scale of large wildland fires. We examined the relationships between fire radiative power (FRP), its temporal integral (fire radiative energy – FRE), and net primary productivity (NPP) using 16 years of data from the MOderate Resolution Imaging Spectrometer (MODIS) for 15 large fires in western United States coniferous forests. The greatest NPP post-fire loss occurred 1 year post-fire and ranged from −67 to −312 g C m−2 yr−1 (−13 to −54 %) across all fires. Forests dominated by fire-resistant species (species that typically survive low-intensity fires) experienced the lowest relative NPP reductions compared to forests with less resistant species. Post-fire NPP in forests that were dominated by fire-susceptible species were not as sensitive to FRP or FRE, indicating that NPP in these forests may be reduced to similar levels regardless of fire intensity. Conversely, post-fire NPP in forests dominated by fire-resistant and mixed species decreased with increasing FRP or FRE. In some cases, this dose–response relationship persisted for more than a decade post-fire, highlighting a legacy effect of fire intensity on post-fire C dynamics in these forests.

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Equilibrium analysis of carbon pools and fluxes of forest biomes in the former Soviet Union

Canadian Journal of Forest Research ◽

10.1139/x93-013 ◽

1993 ◽

Vol 23 (1) ◽

pp. 81-88 ◽

Cited By ~ 49

Author(s):

Tatyana P. Kolchugina ◽

Ted S. Vinson

Keyword(s):

Soviet Union ◽

Carbon Cycle ◽

Primary Productivity ◽

Boreal Forests ◽

Former Soviet Union ◽

Net Primary Productivity ◽

Terrestrial Ecosystems ◽

Carbon Pool ◽

Equilibrium Analysis ◽

Terrestrial Carbon

Natural processes in ocean and terrestrial ecosystems together with human activities have caused a measurable increase in the atmospheric concentration of CO2. It is predicted that an increase in the concentration of CO2 will cause the Earth's temperatures to rise and will accelerate rates of plant respiration and the decay of organic matter, disrupting the equilibrium of the terrestrial carbon cycle. Forests are an important component of the biosphere, and sequestration of carbon in boreal forests may represent one of the few realistic alternatives to ameliorate changes in atmospheric chemistry. The former Soviet Union has the greatest expanse of boreal forests in the world; however, the role of Soviet forests in the terrestrial carbon cycle is not fully understood because the carbon budget of the Soviet forest sector has not been established. In recognition of the need to determine the role of Soviet forests in the global carbon cycle, the carbon budget of forest biomes in the former Soviet Union was assessed based on an equilibrium analysis of carbon cycle pools and fluxes. Net primary productivity was used to identify the rate of carbon turnover in the forest biomes. Net primary productivity was estimated at 4360 Mt of carbon, the vegetation carbon pool was estimated at 110 255 Mt, the litter carbon pool was estimated at 17 525 Mt, and the soil carbon pool was estimated at 319 100 Mt. Net primary productivity of Soviet forest biomes exceeded industrial CO2 emissions in the former Soviet Union by a factor of four and represented approximately 7% of the global terrestrial carbon turnover. Carbon stores in the phytomass and soils of forest biomes of the former Soviet Union represented 16% of the carbon concentrated in the biomass and soils of the world's terrestrial ecosystems. All carbon pools of Soviet forest biomes represented approximately one-seventh of the world's terrestrial carbon pool.

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Synthetic Constraint of Soil C Dynamics Using 50 Years of 14C and Net Primary Production (NPP) in a New Zealand Grassland Site

Radiocarbon ◽

10.1017/s0033822200058203 ◽

2013 ◽

Vol 55 (2) ◽

pp. 1071-1076 ◽

Cited By ~ 4

Author(s):

W Troy Baisden ◽

E D Keller

Keyword(s):

Time Series ◽

New Zealand ◽

Net Primary Productivity ◽

Net Primary Production ◽

Turnover Rates ◽

Full Data ◽

Soil System ◽

Soil C ◽

Plant Soil ◽

C Cycle

Time-series radiocarbon measurements have substantial ability to constrain the size and residence time of the soil C pools commonly represented in ecosystem models. 14C remains unique in its ability to constrain the size and turnover rate of the large stabilized soil C pool with roughly decadal residence times. The Judgeford soil, near Wellington, New Zealand, provides a detailed 11-point 14C time series enabling observation of the incorporation and loss of bomb 14C in surface soil from 1959–2002. Calculations of the flow of C through the plant-soil system can be improved further by combining the known constraints of net primary productivity (NPP) and 14C-derived C turnover. We show the Biome-BGC model provides good estimates of NPP for the Judgeford site and estimates NPP from 1956–2010. Synthesis of NPP and 14C data allows parameters associated with the rapid turnover “active” soil C pool to be estimated. This step is important because it demonstrates that NPP and 14C can provide full data-based constraint of pool sizes and turnover rates for the 3 pools of soil C used in nearly all ecosystem and global C-cycle models.

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Biogeophysical feedbacks enhance Arctic terrestrial carbon sink in regional Earth system dynamics

Biogeosciences Discussions ◽

10.5194/bgd-11-6715-2014 ◽

2014 ◽

Vol 11 (5) ◽

pp. 6715-6754 ◽

Cited By ~ 1

Author(s):

W. Zhang ◽

C. Jansson ◽

P. A. Miller ◽

B. Smith ◽

P. Samuelsson

Keyword(s):

Land Surface ◽

General Circulation ◽

Terrestrial Ecosystems ◽

General Circulation Models ◽

The Arctic ◽

Earth System ◽

Terrestrial Carbon ◽

Near Surface ◽

C Cycle ◽

Biogeophysical Feedbacks

Abstract. Continued warming of the Arctic will likely accelerate terrestrial carbon (C) cycling by increasing both uptake and release of C. There are still large uncertainties in modelling Arctic terrestrial ecosystems as a source or sink of C. Most modelling studies assessing or projecting the future fate of C exchange with the atmosphere are based an either stand-alone process-based models or coupled climate–C cycle general circulation models, in either case disregarding biogeophysical feedbacks of land surface changes to the atmosphere. To understand how biogeophysical feedbacks will impact on both climate and C budget over Arctic terrestrial ecosystems, we apply the regional Earth system model RCA-GUESS over the CORDEX-Arctic domain. The model is forced with lateral boundary conditions from an GCMs CMIP5 climate projection under the RCP 8.5 scenario. We perform two simulations with or without interactive vegetation dynamics respectively to assess the impacts of biogeophysical feedbacks. Both simulations indicate that Arctic terrestrial ecosystems will continue to sequester C with an increased uptake rate until 2060s–2070s, after which the C budget will return to a weak C sink as increased soil respiration and biomass burning outpaces increased net primary productivity. The additional C sinks arising from biogeophysical feedbacks are considerable, around 8.5 Gt C, accounting for 22% of the total C sinks, of which 83.5% are located in areas of Arctic tundra. Two opposing feedback mechanisms, mediated by albedo and evapotranspiration changes respectively, contribute to this response. Albedo feedback dominates over winter and spring season, amplifying the near-surface warming by up to 1.35 K in spring, while evapotranspiration feedback dominates over summer exerting the evaporative cooling by up to 0.81 K. Such feedbacks stimulate vegetation growth with an earlier onset of growing-season, leading to compositional changes in woody plants and vegetation redistribution.

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Methanogens Are Major Contributors to Nitrogen Fixation in Soils of the Florida Everglades

Applied and Environmental Microbiology ◽

10.1128/aem.02222-17 ◽

2018 ◽

Vol 84 (7) ◽

Cited By ~ 16

Author(s):

Hee-Sung Bae ◽

Elise Morrison ◽

Jeffrey P. Chanton ◽

Andrew Ogram

Keyword(s):

Primary Productivity ◽

Methane Production ◽

Water Conservation ◽

Significant Proportion ◽

Florida Everglades ◽

Freshwater Wetland ◽

Rrna Genes ◽

Content Type ◽

N Cycle ◽

N Limitation

ABSTRACTThe objective of this study was to investigate the interaction of the nitrogen (N) cycle with methane production in the Florida Everglades, a large freshwater wetland. This study provides an initial analysis of the distribution and expression of N-cycling genes in Water Conservation Area 2A (WCA-2A), a section of the marsh that underwent phosphorus (P) loading for many years due to runoff from upstream agricultural activities. The elevated P resulted in increased primary productivity and an N limitation in P-enriched areas. Results from quantitative real-time PCR (qPCR) analyses indicated that the N cycle in WCA-2A was dominated bynifHandnirK/S, with an increasing trend in copy numbers in P-impacted sites. ManynifHsequences (6 to 44% of the total) andnifHtranscript sequences (2 to 49%) clustered with the methanogenicEuryarchaeota, in stark contrast to the proportion of core gene sequences representingArchaea(≤0.27% of SSU rRNA genes) for the WCA-2A microbiota. Notably, archaealnifHgene transcripts were detected at all sites and comprised a significant proportion of totalnifHtranscripts obtained from the unimpacted site, indicating that methanogens are actively fixing N2. Laboratory incubations with soils taken from WCA-2A producednifHtranscripts with the production of methane from H2plus CO2and acetate as electron donors and carbon sources. Methanogenic N2fixation is likely to be an important, although largely unrecognized, route through which fixed nitrogen enters the anoxic soils of the Everglades and may have significant relevance regarding methane production in wetlands.IMPORTANCEWetlands are the most important natural sources of the greenhouse gas methane, and much of that methane emanates from (sub)tropical peatlands. Primary productivity in these peatlands is frequently limited by the availability of nitrogen or phosphorus; however, the response to nutrient limitations of microbial communities that control biogeochemical cycling critical to ecosystem function may be complex and may be associated with a range of processes, including methane production. We show that many, if not most, of the methanogens in the peatlands of the Florida Everglades possess thenifHgene and actively express it for N2fixation coupled with methanogenesis. These findings indicate that archaeal N2fixation would play crucial role in methane emissions and overall N cycle in subtropical wetlands suffering N limitation.

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Biogeophysical feedbacks enhance the Arctic terrestrial carbon sink in regional Earth system dynamics

Biogeosciences ◽

10.5194/bg-11-5503-2014 ◽

2014 ◽

Vol 11 (19) ◽

pp. 5503-5519 ◽

Cited By ~ 37

Author(s):

W. Zhang ◽

C. Jansson ◽

P. A. Miller ◽

B. Smith ◽

P. Samuelsson

Keyword(s):

Land Surface ◽

General Circulation ◽

Terrestrial Ecosystems ◽

General Circulation Models ◽

The Arctic ◽

Earth System ◽

Terrestrial Carbon ◽

Near Surface ◽

C Cycle ◽

Biogeophysical Feedbacks

Abstract. Continued warming of the Arctic will likely accelerate terrestrial carbon (C) cycling by increasing both uptake and release of C. Yet, there are still large uncertainties in modelling Arctic terrestrial ecosystems as a source or sink of C. Most modelling studies assessing or projecting the future fate of C exchange with the atmosphere are based on either stand-alone process-based models or coupled climate–C cycle general circulation models, and often disregard biogeophysical feedbacks of land-surface changes to the atmosphere. To understand how biogeophysical feedbacks might impact on both climate and the C budget in Arctic terrestrial ecosystems, we apply the regional Earth system model RCA-GUESS over the CORDEX-Arctic domain. The model is forced with lateral boundary conditions from an EC-Earth CMIP5 climate projection under the representative concentration pathway (RCP) 8.5 scenario. We perform two simulations, with or without interactive vegetation dynamics respectively, to assess the impacts of biogeophysical feedbacks. Both simulations indicate that Arctic terrestrial ecosystems will continue to sequester C with an increased uptake rate until the 2060–2070s, after which the C budget will return to a weak C sink as increased soil respiration and biomass burning outpaces increased net primary productivity. The additional C sinks arising from biogeophysical feedbacks are approximately 8.5 Gt C, accounting for 22% of the total C sinks, of which 83.5% are located in areas of extant Arctic tundra. Two opposing feedback mechanisms, mediated by albedo and evapotranspiration changes respectively, contribute to this response. The albedo feedback dominates in the winter and spring seasons, amplifying the near-surface warming by up to 1.35 °C in spring, while the evapotranspiration feedback dominates in the summer months, and leads to a cooling of up to 0.81 °C. Such feedbacks stimulate vegetation growth due to an earlier onset of the growing season, leading to compositional changes in woody plants and vegetation redistribution.

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Fire intensity impacts on post-fire temperate coniferous forest net primary productivity

10.5194/bg-2017-348 ◽

2017 ◽

Author(s):

Aaron M. Sparks ◽

Crystal A. Kolden ◽

Alistair M. S. Smith ◽

Luigi Boschetti ◽

Daniel M. Johnson ◽

...

Keyword(s):

Primary Productivity ◽

Tree Mortality ◽

Net Primary Productivity ◽

Coniferous Forest ◽

Radiative Energy ◽

Fire Intensity ◽

Wildland Fires ◽

Resistant Species ◽

Legacy Effect ◽

C Cycle

Abstract. Fire is a dynamic ecological process in forests and impacts the carbon (C) cycle through direct combustion emissions, tree mortality, and by impairing the ability of surviving trees to sequester carbon. While studies on young trees have demonstrated that fire intensity is a determinant of post-fire net primary productivity, wildland fires at landscape to regional scales have largely been assumed to either cause tree mortality, or conversely, cause no physiological impact, ignoring the impacted but surviving trees. Our objective was to understand how fire intensity affects post-fire net primary productivity in conifer-dominated forested ecosystems at the spatial scale of large wildland fires. We examined the relationships between fire radiative power (FRP), its temporal integral (fire radiative energy – FRE), and net primary productivity (NPP) using 16 years of data from the MOderate Resolution Imaging Spectrometer (MODIS) for 15 large fires in western United States coniferous forests. The greatest NPP post-fire loss occurred one year post-fire and ranged from −67 to −312 g C m−2 yr−1 (−13 to −54%) across all fires. Forests dominated by fire-resistant species (species that typically survive low intensity fires) experienced the lowest relative NPP reductions compared to forests with less resistant species. Post-fire NPP in forests that were dominated by fire-susceptible species were not as sensitive to FRP or FRE, indicating that NPP in these forests may be reduced to similar levels regardless of fire intensity. Conversely, post-fire NPP in forests dominated by fire resistant and mixed species decreased with increasing FRP or FRE. In some cases, this dose-response relationship persisted for more than a decade post-fire, highlighting a legacy effect of fire intensity on post-fire C dynamics in these forests.

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