Stable carbon isotopes as powerful tools for studying land-atmosphere flux exchanges and improving land surface models

The stable isotopic compositions of carbon and oxygen in terrestrial plants can provide valuable insights into plant eco-physiological responses to environmental changes at seasonal to annual resolution. Yet, the potential of these datasets to study land-atmosphere interactions remains under-exploited. Here, we present some examples of how stable carbon isotopes (&#948;13C) measured in plant materials (leaves and tree-rings) can be used to explore changes in the magnitude and variability of carbon and water flux exchanges between the vegetation and the atmosphere and to improve land surface models. First, we show that the discrimination against 13C (&#916;13C), calculated as the difference in &#948;13C between the source atmospheric CO2 and the plant material studied, varies strongly between regions and biomes and is useful for better understanding the CO2 fertilisation effect of plant growth. For example, tree-ring &#916;13C records from boreal evergreen forests in North America increased linearly with rising CO2 during the 20th century, suggesting that those forests have actively contributed to the land carbon sink by removing CO2 from the atmosphere at a relatively constant rate. However, such an increase in&#160;&#916;13C with rising CO2 is not observed everywhere. We found that over the same time period, while some forests had a fairly constant &#916;13C, others exhibited a slight decrease in &#916;13C over time, which might indicate a reduction of the capacity of trees to absorb CO2. Using a response function approach, we show that the differences between sites and regions are most likely the result of different evaporative demands and soil water availability conditions experienced by forests. We then discuss how predictions of the coupled carbon and water cycles by vegetation models can be improved by incorporating stable carbon isotopes to constrain the model representation of carbon-water fluxes regulation by leaf stomata. Specifically, we examine and evaluate simulations from the JULES vegetation model at different eddy-covariance forest sites where stable carbon isotopic data and canopy flux measurements are available. Overall, our analyses have strong implications for the understanding of historical changes in the strength of the CO2 fertilisation effect and in the water use efficiency of terrestrial ecosystems across regions.&#160;

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Holocene environmental changes in Red River delta, Vietnam as inferred from the stable carbon isotopes and C/N ratios

Journal of Earth System Science ◽

10.1007/s12040-018-1041-1 ◽

2018 ◽

Vol 128 (1) ◽

Author(s):

Nguyen Tai Tue ◽

Dang Minh Quan ◽

Pham Thao Nguyen ◽

Luu Viet Dung ◽

Tran Dang Quy ◽

...

Keyword(s):

Carbon Isotopes ◽

Stable Carbon Isotopes ◽

Environmental Changes ◽

River Delta ◽

Red River ◽

Stable Carbon ◽

Red River Delta

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Including Stable Carbon Isotopes to Evaluate the Dynamics of Soil Carbon in the Land‐Surface Model ORCHIDEE

Journal of Advances in Modeling Earth Systems ◽

10.1029/2018ms001392 ◽

2019 ◽

Vol 11 (11) ◽

pp. 3650-3669 ◽

Cited By ~ 2

Author(s):

Marta Camino‐Serrano ◽

Marwa Tifafi ◽

Jérôme Balesdent ◽

Christine Hatté ◽

Josep Peñuelas ◽

...

Keyword(s):

Soil Carbon ◽

Carbon Isotopes ◽

Land Surface ◽

Stable Carbon Isotopes ◽

Land Surface Model ◽

Surface Model ◽

Stable Carbon

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Stable carbon isotopes in the shell of Corbicula fluminea (Müller 1774): Implications for understanding environmental changes in drainage basins

Chinese Science Bulletin ◽

10.1007/s11434-010-4227-8 ◽

2010 ◽

Vol 55 (36) ◽

pp. 4162-4167 ◽

Cited By ~ 4

Author(s):

Hui Zhou ◽

CongQiang Liu ◽

Qian Jiang ◽

Wei Jiang ◽

YanLong Zhao ◽

...

Keyword(s):

Carbon Isotopes ◽

Stable Carbon Isotopes ◽

Environmental Changes ◽

Corbicula Fluminea ◽

Stable Carbon ◽

Drainage Basins

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Using the International Tree-Ring Data Bank (ITRDB) records as century-long benchmarks for land-surface models

10.5194/gmd-2020-29 ◽

2020 ◽

Author(s):

Jina Jeong ◽

Jonathan Barichivich ◽

Philippe Peylin ◽

Vanessa Haverd ◽

Matthew J. McGrath ◽

...

Keyword(s):

Data Processing ◽

Tree Ring ◽

Land Surface ◽

Environmental Changes ◽

Ring Width ◽

Data Bank ◽

Tree Ring Width ◽

Land Surface Models ◽

Tree Ring Data ◽

Surface Models

Abstract. The search for a long-term benchmark for land-surface models (LSM) has brought tree-ring data to the attention of the land-surface community as they record growth well before human-induced environmental changes became important. The most comprehensive archive of publicly shared tree-ring data is the International Tree-ring Data Bank (ITRDB). Many records in the ITRDB have, however, been collected almost exclusively with a view on maximizing an environmental target signal (e.g. climate), which has resulted in a biased representation of forested sites and landscapes and thus limits its use as a data source for benchmarking. The aim of this study is to propose advances in land-surface modelling and data processing to enable the land-surface community to re-use the ITRDB data as a much-needed century-long benchmark. Given that tree-ring width is largely explained by phenology, tree size, and climate sensitivity, LSMs that intend to use it as a benchmark should at least simulate tree phenology, size-dependent growth, differently-sized trees within a stand, and responses to changes in temperature, precipitation and atmospheric CO2 con¬cen¬tra¬tions. Yet, even if LSMs were capable of accurately simulating tree-ring width, sampling biases in the ITRDB need to be accounted for. This study proposes two solutions: exploiting the observation that the variation due to size-related growth by far exceeds the variation due to environmental changes; and simulating a size-structured population of trees. Combining the proposed advances in modelling and data processing resulted in four complementary benchmarks - reflecting different usage of the information contained in the ITRDB - each described by two metrics rooted in statistics that quantify the performance of the benchmark. Although the proposed benchmarks are unlikely to be precise, they advance the field by providing a much-needed large-scale constraint on changes in the simulated maximum tree diameter and annual growth increment for the transition from pre-industrial to present-day environmental conditions over the past century. Hence, the proposed benchmarks open up new ways of exploring the ITRDB archive, stimulate the dendrochronological community to refine its sampling protocols to produce new and spatially unbiased tree-ring networks, and help the modelling community to move beyond the short-term benchmarking of LSM.

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An observational constraint on stomatal function in forests: evaluating coupled carbon and water vapor exchange with carbon isotopes in the Community Land Model (CLM 4.5)

10.5194/bg-2016-73 ◽

2016 ◽

Author(s):

Brett Raczka ◽

Henrique F. Duarte ◽

Charles D. Koven ◽

Daniel Ricciuto ◽

Peter E. Thornton ◽

...

Keyword(s):

Carbon Isotopes ◽

Land Surface ◽

Nitrogen Limitation ◽

Stable Carbon Isotopes ◽

Stable Carbon Isotope ◽

Atmospheric Co2 ◽

Stable Carbon ◽

Conifer Forest ◽

Isotope Discrimination ◽

Community Land Model

Abstract. Land surface models are useful tools to quantify contemporary and future climate impact on terrestrial carbon cycle processes, provided they can be appropriately constrained and tested with observations. Stable carbon isotopes of CO2 offer the potential to improve model representation of the coupled carbon and water cycles because they are strongly influenced by stomatal function. Recently, a representation of stable carbon isotope discrimination was incorporated into the Community Land Model component of the Community Earth System Model. Here, we tested the model's capability to simulate whole-forest isotope discrimination in a subalpine conifer forest at Niwot Ridge, Colorado, USA. We distinguished between isotopic behavior in response to a decrease of δ13C within atmospheric CO2 (Suess effect) vs. photosynthetic discrimination (Δcanopy), by creating a site-customized atmospheric CO2 and δ13C of CO2 time series. We implemented a seasonally-varying Vcmax model calibration that best matched site observations of net CO2 carbon exchange, latent heat exchange and biomass. The model accurately simulated observed δ13C of needle and stem tissue, but underestimated the δ13C of bulk soil carbon by 1–2 ‰. The model overestimated the multi-year (2006–2012) average Δcanopy relative to prior data-based estimates by 5–6 ‰. The amplitude of the average seasonal cycle of Δcanopy (i.e. higher in spring/fall as compared to summer) was correctly modeled but only with an alternative nitrogen limitation formulation for the model. The model attributed most of the seasonal variation in discrimination to the net assimilation rate (An), whereas inter-annual variation in simulated Δcanopy during the summer months was driven by stomatal response to vapor pressure deficit. Soil moisture did not influence modeled Δcanopy. The model simulated a 10 % increase in both photosynthetic discrimination and water use efficiency (WUE) since 1850 as a result of CO2 fertilization, forced by constant climate conditions. This increasing trend in discrimination is counter to well-established relationships between discrimination and WUE. The isotope observations used here to constrain CLM suggest 1) the model overestimated stomatal conductance and 2) the default CLM approach to representing nitrogen limitation (post-photosynthetic limitation) was not capable of reproducing observed trends in discrimination. These findings demonstrate that isotope observations can provide important information related to stomatal function driven by environmental stress from VPD and nitrogen limitation.

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Plant phenology evaluation of CRESCENDO land surface models – Part 1: Start and end of the growing season

Biogeosciences ◽

10.5194/bg-18-2405-2021 ◽

2021 ◽

Vol 18 (7) ◽

pp. 2405-2428

Author(s):

Daniele Peano ◽

Deborah Hemming ◽

Stefano Materia ◽

Christine Delire ◽

Yuanchao Fan ◽

...

Keyword(s):

Land Surface ◽

Model Comparison ◽

Environmental Changes ◽

Growing Season ◽

Plant Phenology ◽

Land Surface Models ◽

Area Index ◽

Carbon Cycles ◽

Vegetation Modelling ◽

Surface Models

Abstract. Plant phenology plays a fundamental role in land–atmosphere interactions, and its variability and variations are an indicator of climate and environmental changes. For this reason, current land surface models include phenology parameterizations and related biophysical and biogeochemical processes. In this work, the climatology of the beginning and end of the growing season, simulated by the land component of seven state-of-the-art European Earth system models participating in the CMIP6, is evaluated globally against satellite observations. The assessment is performed using the vegetation metric leaf area index and a recently developed approach, named four growing season types. On average, the land surface models show a 0.6-month delay in the growing season start, while they are about 0.5 months earlier in the growing season end. The difference with observation tends to be higher in the Southern Hemisphere compared to the Northern Hemisphere. High agreement between land surface models and observations is exhibited in areas dominated by broadleaf deciduous trees, while high variability is noted in regions dominated by broadleaf deciduous shrubs. Generally, the timing of the growing season end is accurately simulated in about 25 % of global land grid points versus 16 % in the timing of growing season start. The refinement of phenology parameterization can lead to better representation of vegetation-related energy, water, and carbon cycles in land surface models, but plant phenology is also affected by plant physiology and soil hydrology processes. Consequently, phenology representation and, in general, vegetation modelling is a complex task, which still needs further improvement, evaluation, and multi-model comparison.

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Plant phenology evaluation of CRESCENDO land surface models – Part I: start and end of growing season

10.5194/bg-2020-319 ◽

2020 ◽

Author(s):

Daniele Peano ◽

Deborah Hemming ◽

Stefano Materia ◽

Christine Delire ◽

Yuanchao Fan ◽

...

Keyword(s):

Land Surface ◽

Model Comparison ◽

Environmental Changes ◽

Growing Season ◽

Plant Phenology ◽

Land Surface Models ◽

Area Index ◽

Vegetation Modelling ◽

Surface Models ◽

Broad Leaf

Abstract. Plant phenology plays a fundamental role in land-atmosphere interactions, and its variability and variations are an indicator of climate and environmental changes. For this reason, current land surface models include phenology parameterizations and related biophysical and biogeochemical processes. In this work, the climatology of beginning and end of the growing season, simulated by seven state-of-the-art European land surface models, is evaluated globally against satellite observations. The assessment is performed using the vegetation metric leaf area index and a recently-developed approach, named four growing season types. On average, the land surface models show a 0.6-month delay in the growing season start, while they are about 0.5 months earlier in the growing season end. Difference with observation tends to be higher in the Southern Hemisphere compared to the Northern Hemisphere. High agreement between land surface models and observations is exhibited in areas dominated by broad-leaf deciduous trees, while high variability is noted in regions dominated by broad-leaf deciduous shrubs. Generally, the timing of the growing season end is accurately simulated in about 25 % of global land grid points versus 16 % in the timing of growing season start. The refinement of phenology parameterization can lead to better representation of vegetation-related energy, water, and carbon cycles in land surface models, but plant phenology is also affected by plant physiology and soil hydrology processes. Consequently, phenology representation and, in general, vegetation modelling is a complex task, which still needs further improvement, evaluation, and multi-model comparison.

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