scholarly journals 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)

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.

scholarly journals An observational constraint on stomatal function in forests: evaluating coupled carbon and water vapor exchange with carbon isotopes in the Community Land Model (CLM4.5)

2016 ◽  
Vol 13 (18) ◽  
pp. 5183-5204 ◽  
Author(s):  
Brett Raczka ◽  
Henrique F. Duarte ◽  
Charles D. Koven ◽  
Daniel Ricciuto ◽  
Peter E. Thornton ◽  
...  
Keyword(s):  
Stomatal Conductance ◽  
Carbon Isotope ◽  
Carbon Isotopes ◽  
Nitrogen Limitation ◽  
Carbon Isotope Discrimination ◽  
Stable Carbon Isotope ◽  
Atmospheric Co2 ◽  
Stable Carbon ◽  
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 multiyear (2006–2012) average Δcanopy relative to prior data-based estimates by 2–4 ‰. The amplitude of the average seasonal cycle of Δcanopy (i.e., higher in spring/fall as compared to summer) was correctly modeled but only when using a revised, fully coupled An − gs (net assimilation rate, stomatal conductance) version of the model in contrast to the partially coupled An − gs version used in the default model. The model attributed most of the seasonal variation in discrimination to An, whereas interannual variation in simulated Δcanopy during the summer months was driven by stomatal response to vapor pressure deficit (VPD). The model simulated a 10 % increase in both photosynthetic discrimination and water-use efficiency (WUE) since 1850 which is counter to 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 (partially coupled model) 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. Future versions of CLM that incorporate carbon isotope discrimination are likely to benefit from explicit inclusion of mesophyll conductance.

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

2021 ◽  
Author(s):  
Aliénor Lavergne ◽  
Laia Andreu-Hayles ◽  
Soumaya Belmecheri ◽  
Rossella Guerrieri ◽  
Heather Graven
Keyword(s):  
Carbon Isotopes ◽  
Land Surface ◽  
Stable Carbon Isotopes ◽  
Environmental Changes ◽  
Carbon Sink ◽  
Stable Carbon ◽  
Land Surface Models ◽  
Terrestrial Plants ◽  
Plant Materials ◽  
Surface Models

<p>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 (δ<sup>13</sup>C) 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.<strong> </strong></p><p>First, we show that the discrimination against <sup>13</sup>C (Δ<sup>13</sup>C), calculated as the difference in δ<sup>13</sup>C between the source atmospheric CO<sub>2 </sub>and the plant material studied, varies strongly between regions and biomes and is useful for better understanding the CO<sub>2</sub> fertilisation effect of plant growth. For example, tree-ring Δ<sup>13</sup>C records from boreal evergreen forests in North America increased linearly with rising CO<sub>2</sub> during the 20<sup>th</sup> century, suggesting that those forests have actively contributed to the land carbon sink by removing CO<sub>2</sub> from the atmosphere at a relatively constant rate. However, such an increase in Δ<sup>13</sup>C with rising CO<sub>2</sub> is not observed everywhere. We found that over the same time period, while some forests had a fairly constant Δ<sup>13</sup>C, others exhibited a slight decrease in Δ<sup>13</sup>C over time, which might indicate a reduction of the capacity of trees to absorb CO<sub>2</sub>. 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.<strong> </strong></p><p>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 CO<sub>2</sub> fertilisation effect and in the water use efficiency of terrestrial ecosystems across regions.</p><p> </p>

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

2019 ◽  
Vol 11 (11) ◽  
pp. 3650-3669 ◽  
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

Vertical stratification of Neotropical leaf-nosed bats (Chiroptera: Phyllostomidae) revealed by stable carbon isotopes

2011 ◽  
Vol 27 (03) ◽  
pp. 211-222 ◽  
Author(s):  
Katja Rex ◽  
Robert Michener ◽  
Thomas H. Kunz ◽  
Christian C. Voigt
Keyword(s):  
Carbon Isotope ◽  
Carbon Isotopes ◽  
Species Interactions ◽  
Rain Forest ◽  
Stable Carbon Isotopes ◽  
Stable Carbon Isotope ◽  
The Body ◽  
Vertical Stratification ◽  
Forest Site ◽  
Stable Carbon

Abstract:Tropical rain forests harbour the most diverse plant and animal assemblages known to science, but our understanding of assemblage structure and species interactions is limited. Bats, as the only flying mammals, have the potential to exploit resources from all strata in forest communities. Thus, fruit-eating phyllostomid bats often have been categorized into canopy-, subcanopy- and understorey-foraging species, based largely upon the height at which they were most frequently captured. Here we challenge this classification and use stable carbon isotopes to assess foraging height of bat species at an Amazonian rain-forest site in Ecuador and at a Caribbean lowland rain-forest site in Costa Rica for comparison with data from mist-net captures. The proportion of the heavy stable carbon isotope13C in relation to the lighter12C isotope increases in plants from ground level to the canopy (0.12‰ m−1–0.18‰ m−1), and these differences in stable carbon isotope signatures are reflected in the body tissue of phytophagous bats. We used the stable carbon isotope ratio (δ13C) of wing tissue to estimate the foraging heights of 54 phyllostomid species in two Neotropical bat assemblages. Based on stable isotope data, phyllostomid species exploit food resources at all vertical strata of the forest. Capture height was not a reliable predictor of foraging height and suggests that bats most likely use lower strata to commute between foraging sites to avoid predators. Vertical stratification is likely to be a key factor promoting niche partitioning, thus promoting high local species richness in many tropical animal assemblages.

scholarly journals Degradation changes stable carbon isotope depth profiles in palsa peatlands

2014 ◽  
Vol 11 (1) ◽  
pp. 1383-1412 ◽  
Author(s):  
J. P. Krüger ◽  
J. Leifeld ◽  
C. Alewell
Keyword(s):  
Carbon Isotope ◽  
Carbon Isotopes ◽  
Stable Carbon Isotopes ◽  
Stable Carbon Isotope ◽  
Stable Carbon ◽  
Δ13c Values ◽  
Depth Profiles ◽  
Degradation Rates ◽  
Aerobic Decomposition ◽  
Permafrost Thawing

Abstract. Palsa peatlands are a significant carbon pool in the global carbon cycle and are projected to change by global warming due to accelerated permafrost thaw. Our aim was to use stable carbon isotopes as indicators of palsa degradation. Depth profiles of stable carbon isotopes generally reflect organic matter dynamics in soils with an increase of δ13C values during aerobic decomposition and stable or decreasing δ13C values with depth during anaerobic decomposition. Stable carbon isotope depth profiles of undisturbed and degraded sites of hummocks as well as hollows at three palsa peatlands in northern Sweden were used to investigate the degradation processes. The depth patterns of stable isotopes clearly differ between intact and degraded hummocks at all sites. Erosion and cryoturbation at the degraded sites significantly changes the stable carbon isotope depth profiles. At the intact hummocks the uplifting of peat material by permafrost is indicated by a turning in the δ13C depth trend and this assessment is supported by a change in the C / N ratios. For hollows isotope patterns were less clear, but some hollows and degraded hollows in the palsa peatlands show differences in their stable carbon isotope depth profiles indicating enhanced degradation rates. We conclude that the degradation of palsa peatlands by accelerated permafrost thawing could be identified with stable carbon isotope depth profiles. At intact hummocks δ13C depth patterns display the uplifting of peat material by a change in peat decomposition processes.

scholarly journals Stable Carbon Isotopes in Zea mays

2018 ◽  
Author(s):  
Robert J. Twohey ◽  
Lucas M. Roberts ◽  
Anthony J. Studer
Keyword(s):  
Zea Mays ◽  
Carbon Isotopes ◽  
Water Use ◽  
Stable Carbon Isotopes ◽  
Carbon Fixation ◽  
Isotope Composition ◽  
Stable Carbon Isotope ◽  
Climate Change Scenarios ◽  
Transpiration Efficiency ◽  
Stable Carbon

SummaryThe increasing demand for food production and predicted climate change scenarios highlight the need for improvements in crop sustainability. The efficient use of water will become increasingly important for rainfed agricultural crops even in fertile regions that have historically received ample precipitation. Improvements in water-use efficiency in Zea mays have been limited, and warrants a renewed effort aided by molecular breeding approaches. Progress has been constrained by the difficulty of measuring water-use in a field environment. The stable carbon isotope composition (δ13C) of the leaf has been proposed as an integrated signature of carbon fixation with a link to stomatal conductance. However, additional factors affecting leaf δ13C exist, and a limited number of studies have explored this trait in Z. mays. Here we present an extensive characterization of leaf δ13C in Z. mays. Significant variation in leaf δ13C exists across diverse lines of Z. mays, which we show to be heritable across several environments.Furthermore, we examine temporal and spatial variation in leaf δ13C to determine the optimum sampling time to maximize the use of leaf δ13C as a trait. Finally, our results demonstrate the relationship between transpiration and leaf δ13C in the field and the greenhouse. Decreasing transpiration and soil moisture are associated with decreasing leaf δ13C. Taken together these results outline a strategy for using leaf δ13C and reveal its usefulness as a measure of transpiration efficiency under well-watered conditions rather than a predictor of performance under drought.Significance StatementThis study identifies sources of variation in stable carbon isotopes of maize leaves and establishes the framework for connecting leaf δ13C and transpiration efficiency.

scholarly journals Stable carbon isotopes as indicators for environmental change in palsa peats

2011 ◽  
Vol 8 (7) ◽  
pp. 1769-1778 ◽  
Author(s):  
C. Alewell ◽  
R. Giesler ◽  
J. Klaminder ◽  
J. Leifeld ◽  
M. Rollog
Keyword(s):  
Environmental Change ◽  
Carbon Isotope ◽  
Carbon Isotopes ◽  
Climate Warming ◽  
Anaerobic Degradation ◽  
Stable Carbon Isotopes ◽  
Stable Carbon Isotope ◽  
Stable Carbon ◽  
Depth Profiles ◽  
Water Saturated

Abstract. Palsa peats are unique northern ecosystems formed under an arctic climate and characterized by a high biodiversity and sensitive ecology. The stability of the palsas are seriously threatened by climate warming which will change the permafrost dynamic and induce a degradation of the mires. We used stable carbon isotope depth profiles in two palsa mires of Northern Sweden to track environmental change during the formation of the mires. Soils dominated by aerobic degradation can be expected to have a clear increase of carbon isotopes (δ13C) with depth, due to preferential release of 12C during aerobic mineralization. In soils with suppressed degradation due to anoxic conditions, stable carbon isotope depth profiles are either more or less uniform indicating no or very low degradation or depth profiles turn to lighter values due to an enrichment of recalcitrant organic substances during anaerobic mineralisation which are depleted in 13C. The isotope depth profile of the peat in the water saturated depressions (hollows) at the yet undisturbed mire Storflaket indicated very low to no degradation but increased rates of anaerobic degradation at the Stordalen site. The latter might be induced by degradation of the permafrost cores in the uplifted areas (hummocks) and subsequent breaking and submerging of the hummock peat into the hollows due to climate warming. Carbon isotope depth profiles of hummocks indicated a turn from aerobic mineralisation to anaerobic degradation at a peat depth between 4 and 25 cm. The age of these turning points was 14C dated between 150 and 670 yr and could thus not be caused by anthropogenically induced climate change. We found the uplifting of the hummocks due to permafrost heave the most likely explanation for our findings. We thus concluded that differences in carbon isotope profiles of the hollows might point to the disturbance of the mires due to climate warming or due to differences in hydrology. The characteristic profiles of the hummocks are indicators for micro-geomorphic change during permafrost up heaving.

scholarly journals Degradation changes stable carbon isotope depth profiles in palsa peatlands

2014 ◽  
Vol 11 (12) ◽  
pp. 3369-3380 ◽  
Author(s):  
J. P. Krüger ◽  
J. Leifeld ◽  
C. Alewell
Keyword(s):  
Carbon Isotope ◽  
Carbon Isotopes ◽  
Stable Carbon Isotopes ◽  
Stable Carbon Isotope ◽  
Stable Carbon ◽  
Δ13c Values ◽  
Depth Profiles ◽  
Degradation Rates ◽  
Aerobic Decomposition ◽  
Permafrost Thawing

Abstract. Palsa peatlands are a significant carbon pool in the global carbon cycle and are projected to change by global warming due to accelerated permafrost thaw. Our aim was to use stable carbon isotopes as indicators of palsa degradation. Depth profiles of stable carbon isotopes generally reflect organic matter dynamics in soils with an increase of δ13C values during aerobic decomposition and stable or decreasing δ13C values with depth during anaerobic decomposition. Stable carbon isotope depth profiles of undisturbed and degraded sites of hummocks as well as hollows at three palsa peatlands in northern Sweden were used to investigate the degradation processes. The depth patterns of stable isotopes clearly differ between intact and degraded hummocks at all sites. Erosion and cryoturbation at the degraded sites significantly changes the stable carbon isotope depth profiles. At the intact hummocks the uplifting of peat material by permafrost is indicated by a turning in the δ13C depth trend, and this assessment is supported by a change in the C / N ratios. For hollows isotope patterns were less clear, but some hollows and degraded hollows in the palsa peatlands show differences in their stable carbon isotope depth profiles indicating enhanced degradation rates. We conclude that the degradation of palsa peatlands by accelerated permafrost thawing can be identified with stable carbon isotope depth profiles. At intact hummocks δ13C depth patterns display the uplifting of peat material by a change in peat decomposition processes.

scholarly journals Nutrient Incorporation in First Feeding Seahorses Evidenced by Stable Carbon Isotopes

Animals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 470
Author(s):  
Sonia Valladares ◽  
Miquel Planas
Keyword(s):  
Carbon Isotopes ◽  
Stable Carbon Isotopes ◽  
Stable Carbon Isotope ◽  
Survival Rates ◽  
Assimilation Efficiency ◽  
Stable Carbon ◽  
Δ13c Values ◽  
Growth And Survival ◽  
Feeding Experiments ◽  
Nutrient Assimilation

Nutritional issues are among the most critical factors in the initial survival of juvenile seahorses. Currently, there is a knowledge gap on the relationship between nutrient assimilation and the effects on initial mortalities and growth. In the present study, the stable isotope approach was used to assess the incorporation of two live preys (Artemia and copepods) in juvenile seahorses Hippocampus guttulatus. The changes in stable carbon isotope (δ13C) values were studied through two feeding experiments: feeding on Artemia or copepods (experiment 1), and shifting feeding from copepods to Artemia (experiment 2). In experiment 1, after 24–48 h of feeding, juvenile seahorses exhibited small but progressive changes in δ13C values towards those of the corresponding diet, indicating that the assimilation of the food offered was progressively enhanced from days 2–3. Similarly, in experiment 2, a diet shifting from copepods to Artemia caused an increase in δ13C values, reflecting a switch towards the isotopically enriched new diet (Artemia metanauplii). Differences in the assimilation efficiency of preys offered are discussed based on growth and survival rates. The enhanced growth performances and survivals achieved when the juveniles were fed on copepods could be related to higher efficient assimilation of copepods compared to Artemia. The present study demonstrates that the consumption and further assimilation of preys by juvenile seahorses could be traced using stable carbon isotopes. The research on nutrient assimilation of juvenile seahorses should enhance our knowledge on nutrient processes in developing seahorses for a better understanding of initial ontogeny in the early life stages of the species.

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