scholarly journals Evaluating the Community Land Model (CLM 4.5) at a Coniferous Forest Site in Northwestern United States Using Flux and Carbon-Isotope Measurements

2016 ◽  
Author(s):  
Henrique F. Duarte ◽  
Brett M. Raczka ◽  
Daniel M. Ricciuto ◽  
John C. Lin ◽  
Charles D. Koven ◽  
...  
Keyword(s):  
United States ◽  
Drought Stress ◽  
Stomatal Conductance ◽  
Carbon Isotope ◽  
Coniferous Forest ◽  
Carbon Fluxes ◽  
Community Land Model ◽  
13C Discrimination ◽  
Isotope Measurements ◽  
Significant Underestimation

Abstract. Summer droughts in the western United States are expected to intensify with climate change. Thus, an adequate representation of ecosystem drought response in land models is critical for predicting carbon dynamics. The goal of this study was to assess the performance of the Community Land Model, Version 4.5 (CLM) for an old-growth coniferous forest in the Pacific Northwest region of the United States (Wind River AmeriFlux site), characterized by a climate that has heavy winter precipitation followed by summer drought. Particular attention was given to the model skill in the simulation of stomatal conductance and its response to drought stress. CLM was driven by site-observed meteorology and calibrated primarily using parameter values observed at the site or at similar stands in the region. Key model adjustments included parameters controlling specific leaf area and stomatal conductance. Default values of these parameters led to significant underestimation of gross primary production, overestimation of evapotranspiration, and consequently overestimation of photosynthetic 13C discrimination, reflected on reduced 13C:12C ratios of carbon fluxes and pools. Adjustments in soil hydraulic parameters within CLM were also critical, preventing significant underestimation of soil water content and unrealistic drought stress during summer. After calibration, CLM was able to simulate energy and carbon fluxes, leaf area index, biomass stocks, and carbon isotope ratios of carbon fluxes and pools in reasonable agreement with site observations. Overall, the calibrated CLM was able to simulate the observed response of canopy conductance to atmospheric vapor pressure deficit and soil water content, reasonably capturing the impact of drought stress on ecosystem functioning. The calibrated parameters may be of use for future modeling studies involving stands of similar age and composition under a similar climate regime. More broadly, the calibration of the Ball-Berry stomatal conductance model in CLM aligned with observations reported in the literature for coniferous trees, suggesting that a future release of CLM would benefit from using a distinct, lower slope value (mbb=6) for conifers, rather than a unique value for all C3 plants (mbb=9). Thanks to the recent implementation of photosynthetic 13C discrimination within CLM, the results of this study indicate that carbon isotope measurements can be used to constrain stomatal conductance and water use efficiency in CLM as an alternative to flux observations. They also have the potential to guide structural improvements in the model in respect to the representation of carbon storage pools.

scholarly journals Evaluating the Community Land Model (CLM4.5) at a coniferous forest site in northwestern United States using flux and carbon-isotope measurements

2017 ◽  
Vol 14 (18) ◽  
pp. 4315-4340 ◽  
Author(s):  
Henrique F. Duarte ◽  
Brett M. Raczka ◽  
Daniel M. Ricciuto ◽  
John C. Lin ◽  
Charles D. Koven ◽  
...  
Keyword(s):  
United States ◽  
Soil Moisture ◽  
Water Stress ◽  
Stomatal Conductance ◽  
Carbon Isotope ◽  
Coniferous Forest ◽  
Carbon Fluxes ◽  
Forest Site ◽  
Community Land Model ◽  
Significant Underestimation

Abstract. Droughts in the western United States are expected to intensify with climate change. Thus, an adequate representation of ecosystem response to water stress in land models is critical for predicting carbon dynamics. The goal of this study was to evaluate the performance of the Community Land Model (CLM) version 4.5 against observations at an old-growth coniferous forest site in the Pacific Northwest region of the United States (Wind River AmeriFlux site), characterized by a Mediterranean climate that subjects trees to water stress each summer. CLM was driven by site-observed meteorology and calibrated primarily using parameter values observed at the site or at similar stands in the region. Key model adjustments included parameters controlling specific leaf area and stomatal conductance. Default values of these parameters led to significant underestimation of gross primary production, overestimation of evapotranspiration, and consequently overestimation of photosynthetic 13C discrimination, reflected in reduced 13C : 12C ratios of carbon fluxes and pools. Adjustments in soil hydraulic parameters within CLM were also critical, preventing significant underestimation of soil water content and unrealistic soil moisture stress during summer. After calibration, CLM was able to simulate energy and carbon fluxes, leaf area index, biomass stocks, and carbon isotope ratios of carbon fluxes and pools in reasonable agreement with site observations. Overall, the calibrated CLM was able to simulate the observed response of canopy conductance to atmospheric vapor pressure deficit (VPD) and soil water content, reasonably capturing the impact of water stress on ecosystem functioning. Both simulations and observations indicate that stomatal response from water stress at Wind River was primarily driven by VPD and not soil moisture. The calibration of the Ball–Berry stomatal conductance slope (mbb) at Wind River aligned with findings from recent CLM experiments at sites characterized by the same plant functional type (needleleaf evergreen temperate forest), despite significant differences in stand composition and age and climatology, suggesting that CLM could benefit from a revised mbb value of 6, rather than the default value of 9, for this plant functional type. Conversely, Wind River required a unique calibration of the hydrology submodel to simulate soil moisture, suggesting that the default hydrology has a more limited applicability. This study demonstrates that carbon isotope data can be used to constrain stomatal conductance and intrinsic water use efficiency in CLM, as an alternative to eddy covariance flux measurements. It also demonstrates that carbon isotopes can expose structural weaknesses in the model and provide a key constraint that may guide future model development.

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.

scholarly journals The Influence of Chronic Ozone Exposure on Global Carbon and Water Cycles

2014 ◽  
Vol 28 (1) ◽  
pp. 292-305 ◽  
Author(s):  
D. Lombardozzi ◽  
Samuel Levis ◽  
G. Bonan ◽  
P. G. Hess ◽  
J. P. Sparks
Keyword(s):  
United States ◽  
Stomatal Conductance ◽  
North America ◽  
Southeast Asia ◽  
Greenhouse Gas ◽  
Eastern North America ◽  
Plant Responses ◽  
Eastern United States ◽  
Community Land Model ◽  
The Impact

Abstract Ozone (O3) is a phytotoxic greenhouse gas that has increased more than threefold at Earth’s surface from preindustrial values. In addition to directly increasing radiative forcing as a greenhouse gas, O3 indirectly impacts climate through altering the plant processes of photosynthesis and transpiration. While global estimates of gross primary productivity (GPP) have incorporated the effects of O3, few studies have explicitly determined the independent effects of O3 on transpiration. In this study, the authors include effects of O3 on photosynthesis and stomatal conductance from a recent literature review to determine the impact on GPP and transpiration and highlight uncertainty in modeling plant responses to O3. Using the Community Land Model, the authors estimate that present-day O3 exposure reduces GPP and transpiration globally by 8%–12% and 2%–2.4%, respectively. The largest reductions were in midlatitudes, with GPP decreasing up to 20% in the eastern United States, Europe, and Southeast Asia and transpiration reductions of up to 15% in the same regions. Larger reductions in GPP compared to transpiration decreased water-use efficiency 5%–10% in the eastern United States, Southeast Asia, Europe, and central Africa; increased surface runoff more than 15% in eastern North America; and altered patterns of energy fluxes in the tropics, high latitudes, and eastern North America. Future climate predictions will be improved if plant responses to O3 are incorporated into models such that stomatal conductance is modified independently of photosynthesis and the effects on transpiration are explicitly considered in surface energy budgets. Improvements will help inform regional decisions for managing changes in hydrology and surface temperatures in response to O3 pollution.

The Effects of Drought on Leaf Gas Exchange and Growth of Three Species of Herbaceous Perennials

HortScience ◽  
1998 ◽  
Vol 33 (3) ◽  
pp. 540a-540
Author(s):  
K.J. Prevete ◽  
R.T. Fernandez
Keyword(s):  
Drought Stress ◽  
Stomatal Conductance ◽  
Gas Exchange ◽  
Drought Tolerance ◽  
Transpiration Rate ◽  
Leaf Gas Exchange ◽  
Gas Analysis ◽  
Herbaceous Perennials ◽  
Effects Of Drought ◽  
Analysis System

Three species of herbaceous perennials were tested on their ability to withstand and recover from drought stress periods of 2, 4, and 6 days. Eupatorium rugosum and Boltonia asteroides `Snowbank' were chosen because of their reported drought intolerance, while Rudbeckia triloba was chosen based on its reported drought tolerance. Drought stress began on 19 Sept. 1997. Plants were transplanted into the field the day following the end of each stress period. The effects of drought on transpiration rate, stomatal conductance, and net photosynthetic rate were measured during the stress and throughout recovery using an infrared gas analysis system. Leaf gas exchange measurements were taken through recovery until there were no differences between the stressed plants and the control plants. Transpiration, stomatal conductance, and photosynthesis of Rudbeckia and Boltonia were not affected until 4 days after the start of stress. Transpiration of Eupatorium decreased after 3 days of stress. After rewatering, leaf gas exchange of Boltonia and Rudbeckia returned to non-stressed levels quicker than Eupatorium. Growth measurements were taken every other day during stress, and then weekly following transplanting. Measurements were taken until a killing frost that occurred on 3 Nov. There were no differences in the growth between the stressed and non-stressed plants in any of the species. Plants will be monitored throughout the winter, spring, and summer to determine the effects of drought on overwintering capability and regrowth.

scholarly journals Candidate genes and SNPs associated with stomatal conductance under drought stress in Vitis

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Massimiliano Trenti ◽  
Silvia Lorenzi ◽  
Pier Luigi Bianchedi ◽  
Daniele Grossi ◽  
Osvaldo Failla ◽  
...  
Keyword(s):  
Drought Stress ◽  
Stomatal Conductance ◽  
Candidate Genes ◽  
Water Deficit ◽  
Genetic Basis ◽  
Phenotypic Diversity ◽  
Snp Array ◽  
A Genome ◽  
Raffinose Synthase ◽  
Response To Water

Abstract Background Understanding the complexity of the vine plant’s response to water deficit represents a major challenge for sustainable winegrowing. Regulation of water use requires a coordinated action between scions and rootstocks on which cultivars are generally grafted to cope with phylloxera infestations. In this regard, a genome-wide association study (GWAS) approach was applied on an ‘ad hoc’ association mapping panel including different Vitis species, in order to dissect the genetic basis of transpiration-related traits and to identify genomic regions of grape rootstocks associated with drought tolerance mechanisms. The panel was genotyped with the GrapeReSeq Illumina 20 K SNP array and SSR markers, and infrared thermography was applied to estimate stomatal conductance values during progressive water deficit. Results In the association panel the level of genetic diversity was substantially lower for SNPs loci (0.32) than for SSR (0.87). GWAS detected 24 significant marker-trait associations along the various stages of drought-stress experiment and 13 candidate genes with a feasible role in drought response were identified. Gene expression analysis proved that three of these genes (VIT_13s0019g03040, VIT_17s0000g08960, VIT_18s0001g15390) were actually induced by drought stress. Genetic variation of VIT_17s0000g08960 coding for a raffinose synthase was further investigated by resequencing the gene of 85 individuals since a SNP located in the region (chr17_10,497,222_C_T) was significantly associated with stomatal conductance. Conclusions Our results represent a step forward towards the dissection of genetic basis that modulate the response to water deprivation in grape rootstocks. The knowledge derived from this study may be useful to exploit genotypic and phenotypic diversity in practical applications and to assist further investigations.

scholarly journals Accumulation of Silicon and Changes in Water Balance under Drought Stress in Brassica napus var. napus L.

Plants ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 280
Author(s):  
Diana Saja-Garbarz ◽  
Agnieszka Ostrowska ◽  
Katarzyna Kaczanowska ◽  
Franciszek Janowiak
Keyword(s):  
Abscisic Acid ◽  
Drought Stress ◽  
Stomatal Conductance ◽  
Water Balance ◽  
Water Content ◽  
Oilseed Rape ◽  
Potential Evapotranspiration ◽  
Leaf Water Content ◽  
Optimal Conditions ◽  
Abscisic Acid Level

The aim of this study was to investigate the accumulation of silicon in oilseed rape and to characterize the changes in chosen water balance parameters in response to drought. The following parameters were estimated: water content, osmotic and water potential, evapotranspiration, stomatal conductance and abscisic acid level under optimal and drought conditions. It was shown that oilseed rape plants accumulate silicon after its supplementation to the soil, both in the case of silicon alone and silicon together with iron. It was revealed that silicon (without iron) helps maintain constant water content under optimal conditions. While no silicon influence on osmotic regulation was observed, a transpiration decrease was detected under optimal conditions after silicon application. Under drought, a reduction in stomatal conductance was observed, but it was similar for all plants. The decrease in leaf water content under drought was accompanied by a significant increase in abscisic acid content in leaves of control plants and those treated with silicon together with iron. To sum up, under certain conditions, silicon is accumulated even in non-accumulator species, such as oilseed rape, and presumably improves water uptake under drought stress.

scholarly journals Predicting photosynthesis and transpiration responses to ozone: decoupling modeled photosynthesis and stomatal conductance

2012 ◽  
Vol 9 (8) ◽  
pp. 3113-3130 ◽  
Author(s):  
D. Lombardozzi ◽  
S. Levis ◽  
G. Bonan ◽  
J. P. Sparks
Keyword(s):  
Carbon Dioxide ◽  
Stomatal Conductance ◽  
Primary Productivity ◽  
Environmental Conditions ◽  
Water Exchange ◽  
Global Scale ◽  
Community Land Model ◽  
Climate Regulation ◽  
The Tropics ◽  
Tulip Poplar

Abstract. Plants exchange greenhouse gases carbon dioxide and water with the atmosphere through the processes of photosynthesis and transpiration, making them essential in climate regulation. Carbon dioxide and water exchange are typically coupled through the control of stomatal conductance, and the parameterization in many models often predict conductance based on photosynthesis values. Some environmental conditions, like exposure to high ozone (O3) concentrations, alter photosynthesis independent of stomatal conductance, so models that couple these processes cannot accurately predict both. The goals of this study were to test direct and indirect photosynthesis and stomatal conductance modifications based on O3 damage to tulip poplar (Liriodendron tulipifera) in a coupled Farquhar/Ball-Berry model. The same modifications were then tested in the Community Land Model (CLM) to determine the impacts on gross primary productivity (GPP) and transpiration at a constant O3 concentration of 100 parts per billion (ppb). Modifying the Vcmax parameter and directly modifying stomatal conductance best predicts photosynthesis and stomatal conductance responses to chronic O3 over a range of environmental conditions. On a global scale, directly modifying conductance reduces the effect of O3 on both transpiration and GPP compared to indirectly modifying conductance, particularly in the tropics. The results of this study suggest that independently modifying stomatal conductance can improve the ability of models to predict hydrologic cycling, and therefore improve future climate predictions.

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