Explaining Global Increases in Water Use Efficiency: Why Have We Overestimated Responses to Rising Atmospheric CO2 in Natural Forest Ecosystems?

Silva, Lucas C. R.; Horwáth, William R.

doi:10.1371/journal.pone.0053089

Cited by 73 publications

(66 citation statements)

References 23 publications

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“…Net photosynthetic carbon assimilation (A net ), stomatal conductance (g s ), and evapotranspiration (E) were subsequently measured at growth light intensity (1400 mmol quanta m 22 s 21 ) once steady-state assimilation was achieved. IWUE was calculated as A/g s , according to Silva and Horwath (2013). A/C i curves were measured on days 0 and 36.…”

Section: Photosynthetic Gas Exchangementioning

confidence: 99%

Elevated temperature and CO2 stimulate late season photosynthesis but impair cold hardening in pine

et al. 2016

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Rising global temperature and CO 2 levels may sustain late-season net photosynthesis of evergreen conifers but could also impair the development of cold hardiness. Our study investigated how elevated temperature, and the combination of elevated temperature with elevated CO 2 , affected photosynthetic rates, leaf carbohydrates, freezing tolerance, and proteins involved in photosynthesis and cold hardening in Eastern white pine (Pinus strobus). We designed an experiment where control seedlings were acclimated to long photoperiod (day/night 14/10 h), warm temperature (22°C/15°C), and either ambient (400 mL L 21 ) or elevated (800 mmol mol 21 ) CO 2 , and then shifted seedlings to growth conditions with short photoperiod (8/16 h) and low temperature/ambient CO 2 (LTAC), elevated temperature/ambient CO 2 (ETAC), or elevated temperature/elevated CO 2 (ETEC). Exposure to LTAC induced down-regulation of photosynthesis, development of sustained nonphotochemical quenching, accumulation of soluble carbohydrates, expression of a 16-kD dehydrin absent under long photoperiod, and increased freezing tolerance. In ETAC seedlings, photosynthesis was not down-regulated, while accumulation of soluble carbohydrates, dehydrin expression, and freezing tolerance were impaired. ETEC seedlings revealed increased photosynthesis and improved water use efficiency but impaired dehydrin expression and freezing tolerance similar to ETAC seedlings. Sixteen-kilodalton dehydrin expression strongly correlated with increases in freezing tolerance, suggesting its involvement in the development of cold hardiness in P. strobus. Our findings suggest that exposure to elevated temperature and CO 2 during autumn can delay down-regulation of photosynthesis and stimulate late-season net photosynthesis in P. strobus seedlings. However, this comes at the cost of impaired freezing tolerance. Elevated temperature and CO 2 also impaired freezing tolerance. However, unless the frequency and timing of extreme low-temperature events changes, this is unlikely to increase risk of freezing damage in P. strobus seedlings.

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Section: Photosynthetic Gas Exchangementioning

confidence: 99%

Elevated temperature and CO2 stimulate late season photosynthesis but impair cold hardening in pine

et al. 2016

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“…For example, tree ring widths potentially record changes in tree productivity, but low-frequency growth trends attributable to rising CO 2 concentrations might be removed by standardization (Melvin and Briffa, 2008;Cecile et al, 2013), in which case the inversion algorithm (like any other reconstruction method) would converge towards unrealistic trends that are exempt of any CO 2 imprint. Similarly, it has been argued by Silva and Horwath (2013) that, due to an artifact of calculation, δ 13 C chronologies might systematically overestimate the response of carbon isotopes to rising CO 2 concentrations, therefore creating artificial increases in reconstructed water use efficiency. However, as mentioned by McCarroll and Loader (2004) and also by Silva and Horwath (2013) for the particular case of CO 2 effects, the solution might lie in the use of multiple proxies, as it is proposed here.…”

Section: Is the Reconstruction Affected By Changes In Atmospheric Co mentioning

confidence: 99%

An inverse modeling approach for tree-ring-based climate reconstructions under changing atmospheric CO<sub>2</sub> concentrations

Boucher¹,

Guiot

Hatté

et al. 2014

Biogeosciences

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Abstract. Over the last decades, dendroclimatologists have relied upon linear transfer functions to reconstruct historical climate. Transfer functions need to be calibrated using recent data from periods where CO 2 concentrations reached unprecedented levels (near 400 ppm -parts per million). Based on these transfer functions, dendroclimatologists must then reconstruct a different past, a past where CO 2 concentrations were far below 300 ppm. However, relying upon transfer functions calibrated in this way may introduce an unanticipated bias in the reconstruction of past climate, particularly if CO 2 has had a noticeable impact on tree growth and water use efficiency since the beginning of the industrial era. As an alternative to the transfer function approach, we run the MAIDENiso ecophysiological model in an inverse mode to link together climatic variables, atmospheric CO 2 concentrations and tree growth parameters. Our approach endeavors to find the optimal combination of meteorological conditions that best simulate observed tree ring patterns. We test our approach in the Fontainebleau Forest (France). By comparing two different CO 2 scenarios, we present evidence that increasing CO 2 concentrations have had a slight, yet significant, effect on the reconstruction results. We demonstrate that realistic CO 2 concentrations need to be inputted in the inversion so that observed increasing trends in summer temperature are adequately reconstructed. Fixing CO 2 concentrations at preindustrial levels (280 ppm) results in undesirable compensation effects that force the inversion algorithm to propose climatic values that lie outside from the bounds of observed climatic variability. Ultimately, the inversion approach has several advantages over traditional transfer function approaches, most notably its ability to separate climatic effects from CO 2 imprints on tree growth. Therefore, our method produces reconstructions that are less biased by anthropogenic greenhouse gas emissions and that are based on sound ecophysiological knowledge.

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“…The results of Berninger et al (2004) show that, although photosynthesis increases in response to increasing CO 2 concentrations, tree growth rate cannot parallel the increase in photosynthesis because the potential growth rate is limited directly by temperature through nitrogen mineralization. The apparent fertilization effect of the models, related to water use efficiency (WUE) enhancement, itself due to a decrease in stomatal area, has not been observed in experimental chambers or in tree-ring series (Gedalof and Berg, 2010;Silva and Horwath, 2013). There is therefore much controversy as to whether the increase in CO 2 since the beginning of the industrial period has enhanced growth, with much recent evidence reporting changes in plant physiological processes but not in growth (Huang et al, 2007;Andreu-Hayles et al, 2011;Peñuelas et al, 2011;Girardin et al, 2012;Lévesque et al, 2014).…”

Section: Tree-growth Process Modelsmentioning

confidence: 99%

“…Without the fertilization effect, tree growth will decrease because of lack of water (the precipitation deficit is amplified by more evapotranspiration), but if the latter effect is included, tree-growth will increase. As mentioned in the literature review in the introduction section, this fertilization effect is not always observed on living trees and is subject to controversy (Gedalof and Berg, 2010;Silva and Horwath, 2013).…”

Section: Calibration and Predictionmentioning

confidence: 99%

Process models and model-data fusion in dendroecology

2014

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Dendrochronology (i.e., the study of annually dated tree-ring time series) has proved to be a powerful technique to understand tree-growth. This paper intends to show the interest of using ecophysiological modeling not only to understand and predict tree-growth (dendroecology) but also to reconstruct past climates (dendroclimatology). Process models have been used for several decades in dendroclimatology, but it is only recently that methods of model-data fusion have led to significant progress in modeling tree-growth as a function of climate and in reconstructing past climates. These model-data fusion (MDF) methods, mainly based on the Bayesian paradigm, have been shown to be powerful for both model calibration and model inversion. After a rapid survey of tree-growth modeling, we illustrate MDF with examples based on series of Southern France Aleppo pines and Central France oaks. These examples show that if plants experienced CO 2 fertilization, this would have a significant effect on tree-growth which in turn would bias the climate reconstructions. This bias could be extended to other environmental non-climatic factors directly or indirectly affecting annual ring formation and not taken into account in classical empirical models, which supports the use of more complex process-based models. Finally, we conclude by showing the interest of the data assimilation methods applied in climatology to produce climate re-analyses.

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Explaining Global Increases in Water Use Efficiency: Why Have We Overestimated Responses to Rising Atmospheric CO2 in Natural Forest Ecosystems?

Cited by 73 publications

References 23 publications

Elevated temperature and CO2 stimulate late season photosynthesis but impair cold hardening in pine

Elevated temperature and CO2 stimulate late season photosynthesis but impair cold hardening in pine

An inverse modeling approach for tree-ring-based climate reconstructions under changing atmospheric CO<sub>2</sub> concentrations

Process models and model-data fusion in dendroecology

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Explaining Global Increases in Water Use Efficiency: Why Have We Overestimated Responses to Rising Atmospheric CO2 in Natural Forest Ecosystems?

Cited by 73 publications

References 23 publications

Elevated temperature and CO2 stimulate late season photosynthesis but impair cold hardening in pine

Elevated temperature and CO2 stimulate late season photosynthesis but impair cold hardening in pine

An inverse modeling approach for tree-ring-based climate reconstructions under changing atmospheric CO&lt;sub&gt;2&lt;/sub&gt; concentrations

Process models and model-data fusion in dendroecology

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Product

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An inverse modeling approach for tree-ring-based climate reconstructions under changing atmospheric CO<sub>2</sub> concentrations