An experimental and modeling study of responses in ecosystems carbon exchanges to increasing CO2 concentrations using a tropical rainforest mesocosm

The ecosystem carbon exchanges in the enclosed rainforest of Biosphere 2, an enclosed apparatus comprised of large synthetic ecosystems, were measured and modeled during the winter of 1995–1996 under different atmospheric CO2 concentrations. On eight separate days, this mesocosm was exposed to various levels of CO2 ranging from about 380 to 820 µmol mol-1 daily mean and then sealed 24 hours for continuous measurements of ecosystem CO2 fluxes. Our results indicated that net ecosystem carbon exchange in the mesocosm was enhanced by increasing CO2 over the short periods studied (2–7 weeks), but, as expected from physiological studies, the response is not linear. The main effect of short-term CO2 change was the enhancement of canopy CO 2 assimilation, while soil respiration was not affected by the atmospheric CO2 concentration. The whole ecosystem radiation use efficiency was significantly higher under higher CO2. The results of direct measurements were predicted well by a simple canopy model (the ‘big-leaf’ model) that incorporates current physiological understanding of the biochemistry of leaf photosynthesis. Validation of this model with a range of CO2 and light levels indicates that it can be used with confidence to predict the responses of natural ecosystems to global climate change. Response of ecosystem processes to elevated CO2 with relaxation time longer than a few weeks could not be resolved in this study, but longer-term closure experiments are planned to examine these processes.

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Effects of CO2, continental distribution, topography and vegetation changes on the climate at the Middle Miocene: a model study

Climate of the Past ◽

10.5194/cp-6-675-2010 ◽

2010 ◽

Vol 6 (5) ◽

pp. 675-694 ◽

Cited By ~ 42

Author(s):

A.-J. Henrot ◽

L. François ◽

E. Favre ◽

M. Butzin ◽

M. Ouberdous ◽

...

Keyword(s):

Atmospheric Carbon Dioxide ◽

Middle Miocene ◽

Co2 Concentration ◽

Atmospheric Co2 ◽

The Tibetan Plateau ◽

Humid Climate ◽

Vegetation Feedback ◽

Co2 Concentrations ◽

Reduced Height ◽

Atmospheric Co2 Concentrations

Abstract. The Middle Miocene was one of the last warm periods of the Neogene, culminating with the Middle Miocene Climatic Optimum (MMCO, approximatively 17–15 Ma). Several proxy-based reconstructions support warmer and more humid climate during the MMCO. The mechanisms responsible for the warmer climate at the MMCO and particularly the role of the atmospheric carbon dioxide are still highly debated. Here we carried out a series of sensitivity experiments with the model of intermediate complexity Planet Simulator, investigating the contributions of the absence of ice on the continents, the opening of the Central American and Eastern Tethys Seaways, the lowering of the topography on land, the effect of various atmospheric CO2 concentrations and the vegetation feedback. Our results show that a higher than present-day CO2 concentration is necessary to generate a warmer climate at all latitudes at the Middle Miocene, in agreement with the terrestrial proxy reconstructions which suggest high atmospheric CO2 concentrations at the MMCO. Nevertheless, the changes in sea-surface conditions, the lowering of the topography on land and the vegetation feedback also produce significant local warming that may, locally, even be stronger than the CO2 induced temperature increases. The lowering of the topography leads to a more zonal atmospheric circulation and allows the westerly flow to continue over the lowered Plateaus at mid-latitudes. The reduced height of the Tibetan Plateau notably prevents the development of a monsoon-like circulation, whereas the reduction of elevations of the North American and European reliefs strongly increases precipitation from northwestern to eastern Europe. The changes in vegetation cover contribute to maintain and even to intensify the warm and humid conditions produced by the other factors, suggesting that the vegetation-climate interactions could help to improve the model-data comparison.

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Evidence of Adaptation to Recent Changes in Atmospheric CO2 in Four Weedy Species

10.20944/preprints201801.0206.v1 ◽

2018 ◽

Author(s):

James Bunce

Keyword(s):

Co2 Concentration ◽

Dry Mass ◽

Atmospheric Co2 ◽

Agricultural Fields ◽

Down Regulation ◽

High Co2 ◽

Co2 Concentrations ◽

C3 Species ◽

Weedy Species ◽

Atmospheric Co2 Concentrations

Seeds of three C3 and one C4 annual weedy species were collected from agricultural fields in Beltsville, Maryland in 1966 and 2006, when atmospheric CO2 concentrations averaged about 320 and 380 mmol mol-1, respectively.  Plants from each collection year were grown over a range of CO2 concentrations to test for adaptation of these weedy species to recent changes in atmospheric CO2.  In all three of the C3 species, the increase in CO2 concentration from 320 to 380 mmol mol-1 increased total dry mass at 24 days in plants from seeds collected in 2006, but not in plants from seeds collected in 1966.  Shoot and seed dry mass at maturity was greater at the higher growth CO2 in plants collected in 2006 than in 1966 in two of the species.  Down regulation of photosynthetic carboxylation capacity during growth at high CO2 was less in the newer seed lots than in the older in two of the species.  Overall, the results indicate that adaptation to recent changes in atmospheric CO2 has occurred in some of these weedy species.

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Dynamics of global atmospheric CO2 concentration from 1850 to 2010: a linear approximation

Biogeosciences Discussions ◽

10.5194/bgd-11-13957-2014 ◽

2014 ◽

Vol 11 (9) ◽

pp. 13957-13983 ◽

Cited By ~ 1

Author(s):

W. Wang ◽

R. Nemani

Keyword(s):

Co2 Emissions ◽

Co2 Concentration ◽

Atmospheric Co2 ◽

Box Model ◽

Modeling Framework ◽

Elevated Atmospheric Co2 ◽

Atmospheric Co2 Concentration ◽

Co2 Concentrations ◽

Anthropogenic Co2 ◽

Atmospheric Co2 Concentrations

Abstract. The increase in anthropogenic CO2 emissions largely followed an exponential path between 1850 and 2010, and the corresponding increases in atmospheric CO2 concentration were almost constantly proportional to the emissions by the so-called "airborne fraction". These observations suggest that the dynamics of atmospheric CO2 concentration through this time period may be properly approximated as a linear system. We demonstrate this hypothesis by deriving a linear box-model to describe carbon exchanges between the atmosphere and the surface reservoirs under the influence of disturbances such as anthropogenic CO2 emissions and global temperature changes. We show that the box model accurately simulates the observed atmospheric CO2 concentrations and growth rates across interannual to multi-decadal time scales. The model also allows us to analytically examine the dynamics of such changes/variations, linking its characteristic disturbance-response functions to bio-geophysically meaningful parameters. In particular, our results suggest that the elevated atmospheric CO2 concentrations have significantly promoted the gross carbon uptake by the terrestrial biosphere. However, such "fertilization" effects are partially offset by enhanced carbon release from surface reservoirs promoted by warmer temperatures. The result of these interactions appears to be a decline in net efficiency in sequestering atmospheric CO2 by ∼30% since 1960s. We believe that the linear modeling framework outlined in this paper provides a convenient tool to diagnose the observed atmospheric CO2 dynamics and monitor their future changes.

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Effects of CO2, continental distribution, topography and vegetation changes on the climate at the Middle Miocene: a model study

Climate of the Past Discussions ◽

10.5194/cpd-6-489-2010 ◽

2010 ◽

Vol 6 (2) ◽

pp. 489-535 ◽

Cited By ~ 2

Author(s):

A.-J. Henrot ◽

L. François ◽

E. Favre ◽

M. Butzin ◽

M. Ouberdous ◽

...

Keyword(s):

Atmospheric Carbon Dioxide ◽

Middle Miocene ◽

Co2 Concentration ◽

Atmospheric Co2 ◽

The Tibetan Plateau ◽

Humid Climate ◽

The North ◽

Co2 Concentrations ◽

Reduced Height ◽

Atmospheric Co2 Concentrations

Abstract. The Middle Miocene was one of the last warm periods of the Neogene, culminating with the Middle Miocene Climatic Optimum (MMCO, approximatively 17–15 Ma). Several proxy-based reconstructions support warmer and more humid climate during the MMCO. The mechanisms responsible for the warming at MMCO and particulary the role of the atmospheric carbon dioxide CO2 are still highly debated. Here we carried out a series of sensitivity experiments with the model of intermediate complexity Planet Simulator, investigating the contributions of the absence of ice on the continents, the opening of the Central American and Eastern Tethys Seaways, the lowering of the topography on land, the effect of various atmospheric CO2 concentrations and the vegetation retroaction. Our results show that a higher than present-day CO2 concentration is necessary to generate a warmer climate at all latitudes at the Middle Miocene, in agreement with the terrestrial proxy reconstructions which suggest high atmospheric CO2 concentrations at MMCO. Nevertheless, the changes in sea-surface conditions and the lowering of the topography on land also produce significant local warming that may, locally, even be stronger than the CO2 induced temperature increases. The lowering of the topography leads to a more zonal atmospheric circulation and allows the westerly flow to continue over the lowered Plateaus at mid-latitudes. The reduced height of the Tibetan Plateau notably prevents the development of a monsoon-like circulation, whereas the reduction of elevations of the North American and European reliefs strongly increases precipitation from northwestern to eastern Europe. The changes in vegetation cover contributes to maintain and even to intensify the the warm and humid conditions produced by the other factors, suggesting that the vegetation-climate interactions could help to improve the model-data comparison.

Download Full-text