Enhanced Seasonal Exchange of CO
            <sub>2</sub>
            by Northern Ecosystems Since 1960

Graven, Heather; Keeling, Ralph F.; Piper, Stephen C.; Patra, Prabir K.; Stephens, Britton B.; Wofsy, Steven C.; Welp, L. R.; Sweeney, Colm; Tans, Pieter P.; Kelley, John J.; Daube, Bruce C.; Kort, E. A.; Santoni, G. W.; Bent, J. D.

doi:10.1126/science.1239207

Cited by 377 publications

(481 citation statements)

References 68 publications

(46 reference statements)

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“…These underestimations could be explained by the underestimation by carbon cycle models of the long-term response of net ecosystem productivity to the increase in atmospheric CO 2 concentration, which in turn could be explained by our finding that models lacking explicit consideration of mesophyll diffusion underestimate the CO 2 fertilization effect. Furthermore, in the northern hemisphere, the increase in the seasonal amplitude of atmospheric CO 2 has been larger in high latitudes than in low latitudes and substantially larger than simulated by carbon cycle models (31), which agrees with our finding that the estimated CO 2 fertilization effect in the regions of >45°N is particularly sensitive to the consideration of mesophyll diffusion (Fig. 2).…”

Section: Resultssupporting

confidence: 82%

Impact of mesophyll diffusion on estimated global land CO ₂ fertilization

Sun

Dickinson

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

143

132

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In C 3 plants, CO 2 concentrations drop considerably along mesophyll diffusion pathways from substomatal cavities to chloroplasts where CO 2 assimilation occurs. Global carbon cycle models have not explicitly represented this internal drawdown and therefore overestimate CO 2 available for carboxylation and underestimate photosynthetic responsiveness to atmospheric CO 2 . An explicit consideration of mesophyll diffusion increases the modeled cumulative CO 2 fertilization effect (CFE) for global gross primary production (GPP) from 915 to 1,057 PgC for the period of 1901-2010. This increase represents a 16% correction, which is large enough to explain the persistent overestimation of growth rates of historical atmospheric CO 2 by Earth system models. Without this correction, the CFE for global GPP is underestimated by 0.05 PgC/y/ppm. This finding implies that the contemporary terrestrial biosphere is more CO 2 limited than previously thought. mesophyll conductance | CO 2 fertilization | carbon cycle | gross primary production | photosynthetic model T o reach Rubisco, the carboxylating enzyme of the Calvin cycle, CO 2 molecules must diffuse through two consecutive segments of a continuous pathway in leaves of C 3 plant species. The first segment connects leaf intercellular air space with ambient air and is controlled by stomata; the second one consists of mesophyll layers from intercellular air space to stroma of chloroplasts where Rubisco resides (1, 2). These two stages differ in the media through which CO 2 moves. Diffusion in the first segment (stomatal diffusion) is through gases only; that in the second segment (mesophyll diffusion) occurs in a variety of media including liquids and lipids, i.e., cell walls, plasmalemma, cytosol, chloroplast envelope membranes, and stroma. The path length of this mesophyll diffusion is generally shorter than that of stomatal diffusion (2). However, diffusion of CO 2 through liquids is several orders of magnitude slower than it is through gases; diffusion through lipids in membranes is even slower than it is through liquid water (3), although it may be facilitated by aquaporin-like channels (4). Consequently, mesophyll layers constitute a major barrier for CO 2 movement inside leaves (5-9).However, the importance of this mesophyll diffusion limitation for photosynthesis has yet to be reflected in carbon cycle modeling. Current large-scale carbon cycle models (10, 11) have explicitly considered stomatal diffusion but not mesophyll diffusion. Most carbon cycle models use some form of the biochemical model of Farquhar, von Caemmerer, and Berry (FvCB) for modeling photosynthesis (12). In theory, the FvCB model should use the CO 2 concentration at the site of carboxylation inside the chloroplast (C c ). Nevertheless, most modelers have knowingly or unknowingly applied it directly to the CO 2 concentration inside the substomatal cavity (C i ). Since C c can be much smaller than C i , because of the mesophyll resistance to CO 2 diffusion, a compensating adjustment is needed to correct...

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Section: Resultssupporting

confidence: 82%

Impact of mesophyll diffusion on estimated global land CO ₂ fertilization

Sun

Dickinson

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

143

132

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“…The seaonsal CO 2 amplitud increase was higher in forest ecosystems (MF, EBF and EBF), whereas there is no distinguishabel amplitude change in WSA and GRA. The same pattern appered in Graven et al (2013), with aircraft-based observation of CO 2 . Their results showed that an increased of 30%e60% in the seasonal exchange of CO 2 by northern extratropical land ecosystems, focused on boreal forests.…”

Section: Evolution and Variation Of Co 2 Concentrations At Individualmentioning

confidence: 89%

Evolution and variation of atmospheric carbon dioxide concentration over terrestrial ecosystems as derived from eddy covariance measurements

Liu

Zhu

et al. 2015

Atmospheric Environment

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h i g h l i g h t sAtmospheric CO 2 concentration over terrestrial ecosystems (ACTE) was analyzed. ACTE was higher by 9.0 ppm in winter and lower 2.1 ppm in summer than global means. Annual mean and seasonal amplitude of ACTE increased with 2.04 and 0.60 ppm yr À1 . The annual CO 2 concentration showed large variation among ecosystems. a r t i c l e i n f o (CO 2 ) is the most important anthropogenic greenhouse gas contributing to global climate change. Understanding the temporal and spatial variations of CO 2 concentration over terrestrial ecosystems provides additional insight into global atmospheric variability of CO 2 concentration. Using 355 site-years of CO 2 concentration observations at 104 eddy-covariance flux tower sites in Northern Hemisphere, we presented a comprehensive analysis of evolution and variation of atmospheric CO 2 concentration over terrestrial ecosystem (ACTE) for the period of 1997e2006. Our results showed that ACTE exhibited a strong seasonal variations, with an average seaonsal amplitude (peak-trough difference) of 14.8 ppm, which was approximately threefold that global mean CO 2 observed in Mauna Loa in the United States (MLO). The seasonal variation of CO 2 were mostly dominant by terrestrial carbon fluxes, i.e., net ecosystem procution (NEP) and gross primary produciton (GPP), with correlation coefficient(r) were À0.55 and À0.60 for NEP and GPP, respectively. However, the influence of carbon fluxes on CO 2 were not significant at interannual scale, which implyed that the inter-annual changing trends of atmospheric CO 2 in Northern Hemisphere were likely to depend more on anthropogenic CO 2 emissions sources than on ecosystem change. It was estimated, by fitting a harmonic model to monthly-mean ACTE, that both annual mean and seasonal amplitude of ACTE increased over the 10-year period at rates of 2.04 and 0.60 ppm yr À1 , respectively. The uptrend of annual ACTE could be attributed to the dramatic global increase of CO 2 emissions during the study period, whereas the increasing amplitude could be related to the increases in Northern Hemisphere biospheric activity. This study also found that the annual CO 2 concentration showed large variation among ecosystems, with the high value appeared in deciduous broadleaf forest, evergreen broadleaf forest and cropland. We attribute these discrepancies to both differential local anthropogenic impacts and carbon sequestration abilities across ecosystem types.

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“…We also found compelling indications that change in soil moisture is an important process that modulates the temperature-productivity correlations, although the models used in this study may be presently less trusted to fully describe this. It is not straightforward to link changes in NDVItemperature relationships with changes in the net carbon balance of northern ecosystems that has an impact on seasonal 33 and spatial gradients of atmospheric CO 2 , because of the concurrent response of respiration and disturbances to temperature. Further study focusing on both the temperature dependence of vegetation productivity and ecosystem respiration and their temporal trajectory is needed.…”

Section: Discussionmentioning

confidence: 99%

Evidence for a weakening relationship between interannual temperature variability and northern vegetation activity

et al. 2014

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Satellite-derived Normalized Difference Vegetation Index (NDVI), a proxy of vegetation productivity, is known to be correlated with temperature in northern ecosystems. This relationship, however, may change over time following alternations in other environmental factors. Here we show that above 30°N, the strength of the relationship between the interannual variability of growing season NDVI and temperature (partial correlation coefficient R NDVI-GT ) declined substantially between 1982 and 2011. This decrease in R NDVI-GT is mainly observed in temperate and arctic ecosystems, and is also partly reproduced by process-based ecosystem model results. In the temperate ecosystem, the decrease in R NDVI-GT coincides with an increase in drought. In the arctic ecosystem, it may be related to a nonlinear response of photosynthesis to temperature, increase of hot extreme days and shrub expansion over grass-dominated tundra. Our results caution the use of results from interannual time scales to constrain the decadal response of plants to ongoing warming.

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Enhanced Seasonal Exchange of CO ₂ by Northern Ecosystems Since 1960

Cited by 377 publications

References 68 publications

Impact of mesophyll diffusion on estimated global land CO ₂ fertilization

Impact of mesophyll diffusion on estimated global land CO ₂ fertilization

Evolution and variation of atmospheric carbon dioxide concentration over terrestrial ecosystems as derived from eddy covariance measurements

Evidence for a weakening relationship between interannual temperature variability and northern vegetation activity

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Enhanced Seasonal Exchange of CO 2 by Northern Ecosystems Since 1960

Cited by 377 publications

References 68 publications

Impact of mesophyll diffusion on estimated global land CO 2 fertilization

Impact of mesophyll diffusion on estimated global land CO 2 fertilization

Evolution and variation of atmospheric carbon dioxide concentration over terrestrial ecosystems as derived from eddy covariance measurements

Evidence for a weakening relationship between interannual temperature variability and northern vegetation activity

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Resources

About

Enhanced Seasonal Exchange of CO ₂ by Northern Ecosystems Since 1960

Impact of mesophyll diffusion on estimated global land CO ₂ fertilization

Impact of mesophyll diffusion on estimated global land CO ₂ fertilization