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- Walker, Anthony P., et al.
(författare)
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Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2
- 2021
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Ingår i: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 229:5, s. 2413-2445
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric carbon dioxide concentration ([CO2]) is increasing, which increases leaf‐scale photosynthesis and intrinsic water‐use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sink would slow the rate of [CO2] increase and thus climate change. However, ecosystem CO2 responses are complex or confounded by concurrent changes in multiple agents of global change and evidence for a [CO2]‐driven terrestrial carbon sink can appear contradictory. Here we synthesize theory and broad, multidisciplinary evidence for the effects of increasing [CO2] (iCO2) on the global terrestrial carbon sink. Evidence suggests a substantial increase in global photosynthesis since pre‐industrial times. Established theory, supported by experiments, indicates that iCO2 is likely responsible for about half of the increase. Global carbon budgeting, atmospheric data, and forest inventories indicate a historical carbon sink, and these apparent iCO2 responses are high in comparison to experiments and predictions from theory. Plant mortality and soil carbon iCO2 responses are highly uncertain. In conclusion, a range of evidence supports a positive terrestrial carbon sink in response to iCO2, albeit with uncertain magnitude and strong suggestion of a role for additional agents of global change.
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| 3. |
- Ehlers, Ina, 1984-, et al.
(författare)
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Limited suppression of photorespiration by 20th century atmospheric CO2 increase in trees worldwide
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Forests are a key component of the global carbon and hydrological cycle and forest responses to environmental drivers create important feedbacks to these cycles. Photosynthetic efficiency of most forest tree species is strongly limited by photorespiration, a side reaction using O2 instead of CO2 as substrate, leading to a carbon loss for the plant. Photorespiration occurs in all trees and is reduced under elevated CO2 concentrations and increased under elevated temperature. Because the CO2 concentration of the atmosphere has increased in past decades, long-lived trees may have benefited from reduced photorespiration, but the temperature increase would have been a compensating detriment; but direct quantification of long-term changes in metabolic fluxes is lacking. Realistic forecasting of responses of trees and forests to future CO2 and temperature demands quantifying the reduction of photorespiration. In twelve tree species from five continents, we observe that photorespiration has been reduced by the CO2 increase during the past century, but for most the reduction is smaller than predicted from plant responses in CO2 alone. Comparison with data from a combined CO2 and temperature manipulation experiment shows that the reduced response can be explained by increases in leaf temperatures, which might result directly from increased air temperatures or indirectly from reduced transpirative cooling. These data suggest that global warming has already inhibited plant fertilization by increasing CO2, and that biomass increases may have been smaller than deduced from measurements of the heavy carbon isotope 13C. Observation of this centennial metabolic shift in tree physiology worldwide provides new insights into forest-climate feedbacks and can be used to improve coupled climate-vegetation models.
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