Limited suppression of photorespiration by 20th century atmospheric CO2 increase in trees worldwide
(English)Manuscript (preprint) (Other academic)
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.
Chemical Sciences Climate Research
IdentifiersURN: urn:nbn:se:umu:diva-97676OAI: oai:DiVA.org:umu-97676DiVA: diva2:775580