No Down-Regulation of Leaf Photosynthesis in Mature Forest Trees after Three Years of Exposure to Elevated CO₂

Abstract

The photosynthetic responses of six species of mature forest trees to long-term exposure to elevated CO₂ (ca. 530 ppm) were determined at the Swiss Canopy Crane (SCC) site near Basel, Switzerland. In the third year of growth in elevated CO₂, using web-FACE technology, net photosynthesis (A_s) in fully sunlit, upper canopy foliage was stimulated by ca. 40 % compared to ambient controls. This enhancement did not differ from the instantaneous increase in A_s found in ambient-grown leaves that were temporarily measured at elevated CO₂. A complete lack of down-regulation of photosynthesis was found in all species and in both the early and the late growing season. Neither was leaf nitrogen content significantly affected by long-term exposure to elevated CO₂. Our results document a persistent enhancement in leaf level photosynthesis in response to elevated CO₂ in mature forest trees over a period of three years. Circumstantial evidence suggests that the additional assimilates feed into large sinks other than stem and shoot growth.

Assimilation - down-regulation - global change - Swiss canopy crane - web-FACE.

References

• 1 Ainsworth E. A., Davey P. A., Hymus G. J., Osborne C. P., Rogers A., Blum H., Nosberger J., Long S. P.. Is stimulation of leaf photosynthesis by elevated carbon dioxide concentration maintained in the long term? A test with Lolium perenne grown for 10 years at two nitrogen fertilization levels under Free Air CO₂ Enrichment (FACE).  Plant, Cell and Environment. (2003);  26 705-714
• 2 Cech P. G., Pepin S., Körner C.. Elevated CO₂ reduces sap flux in mature deciduous forest trees.  Oecologia. (2003);  137 258-268
• 3 Curtis P. S., Wang X. Z.. A meta-analysis of elevated CO₂ effects on woody plant mass, form, and physiology.  Oecologia. (1998);  113 299-313
• 4 Farquhar G. D., Von Caemmerer S., Berry J. A.. A biochemical model of photosynthetic CO₂ assimilation in leaves of C₃ species.  Planta. (1980);  149 78-90
• 5 Herrick J. D., Thomas R. B.. No photosynthetic down-regulation in sweetgum trees (Liquidambar styraciflua L.) after three years of CO₂ enrichment at the Duke Forest FACE experiment.  Plant, Cell and Environment. (2001);  24 53-64
• 6 Houghton J. T., Ding Y., Griggs D. J., Noguer M., van der Linden P. J., Xiaosu D.. eds. .Climate Change 2001. The Scientific Basis. Cambridge; Cambridge University Press (2001)
• 7 Körner C.. Biosphere responses to CO₂ enrichment.  Ecological Applications. (2000);  10 1590-1619
• 8 Körner C.. Carbon limitation in trees.  Journal of Ecology. (2003);  91 4-17
• 9 Körner C., Miglietta F.. Long term effects of naturally elevated CO₂ on Mediterranean grassland and forest trees.  Oecologia. (1994);  99 343-351
• 10 Long S. P., Drake B. G.. Effect of long-term elevation of CO₂ concentration in the field on quantum yield of photosynthesis of the C₃ sedge, Scirpus olneyi. .  Plant Physiology. (1991);  96 221-226
• 11 Medlyn B. E., Badeck F.-W., Pury D. G. G. D., Barton C. V. M., Broadmeadow M., Ceulemans R., Angelis P. D., Forstreuter M., Jach M. E., Kellomäki S., Laitat E., Marek M., Philippot S., Rey A., Strassemeyer J., Laitinen K., Liozon R., Portier B., Roberntz P., Wang K., Jstbid P. G.. Effects of elevated [CO₂] on photosynthesis in European forest species: a meta-analysis of model parameters.  Plant, Cell and Environment. (1999);  22 1475-1495
• 12 Medlyn B. E., Barton C. V. M., Broadmeadow M. S. J., Ceulemans R., De Angelis P., Forstreuter M., Freeman M., Jackson S. B., Kellomaki S., Laitat E., Rey A., Roberntz P., Sigurdsson B. D., Strassemeyer J., Wang K., Curtis P. S., Jarvis P. G.. Stomatal conductance of forest species after long-term exposure to elevated CO₂ concentration: a synthesis.  New Phytologist. (2001);  149 247-264
• 13 Melillo J. M., McGuire A. D., Kicklighter D. W., Moore III. B., Vorosmarty C. J., Schloss A. L.. Global climate change and terrestrial net primary production.  Nature. (1993);  363 234-240
• 14 Norby R. J., Wullschleger S. D., Gunderson C. A., Johnson D. W., Ceulemans R.. Tree responses to rising CO₂ in field experiments: implications for the future forest.  Plant, Cell and Environment. (1999);  22 683-714
• 15 Nowak R. S., Ellsworth D. S., Smith S. D.. Functional responses of plants to elevated atmospheric CO₂ - do photosynthetic and productivity data from FACE experiments support early predictions?.  New Phytologist. (2004);  162 253-280
• 16 Oren R., Ellsworth D. S., Johnsen K. H., Phillips N., Ewers B. E., Maier C., Schafer K. V. R., McCarthy H., Hendrey G., McNulty S. G., Katul G. G.. Soil fertility limits carbon sequestration by forest ecosystems in a CO₂-enriched atmosphere.  Nature. (2001);  411 469-472
• 17 Pepin S., Körner C.. web-FACE: a new canopy free-air CO₂ enrichment system for tall trees in mature forests.  Oecologia. (2002);  133 1-9
• 18 Rogers A., Ellsworth D. S.. Photosynthetic acclimation of Pinus taeda (loblolly pine) to long-term growth in elevated pCO₂ (FACE).  Plant, Cell and Environment. (2002);  25 851-858
• 19 Saxe H., Ellsworth D. S., Heath J.. Tree and forest functioning in an enriched CO₂ atmosphere.  New Phytologist. (1998);  139 395-436
• 20 Sholtis J. D., Gunderson C. A., Norby R. J., Tissue D. T.. Persistent stimulation of photosynthesis by elevated CO₂ in a sweetgum (Liquidambar styraciflua) forest stand.  New Phytologist. (2004);  162 343-354
• 21 Steinmann K., Siegwolf R., Saurer M., Körner C.. Carbon fluxes to the soil in a mature temperate forest assessed by ¹³C isotope tracing.  Oecologia. (2004);  141 489-501
• 22 Stitt M.. Rising CO₂ levels and their potential significance for carbon flow in photosynthetic cells.  Plant, Cell and Environment. (1991);  14 741-762

Editor: M. C. Ball