Nearly all woody species respond to increases in the air's CO2 content by displaying enhanced rates of photosynthesis and biomass production. In this summary, we review several recently published responses of oak (genus Quercus) trees to atmospheric CO2 enrichment.
In the two-month study of Anderson and Tomlinson (1998), northern red oak seedlings exposed to 700 ppm CO2 displayed photosynthetic rates that were 34 and 69% greater than those displayed by control plants growing under well-watered and water-stressed conditions, respectively. Similarly, in the four-month study of Li et al. (2000), Quercus myrtifolia seedlings growing at twice-ambient CO2 concentrations exhibited rates of photosynthesis at the onset of senescence that were 97% greater than those displayed by ambiently-growing seedlings.
Because elevated CO2 enhances photosynthetic rates in oak trees, it should also lead to increased biomass production in them; and indeed it does. In the year-long study of Staudt et al. (2001), for example, Quercus ilex seedlings grown at 700 ppm CO2 displayed trunk and branch biomasses that were 90% greater than those measured on seedlings growing at 350 ppm CO2. Also, in the eight-month inter-generational study performed by Polle et al. (2001), seedlings produced from acorns collected from ambient and CO2-enriched mother trees and germinated in air of either ambient or twice-ambient atmospheric CO2 concentration displayed whole-plant biomass values that were 158 and 246% greater, respectively, than those exhibited by their respective control seedlings growing in ambient air.
In another study, Schulte et al. (1998) grew oak seedlings for 15 weeks at twice-ambient CO2 concentrations, finding that elevated CO2 enhanced seedling biomass by 92 and 128% under well-watered and water-stressed conditions, respectively; and in a similar study conducted by Tomlinson and Anderson (1998), water-stressed seedlings growing at 700 ppm CO2 displayed biomass values that were similar to those exhibited by well-watered plants growing in ambient air. Thus, atmospheric CO2 enrichment continues to benefit oak trees even under water-stressed conditions.
Additional studies have demonstrated that oak seedlings also respond positively to atmospheric CO2 enrichment when they are faced with other environmental stresses and resource limitations. When pedunculate oak seedlings were subjected to two different soil nutrient regimes, for example, Maillard et al. (2001) reported that a doubling of the atmospheric CO2 concentration enhanced seedling biomass by 140 and 30% under high and low soil nitrogen conditions, respectively. And in the study of Usami et al. (2001), saplings of Quercus myrsinaefolia that were grown at 700 ppm CO2 displayed biomass increases that were 110 and 140% greater than their ambiently-grown counterparts when they were simultaneously subjected to air temperatures that were 3 and 5°C greater than ambient temperature, respectively. Thus, elevated CO2 concentrations tend to ameliorate some of the negative effects caused by growth-reducing stresses in oaks. In fact, when Schwanz and Polle (1998) reported that elevated CO2 exposure caused reductions in the amounts of several foliar antioxidative enzymes in mature oak trees, they suggested that this phenomenon was the result of atmospheric CO2 enrichment causing the trees to experience less oxidative stress and, therefore, that they had less need for antioxidative enzymes.
In some studies, elevated CO2 has also been shown to reduce stomatal conductances in oak trees, thus contributing to greater tree water-use efficiencies. Tognetti et al. (1998a), for example, reported that oak seedlings growing near a natural CO2-emitting spring exhibited less water loss and more favorable turgor pressures than trees growing further away from the springs. In fact, the resulting improvement in water-use efficiency was so significant that Tognetti et al. (1998b) stated that "such marked increases in water-use efficiency under elevated CO2 might be of great importance in Mediterranean environments in the perspective of global climate change."
In summary, it is clear that as the CO2 content of the air increases, oak seedlings will likely display enhanced rates of photosynthesis and biomass production, regardless of air temperature, soil moisture, and soil nutrient status. Consequently, greater amounts of carbon will likely be removed from the atmosphere by the trees of this abundant genus and stored in their tissues and the soils in which they are rooted.
For more information on oak growth responses to atmospheric CO2 enrichment see Plant Growth Data: Cork Oak (photosynthesis), Downy Oak (photosynthesis), Durmast Oak (dry weight), Holly Oak (dry weight, photosynthesis), Northern Red Oak (dry weight, photosynthesis), Pedunculate Oak (dry weight, photosynthesis), and White Oak (photosynthesis).
References
Anderson, P.D. and Tomlinson, P.T. 1998. Ontogeny affects response of northern red oak seedlings to elevated CO2 and water stress. I. Carbon assimilation and biomass production. New Phytologist 140: 477-491.
Li, J.-H., Dijkstra, P., Hymus, G.J., Wheeler, R.M., Piastuchi, W.C., Hinkle, C.R. and Drake, B.G. 2000. Leaf senescence of Quercus myrtifolia as affected by long-term CO2 enrichment in its native environment. Global Change Biology 6: 727-733.
Maillard, P., Guehl, J.-M., Muller, J.-F. and Gross, P. 2001. Interactive effects of elevated CO2 concentration and nitrogen supply on partitioning of newly fixed 13C and 15N between shoot and roots of pedunculate oak seedlings (Quercus robur L.). Tree Physiology 21: 163-172.
Polle, A., McKee, I. and Blaschke, L. 2001. Altered physiological and growth responses to elevated [CO2] in offspring from holm oak (Quercus ilex L.) mother trees with lifetime exposure to naturally elevated [CO2]. Plant, Cell and Environment 24: 1075-1083.
Schwanz, P. and Polle, A. 1998. Antioxidative systems, pigment and protein contents in leaves of adult mediterranean oak species (Quercus pubescens and Q. ilex) with lifetime exposure to elevated CO2. New Phytologist 140: 411-423.
Schulte, M., Herschbach, C. and Rennenberg, H. 1998. Interactive effects of elevated atmospheric CO2, mycorrhization and drought on long-distance transport of reduced sulphur in young pedunculate oak trees (Quercus robur L.). Plant, Cell and Environment 21: 917-926.
Staudt, M., Joffre, R., Rambal, S. and Kesselmeier, J. 2001. Effect of elevated CO2 on monoterpene emission of young Quercus ilex trees and its relation to structural and ecophysiological parameters. Tree Physiology 21: 437-445.
Tognetti, R., Longobucco, A., Miglietta, F. and Raschi, A. 1998a. Transpiration and stomatal behaviour of Quercus ilex plants during the summer in a Mediterranean carbon dioxide spring. Plant, Cell and Environment 21: 613-622.
Tognetti, R., Johnson, J.D., Michelozzi, M. and Raschi, A. 1998b. Response of foliar metabolism in mature trees of Quercus pubescens and Quercus ilex to long-term elevated CO2. Environmental and Experimental Botany 39: 233-245.
Tomlinson, P.T. and Anderson, P.D. 1998. Ontogeny affects response of northern red oak seedlings to elevated CO2 and water stress. II. Recent photosynthate distribution and growth. New Phytologist 140: 493-504.
Usami, T., Lee, J. and Oikawa, T. 2001. Interactive effects of increased temperature and CO2 on the growth of Quercus myrsinaefolia saplings. Plant, Cell and Environment 24: 1007-1019.