Nearly all of earth's plants respond favorably to increases in the air's CO2 concentration in terms of their net carbon assimilation and biomass production rates. Is part of this positive response due to CO2-induced reductions in respiratory carbon losses? In this summary, we highlight what has been learned about this phenomenon from studies of deciduous trees that we have reviewed on our website.
Wang and Curtis (2001) grew cuttings of two male and two female trembling aspen trees for about five months on soils containing low and high nitrogen contents in open-top chambers maintained at atmospheric CO2 concentrations of 380 and 765 ppm, finding that gender had little effect on dark respiration rates, but that elevated CO2 increased them, by 6% and 32% in the low and high soil nitrogen treatments, respectively. On the other hand, Karnosky et al. (1999) grew both O3-sensitive and O3-tolerant aspen clones for one full year in free-air CO2-enrichment (FACE) plots maintained at atmospheric CO2 concentrations of 360 and 560 ppm, finding that the extra CO2 decreased dark respiration rates by 24%.
Gielen et al. (2003) measured stem respiration rates of white, black and robusta poplar trees in a high-density forest plantation in the third year of a FACE experiment in which the CO2 concentration of the air surrounding the trees was increased to a value of approximately 550 ppm. This study revealed, in their words, that "stem respiration rates were not affected by the FACE treatment," and that "FACE did not influence the relationships between respiration rate and both stem temperature and relative growth rate." In addition, they say they could find "no effect of the FACE treatment on Rm [maintenance respiration, which is related to the sustaining of existing cells] and Rg [growth respiration, which is related to the synthesis of new tissues]."
Hamilton et al. (2001) studied respiratory responses of sweetgum trees growing in the understory of a loblolly pine plantation (but occasionally reaching the top of the canopy) to an extra 200 ppm of CO2 in a FACE study conducted in North Carolina, USA. As a result of their measurement program, they determined that the modest increase in atmospheric CO2 concentration did not appear to alter maintenance respiration to any significant degree, but that it reduced dark respiration by an average of 10% and growth respiration of leaves at the top of the canopy by nearly 40%.
In reviewing the results of these several deciduous tree studies, we see cases of both increases and decreases in respiration rates in response to atmospheric CO2 enrichment, as well as cases of no change in respiration. Hence, as we concluded to be the situation with conifers, more data are needed before any general conclusions may safely be drawn about the effects of atmospheric CO2 enrichment on the respiration rates of deciduous trees. However, more such data are archived under the other sub-headings of Respiration (Response to CO2) in our Subject Index; and they can be helpful in making an ultimate determination on the matter.
References
Gielen, B., Scarascia-Mugnozza, G. and Ceulemans, R. 2003. Stem respiration of Populus species in the third year of free-air CO2 enrichment. Physiologia Plantarum 117: 500-507.
Hamilton, J.G., Thomas, R.B. and DeLucia, E.H. 2001. Direct and indirect effects of elevated CO2 on leaf respiration in a forest ecosystem. Plant, Cell and Environment 24: 975-982.
Karnosky, D.F., Mankovska, B., Percy, K., Dickson, R.E., Podila, G.K., Sober, J., Noormets, A., Hendrey, G., Coleman, M.D., Kubiske, M., Pregitzer, K.S. and Isebrands, J.G. 1999. Effects of tropospheric O3 on trembling aspen and interaction with CO2: results from an O3-gradient and a FACE experiment. Water, Air, and Soil Pollution 116: 311-322.
Wang, X. and Curtis, P.S. 2001. Gender-specific responses of Populus tremuloides to atmospheric CO2 enrichment. New Phytologist 150: 675-684.
Last updated 19 July 2006