Changes in growth, leaf abscission, and biomass associated with seasonal tropospheric ozone exposures of Populus tremuloides clones and seedlings

Abstract

The effects of single-season tropospheric ozone (0₃) exposures on growth, leaf abscission, and biomass of trembling aspen (Populus tremuloides Michx.) rooted cuttings and seedlings were studied. Plants were grown in the Upper Peninsula of Michigan in open-top chambers with 0₃ exposures that ranged from 7 to 92 ppm-h. Depending on the genotype, total seasonal 0₃ exposure in the range of 50-92 ppm-h had negative impacts on stem, retained leaf, and root biomass accumulation and on diameter growth. Leaf abscission generally increased with increasing 0₃ exposure and was the principal cause of the decrease in leaf biomass of the O₃-treated plants. Considerable genetic variation in 0₃ responses occurred, as shown by differences in sensitivities among clones and among seedlings. However, the responses to 0₃ of rooted cuttings and seedlings were similar when seedling means were compared with clonal means for leaf abscission, diameter growth, retained leaf biomass, and root biomass. Comparison of a single square-wave treatment (52 ppm-h) with 70 and 92 ppm-h episodic exposures suggested that the plant response to the square-wave exposure was similar to the response to the highest episodic exposure even though the 92 ppm-h episodic exposure was almost twice the square-wave exposure. Our results are consistent with previous studies that show that P. tremuloides is highly responsive to O₃ exposure and this response has a strong genetic component.

Citation

Karnosky, D.F.; Gagnon, Z.E.; Dickson, R.E.; Coleman, M.D.; Lee, E.H.; Isebrands, J.G. 1996. Changes in growth, leaf abscission, and biomass associated with seasonal tropospheric ozone exposures of Populus tremuloides clones and seedlings. Can. J. For. Res. 26: 23-37 (1996).