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Genotypic variation in physiological and growth responses of Populus tremuloides to elevated atmospheric CO₂ concentration

Xianzhong Wang (1, 5), Peter S. Curtis (2), Kurt S. Pregitzer (3) and Donald R. Zak (4)

1. Environmental Science Graduate Program, Ohio State University, Columbus, OH 43210, USA / 2. Department of Evolution, Ecology and Organismal Biology, Ohio State University, Columbus, OH 43210, USA / 3. Department of Forestry, Michigan Technological University, Houghton, MI 49931, USA / 4. School of Natural Resources and Environment, University of Michigan, Ann Arbor, MI 48109, USA / 5. 6 Marine Biology, Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, USA / Received November 9, 1999

Summary

Physiological and biomass responses of six genotypes of Populus tremuloides Michx., grown in ambient (357 μmol mol^–1) or twice ambient (707 μmol mol^–1) CO₂ concentration ([CO₂]) and in low-N or high-N soils, were studied in 1995 and 1996 in northern Lower Michigan, USA. There was a significant CO₂ × genotype interaction in photosynthetic responses. Net CO₂ assimilation (A) was significantly enhanced by elevated [CO₂] for five genotypes in high-N soil and for four genotypes in low-N soil. Enhancement of A by elevated [CO₂] ranged from 14 to 68%. Genotypes also differed in their biomass responses to elevated [CO₂], but biomass responses were poorly correlated with A responses. There was a correlation between magnitude of A enhancement by elevated [CO₂] and stomatal sensitivity to CO₂. Genotypes with low stomatal sensitivity to CO₂ had a significantly higher A at elevated [CO₂] than at ambient [CO₂], but elevated [CO₂] did not affect the ratio of intercellular [CO₂] to leaf surface [CO₂]. Stomatal conductance and A of different genotypes responded differentially to recovery from drought stress. Photosynthetic quantum yield and light compensation point were unaffected by elevated [CO₂]. We conclude that P. tremuloides genotypes will respond differentially to rising atmospheric [CO₂], with the degree of response dependent on other abiotic factors, such as soil N and water availability. The observed genotypic variation in growth could result in altered genotypic representation within natural populations and could affect the composition and structure of plant communities in a higher [CO₂] environment in the future.

Keywords: biomass, drought stress, elevated CO₂ concentration, genotype, photosynthesis, soil N, stomatal conductance, trembling aspen.

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