Gas exchange, leaf nitrogen, and growth efficiency of Populus tremuloides in a CO_2 enriched atmosphere

Predicting forest responses to rising atmospheric CO_2 will require an understanding of key feedbacks in the cycling of carbon and nitrogen between plants and soil microorganisms. We conducted a study for 2.5 growing seasons with Populus tremuloides grown under experimental atmospheric CO_2 and soil-N-availability treatments. Our objective was to integrate the combined influence of atmospheric CO_2 and soil-N availability on the flow of C and N in the plant–soil system and to relate these processes to the performance of this widespread and economically important tree species. Here we consider treatment effects on photosynthesis and canopy development and the efficiency with which this productive capacity is translated into aboveground, harvestable yield. We grew six P. tremuloides genotypes at ambient (35 Pa) or elevated (70 Pa) CO_2 and in soil of low or high N mineralization rate at the University of Michigan Biological Station, Pellston, Michigan, USA (45°35′ N, 84°42′ W). In the second year of growth, net CO_2 assimilation rate was significantly higher in elevated-CO_2 compared to ambient-CO_2 plants in both soil-N treatments, and we found little evidence for photosynthetic acclimation to high CO_2. In the third year, however, elevated-CO_2 plants in low-N soil had reduced photosynthetic capacity compared to ambient-CO_2, low-N plants. Plants in high-N soil showed the opposite response, with elevated-CO_2 plants having higher photosynthetic capacity than ambient-CO_2 plants. Net CO_2 assimilation rate was linearly related to leaf N concentration (log:log scale), with identical slopes but different intercepts in the two CO_2 treatments, indicating differences in photosynthetic N-use efficiency. Elevated CO_2 increased tissue dark respiration in high-N soil (+22%) but had no significant effect in low-N soil (+9%). There were no CO_2 effects on stomatal conductance. At the final harvest, stem biomass and total leaf area increased significantly due to CO_2 enrichment in high-N but not in low-N soil. Treatment effects on wood production were largely attributable to changes in leaf area, with no significant effects on growth efficiency. We conclude that harvest intervals for P. tremuloides on fertile sites will shorten with rising atmospheric CO_2, but that tree size at canopy closure may be unaffected.

Citation

Peter S. Curtis et al, "Gas exchange, leaf nitrogen, and growth efficiency of Populus tremuloides in a CO_2 enriched atmosphere," Ecological Applications 10, no. 1 (2000), doi: http://dx.doi.org/10.1890/1051-0761(2000)010[0003:GELNAG]2.0.CO;2

URI

http://hdl.handle.net/1811/49020

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Ohio State University Research and Scholarship

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