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Photosynthetic responses of Scots pine to elevated CO₂ and nitrogen supply: results of a branch-in-bag experiment

Seppo Kellomäki and Kai-Yun Wang

University of Joensuu, Faculty of Forestry, P.O. Box 111, FIN-80101 Joensuu, Finland / Received February 28, 1996

Summary

Naturally seeded Scots pine (Pinus sylvestris L.) trees, age 25–30 years, were subjected to two soil-nitrogen-supply regimes and to elevated atmospheric CO₂ concentrations by the branch-in-bag method from April 15 to September 15 for two or three years. Gas exchange in detached shoots was measured in a diffuse radiation field. Seven parameters associated with photosynthetic performance and two describing stomatal conductance were determined to assess the effects of treatments on photosynthetic components. An elevated concentration of CO₂ did not lead to a significant downward regulation in maximum carboxylation rate (V_cmax) or maximum electron transport rate (J_max), but it significantly decreased light-saturated stomatal conductance (g_sat) and increased minimum stomatal conductance (g_min). Light-saturated rates of CO₂ assimilation were higher (24–31%) in shoots grown and measured at elevated CO₂ concentration than in shoots grown and measured at ambient CO₂ concentration, regardless of treatment time or nitrogen-supply regime. High soil-nitrogen supply significantly increased photosynthetic capacity, corresponding to significant increases in V_cmax and J_max. However, the combined elevated CO₂ + high nitrogen-supply treatment did not enhance the photosynthetic response above that observed in the elevated CO₂ treatment alone.

Keywords: carboxylation rate, electron transport rate, Pinus sylvestris, stomatal conductance.

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ISSN 0829-318X Copyright © 2002–2008 Heron Publishing