DOI: 10.1007/s11099-012-0014-x PHOTOSYNTHETICA 50 (1): 141-151, 2012 141 Acclimation of photosynthesis in a boreal grass (Phalaris arundinacea L.) under different temperature, CO 2 , and soil water regimes Z.-M. GE *,**,+ , X. ZHOU ** , S. KELLOMÄKI ** , C. ZHANG ** , H. PELTOLA ** , P.J. MARTIKAINEN *** , and K.Y. WANG ** State Key Laboratory of Estuarine and Coastal Research, East China Normal University, 3663 Zhongshan Road North, 200062 Shanghai, China * School of Forest Sciences, University of Eastern Finland, Yliopistokatu 7, P.O. Box 111, 80101 Joensuu, Finland ** Department of Environmental Science, University of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland *** Abstract The aim of this work was to study the acclimation of photosynthesis in a boreal grass (Phalaris arundinacea L.) grown in controlled environment chambers under elevated temperature (ambient + 3.5 o C) and CO 2 (700 μmol mol −1 ) with varying soil water regimes. More specifically, we studied, during two development stages (early: heading; late: florescence completed), how the temperature response of light-saturated net photosynthetic rate (P sat ), maximum rate of ribulose-1,5-bisphosphate carboxylase/oxygenase activity (V cmax ) and potential rate of electron transport (J max ) acclimatized to the changed environment. During the early growing period, we found a greater temperature-induced enhancement of P sat at higher measurement temperatures, which disappeared during the late stage. Under elevated growth temperature, V cmax and J max at lower measurement temperatures (5–15°C) were lower than those under ambient growth temperature during the early period. When the measurements were done at 20–30°C, the situation was the opposite. During the late growing period, V cmax and J max under elevated growth temperature were consistently lower across measurement temperatures. CO 2 enrichment significantly increased P sat with higher intercellular CO 2 compared to ambient CO 2 treatment, however, elevated CO 2 slightly decreased V cmax and J max across measurement temperatures, probably due to down-regulation acclimation. For two growing periods, soil water availability affected the variation in photosynthesis and biochemical parameters much more than climatic treatment did. Over two growing periods, V cmax and J max were on average 36.4 and 30.6%, respectively, lower with low water availability compared to high water availability across measurement temperatures. During the late growing period, elevated growth temperature further reduced the photosynthesis under low water availability. V cmax and J max declined along with the decrease in nitrogen content of leaves as growing period progressed, regardless of climatic treatment and water regime. We suggest that, for grass species, seasonal acclimation of the photosynthetic parameters under varying environmental conditions needed to be identified to fairly estimate the whole-life photosynthesis. Additional key words: acclimation of photosynthesis; carbon dioxide; carboxylation efficiency; electron transport; temperature; water deficit. ——— Received 12 April 2011, accepted 9 January 2012. + Corresponding author; tel.: +358-13-251-4441, fax: +358-13-251-4444, e-mail: zhenming.ge@uef.fi Abbreviations: C a – CO 2 concentration; C c – chloroplast CO 2 concentration; C i – intercellular CO 2 concentration; CON – ambient environment in chamber; EC – elevated CO 2 concentration in chamber; ET – elevated temperature in chamber; ETC – chamber with combination of temperature and CO 2 elevation; g m – mesophyll conductance; g sat – light-saturated stomatal conductance; ΔH a – enthalpy of activation; ΔH d – enthalpy of deactivation; J – rate of electron transport; J max – maximum rate of electron transport; K c , K o – Rubisco Michaelis constants for CO 2 , O 2 ; N L – nitrogen content based on leaf area; O – O 2 concentration; P c – Rubisco- limited rate of photosynthesis; P j – RuBP-regeneration-limited rate of photosynthesis; P N – net photosynthetic rate; P sat – light- saturated net photosynthetic rate; PPFD – photosynthetic photon flux densities; R – molar gas constant; RCG – reed canary grass; R d – mitochondrial respiration in light; ΔS – entropy of the desaturation equilibrium; T opt – optimal temperature; V cmax – maximum rate of carboxylation by Rubisco; α – quantum efficiency; Γ * – CO 2 compensation point (absence of dark respiration); θ – curvature of the light-response curve. Acknowledgments: This work was funded through the Finland Distinguished Professor Programme (FiDiPro) of the Academy of Finland (No. 127299-A5060-06) and the Finnish Network Graduate School in Forest Sciences of the Academy of Finland (No. 49996). Thanks are due to Matti Turpeinen of Vapo Ltd. for providing relevant logistical information on the field sites. The controlled environment chamber system was funded by European Regional Development Fund (ERDF) granted by the State Provincial Office of Eastern Finland. Matti Lemettinen, Alpo Hassinen, Risto Ikonen and Eine Ihanus at the Mekrijärvi Research Station, are thanked for their technical assistance. Dr. David Gritten is greatly thanked for revising the language of this paper.