Environmental and Experimental Botany 75 (2012) 150–158 Contents lists available at SciVerse ScienceDirect Environmental and Experimental Botany journa l h o me pa g e: www.elsevier.com/locate/envexpbot Carbon assimilation and allocation ( 13 C labeling) in a boreal perennial grass (Phalaris arundinacea) subjected to elevated temperature and CO 2 through a growing season Zhen-Ming Ge a,b,∗ , Xiao Zhou a , Seppo Kellomäki a , Christina Biasi c , Kai-Yun Wang a,b , Heli Peltola a , Pertti J. Martikainen c a School of Forest Sciences, University of Eastern Finland, P.O. Box 111, FIN-80101 Joensuu, Finland b Key Laboratory of Urbanization and Ecological Restoration, East China Normal University, 200062 Shanghai, PR China c Department of Environmental Sciences, University of Eastern Finland, P.O. Box 1627, FIN-70211 Kuopio, Finland a r t i c l e i n f o Article history: Received 12 May 2011 Received in revised form 8 September 2011 Accepted 16 September 2011 Keywords: 13 C pulse labeling Boreal perennial grass Climate change Temperature and CO2 Seasonal variability Carbon storage and allocation a b s t r a c t The responses of carbon assimilation and allocation in different plant organs to changed environment depend on the species, their phenology and growth conditions. An integrated experiment was conducted over an entire growing season to understand the effects of elevated growth temperature (ambient + 3.5 ◦ C) and CO 2 (700 mol mol -1 ) on the seasonal photosynthetic capacity, carbon accumulation and allocation (four 21-day periods of 13 C pulse labeling-to-harvest) in a boreal perennial grass (Phalaris arundinacea) using controlled environmental chambers. Elevated temperature was found to significantly enhance leaf photosynthesis and total carbon accumulation in biomass during the early stages of the growing season, while it also resulted in earlier senescence and lower carbon storage at the final harvest. CO 2 enrichment significantly stimulated photosynthesis and total carbon accumulation over the growing season. The combination of elevated temperature and CO 2 caused a lower total carbon accumulation in biomass at maturity compared to elevated CO 2 alone, indicating that this boreal crop grown under increased temperature could not take advantage of CO 2 enrichment. Elevated temperature significantly increased 13 C assimilation and allocation to the leaves and the stems during the first labeling period, and resulted in 5–6% higher percentage of carbon allocation in the roots during the final two labeling periods. This did not result in increased carbon storage in the roots, but much less carbon accumulation in the shoots during the latter growing periods. Elevated CO 2 caused a higher 13 C assimilation in the roots, but did not significantly increase the below-ground 13 C allocation percentage. This was because of the higher growth of the shoots under high nitrogen availability and CO 2 enrichment. The response of carbon allocation pattern to the combined elevation of temperature and CO 2 was similar to the responses to elevated temperature alone. We conclude that plant growth and carbon assimilation are clearly controlled by phenology in this boreal crop under the climatic treatments, however, seasonal carbon allocation pattern within the plants was not significantly changed by the treatments. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Increasing anthropogenic emissions of atmospheric trace gases (e.g., CO 2 , CH 4 , N 2 O) is seen to be the main cause of the current and forecasted global warming trend (IPCC, 2007). In Finland, for example, an increase of 2–6 ◦ C in the annual mean temperature with a concurrent elevation of CO 2 (up to 540–840 ppm) by the end ∗ Corresponding author at: School of Forest Sciences, University of Eastern Finland (Joensuu campus), Yliopistokatu 7, P.O. Box 111, FIN-80101 Joensuu, Finland. Tel.: +358 13 251 4441; fax: +358 13 251 4444. E-mail address: zhenming.ge@uef.fi (Z.-M. Ge). of 21st century may occur (Carter et al., 2005; Ruosteenoja et al., 2005). Numerous studies have been conducted to examine the effects of elevated temperature and CO 2 on C 3 plants in environmental chambers and field experiments (Drake et al., 1997; Ziska et al., 1997; Adam et al., 2000; Crafts-Brandner and Salvucci, 2000; Ziska, 2001; Long et al., 2004; Ainsworth and Long, 2005; Pérez et al., 2005; Qaderi et al., 2006). Carbon assimilation and yield of many C 3 crops are enhanced by CO 2 enrichment (Drake et al., 1997; Ziska et al., 1997), due to the increased availability of CO 2 which increases carboxylation and suppresses photorespiratory CO 2 release (Drake et al., 1997; Long et al., 2004). However, greatly increased temperature has been found to reduce crop biomass by decreasing photosynthesis, which could be a result of earlier 0098-8472/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2011.09.008