1. Aarhus University Department of Agroecology Results All the genotypes measured showed a decline in CO 2 -assimilation rate at leaf level when the environmental temperature decreased from 25ºC (Fig. 3) to 14ºC (Fig. 4). A sat measured on clone no. KK55 showed the smallest decline (40%) after transfer from 25 to 14 ℃ for seven days (Fig. 5). A large decline of 61 and 68% occurred in clone no. EMI3 and KK39, respectively. Under both conditions, the M. tinctorius species, clone no. KK24, showed the lowest level of photosynthesis (Fig. 3 and 4). The M. sacchariflorus species or crossings, clone no. KK55, EMI4, M114 and EMI3, showed the highest photosynthetic capacity at the leaf level measured under cold conditions. Leaf photosynthesis and cold tolerance in Miscanthus genotypes Kirsten Kørup 1, Xiurong Jiao 1,5, Helle Baadsgaard 1, Thomas Prade 2, Stanisław Jeżowski 3, Szymon Ornatowski 3, Robert Borek 4, Mathias N. Andersen 1, Poul Erik Lærke 1 and Uffe Jørgensen 1 1 Aarhus University, Department of Agroecology, Blichers Allé 20, DK-8830 Tjele, Denmark; 2 Swedish University of Agricultural Sciences, Department of Agrosystems, SE-230 53 Alnarp, Sweden; 3 Institute of Plant Genetics of the Polish Academy of Sciences, Strzeszyńska 34, 60-479 Poznań, Poland; 4 Institute of Soil Science and Plant Cultivation - State Research Institute, Czartoryskich 8, 24-100 Puławy, Poland; 5 Xiurong.Jiao@agrsci.dk Introduction Miscanthus species, which are C4 perennial grasses, are considered to be good candidates for a potential high production of biomass. They are of particular interest to meet the bioenergy goals using less land (Somerville et al., 2010). However, the productivity is challenged by inhibition of the photosynthetic capacity at temperatures below 15°C (Purdy et al., 2013). In unbred Miscanthus, biomass production of up to 20 Mg/ha dry matter has been recorded in Denmark (Jørgensen and Sander, 1997). Identification of genetic differences in cold tolerance may be useful to breed new genotypes with high photosynthetic capacity in a cool temperate climate, which might increase the yield further. Objective To identify Miscanthus genotypes with high photosynthetic activity and productivity under cool growth conditions Materials and methods Figure 1 Miscanthus in the field (left) and greenhouse (right) Figure 2 Leaf growth measurements in the field (left) and gas exchange measurements in the climate chamber (right) Plant material (Fig 1): A total of 15 genotypes of M. sacchariflorus, M. sinensis, M. tinctorius, M. ×giganteus or M.sinensis × M. sacchariflorus. Leaf growth measurements (Fig. 2, left) Shoot length was measured every second or third day. Daily growth was calculated for cold and warm periods. Gas exchange measurements, response of leaf photosynthesis to light measured by CIRAS-2 (PP Systems, Amesbury, MA, US) (Fig. 2, right) Climate chamber conditions : Day/night period: 14/10 hour; Temp. (d/n): 24/20ºC (warm), 14/10ºC (cold). Relative humidity (d/n): 85/85% (warm), 75/85% (cold); PAR: 670 µmol m -2 s -1 ; CO 2 -conc.: 400 ppm Cuvette conditions: Leaf temp.:24/14ºC (warm/cold); VPD:1.2/1.0 kPa(warm/cold); CO 2 -conc.: 400 ppm PAR: decreased from 2000 to 0 μmol m -2 s -1 in fourteen steps Results Clone no. KK39 showed the highest rate in daily leaf growth during the cool period, while EMI3 showed the highest growth rate during the warm period (Table 1). Most M. sacchariflorus genotypes showed a high daily growth rate during the cool period. Growth rate 2012 (cm/day ± s.e.) Clone no.GenotypeCool 1 Warm 1 KK39/79M. sinensis3.6 ± 3.35.0 ± 0.7 EMI 3 (Clone 5)M. sacchariflorus3.1 ± 1.06.7 ± 1.8 KK55M. sacchariflorus3.0 ± 0.53.9 ± 0.9 KK36/73M. sinensis2.3 ± 0.56.1 ± 1.1 EMI 4 (Clone 1)M. ×giganteus2.3 ± 0.54.9 ± 1.3 KK30M. sacchariflorus2.2 ± 0.54.3 ± 1.2 26M. sinensis2.0 3 2.2 3 K8/KK5/22M. sinensis1.8 ± 0.54.1 ± 0.5 EMI 9 (Clone 6)M. sinensis hybrids1.8 ± 1.04.2 ± 0.8 KK24/133M. tinctorius1.6 ± 0.63.6 ± 1.0 MS16(2x)M. sinensis (2x)1.6 2 ± 0.11.8 2 ± 0.9 M114M. sinensis X M. sacchariflorus1.5 2 ± 0.63.6 2 ± 1.0 KK10/26M. sinensis1.1 ± 0.64.7 ± 2.5 KK19/132M. tinctorius1.0 ± 0.63.2 ± 1.9 1 Mean /max. daily temp.: 9.8/15.5°C (cool) and 18.8/28.1°C (warm) - 2 Daily temp 10.5°C (cool) and 24°C (warm) - Poland Denmark 3 Mean daily temp 9.5 (cool) and 15.1°C (warm) - Sweden Table 1 Daily leaf growth rates measured in field experiments during a cold and a warm period in May 2012 Conclusion The genotypes showed large variation in the leaf photosynthesis level under both warm and cold growth conditions. Some correlation between measurements of leaf growth and photosynthesis rate at the leaf level under both growth conditions was found. The M. sacchariflorus genotypes were found to have the highest level of photosynthesis at 14ºC, but none were superior to M. ×giganteus (clone no. EMI4). References Somerville C, Youngs H, Taylor C, Davis SC & Long SP (2010). Feedstocks for Lignocellulosic Biofuels. Science. 329:790-792. Purdy SJ, Maddison AL & Jones LE et al. (2013) Characterization of chilling-shock responses in four genotypes of Miscanthus reveals the superior tolerance of M. ×giganteus compared with M. sinensis and M. sacchariflorus. Annals of Botany. 111: 999-1013 Jørgensen U & Sander B (1997). Biomass requirement for power production: How to optimise the quality by agricultural management. Biomass and bioenergy. 12: 145-147 Acknowledgements Projects and financial support: BIORESOURCE www.bioresource.dk, The Danish Council for Strategic Research GrassMargins www.grass,argin.com.The European Unions’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 289461 Figure 3 Net photosynthetic rate versus photosynthetic active radiation (PAR) of six Miscanthus genotypes grown under warm conditions (25 ℃ ). Figure 4 Net photosynthetic rate versus photosynthetic active radiation (PAR) of six Miscanthus genotypes grown under cold conditions (14 ℃ ). Figure 5 Reduction in A sat from warm to cold conditions. A sat is the net photosynthetic rate at a PAR of 1500 µmol m -2 s -1