158 Radiation use efficiency of wheat in OTC December 2015 Journal of Agrometeorology 17 (2) : 158-164 (December 2015) Fossil fuel combustion and deforestation have resulted in a rapid increase in atmospheric carbon dioxide concentration CO 2 since the 1950s. It is predicted that the concentration will reach about 550 ppm in 2050. Numerous studies have been conducted to examine the response of agricultural food production to elevated CO 2 . Elevated CO 2 generally stimulates plant photosynthetic processes, thereby increasing crop growth and yield (Drake et al, 1997, Kimball et al , 2002 and Singh, et al, 2013). Rising CO 2 can be sensed by plant tissues, which are directly in contact with the atmosphere IPCC, 2007). Several reviews have shown that the above increase in photosynthetic rates is translated to increases in biomass production and yield of agricultural crops and natural plant species (Kimball et al , 2002). Globally, wheat is a major staple crop and it is also significant for India. Because of wheat’s importance, effects of ongoing regional and global environmental changes on wheat yield need to be better understood. Warming generally reduces wheat yield (van Oijen et al, 1999), probably because of a shorter grain filling period caused by more rapid development. On the other hand, beneficial effects of elevated (CO 2 ) on photosynthesis and growth are sometimes thought to increase with warming (Monteith 1977 and Moiser et al, 1998). A complication is that elevated CO 2 reduces stomatal conductance and increases water-use efficiency in C3 crops (Erice et al, 2007, Qiu et al, 2008, Pritchard et al., 2000 and Lawlor and Mitchel, 1991), so beneficial effects of elevated CO 2 on yield may be due to changes in photosynthesis, changes in water use or water-use efficiency or both. Keeping in view the importance of global climate change, this study was undertaken with the objective to study the yield and physiological behavior of wheat under elevated CO 2 . MATERIALS AND METHODS Field experiment This study was conducted in the experimental farm of ICAR Research Complex for Eastern Region, Patna located at 25°35’37" N latitude and85°05’ E longitude and at an altitude of 51.8 m above mean sea level during 2011-12 and 2012-13. The land area of open-top chambers (OTCs) had a fairly level topography. The climate of the experimental site is semi-arid with dry hot summer and mild winters. The soil at the experimental site belongs to the major group of Indo-Gangetic alluvium (Table 1). Radiation use efficiency and yield of wheat grown under elevated CO 2 and temperature in open top chamber at Patna, Bihar JOYDEEP MUKHERJEE 1 , S.S. SINGH 2 , SANTOSH KUMAR and MOHD. IDRIS ICAR Research Complex for Eastern Region, BV College, Patna 800014, India 1 ICAR-Indian Agricultural Research institute, New Delhi 110012 2 ICAR-Indian Institute of Pulses Research, Kanpur 208024 Email: mjoydeep2k@yahoo.com ABSTRACT Elevated CO 2 increases the C3 photosynthetic rate at the cellular level through increased carboxylation and decreased oxygenation, both of which are catalyzed by Rubisco. The study was conducted in the experimental farm of ICAR Research Complex for Eastern Region, Patna (Lat. 25°35’37" N, Long. 85°05’ E and altitude 51.8 m amsl) under open top chamber (OTC). The circular structure of OTCs were made with an aluminum frame covered with UV-treated poly carbonate sheet, which transmits 85% of natural sunlight. The higher grain yields in wheat crop under elevated CO 2 were primarily due to their greater biomass production capacity and not due to a greater fraction of total biomass being partitioned to grains. The percentage of filled grains also was significantly greater in the elevated treatment. Harvest index (HI) differed significantly between the elevated and ambient treatments in both the years. However, HI of the open treatment was significantly lower than the other two. Seed yields under elevated CO 2 were greater than the ambient and open field treatment. Key words: GHG, OTC, elevated CO 2 , wheat, climate change and RUE