RESEARCH ARTICLES CURRENT SCIENCE, VOL. 113, NO. 12, 25 DECEMBER 2017 2305 *For correspondence. (e-mail: nklenka@rediffmail.com) Interactive effect of elevated carbon dioxide and elevated temperature on growth and yield of soybean Narendra K. Lenka 1, *, Sangeeta Lenka 1 , J. K. Thakur 1 , R. Elanchezhian 1 , S. B. Aher 1 , Vidya Simaiya 1 , D. S. Yashona 1 , A. K. Biswas 1 , P. K. Agrawal 2 and A. K. Patra 1 1 Indian Institute of Soil Science, Nabibagh, Bhopal 462 038, India 2 Indian Council of Agricultural Research, Pusa, KAB-1, New Delhi 110 012, India A field experiment was undertaken in the kharif sea- son of 2016 in open-top chambers to study the indi- vidual and combined effects of elevated carbon dioxide and temperature on growth and yield parame- ters in soybean crop. The soybean (var. JS 20–29) crop was grown under two levels of CO 2 (ambient, 550 ppmv) in combination with two levels of air tem- perature (ambient, +2.0C). The five different climate treatments were: open field (OF), ambient chamber (AC), elevated temperature (eT), elevated CO 2 (eC) and elevation of both temperature and CO 2 (eCeT). At the time of sowing, vermicompost @ 2.0 tonnes ha –1 was applied along with 30 kg N ha –1 (in the form of urea), 60 kg P 2 O 5 ha –1 (through single super phos- phate) and 40 kg K 2 O ha –1 (through muriate of potash) to the soybean crop. Impact of the climate variables was studied in terms of selected plant attributes, viz. plant height, leaf area, biomass, number of pods, number of grains per pod, grain yield and seed index (100 seed weight). Results indicated significant posi- tive effect of elevated CO 2 and temperature on plant growth parameters, pod attributes and grain yield. Compared to AC, leaf area at 50 days after sowing was higher by 143%, 281% and 259% and above- ground biomass at harvest was higher by 47%, 31% and 47% under eC, eT and eCeT treatments respec- tively. The difference in biomass under OF and AC was not significant. The increase in grain yield over ambient varied from 30% under eT to 51% and 65% under eC and eCeT treatments respectively. The seed index as measured through weight of 100 numbers of seeds, was significantly higher under elevated CO 2 and/or elevated temperature treatments than the ambient chamber and open field treatments. Keywords: Carbon dioxide fertilization, climate change, elevated temperature, seed index, soybean biomass. INDUSTRIAL revolution along with increased fossil-fuel burning has caused a large increase in the atmospheric concentration of three key greenhouse gases (GHGs). Since 1750, the concentrations of the three GHGs, viz. carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) have increased by 40%, 150% and 20% respectively. According to the 5th Assessment Report (AR) of the Intergovernmental Panel on Climate Change (IPCC), among the total anthropogenic CO 2 emissions between 1750 and 2011, about half have occurred in the last 40 years 1 . The atmospheric CO 2 concentration is increasing at an unprecedented rate and for the first time in recorded history has crossed 400 ppmv (parts per million by vol- ume). Considering a value of 280 ppmv in 1800 (prior to the Industrial Revolution), the increase is by about 120 ppmv. According to the measurement at Mauna Loa Observatory in Hawaii, the largest year-to-year increase occurred during the two consecutive years of 2015 and 2016, with the annual growth rate of more than 3 ppmv in both the years 2 . The steep annual growth rate of atmos- pheric CO 2 particularly in the last few years is significant in the context of global warming and climate change. In addition, there has been an increase of 0.85C in the global mean surface temperature over the period 1880– 2012 according to the 5th AR of the IPCC 1 . The period from 1983 to 2012 was likely the warmest 30-year-period in the last 1400 years in the northern hemisphere. The global mean surface temperature is projected to increase further under all the representative concentration path- ways (RCPs). According to the 5th AR of the IPCC, the RCPs describe four different 21st century pathways of GHG emissions and atmospheric concentrations, air pol- lutant emissions and land use. The increase in global mean surface temperature by 2080–2100 is in the range 0.3–1.7, 1.1–2.6, 1.4–3.1C and 2.6–4.8C under RCP 2.6, 4.5, 6.0 and 8.5 respectively 1 . The rising CO 2 concentration and increase in global surface temperature have a direct linkage with the growth and metabolism of plants. As CO 2 is a primary raw mate- rial in the process of photosynthesis, increase in atmos- pheric CO 2 concentration has been reported to cause fertilization effect resulting in enhanced crop biomass and yields, particularly in C 3 plants 3,4 . This has been pri- marily attributed to the enhanced rate of photosynthesis