181 N Save Nature to Survive 8 (1&2) : 181-184, 2014 www.theecoscan.in RESPONSE OF RHIZOSPHERIC SOIL MICROBIOTA TO ELEVATED CO 2 IN A RICE ECOSYSTEM M. DAS*, S. K. DASH, S. N. PASUPALAK AND A. K. KAR Orissa University of Agriculture and Technology, Bhubaneswar - 751 003, Odisha, INDIA e-mail:dasmahasweta3@gmail.com INTRODUCTION A major concern of the global climate change is the elevation of the atmospheric CO 2 from 280 µ mol mol -1 in 1750 to 386 µ mol mol -1 in 2008 (IPCC,2008). This increase of CO 2 level in the atmosphere within the last century has led to the prediction that during the second half of the 21 st century values around 600 ppm could be reached. This dramatic increase in atmospheric CO 2 may alter a variety of ecological processes in the environment. While plant responses to elevated atmospheric CO 2 are fairly well understood, the information on responses of soil microbial communities are highly variable. Because the concentration of CO 2 in soil is 10 to 15 times higher than in the atmosphere, elevated atmospheric CO 2 would not be expected to have a direct effect on soil microorganisms (Kandeler, Tscherko, Bardgett, Hobbs, Kampichler, and Jones, 1998). However, elevated atmospheric CO 2 may affect the soil ecosystem indirectly through CO 2 -induced plant responses that influence below-ground processes. It has been suggested that CO 2 -stimulated plant growth might result in an increased uptake of mineral nutrients such as nitrogen from the soil, possibly leading to decreases in soil nitrogen ( Hungate, Holland, Jackson, Chapin, Mooneyk and Field, 1997) and data from several researchers has supported this theory ( Insam, Berreck, Frostegard, Gerzabek, . Kraft, Schinner, Schweiger, Tschuggnall, 1999 and Niklaus, Kandeler, Leadley, Schmid, Tscherko and Korner, 2001). CO 2 enrichment can also increase the input of organic carbon to soils by increasing plant root biomass as well as root exudates (Van , Gorissen, Polci, 2000 and Zak, Pregitzer, Curtis, Teeri, Fogel, Randlett, 1993) Because plant roots are often the single largest source of organic carbon for soil microbial metabolism, increases in carbon inputs could have significant effects on the soil microbial communities. Rice (Oryza sativa L) being the predominant food grain crop of India, this study was intended to find out the impact of elevated CO 2 on the soil microbes in a rice based cropping system. As roots are the major source of additional C input into the soil, it is expected that the first effects of elevated CO 2 on soil microbial populations would occur in the rhizosphere. Moreover, because of their intimate contact with roots, soil microbes colonizing the rhizosphere will be more affected by these changes, than those microbes living in the bulk soil at some greater distance from plant roots (Sadowsky, and Schortemeyer, 1997). In ecosystems with a fast turnover, like tropical ecosystems, the importance of the microbial biomass as a nutrient sink and source is especially important (Ding, Yi, Liao, Martens, and Insam , 1992 ). The soil microbial biomass has been found to be a very useful ’early warning’ of changes in soil organic C which may take years to detect by classical chemical analyses ( Powlson, Brookes, and Christensen, 1987). Soil microorganisms control aspects of nutrient cycling; some of which are pivotal in the response of ecosystems to climate change. Examples include soil organic matter (SOM) transformations that may result in carbon (C) storage instable soil pools and mobilization of nutrients that are required for C assimilation into plant biomass. The primary impacts of altered rhizo deposition under elevated CO 2 will be mediated by the rhizospheric microorganisms. Though it is well established ABSTRACT Increase in atmospheric CO 2 concentration, which is one of the important factors for climate change, is considered to affect the soil microbial ecosystem. An attempt was made in the present investigation to study the effect of elevated CO 2 on rhizospheric soil microorganisms in the rice based cropping system. Response of rhizosperic soil microbiota of rice crop to elevated CO 2 were studied in the Open Top Chambers (OTC) at Agronomy Research Farm, OUAT and Bhubaneswar in 2010. Rice cultivar Lalat was planted under ambient condition (376ppm) in one OTC and under eCO 2 (476ppm) condition in another OTC. The crop was grown under standard agronomic practices. The microbiological analysis of the rhizospheric soil includes population count of the culturable aerobic and anaerobic heterotrophic bacteria, actinobacteria and fungi. The soil biology parameters studied includes microbial biomass carbon (MBC), dehydrogenase activity (DHA), Soil Organic Carbon (SOC) and available nitrogen. Soil samples were collected from Open Top Chambers prior to rice transplanting and harvesting. Aerobic heterotrophic bacterial population found to be dominated over anaerobes, actinobacteria and fungal population in ambient condition. The aerobic heterotrophic bacterial population was decreased under eCO 2 condition, where as actinobacteria and fungal population are significantly higher under eCO 2 condition Received : 31.01.2014 Revised : 16.03.2014 Accepted : 07.05.2014 *Corresponding author KEY WORDS Open Top Chambers (OTC) ECO 2 MBC DHA