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Not AvailableSoil respiration contributes significantly to ecosystem respiration and is vital in the context of climate change research. In a season-long experiment we studied total soil respiration (TSR) and its partitioning into root respiration, rhizospheric respiration (RhR) and basal-soil respiration in four contrasting rice production systems: irrigated lowland (IL) (cv. Gayatri); organic nutrient managed irrigated lowland (OIL) (cv. Geetanjali); system of rice intensification (SRI) (cv. Swarna); and aerobic rice system (Aerobic) (cv. APO). We considered TSR to be the sum of root respiration, RhR and basal-soil respiration. Irrespective of the rice production system, TSR was higher at panicle initiation stage. Considering all four systems, the RhR contributed the most (59–83%) and basal-soil respiration the least (10–19%) to the TSR. Mean RhR showed the trend of Aerobic SRI IL OIL across the growing seasons and indicated higher rhizosphere activities in the aerobic system. Mean root respiration showed a trend of IL OIL SRI Aerobic and mean basal-soil respiration had SRI IL OIL Aerobic. Soil labile carbon pools and heterotrophic populations were higher in OIL and dehydrogenase activity was higher in SRI. Microbial biomass carbon, readily mineralisable carbon, dehydrogenase activity and the heterotroph population showed positive correlations with RhR. Hence, regulation of RhR is crucial and can be achieved through rhizosphere modifications linked with labile carbon pools and soil enzymatic activities by plant physiological modification or through soil carbon stabilisation.ICA

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Not AvailableSulfur (S) metabolism is an important biogeochemical cycles in lowland rice. However, S biogeochemistry in rice soil is underestimated due to low standing pools of sulfate and unknown taxa of sulfur-reducing microorganisms. A whole-genome metagenomic study considering KEGG pathways and prevalence of enzymatic assay could provide an insight of dominating pathways of S-metabolism which are important in the context of S nutrition to plant and of mitigating GHGs emission in relation to climate change feedback. In this study, soil bacterial diversity and S-metabolism pathways were studied under ambient CO2 (a-CO2) and elevated CO2 þ temperature (e-CO2T) in lowland rice. The assimilatory pathway was the dominant irrespective of atmospheric CO2 concentrations indicated higher influence of ecology than atmospheric condition. The phylum Proteobacteria and Firmicutes were dominant and showed an abundance of 54 and 12%, under aCO2 and e-CO2T, respectively. Desulfovibrio was the most dominant genus. Desulfatibacillum, Desulfotomaculum, Desulfococcus, and Desulfitobacterium also showed higher abundance reads under e-CO2T. As a whole, total bacterial diversities were more under a-CO2, whereas, the activities of dominant bacteria were higher under e-CO2T. Shannon–Weaver and Simpson indices were higher under e-CO2T than a-CO2. The targeted gene-based quantification of bacteria responsible for S-metabolism is the future need.ICA

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Not AvailableLowland rice along with wetland sequesters one third of terrestrial carbon (C) which is responsible for both positive and negative feed-back to climate change. Labile C pools are sensitive to anticipated climate change condition (elevated CO2 and temperature). Those may eventually affect the C-stock in soil-microbes-plant-atmospheric (SMPA) continuum through priming effect and could enhance positive climate change feedback. Therefore, the objectives of the study were to analysis the effect elevated CO2 on C partitioning in rice-plant parts, soil labile C pools, and methane emission; along with identify related bacterial diversities and C-fixation pathways through whole genome metagenomic approach. The labile carbon flow in SMPA continuum was estimated for 3 years in lowland rice under elevated CO2 and temperature in open top chambers (OTCs). Rice was grown under ambient CO2 (a-CO2; 390 ± 20 μmol mol-1) and elevated CO2 and temperature (e-CO2T; 550 ± 20 μmol mol-1; 2 °C above ambient) under OTCs with replications. Soil labile C pools were increased by 25.4 to 38.9%, under e-CO2T over a-CO2. In microbes, biomass C, C-fixation pathways (metagenomic analysis) and C related soil enzymes were assayed. In atmosphere, the methane emission was measured and in plant system, C in different plant- parts, photosynthetic rates, root exudates-C were estimated to quantify labile C flow. Root exudates C was increased by 31.9% and microbial biomass C was enhanced by 23.3% under e-CO2T. Primarily, 12 soil bacterial genera which were responsible for C-fixation were dominant with higher abundance reads under e-CO2T. In C-fixation, dicarboxylate hydroxybutyrate cycle pathway and reductive citric acid cycle pathway were predominant under a-CO2 and e-CO2T, respectively. The methane emission was 26.0 and 26.8% higher under e-CO2T than a-CO2 at vegetative and reproductive stage of crop, respectively. Further, we got higher biomass accumulation, photosynthetic rate and stomatal conductance of rice under e-CO2T. Therefore, these augmented labile C flows in SMPA continuum may trigger the priming of soil C stocks, and at the same time could affect the system as a whole and results a positive feedback to climate change.ICA

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Not AvailableArbuscular mycorrhizal fungi (AMF) are one of the beneficial soil microbial communities, playing an important role in abiotic and biotic stress management in agricultural crops, including rice. Climate change, particularly elevated CO2 (eCO2) alters the soil microbial community, but the alteration of AMF community has received little attention, partly because of inadequacy in understanding of AMF taxonomy. Therefore, an attempt was made to understand AMF community in paddy soil under long-term exposure (8 years) to eCO2 through sequencing 18S rRNA small subunit SSU based Illumina Miseq technique using the primer pair AML1/AML2. Changes in OTUs belonging to 23 AMF species were identified in the ambient (400 ± 10 μmol mol-1) and eCO2 (550 ± 20 μmol mol-1) conditions, respectively based on reads alignment using MaarjAM VT database. Moreover, principal coordinate (PCO) analysis clustered the related OTUs and suggested that long-term exposure of eCO2 suppressed the OTUs of Glomerales and encouraged the OTUs of Diversisporales. Overall, the present study indicates that long-term exposure of paddy soil to eCO2 (550 ppm) drastically reduced the commonly occuring AMF such as Claroideoglomus and Glomus species in sub-humid tropical condition.ICA

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Not AvailableRice straw is a useful bio-resource with worldwide annual production of approximately 731 million tons. However, this valuable biomass is unfortunately burnt on field as waste that causes air pollution, global warming, plant nutrient losses and environment menace. About 60% of rice straw produced in Asia in general and India in particular is burnt in field. As for the basic requirement to predict their suitability for best alternative industrial uses biochemical, morphological and chemical (functional group) characterization of straws of 18 most widely grown rice cultivars from eastern region of India was carried out. Biochemical characterization was done on the basis of cellulose, hemicellulose, lignin and silica content. The surface morphology of straws was observed through Scanning Electron Microscopy (SEM), while, presence of functional groups were analyzed through Fourier Transform Infrared (FTIR) spectroscopy. Primarily, quantified biochemical profiles were used to group cultivars for best alternate uses of straw like bio-ethanol, biochar, compost and mushroom production. Morphological feature (from SEM) of straw and functional group (through FTIR) were used to support the grouping. Cultivars with higher hemicelluloses and cellulose with low to medium lignin and Si were better suited for bio-ethanol production while, straw having higher lignin and low to medium cellulose and hemicelluloses were selected for biochar. Therefore, considering all the three characterization methods (chemical composition, morphological features, presence or absence of functional groups), we found straws of rice cultivars, Tapaswini and IR 64 were best suited for bio-ethanol and biochar production, respectively. There are overlapping as well as contradictory observations found during grouping, when the three approaches were followed together. This indicate that the grouping of straw for better alternative uses could be done by biochemical and morphological characterization but this should be validated in small scale at farm or factory level for final recommendation.ICA