With stainless steel corer (?22 mm, 210 mm in length). Two to three soil cores (about 100 g in total) were collected from each pot and transferred into a 250-ml bottle. The soil samples were turned into slurry using N2-gassed deionized sterile water so that the ratio of dry weight of soil to water was 1:1. After flushing the samples with N2, the bottles were sealed with butyl rubber stoppers and, after shaking, flushed again with N2 to remove residual O2 and CH4. Incubation was performed statically at 25uC in the dark for 24 h. Headspace samples were taken every 12 h after shaking the bottles, and analyzed for concentration of CH4 and CO2 and their d13C. The CH4 and CO2 production from planted soil microcosms was due to decomposition of SOM plus ROC (unamneded control) or of SOM, ROC plus RS (RS treatments). CH4 production rates were calculated by linear regression of the CH4 increase with incubation time, and expressed in nmol CH4 gdw21 h21 of soil. The CO2 production rates were determined analogously. For unplanted soil microcosms, the methods for collection and incubation of soil core samples were similar, but these pots were not sacrificed, but at each sampling day (day 41, 55, 70 and 90), a 60-g soil core was taken from the pot. After removal of the soil core the residual soil in the pot was compacted, and water was added to maintain a water level of 5 cm depth. Using this procedure about 2.1 of the total amount of soil in the pot was collected during each sampling. The CH4 and CO2 production from unplanted soil microcosms was only due to decomposition of SOM (unamneded control) or of SOM plus RS (RS treatments).CH4 and CO2 productionAnalytical techniquesThe gas samples were analyzed for CH4 and CO2 using a gas chromatograph (GC) equipped with flame ionization detector (FID) [29]. Stable isotopic analysis of gas samples (CH4 and CO2) from pore water and soil core incubation were performed directly using the GCC-IRMS, samples from flux measurements (low in CH4) were preconcentrated on a Precon (Finnigan, Bremen, Germany). The principal operation of the GCC-IRMS has been previously described [30,31]. The isotope reference gas was CO2 (99.998 purity; Messer-Griessheim, Dusseldorf, Germany) cali?brated with the working standard methyl stearate (Merck). The latter was intercalibrated at the Max-Planck-Institute for BiogeoCH4 flux, soil pore water and plant parametersRates of CH4 emission was measured on day 41, 55, 70 and 90 of incubation in the greenhouse as described previously [27]. For flux measurements, planted rice microcosms were covered by flux chambers, and gas samples were taken every 30 min for 2 h. CH4 emission rates were determined from the slope of the linearly increasing CH4 mixing ratio and expressed in mmol CH4 m22 h21.Sources of Methane Production in Rice Fieldschemistry, Jena, Germany (Anlotinib site courtesy of Dr. W.A. Brand) against NBS 22 and USGS 24, and reported in the delta notation vs. VPDB: d13C = 103 (Rsa/Rst 21), with R = 13C/12C of sample (sa) and standard (st), respectively. The precision of repeated analysis was 6 0.2 , when 1.3 nmol CH4 were injected [23]. The determination of the stable isotopic signatures of dried plant and soil samples was carried out at the Institute for Soil Science and Forest Nutrition (IBW) at the University of LED-209 web Gottingen, Germany. ?Calculations1. Fraction of CH4 production from ROC (fROC). The fraction of CH4 derived from ROC (fROC) can be determined from the following mass balance equation:.With stainless steel corer (?22 mm, 210 mm in length). Two to three soil cores (about 100 g in total) were collected from each pot and transferred into a 250-ml bottle. The soil samples were turned into slurry using N2-gassed deionized sterile water so that the ratio of dry weight of soil to water was 1:1. After flushing the samples with N2, the bottles were sealed with butyl rubber stoppers and, after shaking, flushed again with N2 to remove residual O2 and CH4. Incubation was performed statically at 25uC in the dark for 24 h. Headspace samples were taken every 12 h after shaking the bottles, and analyzed for concentration of CH4 and CO2 and their d13C. The CH4 and CO2 production from planted soil microcosms was due to decomposition of SOM plus ROC (unamneded control) or of SOM, ROC plus RS (RS treatments). CH4 production rates were calculated by linear regression of the CH4 increase with incubation time, and expressed in nmol CH4 gdw21 h21 of soil. The CO2 production rates were determined analogously. For unplanted soil microcosms, the methods for collection and incubation of soil core samples were similar, but these pots were not sacrificed, but at each sampling day (day 41, 55, 70 and 90), a 60-g soil core was taken from the pot. After removal of the soil core the residual soil in the pot was compacted, and water was added to maintain a water level of 5 cm depth. Using this procedure about 2.1 of the total amount of soil in the pot was collected during each sampling. The CH4 and CO2 production from unplanted soil microcosms was only due to decomposition of SOM (unamneded control) or of SOM plus RS (RS treatments).CH4 and CO2 productionAnalytical techniquesThe gas samples were analyzed for CH4 and CO2 using a gas chromatograph (GC) equipped with flame ionization detector (FID) [29]. Stable isotopic analysis of gas samples (CH4 and CO2) from pore water and soil core incubation were performed directly using the GCC-IRMS, samples from flux measurements (low in CH4) were preconcentrated on a Precon (Finnigan, Bremen, Germany). The principal operation of the GCC-IRMS has been previously described [30,31]. The isotope reference gas was CO2 (99.998 purity; Messer-Griessheim, Dusseldorf, Germany) cali?brated with the working standard methyl stearate (Merck). The latter was intercalibrated at the Max-Planck-Institute for BiogeoCH4 flux, soil pore water and plant parametersRates of CH4 emission was measured on day 41, 55, 70 and 90 of incubation in the greenhouse as described previously [27]. For flux measurements, planted rice microcosms were covered by flux chambers, and gas samples were taken every 30 min for 2 h. CH4 emission rates were determined from the slope of the linearly increasing CH4 mixing ratio and expressed in mmol CH4 m22 h21.Sources of Methane Production in Rice Fieldschemistry, Jena, Germany (courtesy of Dr. W.A. Brand) against NBS 22 and USGS 24, and reported in the delta notation vs. VPDB: d13C = 103 (Rsa/Rst 21), with R = 13C/12C of sample (sa) and standard (st), respectively. The precision of repeated analysis was 6 0.2 , when 1.3 nmol CH4 were injected [23]. The determination of the stable isotopic signatures of dried plant and soil samples was carried out at the Institute for Soil Science and Forest Nutrition (IBW) at the University of Gottingen, Germany. ?Calculations1. Fraction of CH4 production from ROC (fROC). The fraction of CH4 derived from ROC (fROC) can be determined from the following mass balance equation:.
