Major Biogeochemical Processes in Soils‐A Microcosm Incubation from Reducing to Oxidizing Conditions (original) (raw)
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Comparison of Redox Indicators in a Paddy Soil during Rice-Growing Season
Soil Science Society of America Journal, 2002
of organic matter in the soil. Under equilibrium conditions, a theoretically well-defined sequence of reduction The objective of this study was to compare three methods of evaluof electron acceptors should take place when the soil ating redox status, i.e., conventional redox potential (E H) measurement, terminal electron-accepting processes (TEAPs) and oxidative goes from oxic to suboxic to anoxic conditions (Sposito, capacity (OXC) in pore waters of a paddy soil during the rice-growing 1989). The principal redox couples in sequence are O 2 / season. The redox potential can be measured readily which can moni-H 2 O, NO Ϫ 3 /N 2 , Mn(IV, III)/Mn(II), Fe(III)/Fe(II), SO 2Ϫ 4 / tor progressive development of reducing conditions and distinguish H 2 S, and CO 2 /CH 4. The reduced conditions in suboxic from anoxic conditions but with little information on specific merged paddy soils may be readily measured by measurredox processes under anoxic conditions. Identifying dominant TEAPs ing E H of the pore water, but E H is a difficult soil paramerequires intensive data collection and analysis. The sequence of TEAPs ter to interpret. Bartlett (1999) described thoroughly development basically followed theoretical predictions but overlapthe redox behavior in soils, providing an important base ping, typically among Mn, Fe, SO 2Ϫ 4-S reductions and methane producto our understanding of equilibrium and dynamic redox tion, was featured throughout the season. The measured dissolved H 2 conditions. He pointed out that a Pt electrode may not gas as the intermediate product, reflected the overlap among electron acceptors. Oxidative capacity integrated all the major oxidized and reflect changes in some species involved in redox reacreduced species to a single conservative parameter and showed clearly tions, such as partial pressure of O 2 and neither Mn or the progressive redox status from oxic to postoxic and then to sulfidic Fe oxides nor nitrate had the expected quantitative efconditions in the paddies with no apparent methanic condition during fect on the Pt electrode measurement. Methane, bicarthis particular growing season. In OXC computations, a more reliable bonate, N 2 gas, nitrate, and sulfate are not electroactive, method to estimate Mn and Fe oxyhydroxide concentrations as eleci.e., they do not readily take up or give off electrons at tron acceptors needs further testing. The measured E H showed a the surface of the Pt electrode used to measure E H higher correlation to redox species Mn(II), Fe(II) and methane con-(Berner, 1981). Since it is a measurement of potential, centrations (r 2 ϭ 0.76, 0.73, and 0.76, respectively) than to dissolved the Pt electrode also responds to changes in pH and O 2 (DO), NO Ϫ 3-N, and SO 2Ϫ 4-S (r 2 ϭ 0.53, 0.37, and 0.16, respectively). other potentials. Thus, measured E H usually reflects a Measured E H was also highly correlated to OXC for low sulfate solutions. The three methods for evaluating redox status all indicated Description of Redox Parameters considers simultaneously the consumption of electron acceptors (DO, NO Ϫ 3-N, Fe(III), SO 2Ϫ 4-S, and CO 2); in-Redox Potential termediate product (dissolved hydrogen gas, H 2) con-Microbes that utilize oxidized species in the soil as centration, and the concentrations of final products terminal electron acceptors mediate the decomposition
Biogeochemistry, 2006
The effects of elevated concentrations of atmospheric CO2 on CH4 and N2O emissions from rice soil were investigated in controlled-environment chambers using rice plants growing in pots. Elevated CO2 significantly increased CH4 emission by 58% compared with ambient CO2. The CH4 emitted by plant-mediated transport and ebullition–diffusion accounted for 86.7 and 13.3% of total emissions during the flooding period under ambient level, respectively; and for 88.1 and 11.9% of total emissions during the flooding period under elevated CO2 level, respectively. No CH4 was emitted from plant-free pots, suggesting that the main source of emitted CH4 was root exudates or autolysis products. Most N2O was emitted during the first 3 weeks after flooding and rice transplanting, probably through denitrification of NO3− contained in the experimental soil, and was not affected by the CO2 concentration. Pre-harvest drainage suppressed CH4 emission but did not cause much N2O emission (−2 h−1) from the rice-plant pots at both CO2 concentrations.
Journal of Environmental Quality, 2007
To understand which soil chemical properties are the best predictors of CH 4 production in rice paddy soils, a model was developed with empirical data from nine types of rice soils collected around Japan and anaerobically incubated at 30°C for 16 wk in laboratory conditions. After 1, 2, 4, 8, and 16 wk of incubation, CO 2 , CH 4 , and Fe(II) were measured to understand soil organic matter decomposition and iron (Fe) reduction. Available N (N ava) was also measured at the end of incubation. Th e results showed that decomposable C and reducible Fe are two key parameters that regulate soil CH 4 production (P CH4). Th ere was a signifi cant relationship between decomposable C and available N (N ava) (r 2 = 0.975**). Except for a sandy soil sample, a signifi cant relationship between total Fe (Fe total) and reducible Fe was found. From this experiment, a simple model of soil CH 4 production was developed: P CH4 = 1.593N ava-2.460Fe total /1000 (each unit was mg kg −1 soil). After simulated CH 4 production by two soil chemical properties as above, there was a signifi cant consistency between model simulation and actual measurement (r 2 = 0.831**).
Influence of heavy metals on methane oxidation in tropical rice soils
2000
In a laboratory incubation study, the effect of select heavy metals on methane (CH 4) oxidation in two rice soils was investigated under two moisture regimes. Heavy metals differed in their effect on CH 4 oxidation in both soils under the two water regimes. Cr significantly inhibited CH 4 oxidation in the alluvial soil at 60% moisture holding capacity, while Cu stimulated the process. On the contrary, Zn inhibited CH 4 oxidation in both alluvial and laterite soils only under flooded conditions. Application of rice straw alleviated the inhibitory effect of heavy metals on CH 4 oxidation and CO 2 production. Inhibition of CH 4 oxidation in the alluvial soil was related to the methanotrophic bacterial population in Cr-and Znamended alluvial soil.
Biogeochemistry, 2000
We have studied the inhibiting effect of fertilisation and soil compaction on CH 4 oxidation by measuring gas fluxes and soil mineral N dynamics in the field, and CH 4 oxidation rates in laboratory-incubated soil samples. The fertilisation and soil compaction field experiment was established in 1985, and the gas fluxes were measured from 1992 to 1994. Methane oxidation was consistently lower in fertilised than in unfertilised soil, but there apparently was no effect of repeated fertiliser additions on the fertilised plots. The measured mineral N in fertilised and unfertilised soil showed large differences in NH + 4 concentrations just after fertilisation, but the levels rapidly converged because of plant uptake and nitrification. The CH 4 oxidation rate did not reflect these contrasting mineral N patterns, suggesting that the CH 4 oxidation capacity remaining in the soil that had been fertilised since 1985 was largely insensitive to ammonia in the new fertiliser. Thus, competitive inhibition by ammonia may have been involved in the early stage of the field fertiliser experiment, but the CH 4 oxidation remaining after 7 to 9 years of continued fertilisation seems not to have been affected by ammonia. The substrate affinity of the CH 4-oxidizing microflora appeared to be the same in both the fertilised soil and the unfertilised control, as judged from the response to elevated CH 4 concentrations (52 µl l −1) in laboratory incubations. Soil compaction resulted in a persistent reduction of CH 4 influx, also seen in laboratory incubations with sieved (4-mm mesh) soil samples. Since the sieving presumably removes diffusion barriers created by the soil compaction, the fact that compaction effects persisted through the sieving may indicate that soil compaction has affected the biological potential for CH 4 oxidation in the soil.
CH 4 production potential in a paddy soil exposed to atmospheric CO 2 enrichment
Soil Science and Plant Nutrition, 2006
An anaerobic incubation experiment was conducted to investigate methane (CH 4) production potential in soil samples collected from a paddy field after exposure to free-air CO 2 enrichment (FACE). The FACE experiment with two CO 2 levels, ambient and ambient + 200 p.p.m.v CO 2 during the rice growing season, was conducted at Shizukuishi, Iwate Prefecture, Japan. The soil was a wet Andosol. Soil samples were taken from the surface (0-1 cm) and the sub-surface (1-10 cm) soil layers 2 months after rice harvest. Subsamples of the fresh soils were put into glass bottles and submerged under N 2 gas headspace during the incubation. The results showed that, prior to incubation, the contents of total C and dissolved organic C (DOC) were significantly greater in FACE soil than ambient soil. During the incubation, CH 4 production potential was approximately 2-4-fold higher in FACE soil than ambient soil and approximately 500-1,000-fold greater in surface soil than sub-surface soil. In general, the FACE soil contained more DOC than ambient soil, particularly in the surface soil layer. These findings suggest that FACE treatment exerted longterm positive effects on CH 4 production and increased organic C content in this paddy soil, particularly in the surface soil layer.
Chemosphere, 1993
The correspondence of soil redox potential to CH 4 and N20 emissions from a rice paddy soil was studied. A Louisiana (USA) rice soil was equilibrated under controlled redox levels, ranging from +500 to -250 mV, and the amount of CH 4 and N20 evolved quantified. A soil redox value of -150 mV was critical for CH 4 emission to occur. The lower the s6il redox level the greater the CH 4 emission rates. A 50 mV decrease in soil redox level resulted in approximately a 10-fold increase in CH 4 emission rate for the -150 mV to -250 mV range. Methane oxidation rates were less than production, irrespectwe of soil redox level. The highest N20 emission rate was observed during nitrification reactions at a redox level of +400 inV. At soil redox levels below +200 mV, N20 was also produced during denitrification reactions. The more reducing the soils, the more N gases were emitted, but the smaller the N20/N 2 ratio of the resulting gas. The maximum amount of N20 evolved during denitrification reactions was observed at 0 mV.
Evaluation of methane oxidation in rice plant-soil system
2002
Mechanisms of methane oxidation in the plant-soil system of rice were studied in a pot experiment using two cultivars (PSBRc-30 and IR72) at two growth stages (flowering and heading). Methane emission was measured by chambers, while methane oxidation was determined through propylene amendment as an alternative substrate to be propylene oxide (PPO) and acetylene as an inhibitor for methane oxidizing (methanotrophic) bacteria. Cell numbers (methanotrophic and methanogenic bacteria) were determined by the most probable number method. The cultivar PSBRc-30 consistently showed higher methane emission rates than IR72. Methane flux clearly decreased from flowering to heading stages in both cultivars. This observation was largely reflected by trends in the mechanisms involved: either methanogenic cell numbers or activities decreased with plant age while methanotrophic cell numbers or activities generally showed an increasing trend. The methanogenic population was in the order of 10 5 g −1 dry soil, while the population of methanotrophs ranged from 10 4 to nearly 10 6 g −1 dry soil. Methanotrophic activity followed the order; root (1.7-2.8 nL PPO g −1 DM h −1) > shoot (0.7-2.0) > soil (0-0.4) when the consumption of alternative substrate was related to dry matter. Derived from the estimated amounts of soil and plant biomass in the pot experiment, however, the soil generally accounted for more than 90% of the total methane oxidation. Within the plant segments, methane oxidation activities in the root exceeded those of the shoot by factor of approximately 10.
Effect of Soil Oxidants KNO3, MnO2, and Air on Methane Production in Flooded Rice Soil Suspension
Water Air and Soil Pollution
To determine effective means to reduce methane (CH4) production from flooded rice soil, laboratory measurements were made on methane (CH4) formation in a Crowley silt loam as affected by the addition of potassium nitrate (KNO3), manganese dioxide (MnO2), and air (O2) under flooded conditions. In the experiment, oxidants were added to the soil prior to flooding at the rate of 300 and 1000 ppm O2 equivalent. Methane production was measured over a 32 d incubation period. Potassium nitrate added at rates of 300 and 1000 ppm O2 equivalent reduced CH4 production by 100% and MnO2, at 300 and 1000 ppm O2 equivalent, significantly decreased CH4 formation approximately 20% and 98-99% over the 32 d period, respectively compared to controls. Air addition did not significantly affect CH4 formation.
Effect of rice plants on CH4 production, transport, oxidation and emission in rice paddy soil
2001
To understand the integrated effects of rice plants (variety Wuyugeng 2) on CH 4 emission during the typical rice growth stage, the production, oxidation and emission of methane related to rice plants were investigated simultaneously through laboratory and greenhouse experiments. CH 4 emission was significantly higher from the rice planted treatment than from the unplanted treatment. In the rice planted treatment, CH 4 emission was higher at tillering stage than at panicle initiation stage. An average of 36.3% and 54.7% of CH 4 produced was oxidized in the rhizosphere at rice tillering stage and panicle initiation stage, respectively, measured by using methyl fluoride (MF) technique. In the meantime, CH 4 production in the planted treatments incubated under O 2-free N 2 condition was reduced by 44.9 and 22.3%, respectively, compared to unplanted treatment. On the contrary, the presence of rice plants strongly stimulated CH 4 production by approximately 72.3% at rice ripening stage. CH 4 emission through rice plants averaged 95% at the tillering stage and 89% at the panicle initiation stage. Based on these results, conclusions are drawn that higher CH 4 emission from the planted treatment than from unplanted treatment could be attributed to the function of rice plants for transporting CH 4 from belowground to the atmosphere at tillering and panicle initiation stage, and that a higher CH 4 emission at tillering stage than at panicle initiation stage is due to the lower rhizospheric CH 4 oxidation and more effective transport mediated by rice plants.