Methanotrophic bacteria in the rhizosphere of rice microcosms and their effect on porewater methane concentration and methane emission

CH₄ emission from irrigated rice field is one of the major sources in the global budget of atmoshperic CH₄. Rates of CH₄ emission depend on both CH₄ production in anoxic parts of the soil and on CH₄ oxidation at oxic-anoxic interfaces. In the present study we used planted and unplanted rice microcosms and characterized them by numbers of CH₄-oxidizing bacteria (MOB), porewater CH₄ and O₂ concentrations and CH₄ fluxes. Plant roots had a stimulating effect on both the number of total soil bacteria and CH₄-oxidizing bacteria as determined by fluorescein isothiocyanate fluorescent staining and the most probable number technique, respectively. In the rhizosphere and on the root surface CH₄-oxidizing bacteria were enriched during the growth period of tice, while their numbers remained constant in unplanted soils. In the presence of rice plants, the porewater CH₄ concentration was significantly lower, with 0.1–0.4mM CH₄, than in unplanted microcosms, with 0.5–0.7mM CH₄. O₂ was detected at depths of up to 16 mm in planted microcosms, whereas it had disappeared at a depth of 2 mm in the unplanted experiments. CH₄ oxidation was determined as the difference between the CH₄ emission rates under oxic (air) and anoxic (N₂) headspace, and by inhibition experiments with C₂H₂. Flux measurements showed varying oxic emission rates of between 2.5 and 29.0 mmol CH₄m^-2 day^-1. An average of 34% of the anoxically emitted CH₄ was oxidized in the planted microcosms, which was surprisingly constant. The rice rhizosphere appeared to be an important oxic-anoxic interface, significantly reducing CH₄ emission.     

稳定性碳同位素方法在稻田甲烷研究中的应用

稻田甲烷产生、氧化等过程不仅影响甲烷排放量,还影响其稳定性碳同位素组成;反之,稻田所排放甲烷的稳定性碳同位素组成也可用来定量研究甲烷的产生和氧化过程。20世纪80年代以来,国外已将稳定性碳同位素方法广泛应用在稻田甲烷的研究中。本文介绍了稳定性碳同位素方法的基本原理及其在稻田甲烷产生、氧化过程研究中的应用,指出了该方法在稻田甲烷研究中的不确定因素,为我国稻田甲烷的深入研究提供了新的有力手段。     

Influence of the insecticide carbofuran on the production and oxidation of methane in a flooded rice soil

Applications of a commercial formulation of carbofuran, a carbamate insecticide, at rates of 2kg and 12kg active ingredient ha^–1 to flooded fields planted to rice led to significant inhibition of methane emission. Likewise, laboratory incubation studies showed that carbofuran applied at low rates (5 and 10μgg^–1soil) inhibited the net methane production relative to that of the control, but stimulated it when applied at a rate of 100μgg^–1soil. Interestingly, carbofuran increased the oxidation of methane when applied at low rates and inhibited it when applied at a rate of 100μgg^–1soil. Received: 5 May 1997     

Effect of silicate fertilizer on reducing methane emission during rice cultivation

Slag-type silicate fertilizer, which contains high amount of active iron oxide, a potential source of electron acceptor, was applied at the rate of 0, 2, 6, 10, and 20 Mg ha⁻¹ to reduce methane (CH₄) emission from rice planted in potted soils. Methane emission rates measured by closed chamber method decreased significantly with increasing levels of silicate fertilizer application during rice cultivation. Soil redox potential (Eh) decreased rapidly after flooding, but floodwater pH and soil pH increased significantly with increasing levels of silicate fertilizer application. Iron concentrations in potted soils and in percolated water significantly increased with the increasing levels of silicate fertilizer application, which acted as oxidizing agents and electron acceptors, and thereby suppressed CH₄ emissions. Silicate fertilization significantly decreased CH₄ production activity, while it increased carbon dioxide (CO₂) production activity. Rice plant growth, yield parameters, and grain yield were positively influenced by silicate application levels. The maximum increase in grain yield (17% yield increase over the control) was found with 10 Mg ha⁻¹ silicate application along with 28% reduction in total CH₄ flux during rice cultivation. It is, therefore, concluded that slag-type silicate fertilizer could be a suitable soil amendment for reducing CH₄ emissions as well as sustaining rice productivity and restoring the soil nutrient balance in rice paddy soil.     

Oxidation of methane in the rhizosphere of rice plants

Oxidation of CH₄ in the rhizosphere of rice plants was quantified using (1) methyl fluoride, a specific inhibitor of CH₄ oxidation, and (2) measuring changes in plant-mediated CH₄ emission after incubation under air, N₂, or 40% O₂. No significant rhizospheric CH₄ oxidation was observed from rice plants in the ripening stage. CH₄ emission from rice plants 1 week before panicle initiation increased by 40% if CH₄ oxidation in the rhizosphere was blocked. The growth stage of the rice plant is an important factor determining the rhizospheric CH₄ oxidation. Fluctuation of rhizospheric CH₄ oxidation during the growing season may help to explain the observed seasonal CH₄ emission patterns in field studies. Measurements from four rice varieties showed that one variety, Pokkali, had higher rhizospheric CH₄ oxidation. This was probably because Pokkali was in an earlier growth stage than the other three varieties. Both in the early and in the late growth stages, incubation under N₂ caused a much stronger CH₄ flux than inhibition of CH₄ oxidation alone. Apparently, N₂ incubation not only blocked CH₄ oxidation but also stimulated methanogenesis in the rhizosphere. Incubation under a higher O₂ atmosphere (40% O₂) than ambient air decreased the CH₄ flux, suggesting that increasing the oxidation of the rice rhizosphere may help in reducing CH₄ fluxes from rice agriculture. The O₂ pressure in the rhizosphere is an important factor that reduces the plant-mediated CH₄ flux. However, inhibition of methanogenesis in the rhizosphere may contribute more to CH₄ flux reduction than rhizospheric CH₄ oxidation.     

The role of rice plants in regulating mechanisms of methane missions

 Rice plants play a pivotal role in different levels of the methane (CH₄) budget of rice fields. CH₄ production in rice fields largely depends on plant-borne material that can be either decaying tissue or root exudates. The quantity and quality of root exudates is affected by mechanical impedance, presence of toxic elements, nutrient deficiencies, water status of growing medium, and nitrogenase activity in the rhizosphere. CH₄ oxidation in rice fields is localized in the rhizosphere where the concentration gradients of CH₄ and oxygen overlap. CH₄ oxidation capacity is a function of the downward transport of oxygen through the aerenchyma, which, in turn, also acts as a conduit for CH₄ from the soil to the atmosphere. The decisive step in the passage of CH₄ through rice plant is the transition from root to stem. However, rice plants show an enormous variety of morphological and physiological properties, including differences in root exudation and gas transfer capacity. Comparative studies on different cultivars are deemed crucial for accomplishing a better understanding of the mechanisms of CH₄ consumption in the rhizosphere and CH₄ transport through the rice plant as well as the interaction of these processes. The results of such studies are considered tools for devising mitigation options. Received: 7 April 1999     

Effect of insecticides on the availability of nutrients,nitrogen fixation,and phosphate solubility in the rhizosphere soil of rice

A field experiment was conducted to investigate the effects of 1,2,3,4,5,6-hexachlorocyclohexane (BHC), phorate, carbofuran, and fenvalerate, at their recommended doses, on some chemical and microbiological properties of the rhizosphere soil in relation to rice yields. In general, the insecticides had a beneficial effect on rhizosphere soil properties. Carbofuran strongly stimulated the mineralization of organic C. BHC and phorate led to the retention of less total N in the soil. BHC released more NH _inf4 ^sup+ -N than the other insecticides. Phorate, however, liberated the most NO _inf3 ^sup- -N. Phorate and fenvalerate released more available P than BHC and carbofuran did. All the insecticides stimulated the proliferation of aerobic non-symbiotic N₂-fixing and phosphate-solubilizing microorganisms, resulting in an overall increase in rice yield. BHC had the greatest effect on rice yields, followed by phorate.     

施肥对稻田甲烷排放的影响

本文综述了N肥和有机肥的种类、施用量、施用方式和施用时间对稻田CH4排放的影响,提出了减少稻田CH4排放的施肥策略,并指出了今后的研究重点:加强对稻田CH4排放机理的研究;针对以往研究中的不足,全面深入研究施肥对稻田CH4排放的影响;进一步研究稻田温室气体排放的交互作用。     

长期定位试验对水稻田土壤甲烷氧化活性和甲烷排放通量的影响

通过对长期定位施肥的黄松稻田土的甲烷氧化活性和甲烷排放通量的研究表明,长期定位施肥对稻田土壤的好氧甲烷氧化活性和甲烷排放通量有显著性的影响(|t|t0.05,P0.05),而对稻田土壤的厌氧甲烷氧化活性有影响但未达显著性水平(|t|t0.05,P0.05)。施加有机肥能显著增加稻田土壤的甲烷氧化活性和甲烷排放通量;当有机肥和无机肥混合施用时,其促进作用明显大于单施有机肥或无机肥。施加尿素后,稻田土壤的甲烷氧化活性及甲烷排放量都有所下降,但钾肥和磷肥能缓解由尿素引起的抑制作用。施肥后耕作的稻田甲烷氧化活性和甲烷排放通量高于施肥后不耕作的稻田;耕作而不施肥的稻田甲烷氧化活性和甲烷排放通量要低于不施肥也不耕作的稻田。     

Effect of fertilizer application on methane emission/production in the paddy soils of Taiwan

Methane production in three types of rice paddy soil was investigated under greenhouse conditions. The amount of methane produced during the first crop season (March to July) was 2–6 times higher than that in the second crop season (August to December). Application of organic fertilizer hastened the drop in redox potential and increased methane production and emission. Methane production also increased with the depth of soil with high values in soil samples from 18 to 30cm depth. Methane production in the first crop season was 18.0, 54.3 and 49.4mgcm^–3 for 6tha^–1 straw application for Linkou, Tzawchyau and Jiaushi soils, respectively. The value was 33.4mgcm^–3 for the second crop season in Jiaushi soil. Methane emission was high during the flowering and maturity stages in the first crop season and the values were high during the tillering and flowering stages in the second crop season. Methane emission was high in Tzawchyau and Jiaushi soils in the first crop season. Methane emission rate reached a maximum from 12 noon to 3p.m. due to high temperature and a minimum at 3 to 6a.m. in both planted and unplanted soils. Received: 17 September 1996     

红壤稻田不同施肥制度对土壤钾平衡和水稻产量的影响

基于14年田间定位试验,研究了红壤稻田系统在不同化肥配施条件下,有机养分循环利用对土壤K素平衡和水稻产量的影响。结果表明:不施肥或仅施化肥,土壤K素严重亏缺,其中以不施K的NP处理最严重,平均每年亏损K120.1kg/hm2,有机物养分循环利用的施肥制度可大幅度降低稻田土壤K素的亏损甚至出现K素盈余,NP C处理平均每年亏损K素2.2kg/hm2,而NPK C处理平均每年盈余K素154.5kg/hm2,但过高的K输入可能导致K营养元素的大量流失,降低K肥资源利用效益并增加环境污染风险,实行有机物养分循环利用时应适当减少化肥K的施用量;在不同施肥基础上的有机物养分循环利用都能显著提高水稻产量,但“循环”增产率随化肥配施程度提高而降低,不施肥基础上有机物养分循环利用的稻谷增产率为56%,与NP配施后,有机物养分循环利用的增产率降至18.8%,而在NPK配施基础上有机物养分循环利用的增产率只有10.2%,处理NPK C2与处理NPK之间的稻谷产量却没有显著差异,可见有机养分循环利用可以代替化肥K的施用;有机养分循环利用降低了K内部利用效率(IKUE)值,大小顺序为NPK C相似文献   

麦秆还田下钾肥减量对水稻产量及钾肥利用率的影响

我国土壤缺钾程度日益加重,作物秸秆中钾素含量较高,还田后可替代部分化学钾肥,缓解土壤钾素不足。为研究秸秆还田替代钾肥的效果,本文采用田间试验方法,以常规施钾[135 kg(K2O)·hm~(-2)]处理为对照,研究了在秸秆粉碎翻压还田(6 000 kg·hm~(-2))条件下钾肥减量10%、20%、30%和40%对水稻钾素吸收累积量、水稻产量、钾肥偏生产力及经济效益的影响。结果表明:在秸秆还田的基础上,水稻植株的钾素含量和累积量随着钾肥施入量的减少而降低。钾肥施用量减少10%~40%,水稻有效穗数、每穗粒数和结实率略有降低,水稻产量和产值有所下降,钾肥减量10%、20%和30%时,对水稻产量和产值的影响不显著(P0.05)。钾肥偏生产力随着钾肥施用量的减少而提高,钾肥减量10%、20%、30%和40%处理的水稻钾肥偏生产力比不减钾处理分别提高8.4%、18.9%、33.8%和44.4%。总体而言,在常规施钾条件下,秸秆还田后随着减钾量(10%~40%)的增加,水稻钾素累积量、产量和产值均呈下降趋势,而钾肥偏生产力呈增加趋势;减钾30%以内可显著提高水稻钾肥偏生产力(P0.05),对水稻产量及产值的影响不显著(P0.05)。     

The differential effects of ammonium and nitrate on methanotrophs in rice field soil

It has been known that nitrogenous fertilizers can either stimulate or inhibit methane oxidation in soils. The mechanism, however, remains unclear. Here we conducted laboratory incubation experiments to evaluate the effects of ammonium versus nitrate amendment on CH₄ oxidation in a rice field soil. The results showed that both N forms stimulated CH₄ oxidation. But nitrate stimulated CH₄ oxidation to a greater extent than ammonium per unit N base. The 16S rRNA genes and the pmoA genes were analyzed to determine the dynamics of total bacterial and methanotrophic populations, respectively. The methanotrophic community consisted of type I and type II methanotrophs and was dominated by type I group after two weeks of incubation. Nitrate promoted both types of methanotrophs, but ammonium promoted only type I. DNA-based stable isotope probing confirmed that ammonium stimulated the incorporation of ¹³CH₄ into type I methanotrophs but not type II, while nitrate caused almost homogenous distribution of ¹³CH₄ in type I and type II methanotrophs. Our study suggests that nitrate can promote CH₄ oxidation more significantly than ammonium and is probably a better N source for both types of methanotrophs in rice field soil. More investigations, e.g. using ¹⁵N labeling, are necessary to elucidate this possibility.     

尿素施用对稻田土壤甲烷产生、氧化及排放的影响

通过田间和培养试验研究了不施尿素(N0kg/hm2)和施用尿素(N300kg/hm2)对水稻生长期稻田土壤CH4产生潜力、氧化潜力和排放通量的影响。结果表明,水稻全生育期内,施用尿素降低土壤CH4产生潜力,并推迟其达到最大值的时间;尿素作为基肥和穗肥施用抑制土壤CH4氧化,而作为分蘖肥施用短暂地促进然后抑制土壤CH4氧化;施用尿素降低稻田CH4排放量。施用尿素通过同时影响CH4产生潜力和氧化潜力来影响稻田CH4排放。     

Effect of continuous and alternate water regimes on methane efflux from rice under greenhouse conditions

In a greenhouse study, the effect of moisture regimes (continuously flooded, continuously nonflooded, alternately flooded) on methane efflux from an alluvial soil planted to rice was studied using the closed chamber method. Methane efflux was almost 10 times more pronounced under continuously flooded conditions than under continuously nonflooded conditions. Intermittently flooded regimes (alternately flooded and nonflooded cycles of 40 or 20 days each) emitted distinctly less methane than the continuously flooded system. A significant negative correlation was found between methane emission under different water regimes and rhizosphere redox potential. Extractable Fe²⁺, readily mineralizable carbon (RMC) and root biomass presented a significant positive correlation with cumulative methane emission. The correlation of methane emission with other plant parameters and microbial biomass was not significant. Our results further suggest the possibility of reduced methane emissions through appropriate water management in a rainfed rice ecosystem. Received: 4 June 1996     

Effect of the herbicide butachlor on methane emission and ebullition flux from a direct-seeded flooded rice field

 Application of a commercial formulation of the herbicide butachlor (N-butoxymethyl-2-chloro-2′,6′-diethyl acetanilide) at 1 kg a.i. ha^–1 to an alluvial soil planted with direct-seeded flooded rice (cv. Annada), significantly inhibited both crop-mediated emission and ebullition fluxes of methane (CH₄). Over a cropping period of 110 days, the crop-mediated cumulative emission flux of CH₄ was lowered by ∼20% in butachlor-treated field plots compared with that of an untreated control. Concurrently, ebollition flux of CH₄ was also retarded in butachlor-treated field plots by about 81% compared with that of control plots. Significant relationships existed between CH₄ emission and redox potential (E _h) and Fe²⁺ content of the flooded soil. Application of butachlor retarded a drop in soil redox potential as well as accumulation of Fe²⁺ in treated field plots. Methanogenic bacterial population, counted at the maturity stage of the crop, was also low in butachlor-treated plots, indicating both direct and indirect inhibitory effects of butachlor on methanogenic bacterial populations and their activity. Results indicate that butachlor, even at field-application level, can effectively abate CH₄ emission and ebollition from flooded soils planted to rice whilst maintaining grain yield. Received: 15 March 2000     

Effect of temperature on reduction of iron and production of carbon dioxide and methane in anoxic wetland rice soils

 Wetland rice soils from Italy (Pavia) and the Philippines (Bugallon, Luisiana, Maligaya) were incubated under anoxic conditions at 31 different temperatures ranging from 4.7  °C to 49.5  °C. Production of CO₂ was most intensive at the beginning of the incubation (0–4 days) and was predominantly coupled to the reduction of free Fe(III). The optimum temperature for these processes was between 32  °C and 41  °C. After 9–16 days, CO₂ production rates had decreased and the available Fe(III) had been completely reduced at the optimum temperatures. However, Fe(III) was still available at temperatures below and above the optimum. Maximum CH₄ production rates were observed after 4–16 days (except in soil from Maligaya) with temperature optima between 32  °C and 41  °C, similar to those for CO₂ production and Fe reduction. Since ongoing Fe reduction is known to suppress CH₄ production, the temperature range of optimum CH₄ production was restricted to those temperatures at which Fe(III) had already been depleted. Nevertheless, the temperature characteristics of both CO₂ and CH₄ production often exhibited two temperature optima at some time during the incubation, suggesting a complex pattern of adaptation of the methanogenic microbial community to temperature. When available Fe(III) was completely depleted by anoxic pre-incubation at 30  °C, CH₄ was produced at a constant rate (steady state conditions) which increased with increasing temperature. Steady state CH₄ production reached a first maximum at about 40  °C, but increased further up to at least 50  °C, suggesting the presence of thermophilic microorganisms whose activity was apparently masked when Fe had not been completely reduced. The apparent activation energy of CH₄ production at steady state ranged between 48 kJ mol^–1 and 65 kJ mol^–1. Received: 26 August 1999     

水稻及其根际土壤中六六六、滴滴涕残留量探析

对四川省水稻及其根际土壤中主要有机氯农药六六六(BCH)和滴滴涕(DDT)残留现状研究结果表明,在抽检的10套样品水稻籽实中均未检出有机氯污染物六六六和滴滴涕,符合国家颁布的食品卫生标准。而根际土壤中普遍检出滴滴涕农药残留,且德阳孝泉镇还检出六六六农药残留,但根据土壤环境质量标准(GB15618—95)其土壤中六六六和滴滴涕的残留尚未超标,符合自然土壤背景值标准。建议继续禁用六六六和滴滴涕农药,并应间断性对食用农产品进行抽样调查,同时尽快禁止食用性植物生产中使用三氯杀螨醇。     

Soil clay mineralogies in relation to fertility management: Effect of soil clay mineral compositions on potassium fixation under conditions of wetland rice culture

Abstract

To evaluate the impact of soil clay mineralogy on the utilization efficiency of potassium fertilizers by rice, potassium fixation studies were made on fourteen soil clays having a range of mineralogical compositions. Soil clay with monomineralic beidellite fixed the highest proportion (76%) of the added potash, followed by clays containing either dominant or major vermiculite (51–66%). Fixation was significantly less severe (<35%) in vermiculitic clays containing hydrous mica. All the clays with mineralogical suites without beidellite or vermiculite, but consisting of montmorillonite, chlorite, hydrous mica, halloysite, kaolinite, and x‐ray amorphous material did not fix appreciable amounts (<18%) of the applied potassium.     

Short- and long-term effects of nitrogen fertilization on methane oxidation in three Swedish forest soils

 Under normal conditions, CH₄, one of the most important greenhouse gases, is subject to biological oxidation in forest soils. However, this process can be negatively affected by N amendment. The reported experiment was conducted in order to study the short- and long-term effects of N amendment on CH₄ oxidation in pine (Pinus sylvestris L.) forest soils. Soil samples were taken from three experimental sites, two of which had been amended with N once, over 20 years earlier, while the third had been amended 3 weeks earlier. The soil samples were incubated fresh at 15  °C at ambient CH₄ concentrations (ca. 1.8 ppmv CH₄). The variation in CH₄-turnover rates was high within the treatments: CH₄ was produced [up to 22.6 pmol CH₄ g dry wt. soil^–1 h^–1] in samples from the recently amended site, whereas it was consumed at high rates (up to 431 pmol CH₄ g dry wt. soil^–1 h^–1) in samples from the plot that had received the highest N amendment 27 years before sampling. Although no significant differences were found between N treatments, in the oldest plots there was a correlation between consumption of atmospheric CH₄ and the total C content at a depth of 7.5–15 cm in the mineral soil (r ²=0.74). This indicates that in the long-term, increased C retention in forest soils following N amendment could lead to increased CH₄ oxidation. Received: 3 September 1997