水分和温度对旱地红壤硝化活力和反硝化活力的影响

采集第四纪红色粘土发育和第三纪红砂岩发育的红壤,分别在4C冰箱内保存(O),室温下湿润(M)和淹水(F)培养110天后测定硝化细菌、反硝化细菌、硝化势、反硝化势和反硝化酶活性。结果表明,低温有利于保持硝化细菌和反硝化细菌的数量,但显著抑制它们的硝化和反硝化活力。湿润有利于保持硝化细菌的硝化活力,而淹水则有利于保持反硝化细菌的反硝化活力,但均不利于硝化细菌和反硝细菌的存活。由此说明,不同的研究目的和需要测定的项目,应采用不同的土壤样本保存方法。     

亚热带土壤亚铁与厌氧反硝化

本文就亚热带土壤亚铁参与反硝化的可能性进行了探讨。研究结果表明:厌氧还原条件下加入KNO3的处理中,Fe2+浓度随培养时间延长而下降,且Fe2+浓度的降低和NO3–-N浓度的降低呈显著正相关。预培养结束后的亚铁浓度(In-Fe2+)和厌氧培养期间Fe2+浓度降低速率与反硝化势表征指标k、b、v7,以及与无定形铁氧化物(活性铁)含量的显著正相关性初步证明,活性铁通过不同价态铁离子(Fe2+和Fe3+)之间的转化,参与了反硝化的电子传递过程。当有机碳等电子供体受限时,Fe2+可作为电子供体参与反硝化还原NO3–-N。这一结果表明,NO3–-N作为电子受体参与厌氧条件下Fe2+氧化成Fe3+的反应可能在铁氧化物含量丰富的亚热带土壤中普遍存在。     

亚热带稻田土壤反硝化动力学参数估算

反硝化作用是土壤氮素损失的重要途径,对反硝化潜势的准确估算是农业精准施肥的必然要求。以亚热带典型红壤稻田土作为研究对象,足量添加外源氮进行室内淹水厌氧培养获取反硝化作用动态,并分别用米氏方程和一级动力学方程对其拟合,最后利用土壤基本理化性质对反硝化动力学参数进行估算。结果表明:米氏方程更适合反硝化动力学拟合,最佳的米氏常数(Km)为35mg/kg;米氏最大速率常数(vmax)与一级动力学速率常数(K)具有显著的相关性(r=0.96, P0.05)。土壤总氮,砂粒和粉粒以及土壤容重对vmax影响最大。利用总氮和粉粒含量作为输入参数估算了vmax,准确度达66%。所构建的参数方程既充分挖掘了土壤基础数据潜能,又能快速地获取土壤反硝化动力学曲线,省时省力。     

硝态氮浓度对亚热带土壤反硝化潜力和产物组成的影响

在实验室条件下,采用密闭、淹水、充 N2 的严格厌氧培养方法研究了NO3--N?浓度对亚热带土壤反硝化潜力和产物组成的影响。研究表明,在NO3-?-N?浓度为 10 ~ 200 mg /kg 范围内,该土壤的反硝化势变化于 0.024 ~ 0.224 mg/(kg×h) 之间,随着NO3--N?浓度的增加而呈显著线性增加(R2 = 0.94,P<0.01)。N2O 始终是反硝化的主要产物,占反硝化产物的 56% ~ 92%;NO 是次要产物,占 6% ~ 40%。在野外原位状态下,土壤的还原条件难以达到供试实验室条件,由此估计,亚热带森林土壤反硝化的主要产物并非 N2,而是 N2O 和 NO,这可能是该类土壤虽反硝化作用弱,但 N2O 排放量大的主要原因。     

温度和氮添加对旱地红壤反硝化功能基因丰度的影响

研究旱地红壤反硝化微生物功能基因nirS、nirK、nosZ I和nosZ Ⅱ的丰度对温度和氮添加的响应，可为农田红壤养分管理和生态环境保护提供指导建议。本研究以长期常规氮磷钾施肥的旱地红壤为研究对象，设置0 mg N/kg、25 mg N/kg、50 mg N/kg三个氮添加处理，15 ℃、25 ℃、35 ℃三个温度处理，进行微宇宙培养实验。在培养的第7和30天破坏性采集土样，进行DNA提取，测定反硝化微生物功能基因丰度。结果表明：培养7天后，nirS、nirK、nosZ I和nosZ Ⅱ基因丰度都在25 ℃时最高。培养30天后，nirS、nirK、nosZ I和nosZ Ⅱ基因丰度在15 ℃时最高，且随着温度升高而下降。氮添加对反硝化微生物功能基因丰度无显著影响。三因素方差分析表明，温度、氮添加和培养时间的交互作用显著影响反硝化微生物功能基因丰度。综上，旱地农田反硝化功能基因丰度受氮添加影响较小，但受温度显著影响，其丰度可能会呈现出日变化和季节变化，在土壤采样和氧化亚氮动态监测时应特别注意。     

草甸沼泽土壤硝化-反硝化作用和有机碳矿化对氮输入的响应

通过室内培养实验.研究了草甸沼泽土壤N2O排放和反硝化损失对氮输入的响应特征,结果表明,在培养期(23 d)内N2O平均排放速率为0.32(NO).0.87(N1).17.69(N2),28.07(N3)μgN2O-N/(kg±·h),反硝化平均损失速率为0.25(NO),0.81(NI),22.29(N2),30.28(N3)μgN2O--N/(kg±·h).两者都随氮输入量增高而升高.其中,N3处理N2O平均排放速率和反硝化平均损失速率与对照差异显著(p<0.05),N1和N2与对照差异不显著.N2O排放总量占氮输入的比例为0.03%(N1),1.04%(N2).1.76%(N3),反硝化损失总量占氮输入的比例为0.04%(N1),1.29%(N2),1.93%(N3).均表现为随氮输入量的增大而增高.N1处理下有机碳矿化速率低于对照,而N2和N3有机碳矿化速率高于对照,说明低氮输入对有机碳矿化有一定抑制作用,.高氮输入促进有机碳矿化.     

区分土壤中硝化与反硝化对N2O产生贡献的方法

土壤是产生N2O的最主要来源之一.硝化和反硝化反应是产生N2O的主要机理,由于硝化和反硝化微生物同时存在于土壤中,因而硝化和反硝化作用能同时产生N2O.N2O的来源可通过使用选择性抑制剂,杀菌剂以及加入的标记底物确定.通过对生成N2O反应的每一步分析,主要从抑制反应发生的催化酶和细菌着手,总结了测量区分硝化、反硝化和DNRA反应对N2O产生的贡献方法.并对15N标记底物法,乙炔抑制法和环境因子抑制法作了详细介绍.     

区分土壤中硝化与反硝化对N2O产生贡献的方法

土壤是产生N2O的最主要来源之一。硝化和反硝化反应是产生N2O的主要机理,由于硝化和反硝化微生物同时存在于土壤中,因而硝化和反硝化作用能同时产生N2O。N2O的来源可通过使用选择性抑制剂,杀菌剂以及加入的标记底物确定。通过对生成N2O反应的每一步分析,主要从抑制反应发生的催化酶和细菌着手,总结了测量区分硝化、反硝化和DNRA反应对N2O产生的贡献方法。并对15N标记底物法,乙炔抑制法和环境因子抑制法作了详细介绍。     

土壤熏蒸剂对土壤硝化、反硝化作用的影响

采用化学分析和变性梯度凝胶电泳(DGGE)技术,以大田威百亩、棉隆、溴甲烷、硫酰氟熏蒸100 d土壤为研究对象,探究土壤熏蒸对土壤硝化活性、反硝化活性及amoA基因型硝化型细菌、nirS基因型反硝化细菌群落结构影响。研究表明,威百亩、棉隆、硫酰氟熏蒸剂处理下,土壤硝化活性与对照无显著差异;而溴甲烷处理的硝化活性比对照降低13.19%,差异显著(P0.05);熏蒸剂之间土壤硝化活性无显著差异。4种熏蒸剂之间以及与对照之间土壤反硝化活性无显著差异。4种熏蒸剂中溴甲烷处理土样amoA型硝化细菌多样性指数、均匀度显著低于对照土样和其他3种熏蒸剂处理土样;而丰富度指数无显著差异。威百亩、棉隆和硫酰氟熏蒸土样之间及与对照之间amoA型硝化细菌3种生态指数无明显差异。4种熏蒸剂处理土壤nirS型反硝化细菌多样性指数、均匀度与对照无显著差异(P0.05);熏蒸剂之间存在显著差异(P0.05)。研究表明,溴甲烷对土壤硝化活性的抑制是通过抑制amoA型硝化细菌的多样性而实现,其他3种熏蒸剂对土壤硝化活性无显著影响。4种熏蒸剂对土壤反硝化活性无显著影响。     

土壤反硝化对磺胺嘧啶及抗性基因消减的影响

农田土壤中抗生素及抗性基因的复合污染已给生态环境安全和人体健康带来了全新隐患。针对厌氧条件下,反硝化作用过程对土壤抗生素乃至抗性基因消减影响的研究一直相对较少。因而,本研究采集牛粪堆积池塘周边底层农田土壤作为目标污染土壤,重点研究反硝化作用过程对土壤磺胺嘧啶及抗性基因消减动态的影响。结果表明:相较于原始污染土壤处理(T1),添加了NO_3~–-N的处理(T2)可以显著强化土壤和水相中反硝化速率,提升N_2O的产气速率,促进土壤中磺胺嘧啶浓度和抗性基因丰度的快速降低;同时发现土壤反硝化基因(nir K、nir S和nos Z)与磺胺类抗性基因(sul Ⅰ和sul Ⅱ)呈显著负相关(P0.05),说明当NO_3~–-N底物越充足,土壤反硝化细菌活性往往被激活,其反硝化功能基因表达就越活跃,土壤反硝化作用过程就越强烈,从而反馈作用促进磺胺嘧啶抗生素的厌氧消减,进而有助于sul系列抗性基因丰度的显著衰减;同时通过高通量测序技术及对反硝化细菌的分离筛选后,发现变形菌门(Proteobacteria)赖氨酸芽胞杆菌属(Lysinibacillus)的细菌是土壤厌氧反应前后的主导优势菌群,对于强化反硝化过程和促进磺胺嘧啶及sul抗性基因的消减发挥了潜在的积极作用。本研究结果可为探明土壤中抗生素的厌氧消减过程和缓解抗性基因的扩散传播提供新颖的认知基础。     

添加生物质炭对红壤水稻土有机碳矿化和微生物生物量的影响

通过室内培育试验,研究了添加生物质炭对江西红壤水稻土有机碳矿化和微生物生物量碳、氮含量的影响。结果表明:红壤有机碳矿化速率在培育第2天达最大值后迅速降低,培养7天后下降缓慢并趋于平稳;添加生物质炭降低了土壤有机碳的矿化速率和累积矿化量,培养结束时,不加生物质炭的对照处理中有机碳的累积矿化量分别比添加0.5%和1.0%生物质炭的处理高10.0%和10.8%。此外,生物质炭的加入显著提高了土壤微生物生物量,添加0.5%生物质炭处理的土壤微生物生物量碳、氮含量分别比对照高111.5%～250.6%和11.6%～97.6%,添加1.0%生物质炭处理的土壤微生物生物量碳、氮含量分别比对照高58.9%～243.6%和55.9%～110.4%。相同处理中,干旱的水分条件下(40%田间持水量)微生物生物量要高于湿润的水分条件(70%田间持水量)。同时,添加0.5%和1.0%的生物质炭使土壤代谢熵分别降低2.4%和26.8%,微生物商减少了43.7%和31.7%。     

Effects of vegetation regime on denitrification potential in two tropical volcanic soils

Effects of vegetation and nutrient availability on potentail denitrification rates were studied in two volcanic, alluvial-terrace soils in lowland Costa Rica that differ greatly in weathering stage and thus in availability of P and base cations. Potential denitrification rates were significantly higher in plots where vegetation had been left undisturbed than in plots where all vegetation had been removed continuously, and were higher on the less fertile of the two soils. The potential denitrification rates were correlated strongly with respiration rates, levels of mineralizable N, microbial biomass, and moisture content, and moderately well with concentrations of extractable NH _inf4 ^sup+ , Kjeldahl N, and total C. In all plots, denitrification rates were stimulated by the removal of O₂ and by the addition of glucose but not by the addition of water or NO _inf3 ^sup- .This is Paper 2772 of the Forest Research Laboratory, Oregon State University     

Interrill erosion from disturbed and undisturbed samples in relation to topsoil aggregate stability in red soils from subtropical China

The assessment of soil erodibility to water erosion in the field is often expensive and time-consuming. This study was designed to reveal the effects of aggregate breakdown mechanisms on interrill erosion dynamics and develop an improved model for assessing interrill soil loss, which incorporated the soil aggregate stability tests as a substitute for the interrill erodibility parameter, from both disturbed and undisturbed samples for red soils in subtropical China. Six cultivated areas of sloping land with red soils were selected, and topsoil aggregate stability was analyzed using the Le Bissonnais method to determine the different disaggregation forces. Laboratory rainfall simulations were designed to distinguish the effects of slaking (at different wetting rates) and mechanical breakdown (with and without screening) on soil erosion characteristics. Field rainstorm simulations with medium and high rainfall intensities were conducted on runoff plots (2 m 1 m) with slope gradients varying from 10% to 20% for each soil type. A new instability index, Ka, which considers aggregate breakdown mechanisms in interrill erosion processes, was proposed based on the disturbed sample results. Ka showed a close relationship with erosion rates in both disturbed and undisturbed samples. Following from the results of undisturbed sample experiments, Ka was used as a substitute for the erodibility factor, and introduced into the WEPP model, establishing a new erosion predication formula for red soils which had a good correlation coefficient (R² = 0.89**). This research made a good attempt at estimating the interrill erosion rate on the basis of aggregate stability from simple laboratory determinations. These results extend the validity of soil aggregation characterization as an appropriate indicator of soil susceptibility to interrill erosion in red soils from subtropical China. The formula based on the instability index, Ka, has the potential to improve the methodology used for assessing interrill erosion rates.     

Effects of organic solvents on denitrification in soil

Summary Although organic solvents such as methanol and ethanol have been shown to act as energy sources for denitrifying microorganisms, no studies on the influence of organic solvents on denitrification in soil have been reported. Organic solvents have been used as an aid in the application of pesticides and other agricultural chemicals to soil, in studying the effects of these chemicals on denitrification in soil. During these applications, the soil is often aerated or heated to remove the solvent while leaving the chemical in the soil. The work reported here shows that treating soils with methanol, ethanol, or acetone had a very marked effect on their denitrifying ability, even when the soils were aerated thoroughly or heated at 50°C to remove these solvents. This indicates either that it is not possible to effect complete removal of organic solvents from soils by aeration or heating or that organic solvents promote denitrification by solubilizing a fraction of soil organic matter that is not available to denitrifying microorganisms before the addition of these solvents. Experiments using phenylmercuric acetate (a herbicide and nitrification inhibitor) showed that although this compound had a marked inhibitory effect on denitrification when added to soil in methanol, ethanol, or acetone, it had no inhibitory effect on denitrification when added to soil in water. The work reported shows that the use of an organic solvent in adding an agricultural chemical to soil can lead to erroneous conclusions in studies on the effects of the chemical on soil denitrification.     

Mineralization and denitrification in upland, nearly saturated and flooded subtropical soil I. Effect of nitrate and ammoniacal nitrogen

 The influence of fertilizer N applied through nitrate and ammoniacal sources on the availability of nitrate, supply of C, and gaseous N losses via denitrification (using acetylene inhibition technique) in a semiarid subtropical soil (Typic Ustochrepts) was investigated in a growth chamber simulating upland [60% water-filled pore space (WFPS)], nearly saturated (90% WFPS), and flooded (120% WFPS) conditions. The rate of denitrification was very low in the upland soil conditions, irrespective of fertilizer N treatments. Increasing water content to nearly saturated and flooded conditions resulted in four- to sixfold higher rates of denitrification within 2 days, suggesting that the denitrifying activity commences quickly. Results of this study reveal that (1) under restricted aeration, these soils could support high rates of denitrification (∼6 mg N kg^–1 day^–1) for short periods when nitrate is present; (2) application of fertilizer N as nitrate enhances N losses via denitrification (∼10 mg N kg^–1 day^–1) – however, the supply of available C determines the intensity and duration of denitrification; (3) when fertilizer N is applied as an ammoniacal form, nitrification proceeds slowly and nitrate availability limits denitrification in flooded soil; (4) the nearly saturated soil, being partially aerobic, supported greater nitrification of applied ammoniacal fertilizer N than flooded soil resulting in higher relative rates of denitrification; and (5) under aerobic soil conditions, 26 mg mineral N kg^–1 accumulated in control soil over a 16-day period, demonstrating a modest capacity of such semiarid subtropical soils, low in organic matter, to supply N to growing plants. Received: 7 June 1999     

Effects of the herbicide Topogard on soil respiration, nitrification, and denitrification in potato-cultivated soils differing in pH

We investigated the effects of Topogard 50 WP (3 kg ha^–1) on soil respiration, mineral N content, and number of denitrifying and total bacteria in four coarse-textured volcanic soils for 91 days. Topogard application decreased CO₂ evolution in acid soils (Tepedibi and Karaçakl) whereas soil respiration was initially increased in neutral and alkaline soils (Kaba and Balar). The herbicide application significantly stimulated ammonification in Kaba and Balar soils, while Tepedibi and Karaçakl soils showed significantly lower NH₄⁺-N contents than the control. The treatment inhibited the activity of nitrifying microorganisms and, thus it decreased the NO₃^–-N content in Tepedibi, Karaçakl, and Kaba soils, whereas the NO₃^–-N content was increased in Balar soil. The NO₂^–-N content of soils was not affected by the treatment. The activity of denitrifying bacteria was stimulated by the addition of herbicide in all soils, whereas the total number of bacteria was not influenced. It may be concluded that the effects of Topogard on the microbiological characteristics of coarse-textured soils are likely to be dependent on soil pH.     

Nitrification activity in submerged soils and its relation to denitrification loss

Summary Nitrification activity (formation of NO ₂ ^– + NO ₃ ^– per unit soil weight) was measured in the surface layer of 15 presubmerged soils incubated in petri dishes under flooded but aerobic conditions. soils with pH above 5 nitrified quickly, whereas soils with pH below this level did not nitrify or nitrified slowly. The pH values between 7 and 8.5 were optimal for nitrification. Organic-matter levels in the 15 soils of our study did not influence their nitrification activities. In a follow-up greenhouse pot study, after a period of 3 weeks, ¹⁵N-balance measurements showed that the loss of N through apparent denitrification did not follow the nitrification patterns of the soils observed in the petri dishes. Apparent denitrification accounted for 16.8% and 18.9% loss of ¹⁵N from a soil with insignificant nitrification activity and a soil with high nitrification activity, respectively. These results, thus, indicate a lack of correspondence between the nitrification activities of soil and the denitrification loss of N when the former was measured in the dark and the latter was estimated in the light. Soils that nitrified in the darkness of the incubator did not nitrify in the daylight in the greenhouse.     

Increase in denitrification capacity of soils due to addition of alkylbenzene sulfonates

 In semi-arid regions wastewater irrigation is a valuable resource for agricultural production. The contamination of irrigated soils with surfactants is one of the ecological risks related to irrigating with untreated wastewater. In this study, the effects of branched alkylbenzene sulfonates (ABS) on microbial biomass, respiratory activity, and denitrification capacity of soil samples (eutric vertisols) taken from an irrigation district in the Mexico City area were investigated in laboratory experiments. Increasing concentrations of ABS lead to a decrease in soil microbial biomass and an increase in soil respiratory activity as well as in the metabolic quotient (qCO₂) of the soils. Denitrification capacity was lowest without the addition of ABS and highest at a medium ABS concentration of 50 μg g^–1. Denitrification capacity seems to be highly sensitive to ABS addition at moderate concentrations. From the laboratory results, high rates of denitrification and N₂O evolution from fields irrigated with wastewater containing ABS are expected. Received: 11 November 1997     

Effects of amino-acid chemistry and soil properties on the behavior of free amino acids in acidic forest soils

Free amino acids (FAAs) in soil solution are increasingly recognized as a potentially important source of nitrogen (N) for plants, yet we are just beginning to understand the behavior of FAAs in soil. I investigated the effects of amino-acid chemistry and soil properties on mineralization, microbial assimilation and sorption of amino-acid N in soils from three ecosystems representing the two endpoints and mid point of a temperate forest fertility gradient ranging from low mineral N availability/high FAA oak forests to high mineral N availability/low FAA maple-basswood forests. Soils were amended with six ¹⁵N-labeled amino-acid substrates that ranged widely in chemical properties, including molecular weight, C:N ratio, average net charge, hydrophobicity, and polarity: Arginine (Arg), Glutamine (Gln), Glutamate (Glu), Serine (Ser), Glycine (Gly) and Leucine (Leu). Mineralization of amino-acid N accounted for 7-45% (18% avg.) of the added label and was most strongly affected by soil characteristics, with mineralization increasing with increasing soil fertility. Mineralization of amino-acid N was unrelated to amino-acid C:N ratio, rather, I observed greater N mineralization from polar FAAs compared to non-polar ones. Assimilation of amino-acid N into microbial biomass accounted for 6-48% (29% avg.) of the added label, and was poorly predicted by either intrinsic amino-acid properties or soil properties, but instead appeared to be explicable in terms of compound-specific demand by soil micoorganisms. Sorption of amino-acid N to soil solids accounted for 4-15% (7% avg.) of the added label and was largely controlled by charge characteristics of individual amino acids. The fact that both positively- and negatively-charged amino acids were more strongly sorbed than neutral ones suggests that cation and anion exchange sites are an important factor controlling sorption of FAAs in these acid forest soils. Together, the findings from this study suggest that there may be important differences in the behavior of free amino acids in sandy, acidic forest soils compared to generalizations drawn from finer-textured grassland soils, which, in turn, might affect the availability of some FAAs in soil solution.     

Comparison of field and laboratory measurement of denitrification and N2O production in the saturated zone of hydromorphic soils

We evaluated a new method to measure in situ denitrification under field conditions in a number of water-saturated subsoils that had a broad range of biogeochemical properties. A test solution containing ¹⁵NO₃⁻ and/or C₂H₂ was introduced to the subsoil and the subsequent production of dissolved denitrification products was measured to quantify denitrification activity. The method showed a clear production of denitrification products over time. Results were compared to laboratory-based measurements from the same soil incubated as anaerobic slurries with added ¹⁵NO₃⁻. Rates of denitrification with the in situ and the laboratory methods ranged from 1-2800 and 1-1700 μg N kg⁻¹ d⁻¹, respectively. Generally the methods gave good agreement and we consider both to be valid. However, there were some significant deviations, which we attribute to spatial heterogeneity and laboratory effects. Because the laboratory method is so much easier to perform, we suggest it should be the preferred method for large-scale studies of denitrification from the soil types we investigated. However, the two methods showed poor agreement in determining the proportion of N₂O in the total denitrification output. This was because this proportion is subject to delicate and complex control. We conclude that neither method was suitable for quantifying N₂O emission from the denitrification measurements.