红壤稻田不同生育期土壤氨氧化微生物群落结构

以福建省红壤稻田土壤为对象,通过提取土壤总DNA,利用特异引物进行PCR(聚合酶链反应)扩增和DGGE(变性梯度凝胶电泳)并结合DNA克隆测序,研究了水稻生长过程中稻田土壤氨氧化细菌和氨氧化古菌群落结构的变化。结果显示:稻田土壤具有丰富的氨氧化细菌和氨氧化古菌资源。水稻生长过程中土壤氨氧化细菌群落组成较为稳定,只表现出水稻生长前期(苗期、分蘖期)和中后期(孕穗期、成熟期)间存在一定差异。而土壤氨氧化古菌群落组成变化较大,在水稻生长的苗期、分蘖期、孕穗期和成熟期4个时期间均存在一定差异。在水稻生长过程中,土壤氨氧化细菌群落多样性指数无显著性变化,但氨氧化古菌群落多样性指数随水稻生长明显提高,孕穗期后才达到平稳。水稻生长前期土壤硝化势也具有显著上升趋势,孕穗期时达到最高,而后有所下降。土壤硝化势与氨氧化古菌群落多样性指数具有显著正相关性,与氨氧化细菌没有相关性。研究表明,氨氧化古菌对红壤稻田土壤硝化作用的影响程度较大,证实了氨氧化微生物尤其是氨氧化古菌在稻田土壤微生物组成及其生态系统功能中的重要性。     

种植水稻和长期施用无机肥对红壤氨氧化细菌多样性和硝化作用的影响

以中国科学院红壤生态试验站发育于第四纪红黏土的植稻红壤为研究对象,研究了长期种植水稻和施用无机肥对土壤β-变形杆菌纲中氨氧化细菌多样性和硝化作用的影响。原始红壤改种水稻13年后,氨氧化细菌16SrDNA的DGGE条带数量增加,条带谱与原始红壤的差异较大,相似性为61%,说明种植水稻后土壤氨氧化细菌群落结构发生了变化。PCR-DGGE方法研究结果也显示,长期施用无机氮肥的处理(NP、NPK和NK),DGGE带谱相似性较高,达到73%,硝化率和硝化势均高于未施用氮肥的处理。逐步回归分析显示硝化率和硝化势均随着土壤脲酶活性的提高而显著增加。推测尿素可提高土壤水解氮含量,使土壤脲酶活性提高,促进硝化细菌的生长,进而提高硝化率和硝化势。     

古水稻土与现代水稻土硝化活性的比较

根据最新的考古发现，中国种植水稻的历史可以追溯到公元前4000多年。据考证，位于长江三角洲的昆山市正仪镇绰墩山古水稻土遗址的地下42～57cm与100～116cm均为古水稻土层，历史耕作时间分别距今约3320a和6280a。硝化细菌在耕作土中的数量及其硝化强度被认为是土壤肥力的指标之一，在土壤氮素循环中起着重要作用，氨氧化细菌在硝化作用过程中将铵氧化为亚硝酸盐，实现亚硝化作用，是硝化过程中必不可少的步骤，同时也是其限速反应。本试验比较研究古水稻土与现代水稻土硝化活性的差别，观察氨氧化细菌沿土壤深度的分布规律，对揭示古水稻土在长期埋藏于土壤深层后的硝化功能演变具有积极的指示意义。     

不同品种水稻土壤氨氧化细菌和氨氧化古菌群落结构组成

本研究通过提取土壤总DNA,利用特异引物进行PCR扩增和变性梯度凝胶电泳(DGGE),研究了不同品种水稻对稻田土壤氨氧化细菌和氨氧化古菌群落结构组成的影响.结果显示:稻田土壤具有丰富的氨氧化细菌和氨氧化古菌,且氨氧化古菌种类更多;不同品种水稻氨氧化细菌群落结构组成差异较大,其中以"天A/Km71"、"闽优1027"和"Km62/1027"3个品种相似性较高,且明显不同于其余3个品种:而氨氧化古菌群落结构组成在不同土层间表现出较大差异,其中以"天A/Km71"和"Km62/1027"的表土与根际土氨氧化古菌群落组成差异最大.研究表明不同水稻品种及土壤层次对氨氧化微生物群落结构组成具有一定影响,证明氨氧化微生物尤其是氨氧化古菌在稻田土壤生态系统中占有重要地位.     

石灰性紫色土硝化作用及硝化微生物对不同氮源的响应

土壤中发生的硝化作用是对p H高度敏感的典型过程。本文采用室内恒温培养法,结合定量PCR和高通量测序,研究石灰性紫色土硝化作用以及氨氧化细菌(Ammonia-oxidizing bacteria,AOB)、氨氧化古菌(Ammonia-oxidizing archaea,AOA)、亚硝酸盐氧化细菌(Nitrite-oxidizing bacteria,NOB)的丰度与群落结构对不同氮源的响应。结果表明:不同氮源均刺激土壤硝化作用的发生,CO(NH2)2处理下的净硝化速率最大,约是CK处理的4.76倍,(NH_4)2SO4和NH_4Cl处理下的净硝化速率分别为N 3.88和3.34 mg kg-1d-1。相比于(NH_4)2SO4和CO(NH2)2处理,NH_4Cl处理降低了硝态氮的累积量,抑制了铵态氮的减少量。AOB amo A基因拷贝数在28 d培养过程中变化显著(p0.05),在(NH_4)2SO4和CO(NH2)2处理中呈先增长后降低趋势,在NH_4Cl处理中呈持续增长趋势;而AOA amo A基因拷贝数无显著变化(p0.05)。说明石灰性紫色土硝化作用的主要推动者是AOB,而不是AOA。在28 d培养过程中,亚硝酸盐氧化细菌占总微生物的比例高于氨氧化细菌和古菌,意味着石灰性紫色土中可能存在全程氨氧化微生物(Comammox)。高通量测序的结果表明:石灰性紫色土中AOB的优势种群为亚硝化螺菌Nitrosospira Cluster 3,AOA的优势种群是土壤古菌Group 1.1b,NOB的优势种群是硝化螺菌Nitrospira。     

长期定位施肥对中性紫色土硝化作用及氨氧化微生物的影响

为了研究长期不同施肥措施对中性紫色土氨氧化微生物及其硝化作用的影响,以国家紫色土肥力与肥料效益监测基地的中性紫色土为研究对象,进行土壤氨氧化细菌和氨氧化古菌amo A基因的Real-time PCR分析,比较长期不同定位施肥对土壤氨氧化潜势和硝化强度的影响,并分析不同施肥制度对功能微生物丰度与功能的作用。数据显示,土壤中氨氧化古菌amo A基因拷贝数(Log值6.21～7.14)远大于氨氧化细菌(Log值3.65～5.73),相对于对氨氧化细菌丰度的影响,施肥对土壤氨氧化古菌丰度影响较小。施用氮肥与磷肥都显著提高了土壤氨氧化细菌丰度,1.5NPK+M处理氨氧化细菌丰度最高(Log值5.73),有机无机肥配施可以显著提高土壤氨氧化微生物丰度;而含氯化肥的施用在一定程度上降低了土壤氨氧化细菌丰度与硝化细菌生长,与施用不含氯的肥料处理相比,含氯肥料处理的土壤氨氧化细菌丰度与硝化细菌数分别降低了3.74%和88.12%。研究表明,长期施肥能影响中性紫色土中氨氧化细菌的丰度,有机无机肥配施能够提高土壤的氨氧化潜力与土壤的硝化能力。     

两个水稻品种根际土壤细菌和氨氧化细菌的群落结构差异

通过根盒试验比较了籼稻汕优63和粳稻武运粳7号苗期不同采样期根际土和土体土壤的硝化强度以及氨氧化细菌数量的差异,并且采用16S rDNA PCR-DGGE(Denaturing gradient gel electrophoresis)指纹图谱技术比较分析了上述两种水稻苗期不同采样期根际和土体土壤中细菌及其氨氧化细菌的群落结构变化。结果表明,两个水稻品种根际土壤中硝化强度和氨氧化细菌的数量随着生育期的延长均表现出一定的正相关性,汕优63籼稻根部土壤中的细菌和氨氧化细菌的丰富度和群落变化特征随着水稻生育时期的延长较武运7号粳稻的变化更为多样,说明籼稻品种根系和根际硝化作用更强,在其根系附近会产生更多的硝态氮。这种差异性严重影响水稻植株对氮素的利用效率。     

不同pH和氧气条件下土壤古菌与海洋古菌的竞争适应机制

pH和氧气是古菌氨氧化活性的关键限制因子。然而,复杂土壤中不同古菌生态型（土壤古菌和海洋古菌）对pH和氧气的竞争适应规律尚未有相关报道。选择活性氨氧化古菌（ammonia-oxidizing archaea, AOA）为类海洋古菌Group1.1a-associated的酸性森林土（ pH5.40）和活性氨氧化古菌为土壤类古菌Group 1.1b的碱性水稻土（ pH8.02）,调节混合土壤pH和氧气浓度;设置稳定性同位素核酸探针实验,通过微宇宙室内培养,监测土壤硝化强度;利用实时荧光定量qPCR和454高通量测序研究pH和氧气对土壤氨氧化古菌和细菌的影响规律。结果表明：pH3.8下没有硝化作用发生,而pH6.0和7.6则发生了强烈硝化作用,且高氧环境下硝化作用强于低氧环境;加底物培养后,氨氧化古菌数量明显增加;活性氨氧化古菌几乎全为土壤类古菌Group 1.1b。研究表明：尽管氧气对硝化作用也有一定影响,但pH是影响硝化作用的主要因素;与类海洋古菌相比,土壤类古菌Group?1.1b更能适应高氧和低氧的碱性土壤环境,因此具有更强的竞争力。     

长期施肥与覆膜对土壤细菌、泉古菌和氨氧化微生物丰度的影响

施肥与覆膜等农田管理措施能够改变土壤的物理化学性质,这直接影响着驱动氨氧化过程的氨氧化微生物,而氨氧化过程是硝化作用的限速步骤。以沈阳农业大学棕壤长期施肥与覆膜试验站为平台,采用荧光定量PCR技术,研究了5种施肥制度下[不施肥(CK)、氮肥(N)、氮磷肥(NP)、有机肥(M)和有机无机配施(MNP)]土壤细菌、泉古菌和氨氧化微生物数量的变化。结果表明,不同施肥处理细菌、泉古菌、氨氧化细菌和氨氧化古菌的基因拷贝数平均值分别为0.52×109～4.20×109、2.14×108～9.69×108、0.21×107～6.89×107和0.26×107～74.70×107copies g-1干土。与CK相比,有机肥处理(M、MNP)能显著增加土壤细菌的丰度,化肥处理(N、NP)则相反;施肥尤其是化肥处理(N、NP)均能降低泉古菌和氨氧化古菌的丰度;有机肥处理(M、MNP)显著增加了氨氧化细菌的丰度。细菌、泉古菌、氨氧化细菌和氨氧化古菌丰度均与pH值存在显著正相关关系(P0.05),细菌和氨氧化细菌丰度则主要受全碳含量的影响,而细菌、泉古菌和氨氧化细菌丰度与铵态氮、硝态氮含量存在极显著负相关关系(P0.01)。研究结果可为进一步探讨农田生态系统中氨氧化微生物对不同管理措施的响应机制及其在氮素转化中的作用提供科学依据。     

南方稻田紫云英作冬绿肥的增产节肥效应与机制

本文对我国南方稻田紫云英作冬绿肥以及紫云英与稻草共同利用的增产和节肥效应及其植物营养学、土壤微生物学等相关作用机制进行综述。2008—2019年间开展的11个联合定位试验结果 (n = 930) 表明，冬种紫云英在不减肥或者减肥20%条件下增产效果显著，水稻产量增加幅度分别为6.53%和4.15%；在减施40%化肥时可保障水稻与常规施肥相比不减产。紫云英的增产和节肥效应随种植年限的增加而增强，5个联合定位试验连续7年的监测结果表明，冬种紫云英减施40%化肥条件下，紫云英种植第一年相对常规施肥增产0.87%，至种植第7年增幅为3.98%。紫云英与稻草联合利用是近些年稻区推行的重要技术模式，2016—2019年间开展的7个联合定位试验结果 (n = 342) 表明，紫云英–稻草联合还田相对于单独稻草还田，水稻产量增加了11.71%。本文分别从优化水稻产量构成、促进水稻养分吸收、提升土壤肥力3方面阐释了紫云英作冬绿肥的增产、节肥机制。稻田冬种紫云英可增加水稻有效穗数和每穗实粒数，优化了产量构成。与常规施肥相比，紫云英配施减量化肥的水稻吸氮量增加了6.4%～6.9%，氮肥利用率提高了6.6%～31.1%。稻田种植紫云英使土壤碳、氮库得到培育，土壤活性有机碳含量和碳转化酶活性提高，土壤速效养分、土壤物理性状明显改善。以有机质和全氮为例，相比常规施肥处理，种植翻压紫云英后减施20%和40%化肥处理的土壤有机质含量分别增加3.95%和4.15%，土壤全氮含量分别增加1.22%和1.74%。在紫云英调控土壤微生物及氮转化机制方面，冬种绿肥有利于土壤微生物的生长繁殖，增强与微生物活性密切相关的土壤酶活性，并通过改变土壤微生物的群落结构及功能微生物影响土壤养分循环。紫云英配施减量化肥可提高土壤固氮菌丰度，通过合理的调控措施可优化紫云英的生物固氮作用。硝化作用对冬绿肥的响应在不同类型土壤中有较大差异，碱性水稻土中冬种绿肥可通过抑制硝化作用降低氮素淋失风险，氨氧化微生物群落结构的变化是冬绿肥影响硝化作用的重要机制。通过近十多年来的研究，逐渐明晰了我国南方稻田冬种紫云英的增产、节肥效应及其机制，为今后稻田绿肥的效应与机制研究提供了重要借鉴和参考。     

Ammonia-oxidizing archaea are more important than ammonia-oxidizing bacteria in nitrification and NO3 −-N loss in acidic soil of sloped land

As part of a long-term sloped land use experiment established in 1995 at Taoyuan Agro-ecosystem Research Station (111°26′ E, 28°55′ N) in China, soil samples were collected from three land use types, including cropland (CL), natural forest, and tea plantation. Quantitative polymerase chain reaction and terminal restriction fragment length polymorphism were used to determine the abundance and community composition of amoA-containing bacteria (AOB) and archaea (AOA). The results indicate that land use type induced significant changes in soil potential nitrification rate and community composition, diversity, and abundance of AOB and AOA. Both AOB and AOA community compositions were generally similar between upper and lower slope positions (UP and LP), except within CL. The LP soils had significantly (p?<?0.05) higher diversity and abundance of both AOB and AOA than in the UP. Potential nitrification rate was significantly correlated (p?<?0.05) with diversity and abundance of AOA, but not with AOB. Among land use types, the NO₃ ^? and amoA-containing AOA runoff loss was greatest in CL. Nitrate-N runoff loss was significantly correlated (p?<?0.05) with the loss of AOA amoA copies in the runoff water. Furthermore, relationships between NO₃ ^?-N runoff loss and abundance of AOA but not of AOB at both slope positions were significantly correlated (p?<?0.05). These findings suggest that AOA are more important than AOB in nitrification and NO₃ ^?-N runoff loss in acidic soils across sloped land use types.     

紫云英与稻秸还田对稻田土壤硝化潜势的影响

  【目的】  种植利用绿肥和稻秸还田是水稻土培肥的重要措施。硝化作用是氮循环中的关键过程,我们研究了绿肥与稻秸还田对土壤硝化作用的影响,以明确紫云英–稻秸联合还田下的稻田硝化作用机制。  【方法】  水稻盆栽试验共设8个处理,分别为:对照(CK)、单独紫云英(MV)、单独稻秸(RS)、紫云英+稻秸(MV+RS)、单施氮肥(N)、紫云英+氮肥(MV+N)、稻秸+氮肥(RS+N)、紫云英+稻秸+氮肥(MV+RS+N)。研究了在不施氮和施氮条件下,紫云英、稻秸不同利用方式对土壤性状及硝化作用的影响,并通过特异性细菌抑制剂(卡那霉素和大观霉素)研究了氨氧化细菌(AOB)和氨氧化古菌(AOA)对硝化作用的相对贡献。  【结果】  MV+RS+N处理提高了土壤全氮和有机质含量,降低了碱性水稻土的pH。在早稻分蘖期,MV+RS+N处理显著提高了土壤中铵态氮和硝态氮含量。早稻移栽前,MV+RS 处理显著增加了土壤硝化潜势(NP), 而MV处理相较CK降低了NP。早稻分蘖期,氮肥添加显著提高了NP。早稻拔节期和晚稻收获期,RS和MV+RS处理均降低了NP。早稻移栽前,MV+RS处理同时降低了土壤恢复硝化强度(RNP),以及AOA和AOB在恢复硝化强度中的贡献(RNP_AOA和RNP_AOB),并降低了RNP_AOB在RNP中的占比。早稻分蘖期,CK和N处理,MV+N处理提高了RNP_AOB,而在早稻拔节期,MV+RS+N处理相比MV+RS处理提高了土壤RNP及RNP_AOB。早稻收获期,MV、RS及MV+RS处理均降低了稻田土壤RNP。在不同生育期中,早稻分蘖期的NP与硝态氮含量显著正相关,其他时期相关不显著。土壤NP与土壤 pH 和硝态氮含量呈显著正相关,与土壤微生物量碳 (SMBC) 和土壤微生物量氮 (SMBN) 含量呈显著负相关。RNP_AOA与土壤pH和铵态氮含量呈显著正相关。  【结论】  紫云英–稻秸联合还田降低了碱性水稻土pH,并在水稻生育早期显著提高而在生育后期显著降低了土壤硝化潜势。硝化潜势与土壤pH和硝态氮含量呈显著正相关。早稻分蘖期和早稻拔节期以RNP_AOB占主导,紫云英–稻秸联合利用较CK降低了RNP_AOB;早稻和晚稻收获期则以RNP_AOA占主导,紫云英–稻秸联合还田相较于单独还田提高了RNP_AOA。     

Long-term fertilization effects on active ammonia oxidizers in an acidic upland soil in China

The effects of long-term fertilization of acidic soils on ammonia-oxidizing archaea (AOA) and bacteria (AOB) communities and its ecological implications remain poorly understood. We chose an acidic upland soil site under long-term (27-year) fertilization to investigate ammonia oxidizer communities under four different regimes: mineral N fertilizer (N), mineral NPK fertilizer (NPK), organic manure (OM) and an unfertilized control (CK). Soil net nitrification rates were significantly higher in OM soils than in CK, N or NPK soils. Quantitative analysis of the distribution of amoA genes by DNA-based stable isotope probing revealed that AOA dominate in CK, N and NPK soils, while AOB dominate in OM soils. Denaturing gradient gel electrophoresis and clone library analyses of amoA genes revealed that Group 1.1a-associated AOA (also referred to as Nitrosotalea) were the most dominant active AOA population (>92%), while Nitrosospira Cluster 3 and Cluster 9 were predominant among active AOB communities. The functional diversity of active ammonia oxidizers in acidic soils is affected by long-term fertilization practices, and the responses of active ammonia oxidizers to mineral fertilizer and organic manure are clearly different. Our results provide strong evidence that AOA are more highly adapted to growth at low pH and low substrate availability than AOB, and they suggest that the niche differentiation and metabolic diversity of ammonia oxidizers in acidic soils are more complex than previously thought.     

石灰和双氰胺对红壤酸化和硝化作用的影响及其机制

施用石灰是改良酸性土壤的重要措施,但其对土壤硝化作用的增强不仅加速土壤酸化,也增加硝态氮流失风险.传统的硝化抑制剂双氰胺(Dicyandiamide,DCD)能否在石灰改变pH的条件下始终有效抑制硝化是当前红壤区生产中亟需解决的问题.采用短期土壤培养试验,探讨了不同用量石灰与DCD配合施用对土壤酸化和硝化作用的影响及其...     

pH regulates key players of nitrification in paddy soils

Increasing lines of evidence have suggested the functional importance of ammonia-oxidizing archaea (AOA) rather than bacteria (AOB) for nitrification in upland soils with low pH. However, it remains unclear whether niche specialization of AOA and AOB occurs in rice paddy wetlands constrained by oxygen availability. Using DNA-based stable isotope probing, we conclude that AOA dominated nitrification activity in acidic paddy soils (pH 5.6) while AOB dominated in alkaline soils (pH 8.2). Nitrification activity was stimulated by urea fertilization and accompanied by a significant increase of AOA in acid soils and AOB in alkaline soils. DNA-based stable isotope probing indicated significant assimilation of ¹³CO₂ for AOA only in acidic paddy soil, while AOB was the solely responsible for ammonia oxidation in the alkaline paddy soil. Phylogenetic analysis further indicated that AOA members within the soil group 1.1b lineage dominated nitrification in acid soils. Ammonia oxidation in the alkaline soil was catalyzed by Nitrosospira cluster 3-like AOB, suggesting that the physiological diversity of AOA is more complicated than previously thought, and soil pH plays important roles in shaping the community structures of ammonia oxidizers in paddy field.     

Responses of ammonia-oxidizing bacteria and archaea to nitrogen fertilization and precipitation increment in a typical temperate steppe in Inner Mongolia

As the first and rate-limiting step of nitrification, ammonia oxidation can be realized either by ammonia-oxidizing bacteria (AOB) or archaea (AOA). However, the key factors driving the abundance, community structure and activity of ammonia oxidizers are still unclear, and the relative importance of AOA and AOB in ammonia oxidation is unresolved. In the present study, we examined the effects of long-term (6 years) nitrogen (N) addition and simulated precipitation increment on the abundance and community composition of AOA and AOB based on a field trial in a typical temperate steppe of northern China. We used combined approaches of quantitative PCR, terminal-restriction fragment length polymorphism (T-RFLP) and clone library analyses of amoA genes. The study objective was to determine (1) AOA and AOB diversity and activity in response to N addition and increased precipitation and (2) the relative contributions of AOA and AOB to soil ammonia oxidation in the typical temperate steppe. The results showed that the potential nitrification rate (PNR) increased with N addition, but decreased with increased precipitation. Both N addition and increased precipitation significantly increased AOB but not AOA abundance, and a significant correlation was only observed between PNR and AOB amoA gene copies. The T-RFLP analysis showed that both N and precipitation were key factors in shaping the composition of AOB, while AOA were only marginally influenced. Phylogenetic analysis indicated that all AOA clones fell within the soil and sediment lineage while all AOB clones fell within the Nitrosospira. The study suggested that AOA and AOB had distinct physiological characteristics and ecological niches. AOB were shown to be more sensitive to N and precipitation than AOA, and the ammonia oxidation process was therefore supposed to be mainly driven by AOB in this temperate steppe.     

Ammonia oxidizer abundance in paddy soil profile with different fertilizer regimes

Studies about ammonia-oxidizing bacteria (AOB) and archaea (AOA) are often focused on topsoil, but little is known about their activity and distribution in subsoil. A long-term fertilizer experiment was conducted to assess the effects of different fertilizer treatments on AOB and AOA in vertical soil profiles of paddy soil plots that received no nitrogen fertilizer control (CK), NPK chemical fertilizers (CF), organic–inorganic mixed fertilizer (OIMF) and organic fertilizer (OF). Soil properties, potential nitrification rate (PNR) and amoA gene abundance of AOB and AOA were measured and analyzed by two-way ANOVA and correlation analysis. Quantitative PCR analysis of amoA genes showed that AOA were more abundant than AOB in all the soil samples. AOB declined sharply with soil depth. Compared with CK and OF treatments, CF and OIMF treatments had higher abundance of AOB throughout the soil profiles. However, AOA tend less responsive to soil depth and fertilizers compared to AOB. This caused the AOA/AOB ratios in subsoil higher than in topsoil, and in CK and OF higher than in CF and OIMF treatments. These results suggest that AOA are more abundant and can be better adapted to nutrient-poor subsoils than AOB, and autotrophic nitrification could likely be determined by a complex suite of environmental factors in vertical profiles of the paddy soil tested.     

亚热带松林中强酸性土壤自养和异养硝化作用的研究

The occurrence of nitrification in some acidic forest soils is still a subject of debate. Identification of main nitrification pathways in acidic forest soils is still largely unknown. Acidic yellow soil (Oxisol) samples were selected to test whether nitrification can occur or not in acidic subtropical pine forest ecosystems. Relative contributions of autotrophs and heterotrophs to nitrification were studied by adding selective nitrification inhibitor nitrapyrin. Soil NH₄⁺-N concentrations decreased, but NO₃^--N concentrations increased significantly for the no-nitrapyrin control during the first week of incubation, indicating that nitrification did occur in the acidic subtropical soil. The calculated net nitrification rate was 0.49 mg N kg^-1 d^-1 for the no-nitrapyrin control during the first week of incubation. Nitrapyrin amendment resulted in a significant reduction of NO₃^--N concentration. Autotrophic nitrification rate averaged 0.28 mg N kg^-1 d^-1 and the heterotrophic nitrification rate was 0.21 mg N kg^-1 d^-1 in the first week. Ammonia-oxidizing bacteria (AOB) abundance increased slightly during incubation, but nitrapyrin amendment significantly decreased AOB amoA gene copy numbers by about 80%. However, the ammonia-oxidizing archaea (AOA) abundance showed significant increases only in the last 2 weeks of incubation and it was also decreased by nitrapyrin amendment. Our results indicated that nitrification did occur in the present acidic subtropical pine forest soil, and autotrophic nitrification was the main nitrification pathway. Both AOA and AOB were the active biotic agents responsible for autotrophic nitrification in the acidic subtropical pine forest soil.     

基于宏基因组学的酸性森林土壤氨氧化微生物群落特征研究

全球30%以上陆地面积是酸性土壤(pH5.5),而酸性土壤中氨氧化微生物群落特征研究是破译其硝化过程微生物学机理的基础。尤其随着完全硝化微生物(Complete ammonia oxidizer,comammox)的发现,亟需重新认知酸性土壤中氨氧化微生物类群。以酸性马尾松林为研究对象,综合利用荧光定量PCR(qPCR)、凝胶电泳半定量和宏基因组测序等技术研究土壤中氨氧化古菌(Ammonia-oxidizing archaea,AOA)、氨氧化细菌(Ammonia-oxidizing bacteria,AOB)和Comammox的相对丰度以及群落组成特征。研究发现AOA和AOB amoA基因丰度分别为2.61×106 copies·g~(-1)和1.45×106copies·g~(-1);而comammoxamoA基因qPCR结果存在显著的非特异性扩增,导致其丰度被高估,而经凝胶电泳半定量矫正后,约为(1.38～1.47)×106copies·g~(-1),该结果和土壤宏基因测序揭示的comammox相对丰度基本吻合。此外,宏基因组分析发现经典嗜酸group1.1a-associated仅占AOA总类群的12%,而group1.1b则占88%,尽管目前仍未有嗜酸group 1.1b AOA纯菌株的报道。AOB主要类群为Nitrosospira(约64%),而Nitrosomonas约占36%。Comammox主要类群为clade B(约64%),而clade A仅占36%且均隶属于clade A.1亚枝,这暗示clade B与已报道的嗜中性comammox clade A纯菌株有极大的生理代谢差异。总之,本研究提供了综合利用qPCR、半定量和宏基因组分析土壤氨氧化微生物群落的策略,并建议优化comammox的qPCR引物,同时本研究系统分析了酸性马尾松林土壤中氨氧化微生物的相对丰度和群落组成特征。     

Biosurfactant in Membrane Separation of Atrazine from Water

This study examines the effects of land use change on nitrate concentration and the abundances of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and narG-containing denitrifiers in shallow groundwater. The results reveal a general increase of nitrate in shallow groundwater following the change of land use from paddy fields to vegetable patches. Furthermore, a significant relationship between NO₃ ^?-N concentrations was observed both in groundwater and in soil at soil depths of 0–20, 20–40, 40–60, 60–80, and 80–100 cm. With regard to gene abundance in groundwater, the AOB amoA gene was most abundant and the AOA amoA gene copy numbers were lowest from the field with long-term paddy cultivation compared with the field under vegetable cultivation. The narG gene copy numbers were higher from the field under short-term vegetable cultivation compared with fields under long-term vegetable cultivation. The NO₃ ^?-N concentrations in groundwater correlated positively with AOA amoA gene copy numbers, negatively with the AOB amoA gene, but with no significant relationship with the narG gene. In conclusion, land use change from paddy fields to vegetable patches increases nitrate in groundwater, which is correlated significantly with nitrate in soil and the abundance of the amoA gene, but is not related to the narG gene in groundwater. This study also suggests that the removal of groundwater nitrate pollution is not feasible through biological denitrification without additional denitrifiers and that it might even become more aggravated because of the AOA.