利用上流式双层厌氧滤器启动厌氧氨氧化研究

厌氧氨氧化是一种高效的脱氮处理工艺,但其启动和运行过程困难,高效反应器是解决此问题的有效手段。本文利用改进的上流式双层厌氧滤器开展厌氧氨氧化启动反应的试验研究。在反应器填料上分别接种反硝化污泥、厌氧污泥、混合污泥,通过模拟废水提供自养反硝化条件,并逐步提高基质浓度和水力负荷,促使菌群向厌氧氨氧化反应转变。试验发现,反硝化污泥、厌氧污泥、混合污泥均可启动厌氧氨氧化反应,启动时间分别为42、54 d和45 d。以反硝化污泥为接种物的启动效果最好,启动时间较短且废水氮素去除率高,总氮去除率最高达到82.2%。双层填料的反应器有效提高了厌氧氨氧化的稳定性,该反应器中厌氧氨氧化菌对氨氮、亚硝氮的适宜浓度负荷为270、360 mg·L~(-1),废水中COD浓度不宜超过150 mg·L~(-1),系统中存在厌氧氨氧化和甲烷化共存的效应。     

中试膜生物反应器中猪场沼液部分亚硝化快速启动试验

膜生物反应器（Membrane Bioreactor,MBR）具有出水水质好、污泥龄（Solid Retention Time,SRT）长等优势,该研究在中试MBR中开展猪场沼液部分亚硝化工艺研究,为部分亚硝化-厌氧氨氧化工艺在实际工程上的示范应用提供技术参数。结果表明,常温状态下控制反应器内溶解氧（Dissolved Oxygen,DO）在0.2～0.5 mg/L,pH值8.0±2.0条件下,成功启动并稳定运行部分亚硝化工艺,亚硝酸盐氮积累率保持稳定,最高达到87.95%,出水的亚硝酸盐氮和氨氮浓度比值稳定在1.1∶1,达到进行厌氧氨氧化反应的基质需求。部分亚硝化过程中,氨氧化细菌活性明显的提高且维持在（0.4±0.02）g/(g·d)。反应器内微生物多样性增加,菌群结构发生明显变化,优势菌门由Chloroflexi（绿弯菌门）、Firmicutes（厚壁菌门）变为Proteobacteria（变形菌门）,Nitrosomonas（亚硝化单胞菌）成为反应器内的优势菌属。     

鸡粪好氧发酵氮转化与相应细菌数量变化规律的研究

为明确鸡粪好氧发酵过程各类氮转化细菌变化及其与氮素转化间的关系,本研究全程测定了氨化、异养亚硝化、异养硝化和好氧反硝化4类细菌数量、有机态氮、氨态氮、硝态氮等含量变化。结果证明,该过程各类氮转化细菌以中温菌居多,最适生长温度35℃。其中,升温段35℃之后,菌数随温度上升而下降;降温段35℃之前,菌数随温度下降而上升。研究的各类氮转化细菌中,氨化细菌最耐热,是高温期发挥作用的主要类群。发酵全程各类氮转化菌数与相应氮素转化量的关系为:升温段,氨化细菌、亚硝化和硝化菌数增加时,氨态氮和硝态氮的增幅较快;此3类菌数降低时,氨态氮和硝态氮的增幅较缓;降温段,氨化细菌数量与氨态氮含量变化之间无相关表现;发酵全程硝态氮含量变化与亚硝化、硝化细菌数量变化呈正偏相关,与反硝化细菌数量变化呈负偏相关。     

海绵铁缓解污水厌氧氨氧化反应器中硝酸盐积累的效果

该文旨在通过向厌氧氨氧化反应器中投加海绵铁来减轻厌氧SBR(sequencingbatchreactoractivatedsludge process)反应器中的硝酸盐积累,试验研究了海绵铁与硝酸盐和亚硝酸盐在静态条件下的反应。在静态条件下,部分硝酸盐和亚硝酸盐被海绵铁还原成了氨。对比动态试验表明投加海绵铁可以将SBR出水硝酸盐质量浓度控制在25～30 mg/L左右。相同条件下不投加海绵铁出水硝酸盐质量浓度不断累积,直至超过55 mg/L。这可能是由于铁将硝酸盐还原为亚硝酸盐并与厌氧氨氧化进行了耦合。采用高通量测序发现投加海绵铁的反应器中厌氧氨氧化菌在微生物群落中所占的比例(22.55%)约为不投加反应器(8.85%)的3倍,表明投加海绵铁有利于反应器中厌氧氨氧化(ANAMMOX)菌的生长和厌氧氨氧化反应器的启动。     

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。     

转基因水稻秸秆还田对土壤硝化反硝化微生物群落的影响

转基因作物可能通过根系分泌物和植株残体组成的改变及外源基因的转移释放令土壤微生物群落产生变化,影响土壤微生物的生态功能。氨氧化细菌和反硝化细菌是驱动土壤硝化和反硝化过程的关键微生物,其群落结构的变化直接关系土壤氮素的转化与利用。本研究利用荧光定量PCR和PCR-DGGE技术分析了转cry1Ac/cpti双价抗虫基因水稻‘Kf8’秸秆还田降解过程中,土壤氨氧化细菌和反硝化细菌群落丰度与组成的变化,探讨转基因水稻是否存在影响稻田土壤氮素转化与N2O排放的可能。结果显示:无论是氨氧化细菌amo A基因还是反硝化细菌nirS基因,其丰度在转基因水稻‘Kf8’与非转基因水稻‘Mh86’的秸秆还田土壤中都没有显著差异;转基因水稻‘Kf8’和非转基因水稻‘Mh86’秸秆还田降解过程中0~10 cm土层中的amo A基因丰度均显著高于10~20 cm及20~30 cm土层(P0.05);各深度土层中的nirS基因丰度均存在随秸秆还田时间延长而增加的趋势。水稻秸秆还田降解过程中,转基因水稻‘Kf8’的土壤氨氧化细菌和反硝化细菌的群落多样性指数及组成,均与非转基因水稻‘Mh86’没有显著差异。相关分析结果表明土壤氨氧化细菌和反硝化细菌群落组成均与水稻秸秆还田时间存在显著相关性(P=0.002),反硝化细菌群落组成还与土层深度显著相关(P=0.024)。本研究表明转cry1Ac/cpti抗虫基因水稻秸秆还田对稻田土壤硝化和反硝化关键微生物群落不会产生明显影响。就土壤微生物群落而言,转cry1Ac/cpti抗虫基因水稻秸秆还田不存在影响土壤氮素转化与N2O排放的可能。     

‘寒富’苹果园生长季土壤氨氧化细菌群落结构与多样性

采用PCR-DGGE技术,对‘寒富’苹果园生长季内土壤氨氧化细菌群落结构、多样性及其与土壤理化因子的相关性进行探讨。结果表明,不同时期土壤硝化强度、氨氧化细菌数量、种群组成及多样性表现出明显差异。其中,11月份土壤硝化强度最高,9月份最低,而氨氧化细菌数量则表现为11月份最低,7月最高。多样性特征分析表明,土壤氨氧化细菌多样性和均匀度指数均表现为11月份最高,9月份最低;而丰富度指数则表现为5月份与7月份最高,11月份最低;优势度指数则为9月份最高,5月份最低。系统发育分析结果表明,苹果园土壤氨氧化细菌均隶属于β-变形菌纲(β-Proteobacteria),多为不可培养菌株,其中亚硝化螺旋菌属(Nitrosospira)为土壤优势菌属。氨氧化细菌与土壤理化性质相关性分析发现,土壤速效磷、速效钾含量与硝化强度、氨氧化细菌多样性指数、均匀度和优势度指数呈显著相关,而与土壤氨氧化细菌数量无明显相关性。说明环境因子时间分布的不均匀性是不同时期土壤氨氧化细菌群落结构组成差异的重要原因。     

红壤稻田不同生育期土壤氨氧化微生物群落结构和硝化势的变化

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。     

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。     

稻田土壤厌氧氨氧化菌群落结构对长期不同施肥的响应

研究长期不同施肥稻田土壤厌氧氨氧化微生物丰度和群落结构组成,深入认识稻田厌氧氨氧化菌对不同施肥的响应机理,可为合理施肥和理解湿地生态系统厌氧氨氧化过程提供科学依据。设置不施肥(CK)、单施无机肥(NPK)、无机肥配施牛粪(NPKM)、无机肥加秸秆还田(NPKS)四个处理,采用荧光定量PCR和高通量测序对不同施肥模式下水稻土厌氧氨氧化细菌丰度和群落结构进行分析。结果发现,不同处理之间厌氧氨氧化细菌丰度具有显著差异(p0.05),表现为NPKMNPKSNPKCK,且与有机质、全氮和铵态氮含量具有显著相关性(p0.05)。高通量测序结果表明,不同施肥处理主要的厌氧氨氧化菌为Candidatus Brocadia、Candidatus Anammoxoglobus和Candidatus Scalindua,其中优势种群为Candidatus Brocadia。菌群的多样性分析表明,CK和NPKS处理的厌氧氨氧化菌群落结构多样性香农指数(Shannon index)、辛普森指数(Simpson index)和丰富度指数(Chao 1 index)显著高于NPKM和NPK处理(p0.05)。上述结果表明,长期施肥改变了厌氧氨氧化菌的数量和群落结构。有机无机肥配施更有利于提高厌氧氨氧化菌丰度。然而,不同施肥措施对厌氧氨氧化菌的多样性影响不同,无机肥加秸秆还田提高了厌氧氨氧化菌多样性,但单施无机肥和无机肥配牛粪降低了厌氧氨氧化菌多样性。厌氧氨氧化菌的数量和群落结构对不同施肥的响应不同。     

Relationship between phosphatase active bacteria and phosphatase activities in forest soils

Acid phosphatase and alkaline phosphatase active colonies of bacteria, isolated from forest soils, were stained. The activity of acid and alkaline phosphatase and other soil properties (the number of aerobic bacteria, basal respiration, the level of ammonification, the number of bacteria active in ammonification, the level of nitrification, the number of micromycetes) were compared with the number of bacteria belonging to the genus Micrococcus. Soil samples were taken from the following horizons: F-AO1 (fermentative), H-AO2 (humic), and A (basic). The soil samples were taken from beneath forest stands in the Izera Mountains (North Bohemia, Czech Republic). The number of acid phosphatase active colonies correlated positively with the number of alkaline phosphatase active colonies in the F-AO1 horizon, and there was a high, positive correlation between the former and the level of ammonification in the H-AO2 horizon. The number of alkaline phosphatase active colonies correlated positively with organic carbon, the number of ammonification bacteria, and the number of micromycetes in the H-AO2 horizon. The A horizon was almost biologically inactive. Neither acid nor alkaline phosphatase activities correlated positively with the number of phosphatase active colonies of bacteria. Received: 6 December 1996     

Anammox bacterial abundance and biodiversity in greenhouse vegetable soil are influenced by high nitrate content

The anaerobic ammonium oxidizing(anammox) process has been found to play an important role in terrestrial ecosystems in recent years. However,the diversity and abundance of anammox bacteria in nitrogen(N)-rich agricultural soils under high fertilizer greenhouse conditions are still unclear. Two greenhouse fields with different N fertilizer input levels were chosen, and their soil profiles were studied with molecular technologies, including quantitative polymerase chain reaction assay, a clone library, and phylogenetic analysis based on hzsB(encoding anammox hydrazine synthase β-subunit) gene. Molecular analyses suggested that anammox bacteria were at their highest density at 10–20 cm soil depth, and that the anammox bacterial abundance was significantly lower at high N than at low N. Candidatus Brocadia was the sole anammox bacterial genus throughout the soil depth profiles. The highest diversity of anammox bacteria was found at 30–40 cm soil depth, and different phylotypic clusters of Candidatus Brocadia were associated with specific soil environmental factors, such as nitrates, soil depth, and total N. Correlation analyses and redundancy analyses confirmed that high nitrate content associated with high N fertilizer input had a significant negative influence on the abundance and biodiversity of anammox bacteria. These results imply that excessive use of N fertilizer would affect arid land soil N loss to the atmosphere by the anammox pathway.     

Nitrogen removal processes coupled with nitrification in coastal sediments off the north East China Sea

Purpose

Denitrification and anaerobic ammonia oxidation (anammox) play key roles in nitrogen (N) loss, and nitrification can supply substrates of NO₂^– and NO₃^– for denitrification and anammox. Coupled nitrification-denitrification/anammox processes are thus crucial for N removal in coastal ecosystems. This study aims to examine the spatial-temporal variations of ambient, coupled, and uncoupled N removal rates in the coastal sediments off the north East China Sea, and to clarify the controlling factors and microbial mechanisms of coupled nitrification-denitrification/anammox.

Materials and methods

The rates of ambient, coupled, and uncoupled denitrification and anammox in coastal sediments off the north East China Sea were quantified using the continuous-flow experiments combined with ¹⁵N isotope pairing technique. The quantitative polymerase chain reaction method was used to determine the abundances of nitrifiers, denitrifiers, and anammox bacteria, with the functional genes of amoA and nirS, and 16S rRNA gene, respectively.

Results and discussion

Ambient denitrification rates varied between 0.43 and 7.39 μmol N m^?2 h^?1, and ambient anammox rates ranged from 0.05 to 0.62 μmol N m^?2 h^?1. Coupled nitrification-denitrification was the dominant N removal pathway. The rates and coupling of N removal processes with nitrification varied distinctly between nearshore and offshore sites, which were driven by diverse environmental factors. Redundancy analysis suggested that nitrate and sulfide were important factors controlling the coupled and uncoupled N removal rates, and nitrate was proved to be the key factor influencing the ratio between coupled and uncoupled N removal via an integrated analysis. Abundances of ammonia oxidizing bacteria (AOB) correlated significantly with coupled denitrification rates and abundances of denitrifiers, suggesting the importance of AOB in coupled nitrification-denitrification.

Conclusions

This study investigated the ambient, coupled, and uncoupled denitrification and anammox rates in coastal sediments off the north East China Sea. Nitrate was proved to be the critical factor influencing the ratio between coupled and uncoupled N removal, and AOB may play important role in coupled nitrification-denitrification. These results emphasized that nitrification is crucial for N removal with important implications on N loss in coastal ecosystems.

     

稻田厌氧氨氧化菌群落结构对氮肥的响应

为探明稻田厌氧氨氧化菌多样性及其对氮肥用量的响应状况,利用厌氧氨氧化菌16S rRNA基因特异引物对定位试验稻田土壤DNA进行PCR-DGGE(聚合酶链反应变性梯度凝胶电泳)并结合DNA克隆测序,研究了氮肥供应量对厌氧氨氧化菌群落结构的影响。DGGE图谱及依据其条带位置和亮度数值计算的多样性指数均显示:高氮处理[N3:225 kg(N).hm 2]的厌氧氨氧化菌群落结构多样性在表层或根层土壤中均显著(P<0.05)高于中、低氮[N2:150 kg(N).hm 2;N1:75 kg(N).hm 2]处理和不施肥对照(CK);同时,高氮处理下表层土壤厌氧氨氧化菌群落多样性指数显著高于根层土壤(P<0.05)。冗余分析(RDA)结果表明,表层土壤中厌氧氨氧化菌群落结构组成与不同氮肥水平处理存在显著相关性(P=0.006)。此外,本试验获得厌氧氨氧化菌DGGE条带DNA序列18条,登录GenBank并获得登录号。研究表明稻田厌氧氨氧化菌群落结构对高氮水平具有较强的响应,尤其是在表层土壤中。     

不同施肥处理稻田系统磷素输移特征研究

磷是水体富营养化限制性元素,近年来由于磷肥的过量施用,农田迁移的磷素已成为水体磷素的主要来源。本研究通过野外测坑定位试验,研究有机肥处理(OT)、混施肥处理(MT)和化肥处理(CT)3种施肥处理下,稻田中磷素的迁移流失特征及这3种处理对水稻产量和磷素利用率的影响,以探求稻田系统的最佳施磷方式。结果表明,CT、MT和OT 3种施肥方式的磷径流流失负荷分别为0.56 kg(P)·hm-2、1.13 kg(P)·hm-2和4.20 kg(P)·hm-2,渗漏流失负荷分别为0.42 kg(P)·hm-2、0.44 kg(P)·hm-2和0.45 kg(P)·hm-2;磷的径流流失占流失总量的56.86%~90.38%,是水稻田磷素流失的主要途径。磷的径流流失主要受施肥和降雨的影响,50%左右磷的流失发生在第1次径流过程;磷素渗漏流失特征不受施磷处理的影响,80%以上的流失发生在施肥后的前30 d。在磷素流失形态上,坑面水、渗漏水和径流水中磷素的主要形态均为可溶性磷;在土壤方面,MT处理和OT处理能保证土壤磷营养,CT处理的土壤有效磷和有机质含量则显著下降。3种施肥处理的水稻产量显著高于空白对照,且MT最高,为6 728.84 kg·hm-2;磷肥利用率CT和MT处理显著高于OT,CT和MT间差异不显著。综合比较,混施肥处理在磷素流失、土壤养分利用和水稻产量等方面更符合我国生态农业发展的要求。     

Response of ammonia oxidizing archaea and bacteria to changing water filled pore space

This study examined the effect of water filled pore space (WFPS) on gross N fluxes and community structure and abundance of ammonia oxidizing archaea and bacteria in a semi-arid soil. Different WFPS altered the community structure of both AOA and AOB. Ammonia oxidizer communities (for both archaea and bacteria) from ‘wet’ soils (95, 85 and 75% WFPS) and ‘dry’ soils (25, 45 and 55% WFPS) were distinctly different from one another. Additionally there was a significant relationship between community structure and gross rates of nitrification. There was also a significant relationship between WFPS and bacterial amoA abundance but not archaeal amoA abundance suggesting that bacterial ammonia oxidizers are more responsive to changes in soil water availability. These results are in agreement with other studies suggesting that both groups of ammonia oxidizers have distinct physiological characteristics and ecological niches with consequences for nitrification in response to WFPS. Overall findings from this study indicate that nitrification, both in terms of process rates and populations responsible for nitrification activity, is highly responsive to soil water availability.     

Frontiers in the microbial processes of ammonia oxidation in soils and sediments

Purpose

Two recent discoveries in nitrogen (N) cycling processes, i.e., archaeal ammonia oxidizers and anaerobic ammonia (ammonium) oxidation (anammox), have triggered great interest in studying microbial ammonia oxidation processes. The purpose of this review is to highlight recent progress in ammonia oxidation processes in soils and sediments and to propose future research activities in this topic.

Results and discussion

Aerobic ammonia oxidation and anammox processes are linked through the production and consumption of nitrite, respectively, thereby removing the reactive N (NH₄ ⁺, NO₂ ^?, NO₃ ^?) from soil and sediment ecosystems. Ammonia-oxidizing microorganisms are widely distributed in soils and sediments, and increasing evidence suggests that ammonia-oxidizing archaea and bacteria are functionally dominant in the ammonia oxidation of acid soils and other soils, respectively. The widespread occurrence and great variation in the abundance of anammox bacteria indicate their heterogeneous distribution and niche differentiation. Therefore, the worldwide distribution of both microbial groups in nature has stimulated researchers to investigate the physiology and metabolism of related groups, as well as appraising their contribution to N cycling.

Conclusions

We summarized the current progress and provided future perspectives in the microbiology of aerobic and anaerobic ammonia oxidation in soils and sediments. With increasing concern and interest in soil and sediment ammonia oxidation processes, studies in the microbial mechanisms underlying nitrification and anammox, as well as their interactions, are essential for understanding their contribution to the loss of N either through nitrate leaching or N-related gas emissions.     

Autotrophic nitrification in a fertilized acid heath soil

The nature of nitrification in fertilized, acid heath soils was studied. Autotrophic ammoniumand nitrite-oxidizing bacteria were enumerated in non-fertilized and fertilized heath soils. Ammoniumoxidizing bacteria were not detected in the non-fertilized soils, whereas nitrite-oxidizing bacteria were only found in the organic layer. Enrichment of acid heath soils with NPK fertilizer increased the number of autotrophic ammonium- and nitrite-oxidizing bacteria in the organic (F + H) layer as well as in the upper part of the mineral (Ah) layer, although the pH of the soil hardly changed with fertilization. In soil suspensions of the upper mineral layer of fertilized heath soils, nitrification was shown to be autotrophic as nitrification was completely inhibited by the addition of nitrapyrin under both neutral and acid conditions. Stimulation of nitrification by addition of peptone appeared to be due to the increase in pH caused by ammonification of peptone. Under acid conditions, nitrification seemed to be coupled with net nitrogen mineralization. The possible influence of vegetation on nitrification is discussed.     

Ecological evaluation of polymetallic soil quality: the applicability of culture-dependent methods of bacterial communities studying

Purpose

This work aimed to study the effect of long-term polymetallic contamination on the state and parameters of soil bacterial communities, including the abundance of different groups of culturable bacteria and the activity of nitrification.

Materials and methods

Monitoring plots were located in the dry lake and surrounding area, which had been formerly used for the discharge of industrial waste. The soils in the 16 plots were characterized by extremely high levels of heavy metal pollution. This study evaluated the main soil physicochemical properties by various methods, total metal contents by X-ray analysis, mobile metal content by atomic absorption spectrophotometry, the abundance of chosen groups of culturable bacteria by inoculation on solid media, and nitrification activity from ammonium and nitrite oxidation rates.

Results and discussion

High adaptation capacity of microbial communities to long-term pollution was revealed through marked lack of decrease in the abundance of some of the bacterial groups in soils with high contamination levels. Among the bacteria determined by the colony count method, copiotrophic and spore-forming bacteria were the least sensitive to contamination, and actinomycetes were the most sensitive. The high levels of soil pollution with heavy metals had pronounced adverse effects on nitrification activity. The decrease in activity was strongly correlated with pollutant concentrations. The oxidation of nitrite was shown to be more affected by pollution that the oxidation of ammonium.

Conclusions

Some groups and parameters of culturable microorganisms can be used for soil status estimation under pollution conditions even though they are only a small fraction of the microbial community. The most sensitive parameter was the nitrification rate, while the number of actinomycetes was found to be most promising parameter among the groups of bacteria determined by plate counts. The use of sensitive groups of culturable microorganisms for bioindication purposes is a method, which may provide a cheap and sufficiently reliable tool for large-scale soil monitoring studies.

     

Effects of 2450 MHz microwave radiation on nitrification,respiration and S-oxidation in soil

A 20 s exposure to 2450 MHz microwave radiation had a marked differential effect on the viable count of soil micro-organisms, had little influence on numbers of heterotrophic bacteria, but reduced fungal colonies on dilution plates to zero. The growth of fungi from soil particles was also reduced following treatment. Prolonging the exposure to microwave radiation progressively inhibited nitrification and S-oxidation, but stimulated ammonification. Brief exposures (20s) also stimulated S-oxidation and increased the numbers of thiobacilli in soil. Most of these effects are explained by reference to the marked increase in soil temperature resulting from microwave treatment.