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1.
Ammonia oxidizing bacteria (AOB) control the rate limiting step of nitrification, the conversion of ammonia (NH4+) to nitrite (NO2−). The AOB therefore have an important role to play in regulating soil nitrogen cycling. Tillage aerates the soil, stimulating rapid changes in soil N cycling and microbial communities. Here we report results of a study of the short term responses of AOB and net nitrification to simulated tillage and NH4+ addition to soil. The intensively farmed vegetable soils of the Salinas Valley, California, provide the context for this study. These soils are cultivated frequently, receive large N fertilizer inputs and there are regional concerns about groundwater N concentrations. An understanding of N dynamics in these systems is therefore important. AOB population sizes were quantified using a real-time PCR approach. In a 15 day experiment AOB populations, increased rapidly following tillage and NH4+ addition and persisted after the depletion of soil NH4+. AOB population sizes increased to a similar degree, over a 1.5-day period, irrespective of the amount of NH4+ supplied. These data suggest selection of an AOB community in this intensively farmed and C-limited soil, that rapidly uses NH4+ that becomes available. These data also suggest that mineralization may play an especially important role in regulating AOB populations where NH4+ pool sizes are very low. Methodological considerations in the study of soil AOB communities are also discussed.  相似文献   

2.
Ammonia-oxidizing archaea (AOA) and bacteria (AOB), which convert NH3 to NO2? in soils, are important for agricultural production. It is well known that N addition can strongly affect soil ammonia oxidizers, but little is known about P addition. Based on microcosm experiments, this study assessed the responses of ammonia oxidizers to chemical P addition in a typically high P agricultural soil with or without N supply. Six treatments examined were neither N nor P, P alone (0.15, 0.45, and 0.75 g P2O5 kg?1 soil, respectively), N alone (0.25 g N kg?1 soil), and N plus P (0.25 g N and 0.15 g P2O5 kg?1 soil). Quantitative real-time PCR for the abundance and high-throughput sequencing for community structure were applied. The results revealed that P addition did not affect the abundances and community structures of AOA and AOB, but N addition significantly increased AOB abundance and alter its community structure. Without N supply, continuously increasing soil P availability did not affect these two groups of ammonia oxidizers. This study highlights the relationship between soil P availability and ammonia oxidizers and suggests that soil P availability could be as a potential indicator for predicting N-related ecosystem functions in agricultural production.  相似文献   

3.
Indirect evidence of the nitrogen (N) status of tropical forests strongly suggests that in heavily weathered soils under old-growth lowland tropical forests nitrogen is in relative excess. However, within the lowland forests of the Amazon basin, there is substantial evidence that soil texture influences soil NH4+ and NO3? concentrations and hence possibly N availability and retention in the soil. Here, we evaluate the soil N status of two heavily weathered soils which contrast in texture (sandy versus clay Oxisol). Using 15N pool dilution, we quantified gross rates of soil N cycling and retention. We also measured the δ15N signatures from the litter layer down to 50-cm depth mineral soil and calculated the overall 15N enrichment factor (ε) for each soil type. The clay soil showed high gross N mineralization and nitrification rates and a high overall 15N enrichment factor, signifying high N losses. The sandy soil had low gross rates of N cycling and 15N enrichment factor, manifesting a conservative soil N cycling. Faster turnover rates of NH4+ compared to NO3? indicated that NH4+ cycles faster through microorganisms than NO3?, possibly contributing to better retention of NH4+ than NO3?. However this was opposite to abiotic retention processes, which showed higher conversion of NO3? to the organic N pool than NH4+. Our combined results suggest that clay Oxisol in Amazonian forest have higher N availability than sandy Oxisol, which will have important consequences for changes in soil N cycling and losses when projected increase in anthropogenic N deposition will occur.  相似文献   

4.

Purpose

Nitrogen (N) is one of the most important elements that can limit plant growth in forest ecosystems. Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are considered as the key drivers of global N biogeochemical cycling. Soil ammonia-oxidizing microbial communities associated with subtropical vegetation remain poorly characterized. The aim of this study was to determine how AOA and AOB abundance and community structure shift in response to four typical forest vegetations in subtropical region.

Materials and methods

Broad-leaved forest (BF), Chinese fir forest (CF), Pinus massoniana forest (PF), and moso bamboo forest (MB) were widely distributed in the subtropical area of southern China and represented typical vegetation types. Four types of forest stands of more than 30 years grew adjacent to each other on the same soil type, slope, and elevation, were chosen for this experiment. The abundance and community structure of AOA and AOB were characterized by using real-time PCR and denaturing gradient gel electrophoresis (DGGE). The impact of soil properties on communities of AOA and AOB was tested by canonical correspondence analysis (CCA).

Results and discussion

The results indicated that AOB dominated in numbers over AOA in both BF and MB soils, while the AOA/AOB ratio shifted with different forest stands. The highest archaeal and bacterial amoA gene copy numbers were detected in CF and BF soils, respectively. The AOA abundance showed a negative correlation with soil pH and organic C but a positive correlation with NO3 ??N concentration. The structures of AOA communities changed with vegetation types, but vegetation types alone would not suffice for shaping AOB community structure among four forest soils. CCA results revealed that NO3 ??N concentration and soil pH were the most important environmental gradients on the distribution of AOA community except vegetation type, while NO3 ??N concentration, soil pH, and organic C significantly affected the distribution of the AOB communities.

Conclusions

These results revealed the differences in the abundance and structure of AOA and AOB community associated with different tree species, and AOA was more sensitive to vegetation and soil chemical properties than AOB. N bioavailability could be directly linked to AOA and AOB community, and these results are useful for management activities, including forest tree species selection in areas managed to minimize N export to aquatic systems.  相似文献   

5.
Disparities in the substrate affinity and tolerance threshold for ammonia have been believed to play a key role in driving niche differentiation between ammonia-oxidizing archaea (AOA) and bacteria (AOB); however, recent surveys argue that direct competition between AOA and AOB is also important in this phenomenon. Accordingly, it is reasonable to predict that diverse AOA lineages would grow in ammonium (NH4+)-rich alkaline arable soils if AOB growth is suppressed. To test this hypothesis, a microcosm study was established using three different types of alkaline arable soils, in which a high NH4+ concentration (200 μg N g-1 dry soil) was maintained by routinely replenishing urea and the activities of AOB were selectively inhibited by 1-octyne or 3,4-dimethylpyrazole phosphate (DMPP). Compared with amendment with urea alone, 1-octyne partially retarded AOB growth, while DMPP completely inhibited AOB. Both inhibitors accelerated the growth of AOA, with significantly higher ratios of abundance of AOA to AOB observed with DMPP amendment across soils. Nonmetric multidimensional scaling analysis (NMDS) indicated that different treatments significantly altered the community structures of both AOA and AOB and AOA OTUs enriched by high-NH4+ amendment were taxonomically constrained across the soils tested and closely related to Nitrososphaera viennensis EN76 and N. garnensis. Given that these representative strains have been demonstrated to be sensitive to high ammonia concentrations, our results suggest that it is the competitiveness for ammonia, rather than disparities in substrate affinity and tolerance threshold for ammonia, that drives niche differentiation between these phylotypes and AOB in NH4+-rich alkaline soils.  相似文献   

6.
Agricultural systems that receive high amounts of inorganic nitrogen (N) fertilizer in the form of either ammonium (NH4+), nitrate (NO3−) or a combination thereof are expected to differ in soil N transformation rates and fates of NH4+ and NO3−. Using 15N tracer techniques this study examines how crop plants and soil microbes vary in their ability to take up and compete for fertilizer N on a short time scale (hours to days). Single plants of barley (Hordeum vulgare L. cv. Morex) were grown on two agricultural soils in microcosms which received either NH4+, NO3− or NH4NO3. Within each fertilizer treatment traces of 15NH4+ and 15NO3− were added separately. During 8 days of fertilization the fate of fertilizer 15N into plants, microbial biomass and inorganic soil N pools as well as changes in gross N transformation rates were investigated. One week after fertilization 45-80% of initially applied 15N was recovered in crop plants compared to only 1-10% in soil microbes, proving that plants were the strongest competitors for fertilizer N. In terms of N uptake soil microbes out-competed plants only during the first 4 h of N application independent of soil and fertilizer N form. Within one day microbial N uptake declined substantially, probably due to carbon limitation. In both soils, plants and soil microbes took up more NO3− than NH4+ independent of initially applied N form. Surprisingly, no inhibitory effect of NH4+ on the uptake and assimilation of nitrate in both, plants and microbes, was observed, probably because fast nitrification rates led to a swift depletion of the ammonium pool. Compared to plant and microbial NH4+ uptake rates, gross nitrification rates were 3-75-fold higher, indicating that nitrifiers were the strongest competitors for NH4+ in both soils. The rapid conversion of NH4+ to NO3− and preferential use of NO3− by soil microbes suggest that in agricultural systems with high inorganic N fertilizer inputs the soil microbial community could adapt to high concentrations of NO3− and shift towards enhanced reliance on NO3− for their N supply.  相似文献   

7.
《Applied soil ecology》2010,46(3):131-137
The effects of bacterial-feeding nematodes on nitrification and the ammonia-oxidizing bacteria (AOB) community composition were studied in soil microcosms. Sterilized soils were inoculated with mixed soil bacteria (obtained by filtering) or with bacteria and bacterial-feeding nematodes, after which the dynamic inorganic nitrogen concentration was measured weekly. After 28 days of incubation, denaturing gradient gel electrophoresis (DGGE) based on PCR amplification of the amoA gene was used to analyze the AOB community composition. In addition, a clone library from the amoA gene fragments was established using clones randomly selected and sequenced from the two treatments. The results showed that the presence of bacterial-feeding nematodes led to significantly greater NH4+ and NO3− contents over the entire incubation period, indicating that bacterial-feeding nematodes promoted both N mineralization and nitrification. The results of DGGE showed that the AOB community composition was significantly changed in the presence of bacterial-feeding nematodes. Furthermore, the sequencing results suggested that Nitrosospira sp. was the dominant species in the treatment without nematodes, while Nitrosomonas sp. and Nitrosospira sp. were the dominant species in the treatment with nematodes. Such changes in the AOB community may be one of explanation of the important role that nematodes play in promoting nitrification.  相似文献   

8.
Denitrification represents one of the main microbial processes producing the primary and secondary greenhouse gases nitrous oxide (N2O) and nitric oxide (NO) in soils. It is well established that abiotic factors like the soil water content and the availability of nitrogen (N) are key parameters determining the activity of denitrifiers in soils. However, soils differing regarding their characteristics such as the content of Corg, the soil texture or the pH value may respond in specific manners to equivalent changes in soil moisture and N input. Thus, short-term incubation experiments were performed to test and compare the capacity of two contrasting Austrian forest soils to respond to mineral N application at increased soil water contents. Soils from the pristine Rothwald forest (rich in Corg) and the more acidic Schottenwald forest (poor in Corg) were amended with either NH 4 + -N or NO 3 ? -N and were incubated at 40% and 70% water-filled pore space for 4 days. Changes in mineral N pools, nitrite reductase activity and NO and N2O emission rates were measured, and the abundance and structural community composition of the functional group involved in nitrite reduction were analysed via quantitative real-time polymerase chain reaction and terminal restriction fragment length polymorphism analysis of the nirK gene. Rapid and distinct activity responses to increased soil moisture and altered mineral nitrogen availability were observed in two contrasting forest soils. In both soils, nitrogen oxide emission rates were stimulated by N inputs and, depending on the soil moisture status, either NO or N2O emission was prevailing. However, different N cycling processes appeared to predominate in either soil under equivalent treatment. Nitrogen oxide emissions peaked following NO 3 ? application in Schottenwald soils but were the highest after NH 4 + application in Rothwald soils. Denitrifying (nirK) communities differed significantly in Rothwald and Schottenwald soils; however, changes in the community structure were marginal during the short-term incubation. Abundances of nirK genes remained unaffected by N application in either soil. The soil water content affected nirK gene abundances only in Rothwald soil, indicating a distinct reaction of nitrite reducing communities in the two soils.  相似文献   

9.
Ammonia oxidation, the first step of nitrification, is mediated by both ammonia-oxidizing archaea (AOA) and bacteria (AOB); however, the relative contributions of AOA and AOB to soil nitrification are not well understood. In this study we used 1-octyne to discriminate between AOA- and AOB-supported nitrification determined both in soil-water slurries and in unsaturated whole soil at field moisture. Soils were collected from stands of red alder (Alnus rubra Bong.) and Douglas-fir (Pseudotsuga menziesii Mirb. Franco) at three sites (Cascade Head, the H.J. Andrews, and McDonald Forest) on acidic soils (pH 3.9–5.7) in Oregon, USA. The abundances of AOA and AOB were measured using quantitative PCR by targeting the amoA gene, which encodes subunit A of ammonia monooxygenase. Total and AOA-specific (octyne-resistant) nitrification activities in soil slurries were significantly higher at Cascade Head (the most acidic soils, pH < 5) than at either the H.J. Andrews or McDonald Forest, and greater in red alder compared with Douglas-fir soils. The fraction of octyne-resistant nitrification varied among sites (21–74%) and was highest at Cascade Head than at the other two locations. Net nitrification rates of whole soil without NH4+ amendment ranged from 0.4 to 3.3 mg N kg−1 soil d−1. Overall, net nitrification rates of whole soil were stimulated 2- to 8-fold by addition of 140 mg NH4+-N kg−1 soil; this was significant for red alder at Cascade Head and the H.J. Andrews. Red alder at Cascade Head was unique in that the majority of NH4+-stimulated nitrifying activity was octyne-resistant (73%). At all other sites, NH4+-stimulated nitrification was octyne-sensitive (68–90%). The octyne-sensitive activity—presumably AOB—was affected more by soil pH whereas the octyne-resistant (AOA) activity was more strongly related to N availability.  相似文献   

10.
不同施肥方式下土壤氨氧化细菌的群落特征   总被引：2，自引：0，他引：2  
为了研究长期定位施肥对棕壤中氨氧化细菌（ammonia-oxidizing bacteria,AOB）种群结构多样性和垂直分布特征的影响,本研究采用化学分析、荧光定量PCR（qPCR）和变性梯度凝胶电泳（PCR-DGGE）技术,针对沈阳农业大学试验区不同施肥方式（不施肥、低量无机氮肥、高量无机氮肥、无机氮肥与有机肥配施）下不同土壤深度（0~20 cm、20~40 cm、40~60 cm）的土壤理化性质、AOB丰度及种群多样性进行分析,比较不同施肥方式对土壤AOB种群的影响。结果显示,与不施肥相比,施肥会降低土壤pH,增加土壤铵态氮（70.5%~939.21%）和硝态氮（253.20%~625.48%）含量。随土壤深度增加,土壤pH升高,铵态氮和硝态氮含量除低量无机氮肥处理外,多呈降低趋势。土壤增施氮肥可提高AOB丰度,降低总细菌丰度。其中,0~20 cm土层中AOB丰度较高,且高量无机氮肥处理的AOB数量最高,为9.65×105拷贝数·g-1（干土）。DGGE图谱分析显示,不同处理下,AOB群落结构多样性指数存在明显差异（P<0.05）,各多样性指数均在表层（0~20 cm）最高,增施氮肥则显著降低AOB的多样性。聚类分析表明,4个施肥处理中,高量无机氮肥处理聚为一类,其他处理则因土壤深度不同而异;3个土壤深度中,除不施肥处理外,所有施肥处理均表现为0~20 cm、20~40 cm土层发生聚类,40~60 cm则明显与其他两层分开。冗余梯度分析（RDA）显示,硝态氮（P=0.027）是造成影响AOB群落结构差异的主要原因。上述研究结果表明,长期定位施肥土壤AOB的数量和群落结构多样性受施肥方式显著影响,并表现出明显的垂直分布特征。与无机氮肥相比,有机无机配施处理有助于改善土壤pH,维持不同土壤深度下AOB群落结构多样性。  相似文献   

11.
A study was carried out to investigate the potential gross nitrogen (N) transformations in natural secondary coniferous and evergreen broad-leaf forest soils in subtropical China. The simultaneously occurring gross N transformations in soil were quantified by a 15N tracing study. The results showed that N dynamics were dominated by NH4+ turnover in both soils. The total mineralization (from labile and recalcitrant organic N) in the broad-leaf forest was more than twice the rate in the coniferous forest soil. The total rate of mineral N production (NH4+ + NO3−) from the large recalcitrant organic N pool was similar in the two forest soils. However, appreciable NO3− production was only observed in the coniferous forest soil due to heterotrophic nitrification (i.e. direct oxidation of organic N to NO3−), whereas nitrification in broad-leaf forest was little (or negligible). Thus, a distinct shift occurred from predominantly NH4+ production in the broad-leaf forest soil to a balanced production of NH4+ and NO3− in the coniferous forest soil. This may be a mechanism to ensure an adequate supply of available mineral N in the coniferous forest soil and most likely reflects differences in microbial community patterns (possibly saprophytic, fungal, activities in coniferous soils). We show for the first time that the high nitrification rate in these soils may be of heterotrophic rather than autotrophic nature. Furthermore, high NO3− production was only apparent in the coniferous but not in broad-leaf forest soil. This highlights the association of vegetation type with the size and the activity of the SOM pools that ultimately determines whether only NH4+ or also a high NO3− turnover is present.  相似文献   

12.
The availability of inorganic N has been shown to be one of the major factors limiting primary productivity in high latitude ecosystems. The factors regulating the rate of transformation of organic N to nitrate and ammonium, however, remain poorly understood. The aim of this study was to investigate the nature of the soluble N pool in forest soils and to determine the relative rate of inorganic N production from high and low molecular weight (MW) dissolved organic nitrogen (DON) compounds in black spruce forest soils. DON was found to be the dominant N form in soil solution, however, most of this DON was of high MW of which >75% remained unidentified. Free amino acids constituted less than 5% of the total DON pool. The concentration of NO3− and NH4+ was low in all soils but significantly greater than the concentration of free amino acids. Incubations of low MW DON with soil indicated a rapid processing of amino acids, di- and tri-peptides to NH4+ followed by a slower transformation of the NH4+ pool to NO3−. The rate of protein transformation to NH4+ was slower than for amino acids and peptides suggesting that the block in N mineralization in taiga forest soils is the transformation of high MW DON to low MW DON and not low MW DON to NH4+ or NH4+ to NO3−. Calculated turnover rates of amino acid-derived C and N immobilized in the soil microbial biomass were similar with a half-life of approximately 30 d indicating congruent C and N mineralization.  相似文献   

13.
We conducted a microcosm experiment with soil being sterilized, reinoculated with native microbial community and subsequently manipulated the bacterivorous nematodes, including three treatments: without (CK) or with introducing one species of the two bacterivores characterized with different body size but similar c-p (colonizer-persister) value (Rhabditis intermedia and Protorhabditis oxyuroides, accounted for 6 and 59% of bacterivores in initially undisturbed soil, respectively). We monitored the N2O and CO2 emissions, soil properties, and especially quantified gross N transformation rates using 15N tracing technique after the 50 days incubation. No significant differences were observed on soil NH4 + and NO3 ? concentrations between the CK and two bacterivores, but this was not the case for gross N transformation rates. In comparison to CK, R. intermedia did not affect soil N transformation rates, while P. oxyuroides significantly increased the rates of mineralization of organic N to NH4 +, oxidation of NH4 + to NO3 ?, immobilization of NO3 ? to organic N and dissimilatory NO3 ? reduction to NH4 +. Furthermore, the mean residence time of NH4 + and NO3 ? pool was greatly lowered by P. oxyuroides, suggesting it stimulated soil N turnover. Such stimulatory effect was unrelated to the changes in abundance of bacteria and ammonia-oxidizing bacteria (AOB). In contrast to CK, only P. oxyuroides significantly promoted soil N2O and CO2 emissions. Noticeably, bacterivores increased the mineralization of recalcitrant organic N but decreased soil δ13C-TOC and δ15N-TN values, in particular for P. oxyuroides. Combining trait-based approach and isotope-based analysis showed high potential in moving forward to a mechanistic understanding of bacterivore-mediated N cycling.  相似文献   

14.
The effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N transformations and composition of ammonia-oxidizing bacteria (AOB) communities was investigated at the centimeter scale in a microcosm experiment under laboratory conditions. After 28 days, samples were collected from soil treated with urea or urea and DMPP at increasing distance from the fertilizer zone; this distance ranged from 0 to 5 cm in both horizontal and vertical directions. The results showed that DMPP application significantly increased soil pH and NH 4 + -N and mineral N (NH 4 + -N, NO 3 ? -N, and NO 2 ? -N) concentrations but decreased (NO 3 ? + NO 2 ? )-N concentration, and such effect was decreased by increasing the distance from the fertilizer zone. Fingerprint profiles of denaturing gradient gel electrophoresis showed that the number of bands decreased by increasing the distance from the fertilizer zone due to decreasing NH 4 + -N concentrations in the urea treatment. Compared to urea applied alone, DMPP application increased NH 4 + -N concentrations and decreased AOB diversity from 0 to 3 cm but promoted diversity from 3 to 5 cm distance from the fertilizer zone. A phylogenetic analysis showed that AOB communities were dominated by Nitrosospira cluster 3. Therefore, the nitrification inhibitor DMPP modified the composition of AOB communities by increasing the distance from the fertilizer zone and this probably was related to the changes in soil pH and inorganic N concentration.  相似文献   

15.
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.  相似文献   

16.
Green manure Sesbania sesban (S. sesban) and the nitrification inhibitor encapsulated calcium carbide (ECC) have been used to improve N supply and management in rice–wheat production systems in India. However, the ecological impact of combined use of these materials is largely unknown. We conducted a net-house pot culture experiment for 2 years, to investigate the effects of S. sesban and ECC on mineral N availability (NH4+ and NO3–), soil enzyme activities (dehydrogenase and nitrate reductase) and populations (MPN) of nitrifying organisms under a rice–wheat cropping system. Green manure S. sesban and ECC (+ECC or –ECC) were applied along with urea in various combinations to hybrid rice under flooded conditions. For wheat, it was urea alone or urea + ECC. Soil samples were studied at 10 days after top dressing, i.e. 40 days after rice transplanting and 35 days after wheat sowing, for above characteristics. The mineral-N in soil revealed the significant effect of combined use of S. sesban and ECC to enhance NH4+ and total mineral-N (NH4+ + NO3–) contents. Dehydrogenase and nitrate reductase activities and population (MPN) of ammonia oxidizing bacteria (AOB) revealed a significant reduction in soils, whereas nitrite oxidizing bacteria (NOB) remained almost unaffected (P > 0.05) in response to application of ECC with S. sesban and urea. Our results suggest that slow release of acetylene (C2H2) from ECC has reduced ammonia mono-oxygenase with reducing population of AOB, and has the potential to retard the enzyme activities in favor of C and N conservations in a semi-arid agro-ecosystem.  相似文献   

17.
Field data have shown that soil nitrifying communities gradually adapt to zinc (Zn) after a single contamination event with reported adaptation times exceeding 1 year. It was hypothesized that this relatively slow adaptation relates to the restricted microbial diversity and low growth rate of the soil nitrifying community. This hypothesis was tested experimentally by recording adaptation rates under varying nitrification activities (assumed to affect growth rates) and by monitoring shifts in community composition. Soils were spiked at various Zn concentrations (0-4000 mg Zn kg−1) and two NH4+-N doses (N1, N2) were applied to stimulate growth. A control series receiving no extra NH4+-N was also included. Soils were incubated in pots under field conditions with free drainage. The pore water Zn concentration at which nitrification was halved (EC50, mg Zn l−1) did not change significantly during 12 months in the control series (without NH4+-N applications), although nitrification recovered after 12 months at the highest Zn dose only. The EC50 after 12 months incubation increased by more than a factor 10 with increasing NH4+-N dose (p < 0.05) illustrating that increased activity accelerates adaptation to Zn. Zinc tolerance tests confirmed the role of Zn exposure, time and NH4+-N dose on adaptation. Zinc tolerance development was ascribed to the AOB community since the AOB/AOA ratio (AOB = ammonia oxidizing bacteria; AOA = ammonia oxidizing archaea) increased from 0.4 in the control to 1.4 in the most tolerant community. Moreover, the AOB amoA DGGE profile changed during Zn adaptation whereas the AOA amoA DGGE profile remained unaffected. These data confirm the slow but pronounced adaptation of nitrifiers to Zn contamination. We showed that adaptation to Zn was accelerated at higher activity and was associated with a shift in soil AOB community that gradually dominated the nitrifying community.  相似文献   

18.
We tested how amendments of different forms of nitrogen (N) affect microbial respiration rates by adding six different forms of N (NH4NO3, (NH2)2CO (urea), KNO3, NH4Cl, (NH4)2SO4, Ca(NO3)2) to three distinct soils. All inorganic N forms led to a net reduction in microbial respiration, and the magnitude of the observed response (up to 60 % reduction) was consistent across all soils and negatively correlated with N concentration. Urea also reduced respiration rates in nearly all cases, but the effect was attenuated by the associated input of labile organic carbon. We observed decreases in respiration regardless of soil type, the specific N counter ion, N added as NH4+ or NO3−, or the effects of N form on soil pH, suggesting that decreases in respiration rates were mainly a direct result of the increase in soil N availability, rather than indirect effects caused by the form of N added.  相似文献   

19.
The short-term effects of excessive NH4+-N on selected characteristics of soil unaffected (low annual N inputs) and affected (high annual N inputs) by cattle were investigated under laboratory conditions. The major hypothesis tested was that above a theoretical upper limit of NH4+ concentration, an excess of NH4+-N does not further increase NO3− formation rate in the soil, but only supports accumulation of NO2−-N and gaseous losses of N as N2O. Soils were amended with 10 to 500 μg NH4+-N g−1 soil. In both soils, addition of NH4+-N increased production of NO3−-N until some limit. This limit was higher in cattle-affected soil than in unaffected soil. Production of N2O increased in the whole range of amendments in both soils. At the highest level of NH4+-N addition, NO2−-N accumulated in cattle-affected soil while NO3−-N production decreased in cattle-unaffected soil. Despite being statistically significant, observed effects of high NH4+-N addition were relatively weak. Uptake of mineral N, stimulated by glucose amendment, decreased the mineral N content in both soils, but it also greatly increased production of N2O.  相似文献   

20.
Terrestrial ecosystems are predicted to experience an increasing level of atmospheric nitrogen (N) deposition, which may cause significant shifts in plant community composition and concomitantly stimulate soil acidification. However, little is known concerning the effects of N deposition on belowground microbial communities in alpine grassland ecosystems such as on the Tibetan Plateau. This study examined the responses of soil N-transforming microbes (measured after DNA extraction and quantitative PCR), soil microbial biomass C (SMBC) and N (SMBN), and soil enzyme activities to different forms (NH4 +-N, NO3 ?-N, and NH4NO3-N) and rates (1.5 and 7.5 g N m?2 year?1, denoted as low and high N, respectively) of N fertilization (addition) in two successive plant growing seasons. The N rate, not N form, influenced the abundance of ammonia-oxidizing archaea (AOA). High N addition significantly increased ammonia-oxidizing bacteria (AOB) abundance which differed across different N form treatments. Nitrogen addition had no significant impact on the abundance of soil denitrifiers. The SMBC and SMBN were significantly decreased by high N additions, but no difference was found among different N forms. Despite higher urease activities being detected in the late plant growing season, the activities of invertase and alkaline phosphomonoesterase stayed unchanged irrespective of the different N amendments and plant growing season. Significant positive correlations were found between potential nitrification rates and AOB abundances. These results highlight that AOB seemed to respond more sensitively to different N fertilization and might have prominent roles in soil N cycling processes in this Tibetan Plateau alpine meadow than AOA.  相似文献   

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