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1.
PurposeDenitrification 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 methodsThe 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 discussionAmbient 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. ConclusionsThis 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. 相似文献
2.
Nitrification is a process in which ammonia is oxidized to nitrite (NO 2 ? ) that is further oxidized to nitrate (NO 3 ? ). The relations between these two steps and ambient ammonia concentrations were studied in surface water of Chinese shallow lakes with different trophic status. For the oxidations of both ammonia and NO 2 ? , more eutrophic lakes generally showed significantly higher potential and actual rates, which was linked with excessive ammonia concentrations. Additionally, both potential and actual rates for ammonia oxidation were higher than those for NO 2 ? oxidation in the more eutrophic lakes, while in the lakes with lower trophic status, both potential and actual rates for ammonia oxidation were almost equivalent to those for NO 2 ? oxidation. This can be explained by the excessive unionized ammonia (NH 3) concentration that inhibits nitrite-oxidizing bacteria in the more eutrophic lakes. The laboratory experiment with different ammonia concentrations, using the surface water in a eutrophic lake, showed that ammonia oxidation rates were proportional to the ammonia concentrations, but NO 2 ? oxidation rates did not increase in parallel. Furthermore, NO 2 ? oxidation was less associated with particles in natural water of the studied lakes. Without effective protection, it would be selectively inhibited by the excessive ammonia in hypereutrophic lakes, resulting in NO 2 ? accumulation. Shortly, the increased concentrations of ammonia cause a misbalance between the NO 2 ? -producing and the NO 2 ? -consuming processes, thereby exacerbating the lake eutrophication. 相似文献
3.
Purpose The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO 3 ?) leaching and nitrous oxide (N 2O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils. Materials and methods Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea. Results and discussion The three soils varied significantly in the microbial biomass C (858 to 542 μg C g ?1 soil) and biomass N (63 to 28 μg N g ?1), protease (361 to 694 μg tyrosine g ?1 soil h ?1) and deaminase (4.3 to 5.6 μg NH 4 + g ?1 soil h ?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?10 9 to 2.77?×?10 9 g ?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?10 7 to 3.01?×?10 8 g ?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use. Conclusions These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities. 相似文献
4.
Purpose The aim of the research was to explore the effect of Chinese milk vetch (CM vetch) addition and different water management practices on soil pH change, C and N mineralization in acid paddy soils. Materials and methods Psammaquent and Plinthudult paddy soils amended with Chinese milk vetch at a rate of 12 g?kg ?1 soil were incubated at 25 °C under three different water treatments (45 % field capacity, CW; alternating 1-week wetting and 2-week drying cycles, drying rewetting (DRW) and waterlogging (WL). Soil pH, dissolved organic carbon, dissolved organic nitrogen (DON), CO 2 escaped, microbial biomass carbon, ammonium (NH 4 +) and nitrate (NO 3 ?) during the incubation period were dynamically determined. Results and discussion The addition of CM vetch increased soil microbial biomass concentrations in all treatments. The CM vetch addition also enhanced dissolved organic N concentrations in all treatments. The NO 3–N concentrations were lower than NH 4–N concentrations in DRW and WL. The pH increase after CM vetch addition was 0.2 units greater during WL than DRW, and greater in the low pH Plinthudult (4.59) than higher pH Paleudalfs (6.11) soil. Nitrogen mineralization was higher in the DRW than WL treatment, and frequent DRW cycles favored N mineralization in the Plinthudult soil. Conclusions The addition of CM vetch increased soil pH, both under waterlogging and alternating wet–dry conditions. Waterlogging decreased C mineralization in both soils amended with CM vetch. Nitrogen mineralization increased in the soils subjected to DRW, which was associated with the higher DON concentrations in DRW than in WL in the acid soil. Frequent drying–wetting cycles increase N mineralization in acid paddy soils. 相似文献
5.
Purpose Few studies have examined the effects of biochar on nitrification of ammonium-based fertilizer in acidic arable soils, which contributes to NO 3 ? leaching and soil acidification. Materials and methods We conducted a 42-day aerobic incubation and a 119-day weekly leaching experiment to investigate nitrification, N leaching, and soil acidification in two subtropical soils to which 300 mg N kg ?1 ammonium sulfate or urea and 1 or 5 wt% rice straw biochar were applied. Results and discussion During aerobic incubation, NO 3 ? accumulation was enhanced by applying biochar in increasing amounts from 1 to 5 wt%. As a result, pH decreased in the two soils from the original levels. Under leaching conditions, biochar did not increase NO 3 ?, but 5 wt% biochar addition did reduce N leaching compared to that in soils treated with only N. Consistently, lower amounts of added N were recovered from the incubation (KCl-extractable N) and leaching (leaching plus KCl-extractable N) experiments following 5 wt% biochar application compared to soils treated with only N. Conclusions Incorporating biochar into acidic arable soils accelerates nitrification and thus weakens the liming effects of biochar. The enhanced nitrification does not necessarily increase NO 3 ? leaching. Rather, biochar reduces overall N leaching due to both improved N adsorption and increased unaccounted-for N (immobilization and possible gaseous losses). Further studies are necessary to assess the effects of biochar (when used as an addition to soil) on N. 相似文献
6.
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 NO 3 ??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 NO 3 ??N concentration and soil pH were the most important environmental gradients on the distribution of AOA community except vegetation type, while NO 3 ??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
7.
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。 相似文献
8.
Purpose Nitrate (NO 3 ? ) is often considered to be removed mainly through microbial respiratory denitrification coupled with carbon oxidation. Alternatively, NO 3 ? may be reduced by chemolithoautotrophic bacteria using sulfide as an electron donor. The aim of this study was to quantify the NO 3 ? reduction process with sulfide oxidation under different NO 3 ? input concentrations in river sediment. Materials and methods Under NO 3 ? input concentrations of 0.2 to 30?mM, flow-through reactors filled with river sediment from the Pearl River, China, were used to measure the processes of potential NO 3 ? reduction and sulfate (SO 4 2? ) production. Molecular biology analyses were conducted to study the microbial mechanisms involved. Results and discussion Simultaneous NO 3 ? removal and SO 4 2? production were observed with the different NO 3 ? concentrations in the sediment samples collected at different depths. Potentially, NO 3 ? removal reached 72 to 91?% and SO 4 2? production rates ranged from 0.196 to 0.903?mM?h ?1. The potential NO 3 ? removal rates were linearly correlated to the NO 3 ? input concentrations. While the SO 4 2? production process became stable, the NO 3 ? reduction process was still a first-order reaction within the range of NO 3 ? input concentrations. With low NO 3 ? input concentrations, the NO 3 ? removal was mainly through the pathway of dissimilatory NO 3 ? reduction to NH 4 + , while with higher NO 3 ? concentrations the NO 3 ? removal was through the denitrification pathway. Conclusions While most of NO 3 ? in the sediment was reduced by denitrifying heterotrophs, sulfide-driven NO 3 ? reduction accounted for up to 26?% of the total NO 3 ? removal under lower NO 3 ? concentrations. The vertical distributions of NO 3 ? reduction and SO 4 2? production processes were different because of the variable bacterial communities with depth. 相似文献
9.
PurposeOrganic matter amendment is usually used to improve soil physicochemical properties and to sequester carbon for counteracting climate change. There is no doubt that such amendment will change microbial activity and soil nitrogen transformation processes. However, the effects of straw and biochar amendment on anammox and denitrification activity and on community structure in paddy soil are unclear.Materials and methodsWe conducted a 30-day pot experiment using rice straw and rice straw biochar to deepen our understanding about the activity, microbial abundance, and community structure associated with soil nitrogen cycling during rice growth.Results and discussionRegarding activity, anammox contributed 3.1–8.1% of N2 production and denitrification contributed 91.9–96.9% of N2 production; straw amendment resulted in the highest denitrification rate (38.9 nmol N g?1 h?1), while biochar amendment resulted in the highest anammox rate (1.60 nmol N g?1 h?1). Both straw and biochar amendments significantly increased the hzsB and nosZ gene abundance (p < 0.05). Straw amendment showed the highest nosZ gene abundance, while biochar amendment showed the highest hzsB gene abundance. Phylogenetic analysis of the anammox bacteria 16S rRNA genes indicated that Candidatus Brocadia and Kuenenia were the dominant genera detected in all treatments.ConclusionsStraw and biochar amendments have different influences on anaerobic ammonia oxidation and denitrification within paddy soil. Our results suggested that the changes in denitrification and anammox rates in the biochar and straw treatments were mainly linked to functional gene abundance rather than microbial community structure and that denitrification played the more major role in N2 production in paddy soil. 相似文献
10.
Denitrification represents one of the main microbial processes producing the primary and secondary greenhouse gases nitrous oxide (N 2O) 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 C org, 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 C org) and the more acidic Schottenwald forest (poor in C org) 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 N 2O 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 N 2O 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
11.
Background Labile carbon (C labile) limits soil microbial growth and is critical for soil functions like nitrogen (N) immobilization. Most experiments evaluating C labile additions use laboratory incubations. We need to field-apply C labile to fully understand its fate and effects on soils, especially at depth, but high cost and logistical difficulties hinder this approach. Aims Here, we evaluated the impact of adding an in situ pulse of an inexpensive and 13C-depleted source of C labile—crude glycerol carbon (C glyc), a by-product from biodiesel production—to agricultural soils under typical crop rotations in Iowa, USA. Methods We broadcast-applied C glyc at three rates (0, 216, and 866 kg C ha −1) in autumn after soybean harvest, tracked its fate, and measured its impact on soil C and N dynamics to four depths (0–5, 5–15, 15–30, and 30–45 cm). Nineteen days later, we measured C glyc in microbial biomass carbon (MBC), salt-extractable organic C, and potentially mineralizable C pools. We paired these measurements with nitrate N (NO 3−–N) and potential net N mineralization to examine short-term effects on N cycling. Results C glyc was found to at least 45-cm depth with the majority in MBC (18%–23% of total C glyc added). The δ13C values of the other measured C pools were too variable to accurately track the C labile fate. NO 3−–N was decreased by 13%–57% with the 216 and 866 kg C ha −1 rates, respectively, and was strongly related to greater microbial uptake of C glyc (i.e., immobilization via microbial biomass). Crude glycerol application had minor effects on soil pH—the greatest rate decreased pH 0.18 units compared to the control. Conclusions Overall, glycerol is an inexpensive and effective way to measure in situ, C labile dynamics with soil depth—analogous to how mobile, dissolved organic C might behave in soils—and can be applied to rapidly immobilize NO 3−–N. 相似文献
12.
Purpose For an alkaline?Csaline region in Northwest China, we examined the responses of soil microbial communities to flue gas desulfurization gypsum by-products (FGDB), a new ameliorant for alkaline?Csaline soils. In 2009 and 2010, we collected soils from 0?C20?cm and 20?C40?cm depths along an experimental FGDB gradient (0, 0.74, 1.49, 2.25, and 3.00?kg FGDB m ?2). Materials and methods As a measure of microbial community composition and biomass, we analyzed phospholipid fatty acids (PLFAs). We used real-time quantitative polymerase chain reaction (qPCR) to measure abundance of bacterial 16?S rRNA copy numbers. Additionally, physicochemical soil parameters were measured by common laboratory methods. Results and discussion Microbial community composition differed along the FGDB gradient; however, the microbial parameters did not follow a linear response. We found that, in 2009, total PLFA concentrations, and concentrations of total bacterial and Gram-negative bacterial PLFAs were slightly higher at intermediate FGDB concentrations. In 2010, total PLFA concentrations, and concentrations of total bacterial, Gram-positive bacterial, Gram-negative bacterial, and fungal PLFAs as well as the fungal:bacterial PLFA ratio were highest at 1.49?kg FGDB m ?2 and 3.00?kg FGDB m ?2. PLFA concentrations often differed between 2009 and 2010; however, the patterns varied across the gradient and across microbial groups. For both years, PLFA concentrations were generally higher at 0?C20?cm depth than at 20?C40?cm depth. Similar results were obtained for the 16?S rRNA copy numbers of bacteria at 0?C20?cm depth. FGDB addition resulted in an increase in soil Ca 2+ and NO 3 ? ?CN and a decrease in pH and electrical conductivity (EC). Shifts in PLFA-based microbial community composition and biomass could partly be explained by pH, soil organic carbon, total nitrogen (TN), soil moisture, EC, inorganic nitrogen, C/N, and Ca 2+. Indirect effects via shifts in abiotic soil properties, therefore, seem to be an important pathway through which FGDB affect soil microbial communities. Conclusions Our results demonstrate that addition of FGDB leads to significant changes in soil physicochemical and microbial parameters. As such, addition of FGDB can have large impacts on the functioning of soil ecosystems, such as carbon and nitrogen cycling processes. 相似文献
13.
Upland soils are the most important terrestrial sink for the greenhouse gas CH 4. The oxidation of CH 4 is highly influenced by reactive N which is increasingly added to many ecosystems by atmospheric deposition and thereby also alters the labile C pool in the soils. The interacting effects of soil N availability and the labile C pool on CH 4 oxidation are not well understood. We conducted a laboratory experiment with soil columns consisting of homogenised topsoil material from a temperate broad-leaved forest to study the net CH 4 flux under the combined or isolated addition of NO 3 ? and glucose as a labile C source. Addition of NO 3 ? and glucose reduced the net CH 4 uptake of the soil by 86% and 83%, respectively. The combined addition of both agents led to a nearly complete inhibition of CH 4 uptake (reduction by 99.4%). Our study demonstrates a close link between the availability of C and N and the rate of CH 4 oxidation in temperate forest soils. Continued deposition of NO 3 ? has the potential to reduce the sink strength of temperate forest soils for CH 4. 相似文献
14.
Purpose In summer 2007, biweekly benthic fluxes of the biogenic elements carbon (C), nitrogen (N), silicon (Si), and phosphorus (P) were studied in the Se?ovlje saltern (salt-making facility) in the northern Adriatic Sea, Slovenia in order to determine the impact of stromatolite (??petola??) on the geochemical properties of saltern sediments. Materials and methods The brine and pore waters were analyzed for salinity, NH 4 + , NO 3 ? , PO 4 3? , SiO 4 4? , total dissolved nitrogen, total dissolved phosphorus, and fluorescent dissolved organic matter. The sediment was analyzed for organic carbon (OC), total nitrogen (TN), total and organic phosphorus (OP), and biogenic Si concentrations, as well as values of ?? 13C OC and ?? 15N TN. Results and discussion Nutrient concentrations in brine water increased along the salinity gradient due to different processes, such as the evaporative concentrations of seawater, bacterial activity, more pronounced transformation and degradation of organic matter, and regeneration of nutrients. The petola from the Se?ovlje saltern, which is predominately composed of cyanobacterial and diatom communities, develops during the early evaporation stage and survives during high salinity and halite crystallization. Nitrogen fixation and P removal were the principal biogeochemical processes controlling dissolved inorganic N and P concentrations. At higher salinities, N limitation was more important. Microbes decomposed at higher salinities, and the remineralized N and P nutrients were released from surface pore waters to the brine. OP remineralization was also an important process influencing the distribution of PO 4 3? concentrations in pore waters deeper in the sediments. The increasing SiO 4 4? concentrations with increasing salinity in the brine waters were due to dissolution of diatom frustules, while the decrease in pore water SiO 4 4? was probably the consequence of microbial uptake. Conclusions This study provides a better understanding of nutrient cycling and the geochemical processes in the Se?ovlje saltern. 相似文献
15.
Purpose The beneficial effect to the environment of nitrate (NO 3 ?) removal by denitrification depends on the partitioning of its end products into nitrous oxide (N 2O), nitric oxide (NO), and dinitrogen (N 2). However, in subtropical China, acidic forest mineral soils are characterized by negligible denitrification capacity and thus reactive forms of N could not be effectively converted to inert N 2, resulting in a negative environmental consequence. In this study, the influences of C input from litter decomposition on denitrification rate and its gaseous products under anoxic conditions in the acidic coniferous and broad-leaved forest soils in subtropical China were investigated using the acetylene (C 2H 2) blockage technique in the laboratory. Materials and methods The coniferous and broad-leaved forest soils with and without litter addition were incubated under anaerobic conditions for 244 h. There were three treatments for each forest soil including addition of 0.5 and 1% corresponding litter (gram of litter per gram of soil) and the control without addition of litter. Results and discussion The results showed that litter addition into the broad-leaved forest soil had no effect on average rates of denitrification (calculated as the sum of NO, N 2O, and N 2), whereas in the coniferous forest soil, the addition resulted in a significant increase in average denitrification rate. In the broad-leaved forest soil, both rates of litter addition decreased the production of NO but increased the production of N 2, and high rates of litter addition into the coniferous forest soil promoted the reduction of N 2O to N 2. Conclusions Increased decomposition of litter in the forest soils could effectively reduce N 2O and NO production through denitrification under anaerobic conditions. 相似文献
16.
Nitrogen dioxide gas was rapidly absorbed by soil. After a 15 min incubation at 25°C, soil at a moisture content of 16% absorbed 99% of the NO 2 introduced into the gas-phase volume of a closed system. The presence of microorganisms hatl no influence on the rate of absorption of the gas by soil. The absorption of NO 2 by sandy clay loam soil was not an oxygen- or temperature-dependent process nor did it depend upon the moisture content of the soil. These physical factors acquired significance only in determining the initial rate of absorption of the gas and the rate at which NO 2 diffused through the soil. Exposure of soil to NO 2 resulted in substantial increases in the levels of NO inf2 sup? N in the soil. Chemical oxidation of the NO inf2 sup? N resulted in an increase in NO inf3 sup? N levels. During a 14-day incubation, NO inf2 sup? N concentrations in sterile soil exposed to an atmosphere containing 100 μg ml ?1 of NO 2 decreased from 190 μg g ?1 of soil to 105 μg g ?1 with an accompanying increase in NO inf3 sup? N from 2 μg g ? 1 to 63 μg g ?1 of soil. Nitrogen dioxide severely inhibited the growth of both aerobic and anaerobic asymbiotic N 2-fixing bacteria in soil. After a 48 h incubation at 25°C, soil aggregates exposed to an atmosphere containing 100 μg ml ?1 of NO 2 contained 88% and 98% fewer aerobic and anaerobic N 2-fixing bacteria, respectively. C 2H 2-reduction measurements showed that nitrogenase synthesis and activity in artificial soil aggregates amended with 2% glucose were inhibited by 20% and 48%, respectively, when exposed to atmospheric concentrations of 35 and 3.5 μg ml ?1 of NO 2, respectively. 相似文献
17.
Purpose Hoop pine ( Araucaria cunninghamii) is a nitrogen (N)-demanding native Australian softwood plantation species. Litter quality and its effects on soil mineral N and 15N transformations have not been well studied in the hoop pine plantation and adjacent native forest. The present study was conducted to determine the impact of 15N injection depth and litter additions on the dynamics and fate of mineral 15N and also to compare the difference in litter quality, 15N dynamics, and fate between the hoop pine plantation (HP) and the adjacent native forest (NF). Materials and methods The experiments were done in the Yarraman State Forest (26°52′ S, 151°51′ E), southeastern Queensland. Materials of litter addition were prepared on the basis of ten random samples of litters taken from the NF and HP sites using a 1?×?1-m quadrat. Litter additions were defined as: SL represented the average condition of forest floor in the forest ecosystems and DL represented the double average amount of litters in the forest ecosystem. Experiment 1 covered 2 forest types (NF and HP)?×?3 litter rates (nil litter, SL, and DL)?×?3 15N injection depths (0, 2.5, and 5.0 cm). Experiment 2 included 2 forest types (NF and HP)?×?2 litter rates (nil litter and SL)?×?3 injection depths (0, 2.5, and 5.0 cm) of distilled water. The in situ core incubation method was used with an incubation period of 28 days. The isotope ratio of mineral N or/and total N (soil and litter) were analyzed using an isotope ratio mass spectrometer with a Eurovector elemental analyzer (Isoprime-EuroEA 3000). Results Total N and δ 15N were significantly higher, and C/N ratios and δ 13C were significantly lower in the NF litters than in the HP litters. The NF litters had significantly lower total 15N and total 15N recovery than the HP litters after 15N addition. Litter addition had no significant effect on mineral 15N transformations and δ 15N in the NF soil, but decreased 15NO 3 ? –N, mineral 15N, and δ 15N and increased immobilized 15N in the HP soil. The depth of added 15NH 4 + significantly altered total 15N, δ 15N, and total 15N recovery in the litters, whereas it did not influence 15NH 4 + –N, 15NO 3 ? –N, mineral 15N, or immobilized 15N in soils in the two forest ecosystems. Discussion The NF litters had significantly higher δ 15N than the HP litters, indicating that the NF soil had a higher rate of nitrification than the HP soil. Higher litter quality in the NF was an important driving force for N cycling to promote strong N dynamics in the NF soil over the HP soil. The HP litters had significantly higher total 15N than the NF litters after 15N addition, implying that soil mineral N was relatively deficient in the HP in comparison with the NF. Litters decreased nitrification and increased immobilization in the HP soil, showing forest litters resulted in more N immobilization to prevent the loss of substantial quantities of NO 3 ? through leaching or denitrification. The depth of 15N injection did not significantly alter concentrations of 15NH 4 + –N, 15NO 3 ? –N, mineral 15N, and immobilized 15N in the NF and HP soils, suggesting that the depth of 15N injection had no significant influence on the evaluation of soil N transformations. Conclusions The NF litters had significantly higher total N and δ 15N and lower C/N ratios and δ 13C than the HP litters. Mineral N was relatively insufficient in the HP soil relative to the NF soil. The HP litters facilitated more N immobilization in the soil to reduce the loss of substantial quantities of NO 3 ? through leaching or denitrification. The depth of 15N added did not significantly alter concentrations of 15NH 4 + –N, 15NO 3 ? –N, mineral 15N, and immobilized 15N in the NF and HP soils. The application of 15N solution by uniform sprinkling onto the soil surface can be used to study in situ field N (including mineral 15N) transformations in the 10-cm depth soils of both forest ecosystems. 相似文献
18.
Purpose The content and composition of dissolved organic matter (DOM) in sediment directly affect nutrient cycling and material exchange in lake ecosystems. This study investigated the content and composition of DOM and its fractions in sediments, as well as the relationship between the different parameters and nitrogen (N) forms in DOM. The main aim of this study was to evaluate the compositional characteristics of DOM, hydrophobic bases (HOB), hydrophobic acids (HOA), hydrophobic neutral fractions (HON), and hydrophilic matter (HIM) in sediments from Erhai Lake, China. Materials and methods Seven surface sediment samples with different environmental characteristics were collected. The DOM in the sediment was fractionated into HOB, HOA, HON, and HIM using XAD-8 resin based on compound hydrophobicity. The contents of DOM and its fractions were measured using a TOC analyzer. The structural characteristics of DOM and its fractions were investigated using fluorescence spectroscopy and UV–Vis absorbance. Correlation analyses were carried out to better understand the relationships between the parameters of the spectral characteristics and the contents of the different N forms in DOM and its fractions. Results and discussion The content, spatial distribution and structure of DOM and its fractions in Erhai Lake sediment were affected by water depth and aquatic plants. The DOM content in sediment ranged from 0.2 to 0.5 g kg ?1. HON accounted for 41.3 to 85.7 % of DOM, whereas HIM constituted 15.0 to 58.7 % and was significantly negatively correlated with HON ( R 2 ?=?0.856, P?0.01). HIM was more dominant than the hydrophobic matter in the southern site, but was less abundant in the north and central sites. Sediment DOM and its fractions comprised protein- and humic-like substances. The HOA and HIM comprised humic-like substances, which were the most abundant in the southern site. Conclusions (1) Hydrophobic fractions are the major components of DOM in the sediments from the seven sites in Erhai Lake. (2) DOM and its fractions mainly originated from microbial sources. (3) The A 253/ A 203 ratio is useful for evaluating the contents of N forms. The structure of DOM and its fractions are important in affecting the contents of DON. Nitrate (NO 3-N) contributes to eutrophication, and thus cannot be ignored from studies of Erhai Lake sediment. 相似文献
20.
PurposeDespite its importance, anammox (anaerobic ammonium oxidation) in estuarine sediment systems remains poorly understood, particularly at the continental scale. This study aimed to understand the abundance, diversity, and activity of anammox bacteria and to determine the main factors influencing the anammox process in estuarine sediments in China.Materials and methodsEstuarine sediments were collected from 18 estuaries spanning over 4000 km. Experiments using an 15 N–tracer, quantitative PCR, and clone library construction were used to determine the activity, abundance, and diversity of anammox bacteria. The impact of environmental factors on anammox processes was also determined.Results and discussionThe abundance of the anammox-specific hydrazine synthase (hzsB) gene ranged from 1.8 × 105 ± 3.4 × 104 to 3.6 × 108 ± 7.5 × 107 copies g?1 dw. Candidatus Scalindua, Brocadia, Kuenenia, Jettenia, and two novel unidentified clusters were detected, with Scalindua dominating the anammox population. Additionally, the abundances of Scalindua, Kuenenia, and Brocadia were found to be significantly correlated with latitude. The anammox rates ranged from 0.29 ± 0.15 to 13.68 ± 3.98 nmol N g?1 dw h?1 and contributed to 2.39–82.61% of total N2 production. Pearson correlation analysis revealed that the anammox rate was positively correlated with total nitrogen, total carbon, and temperature, and was negatively correlated with dissolved oxygen (DO). The key factors influencing the hzsB gene abundance were ammonium concentration, salinity, and DO. Ammonium concentration, pH, temperature, and latitude were main variables shaping the anammox-associated bacterial community.ConclusionsOur results suggested that anammox bacteria are ubiquitous in coastal estuaries in China and underline the importance of anammox resulting in N loss at a continental scale. 相似文献
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