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1.
Biological N2 fixation (BNF) by associative diazotrophic bacteria is a spontaneous process where soil N is limited and adequate C sources are available. Yet the ability of these bacteria to contribute to yields in crops is only partly a result of BNF. A range of diazotrophic plant growth-promoting rhizobacteria participate in interactions with C3 and C4 crop plants (e.g. rice, wheat, maize, sugarcane and cotton), significantly increasing their vegetative growth and grain yield. We review the potential of these bacteria to contribute to yield increases in a range of field crops and outline possible strategies to obtain such yield increases more reliably. The mechanisms involved have a significant plant growth-promoting potential, retaining more soil organic-N and other nutrients in the plant-soil system, thus reducing the need for fertiliser N and P. Economic and environmental benefits can include increased income from high yields, reduced fertiliser costs and reduced emission of the greenhouse gas, N2O (with more than 300 times the global warming effect of CO2), as well as reduced leaching of NO3−-N to ground water. Obtaining maximum benefits on farms from diazotrophic, plant growth promoting biofertilisers will require a systematic strategy designed to fully utilise all these beneficial factors, allowing crop yields to be maintained or even increased while fertiliser applications are reduced.  相似文献   

2.
In this study the contribution of biological N2 fixation (BNF) to several green manure crops used at planting of sugar cane, or in the inter-rows of the ratoon crop, was evaluated. The subsequent effects of these legumes on the N supply and yield of the sugar cane crop was also investigated. The experiment was conducted in an extremely sandy N-deficient soil over two consecutive years. In the first year the legumes were planted on the same day as the sugar cane and in the second year they were planted immediately after the harvesting of the cane. The treatments consisted of four legume species (Crotalaria juncea, C. spectabilis, Canavalia ensiformis and Mucuna deeringiana), 100 kg N as urea fertiliser in a split addition, and no fertiliser N addition. The legumes were planted as two rows spaced 40 cm apart between each row of cane. Sorghum (Sorghum vulgare) and maize (Zea mays) were planted along the side of the experiment to act as non-N2-fixing reference plants for the application of the 15N natural abundance technique to quantify the BNF input to the legumes and the sugar cane. The soil cover, monitored using an overhead digital camera, showed that Crotalaria juncea was the quickest to establish and cover the soil. At 31 days after planting (DAP) it reached a height of over 60 cm, more than twice that of any of the other green manures, and covered 55% of the soil, 16% more than that of the second most vigorous legume, Canavalia ensiformis. Using the natural abundance 15N technique it was deduced that all of the legumes had obtained over 60% of their N from BNF. BNF inputs to some of the green-manure legumes were quite significant, ranging from 35 to 55 kg N ha?1 for Canavalia ensiformis, Crotalaria juncea and Mucuna deeringiana at plant crop, whereas the effect of the presence of these legumes on final cane yield and dry matter and N accumulation was not significant. There was also considerable evidence of negative (allelopathic) effects on cane growth induced by the presence of some of the legumes, especially Crotalaria juncea.  相似文献   

3.
The turnover of N derived from rhizodeposition of faba bean (Vicia faba L.), pea (Pisum sativum L.) and white lupin (Lupinus albus L.) and the effects of the rhizodeposition on the subsequent C and N turnover of its crop residues were investigated in an incubation experiment (168 days, 15 °C). A sandy loam soil for the experiment was either stored at 6 °C or planted with the respective grain legume in pots. Legumes were in situ 15N stem labelled during growth and visible roots were removed at maturity. The remaining plant-derived N in soil was defined as N rhizodeposition. In the experiment the turnover of C and N was compared in soils with and without previous growth of three legumes and with and without incorporation of crop residues. After 168 days, 21% (lupin), 26% (faba bean) and 27% (pea) of rhizodeposition N was mineralised in the treatments without crop residues. A smaller amount of 15–17% was present as microbial biomass and between 30 and 55% of mineralised rhizodeposition N was present as microbial residue pool, which consists of microbial exoenzymes, mucous substances and dead microbial biomass. The effect of rhizodeposition on the C and N turnover of crop residues was inconsistent. Rhizodeposition increased the crop residue C mineralisation only in the lupin treatment; a similar pattern was found for microbial C, whereas the microbial N was increased by rhizodeposition in all treatments. The recovery of residual 15N in the microbial and mineral N pool was similar between the treatments containing only labelled crop residues and labelled crop residues + labelled rhizodeposits. This indicates a similar decomposability of both rhizodeposition N and crop residue N and may be attributable to an immobilisation of both N sources (rhizodeposits and crop residues) as microbial residues and a subsequent remineralisation mainly from this pool.Abbreviations C or Ndec C or N decomposed from residues - C or Nmic microbial C or N - C or Nmicres microbial residue C or N - C or Nmin mineralised C or N - C or Ninput added C or N as crop residues and/or rhizodeposits - dfr derived from residues - dfR derived from rhizodeposition - Ndfr N derived from residues - NdfR N derived from rhizodeposition - Nloss losses of N derived from residues - SOM soil organic matter - WHC water holding capacity  相似文献   

4.
不同类型水稻土微生物群落结构特征及其影响因素   总被引：4，自引：1，他引：4  
选取基于我国土壤地理发生分类的不同类型土壤发育的四种水稻土,利用15N2气体示踪法测定生物固氮速率,采用实时荧光定量PCR（Real-time PCR）技术测定细菌丰度,通过16S rRNA基因高通量测序分析微生物群落组成和多样性。结果表明：变形菌门（Proteobacteria）、酸杆菌门（Acidobacteria）、绿弯菌门（Chloroflexi）和蓝藻门（Cyanobacteria）是水稻土中优势微生物类群。四种类型土壤发育的水稻土细菌群落结构差异显著（Stress<0.001）,群落结构分异（NMDS1）与土壤pH存在极显著正相关关系（P<0.01）。土壤有机碳和碱解氮含量显著影响水稻土中细菌丰度和群落多样性（P<0.01）。红壤发育的水稻土细菌16S rRNA基因拷贝数显著高于其他三种类型水稻土,但OTU数量、Chao1指数和PD指数均低于其他三种类型水稻土。土壤pH对水稻土生物固氮速率有显著影响（P<0.01）,紫色土发育的水稻土具有最高的生物固氮速率（3.2±0.7 mg×kg-1×d-1）,其中优势类群细鞘丝藻属（Leptolyngbya）可能是生物固氮的主要贡献者。研究结果丰富了对水稻土微生物多样性的认识,为通过调控土壤pH和微生物群落组成来提高稻田生物固氮潜力提供了理论依据。  相似文献   

5.
Improvement in sustainable production of switchgrass (SG, Panicum virgatum L), as a purpose-grown biomass feedstock crop, could be realized through investigation of plant–microbe interactions associated with plant growth promoting rhizobacteria (PGPR), capable of biological nitrogen fixation (BNF). The objective of this study is to increase establishment year production of SG biofuels by inoculation with a mixed PGPR inoculum. We isolated pure strains of N2-fixing, and other PGPR, from SG rhizomes. The bacteria were identified as Paenibacillus polymyxa, an N2-fixing bacterium, and other PGPR capable of solubilizing phosphate and/or producing auxins. Field trials utilizing these strains in a mixed PGPR inoculum showed that inoculated plants contained more N in tillers during anthesis but not at senescence, suggesting that more N could be cycled to belowground roots and rhizomes for winter storage. The amount of N removal in biomass and recovery of fertilizer N were also greater for inoculated than uninoculated plants. PGPR inoculation also resulted in positive N balances, suggesting improved access to N from non-fertilizer N sources, possibly through BNF and improved soil N uptake. Overall, inoculation of SG with PGPR enhanced N acquisition and could be an effective strategy to increase the establishment year production of this crop.  相似文献   

6.
Amino sugars, as a microbial residue biomarker, are highly involved in microbial-mediated soil organic matter formation. However, accumulation of microbial biomass and responses of bacterial and fungal residues to the management practices are different and poorly characterized in rice soils. The objectives of this study were to evaluate the effects of mineral fertiliser (MIN), farmyard manure (FYM) and groundnut oil cake (GOC) on crop yield and co-accumulation of microbial residues and microbial biomass under rice-monoculture (RRR) and rice–legume–rice (RLR) systems. In the organic fertiliser treatments and RLR, rice grain yield and stocks of soil and microbial nutrients were significantly higher than those of the MIN treatment and RRR, respectively. The increased presence of saprotrophic fungi in the organic fertiliser treatments and RRR was indicated by significantly increased ergosterol/Cmic ratio and extractable sulphur. In both crop rotation systems, the long-term application of FYM and GOC led to increased bacterial residues as indicated by greater accumulation of muramic acid. In contrast, the higher fungal C/bacterial C ratio and lower ergosterol/Cmic ratio in the MIN treatment, is likely caused by a shift within the fungal community structure towards ergosterol-free arbuscular mycorrhizal fungi (AMF). The organic fertiliser treatments contributed 22 % more microbial residual C to soil organic C compared to the MIN treatment. Our results suggest that the negative relationship between the ratios ergosterol/Cmic and fungal C/bacterial C encourages studying responses of both saprotrophic fungi and AMF when assessing management effects on the soil microbial community.  相似文献   

7.
The effect of organic and inorganic fertiliser amendments is often studied shortly after addition of a single dose to the soil but less is known about the long-term effects of amendments. We conducted a study to determine the effects of long-term addition of organic and inorganic fertiliser amendments at low rates on soil chemical and biological properties. Surface soil samples were taken from an experimental field site near Cologne, Germany in summer 2000. At this site, five different treatments were established in 1969: mineral fertiliser (NPK), crop residues removed (mineral only); mineral fertiliser with crop residues; manure 5.2 t ha−1 yr−1; sewage sludge 7.6 t ha−1 yr−1 or straw 4.0 t ha−1 yr−1 with 10 kg N as CaCN2 t straw−1. The organic amendments increased the Corg content of the soil but had no significant effect on the dissolved organic C (DOC) content. The C/N ratio was highest in the straw treatment and lowest in the mineral only treatment. Of the enzymes studied, only protease activity was affected by the different amendments. It was highest after sewage amendment and lowest in the mineral only treatment. The ratios of Gram+ to Gram− bacteria and of bacteria to fungi, as determined by signature phospholipid fatty acids, were higher in the organic treatments than in the inorganic treatments. The community structure of bacteria and eukaryotic microorganisms was assessed by denaturing gradient gel electrophoresis (DGGE) and redundancy discriminate analyses of the DGGE banding patterns. While the bacterial community structure was affected by the treatments this was not the case for the eukaryotes. Bacterial and eukaryotic community structures were significantly affected by Corg content and C/N ratio.  相似文献   

8.
It is a common agricultural practice for crop residues to be plowed into the soil or left on the soil surface. Soil addition of crop residues can considerably modify soil microbial activity and net N mineralization, and in general such modifications are negatively related to the C:N ratios of crop residues. Yet, little is known on the impacts of crop residues of different C:N ratios on soil nitrous oxide (N2O) production under different aeration conditions via nitrification and denitrification. In this study, an 84-day laboratory incubation was conducted under aerobic and O2-limited conditions and soil N2O production was measured every 3 days after the addition of plant materials with a wide range of C:N ratios from 14 to 297. Two aerobic conditions were created by adjusting the water content of soil at a bulk density of 1.1 g cm−3 to 30% water-filled pore space (WFPS) and 60% WFPS, and two O2-limited conditions were made by 90% WFPS and fluctuation between 90% and 30% WFPS. Each fluctuation cycle lasted 9 days and soil water content was readjusted to 90% WFPS at the end of each cycle. We also measured microbial respiration activity and net N mineralization periodically (i.e., 3, 7, 14, 28, 42, 56, 70, and 84 days) during the incubation and microbial biomass C at the end of incubation. At aerobic conditions, soil amendments of plant materials, regardless of their C:N ratios, all enhanced soil N2O production. However, net N mineralization was dependent on plant material C:N ratios, being significantly higher or lower than the control for C:N ratios ∼15 and C:N ratios ≥44, respectively. Such inconsistent responses indicated that nitrifiers mediating nitrification and therefore byproduct N2O production could strongly compete with heterotrophic microbes for NH4+ and therefore net N mineralization was not a good predictor for nitrification-associated N2O production. Interestingly, plant material additions reduced soil N2O production by up to ∼95% at O2-limited conditions, perhaps due to NO3− limitation. Soil NO3− production via nitrification could be low at O2-limited conditions, and soil NO3− availability could be further reduced due to increases in microbial biomass and thus microbial N assimilation after plant material additions. This NO3− limitation might enhance N2O reduction to N2, by which denitrifiers could harvest more energy from the consumption of limited NO3−. Nonetheless, our results revealed contrasting differences in N2O production between aerobic and O2-limited conditions following soil amendments of plant materials.  相似文献   

9.
Soil moisture and nitrogen (N) are two important factors influencing N2O emissions and the growth of microorganisms. Here, we carried out a microcosm experiment to evaluate effects of soil moisture level and N fertilizer type on N2O emissions and abundances and composition of associated microbial communities in the two typical arable soils. The abundances and community composition of functional microbes involved in nitrification and denitrification were determined via quantitative PCR (qPCR) and terminal restriction length fragment polymorphism (T-RFLP), respectively. Results showed that N2O production was higher at 90% water-filled pore (WFPS) than at 50% WFPS. The N2O emissions in the two soils amended with ammonium were higher than those amended with nitrate, especially at relatively high moisture level. In both soils, increased soil moisture stimulated the growth of ammonia-oxidizing bacteria (AOB) and nitrite reducer (nirK). Ammonium fertilizer treatment increased the population size of AOB and nirK genes in the alluvial soil, while reduced the abundances of ammonia-oxidizing archaea (AOA) and denitrifiers (nirK and nosZ) in the red soil. Nitrate addition had a negative effect on AOA abundance in the red soil. Total N2O emissions were positively correlated to AOB abundance, but not to other functional genes in the two soils. Changed soil moisture significantly affected AOA rather than AOB community composition in both soils. The way and extent of N fertilizers impacted on nitrifier and denitrifier community composition varied with N form and soil type. These results indicate that N2O emissions and the succession of nitrifying and denitrifying communities are selectively affected by soil moisture and N fertilizer form in the two contrasting types of soil.  相似文献   

10.
On acid sandy soils of Niger (West Africa) fertilizer N recovery by pearl millet (Pennisetum glaucum L.) is often more than 100 per cent in years with normal or above average rainfall. Biological nitrogen fixation (BNF) by N2-fixing bacteria may contribute to the N supply in pearl millet cropping systems. For a long-term field experiment comprising treatments with and without mineral fertilizer (F) and with and without crop residue application (CR) a N balance sheet was calculated over a period of six years (1983-1988). After six years of successive millet cropping total N uptake (36-77 kg N ha?1 yr?1) was distinctly higher than the amount of fertilizer N applied (30 kg N ha?1 yr?1). The atmospheric input of NH4-N and NO3-N in the rainwater was about 2 kg N ha?1 yr?1, 70 % in the form of NH4-N. Gaseous NH3 losses from urea (broadcast, incorporated) were estimated from other experiments to amount to 36 % of the fertilizer N applied. Nitrogen losses by leaching (15 to > 25 kg N ha?1 yr?1) were dependent on the treatment and on the quantity and distribution of single rainfall events (>50 mm). Decline in total soil N content (0-60 cm) ranged from 15 to 48 kg N ha?1 yr?1. The long-term N balance (1983-1988) indicated an annual net gain between 6 (+CR-F) and 13 (+CR+F) kg N ha?1 yr?1. For the control (-CR-F) the long-term N balance was negative (10 kg N ha?1 yr?1). In the treatment with crop residues only, the N balance was mainly determined by leaching losses, whereas in treatments with mineral fertilizer application the N balance depended primarily on N removal by the millet crop. The annual net gain in the N balance increased from 7 kg ha?1 with mineral fertilizer to 13 kg ha?1 in the combination mineral fertilizer plus crop residues. In both the rhizosphere and the bulk soil (0-15 cm), between 9 and 45% of the total bacterial population were N2-fixing (diazotrophic) bacteria. The increased N gain upon crop residue application was positively correlated with an increase in the number of diazotrophic and total bacteria. The data on bacterial numbers suggest that the gain of N in the longterm N balance is most likely due to an N input by biological nitrogen fixation. In addition, evidence exists from related studies that the proliferation of diazotrophs and total bacteria in the rhizosphere due to crop residue application stimulated root growth of pearl millet, and thus improved the phosphorus (P) acquisition in the P deficient soil.  相似文献   

11.
森林土壤氧化亚氮排放对大气氮沉降增加的响应研究进展   总被引：1，自引：1，他引：1  
森林土壤N2O来源于土壤氮素的氧化还原反应,硝化、反硝化、硝化细菌反硝化以及化学反硝化是其产生的四个关键过程。当前,氮素富集条件下森林土壤N2O排放存在硝化和反硝化主导作用之争,对大气氮沉降增加的响应模式以及微生物驱动机制尚不清楚。综述了森林土壤N2O来源的稳定性同位素拆分,森林土壤总氮转化和N2O排放对增氮的响应规律,增氮对N2O产生菌群落活性和组成的影响,并指出研究的薄弱环节与未来的研究重点。总体而言,森林土壤N2O排放对大气氮沉降增加的响应呈现非线性,包括初期无明显响应、中期缓慢增加和后期急剧增加三个阶段,取决于森林生态系统"氮饱和"程度。施氮会引起森林土壤有效氮由贫氮向富氮的转变,相应地改变了土壤硝化细菌和反硝化细菌群落丰度与组成,进而影响土壤N2O排放。由于森林土壤N2O排放监测、土壤总氮转化和N2O产生菌群落动态研究多为独立进行的,难以阐明微生物功能群与N2O排放之间的耦合关系。未来研究应该有机结合15N-18O标记和分子生物学技术,准确量化森林土壤N2O的来源,揭示森林土壤N2O排放对增氮的非线性响应机理。  相似文献   

12.
Biological nitrogen(N) fixation(BNF) plays a significant role in maintaining soil fertility in paddy field ecosystems. Rice variety influences BNF, but how different rice varieties regulate BNF and associated diazotroph communities has not been quantified. Airtight,field-based ~(15)N_2-labelling growth chamber experiments were used to assess the BNF capacity of different rice varieties. In addition,both the 16 S rRNA and nifH genes were sequenced to assess the influence of different rice varieties on bacterial and diazotrophic communities in paddy soils. After subjecting a rice-soil system to 74 d of continuous airtight, field-based ~(15)N_2 labelling in pots in a growth chamber, the amounts of fixed N were 22.3 and 38.9 kg ha~(-1) in inbred japonica(W23) and hybrid indica(IIY) rice cultivars planted in the rice-soil systems, respectively, and only 1%–2.5% of the fixed N was allocated to the rice plants and weeds. A greater abundance of diazotrophs was found in the surface soil(0–1 cm) under IIY than under W23. Sequencing of the 16 S rRNA gene showed significantly greater abundances of the cyanobacterial genera Nostoc, Anabaena, and Cylindrospermum under IIY than under W23.Sequencing of the nifH gene also showed a significantly greater abundance of Nostoc under IIY than under W23. These results indicate that the hybrid rice cultivar(IIY) promoted BNF to a greater extent than the inbred rice cultivar(W23) and that the increase in BNF might have been due to the enhanced heterocystous cyanobacteria Nostoc.  相似文献   

13.
ABSTRACT

Biological nitrogen fixation (BNF) is an important nitrogen source for both N2-fixers and their neighboring plants in natural and managed ecosystems. Biological N fixation can vary considerably depending on soil conditions, yet there is a lack of knowledge on the impact of varying soils on the contribution of N from N2-fixers in mixed swards. In this study, the amount and proportion of BNF from red clover were assessed using three grassland soils. Three soil samples, Hallsworth (HH), Crediton (CN), and Halstow (HW) series, were collected from three grassland sites in Devon, UK. A pot experiment with 15N natural abundance was conducted to estimate BNF from red clover, and the proportion of N transferred from red clover to the non-N2 fixing grass in a grass-clover system. The results showed that BNF in red clover sourced from atmosphere in the HH soil was 2.92 mg N plant?1, which was significantly lower than that of the CN (6.18 mg N plant?1) and HW (8.01 mg N plant?1) soils. Nitrogen in grass sourced from BNF via belowground was 0.46 mg N plant?1 in the HH soil, which was significantly greater than that in CN and HW soils. However, proportionally there were no significant differences in the percentage N content of both red clover and grass sourced from BNF via belowground among soils, at 65%, 67%, 65% and 35%, 27%, 31% in HH, CN, and HW, respectively. Our observations indicate that the amount of BNF by red clover varies among grassland soils, as does the amount of N sourced from BNF that is transferred to neighboring plants, which is linked to biomass production. Proportionally there was no difference among soils in N sourced from BNF in both the red clover plants and transferred to neighboring plants.  相似文献   

14.
Large accumulation of heavy metals in organic layers of forest soils may adversely affect the structure and diversity of microbial communities. The objective of this study was to assess the influence of different soil chemical properties on structure and diversity of microbial communities in soils polluted with different levels of heavy metals. The soil samples were taken at ten sites located in the vicinity of the cities of Legnica and Olkusz, differently polluted with Cu, Zn and Pb. The samples were measured for pH and the contents of organic C (Corg), total N (Nt), total S (St) and total Zn, Cu and Pb. The measured gross microbial properties included microbial biomass (Cmic) and soil respiration (RESP). The structure of soil microbial communities was assessed using phospholipid fatty acid (PLFA) analysis and the structure of soil bacterial communities using pyrosequencing of 16S rRNA genes. To assess diversity of the bacterial communities the Chao1 index was calculated based on the pyrosequencing data. For Cmic and RESP the most important factors were Nt and Corg, respectively. The structure and diversity of soil microbial communities revealed by PLFA profiles and pyrosequencing depended mainly on soil pH. The effect of high heavy metal contents on soil microbial properties was weaker compared with other soil properties. High concentrations of heavy metals negatively affected RESP and the Chao1 diversity index. The heavy metal pollution altered the structure of microbial communities measured with PLFA analysis, but the effect of heavy metal pollution was not observed for the structure of soil bacteria measured by pyrosequencing. The obtained results indicate that the use of soil microbial properties to study heavy metal effects may be difficult due to confounding influences of other environmental factors. In large-scale studies local variability of soil properties may obscure the effect of heavy metals.  相似文献   

15.
In 11 rain‐fed arable soils of the Potohar plateau, Pakistan, the amounts of microbial‐biomass C (Cmic), biomass N (Nmic), and biomass P (Pmic) were analyzed in relation to the element‐specific total storage compartment, i.e., soil Corg, Nt, and Pt. The effects of climatic conditions and soil physico‐chemical properties on these relationships were highlighted with special respect to crop yield levels. Average contents of soil Corg, Nt, and Pt were 3.9, 0.32, and 0.61 mg (g soil)–1, respectively. Less than 1% of Pt was extractable with 0.5 M NaHCO3. Mean contents of Cmic, Nmic, and Pmic were 118.4, 12.0, and 3.9 µg (g soil)–1. Values of Cmic, Nmic, Pmic, soil Corg, and Nt were all highly significantly interrelated. The mean crop yield level was closely connected with all soil organic matter– and microbial biomass–related properties, but showed also some influence by the amount of precipitation from September to June. Also the fraction of NaHCO3‐extractable P was closely related to soil organic matter, soil microbial biomass, and crop yield level. This reveals the overwhelming importance of biological processes for P turnover in alkaline soils.  相似文献   

16.
The N requirement of rice crops is well known. To overcome acute N deficiency in rice soils, this element is usually supplied to the rice crop as the commercially available fertilizer urea. But unfortunately a substantial amount of the urea-N is lost through different mechanisms causing environmental pollution problems. Utilization of biological N fixation (BNF) technology can decrease the use of urea-N, reducing the environmental problems to a considerable extent. Different BNF systems have different potentials to provide a N supplement, and it is necessary to design appropriate strategies in order to use BNF systems for efficient N supply to a rice crop. Research has been conducted around the world to evaluate the potential of different BNF systems to supply N to rice crops. This paper reviews salient findings of these works to assess all the current information available. This review indicates that the aquatic biota Cyanobacteria and Azolla can supplement the N requirements of plants, replacing 30–50% of the required urea-N. BNF by some diazotrophic bacteria like Azotobacter, Clostridium, Azospirillum, Herbaspirillum and Burkholderia can substitute for urea-N, while Rhizobium can promote the growth physiology or improve the root morphology of the rice plant. Green manure crops can also fix substantial amounts of atmospheric N. Among the green manure crops, Sesbania rostrata has the highest atmospheric N2-fixing potential, and it has the potential to completely substitute for urea-N in rice cultivation.  相似文献   

17.
丛枝菌根真菌调控土壤氧化亚氮排放的机制   总被引：2，自引：1，他引：1  
氮素是陆地生态系统初级生产力的主要限制因子,自Haber-Bosch反应以来,氮肥的生产和施用极大地提高了粮食产量.然而过量施用氮肥导致氮肥利用率低,并造成了严重的环境污染,包括氮沉降、硝态氮淋洗以及N2O排放等.微生物直接参与土壤氮素循环,固氮微生物、氨氧化和反硝化微生物分别在土壤固氮、铵态氮转化和硝态氮转化过程中起...  相似文献   

18.
Estimates of asymbiotic biological N fixation (BNF) in temperate grasslands are few with large variations. In the past six decades, European grasslands have been subjected to intensive management practices and presently it is not known how asymbiotic BNF is influenced by these practices. Our objective was to assess the impact of fertilizer application and mowing frequency on asymbiotic BNF in a Central European grassland. In 2008, we established a three-factorial experiment with two fertilizer treatments (no fertilizer application and combined nitrogen (N), phosphorus (P) and potassium (K) fertilization at 180–30–100 kg ha−1 yr−1), two mowing frequencies (cut once and thrice per year) and three sward compositions through the application of herbicides (control, monocot- and dicot-enhanced swards). Three years after the initial sward manipulation, there was no more difference in functional group composition. Between June 2011 and May 2012, we measured in-situ asymbiotic BNF using the acetylene reduction assay, calibrated with 15N2-fixation method. Across treatments, asymbiotic BNF rates in the 0–5-cm soil depth ranged from 1.7 (±0.2 SE) kg ha−1 yr−1 for fertilized plots cut once a year to 5.7 (±2.3 SE) kg ha−1 yr−1 for unfertilized plots cut thrice a year. Fertilization decreased asymbiotic BNF, suggesting that the potential positive effect of increased soil P levels might have been overruled by the negative effect of increased soil mineral N levels. Intensive mowing stimulated asymbiotic BNF, which was probably due to an increase in rhizodeposition. Our calibration of the acetylene reduction assay with the 15N2-fixation method resulted in a conversion factor of 0.61, which largely deviates from the theoretical conversion factor of 3. Furthermore, laboratory incubations under increased soil moisture and temperature conditions overestimated BNF rates compared to in-situ measurements. Thus, laboratory measurements with altered soil moisture, temperature or disturbed soil may lead to strong biases in estimates of asymbiotic BNF. Our results suggest that input of N through BNF may be considerable in temperate grasslands. We conclude that BNF studies should be conducted in-situ and that the acetylene reduction assay should be calibrated against 15N2-fixation calibration for reliable estimates.  相似文献   

19.
Disinfectants and fertilisers exert strong impact on soil processes by affecting the structure and the activity of the soil microbial community. Most relevant studies examined these impacts independently, under laboratory conditions and without crop cover. In this study, we have monitored the response of soil chemical, microbial, and biochemical properties to disinfectant and fertiliser treatments in field plots cultivated with beans. The measured properties comprised microbial C and N, asparaginase, gultaminase, urease, and acid phosphomonoesterase activities and contents of organic N, organic C, inorganic N, and inorganic P. We ran four different treatments using different combinations of chemical (metham sodium) and biological disinfectant (a mixture of neem cake and essential oils) and fertilisers (NPK 8-16-24 and cow manure) in plots cultivated with shell beans, while the control soil was neither treated nor cropped with beans. The data were expressed as percentage (%RC) in relation to the control values. The disinfectant and fertiliser treatments had less impact on soil properties compared to bean crop growth (except for microbial C and N, and content of organic C). In comparison to the control, higher activities of urease and asparaginase and content of inorganic N were recorded in bean cropped plots at the stage of seedlings (June), while higher activities of acid phosphomonoesterase and glutaminase and content of organic N were recorded at the stage of plant flowering (August). In October, the values of all properties were higher in the control plots compared to the treated plots. The joint effect of disinfectants x fertilisers affected the response of content of organic C and N and extractable P and glutaminase activity. The %RC of the properties exhibited more negative values in plots treated with chemical disinfectant and chemical fertiliser than in the other treatments. We suggested that the response of soil properties to disinfectants and fertilisers were influenced by the growth of P. vulgaris.  相似文献   

20.
Over half of the 21 Mha of soybean planted in Brazil is now transgenic glyphosate-resistant (GMRR). A field experiment was carried out to investigate whether the application of glyphosate or imazethapyr to the GMRR variety reduced the input of N2 fixation (BNF). No effects on yield, total N accumulation, nodulation and BNF (δ15N) could be assigned to the genetic modification of the plant. Imazethapyr reduced soybean yield but had no significant effect on BNF. Even though yields were not affected by glyphosate, the significant reduction of nodule mass and BNF to the GMRR suggests that the use of this herbicide could lead to an increased dependence on soil N and consequently an eventual decrease of SOM reserves.  相似文献   

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