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1.
This research aimed to determine whether a diluted nutrient broth (DNB) medium was different from a conventional nutrient broth (NB) medium when counting and isolating denitrifying bacteria in surface and subsurface upland soils. To this end, we investigated populations of denitrifying bacteria isolated from the surface to a depth of 4 m of subsurface upland soil that had received slurry. The DNB medium gave higher viable counts of denitrifying bacteria than the NB medium and a higher isolation ratio of denitrifying bacterial isolates. In total, 74 isolates from the DNB medium (D-isolates) and 26 isolates from the NB medium (N-isolates) were collected. We characterized their denitrifying activity and analyzed the diversity of 16S rDNA and denitrifying-related genes. Seventy-three percent of the D-isolates were oligotrophic denitrifying bacteria. The N2-producing, oligotrophic denitrifying bacteria, largely of α-Proteobacteria, increased in the D-isolates. The D-isolates and the N-isolates had some taxonomic overlapping on a phylogenetic tree based on 16S rDNA. It was not possible to identify the denitrification phenotype (N2-producing or N2O-producing) on the phylogenetic tree. Phylogenetic groups of isolates corresponded to nirK groups, except in some isolates in which horizontal gene transfer might have occurred. The terminal gas emission of the isolates was consistent with the existence of the nosZ gene. The DNB medium may be very useful in isolating N2-producing denitrifying α-Proteobacteria. Its use highlights the ecological significance of oligotrophic isolates and the different viable counts resulting from the selectivity of conventional and diluted media.  相似文献   

2.
Diversity of denitrifying microflora and ability to reduce N2O in two soils   总被引：1，自引：0，他引：1  
 The ozone-depleting gas N2O is an intermediate in denitrification, the biological reduction of NO3 – to the gaseous products N2O and N2 gas. The molar ratio of N2O produced (N2O/N2O+N2) varies temporally and spatially, and in some soils N2O may be the dominant end product of denitrification. The fraction of NO3 –-N emitted as N2O may be due at least in part to the abundance and activity of denitrifying bacteria which possess N2O reductase. In this study, we enumerated NO3 –-reducing and denitrifying bacteria, and compared and contrasted collections of denitrifying bacteria isolated from two agricultural soils, one (Auxonne, soil A) with N2O as the dominant product of denitrification, the other (Chalons, soil C) with N2 gas as the dominant product. Isolates were tested for the ability to reduce N2O, and the presence of the N2O reductase (nosZ)-like gene was evaluated by polymerase chain reaction (PCR) using specific primers coupled with DNA hybridization using a specific probe. The diversity and phylogenetic relationships of members of the collections were established by PCR/restriction fragment length polymorphism of 16s rDNA. The two soils had similar numbers of bacteria which used NO3 – as a terminal electron acceptor anaerobically. However, the soil A had many more denitrifiers which reduced NO3 – to gaseous products (N2O or N2) than did soil C. Collections of 258 and 281 bacteria able to grow anaerobically in the presence of NO3 – were isolated from soil A and soil C, respectively. These two collections contained 66 and 12 denitrifying isolates, respectively, the others reducing NO3 – only as far as NO2 –. The presence of nosZ sequences was generally a poor predictor of N2O reducing ability: there was agreement between the occurrence of nosZ sequences and the N2O reducing ability for only 42% of the isolates; 35% of the isolates (found exclusively in soil A) without detectable nosZ sequences reduced N2O whereas 21% of the isolates carrying nosZ sequences did not reduce this gas under our assay conditions. Twenty-eight different 16S rDNA restriction patterns (using two restriction endonucleases) were distinguished among the 78 denitrifying isolates. Two types of patterns appeared to be common to both soils. Twenty-three and three types of patterns were found exclusively among bacteria isolated from soils A and C, respectively. The specific composition of denitrifying communities appeared to be different between the two soils studied. This may partly explain the differences in the behaviour of the soils concerning N2O reduction during denitrification. Received: 31 October 1997  相似文献   

3.
The distribution of heterotrophic bacteria on organic debris and roots of rice plants in a paddy field were studied. The heterotrophic bacteria consisted of two main groups: those which grew on full-strength nutrient broth (NB) and those which did not grow on NB but on a 100-fold dilution of NB (DNB). The latter group was called ‘DNB organisms’ and were considered to be oligotrophic. In both manured and unmanured soils, DNB organisms were predominant in the bacterial communities on organic debris and the rice roots throughout most of the entire period of rice cultivation, although a transient decrease in the proportion of DNB organisms was observed immediately after an application of manure. Morphological and physiological characteristics of DNB isolates from organic debris and rice roots were studied: five types of cell shape were observed, (1) regular rods, (2) filament-forming rods, (3) irregular rods, (4) prosthecate organisms and (5) large oval cells. Regular rods (42% of the total DNB isolates) and irregular rods (46%) were abundant. The ecological roles of DNB organisms in paddy soil are discussed in relation to their physiological characteristics.  相似文献   

4.
Added nitrate did not disappear from two soils maintained under anerobiosis for 7 days at 1°C. Nitrate was reduced slowly at 7°C, and the rate increased with increasing temperature. The rate was markedly enhanced by glucose, but succinate and methanol were less stimulatory. Sewage effluent enhanced the rate to a small extent or inhibited the reduction. During the phase of rapid NO3? reduction, the population of denitrifying bacteria rose rapidly, but the cell density quickly declined as the rate of NO3? loss declined. From 1.8 to 8.4 pg of NO3?-N was reduced per denitrifying cell that proliferated during exponential NO3? reduction in soil. In culture, strains of Pseudomonas and Flavobacterium reduced 0.82–2.0 pg of NO3?-N per cell that appeared during exponential growth.  相似文献   

5.
The soil chemical properties and microbial numbers in three volcanic ash soils and two non-volcanic ash soils, which had been continuously subjected to the same tea cultivation practices (21 y), were investigated. The results obtained were as follows. 1) pH values of all the soils gradually decreased from the original pH value (near neutral or mildly acid pH) to strongly acid values of about 4 or lower. In contrast, long-term tea cultivation practices resulted in the increase of the total C and N contents in the surface layers (0–20 cm) while the contents remained stable in the subsurface layers (20–40 cm). The increase in the organic matter content in non-volcanic ash soils was presumably due to the accumulation of microbial residues. The availability of P increased markedly. 2) Numbers of bacteria, actinomycetes, fungi, and denitrifiers were higher in volcanic ash soils than in non-volcanic ash soils, and also higher in surface layers than in subsurface layers. The results suggest that in spite of the same cultivation practices, the soil depth and soil type affected the microbial numbers in the tea soils. Numbers of autotrophic NH4 + oxidizers were low in comparison with the numbers of autotrophic NO2 - oxidizers. Influence of soil type and soil depth on autotrophic nitrifiers was not clear. 3) Total C and N contents in the tea soils were parameters closely related to the numbers of bacteria, actinomycetes, and fungi. For actinomycetes and fungi, the prediction could be more accurate, especially for total N content, if the estimations could be made within the same soil layers. The numbers per unit of C or N were higher in the surface layers than in the subsurface layers. 4) High concentration of NO3 --N in the tea soils used suggests that nitrification could occur despite the low pH value (3.2-3.8). The negative relationship between the number of total bacteria or actinomycetes and soil NH4 +-N concentration suggests that some NH4 +-N was converted to organic microbial biomass-No.  相似文献   

6.
Nitrous oxide, one of the earth-warming and ozone-destructing gases, is produced through either nitrification or denitrification depending on the O2 availability in soil. Aerobically denitrifying bacteria express denitrification tract even under the gas phase containing O2 at the ambient air level. The net reduction of exogenous N2O by novel aerobically denitrifying bacteria were studied. We carried out two different isolation strategies in the primary screening. One was to select isolates of interest out of periplasmic nitrate reductase-dependent denitrifying bacteria in a eutrophic condition. The other was to use diluted nutrient agar to allow the formation of colonies of diverse bacteria. Among aerobically denitrifying bacteria, those which showed net aerobic N2O reduction were only minor populations. As a result, eight isolates belonging to Proteobacteria were obtained from soil and cow manure. The denitrification and net N2O reduction properties of the three representative isolates, Pseudomonas sp. CM1, Thauera sp. PM2 and Paracoccus denitrificans 96, were determined separately by the acetylene inhibition method after exposure to aerobic or low O2 conditions, a 24 h starvation prior to the determination of the aerobic activity and inoculation to a cow manure-amended sterile soil. The phenotype inversion from net N2O-reducing to N2O-emitting, and vice versa, attested to the fact that activity of the N2O-producing and -reducing steps changed in different intensities to each other. The activity values and the direction of activity changes varied among the isolates. When they were inoculated in a sterilized soil microcosm at 40% maximum water holding capacity, the denitrification and the N2O-reducing activities were comparable with or, in some cases, facilitated more than those determined under the low-O2 condition. It is possible that these isolates sensed the O2 deficiency even in such a relatively dry condition. Pseudomonas sp. CM1 was unique because it lacked nitrate reducing activity and acted as a net aerobic N2O reducer.  相似文献   

7.
Fertilization produces many nutrient patches that have been confirmed to affect root growth. However, it is not clear how nutrient transformation and microbial community composition are affected in an inorganic nutrient patch. In this experiment, a nitrogen enrichment patch was formed by the diffusion of a urea fertilizer layer in a specially-designed container. Responses of nitrogen transformation and microbial community composition to the nitrogen enrichment patch were investigated at different incubation times. Results showed that nitrogen status and microbial community composition were slightly affected in the control patch (CK patch). In the nitrogen enrichment patch, however, soil pH was significantly increased in most soil layers close to the urea fertilizer layer; NO2?–N was the predominant form of mineral N, and its transformation to NO3?–N was delayed. Microbial community composition shifted significantly, especially before day 28 of incubation. Principal components analysis (PCA) of phospholipid fatty acids (PLFAs) patterns showed that the microbial community presented different sensitivity to high nitrogen concentration. Fungi (18:2ω6,9) showed the least sensitivity to high concentrations of NO2?–N and NO3?–N. Gram-positive bacteria showed the most sensitivity to NO2?–N. Gram-negative bacteria (cy17:0, cy19:0, 18:1ω9, and 18:1ω7) and actinomycetes (10Me17:0 and 10Me18:0) presented similar responses to NO2?–N and NO3?–N. Results of this study indicate that changes in nitrogen transformation and microbial community composition are likely to occur in nitrogen enrichment patches, but the extent of those changes depend on the microbial species and the distance of soil layers from the urea layer.  相似文献   

8.
太湖地区水稻土优势反硝化细菌的数量、组成与酶活性   总被引：4，自引：1，他引：4  
本研究结果表明太湖地区主要水稻土中反硝化细菌常在百万/克干土以上,占细菌总数的50—80%。同一类型土壤中,肥力高者含菌数多于肥力低者。各类土壤中反硝化细菌数与细菌总数呈显著正相关。其优势种中,以巨大芽孢杆菌、荧光假单胞菌和施氏假单胞菌等出现的机率最高,占反硝化细菌的10—50%;地衣芽孢杆菌及坚强芽孢杆菌等出现的机率较少。具有使NO3-还原为N2O的菌株和使N2O还原为N2的菌株,分别占供试菌株的67%和56%;使15NO3-异化还原为15NH4+的菌株占供试菌株的92%,其中以蜡质芽孢杆菌和地衣芽孢杆菌的这种能力特别强。  相似文献   

9.
Fertilization produces many nutrient patches that have been confirmed to affect root growth. However, it is not clear how nutrient transformation and microbial community composition are affected in an inorganic nutrient patch. In this experiment, a nitrogen enrichment patch was formed by the diffusion of a urea fertilizer layer in a specially-designed container. Responses of nitrogen transformation and microbial community composition to the nitrogen enrichment patch were investigated at different incubation times. Results showed that nitrogen status and microbial community composition were slightly affected in the control patch (CK patch). In the nitrogen enrichment patch, however, soil pH was significantly increased in most soil layers close to the urea fertilizer layer; NO2−-N was the predominant form of mineral N, and its transformation to NO3−-N was delayed. Microbial community composition shifted significantly, especially before day 28 of incubation. Principal components analysis (PCA) of phospholipid fatty acids (PLFAs) patterns showed that the microbial community presented different sensitivity to high nitrogen concentration. Fungi (18:2ω6,9) showed the least sensitivity to high concentrations of NO2−-N and NO3−-N. Gram-positive bacteria showed the most sensitivity to NO2−-N. Gram-negative bacteria (cy17:0, cy19:0, 18:1ω9, and 18:1ω7) and actinomycetes (10Me17:0 and 10Me18:0) presented similar responses to NO2−-N and NO3−-N. Results of this study indicate that changes in nitrogen transformation and microbial community composition are likely to occur in nitrogen enrichment patches, but the extent of those changes depend on the microbial species and the distance of soil layers from the urea layer.  相似文献   

10.
A rapid, precise and accurate microtiter most-probable-number (MPN) procedure has been developed and tested for simultaneous (two reagent addition) enumeration of denitrifier and nitrate reducer populations in an agricultural soil. Values from 0.12 × 106 to 0.22 × 106 denitrifiers g?1 soil were determined using two concentrations of each terminal electron acceptor (3.5 and 7.2 mm NO2? or 3.5 and 9.9 mm NO3? in nutrient broth. Nitrate reducer populations ranged from 0.97 × 106 to 1.1 × 106 organisms g?1 soil when two concentrations of NO3? (3.5 and 9.9 mm) were employed. The denitrifiers thus constituted 12–20% of the nitrate reducer population. Neither method (tube or microtiter) or medium significantly altered the values obtained for these two groups of microorganisms.  相似文献   

11.
The long-term (9 years) effect of pig slurry applications vs mineral fertilization on denitrifying activity, N2O production and soil organic carbon (C) (extractable C, microbial biomass C and total organic C) was compared at three soil depths of adjacent plots. The denitrifying activities were measured on undisturbed soil cores and on sieved soil samples with acetylene method to estimate denitrification rates under field or potential conditions. Pig slurry applications had a moderate impact on the C pools. Total organic C was increased by +6.5% and microbial biomass C by ≥25%. The potential denitrifying activity on soil suspension was stimulated (×1.8, P<0.05) 12 days after the last slurry application. This stimulation was still apparent, but not significant, 10 months later and, according to both methods of denitrifying activity measurement (r 2=0.916, P<0.01 on sieved soil; r 2=0.845, P<0.001 on soil cores), was associated with an increase in microbial biomass C above a threshold of about 105 mg kg−1. The effect of pig slurry on denitrification and N2O reduction rates was detected on the surface layer (0–20 cm) only. However, no pig slurry effect could be detected on soil cores at field conditions or after NO3 − enrichments at 20°C. Although the potential denitrifying activity in sieved soil samples was stimulated, the N2O production was lower (P<0.03) in the plot fertilized with pig slurry, indicating a lower N2O/(N2O + N2) ratio of the released gases. The pig-slurry-fertilized plot also showed a higher N2O reduction activity, which is coherent with the lower N2O production in anaerobiosis.  相似文献   

12.
在实验室条件下,对黄松稻田土壤、紫色稻田土壤和红壤稻田土的反硝化细菌(DenitrifyingBacteria,DNB)种群数量及其反硝化活性,以及Cr2(SO4)36H2O处理4周后Cr3+污染对DNB种群数量及其反硝化活性影响进行了研究。结果表明,紫色稻田土壤、黄松稻田土壤和红壤稻田土的DNB种群数量每克干土分别为(59.04～157.59)104cfu、(42.89～108.97)104cfu和(32.14～75.30)104cfu。在每千克干土中加入200mgCr3+时,对稻田土的DNB种群数量及其活性有明显的抑制作用,但稻田土壤还能通过自身的能力,在培养3周后完全恢复稻田土壤的DNB种群数量及其活性。随着Cr3+加入量的增加,Cr3+对DNB的毒性越来越大,稻田土壤通过自身来恢复DNB种群数量及其活性越来越困难,但可通过外界力量(如调节土壤pH)逐渐恢复稻田土壤的生物活性。  相似文献   

13.
A study was made of the formation of anaerobiosis in a waterlogged soil. A dilute soil suspension containing NO?3, Fe3+, sodium citrate, a limited amount of O2, and trace elements was used as a model of waterlogged soil. Polarography was used to detect dissolved O2, Fe3+ and Fe2+. The fates of the NO?3 and Fe3+ during and after O2 consumption by the microorganisms were studied in a specially designed vessel. A close correspondence was obtained between the reduction of NO?3, NO?2 and Fe3+ and the growth of denitrifying bacteria in the closed system employed. From the experimental results we presume that microorganisms which respire NO?3 are also capable of utilising Fe3+ in their respiration. The mechanisms of reduction of these chemical species by the microorganisms are also discussed, emphasising the possibility of the participation of chemical reduction of NO?2 by Fe2+ in the over-all reduction process.  相似文献   

14.
Nitrate (NO-3) and nitrite (NO2-) leaching threatens groundwater quality.Soil C:N ratio,i.e.,the ratio of soil organic carbon to total nitrogen,affects mineralization,nitrification,and denitrification;however,its mechanism for driving soil NO-3 and NO-2 accumulation and leaching remains unclear.Here,a field investigation in a fluvo-aquic soil and a soil column experiment were performed to explore the relation...  相似文献   

15.
In situ and laboratory measurements of aerobic respiratory and denitrifying activities were studied in the vadose zone (almost 2.5 m thick) of a fluvic hypercalcaric cambisol characterized by transitory anaerobic conditions. A field experiment was conducted in a bare soil, over a 7-month period starting just after maize harvest and incorporation of maize crop residues. Weather variables (air and soil temperature, rainfall), soil water content, soil solutes (NO3− and dissolved organic carbon) and soil gases (CO2 and N2O), were recorded throughout the experiment. Four soil layers were defined. Bacterial counts were performed in each layer using the most probable number (MPN) method. Aerobic respiratory and denitrifying activities were estimated from laboratory measurements. In situ microbial activity, as revealed by CO2 and N2O measurements in the soil atmosphere, was strongly influenced by weather. Laboratory measurements showed that potential aerobic respiratory activity (ARA) occurred throughout the soil profile, whereas semi-potential denitrifying activities SPDA (i.e. measured under organic-C limiting condition) occurred mainly in the top 30 cm soil layer. In the soil profile, the CO2 concentration gradient was stronger than the N2O concentration gradient. Seasonal variations in microbial activities increased with depth, whereas DOC concentrations, and variations in those concentrations, decreased with depth, suggesting that DOC quality investigations are necessary in the deep vadose zone to understand microbial activities seasonal variations. Laboratory measurements of potential activities agreed well with in situ microbial activity in natural environmental conditions. NO3− was a stronger limiting factor for SPDA than was denitrifier density in the soil profile.  相似文献   

16.
Rhizobial symbionts were isolated from the surface (0-0.5 M) and phreatic (3.9-5.0 M) root environments of a mature mesquite woodland in the Sonoran Desert of Southern California, and from variable depths (0-12 m) of non-phreatic mesquite ecosystems in the Chihuahuan Desert of New Mexico. They were tested for their ability to tolerate high salinity, and respire NO3− as mechanisms of free-living survival. Sixteen of 25 isolates were grown in yeast-extract mannitol (YEM) broth at NaCl concentrations of 2 (basal concentration), 100, 300, 500 and 600 mM, and their specific growth rates, cell dry weight and lag times were determined. Twenty of the 25 isolates were also grown in YEM broth under anaerobic conditions with or without 10 mM KNO3. Three categories of NaCl salinity responses were observed: (1) eight isolates showed decreased specific growth rates at NaCl concentrations of 100, 300 and 500 mM, but they nevertheless remained viable at 500 mM NaCl concentration; (2) the specific growth rate of six isolates increased significantly at 100 and 300 mM NaCl; and (3) specific growth rates of two isolates were significantly greater than the base-rate at all concentrations of NaCl. Five of 11 of the Bradyrhizobium isolates tested respired NO3−, but showed no growth. Seven Rhizobium isolates, three from the deep (3.9-5 m) phreatic rhizobial community, and four from the surface community denitrified NO3− but only the isolates from the phreatic community displayed anaerobic growth. Long-term interactions between rhizobial and bradyrhizobial communities and the surface and phreatic root environments of the mature Sonoran Desert mesquite woodland appear to have selected for strains of NO3− respiring rhizobia, general salt tolerance of both rhizobial and bradyrhizobial symbionts, and strains of weak facultative halophilic bradyrhizobia. These survival characteristics of mesquite rhizobia may be important regarding mesquite's establishment and long-term productivity in marginal desert soils, and may provide novel types of rhizobia for food crops growing in harsh environments.  相似文献   

17.

Purpose  

The oxidation of ammonium (NH4+) to nitrate (NO3−) in the soil is an important biogeochemical process, which has major environmental implications as it can contribute to NO3− leaching and nitrous oxide (N2O) emissions. Nitrification inhibitors have been used to slow down this process to reduce NO3− leaching and N2O emissions from agricultural land. The objective of this study was to determine the effectiveness of a liquid formulation of 3,4-Dimethylpyrazole phosphate (DMPP) compared with a dicyandiamide (DCD) solution in inhibiting the growth of ammonium-oxidizing bacteria (AOB) and ammonium oxidizing archaea (AOA) and slowing down the rate of NH4+ oxidation in soil.  相似文献   

18.
氮肥对稻田土壤反硝化细菌群落结构和丰度的影响   总被引：5，自引：1，他引：5  
以氮肥田间定位试验为研究对象,利用PCR-DGGE(聚合酶链反应变性梯度凝胶电泳)和荧光定量PCR(real-time PCR)技术,通过对反硝化细菌nirS基因的检测,分析了定位试验第2年稻田反硝化细菌群落结构和丰度的变化。DGGE图谱及依据其条带位置和亮度数字化数值进行的主成分分析(PCA)结果均显示:在氮肥定位试验第2年,与不施肥对照(CK)比较,在水稻各个生育期(分蘖期、齐穗期和成熟期)内,施用氮肥[150kg(N)·hm-2]的稻田根层土或表土中的反硝化细菌群落结构均无明显变化;且稻田根层土或表土中的反硝化细菌群落结构在水稻各个生育期间也均无明显差异。荧光定量PCR结果显示,在水稻生长发育过程中,施用氮肥的稻田根层土或表土中的反硝化细菌nirS基因拷贝数始终显著(P<0.05)高于其对应的不施肥对照。此外,无论施用氮肥与否,根层土中的反硝化细菌nirS基因拷贝数在水稻成熟期时都会显著(P<0.05)降低;但表土中的nirS基因拷贝数在水稻各生育期间无明显变化;且水稻成熟期时施用氮肥和不施肥的稻田表土中nirS基因拷贝数都显著(P<0.05)高于根层土。同时,与对照比较施用氮肥可促进水稻增产44%。研究表明,短期定位试验中施用氮肥能够显著提高稻田土壤反硝化细菌的丰度,但对其群落结构没有明显影响。  相似文献   

19.
Land-use and management practices can affect soil nitrification. However, nitrifying microorganisms responsible for specific nitrification process under different land-use soils remains unknown. Thus, we investigated the relative contribution of bacteria and fungi to specific soil nitrification in different land-use soils (coniferous forest, upland fields planted with corn and rice paddy) in humid subtropical region in China. 15N dilution technique in combination with selective biomass inhibitors and C2H2 inhibition method were used to estimate the relative contribution of bacteria and fungi to heterotrophic nitrification and autotrophic nitrification in the different land-use soils in humid subtropical region. The results showed that autotrophic nitrification was the predominant nitrification process in the two agricultural soils (upland and paddy), while the nitrate production was mainly from heterotrophic nitrification in the acid forest soil. In the upland soils, streptomycin reduced autotrophic nitrification by 94%, whereas cycloheximide had no effect on autotrophic nitrification, indicating that autotrophic nitrification was mainly driven by bacteria. However, the opposite was true in another agricultural soil (paddy), indicating that fungi contributed to the oxidation of NH4+ to NO3?. In the acid forest soil, cycloheximide, but not streptomycin, inhibited heterotrophic nitrification, demonstrating that fungi controlled the heterotrophic nitrification. The conversion of forest to agricultural soils resulted in a shift from fungi-dominated heterotrophic nitrification to bacteria- or fungi-dominated autotrophic nitrification. Our results suggest that land-use and management practices, such as the application of N fertilizer and lime, the long-term waterflooding during rice growth, straw return after harvest, and cultivation could markedly influence the relative contribution of bacteria and fungi to specific soil nitrification processes.  相似文献   

20.
长期定位施肥对黑垆土剖面养分分布特征的影响   总被引：17，自引：4，他引：17  
对黄土高原旱地 15年连续施肥后土壤剖面养分分布的研究发现 ,施化肥对土壤剖面有机质、全N、全P含量的影响深达 100cm以下 ,所有施肥处理有机质、全N、全P、NO3--N、有效P含量在耕层 (0～20cm)都有不同程度增加 ;40～60、60～80cm土层有机质、全N、全P都低于长年不施肥处理 ,造成土壤下层养分的亏缺。长期大量施用氮肥造成N素养分下淋累积 ;长期大量施用磷肥土壤耕层有效P显著提高 ,而 20cm以下土层变化不大。  相似文献   

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