Variation in NH₄ mineralization and microbial communities with stand age in lodgepole pine (Pinus contorta) forests, Yellowstone National Park (USA)     

Erica A.H. Smithwick  Teri C. Balser 《Soil biology & biochemistry》2005,37(8):1546-1559

Soils and vegetation were analyzed in 20 lodgepole pine (Pinus contorta) forest stands, varying in age from 50 to 350 years, that had initiated following stand-replacing fire. Our goal was to determine how nitrogen availability (NH₄⁺-N) and microbial community composition varied with stand age-class and to determine whether differences could be explained by canopy, soil, or understory characteristics. Gross NH₄⁺ mineralization was measured using laboratory isotopic pool dilution, and microbial community composition was evaluated using microbial membrane lipids. The microbial community composition of stands in the 300-350 age class was distinct from stands in younger age classes. Microbial community composition among sites varied with pH, % organic matter, and phosphorus. Gross NH₄⁺ mineralization rates averaged 1.45±0.07 mg NH₄⁺ kg soil⁻¹ d⁻¹ while consumption averaged 1.37±0.20 mg NH₄⁺ kg soil⁻¹ d⁻¹, resulting in low net NH₄⁺ mineralization rates (0.08±0.18 mg NH₄⁺ kg soil⁻¹ d⁻¹), but rates were not significantly different with stand age-class at p<0.05. At p<0.10, net NH₄⁺ mineralization was significantly higher in the 300-350 age class compared to the 125-175 age class. None of the measured variables significantly explained NH₄⁺ consumption and net mineralization patterns. However, gross NH₄⁺ mineralization rates were best explained by information on microbial community structure (i.e. lipids). Variation among stands within a given age-classes was high, indicating that patterns of N cycling across landscapes reflect substantial heterogeneity among mature stands.  相似文献   

C and N turnover in structurally intact soils of different texture     

Ingrid K Thomsen  Per SchjønningJørgen E Olesen  Bent T Christensen 《Soil biology & biochemistry》2003,35(6):765-774

The turnover of native and applied C and N in undisturbed soil samples of different texture but similar mineralogical composition, origin and cropping history was evaluated at −10 kPa water potential. Cores of structurally intact soil with 108, 224 and 337 g clay kg⁻¹ were horizontially sliced and ¹⁵N-labelled sheep faeces was placed between the two halves of the intact core. The cores together with unamended treatments were incubated in the dark at 20 °C and the evolution of CO₂-C determined continuously for 177 d. Inorganic and microbial biomass N and ¹⁵N were determined periodically. Net nitrification was less in soil amended with faeces compared with unamended soil. When adjusted for the NO₃-N present in soil before faeces was applied, net nitrification became negative indicating that NO₃-N had been immobilized or denitrified. The soil most rich in clay nitrified least N and ¹⁵N. The amounts of N retained in the microbial biomass in unamended soils increased with clay content. A maximum of 13% of the faeces ¹⁵N was recovered in the microbial biomass in the amended soils. CO₂-C evolution increased with clay content in amended and unamended soils. CO₂-C evolution from the most sandy soil was reduced due to a low content of potentially mineralizable native soil C whereas the rate constant of C mineralization rate peaked in this soil. When the pool of potentially mineralizable native soil C was assumed proportional to volumetric water content, the three soils contained similar proportions of potentially mineralizable native soil C but the rate constant of C mineralization remained highest in the soil with least clay. Thus although a similar availability of water in the three soils was ensured by their identical matric potential, the actual volume of water seemed to determine the proportion of total C that was potentially mineralizable. The proportion of mineralizable C in the faeces was similar in the three soils (70% of total C), again with a higher rate constant of C mineralization in the soil with least clay. It is hypothesized that the pool of potentially mineralizable C and C rate constants fluctuate with the soil water content.  相似文献   

Impact of land-use types on soil nitrogen net mineralization in the sandstorm and water source area of Beijing,China   总被引：1，自引：0，他引：1  

Lilin Yang  Fusuo Zhang  Qiang Gao  Renzhao Mao  Xiaojing Liu 《CATENA》2010

Changes of land-use type (LUT) can affect soil nutrient pools and cycling processes that relate long-term sustainability of ecosystem, and can also affect atmospheric CO₂ concentrations and global warming through soil respiration. We conducted a comparative study to determine NH₄⁺ and NO₃⁻ concentrations in soil profiles (0–200 cm) and examined the net nitrogen (N) mineralization and net nitrification in soil surface (0–20 cm) of adjacent naturally regenerated secondary forests (NSF), man-made forests (MMF), grasslands and cropland soils from the windy arid and semi-arid Hebei plateau, the sandstorm and water source area of Beijing, China. Cropland and grassland soils showed significantly higher inorganic N concentrations than forest soils. NO₃⁻-N accounted for 50–90% of inorganic N in cropland and grassland soils, while NH₄⁺-N was the main form of inorganic N in NSF and MMF soils. Average net N-mineralization rates (mg kg⁻¹ d⁻¹) were much higher in native ecosystems (1.51 for NSF soils and 1.24 for grassland soils) than in human disturbed LUT (0.15 for cropland soils and 0.85 for MMF soils). Net ammonification was low in all the LUT while net nitrification was the major process of net N mineralization. For more insight in urea transformation, the increase in NH₄⁺ and, NO₃⁻ concentrations as well as C mineralization after urea addition was analyzed on whole soils. Urea application stimulated the net soil C mineralization and urea transformation pattern was consistent with net soil N mineralization, except that the rate was slightly slower. Land-use conversion from NSF to MMF, or from grassland to cropland decreased soil net N mineralization, but increased net nitrification after 40 years or 70 years, respectively. The observed higher rates of net nitrification suggested that land-use conversions in the Hebei plateau might lead to N losses in the form of nitrate.  相似文献   

Dynamics of microbial biomass and nitrogen supply during primary succession on blastfurnace slag dumps in dry tropics     

A Roy K.P Singh 《Soil biology & biochemistry》2003,35(3):365-372

This paper reports the role of microbial biomass in the establishment of N pools in the substratum during primary succession (till 40-year age) in Blastfurnace Slag Dumps, an anthropogenically created land form in the tropics. Initially in the depressions in the slag dumps fine soil particles (silt+clay) accumulate, retaining moisture therein, and providing microsites for the accumulation of microbial biomass. In all sites microbial biomass showed distinct seasonality, with summer-peak and rainy season-low standing crops. During the summer season microbial biomass C ranged from 18.6 μg g⁻¹ in the 1-year old site to ca. 235 μg g⁻¹ in the 40-year old site; correspondingly, microbial biomass N ranged from 1.22 to 40 μg g⁻¹. On sites 2.5-years of age and younger, the microbial biomass N content accounted for more than 50% of the organic N in the soil, whereas the proportion of microbial biomass N was ca. 7% of organic N in 40-year old site. The strong correlation between microbial biomass and total N in soil indicated a significant role of microbes in the build-up of nitrogen during the initial stages of succession in the slag dumps. Though the organic N pool in the soil was low (594 mg kg⁻¹) even after 40 years of succession, the available N (NH₄-N and NO₃-N) contents in the soil were generally high through the entire age series (ca. 16-32 μg g⁻¹) during the rainy season (which supports active growth of the herbaceous community). The high mineral-N status on the slag dump was related with high N-mineralization rates, particularly in the young sites (20.6 and 13.9 μg g⁻¹ month⁻¹ at 1 and 2.5-year age). We suggest that along with the abiotic factors having strong effect on ecosystem functioning, the microbial biomass, an important biotic factor, shows considerable influence on soil nutrient build-up during early stages of primary succession on the slag dumps. The microbial biomass dynamics initiates biotic control in developing slag dumps ecosystem through its effect on nitrogen pools and availability.  相似文献   

Basal organic phosphorus mineralization in soils under different farming systems     

Fritz Oehl  Andreas Fliessbach  Astrid Oberson 《Soil biology & biochemistry》2004,36(4):667-675

Soil organic P (P_o) mineralization plays an important role in soil P cycling. Quantitative information on the release of available inorganic P (P_i) by this process is difficult to obtain because any mineralized P_i gets rapidly sorbed. We applied a new approach to quantify basal soil P_o mineralization, based on ³³PO₄ isotopic dilution during 10 days of incubation, in soils differing in microbiological activity. The soils originated from a 20 years old field experiment, including a conventional system receiving exclusively mineral fertilizers (MIN), a bio-organic (ORG) and bio-dynamic (DYN) system. Indicators of soil microbiological activity, such as size and activity of the soil microbial biomass and phosphatase activity, were highest in DYN and lowest in MIN. In order to assess P_o hydrolysis driven by phosphatase in sterile soils, a set of soil samples was γ-irradiated. Basal P_o mineralization rates in non-irradiated samples were between 1.4 and 2.5 mg P kg⁻¹ day⁻¹ and decreased in the order DYN>ORG≥MIN. This is an amount lower, approximately equivalent to, or higher than water soluble P_i of MIN, ORG and DYN soils, respectively, but in every soil was less than 10% of the amount of P isotopically exchangeable during one day. This shows that physico-chemical processes are more important than basal mineralization in releasing plant available P_i. Organic P mineralization rates were higher, and differences between soils were more pronounced in γ-irradiated than in non-irradiated soils, with mineralization rates ranging from 2.2 to 4.6 mg P kg⁻¹ day⁻¹. These rates of hydrolysis, however, cannot be compared to those in non-sterile soils as they are affected by the release of cellular compounds, e.g. easily mineralizable P_o, derived from microbial cells killed by γ-irradiation.  相似文献   

Immobilization and remineralization of N following addition of wheat straw into soil: determination of gross N transformation rates by N-ammonium isotope dilution technique     

H. Shindo  T. Nishio 《Soil biology & biochemistry》2005,37(3):425-432

N dynamics in soil where wheat straw was incorporated were investigated by a soil incubation experiment using ¹⁵N-labelled nitrate or ¹⁵N-labelled wheat straw. The incubated soils were sampled after 7, 28, 54 days from the incorporation of wheat straw, respectively, and gross rates of N transformations including N remineralization and temporal changes in the amount of microbial biomass were determined.Following the addition of wheat straw into soils, rapid decrease of nitrate content in soil and increase of microbial biomass C and N occurred within the first week from onset of the experiment. Both the gross rates of mineralization and immobilization determined by ¹⁵N-ammonium isotope dilution technique were remarkably enhanced by the addition of wheat straw, and gradually decreased with time. Remineralization rate of N derived from ¹⁵N-labelled nitrate, and mineralization rate of N derived from ¹⁵N-labelled wheat straw was estimated by ¹⁵N isotope dilution technique using non-labelled ammonium. Remineralization rates of N derived from ¹⁵N-labelled nitrate were calculated to be 0.71 mg N kg⁻¹ d⁻¹ after 7 days, 0.55 mg N kg⁻¹ d⁻¹ after 28 days, and 0.29 mg N kg⁻¹ d⁻¹ after 54 days.Nearly 10% of the ¹⁵N-labelled N originally contained in the wheat straw was held in the microbial biomass irrespective of the sampling time. The amount of inorganic N in soil which was derived from ¹⁵N-labelled wheat straw ranged between 1.93 and 2.37 mg N kg⁻¹.Rates of N transformations in soil with ¹⁵N-labelled wheat straw were obtained by assuming that the k value was equal to the ¹⁵N abundance of biomass N, and the obtained values were considered to be valid.  相似文献   

Measuring microbial uptake of nitrogen in nutrient-amended sandy soils—A mass-balance based approach     

Song Qiu  Arthur J. McComb  Richard W. Bell 《Soil biology & biochemistry》2007,39(2):581-589

Soil microbial biomass N is commonly determined through fumigation-extraction (FE), and a conversion factor (K_EN) is necessary to convert extractable N to actual soil biomass N. Estimation of K_EN has been constrained by various uncertainties including potential microbial immobilisation. We developed a mass-balance approach to quantify changes in microbial N storage during nutrient-amended incubation, in which microbial uptake is determined as the residual in a ‘mass-balance’ based on soil-water N before and after amended incubation. The approach was applied to three sandy soils of southwestern Australia, to determine microbial N immobilisation during 5-day incubation in response to supply of 2.323 mg C g⁻¹, 100 μg N g⁻¹ and 20 μg P g⁻¹. The net N immobilisation was estimated to be 95-114 μg N g⁻¹ in the three soils, equivalent to 82.7-85.1% of soil-water N following the amendment. Such estimation for microbial uptake does not depend on fumigation and K_EN conversion, but for comparison purposes we estimated ‘nominal’ K_EN values (0.11-0.14) for the three soils, which were comparable to previously reported K_EN from soils receiving C and N amendment. The accuracy of our approach depends on the mass-balance equation and the integrated measurement errors of the multiple N pools, and was assessed practically through recoveries of added-N when microbial uptake can be minimised. Near-satisfactory recoveries were achieved under such conditions. Our mass-balance approach provides information not only about changes in the microbial biomass nitrogen storage, but also major N-pools and their fluxes in regulating soil N concentrations under substrate and nutrient amended conditions.  相似文献   

A mass-balance approach to measuring microbial uptake and pools of phosphorus in nutrient-amended soils     

S. Qiu  A.J. McComb  R.W. Bell 《Soil biology & biochemistry》2007,39(1):187-193

Soil microbial biomass P is usually determined through fumigation-extraction (FE), in which partially extractable P from lysed biomass is converted to biomass P using a conversion factor (K_p). Estimation of K_p has been usually based on cultured microorganisms, which may not adequately represent the soil microbial community in either nutrient-poor or in altered carbon and nutrient conditions following fertilisation. We report an alternative approach in which changes in microbial P storage are determined as the residual in a mass balance of extractable P before and after incubation. This approach was applied in three low-fertility sandy soils of southwestern Australia, to determine microbial P immobilisation during 5-day incubations in response to the amendment by 2.323 mg C g⁻¹, 100 μg N g⁻¹ and 20 μg P g⁻¹. The net P immobilisation during the amended incubations determined to be 18.1, 14.1 and 16.3 μg P g⁻¹ in the three soils, accounting for 70.6-90.5% of P added through amendment. Such estimates do not rely on fumigation and K_p values, but for comparison with the FE method we estimated ‘nominal’ K_p values to be 0.20-0.31 for the soils under the amended conditions. Our results showed that microbial P immobilisation was a dominant process regulating P concentration in soil water following the CNP amendment. The mass-balance approach provides information not only about changes in the microbial P compartment, but also about other major P-pools and their fluxes in regulating soil-water P concentrations under substrate- and nutrient-amended conditions.  相似文献   

Initial recovery of soil carbon and nitrogen pools and dynamics following disturbance in jack pine forests: A comparison of wildfire and clearcut harvesting     

Stephen D. LeDuc  David E. Rothstein 《Soil biology & biochemistry》2007,39(11):2865-2876

Forests naturally maintained by stand-replacing wildfires are often managed with clearcut harvesting, yet we know little about how replacing wildfire with clearcutting affects soil processes and properties. We compared the initial recovery of carbon (C) and nitrogen (N) pools and dynamics following disturbance in jack pine (Pinus banksiana) stands in northern Lower Michigan, USA, by sampling soils (Oa+A horizons) from three “treatments”: 3-6-year-old harvest-regenerated stands, 3-6-year-old wildfire-regenerated stands and 40-55-year-old intact, mature stands (n=4 stands per treatment). We measured total C and N; microbial biomass and potentially mineralizable C and N; net nitrification; and gross rates of N mineralization and nitrification. Burned stands exhibited reduced soil N but not C, whereas clearcut and mature stands had similar quantities of soil organic matter. Both disturbance types reduced microbial biomass C compared to mature stands; however, microbial biomass N was reduced in burned stands but not in clearcut stands. The experimental C and N mineralization values were fit to a first-order rate equation to estimate potentially mineralizable pool size (C₀ and N₀) and rate parameters. Values for C₀ in burned and clearcut stands were approximately half that of the mature treatment, with no difference between disturbance types. In contrast, N₀ was lowest in the wildfire stands (170.2 μg N g⁻¹), intermediate in the clearcuts (215.4 μg N g⁻¹) and highest in the mature stands (244.6 μg N g⁻¹). The most pronounced difference between disturbance types was for net nitrification. These data were fit to a sigmoidal growth equation to estimate potential NO₃⁻ accumulation (Nit_max) and kinetic parameters. Values of Nit_max in clearcut soils exceeded that of wildfire and mature soils (149.2 vs. 83.5 vs. 96.5 μg NO₃⁻-N g⁻¹, respectively). Moreover, the clearcut treatment exhibited no lag period for net NO₃⁻ production, whereas the burned and mature treatments exhibited an approximate 8-week lag period before producing appreciable quantities of NO₃⁻. There were no differences between disturbances in gross rates of mineralization or nitrification; rather, lower NO₃⁻ immobilization rates in the clearcut soils, 0.20 μg NO₃⁻ g⁻¹ d⁻¹ compared to 0.65 in the burned soils, explained the difference in net nitrification. Because the mobility of NO₃⁻ and NH₄⁺ differs markedly in soil, our results suggest that differences in nitrification between wildfire and clearcutting could have important consequences for plant nutrition and leaching losses following disturbance.  相似文献   

Microbial use of maize cellulose and sugarcane sucrose monitored by changes in the C/C ratio     

Brigitte Engelking  Rainer Georg Joergensen 《Soil biology & biochemistry》2007,39(8):1888-1896

An arable soil with organic matter formed from C₃-vegetation was amended initially with maize cellulose (C₄-cellulose) and sugarcane sucrose (C₄-sucrose) in a 67-day laboratory incubation experiment with microcosms at 25 °C. The amount and isotopic composition (¹³C/¹²C) of soil organic C, CO₂ evolved, microbial biomass C, and microbial residue C were determined to prove whether the formation of microbial residues depends on the quality of the added C source adjusted with NH₄NO₃ to the same C/N ratio of 15. In a subsequent step, C₃-cellulose (3 mg C g⁻¹ soil) was added without N to soil to determine whether the microbial residues formed initially from C₄-substrate are preferentially decomposed to maintain the N-demand of the soil microbial community. At the end of the experiment, 23% of the two C₄-substrates added was left in the soil, while 3% and 4% of the added C₄-cellulose and C₄-sucrose, respectively, were found in the microbial biomass. The addition of the two C₄-substrates caused a significant 100% increase in C₃-derived CO₂ evolution during the 5-33 day incubation period. The addition of C₃-cellulose caused a significant 50% increase in C₄-derived CO₂ evolution during the 38-67 day incubation period. The decrease in microbial biomass C₄-C accounted for roughly 60% of this increase. Cellulose addition promoted microorganisms strongly able to recycle N immediately from their own tissue by “cryptic growth” instead of incorporating NO₃⁻ from the soil solution. The differences in quality of the microbial residues produced by C₄-cellulose and C₄-sucrose decomposing microorganisms are also reflected by the difference in the rates of CO₂ evolution, but not in the rates of net N mineralization.  相似文献   

Microbial community composition and substrate use in a highly weathered soil as affected by crop rotation and P fertilization     

E.K. Bünemann  D.A. Bossio  P.C. Smithson  E. Frossard 《Soil biology & biochemistry》2004,36(6):889-901

A better understanding of soil microbial processes is required to improve the synchrony between nutrient release from plant residues and crop demand. Phospholipid fatty acid analysis was used to investigate the effect of two crop rotations (continuous maize and maize-crotalaria rotation) and P fertilization (0 and 50 kg P ha⁻¹ yr⁻¹, applied as triple superphosphate) on microbial community composition in a highly weathered soil from western Kenya. Microbial substrate use in soils from the field experiment was compared in incubation experiments. Higher levels of soil organic matter and microbial biomass in the maize-crotalaria rotation were connected with higher total amounts of phospholipid fatty acids and an increase in the relative abundances of indicators for fungi and gram-negative bacteria. P fertilization changed the community profile only within the continuous maize treatment. The decomposition of glucose, cellulose and three plant residues (all added at 2.5 g C kg⁻¹ soil) proceeded faster in soil from the maize-crotalaria rotation, but differences were mostly transient. Microbial P and N uptake within one week increased with the water-soluble carbon content of added plant residues. More P and N were taken up by the greater microbial biomass in soil from the maize-crotalaria rotation than from continuous maize. Re-mineralization of nutrients during the decline of the microbial biomass increased also with the initial biological activity of the soil, but occurred only for a high quality plant residue within the half year incubation period. Compared to the effect of crop rotation, P fertilization had a minor effect on microbial community composition and substrate use.  相似文献   

Responses of nitrogen transformation and microbial community composition to nitrogen enrichment patch   总被引：1，自引：0，他引：1  

Shu-Guang Wang  Yan-Lin Hou 《Pedobiologia》2010,54(1):9-17

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   

Soil microbial biomass C:N:P stoichiometry and microbial use of organic phosphorus     

《Soil biology & biochemistry》2015

Microbial mineralization and immobilization of nutrients strongly influence soil fertility. We studied microbial biomass stoichiometry, microbial community composition, and microbial use of carbon (C) and phosphorus (P) derived from glucose-6-phosphate in the A and B horizons of two temperate Cambisols with contrasting P availability. In a first incubation experiment, C, nitrogen (N) and P were added to the soils in a full factorial design. Microbial biomass C, N and P concentrations were analyzed by the fumigation-extraction method and microbial community composition was analyzed by a community fingerprinting method (automated ribosomal intergenic spacer analysis, ARISA). In a second experiment, we compared microbial use of C and P from glucose-6-phosphate by adding ¹⁴C or ³³P labeled glucose-6-phosphate to soil. In the first incubation experiment, the microbial biomass increased up to 30-fold due to addition of C, indicating that microbial growth was mainly C limited. Microbial biomass C:N:P stoichiometry changed more strongly due to element addition in the P-poor soils, than in the P-rich soils. The microbial community composition analysis showed that element additions led to stronger changes in the microbial community in the P-poor than in the P-rich soils. Therefore, the changed microbial biomass stoichiometry in the P-poor soils was likely caused by a shift in the microbial community composition. The total recovery of ¹⁴C derived from glucose-6-phosphate in the soil microbial biomass and in the respired CO₂ ranged between 28.2 and 37.1% 66 h after addition of the tracer, while the recovery of ³³P in the soil microbial biomass was 1.4–6.1%. This indicates that even in the P-poor soils microorganisms mineralized organic P and took up more C than P from the organic compound. Thus, microbial mineralization of organic P was driven by microbial need for C rather than for P. In conclusion, our experiments showed that (i) the microbial biomass stoichiometry in the P-poor soils was more susceptible to additions of C, N and P than in the P-rich soils and that (ii) even in the P-poor soils, microorganisms were C-limited and the mineralization of organic P was mainly driven by microbial C demand.  相似文献   

Microbial performance under increasing nitrogen availability in a Mediterranean forest soil     

D. Dalmonech  A. Lagomarsino  T. Chiti 《Soil biology & biochemistry》2010,42(9):1596-1606

In forest ecosystems, the external nitrogen (N) inputs mainly involve wet and dry depositions that potentially alter inorganic N availability in the soil and carbon (C) turnover. This study assesses the effect of a slow increase of inorganic N availability on microbial community activity and functionality in a Mediterranean forest soil. A four-month incubation experiment was performed with soil collected from the organic layer of a forest site and fertilized with a solution of ammonium nitrate. The fertilizer was supplied at an equivalent of 0, 10, 25, 50 and 75 kg N ha⁻¹ (0, 0.3, 0.7, 1.3 and 2 mg N g⁻¹ for control N0 and treatments N1, N2, N3 and N4, respectively). The incubation was carried out under optimal conditions, with the addition of the nutritive solution in small aliquots once a week to mimic the phenomenon of N deposition. In order to isolate the effect of N, the pH of the NH₄NO₃ solutions was adjusted to soil pH, and phosphorus was added in order to prevent any nutrient limitation effect. Inorganic N, C-mineralization, the activity of one oxidative enzyme (o-diphenol oxidase) and 8 hydrolitic enzymes (α-glucosidase, β-glucosidase, N-acetyl-β-d-glucosaminidase, cellulase, leucine amino-peptidase, acid phosphatase, butyric esterase and β-xylosidase) and the community level physiological profile (CLPP) were measured and analyzed during the whole incubation and at the end of the experiment as a proxy for microbial decomposition activity. In the first month, the highest N availability (N4) repressed the microbial respiration activity but stimulated microbial enzymatic activity, suggesting a change of C-pathways from spilling to enzymes and biomass investment. The treatments N1, N2 and N3 had no effect in the same period. Throughout the incubation, a general stress condition affected all the treated soils. As a consequence, treated soils exhibited higher respiration rates than the control. This was accompanied by a loss of functional diversity and an end-detected decline in biomass C. Although at the end of incubation most of the soil features showed a clear correlation with the inorganic N pool, the organic C content was strongly affected by different patterns of microbial activity during the experiment: the highest N treatment (N4) showed a lower C loss than the N3 treatment. Overall, the experiment showed how inorganic N availability can potentially alter the C cycle in a Mediterranean forest soil. The effect is non linear, depending on microbial community dynamics, on the community’s ability to adapt given the time scale of the process, and on N supply amount. Our study also revealed a common pattern in the short-term response to N addition in other, similar ecosystems with different climatic conditions.  相似文献   

Use of acetylene as a nitrification inhibitor to reduce biases in gross N transformation rates in a soil showing rapid disappearance of added ammonium     

Anke M. Herrmann  Ernst Witter  Thomas Kätterer 《Soil biology & biochemistry》2007,39(9):2390-2400

  相似文献   

Carbon and net nitrogen mineralisation in two forest soils amended with different concentrations of biuret     

J.M. Xue  R. SandsP.W. Clinton  T.W. PaynM.F. Skinner 《Soil biology & biochemistry》2003,35(6):855-866

Biuret is a known contaminant of urea fertilisers that might be useful as a slow release N fertiliser for forestry. We studied carbon (C), net nitrogen (N) mineralisation and soil microbial biomass C and N dynamics in two forest soils (a sandy loam and a silt loam) during a 16-week long incubation following application of biuret (C 23.3%, N 40.8%, O 30.0% and H 4.9%) at concentrations of 0, 2, 10, 100 and 1000 mg kg⁻¹ (oven-dried) soil to assess the potential of biuret as a slow-release N fertiliser. Lower concentrations of biuret specifically increased C mineralisation and soil microbial biomass C in the sandy loam soil, but not in the silt loam soil. A significant decrease of microbial biomass C was found in both soils at week 16 after biuret was applied at higher concentrations. C mineralisation declined with duration of incubation in both soils due to decreased C availability. Biuret at concentrations from 10 to 100 mg kg⁻¹ soil had a significantly positive priming effect on soil organic N mineralisation in both soils. The causes for the priming effects were related to the stimulation of microbial growth and activity at an early stage of the incubation and/or the death of microbes at a later stage, which was biuret-concentration-dependent. The patterns in NH₄⁺-N accumulation differed markedly between the two soils. Net N mineralisation and nitrification were much greater in the sandy loam soil than in the silt loam soil. However, the onset of net nitrification was earlier in the silt loam soil. Biuret might be a potential slow-release N source in the silt loam soil.  相似文献   

Respiration pattern and microbial use of field-grown transgenic Bt-maize residues     

Markus Raubuch  Katja Roose  Florian Wichern 《Soil biology & biochemistry》2007,39(9):2380-2389

A 49-day incubation experiment was carried out with the addition of field-grown maize stem and leaf residues to soil at three different temperatures (5, 15, and 25 °C). The aim was to study the effects of two transgenic Bt-maize varieties in comparison to their two parental non-Bt varieties on the mineralization of the residues, on their incorporation into the microbial biomass and on changes in the microbial community structure. The stem and leaf residues of Novelis-Bt contained 3.9 μg g⁻¹ dry weight of the Bt toxin Cry1Ab and those of Valmont-Bt only 0.8 μg g⁻¹. The residues of the two parental non-Bt varieties Nobilis and Prelude contained higher concentrations of ergosterol (+220%) and glucosamine (+190%) and had a larger fungal C-to-bacterial C ratio (+240%) than the two Bt varieties. After adding the Bt residues, an initial peak in respiration of an extra 700 μg CO₂-C g⁻¹ soil or 4% of the added amount was observed in comparison to the two non-Bt varieties at all three temperatures. On average of the four varieties, 19-38% of the maize C added was mineralized during the 49-day incubation at the three different temperatures. The overall mean increase in total maize-derived CO₂ evolution corresponded to a Q₁₀ value of 1.4 for both temperature steps, i.e. from 5 to 15 °C and from 15 to 25 °C. The addition of maize residues led to a strong increase in all microbial properties analyzed. The highest contents were always measured at 5 °C and the lowest at 25 °C. The variety-specific contents of microbial biomass C, biomass N, ATP and adenylates increased in the order Novelis-Bt ? Prelude<Valmont-Bt ? Nobilis. The mineralization of Novelis-Bt residues with the highest Bt concentration and lowest N concentration and their incorporation into the microbial biomass was significantly reduced compared to the parental non-Bt variety Nobilis. These negative effects increased considerably from 5 to 25 °C. The transgenic Bt variety Valmont did not show further significant effects except for the initial peak in respiration at any temperature.  相似文献   

The influence of two agricultural biostimulants on nitrogen transformations, microbial activity, and plant growth in soil microcosms     

Shu-Kang ChenClive A Edwards  Scott Subler 《Soil biology & biochemistry》2003,35(1):9-19

The influence of two experimental soil treatments, Z93 and W91, on nitrogen transformations, microbial activity and plant growth was investigated in soil microcosms. These compounds are commercially marketed fermentation products (Agspectrum) that are sold to be added to field soils in small amounts to promote nitrogen and other nutrient uptake by crops in USA. In laboratory microcosm experiments, soils were amended with finely ground alfalfa-leaves or wheat straw, or left unamended, in an attempt to alter patterns of soil nitrogen mineralization and immobilization. Soils were treated in the microcosms with Z93 and W91 at rates equivalent to the recommended field application rates, that range from 0.2 to 1.1 l ha⁻¹, (0.005-0.03 μl g⁻¹ soil). We measured their effects on soil microbial activity (substrate-induced respiration (SIR), dehydrogenase activity (DHA) and acid phosphatase activity (PHOS)), soil nitrogen pools (microbial biomass N, mineral N, dissolved organic N), and transformations (net N mineralization and nitrification, ¹⁵N dilution of the mineral N pool, and accumulation of mineral N on ion-exchange resins), and on wheat plant germination and growth (shoot and root biomass, shoot length, N uptake and ¹⁵N enrichment of shoot tissues), for up to 56 days after treatment. To follow the movement of nitrogen from inorganic fertilizer into plant biomass we used a ¹⁵N isotopic tracer. Most of the soil and plant responses to treatment with Z93 or W91 differed according to the type of organic amendment that was used. Soil treatment with either Z93 or W91 influenced phosphatase activity strongly but did not have much effect on SIR or DHA. Both chemicals altered the rates of decomposition and mineralization of organic materials in the soil, which was evidenced by significant increases in the rates of the decomposition of buried wheat straw, and by the acceleration of net, rates of N mineralization, relative to those of the controls. Soil nitrate availability increased at the end of the experiment in response to both chemical treatments. In alfalfa-amended soils, the final plant biomass was decreased significantly by treatment with W91. Increased plant growth and N-use efficiency in straw-amended soil, resulting from treatments with Z93 or W91, was linked to increased rates of N mineralization from indigenous soil organic materials. This supports the marketing of these compounds as promoters of N uptake at these low dosage inputs.  相似文献   

Sulphur immobilization and availability in soils assessed using isotope dilution     

Generose Nziguheba  Erik Smolders  Roel Merckx 《Soil biology & biochemistry》2005,37(4):635-644

Increasing recognition of S deficiency in soils has raised the need for understanding processes governing S cycling and availability in soils. However, the quantification of the two main processes of S cycling, i.e. mineralization and immobilization, remains difficult as these processes occur simultaneously. A modified isotope ³⁵SO₄ dilution technique was developed and used to measure the effect of sulphate (SO₄) fertilization on S mineralization and immobilization in planted (pot experiment with ryegrass (Lolium multiflorum L.)) and unplanted soils (incubation). The immobilization and mineralization of S was calculated from the dynamics of stable and labelled S in soil KH₂PO₄ extracts containing an anion exchange membrane that concentrates SO₄ and mainly excludes other S species. The mathematical analysis of the isotope dilution data differs from methods proposed earlier. The radiolabile S in unplanted soil (E value) and in ryegrass (L value) were used as a measure of total available S in soils. Sulphate immobilization rate significantly declined during incubation. Sulphate application reduced gross mineralization but surprisingly reduced SO₄ immobilization. The E value significantly increased during the incubation in all soils as a result of gross mineralization, e.g. from 3.8 mg S kg⁻¹ at day 0 to 11.5 mg S kg⁻¹ at day 43 in the sandy soil with no sulphate addition. A full recovery in the E value of S added in (+S) treatments was achieved. Similarly, radiolabile S in the above-ground ryegrass biomass (L value) increased with S addition, with a full recovery of added S. The E and L values nearly fit a 1:1 line suggesting identical S dynamics in a planted and unplanted soil. The method proposed has operational advantages compared to methods used earlier.  相似文献   

Biological degradation of pyrogenic organic matter in temperate forest soils     

《Soil biology & biochemistry》2012

Pyrogenic organic matter (PyOM), derived from the incomplete combustion of plant biomass and fossil fuels, has been considered one of the most stable pools of soil organic matter (SOM) and a potentially important terrestrial sink for atmospheric CO₂. Recent evidence suggests that PyOM may degrade faster in soil than previously thought, and can affect native SOM turnover rates. We conducted a six-month laboratory incubation study to better understand the processes controlling the degradation of PyOM in soils using dual-enriched (¹³C/¹⁵N) PyOM and its precursor wood (Pinus ponderosa). We examined the effects of soil type and inorganic N addition on PyOM and wood C and N mineralization rates, microbial C utilization patterns, and native SOM turnover rates. PyOM charred at 450 °C or its precursor pine wood was incubated in two temperate forest subsoils with contrasting short range order (SRO) clay mineralogy (granite versus andesite parent material). Duplicates of experimental treatments with and without PyOM added were sterilized and abiotic C mineralization was quantified. In a second incubation, PyOM or wood was incubated in granitic soil with and without added NH₄NO₃ (20 kg N ha⁻¹). The fate of ¹³C/¹⁵N-enriched PyOM and wood was followed as soil-respired ¹³CO₂ and total extractable inorganic ¹⁵N. The uptake of ¹³C from PyOM and wood by soil microbial community groups was quantified using ¹³C-phospholipids fatty acids (PLFA). We found that (1) The mean residence time (MRT) of PyOM-C was on a centennial time scale (390–600 yr) in both soil types; (2) PyOM-C mineralization was mainly biologically mediated; (3) Fungi more actively utilized wood-C than PyOM-C, which was utilized by all bacteria groups, especially gram (+) bacteria in the andesite (AN) soil; (4) PyOM-N mineralization was 2 times greater in granite (GR) than in AN soils; (5) PyOM additions did not affect native soil C or N mineralization rates, microbial biomass, or PLFA-defined microbial community composition in either soil; (6) The addition of N to GR soil had no effect on the MRT of C from PyOM, wood, or native SOM. The centennial scale MRT for PyOM-C was 32 times slower than that for the precursor pine wood-C or native soil C, which is faster than the MRT used in ecosystem models. Our results show that PyOM-C is readily utilized by all heterotrophic microbial groups, and PyOM-C and -N may be more dynamic in soils than previously thought.  相似文献