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1.
Microbial response to the addition of glucose in low-fertility soils   总被引:1,自引:0,他引:1  
Addition of soluble organic substrates to soil has been shown to either increase or restrict the rate of microbial CO2–C evolution. This has been attributed to a priming effect resulting from accelerated or decreased turnover of the soil organic matter including the soil microflora. We investigated microbial responses to small glucose-C additions (10–50 μg C g1 soil) in arable soils either amended or not with cellulose. An immediate CO2–C release between 0 and 69 h (equivalent to 59% of glucose-C applied) was measured. However, only half of the CO2–C respired could be attributed to the utilisation of glucose-C substrate, based on the percentage of 14C–CO2 evolved after the addition of a 14C-labelled glucose tracer. Thus, although no evidence of an immediate release of ‘extra’ C above the rate applied as glucose-C was observed, the pattern of decomposition for 14C-glucose suggested utilisation of an alternate C source. Based on this, a positive priming effect (1.5 to 4.3 times the amount CO2–C evolved that was attributed to glucose-C decomposition) was observed for at least 170 h in non-cellulose-amended soil and 612 h in cellulose-amended soil. Two further phases of microbial activity in cellulose-amended soils were attributed to either activation of different microbial populations or end-product inhibition of cellulase activity after glucose addition. During these subsequent phases, a negative priming effect of between 0.1 and 1.5 times was observed. Findings indicate that the response of the microbial community to small additions of soluble organic C substrate is not consistent and support the premise that microbial response varies in a yet to be predicted manner between soil type and ecosystems. We hypothesise that this is due to differences in the microbial community structure activated by the addition of organic C and the timing of soluble organic substrate addition with respect to the current dissolved organic C status of the soil.  相似文献   

2.
Soil microbial biomass data derived from fumigation–extraction (FE), substrate-induced respiration (SIR) and ATP estimations differed significantly and were significantly correlated, which agrees to previous studies. In a second step, the SIR/FE, ATP/FE and SIR/ATP ratios were calculated to evaluate the glucose-responsive and active component of the microbial (active and resting) biomass and the glucose-responsive component of the active microbiota. Soils were sampled along gradients within and between associated ecosystems in Northern Germany, Denmark and along a gradient of heavy metal pollution in Finland. The ratios indicated that the active portion and glucose-responsive component decreased with proceeding litter decomposition, higher degree of sustainable land management practices and higher degree of heavy metal contamination. This work was presented at the workshop ‘Non-molecular manipulation of soil microbial communities’ at the University of Udine, Udine, Italy, 17–20 October 2004; convened by P.C. Brookes and M. De Nobili and supported by European Science Foundation.  相似文献   

3.
 Soil microbial biomass and the emission of CO2 from the soil surface were measured in yellow soils (Ultisols) of the karst areas of southwest China. The soils are relatively weathered, leached and impoverished, and have a low input of plant residues. The measurements were made for a 1-year period and show a reciprocal relationship between microbial biomass and surface CO2 efflux. The highest (42.6±2.8 mg CO2-C m–2 h–1) and lowest (15.6±0.6 mg CO2-C m–2 h–1) CO2 effluxes are found in the summer and winter, respectively. The cumulative CO2 efflux is 0.24 kg CO2-C m–2 year–1. There is also a marked seasonal variation in the amount of soil microbial biomass carbon, but with the highest (644±71 μg C g–1 soil) and lowest (270±24 μg C g–1 soil) values occurring in the winter and summer, respectively. The cumulative loss of soil microbial biomass carbon in the top 10 cm of the soil was 608 μg C g–1 year–1 soil over 17 sampling times. The mean residence time of microbial biomass is estimated at 105 days, suggesting that the carbon in soil microbial biomass may act as a source of the CO2 released from soils. Received: 13 July 1999  相似文献   

4.
During the first few days after rewetting of an air-dried soil (AD-RW), microbial activity increases compared to that in the original moist soil, causing increased mineralisation (a flush) of soil organic carbon (C) and other nutrients. The AD-RW flush is believed to be derived from the enhanced mineralisation of both non-biomass soil organic matter (due to its physical release and enhanced availability) and microbial biomass killed during drying and rewetting. Our aim was to determine the effects of AD-RW on the mineralisation of soil organic matter and microbial biomass during and after repeated AD-RW cycles and to quantify their proportions in the CO2-C flushes that resulted. To do this, a UK grassland soil was amended with 14C-labelled glucose to label the biomass and then given five AD-RW cycles, each followed by 7 d incubation at 25 °C and 50% water holding capacity. Each AD-RW cycle increased the amount of CO2-C evolved (varying from 83 to 240 μg g−1 soil), compared to the control with, overall, less CO2-C being evolved as the number of AD-RW cycles increased. In the first cycle, the amount of biomass C decreased by 44% and microbial ATP by 70% while concentrations of extractable C nearly doubled. However, all rapidly recovered and within 1.3 d after rewetting, biomass C was 87% and ATP was 78% of the initial concentrations measured prior to air-drying. Similarly, by 2 d, extractable organic C had decreased to a similar concentration to the original. After the five AD-RW cycles, the amounts of total and 14C-labelled biomass C remaining in the soil accounted for 60 and 40% of those in the similarly incubated control soil, respectively. Soil biomass ATP concentrations following the first AD-RW cycle remained remarkably constant (ranging from about 10 to 14 μmol ATP g−1 biomass C) and very similar to the concentration in the fresh soil prior to air-drying. We developed a simple mathematical procedure to estimate the proportion of CO2-C derived from biomass C and non-biomass C during AD-RW. From it, we estimate that, over the five AD-RW cycles, about 60% of the CO2-C evolved came from mineralisation of non-biomass organic C and the remainder from the biomass C itself.  相似文献   

5.
High concentrations of Se in soil might have negative effects on microorganisms. For this reason, the effect of organic substrate addition (glucose + maize straw) on Se volatilisation in relation to changes in microbial biomass and activity indices was investigated using an artificially Se-contaminated soil. Microbial biomass N was reduced on average by more than 50% after substrate addition, but adenylate energy charge (AEC) and metabolic quotient qCO2 were both increased. The Se content decreased by nearly 30% only with the addition of the organic substrate at 25°C. No significant Se loss occurred without substrate at 25°C or with substrate at 5°C. In the two treatments with substrate addition, the substrate-derived CO2 evolution was about 30% lower with Se addition than without. In contrast, Se had no effect on any of the other soil microbial indices analysed, i.e. microbial biomass C, microbial biomass N, adenosine triphosphate (ATP), AEC, ATP-to-microbial biomass C, and qCO2.  相似文献   

6.
This study examines the effects of atrazine on both microbial biomass C and C mineralization dynamics in two contrasting agricultural soils (organic C, texture, and atrazine application history) located at Galicia (NW Spain). Atrazine was added to soils, a Humic Cambisol (H) and a Gleyic Cambisol (G), at a recommended agronomic dose and C mineralization (CO2 evolved), and microbial biomass measurements were made in non-treated and atrazine-treated samples at different time intervals during a 12-week aerobic incubation. The cumulative curves of CO2–C evolved over time fit the simple first-order kinetic model [Ct = Co (1 − e kt )], whose kinetic parameters were quantified. Differences in these parameters were observed between the two soils studied; the G soil, with a higher content in organic matter and microbial biomass C and lower atrazine application history, exhibited higher values of the total C mineralization and the potentially mineralizable labile C pool than those for the H soil. The addition of atrazine modified the kinetic parameters and increased notably the C mineralized; by the end of the incubation the cumulative CO2–C values were 33–41% higher than those in the corresponding non-added soils. In contrast, a variable effect or even no effect was observed on the soil microbial biomass following atrazine addition. The data clearly showed that atrazine application at normal agricultural rates may have important implications in the C cycling of these two contrasting acid soils.  相似文献   

7.
 Fatty acid methyl ester (FAME) profiles, together with Biolog substrate utilization patterns, were used in conjunction with measurements of other soil chemical and microbiological properties to describe differences in soil microbial communities induced by increased salinity and alkalinity in grass/legume pastures at three sites in SE South Australia. Total ester-linked FAMEs (EL-FAMEs) and phospholipid-linked FAMEs (PL-FAMEs), were also compared for their ability to detect differences between the soil microbial communities. The level of salinity and alkalinity in affected areas of the pastures showed seasonal variation, being greater in summer than in winter. At the time of sampling for the chemical and microbiological measurements (winter) only the affected soil at site 1 was significantly saline. The affected soils at all three sites had lower organic C and total N concentrations than the corresponding non-affected soils. At site 1 microbial biomass, CO2-C respiration and the rate of cellulose decomposition was also lower in the affected soil compared to the non-affected soil. Biomarker fatty acids present in both the EL- and PL-FAME profiles indicated a lower ratio of fungal to bacterial fatty acids in the saline affected soil at site 1. Analysis of Biolog substrate utilization patterns indicated that the bacterial community in the affected soil at site 1 utilized fewer carbon substrates and had lower functional diversity than the corresponding community in the non-affected soil. In contrast, increased alkalinity, of major importance at sites 2 and 3, had no effect on microbial biomass, the rate of cellulose decomposition or functional diversity but was associated with significant differences in the relative amounts of several fatty acids in the PL-FAME profiles indicative of a shift towards a bacterial dominated community. Despite differences in the number and relative amounts of fatty acids detected, principal component analysis of the EL- and PL-FAME profiles were equally capable of separating the affected and non-affected soils at all three sites. Redundancy analysis of the FAME data showed that organic C, microbial biomass, electrical conductivity and bicarbonate-extractable P were significantly correlated with variation in the EL-FAME profiles, whereas pH, electrical conductivity, NH4-N, CO2-C respiration and the microbial quotient were significantly correlated with variation in the PL-FAME profiles. Redundancy analysis of the Biolog data indicated that cation exchange capacity and bicarbonate-extractable K were significantly correlated with the variation in Biolog substrate utilization patterns. Received: 8 March 2000  相似文献   

8.
Salinity and sodicity effects on respiration and microbial biomass of soil   总被引:4,自引:2,他引:2  
An understanding of the effects of salinity and sodicity on soil carbon (C) stocks and fluxes is critical in environmental management, as the areal extents of salinity and sodicity are predicted to increase. The effects of salinity and sodicity on the soil microbial biomass (SMB) and soil respiration were assessed over 12weeks under controlled conditions by subjecting disturbed soil samples from a vegetated soil profile to leaching with one of six salt solutions; a combination of low-salinity (0.5dSm−1), mid-salinity (10dSm−1), or high-salinity (30dSm−1), with either low-sodicity (sodium adsorption ratio, SAR, 1), or high-sodicity (SAR 30) to give six treatments: control (low-salinity low-sodicity); low-salinity high-sodicity; mid-salinity low-sodicity; mid-salinity high-sodicity; high-salinity low-sodicity; and high-salinity high-sodicity. Soil respiration rate was highest (56–80mg CO2-C kg−1 soil) in the low-salinity treatments and lowest (1–5mg CO2-C kg−1 soil) in the mid-salinity treatments, while the SMB was highest in the high-salinity treatments (459–565mg kg−1 soil) and lowest in the low-salinity treatments (158–172mg kg−1 soil). This was attributed to increased substrate availability with high salt concentrations through either increased dispersion of soil aggregates or dissolution or hydrolysis of soil organic matter, which may offset some of the stresses placed on the microbial population from high salt concentrations. The apparent disparity in trends in respiration and the SMB may be due to an induced shift in the microbial population, from one dominated by more active microorganisms to one dominated by less active microorganisms.  相似文献   

9.
The roles of microbial biomass (MBC) and substrate supply as well as their interaction with clay content in determining soil respiration rate were studied using a range of soils with contrasting properties. Total organic C (TOC), water-soluble organic carbon, 0.5 M K2SO4-extractable organic C and 33.3 mM KMnO4-oxidisable organic carbon were determined as C availability indices. For air-dried soils, these indices showed close relationship with flush of CO2 production following rewetting of the soils. In comparison, MBC determined with the chloroform fumigation-extraction technique had relatively weaker correlation with soil respiration rate. After 7 d pre-incubation, soil respiration was still closely correlated with the C availability indices in the pre-incubated soils, but poorly correlated with MBC determined with three different techniques—chloroform fumigation extraction, substrate-induced respiration, and chloroform fumigation-incubation methods. Results of multiple regression analyses, together with the above observations, suggested that soil respiration under favourable temperature and moisture conditions was principally determined by substrate supply rather than by the pool size of MBC. The specific respiratory activity of microorganisms (CO2-C/MBC) following rewetting of air-dried soils or after 7 d pre-incubation was positively correlated with substrate availability, but negatively correlated with microbial pool size. Clay content had no significant effect on CO2 production rate, relative C mineralization rate (CO2-C/TOC) and specific respiratory activity of MBC during the first week incubation of rewetted dry soils. However, significant protective effect of clay on C mineralization was shown for the pre-incubated soils. These results suggested that the protective effect of clay on soil organic matter decomposition became significant as the substrate supply and microbial demand approached to an equilibrium state. Thereafter, soil respiration would be dependent on the replenishment of the labile substrate from the bulk organic C pool.  相似文献   

10.
Low molecular weight carbon (C) substrates are major drivers of bacterial activity and diversity in the soil environment. However, it is not well understood how specific low molecular weight C compounds, which are frequently found in root exudates and litter leachates, influence bacterial community structure or if there are specific groups of soil bacteria that preferentially respond to these C inputs. To address these knowledge gaps, we added three simple C substrates representative of common root exudate compounds (glucose, glycine, and citric acid) to microcosms containing three distinct soils from a grassland, hardwood forest, and coniferous forest. CO2 production was assessed over a 24 h incubation period and, at the end of the incubation, DNA was extracted from the samples for assessment of bacterial community structure via bar-coded pyrosequencing of the 16S rRNA gene. All three C substrates significantly increased CO2 production in all soils; however, there was no relationship between the magnitude of the increase in CO2 production and the shift in bacterial community composition. All three substrates had significant effects on overall community structure with the changes primarily driven by relative increases in β-Proteobacteria, γ-Proteobacteria, and Actinobacteria. Citric acid additions had a particularly strong influence on bacterial communities, producing a 2-5-fold increase in the relative abundance of the β-Proteobacteria subphylum. These results suggest that although community-level responses to substrate additions vary depending on the substrate and soil in question, there are specific bacterial taxa that preferentially respond to the substrate additions across soil types.  相似文献   

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