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1.
《Applied soil ecology》2011,47(3):329-334
The effects of rape oil application on soil microbial communities and phenanthrene degradation were characterized by examining phenanthrene concentrations, changes in microbial composition and incorporation of [13C] phenanthrene-derived carbon into phospholipid fatty acids (PLFAs). A Haplic Chernozem was incubated with and without rape oil in combination with and without phenanthrene over 60 days. High-performance liquid chromatography (HPLC) analysis showed a net reduction in extractable phenanthrene in the soils treated with rape oil but no net reduction in the soils without rape oil. Rape oil application increased the total PLFA content and changed microbial community composition predominantly due to growth of fungal groups and Gram-positive bacterial groups. Under rape oil and phenanthrene amendment all detected microbial groups grew until day 24 of incubation. The 13C PLFA profiles showed 13C enrichment for the PLFAs i14:0, 15:0, 18:0, 18:1ω5 and the fungal biomarker 18:2ω6,9 under rape oil application. Fungal PLFA growth was highest among detected all PLFAs, but its 13C incorporation was lower compared to the Gram-positive and Gram-negative bacteria PLFAs. Our results demonstrate the effect of rape oil application on the abundance of microbial groups in soil treated with phenanthrene and its impact on phenanthrene degradation.  相似文献   

2.

Purpose

Soil microorganisms are important in the cycling of plant nutrients. Soil microbial biomass, community structure, and activity are mainly affected by carbon substrate and nutrient availability. The objective was to test if both the overall soil microbial community structure and the community-utilizing plant-derived carbon entering the soil as rhizodeposition were affected by soil carbon (C) and nitrogen (N) availability.

Materials and methods

A 13C-CO2 steady-state labeling experiment was conducted in a ryegrass system. Four soil treatments were established: control, amendment with carboxymethyl cellulose (CMC), amendment with ammonium nitrate (NF), combined CMC and NF. Soil phospholipid fatty acid (PLFA) and 13C labeling PLFA were extracted and detected by isotope ratio mass spectrometer.

Results and discussion

The combined CMC and NF treatment with appropriate C/N ratio (20) significantly enhanced soil microbial biomass C and N, but resulted in lower soil inorganic N concentrations. There was no significant difference in soil PLFA profile pattern between different treatments. In contrast, most of the 13C was distributed into PLFAs 18:2ω6,9c, 18:1ω7c, and 18:1ω9c, indicative of fungi and gram-negative bacteria. The inorganic-only treatment was distinct in 13C PLFA pattern from the other treatments in the first period of labeling. Factor loadings of individual PLFAs confirmed that gram-positive bacteria had relatively greater plant-derived C contents in the inorganic-only treatment, but fungi were more enriched in the other treatments.

Conclusions

Amendments with CMC can improve N transformation processes, and the ryegrass rhizodeposition carbon flux into the soil microbial community is strongly modified by soil N availability.
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3.
Rhizodeposits have received considerable attention, as they play an important role in the regulation of soil carbon (C) sequestration and global C cycling and represent an important C and energy source for soil microorganisms. However, the utilization of rhizodeposits by microbial groups, their role in the turnover of soil organic matter (SOM) pools in rice paddies, and the effects of nitrogen (N) fertilization on rhizodeposition are nearly unknown. Rice (Oryza sativa L.) plants were grown in soil at five N fertilization rates (0, 10, 20, 40, or 60 mg N kg?1 soil) and continuously labeled in a 13CO2 atmosphere for 18 days during tillering. The utilization of root-derived C by microbial groups was assessed by 13C incorporation into phospholipid fatty acids. Rice shoot and root biomass strongly increased with N fertilization. Rhizodeposition increased with N fertilization, whereas the total 13C incorporation into microorganisms, as indicated by the percentage of 13C recovered in microbial biomass, decreased. The contribution of root-derived 13C to SOM formation increased with root biomass. The ratio of 13C in soil pools (SOM and microbial biomass) to 13C in roots decreased with N fertilization showing less incorporation and faster turnover with N. The 13C incorporation into fungi (18:2ω6,9c and 18:1ω9c), arbuscular mycorrhizal fungi (16:1ω5c), and actinomycetes (10Me 16:0 and 10Me 18:0) increased with N fertilization, whereas the 13C incorporation into gram-positive (i14:0, i15:0, a15:0, i16:0, i17:0, and a17:0) and gram-negative (16:1ω7c, 18:1ω7c, cy17:0, and cy19:0) bacteria decreased with N fertilization. Thus, the uptake and microbial processing of root-derived C was affected by N availability in soil. Compared with the unfertilized soil, the contribution of rhizodeposits to SOM and microorganisms increased at low to intermediate N fertilization rates but decreased at the maximum N input. We conclude that belowground C allocation and rhizodeposition by rice, microbial utilization of rhizodeposited C, and its stabilization within SOM pools are strongly affected by N availability: N fertilization adequate to the plant demand increases C incorporation in all these polls, but excessive N fertilization has negative effects not only on environmental pollution but also on C sequestration in soil.  相似文献   

4.
A 13C natural abundance experiment including GC-c-IRMS analysis of phospholipid fatty acids (PLFAs) was conducted to assess the temporal dynamics of the soil microbial community and carbon incorporation during the mineralization of plant residues under the impact of heavy metals and acid rain. Maize straw was incorporated into (i) control soil, (ii) soil irrigated with acid rain, (iii) soil amended with heavy metal-polluted filter dust and (iv) soil with both, heavy metal and acid rain treatment, over a period of 74 weeks. The mineralization of maize straw carbon was significantly reduced by heavy metal impact. Reduced mineralization rate of the added carbon likely resulted from a reduction of the microbial biomass due to heavy metal stress, while the efficiency of 13C incorporation into microbial PLFAs was hardly affected. Since acid rain did not significantly change soil pH, little impact on soil microorganisms and mineralization rate was found. Temporal dynamics of labelling of microbial PLFAs were different between bacterial and fungal PLFA biomarkers. Utilization of maize straw by bacterial PLFAs peaked immediately after the application (2 weeks), while labelling of the fungal biomarker 18:2ω6,9 was most pronounced 5 weeks after the application. In general, 13C labelling of microbial PLFAs was closely linked to the amounts of maize carbon present in the soil. The distinct higher labelling of microbial PLFAs in the heavy metal-polluted soils 74 weeks after application indicated a large fraction of available maize straw carbon still present in the soil.  相似文献   

5.
Root-derived rhizodeposits of recent photosynthetic carbon (C) are the foremost source of energy for microbial growth and development in rhizosphere soil. A substantial amount of photosynthesized C by the plants is translocated to belowground and is released as root exudates that influence the structure and function of soil microbial communities with potential inference in nutrient and C cycling in the ecosystem. We applied the 13C pulse chase labeling technique to evaluate the incorporation of rhizodeposit-C into the phospholipid fatty acids (PLFAs) in the bulk and rhizosphere soils of switchgrass (Panicum virgatum L.). Soil samples of bulk and rhizosphere were taken at 1, 5, 10 and 20 days after labeling and analyzed for 13C enrichment in the microbial PLFAs. Temporal differences of 13C enrichment in PLFAs were more prominent than spatial differences. Among the microbial PLFA biomarkers, fungi and Gram-negative (GM-ve) bacterial PLFAs showed rapid enrichment with 13C compared to Gram-positive (GM+ve) and actinomycetes in rhizosphere soil. The 13C enrichment of actinomycetes biomarker PLFA significantly increased along with sampling time in both soils. PLFAs indicative to fungi, GM-ve and GM+ve showed a significant decrease in 13C enrichment over sampling time in the rhizosphere, but a decrease was also observed in GM-ve (16:1ω5c) and fungal biomarker PLFAs in the bulk soil. The relative 13C concentration in fungal PLFA decreased on day 10, whereas those of GM-ve increased on day 5 and GM+ve remained constant in the rhizosphere soil. However, the relative 13C concentrations of GM-ve and GM+ve increased on days 5 and 10, respectively, and those of fungal remain constant in the bulk soil. The present study demonstrates the usefulness of 13C pulse chase labeling together with PLFA analysis to evaluate the active involvement of microbial community groups for utilizing rhizodeposit-C.  相似文献   

6.
Photosynthetically derived rhizodeposits are an important source of carbon (C) for microbes in root vicinity and can influence the microbial community dynamics. Pulse labeling of carbon dioxide (13CO2) coupled with stable isotope probing techniques have potential to track recently fixed photosynthate into rhizosphere microbial taxa. Therefore, the present investigation assessed the microbial community change associated with the rhizosphere and bulk soil in Jatropha curcas L. (a biofuel crop) by combining phospholipid fatty acid (13C-PLFA) profiling using a stable isotope 13CO2 labeling approach. The labeling (13C) took place after 45 days of germination, PLFAs were extracted from both soils (rhizosphere and bulk) after 1 and 20 days pulse labeling and analyzed by gas chromatography-isotope ratio mass spectrometry. There was no significant temporal effect on the PLFA profiles in the bulk soil, but significantly increased abundance of Gram positive (i15:0) and Gram negative (16:1ω7c and 16:1ω5c) biomarkers was observed in the rhizosphere soil from day 1 to day 20 after labeling. The Gram negative (16:1ω7c) decreased and fungal (18:2ω6,9c) increased significantly in rhizospheric soil compared to bulk soil after day 1 of labeling. Whereas, after 20 days of labeling, the Gram negative biomarker (16:1ω7c and 18:1ω7c) decreased and Gram positive (a15:0) increased significantly in rhizospheric soil compared to bulk soil. One day following labeling, i15:0, a15:0, i16:0, 16:1ω5c, 16:0, i17:0, a17:0, 18:2ω6,9c, 18:1ω9c, and 18:0 PLFAs were significantly more enriched in δ13C in the rhizosphere than in the bulk soil. Twenty days after labeling, 16:1ω5c (Gram negative) and 18:2ω6,9c (fungal) were significantly more enriched in δ13C in the rhizosphere than in the bulk soil. These results shows the effectives of PLFA coupled using the pulse chase labeling technique to examine the microbial community changes in response to recently fixed photosynthetic C flow in rhizodeposits.  相似文献   

7.
To identify the microbial communities responsible for the decomposition of rice straw compost in soil during the rice cultivation period, phospholipid fatty acid (PLFA) composition of rice straw compost was determined by periodically sampling the compost from a Japanese rice field under flooded conditions. About 21% of the compost was decomposed within a period of 3 months. The total amount of PLFAs, as an indicator of microbial biomass, was significantly lower under drained conditions than under flooded conditions and was relatively constant during the flooding period. This indicates that the microbial biomass in the compost samples did not increase during the gradual decomposition of rice straw compost under flooded conditions. The proportion of branched-chain PLFAs (biomarker of Grampositive and anaerobic Gram-negative bacteria) slightly decreased during the early period after placement, and increased gradually afterwards. Among the branched-chain PLFAs, i15:0, ail5:0, i16:0 and i17:0 PLFAs predominated and their proportions increased gradually except for i16:0. The proportion of straight mono-unsaturated PLFAs (biomarker of Gramnegative bacteria) was almost constant throughout the period, and 18:1ω9 and 18:1ω7 PLFAs predominated. The proportion of straight poly-unsaturated PLFAs as a biomarker of eukaryotes including fungi was also constant throughout the period, except for a decrease under drained conditions. Straight poly-unsaturated PLFAs consisted mainly of 18:2ω6c PLFA. Therefore, these results suggest that the proportions of Gram-positive and anaerobic Gram-negative bacteria increased during the decomposition of rice straw compost in flooded paddy field. Statistical analyses enabled to divide PLFA patterns of microbiota in the rice straw compost into two groups, one group consisting of rice straw compost samples collected before mid-season drainage and the other of samples collected after mid-season drainage. Small squared distances among samples in cluster analysis indicated that the community structure of microbiota was similar to each other as a whole. These results suggest that the microbial communities changed gradually during the period of placement, and that mid-season drainage may have affected the community structure of microbiota. Principal component analysis of the PLFA composition suggested that the succession of microbiota along with the decomposition in flooded soil was similar between rice straw compost and rice straw and that the changes in the community structure during the decomposition in flooded soil were more conspicuous for rice straw than for rice straw compost.  相似文献   

8.
The microbiota in the percolating water from the plow layer soil in paddy fields was studied based on the composition of phospholipid fatty acids (PLFAs) in a pot experiment. The mean concentrations of PLFAs in the percolating water were 17±5 and 11±4 µg L-1 in the planted and non-planted pots, respectively. The dominant PLFAs in the percolating water were 16: 0, 16: 1ω7c, 18: 1ω7, 18: 1ω9, il5: 0, and ail5: 0 PLFAs in both the planted and non-planted pots. The dominance percentage of 18: 3ω6c and 17: 1ω8 PLFAs increased at the late stage of rice growth in the planted pots. The percolating water from the planted pots contained in a higher percentage of straight mono-unsaturated PLFAs and a lower percentage of branched-chain PLFAs than that from the non-planted pots. Considerable differences in the PLFA composition in the percolating water were observed between the planted and non-planted treatments and with the duration of the growth period. Principal component analysis indicated that the microbiota in the percolating water was derived from the microbiota in the floodwater and in the plow layer soil. Cluster analysis showed that the similarity of the PLFA composition in the percolating water to the PLFA composition in the plow layer soil was higher than that in the floodwater. The stress factor that was estimated from the trans/cis ratio of 16: 1ω7 PLFA was 0.08±0.04 and 0.14±0.05 in the percolating water from the planted and non-planted pots, respectively, which indicated that the degree of stress on the microbiota in the percolating water from the planted pots was low in a similar way to the degree of stress on the microbiota in the floodwater, while the degree in the percolating water from the non-planted pots was similar to that in the plow layer soil, respectively.  相似文献   

9.
We have compared the total microbial biomass and the fungal/bacterial ratio estimated using substrate-induced respiration (SIR) in combination with the selective inhibition technique and using the phospholipid fatty acid (PLFA) technique in a pH gradient (3.0-7.2) consisting of 53 mature broad-leaved forest soils. A fungal/bacterial biomass index using the PLFA technique was calculated using the PLFA 18:2ω6,9 as an indicator of fungal biomass and the sum of 13 bacterial specific PLFAs as indicator of the bacterial biomass. Good linear correlation (p<0.001) was found between the total microbial biomass estimated with SIR and total PLFAs (totPLFA), indicating that 1 mg biomass-C was equivalent to 130 nmol totPLFA. Both biomass estimates were positively correlated to soil pH. The fungal/bacterial ratio measured using the selective inhibition technique decreased significantly with increasing pH from about 9 at pH 3 to approximately 2 at pH 7, while the fungal/bacterial biomass index using PLFA measurements tended to increase slightly with increasing soil pH. Good correlation between the soil content of ergosterol and of the PLFA 18:2ω6,9 indicated that the lack of congruency between the two methods in estimating fungal/bacterial ratios was not due to PLFA 18:2ω6,9-related non-fungal structures to any significant degree. Several PLFAs were strongly correlated to soil pH (R2 values >0.8); for example the PLFAs 16:1ω5 and 16:1ω7c increased with increasing soil pH, while i16:0 and cy19:0 decreased. A principal component analysis of the total PLFA pattern gave a first component that was strongly correlated to soil pH (R2=0.85, p<0.001) indicating that the microbial community composition in these beech/beech-oak forest soils was to a large extent determined by soil pH.  相似文献   

10.
Compound specific stable isotope analysis (13C/12C ratio of fatty acids) was used to assess the allocation of plant carbon in soil microbiota, and to identify the trophic links to microbial grazers in an arable field with long-term mineral and organic fertilizer amendments. The feeding strategy of two dominant Collembola species, epedaphic Isotoma viridis and euedaphic Willemia anophthalma was determined. The investigation was conducted following a shift to amaranth, a C4 plant, after 27 years of continuous C3 crop rotation. The influence of new C4 plant carbon was observed in microbial phospholipids (PLFAs) with higher δ13C recorded in C4 amaranth than in C3 clover soils. The strongest enrichment occurred in the fungal PLFA 18:2ω6,9c and bacterial PLFA 18:1ω9t with 11.2‰ and 6.6‰, respectively. However, other bacterial PLFAs showed no isotopic change, suggesting that the microbial community simultaneously utilized “new” and “old” plant carbon. The δ13C of Collembola fatty acids displayed species specific lipid pattern, which was affected by crop type, but not fertilizer amendments. Isotopic separation of Collembola lipids from amaranth and clover plots was more distinct in I. viridis than W. anophthalma. With up to 18‰, the enrichment in Collembola lipids was stronger than in microbial PLFAs, pointing to a distinct incorporation of carbon resources originating from the actual plant residues. The δ13C pattern in I. viridis indicated trophic links with bacteria, saprotrophic fungi and plant tissues, while saprotrophic fungi and plant tissues were accountable for the patterns observed in W. anophthalma.  相似文献   

11.
Rhizodeposit-carbon (rhizo-C) serves as a primary energy and C source for microorganisms in the rhizosphere. Despite important progress in understanding the fate of rhizo-C in upland soils, little is known about microbial community dynamics associated with rhizo-C in flooded soils, especially depending on water regimes in rice systems. In this study, rice grown under non-flooded, continuously flooded and alternating water regimes was pulse labeled with 13CO2 and the incorporation of rhizo-C into specific microbial groups was determined by 13C in phospholipid fatty acids (PLFAs) at day 2 and 14 after the labeling.A decreased C released from roots under continuously flooded condition was accompanied with lower total 13C incorporation into microorganisms compared to the non-flooded and alternating water regimes treatments. Continuous flooding caused a relative increase of 13C incorporation in Gram positive bacteria (i14:0, i15:0, a15:0, i16:0, i17:0, a17:0). In contrast, Gram negative bacteria (16:1ω7c, 18:1ω7c, cy17:0, cy 19:0) and fungi (18:2ω6, 9c, 18:1ω9c) showed greater rhizo-C incorporation coupled with a higher turnover under non-flooded and alternating water regimes treatments. These observations suggest that microbial groups processing rhizo-C differed among rice systems with varying water regimes. In contrast to non-flooded and alternating water regimes, there was little to no temporal 13C change in most microbial groups under continuous flooding condition between day 2 and 14 after the labeling, which may demonstrate slower microbial processing turnover. In summary, our findings indicate that belowground C input by rhizodeposition and its biological cycling was significantly influenced by water regimes in rice systems.  相似文献   

12.
The objective of this study was to investigate changes in the composition of the soil microbial community brought about by urea application and differences in the incorporation of urea-derived C into the soil phospholipid fatty acid (PLFA) pool at differing soil pH. We selected four soils which ranged in pH from 3.9 to 7.8. 13C-labeled urea was applied at two concentrations 100 and 200 mg N kg?1 which represents commonly used and high levels of application. Significant hydrolysis of applied urea occurred within 2 h; less than 2 % of urea-C was retained in the soil with one exception, the fluvo-aquic soil at pH 7.8 amended with 200 mg kg?1 urea-N 3 days after urea application. According to principal component analysis (PCA), the effect of urea and incubation time on microbial community composition was far weaker than differences between the four soils due to their large differences in basic properties; the scores of PC2 were significantly correlated with pH values. The incorporation of 13C-urea to PLFAs increased with soil pH; this may be related to increases in the speciation of inorganic C into bicarbonate.13C label was primarily incorporated into 16:1ω5c, 16:0, and cy19:0 in red soil, pH 3.9; and into 16:1ω7c, 16:0, and 16:1ω5c in fluvo-aquic soil, pH 7.8. A wider range of PLFAs became labeled in the two paddy soils at pH 5.2 and 6.7. This suggests that the profile of PLFAs labeled from the application of 13C-urea may be affected by redox potential.  相似文献   

13.
Rhizodeposit-carbon provides a major energy source for microbial growth in the rhizosphere of grassland soils. However, little is known about the microbial communities that mediate the rhizosphere carbon dynamics, especially how their activity is influenced by changes in soil management. We combined a 13CO2 pulse-labeling experiment with phospholipid fatty acid (PLFA) analysis in differently managed Belgian grasslands to identify the active rhizodeposit-C assimilating microbial communities in these grasslands and to evaluate their response to management practices. Experimental treatments consisted of three mineral N fertilization levels (0, 225 and 450 kg N ha−1 y−1) and two mowing frequencies (3 and 5 times y−1). Phospholipid fatty acids were extracted from surface (0-5 cm) bulk (BU) and root-adhering (RA) soil samples prior to and 24 h after pulse-labeling and were analyzed by gas chromatography-combustion-isotope ratio mass spectrometry (GC-c-IRMS). Soil habitats significantly differed in microbial community structure (as revealed by multivariate analysis of mol% biomarker PLFAs) as well as in gram-positive bacterial rhizodeposit-C uptake (as revealed by greater 13C-PLFA enrichment following pulse-labeling in RA compared to BU soil in the 450N/5M treatment). Mowing frequency did not significantly alter the relative abundance (mol%) or activity (13C enrichment) of microbial communities. In the non-fertilized treatment, the greatest 13C enrichment was seen in all fungal biomarker PLFAs (C16:1ω5, C18:1ω9, C18:2ω6,9 and C18:3ω3,6,9), which demonstrates a prominent contribution of fungi in the processing of new photosynthate-C in non-fertilized grassland soils. In all treatments, the lowest 13C enrichment was found in gram-positive bacterial and actinomycetes biomarker PLFAs. Fungal biomarker PLFAs had significantly lower 13C enrichment in the fertilized compared to non-fertilized treatments in BU soil (C16:1ω5, C18:1ω9) as well as RA soil (all fungal biomarkers). While these observations clearly indicated a negative effect of N fertilization on fungal assimilation of plant-derived C, the effect of N fertilization on fungal abundance could only be detected for the arbuscular mycorrhizal fungal (AMF) PLFA (C16:1ω5). On the other hand, increases in the relative abundance of gram-positive bacterial PLFAs with N fertilization were found without concomitant increases in 13C enrichment following pulse-labeling. We conclude that in situ13C pulse-labeling of PLFAs is an effective tool to detect functional changes of those microbial communities that are dominantly involved in the immediate processing of new rhizosphere-C.  相似文献   

14.
Abstract

The amount and composition of phospholipid fatty acids (PLFAs) in the percolating water taken from different depths of soil (10 cm, PW10; 40 cm, PW40) and floodwater (FW) in a paddy field were compared during the period of rice cultivation. The amounts of PLFAs in PW10, PW40, and FW ranged from 22.6 to 46.2 μg L?1, from 22.3 to 54.5 μg L?1, and from 82.9 to 179.0 μg L?1, respectively. The PLFA profiles in PW10, PW40, and FW were similar to each other and 16 : 1ω7c, 18 : 1ω7, and 16 : 0 PLFAs were dominant components, irrespective of the sampling site and sampling time. High proportions of straight mono-unsaturated PLFAs ranging from 42.0 to 76.5% suggested that Gram-negative bacteria were the major members in the microbial communities of the water samples studied. A potential indicator of the environmental stresses imposed upon the microbiota that was represented by the trans vs. cis ratio of 16 : 17 PLFA was constantly low (< 0.05), indicating that the microbial communities at these sites were hardly stressed.  相似文献   

15.
We conducted a 13CO2 pulse-chase labelling experiment in a drained boreal organic (peat) soil cultivated with perennial crop, reed canary grass (RCG; Phalaris arundinacea) to study the flow of carbon from plants to soil microbes. Both limed and unlimed soils were studied, since liming is a common agricultural practice for acidic organic soils. Soil samples taken within three months after the labelling and three times in the following year were used for the δ13C analysis of microbial phospholipid fatty acids (PLFAs), root sugars and root lipids. We estimated the contribution of carbon from root exudates to microbial PLFA synthesis. The flow of carbon from plants to microbes was fast as the label allocation in PLFAs had a peak 1–3 days after labelling. The results showed that fungi were important in the incorporation of fresh, plant-derived carbon, including root sugars. None of the main microbial PLFA biomarker groups (fungi, Gram-positive bacteria, Gram-negative bacteria, arbuscular mycorrhizal fungi) was completely lacking label over the measurement period. One year after the labelling, when the labelled carbon was widely distributed into plant biomass and soil, bacterial biomarkers increased their share of the label allocation. Liming had a minor effect on the label allocation rate into PLFAs. The mixing model approach used to calculate the root exudate contribution to microbial biomass resulted in a highly conservative estimate of utilization of this important C-source (0–6.5%, with highest incorporation into fungi). In summary, the results of this study provide new information about the role of various microbial groups in the turnover of plant-derived, fresh carbon in boreal organic soil.  相似文献   

16.
Rice straw is a major organic material applied to rice fields. The microorganisms growing on rice-straw-derived carbon have not been well studied. Here, we applied 13C-labeled rice straw to submerged rice soil microcosms and analyzed phospholipid fatty acids (PLFAs) in the soil and percolating water to trace the assimilation of rice-straw-derived carbon into microorganisms. PLFAs in the soil and water were markedly enriched with 13C during the first 3 days of incubation, which indicated immediate incorporation of rice-straw-derived carbon into microbial biomass. The enrichment of PLFAs in the percolating water with 13C suggested that microorganisms other than the population colonizing rice straw also assimilated rice-straw-derived carbon or that some bacterial groups were selectively released from the straw. The microbial populations could be categorized into two communities based on the carbon isotope data of the PLFAs: those derived from rice straw and those derived from soil organic matter (SOM). The composition of the PLFAs from the two communities differed, which indicated the assimilation of rice-straw-derived carbon by a subset of microbial populations. The composition of rice-straw-derived PLFAs in the percolating water was also distinct from that in the soil.  相似文献   

17.
The influence of soil pH on the phospholipid fatty acid (PLFA) composition of the microbial community was investigated along the Hoosfield acid strip, Rothamsted Research, UK - a uniform pH gradient between pH 8.3 and 4.5. The influence of soil pH on the total concentration of PLFAs was not significant, while biomass estimated using substrate induced respiration decreased by about 25%. However, the PLFA composition clearly changed along the soil pH gradient. About 40% of the variation in PLFA composition along the gradient was explained by a first principal component, and the sample scores were highly correlated to pH (R2 = 0.97). Many PLFAs responded to pH similarly in the Hoosfield arable soil compared with previous assessments in forest soils, including, e.g. monounsaturated PLFAs 16:1ω5, 16:1ω7c and 18:1ω7, which increased in relative concentrations with pH, and i16:0 and cy19:0, both of which decreased with pH. Some PLFAs responded differently to pH between the soil types, e.g. br18:0. We conclude that soil pH has a profound influence on the microbial PLFA composition, which must be considered in all applications of this method to detect changes in the microbial community.  相似文献   

18.
The soil microbial communities of a landfill cover substrate, which was treated with landfill gas (100 l CH4 m?2 d?1) and landfill leachate for 1.5 years, were investigated by phospholipid fatty acid (PLFA), ergosterol and respiratory quinone analyses. The natural 13C depletion of methane was used to assess the activity of methanotrophs and carbon turnover in the soil system. Under methane addition, the soil microbial community was dominated by PLFAs (14:0 and 16:1 isomers) and quinones (ubiquinone-8 and 18-methylene-ubiquinone-8) related to type I methanotrophs, and 18:1 PLFAs contained in type II methanotrophs. While type I methanotrophic PLFAs were 13C depleted, i.e. type I methanotrophs were actively oxidising and assimilating methane, 13C depletion of 18:1 PLFAs was low and inconsistent with their abundance. This, possibly reflects isotopic discrimination, assimilation of carbon derived from type I methanotrophs and a high contribution of non-methanotrophic bacteria to the 18:1 isomers. Landfill leachate irrigation caused the methanotrophic community to shift closer to the soil surface. It also decreased 18:1 PLFAs, while type I methanotrophs were probably stimulated. Gram positive bacteria, but not fungi, were also 13C depleted and consequently involved in the secondary turnover of carbon originating from methanotrophic bacteria. Cy17:0 PLFA was 13C depleted in deep soil layers, indicating anaerobic methane oxidation.  相似文献   

19.
Our aim was to determine whether the smaller biomasses generally found in low pH compared to high pH arable soils under similar management are due principally to the decreased inputs of substrate or whether some factor(s) associated with pH are also important. This was tested in a soil incubation experiment using wheat straw as substrate and soils of different pHs (8.09, 6.61, 4.65 and 4.17). Microbial biomass ninhydrin-N, and microbial community structure evaluated by phospholipid fatty acids (PLFAs), were measured at 0 (control soil only), 5, 25 and 50 days and CO2 evolution up to 100 days. Straw addition increased biomass ninhydrin-N, CO2 evolution and total PLFA concentrations at all soil pH values. The positive effect of straw addition on biomass ninhydrin-N was less in soils of pH 4.17 and 4.65. Similarly total PLFA concentrations were smallest at the lowest pH. This indicated that there is a direct pH effect as well as effects related to different substrate availabilities on microbial biomass and community structure. In the control soils, the fatty acids 16:1ω5, 16:1ω7c, 18:1ω7c&9t and i17:0 had significant and positive linear relationships with soil pH. In contrast, the fatty acids i15:0, a15:0, i16:0 and br17:0, 16:02OH, 18:2ω6,9, 17:0, 19:0, 17:0c9,10 and 19:0c9,10 were greatest in control soils at the lowest pHs. In soils given straw, the fatty acids 16:1ω5, 16:1ω7c, 15:0 and 18:0 had significant and positive linear relationships with pH, but the concentration of the monounsaturated 18:1ω9 PLFA decreased at the highest pHs. The PLFA profiles indicative of Gram-positive bacteria were more abundant than Gram-negative ones at the lowest pH in control soils, but in soils given straw these trends were reversed. In contrast, straw addition changed the microbial community structures least at pH 6.61. The ratio: [fungal PLFA 18:2w6,9]/[total PLFAs indicative of bacteria] indicated that fungal PLFAs were more dominant in the microbial communities of the lowest pH soil. In summary, this work shows that soil pH has marked effects on microbial biomass, community structure, and response to substrate addition.  相似文献   

20.
To better understand how residue quality and seasonal conditions influence the flow of C from both root and straw residues into the soil microbial community, we followed the incorporation of 13C-labeled crimson clover (Trifolium incarnatum) and ryegrass (Lolium multiflorum) root and straw residues into the phospholipid fatty acids (PLFA) of soil microbial biomass. After residue incorporation under field conditions in late summer (September), the 13C content of soil PLFA was measured in September, October, and November, 2002, and April and June, 2003. Multivariate non-metric multidimensional scaling techniques showed that the distribution of 13C among microbial PLFA differed among the four primary treatments (ryegrass straw and roots, clover straw and roots). Regardless of treatment, some PLFA remained poorly labeled with 13C throughout much of the study (16:1ω5, 10Me17:0; 0-5%), whereas other PLFA consistently contained a larger percentage of residue-derived C (16:0; 18:1ω9, 18:2ω6,9; 10-25%). The distribution of residue 13C among individual PLFA differed from the relative contributions of individual PLFA (mol%) to total PLFA-C, suggesting that a subset of the soil biomass was primarily responsible for assimilating residue-derived C. The distribution of 13C among soil PLFA differed between the sampling times, indicating that residue properties and soil conditions influenced which members of the community were assimilating residue-derived C. Our findings will provide the foundation for further studies to identify the nature of the community members responsible for residue decomposition at different times of the year, and what factors account for the dynamics of the community involved.  相似文献   

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