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1.
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   

2.
We combined microbial community phospholipid fatty acid (PLFA) analyses with an in situ stable isotope 13CO2 labelling approach to identify microbial groups actively involved in assimilation of root-derived C in limed grassland soils. We hypothesized that the application of lime would stimulate more rapid 13C assimilation and turnover in microbial PLFAs. Four and 8 d after label application, 18:1ω9, 18:2ω6,9 (fungal biomarkers) and 16:1ω7, 18:1ω7, 19:0cy (Gram-negative bacterial biomarkers) showed the most 13C enrichment and rapid turnover rates. This suggests that these microorganisms were assimilating recently-photosynthesized root C inputs to soils. Contrary to our hypothesis, liming did not affect assimilation or turnover rates of 13C-labelled C. 13C stable isotope pulse-labelling technique paired with analyses of PLFA microbial biomarkers shows promise for in situ investigations of microbial function in soils.  相似文献   

3.
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   

4.
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   

5.
磷脂脂肪酸(PLFA)是微生物细胞膜的重要组成成分,不同微生物群落可通过不同生化途径合成不同的PLFA,因此可选择某些PLFA作为微生物群落结构变化的生物标志物。PLFA与稳定性同位素~(13)C标记(~(13)C-PLFA)技术结合,不仅能够确定原位土壤环境中微生物群落组成,而且能够定向发掘土壤生态系统中参与碳源代谢过程的微生物群落,提供复杂群落中土壤微生物相互作用的信息,具有广阔的应用前景。其基本原理为:将富集~(13)C稳定同位素的基质加入土壤中,土壤中的某些微生物群落利用基质~(13)C合成PLFA,提取并纯化土壤微生物的PLFA,利用气相色谱-燃烧-同位素比例质谱(GC-C-IRMS)测定其~(13)C丰度,通过对比分析,从而获取微生物群落组成与其功能的直接信息。本文在介绍了~(13)C-PLFA原理的基础上,综述了该技术在光合同化碳的根际微生物利用、土壤有机质分解的激发效应、甲烷氧化、有机污染物降解、外源简单碳源和外源复杂碳源的微生物利用等方面的应用,对此项技术的优缺点进行了分析并展望了其未来应用。  相似文献   

6.
Plant species effects on microbial communities are attributed to changes in microbial community composition and biomass, and may depend on plant species specific differences in the quality of resources (carbon) inputs. We examined the idea that plant-soil feedbacks can be explained by a chance effect, which is the probability of a highly productive or keystone plant species is present in the community and will influence the functions more than the number of species per se. A 13C pulse labelling technique was applied to three plant species and a species mixture in a greenhouse experiment to examine the carbon flow from plants to soil microbial communities. The 13C label was given as CO2 to shoots of a legume (Lotus corniculatus), a forb (Plantago lanceolata), a grass (Holcus lanatus) and a mixture of the three species. Microbial phospholipid fatty acids (PLFA) was analysed in order to determine the biomass and composition of the soil microbial community. The incorporation of the stable isotope into soil microorganisms was determined through GC-IRMS analyses of the microbial PLFAs. Plant species identity did not influence the microbial biomass when determined as total carbon of microbial phospholipid fatty acids. However, the labelled carbon showed that the grass monoculture (H. lanatus) and the plant mixture allocated more 13C into bacteria and actinomycete biomass than the other plant species. H. lanatus monocultures had also the highest amounts of 13C allocated to AM-fungi and saprophytic fungi. The carbon allocation from plants to soil microorganisms in a plant species mixture can thus be explained by the presence of a highly productive species that influence soil functions.  相似文献   

7.
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   

8.
The overall processes by which carbon is fixed by plants in photosynthesis then released into the soil by rhizodeposition and subsequently utilized by soil micro-organisms, links the atmospheric and soil carbon pools. The objective of this study was to determine the plant derived 13C incorporated into the phospholipid fatty acid (PLFA) pattern in paddy soil, to test whether utilization of rice rhizodeposition carbon by soil micro-organisms is affected by soil water status. This is essential to understand the importance of flooded conditions in regulating soil microbial community structure and activity in wetland rice systems. Rice plants were grown in soil derived from a paddy system under controlled irrigation (CI), or with continuous waterlogging (CW). Most of the 13C-labelled rice rhizodeposition carbon was distributed into the PLFAs 16:0, 18:1ω7 and 18:1ω9 in both the CW and CI treatments. The bacterial PLFAs i15:0 and a15:0, both indicative of gram positive bacteria, were relatively more abundant in the treatments without rice plants. When rice plants were present rates of 13C-incorporation into i15:0 and a15:0 was slow; the microbes containing these PLFAs may derive most of their carbon from more recalcitrant C (soil organic matter). PLFAs, 18:1ω7 and 16:1ω7c, indicative of gram negative bacteria showed a greater amount incorporation of labelled plant derived carbon in the CW treatment. In contrast, 18:2ω6,9 indicative of fungi and 18:1ω9 indicative of aerobes but also potentially fungi and plant roots had greater incorporation in the CI treatment. The greater root mass concomitant with lower incorporation of 13C into the total PLFA pool in the CW treatment suggests that the microbial communities in wetland rice soil are limited by factors other than substrate availability in flooded conditions. In this study differing soil microbial communities were established through manipulating the water status of paddy soils. Steady state 13C labelling enabled us to determine that the microbial community utilizing plant derived carbon was also affected by water status.  相似文献   

9.
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   

10.
《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   

11.
Lumbricus terrestris is a deep-burrowing anecic earthworm that builds permanent, vertical burrows with linings (e.g., drilosphere) that are stable and long-lived microhabitats for bacteria, fungi, micro- and mesofauna. We conducted the first non-culture based field study to assess simultaneously the drilosphere (here sampled as 0–2 mm burrow lining) composition of microbial and micro/mesofaunal communities relative to bulk soil. Our study also included a treatment of surface-applied 13C- and 15N-labeled plant residue to trace the short-term (40 d) translocation of residue C and N into the drilosphere, and potentially the assimilation of residue C into drilosphere microbial phospholipid fatty acids (PLFAs). Total C concentration was 23%, microbial PLFA biomass was 58%, and PLFAs associated with protozoa, nematodes, Collembola and other fauna were 200-to-300% greater in the drilosphere than in nearby bulk soil. Principal components analysis of community PLFAs revealed that distributions of Gram-negative bacteria and actinomycetes and other Gram-positive bacteria were highly variable among drilosphere samples, and that drilosphere communities were distinct from bulk soil communities due to the atypical distribution of PLFA biomarkers for micro- and mesofauna. The degree of microbial PLFA 13C enrichment in drilosphere soils receiving 13C-labeled residue was highly variable, and only one PLFA, 18:1ω9c, was significantly enriched. In contrast, 11 PLFAs from diverse microbial groups where enriched in response to residue amendment in bulk soil 0–5 cm deep. Among control soils, however, a significant δ13C shift between drilosphere and bulk soil at the same depth (5–15 cm) revealed the importance of L. terrestris for translocating perennial ryegrass-derived C into the soil at depth, where we estimated the contribution of the recent grass C (8 years) to be at least 26% of the drilosphere soil C. We conclude that L. terrestris facilitates the translocation of plant C into soil at depth and promotes the maintenance of distinct soil microbial and faunal communities that are unlike those found in the bulk soil.  相似文献   

12.

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.
  相似文献   

13.
Partitioning of the quantities of C lost by leaf litter through decomposition into (i) CO2 efflux to the atmosphere and (ii) C input to soil organic matter (SOM) is essential in order to develop a deeper understanding of the litter-soil biogeochemical continuum. However, this is a challenging task due to the occurrence of many different processes contributing to litter biomass loss. With the aim of quantifying different fluxes of C lost by leaf litter decomposition, a field experiment was performed at a short rotation coppice poplar plantation in central Italy. Populus nigra leaf litter, enriched in 13C (δ13C ∼ +160‰) was placed within collars to decompose in direct contact with the soil (δ13C ∼ −26‰) for 11 months. CO2 efflux from within the collars and its isotopic composition were determined at monthly intervals. After 11 months, remaining litter and soil profiles (0-20 cm) were sampled and analysed for their total C and 13C content. Gas chromatography (GC), GC-mass spectrometry (MS) and GC-combustion-isotope ratio (GC/C/IRMS) were used to analyse phospholipid fatty acids (PLFA) extracted from soil samples to identify the groups of soil micro-organisms that had incorporated litter-derived C and to determine the quantity of C incorporated by the soil microbial biomass (SMB). By the end of the experiment, the litter had lost about 80% of its original weight. The fraction of litter C lost as an input into the soil (67 ± 12% of the total C loss) was found to be twice as much as the fraction released as CO2 to the atmosphere (30 ± 3%), thus demonstrating the importance of quantifying litter-derived C input to soils, in litter decomposition studies. The mean δ13C values of PLFAs in soil (δ13C = −12.5‰) showed sustained incorporation of litter-derived C after one year (7.8 ± 1.6% of total PLFA-C). Thus, through the application of stable 13C isotope analyses, we have quantified two major C fluxes contributing to litter decomposition, at macroscopic and microscopic levels.  相似文献   

14.
Microbial uptake and utilisation are the main transformation pathways of low molecular weight organic substances (LMWOS) in soil, but details on transformations are strongly limited. As various LMWOS classes enter biochemical cycles at different steps, we hypothesize that the percentage of their carbon (C) incorporation into microbial biomass and consequently stabilisation in soil are different.Representatives of the three main groups of LMWOS: amino acids (alanine, glutamate), sugars (glucose, ribose) and carboxylic acids (acetate, palmitate) – were applied at naturally-occurring concentrations into a loamy arable Luvisol in a field experiment. Incorporation of 13C from these LMWOS into extractable microbial biomass (EMB) and into phospholipid fatty acids (PLFAs) was investigated 3 d and 10 d after application. The microbial utilisation of LMWOS for cell membrane construction was estimated by replacement of PLFA-C with 13C.35–80% of initially applied LMWOS-13C was still present in the composition of soil organic matter after 10 days of experiment, with 10–24% of 13C incorporation into EMB at day three and 1–15% at day 10. Maximal incorporation of 13C into EMB was observed from sugars and the least from amino acids. Strong differences in microbial utilisation between LMWOS were observed mainly at day 10. Thus, despite similar initial rapid uptake by microorganisms, further metabolism within microbial cells accounts for the specific fate of C from various LMWOS in soils.13C from each LMWOS was incorporated into each PLFA. This reflects the ubiquitous utilisation of all LMWOS by all functional microbial groups. The preferential incorporation of palmitate into PLFAs reflects its role as a direct precursor for fatty acids. Higher 13C incorporation from alanine and glucose into specific PLFAs compared to glutamate, ribose and acetate reflects the preferential use of glycolysis-derived substances in the fatty acids synthesis.Gram-negative bacteria (16:1ω7c and 18:1ω7c) were the most abundant and active in LMWOS utilisation. Their high activity corresponds to a high demand for anabolic products, e.g. to dominance of pentose-phosphate pathway, i.e. incorporation of ribose-C into PLFAs. The 13C incorporation from sugars and amino acids into filamentous microorganisms was lower than into all prokaryotic groups. However, for carboxylic acids, the incorporation was in the same range (0.1–0.2% of the applied carboxylic acid 13C) as that of gram-positive bacteria. This may reflect the dominance of fungi and other filamentous microorganisms for utilisation of acidic and complex organics.Thus, we showed that despite similar initial uptake, C from individual LMWOS follows deviating metabolic pathways which accounts for the individual fate of LMWOS-C over 10 days. Consequently, stabilisation of C in soil is mainly connected with its incorporation into microbial compounds of various stability and not with its initial microbial uptake.  相似文献   

15.
This study coupled stable isotope probing with phospholipid fatty acid analysis (13C-PLFA) to describe the role of microbial community composition in the short-term processing (i.e., C incorporation into microbial biomass and/or deposition or respiration of C) of root- versus residue-C and, ultimately, in long-term C sequestration in conventional (annual synthetic fertilizer applications), low-input (synthetic fertilizer and cover crop applied in alternating years), and organic (annual composted manure and cover crop additions) maize-tomato (Zea mays - Lycopersicum esculentum) cropping systems. During the maize growing season, we traced 13C-labeled hairy vetch (Vicia dasycarpa) roots and residues into PLFAs extracted from soil microaggregates (53-250 μm) and silt-and-clay (<53 μm) particles. Total PLFA biomass was greatest in the organic (41.4 nmol g−1 soil) and similar between the conventional and low-input systems (31.0 and 30.1 nmol g−1 soil, respectively), with Gram-positive bacterial PLFA dominating the microbial communities in all systems. Although total PLFA-C derived from roots was over four times greater than from residues, relative distributions (mol%) of root- and residue-derived C into the microbial communities were not different among the three cropping systems. Additionally, neither the PLFA profiles nor the amount of root- and residue-C incorporation into the PLFAs of the microaggregates were consistently different when compared with the silt-and-clay particles. More fungal PLFA-C was measured, however, in microaggregates compared with silt-and-clay. The lack of differences between the mol% within the microbial communities of the cropping systems and between the PLFA-C in the microaggregates and the silt-and-clay may have been due to (i) insufficient differences in quality between roots and residues and/or (ii) the high N availability in these N-fertilized cropping systems that augmented the abilities of the microbial communities to process a wide range of substrate qualities. The main implications of this study are that (i) the greater short-term microbial processing of root- than residue-C can be a mechanistic explanation for the higher relative retention of root- over residue-C, but microbial community composition did not influence long-term C sequestration trends in the three cropping systems and (ii) in spite of the similarity between the microbial community profiles of the microaggregates and the silt-and-clay, more C was processed in the microaggregates by fungi, suggesting that the microaggregate is a relatively unique microenvironment for fungal activity.  相似文献   

16.
In this study we used compound specific 13C and 14C isotopic signatures to determine the degree to which recent plant material and older soil organic matter (SOM) served as carbon substrates for microorganisms in soils. We determined the degree to which plant-derived carbon was used as a substrate by comparison of the 13C content of microbial phospholipid fatty acids (PLFA) from soils of two sites that had undergone a vegetation change from C3 to C4 plants in the past 20-30 years. The importance of much older SOM as a substrate was determined by comparison of the radiocarbon content of PLFA from soils of two sites that had different 14C concentrations of SOM.The 13C shift in PLFA from the two sites that had experienced different vegetation history indicated that 40-90% of the PLFA carbon had been fixed since the vegetation change took place. Thus PLFA were more enriched in 13C from the new C4 vegetation than it was observed for bulk SOM indicating recent plant material as preferentially used substrate for soil microorganisms. The largest 13C shift of PLFA was observed in the soil that had high 14C concentrations of bulk SOM. These results reinforce that organic carbon in this soil for the most part cycles rapidly. The degree to which SOM is incorporated into microbial PLFA was determined by the difference in 14C concentration of PLFA derived from two soils one with high 14C concentrations of bulk SOM and one with low. These results showed that 0-40% of SOM carbon is used as substrate for soil microorganisms. Furthermore a different substrate usage was identified for different microorganisms. Gram-negative bacteria were found to prefer recent plant material as microbial carbon source while Gram-positive bacteria use substantial amounts of SOM carbon. This was indicated by 13C as well as 14C signatures of their PLFA. Our results find evidence to support ‘priming’ in that PLFA indicative of Gram-negative bacteria associated with roots contain both plant- and SOM-derived C. Most interestingly, we find PLFA indicative of archeobacteria (methanothrophs) that may indicate the use of other carbon sources than plant material and SOM to a substantial amount suggesting that inert or slow carbon pools are not essential to explain carbon dynamics in soil.  相似文献   

17.
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   

18.
The oxidation of atmospheric methane by methanotrophic bacteria residing in soils constitutes an important terrestrial methane sink with previous studies having revealed the inhibition of microbially mediated methane oxidation in the presence of salt ions. The bacteria responsible for ambient methane oxidation are not amenable to currently available methods of culturing, resulting in the need for a method of in situ analysis. A combination of phospholipid fatty acid (PLFA) analysis and stable isotopic labelling has been employed in this investigation as a means of cultivation-independent bacterial analysis. Soil samples were treated with an ammonium sulfate solution at a concentration that was known to inhibit methane oxidation or with distilled water, serving as a control, and incubated with 13C-labelled methane. PLFAs were analysed by GC/C/IRMS in order to determine their 13C content and, hence, the PLFA distribution of the methane oxidising bacteria. Ammonium sulfate treatment reduced the amount of 13C incorporated into the majority of PLFAs except the i17:0 PLFA in the presence of high concentrations of methane. These results implied a shift in the composition of the methane oxidising bacterial community in the soils treated with ammonium ions, with the treatment appearing to suppress one group of organisms more than another.  相似文献   

19.
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   

20.
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   

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