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1.
To assess the potential of fatty acid (FA) compositions to act as biomarkers in the soil food web, two species of Collembola, Folsomia candida and Proisotoma minuta, were switched to four possible diets: Cladosporium cladosporioides (a common soil fungus), Panagrellus redivivus (a bacteria feeding nematode), Zea mays (maize) and Alnus glutinosa (alder). The change in FA content of the Collembola was observed over the following 39 days. The four diets produced significant shifts in the FA compositions of the Collembola, with P. redivivus causing the most extreme changes; Collembola fed P. redivivus gained complex FA compositions similar to those of the nematode diet. Changes in the relative abundances of some FAs were found to follow negative exponential curves, as the components either accumulated in, or were removed from, the FA pool in the Collembola; abundance half-lives varied between 0.5 and 22.4 days, indicating that Collembolan FA compositions changed readily with the input of new exogenous components. The results demonstrate that Collembolan FA compositions are influenced by diet, and that the abundances of FAs such as i15:0, i17:0 and 18:1(n-7) may be used as biomarkers of nematode consumption by Collembola. In contrast, the C20 polyunsaturated FAs cannot be used as biomarkers for nematode predation as Collembola possess the ability to biosynthesise high abundances of these compounds when not provided by the diet.  相似文献   

2.
Fatty acid (FA) analysis is becoming increasingly important for investigating trophic interactions in soil food webs. FA profiles of neutral lipids are affected by diet, and the occurrence and amount of certain FAs can reflect feeding strategies. However, to draw conclusions on feeding strategies in the field it is necessary to know physiological parameters of fatty acid metabolism such as the detection time and storage period of FAs. In this study we investigated the chronological change of FA biomarkers in the Collembola Heteromurus nitidus when switched between different food sources: leaves (Tilia europaea), a fungus (Chaetomium globosum) and two bacteria (Stenotrophomonas maltophilia, Bacillus amyloliquefaciens). Additionally, we followed the change of bacterial FA biomarkers during starvation. After 14 days of food deprivation bacterial FAs were still detectable in a sufficient amount to use them as dietary markers. Switching diet experiments demonstrated that FAs typical for a specific diet are already present after one day and are still detectable after 14 days of feeding on a different food source, suggesting that FA analysis can integrate the food choice of Collembola over a longer period of time, in contrast to snapshot methods such as gut content analysis.  相似文献   

3.
Fatty acid (FA) analysis is used increasingly to investigate the trophic structure of soil animal food webs as the technique allows separation of the role of detrital resources such as bacteria, fungi and plant material for consumer nutrition. The applicability of FAs as biomarkers for different diets has been verified for Collembola and Nematoda. However, for the analysis of whole food webs it is crucial to know whether marker FA are valid for different taxa and whether they are transferred along the food chain to higher trophic levels, i.e. predators. Top-predators are integrators of lower level energy fluxes in food webs; therefore analysis of their FAs may allow to identify trophic pathways and to separate bacterial vs. fungal based energy channels. Chilopoda and Arachnida are among the main predators in soil food webs. Our aim was to test the applicability of marker FAs for these two predator taxa and to verify the trophic transfer of marker FAs of different basal resources via first order consumers into predators, i.e. over three trophic levels. Therefore, we investigated the transfer of FAs from different basal resources [fungi (Chaetomium globosum), plant leaf litter (Tilia europaea), Gram-positive (Bacillus amyloliquefaciens) and Gram-negative bacteria (Stenotrophomonas maltophilia)] via Collembola (Heteromurus nitidus) as first order consumers into predators [Lithobius forficatus (Chilopoda) and Pardosa lugubris (Arachnida)]. Fatty acid profiles of predators of food chains with different basal resources differed significantly. Marker FAs of basal resources were clearly detectable in predators, suggesting that FA analysis allows to separate trophic channels of soil food webs. By reflecting basal resources, FAs of predators allow tracking energy/resource fluxes through the food web and thereby clarifying the relative importance of bacterial vs. fungal vs. plant resources for soil animal food webs.  相似文献   

4.
In soil a high number of species co-exist without extensive niche differentiation, which was assigned as ‘the enigma of soil animal species diversity’. In particular, the detritivores are regarded as food generalists. We have investigated nitrogen stable isotope ratios (15N/14N) of a major decomposer group, the Collembola, to evaluate trophic relationship and determine feeding guilds. Additionally, the δ15N values of potential food sources such as mosses, lichens and other plant derived material (bark, nuts, leaves) were analysed. The natural variation in nitrogen isotopes was assessed in 20 Collembola taxa from three deciduous forest stands. The δ15N signature formed a continuum from phycophages/herbivores to primary and secondary decomposers, reflecting a gradual shift from more detrital to more microbial diets. The δ15N gradient spanned over 9 δ units, which implies a wide range in food sources used. Assuming a shift in 15N of about 3 ‰ per trophic level, the results indicate a range of three trophic levels. These variations in 15N/14N ratios suggest that trophic niches of Collembola species differ and this likely contributes to Collembola species diversity.  相似文献   

5.
The lipid composition of Collembola and their potential food resources was assessed in three deciduous forest stands, in order to gain insight into food web linkages under field conditions. Fatty acids (FAs) previously assigned as trophic markers in laboratory experiments were used to investigate feeding strategies in situ. As potential food sources soil microbiota and plant debris were characterised by their phospholipid fatty acid (PLFA) composition. Both the amount and the pattern of PLFAs differed between sites and soil depth, in particular the bacterial and plant marker FAs in the upper soil layer. Thus, the availability of resources for micro-detritivores varied due to forest and soil layer. The lipid composition of vital and senescent beech leaves was predominantly influenced by metabolic status and represented a quite homogenous FA resource across forest stands. Comparing Folsomia quadrioculata, Lepidocyrtus lignorum, Neanura muscorum and Pogonognathellus longicornis between the different forests revealed FA profiles to be predominantly affected by site, suggesting a diet shift depending on resources at hand. However, species-specific differences in individual FAs occurred, likely related to feeding strategy and physiological activity. Lipids of Collembola comprised low amounts of bacterial marker FAs, and bacterial consumption may occur to some extent, particularly on Gram-positives. The marker FA for predatory feeding, 20:1ω9, was found in several species, although in low amounts. This contradicts known feeding habits and caution is advisable in using 20:1ω9 as trophic marker. Overall, as indicated by high proportions of oleic (18:1ω9) or linoleic (18:2ω6,9) acid, most species were either plant litter or fungal feeders, with some transitions. The ratio 18:1ω9/18:2ω6,9 is proposed as a tool to distinguish between these two major feeding strategies in Collembola.  相似文献   

6.
Fertilizer costs are a major component of corn production. The use of biofertilizers may be one way of reducing production costs. In this study we present isolation and identification of three plant growth promoting bacteria that were identified as Enterobacter cloacae (CR1), Pseudomonas putida (CR7) and Stenotrophomonas maltophilia (CR3). All bacterial strains produced IAA in the presence of 100 mg l−1 of tryptophan and antifungal metabolites to several soilborne pathogens. S. maltophilia and E. cloacae had broad spectrum activity against most Fusarium species. The only strain that was positive for nitrogen fixation was E. cloacae and it, and P. putida, were also positive for phosphate solubilization. These bacteria and the corn isolate Sphingobacterium canadense CR11, and known plant growth promoting bacterium Burkholderia phytofirmans E24 were used to inoculate corn seed to examine growth promotion of two lines of corn, varieties 39D82 and 39M27 under greenhouse conditions. When grown in sterilized sand varieties 39M27 and 39D82 showed significant increases in total dry weights of root and shoot of 10-20% and 13-28% and 17-32% and 21-31% respectively. Plants of the two varieties grown in soil collected from a corn field had respective increases in dry weights of root and shoot of 10-30% and 12-35% and 11-19% and 10-18%. In sand, a bacterial mixture was highly effective whereas in soil individual bacteria namely P. putida CR7 and E. cloacae CR1 gave the best results with 39M27 and 39D82 respectively. These isolates and another corn isolate, Azospirillum zeae N7, were tested in a sandy soil with a 55 and 110 kg ha−1 of nitrogen fertility at the Delhi research Station of Agriculture and Agri-Food Canada over two years. Although out of seven bacterial treatments, no treatment provided a statistically significant yield increase over control plots but S. canadense CR11 and A. zeae N7 provided statistically significant yield increase as compared to other bacteria. The 110 kg rate of nitrogen provided significant yield increase compared to the 55 kg rate in both years.  相似文献   

7.
Fatty acid (FA) analysis is used as a promising tool to investigate trophic interactions in soil food webs. The FA profile of neutral lipids in consumers is affected by the diet, and the occurrence and amount of certain FAs can reflect feeding strategies. We investigated the lipid composition of the Collembola Folsomia candida, Heteromurus nitidus and Protaphorura fimata with the fungus Chaetomium globosum as food source. The impact of environmental temperature and life stage was assessed, with special respect to linoleic acid (18:2ω6,9) as a marker FA for fungal feeding. In all Collembola species the ratio of C16/C18 in neutral lipid fatty acids (NLFAs) increased with decreasing temperature. In the NLFAs of F. candida and H. nitidus the Unsaturation Index and the amount of 18:2ω6,9 decreased with temperature, whereas in P. fimata effects were the opposite. The composition of phospholipid fatty acids (PLFAs) differed between species, but was little affected by temperature. The degree of unsaturation in NLFAs increased with the age of Collembola, mainly due to higher amounts of 18:2ω6,9 and a lower proportion of 18:1ω9. The biomarker linoleic acid represented over 20% of FAs in all fungal feeding Collembola. Despite considerable influence of temperature and life stage on its proportion, the amount was always higher than in individuals reared on other diets. This suggests that linoleic acid can serve as marker for fungal feeding independent of such physiological variations in Collembola.  相似文献   

8.
Microbial colonization of soil-incorporated, 13C-labeled, crimson clover and ryegrass straw residues was followed under western Oregon field conditions from late summer (September) to the following early summer (mid-June) by measuring the 13C content of phospholipid fatty acid (PLFA) extracted from residues recovered from soil. Residue type influenced the rate of appearance of specific PLFA during early decomposition, with branch chain bacterial PLFA (i15:0, a15:0, i16:0) appearing on clover and ryegrass residues in October and November, respectively. By April, additional PLFA (16:1ω5, 16:1ω7, cy17:0, 18:0, 18:1ω9) had appeared on both residues. Between April and June, microbial community structure shifted again with significant increases (cy17:0, 18:0, 18:1ω9), and decreases (18:1ω7+10Me18:0) detected in the quantities of specific PLFA on both residue types. In the case of clover, the PLFA-C was derived primarily from residue C (85-100%), whereas in the case of ryegrass, both residue C (57-66%), and soil C contributed substantially to the PLFA-C.  相似文献   

9.
Colonization and survival of the inoculated bacteria in rhizosphere of maize were investigated in field and pot experiments conducted for 3 consecutive years under rainfed conditions of Himalayan region. The effect of bacterial inoculations on growth and yield related parameters of maize were also evaluated. While three bacterial species, viz. Bacillus megaterium, Bacillus subtilis and Pseudomonas corrugata were tested in 1st year experiments, P. corrugata (based on the 1st year results) was chosen for inoculation in the subsequent experiments. All the three bacterial inoculants showed good rhizosphere competence giving high inoculum numbers (log10 11.13-11.34 cfu g−1). The bacterial inoculations by B. megaterium, B. subtilis and P. corrugata resulted in an increment in grain yield of maize up to 122.4%, 135.2% and 194.3%, respectively, as compared to respective control. In 1st year, the antibiotic marked (Nalr Rifr) inoculant P. corrugata resulted in the highest increase in grain yield, statistically significant (P<0.05) as compared to control, B. megaterium and B. subtilis. In 2nd and 3rd year experiments, P. corrugata increased the grain yield up to 147.28% and 149.93%, respectively, as compared to control. The best performance and consistent trend of P. corrugata to increase plant yields was credited to its initial isolation from rhizosphere of maize growing under temperate conditions. The overall beneficial effects of bacterial inoculations on maize were contributed to (1) the colonization and survival of the introduced bacteria, and (2) stimulation of the indigenous microflora in the rhizosphere. Based on the comprehensive results obtained in this study, P. corrugata may be recommended as suitable bioinoculant for maize fields of temperate climate grown under rainfed conditions.  相似文献   

10.
Naturally occurring stable isotopes of carbon and nitrogen are powerful tools to investigate food webs, where the ratio of 15N/14N is used to assign trophic levels and of 13C/12C to determine the food source. A shift in δ15N value of 3‰ is generally suggested as mean difference between two trophic levels, whereas the carbon isotope composition of a consumer is assumed to reflect the signal of its diet. This study investigates the effects of food quality, starvation and life stage on the stable isotope fractionation in fungal feeding Collembola. The fractionation of nitrogen was strongly affected by food quality, i.e. the C/N ratio of the fungal diet. Collembola showed enrichment in the heavier isotope with increasing N concentration of the food source. Δ15N varied between 2.4‰, which assigns a shift in one trophic level, and 6.3‰, suggesting a shift in two trophic levels. Starvation up to 4 weeks resulted in an increase in the total δ15N value from 2.8‰ to 4.0‰. Different life stages significantly affected the isotope discrimination by Collembola with juveniles showing a stronger enrichment (Δ15N=4.9‰) compared to adults (Δ15N=3.5‰). Δ13C varied between −2.1‰ and −3.3‰ depending on the food quality, mainly due to compensational feeding on low quality diet. During starvation δ13C value decreased by 1.1‰, whereas the life stage of Collembola had no significant effect on isotopic ratios. The results indicate that the food resource and the physiological status of the consumer have important impact on stable isotope discrimination. They may cause differences in fractionation rate comparable to trophic level shifts, a fact to consider when analysing food web structure.  相似文献   

11.
We used fatty acid (FA) analysis to investigate green algae and cyanobacteria as food sources for Collembola. We studied the effects of food quality on body mass and on neutral lipid (NLFA) and phospholipid (PLFA) fatty acid patterns of Collembola. Folsomia candida, Heteromurus nitidus and Protaphorura fimata were fed with common green algae (Chlorella vulgaris), filamentous soil algae (Klebsormidium flaccidum), cyanobacteria (Nostoc commune) and baker's yeast (Saccharomyces cerevisiae). Body mass of F. candida and H. nitidus was highest when reared on C. vulgaris and S. cerevisiae. P. fimata gained the most weight when fed baker's yeast. K. flaccidum and N. commune as resources resulted to low biomass in all Collembola. The four diets caused significant differences in the NLFA and PLFA composition of Collembola after six weeks of feeding. Two new trophic biomarker FAs indicating algal diets were assigned with 16:3ω3,6,9 and 16:2ω6,9, which were only present in NLFAs of Collembola consuming C. vulgaris and K. flaccidum. The amount of FAs from the ω7 family was high in Collembola lipids with cyanobacteria and yeast as food sources, whereas only trace amounts occurred in the NLFA fraction with algae as the resource. In summary, common soil algae and cyanobacteria differed in food quality for Collembola, depending on their growth form (unicellular versus filamentous) and/or secondary metabolites (e.g. cyanobacteria). The new FA biomarkers detected will allow further investigation of these trophic interactions under field conditions; for example, assessing the role of collembolan grazers in the formation of biological soil crusts.  相似文献   

12.
Feeding relationships between organisms may be determined by observations of behaviour in manipulative experiments or, as in more recent times, by the use of stable isotope labelling to trace the passage of 13C and 15N through food webs. Here we introduce living bacteria, labelled with both 13C and 15N into intact soil cores to understand further the movement of bacterially sourced C and N into the meso- and macrofauna of a grassland soil. We found that these groups showed a range of isotope levels which relate to their feeding strategies. Some had no label (e.g. dipterous larvae), whilst others were highly labelled which may indicate a preference for the added bacteria. This latter group included Collembola, generally perceived as being predominantly fungal feeders. This work describes a novel technique which has the potential to provide critical information about the dissipation of bacterially derived C and N through the soil food web.  相似文献   

13.
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   

14.
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   

15.
Isotope fractionation during composting may produce organic materials with a more homogenous δ13C and δ15N signature allowing study of their fate in soil. To verify this, C, N, δ13C and δ15N content were monitored during nine months covered (thermophilic; >40 °C) composting of corn silage (CSC). The C concentration reduced from 10.34 to 1.73 g C (g ash)−1, or 83.3%, during composting. Nitrogen losses comprised 28.4% of initial N content. Compost δ13C values became slightly depleted and increasingly uniform (from −12.8±0.6‰ to −14.1±0.0‰) with composting. Compost δ15N values (0.3±1.3 to 8.2±0.4‰) increased with a similar reduced isotope variability.The fate of C and N of diverse composts in soil was subsequently examined. C, N, δ13C, δ15N content of whole soil (0-5 cm), light (<1.7 g cm−3) and heavy (>1.7 g cm−3) fraction, and (250-2000 μm; 53-250 μm and <53 μm) size separates, were characterized. Measurements took place one and two years following surface application of CSC, dairy manure compost (DMC), sewage sludge compost (SSLC), and liquid dairy manure (DM) to a temperate (C3) grassland soil. The δ13C values and total C applied (Mg C ha−1) were DM (−27.3‰; 2.9); DMC (−26.6‰; 10.0); SSLC (−25.9‰; 10.9) and CSC (−14.0‰; 4.6 and 9.2). The δ13C of un-amended soil exhibited low spatial (−28.0‰±0.2; n=96) and temporal (±0.1‰) variability. All C4 (CSC) and C3 (DMC; SSLC) composts, except C3 manure (DM), significantly modified bulk soil δ13C and δ15N. Estimates of retention of compost C in soil by carbon balance were less sensitive than those calculated by C isotope techniques. One and two years after application, 95 and 89% (CSC), 75 and 63% (SSLC) and 88 and 42% (DMC) of applied compost C remained in the soil, with the majority (80-90%) found in particulate (>53 μm) and light fractions. However, C4 compost (CSC) was readily detectable (12% of compost C remaining) in mineral (<53 μm) fractions. The δ15N-enriched N of compost supported interpretation of δ13C data. We can conclude that composts are highly recalcitrant with prolonged C storage in non-mineral soil fractions. The sensitivity of the natural abundance tracer technique to characterize their fate in soil improves during composting, as a more homogeneous C isotope signature develops, in addition to the relatively large amounts of stable C applied in composts.  相似文献   

16.
The diet of earthworms includes soil organic matter, soil microbes and other microfauna, but the relative contribution of these dietary components to earthworm nutrition is not well known. Analysis of fatty acid (FA) profiles can reveal trophic relationships in soil food webs, leading to a better understanding of the energy and nutrient flows from microbiota to earthworms. The objective of this study was to determine the origin of FAs assimilated by the earthworm Lumbricus terrestris L. We analysed the pattern of FAs in: (i) the bulk soil, (ii) soil in the earthworm gut, (iii) the absorptive tissue of the earthworm gut wall, and (iv) the muscular layers of the earthworm body wall. Multivariate analyses performed on the FA profiles suggest that the microbial community in the earthworm gut differs from that in bulk soil. Diverse bacterial and fungal derived FAs, which earthworms cannot synthesize, were found in the earthworm gut wall and body wall, and in the neutral lipids (storage lipids) of the gut wall. The major compounds isolated were 20:4ω6, 20:5ω3 and 18:2ω6, followed by the monoenoic 18:1ω7 and 18:1ω9c, and the saturated 18:0. The microbial FA assemblage in the gut wall resembled the gut soil more than the bulk soil, and the body wall of L. terrestris showed the same microbial derived FA pattern as the gut wall, although at reduced concentrations. We propose the existence of a specific microbial community in the earthworm gut that provides FAs to the earthworm. It appears that L. terrestris may derive more of its energy and nutrients from gut specific microbiota than from microbiota already present in the ingested soil, based on the trophic relationships revealed through FA analysis.  相似文献   

17.
The trophic preferences of soil invertebrates such as Collembola are often determined by the analysis of gut contents, or through visual observations of the location of individuals. As an alternative approach, two species of Collembola, Folsomia candida and Proisotoma minuta, were offered a choice of the soil fungus Cladosporium cladosporioides or the bacterial feeding nematode Panagrellus redivivus; each exhibited distinct fatty acid profiles and stable carbon isotopic compositions. Over 21 days, the fatty acids i15:0, i17:0, 18:1(n-7) and 18:2(n-6) all increased in abundance in both collembolan species consistent with direct routing from the nematode dietary choice which contained a high concentration of these components. Collembolan fatty acid δ13C values increased by between 5.7 and 21.6‰ over 21 days reflecting those of the nematode diet. Therefore, both fatty acid profiles and δ13C values were consistent with a strong feeding preference of F. candida and P. minuta for the nematodes over the offered fungi. In fact, neither collembolan species consumed any detectable amount of C. cladosporioides. Comparison of the δ13C values of the 16:0 and 18:0 fatty acids (which are biosynthesised by the Collembola as well as directly incorporated from the diet) and the 16:1(n-7) and 18:2(n-6) components (which are not biosynthesised by the Collembola) demonstrated that the input of distinct pools of C can lead to large shifts in δ13C values between diet and consumer. The fatty acids that were not biosynthesised by Collembola better reflected the δ13C values of the diet helping to differentiate between biosynthesised and directly incorporated compounds; an important prerequisite in the interpretation of compound-specific δ13C values in trophic behaviour tests. The combination of fatty acid distributions and δ13C values is a significant improvement on traditional methods of examining feeding preferences, since it determines directly the assimilated dietary carbon rather than relying on indirect observations, such as the proximity of individuals to a defined food source.  相似文献   

18.
Combined compound-specific stable carbon isotopic methods and fatty acid abundance determinations have been used to examine feeding preferences and C allocation in organisms where direct observation of feeding is difficult. In order to examine the effect of differing diets on the δ13C values of fatty acids and sterols of Collembola, the diets of two collembolan species, Folsomia candida and Proisotoma minuta, were switched from a yeast diet to one of four isotopically distinct diets, and the δ13C values of the lipids monitored over the next 39 d. Cholesterol remained the only sterol detected in both collembolan species, despite the diets containing widely differing sterol compositions. The δ13C values of collembolan lipids recorded after long term feeding were often different to those of the same components in the diet, indicating that fractionation or partitioning occurs during digestion, assimilation and biosynthesis within the Collembola, thereby shifting consumer lipid δ13C values away from those of the corresponding dietary components. The rates of change of δ13C values differed among compounds, with half-lives ranging between 29 min and 14 d. Some of these differences appear to be related to the abundance of dietary components, such that fatty acids present in high abundance in the diet (e.g. 18:2(n−6)) were rapidly assimilated in high proportions into collembolan lipids, leading to a rapid change in δ13C values. Similarly, isotopic turnover in the 16:1(n−7) fatty acid, present in the newly presented diets in only low abundances, was significantly correlated to the rate of removal of this component from the consumer fatty acid pool. The rates of change of δ13C values in P. minuta lipids did not vary significantly with diet, whilst the rates of change of δ13C values of lipids in F. candida were affected by the diets the Collembola consumed. Results of an experiment providing F. candida and P. minuta with two diets of different quality demonstrated that F. candida responded to the high quality diet with increased growth and fecundity, whilst P. minuta responded with increased fecundity only. Thus, the abilities of the two species to respond to diets of varying quality, amongst other factors, is concluded to lead to differences in the rates of change of δ13C values reflecting differences in lipid turnover.  相似文献   

19.
Diagnostic tests for organic production of crops would be useful. In this study, the difference in natural 15N abundances (δ15N) of soils and plants between fertilizer-applied upland (FU) and compost-applied upland (CU) fields was investigated to study using δ15N as a marker of organic produce. Twenty samples each of soils and plants were collected from each field in early summer after applying fertilizer or compost. The δ15N of fertilizers and composts was −1.6±1.5‰ (n=8) and 17.4±1.2‰ (n=10), respectively. The δ15N of total soil-N was significantly (P<0.05) higher in CU fields (8.8±2.0‰) than in FU fields (5.9±0.7‰) due to long-term continuous application of 15N-enriched compost, as indicated by a positive correlation (r=0.62) between N content and δ15N of total soil-N. The NO3− pool of CU soils (11.6±4.5‰) was also significantly (P<0.05) enriched in 15N compared to FU soils (4.7±1.1‰), while the 15N contents of NH4+ pool were not different between both soils. Compost application resulted in 15N enrichment of plants; the δ15N values were 14.6±3.3‰ for CU and 4.1±1.7‰ for FU fields. These results showed that long-term application of compost resulted in a significant 15N-enrichment of soils and plants relative to fertilizer. Therefore, this study suggested that δ15N could serve as promising indicators of organic fertilizers application when used with other independent evidence. However, further studies under many conditions should be conducted to prepare reliable δ15N guidelines for organic produce, since the δ15N of inorganic soil-N and plant-N are influenced by various factors such as soil type, plant species, the rate of N application, and processes such as mineralization, nitrification, and denitrifcation.  相似文献   

20.
We studied the effects of varied collembolan numbers on three compensatory mechanisms of nutrient uptake: fine root mass, endomycorrhizal development, and physiological uptake capacity. We grew ash (Fraxinus pennsylvanica) with or without the arbuscular mycorrhizal fungus Glomusintraradices, with 0, 10 or 50 initial Collembola (Folsomia candida). After 83 d root and uptake rates, endomycorrhizal development, and plant biomass were determined. Plant mass increased with Collembola number. Collembola interacted with mycorrhizae in their effects on N uptake and leaf N. Collembola in the absence of mycorrhizal roots were associated with lower N uptake and leaf N at 10 than at 0 or 50 initial Collembola. In contrast, Collembola in the presence of mycorrhizal roots were associated with the highest rate of N uptake and leaf N at 10 versus 0 or 50 initial Collembola. Hence as initial Collembola number increased, the relative importance of root system traits that determined N uptake changed from root physiological uptake capacity, presence of mycorrhizal roots, to fine root biomass.  相似文献   

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