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1.
We studied the influence of an immobilized laccase from Trametes versicolor on non-extractable residue (NER) formation of the systemic fungicide 14C-metalaxyl in soil. We added the enzyme (130 mU/g DW) to soil sterilized by gamma irradiation and observed that the amount of NER (6.3 % of applied radioactivity) after 10 days of incubation was enhanced about twofold compared to the sterile soil without laccase addition. Residues formed within samples without enhanced enzyme activity were mainly bound via ester linkages to all fractions of humic matter, i.e., fulvic acids, humic acids, non-humines, and humines, respectively. In contrast, residues formed in presence of immobilized laccase were more strongly bound by covalent linkages such as ether and C-C bonds, especially to humic acids. After chemical degradation of the humic matter, it could be observed that all NER contained the first major transformation product, i.e., metalaxyl acid. The findings underline that the residue formation of metalaxyl in soil may be partly catalyzed by immobilized extracellular oxidative enzymes through oxidative coupling reactions within the humic matter.  相似文献   

2.
Lichen phenolics that are known to leach out from lichen thalli during rainfall episodes are considered to be allelopathic or antimicrobial agents. On the other hand, small organic molecules originating from aboveground vegetation generally constitute an important C source for the soil microbial community. We studied the effects of leaching lichen acids on soil microbial processes by chemically removing usnic (UA) and perlatolic acid (PA) from the extracellular space of mat-forming lichen, Cladina stellaris, a dominant component of the ground vegetation in boreal oligotrophic forests. Removal of UA and PA did not affect the intracellular contents of the lichen. We hypothesized that if lichen acids have an adverse effect on soil biota, microbial respiration would increase underneath chemically manipulated lichen mats. In turn, if these substances provide energy source for the microorganisms, microbial respiration would decline under lichens from which PA and UA has been removed. Microbial metabolic activity, qCO2 was significantly lower under the lichens from which UA and PA had been removed, thus supporting the latter hypothesis. Removing UA and PA did not affect the amount of microbial C, N and P, or soil nutrient concentrations. Our results suggest that the microbial community in the soil under a lichen carpet is adapted to the presence of these lichen secondary metabolites and can utilize them as a C source. The approach of removing lichen substances from the system could be used as an effective research tool as it can overcome several problems that are often common in the studies on allelopathic interactions.  相似文献   

3.
Humic substances play a key role in the global carbon cycling and the sequestration of micropollutants in soil. The transformation of these substances by earthworms, the dominant soil macroinvertebrates of many terrestrial ecosystems, and the mechanisms involved are still obscure. We prepared two chemically identical humic model compounds that were specifically 14C-labeled either in the aromatic or the proteinaceous component, and added them to soil incubated with the geophagous earthworm species Metaphire guillelmi (anecic) and Amynthas corrugatus (endogeic). In the absence of the earthworms, both the aromatic and the proteinaceous components were mineralized at similarly low rates (5−8% after 9 days of incubation). In the presence of the earthworms, mineralization rate of the proteinaceous component was strongly stimulated (2-fold by M. guillelmi and 1.4-fold by A. corrugatus). The mineralization rate of the aromatic component was (slightly) stimulated (1.2-fold; P < 0.05) only by A. corrugatus. In all cases, the stimulated mineralization was accompanied by a transformation of radiolabeled humic acids to fulvic acids within the earthworm guts and by an incorporation of radiolabel into the earthworm tissues. Digestion of the proteinaceous component of humic acids by the earthworms was corroborated also by a decrease of extractable humic acids in fresh cast and a stimulated mineralization of soil nitrogen; in the case of M. guillelmi, the fresh cast contained sixfold more NH4+ than the non-ingested soil. Our study provides direct evidence for the selective digestion of humic components by earthworms. Considering the ubiquity of geophagous earthworms and their large biomass, the alteration of the chemical structure of humic substances by the earthworms through their selective digestion of peptidic components may have significant impacts on the stability of humic substances and the bioavailability of micropollutants in soil.  相似文献   

4.
Laecases of Polyporus versicolor in soil and litter. The laccases forms A and B, prepared from Polyporus versicolor, were compared with the laccases liberated from soil and litter by means ofchromatography on G100 Sephadex and DEAE DE 52 Cellulose. It appears that the soil and litter enzymes were of the form A that is strongly electronegative. These results suggest that because of their negative charges, laccases A, were weakly adsorbed onto humic colloids. Consequently, protection might be given to the active sites of the enzymes without preventing the formation of “humo-laccases” complexes in soil and litter.  相似文献   

5.
Despite the critical role of biological soil crusts (BSCs) in arid and semi-arid ecosystem function, few studies are found concerning the most important environmental variables affecting their distribution and physiology. This study seeks to determine soil and microenvironmental factors affecting the spatial distribution and pigment production of BSC-forming lichens and mosses in open patches of a semi-arid Mediterranean kermes oak thicket. We measured late-successional BSC cover, shrub cover, distance to nearest kermes oak (to test for effects of kermes oak thicket microenvironment on BSC), and pigment concentration of one lichen (Cladonia foliacea) and one moss (Pleurochaete squarrosa) species in the Nature Reserve El Regajal-Mar de Ontígola (Central Spain). At the macroscale (>0.5 m), results showed that BSC distribution and pigments were tightly coupled to a suite of soil properties, in particular soil pH, Fe, and Ca. Specifically, soil pH had a positive relationship with the cover of five individual BSC-forming lichen species and was negatively related to pigment production in C. foliacea. When pH was excluded from the analysis, Ca appeared as the main soil variable and was correlated with total BSC cover and total lichen cover. The micronutrient Fe had a significant positive relationship with the concentration of eight pigments in P. squarrosa and was also coupled with the cover of two BSC-forming lichens. Manganese, previously proposed as a key limiting micronutrient for BSCs, affected lichen diversity in a negative way. At the microscale (∼0.5 m), kermes oak microenvironment, shrub cover, and moss cover were determinants of BSC distribution, and total lichen and total BSC cover were overrepresented on N and E-facing shrub microsites. Our findings suggest that soil chemical variability and microsite diversity created by neighbouring vegetation affect BSC distribution in complex and essential ways and that studies aiming to explore BSC-environment relationships should be conducted at various spatial scales. Studies based on species- or group-specific responses are, thus, inadequate to unveil the main factors determining the distribution of the diverse organisms that constitute BSCs and/or to propose potential tools aiming to restore BSC in arid and semiarid ecosystems.  相似文献   

6.
Laccases of fungal origin have been intensively studied due to their importance in various biotechnological applications. There is a constant demand for new laccases with improved properties such as stability at higher temperatures or at an alkaline pH. Growing molecular evidence suggests that laccases may also be widespread in bacteria. While only a handful of bacterial laccases have been purified and characterized, several novel traits have already been discovered (e.g. pH-stability and 2-domain organization of the enzyme as opposed to the usual 3-domain structure of fungal laccases). The aim of this study was to examine the diversity of bacterial laccase-like genes in two types of high-organic peat soil using a cloning and sequencing approach. Gene libraries prepared of small fragments (150 base pairs) revealed an amazing diversity of bacterial laccases. The fragments clustered in 11 major lineages, and one third of the 241 sequences resembled laccase-like genes of Acidobacteria. Additionally, a new primer was used to retrieve several larger fragments of the putative bacterial laccase genes that spanned all four copper-binding sites. Both “conventional” 3-domain laccases and the recently described 2-domain small laccases have been obtained using this approach, demonstrating the potential of the primer. The present study thus contributes to the understanding of the diversity of bacterial laccases and provides a new tool for finding laccase-like sequences in bacterial strains and soil samples.  相似文献   

7.
Phenolic compounds have been shown in several studies to have important ‘carryover effects’ on litter decomposition, microbial nutrient immobilization and nutrient availability. These effects arise in part because of the adverse effect they have on the feeding activities of litter-feeding invertebrates such as micro-arthropods that drive decomposition processes. However, the interactive effects of phenolic compounds and soil micro-arthropods on litter decomposition are poorly understood. Phenolic compounds can easily be removed by acetone rinsing from living lichens, allowing us to specifically test the role that phenolic compounds (and their removal) have in controlling the effects of micro-arthropods on the decomposition of their litter. We performed a litter-bag experiment aimed at exploring how lichen litter mass loss and nutrient release during decomposition was affected by phenolics (by using acetone rinsed and non-rinsed lichen material) and micro-arthropod activity (by using different mesh sizes to allow or exclude entry by micro-arthropods) for each of six contrasting lichen species (Cladonia rangiferina, Cladonia stellaris, Evernia prunastri, Hypogymnia physodes, Pseudevernia furfuracea and Usnea dasypoga). Both the removal of phenolic compounds and the presence of micro-arthropods accelerated mass and nutrient release overall, but not for either of the two Cladonia species. Removal of phenolics also had an overall positive effect on the effects of arthropods on the loss of P, but not mass and N, from the decomposing lichens. Further, for U. dasypoga, but not the other species, natural levels of phenolic compounds deterred micro-arthropods from accelerating mass loss, and the removal of these compounds enabled micro-arthropods to enhance its decomposition. Our findings that lichen phenolic compounds can sometimes interact with micro-arthropods to influence lichen litter mass loss and nutrient release during decomposition assists our understanding of how lichens and their consumers may impact on organic matter dynamics, biochemical nutrient cycling and other related ecosystem processes.  相似文献   

8.
We describe here the role of the polyphenoloxidases in the oxidation of recalcitrant soil organic compounds and consider what changes occur in their structure during experiments on the biotransformation of soil and peat-derived humic acids (HA). These transformations were carried out by laccase (EC 1.10.3.2.) of the white-rot basidiomycete Panus tigrinus 8/18. It was shown that purified laccase alone is capable both of polymerizing and depolymerizing HA in vitro. The direction of transformations depends on the nature and properties of HA. Those fractions of HA are affected by laccase, which cause the lowest inhibitory effect on the enzyme. Contrary to previous studies depolymerization of HA was not necessarily accompanied by decolorization: chernozem-derived HA showed increase in absorbance of its aqueous solution in the region of 240-500 nm during depolymerization, while peat-derived HA showed decrease in absorbance throughout the entire spectrum during polymerization. All studied HA were competitive inhibitors of laccase towards oxidation of synthetic substrate 2,2′-azino-bis-(3-ethylthiazoline-6-sulfonate) (ABTS). When studying the nature of the inhibitory effect, it was shown that more ‘hydrophobic’ HA as well as more ‘hydrophobic’ HA fragments were stronger inhibitors of blue laccase.  相似文献   

9.
Humic acids are ubiquitous and abundant in terrestrial environments; therefore, they are often co-extracted with nucleic acids and interfere with quantitative PCR (qPCR) assays. In this study a recently developed NanoGene assay that is resistant to interference by humic acids was evaluated for gene detection in soil samples. The NanoGene assay utilizes a combination of magnetic beads, dual quantum dots labels, and DNA hybridization in solution. Seven soil samples containing different amounts of organic matter were tested to compare NanoGene and qPCR assays for their respective ability to detect a bacterial pathogen. We spiked the soils with Escherichia coli O157:H7, extracted genomic DNA, and conducted NanoGene and qPCR assays targeting the E. coli O157:H7-specific eaeA gene. To prevent the inhibition of PCR that is common when using DNA extracted from soils, we used a range of template DNA concentrations and BSA addition in the qPCR assay. Compared to the qPCR assay the NanoGene assay was significantly more resistant to the inhibitory effect of humic acids, successfully quantifying the eaeA gene within a linear (R2 = 0.99) range of 105 through 108 CFU/g soil for all seven soil samples tested. In contrast, the qPCR assay was significantly inhibited using the same template DNA isolated from soils containing a range of organic content (2.0%–12%). Interestingly, the qPCR assay was still inhibited despite additional purification steps, suggesting that humic acids were still associated with DNA at a level that was inhibitory to qPCR. This study demonstrated that the NanoGene assay is suitable for quantitative gene detection in diverse soil types and is not susceptible to inhibition by humic acids and other organic compounds that commonly lead to false negative results in qPCR assays.  相似文献   

10.
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11.
The total Hg content in soil and in the epiphytic lichen Parmelia sulcata was determined in a former cinnabar mining area on Mt. Amiata. Metal concentrations in soil and in lichen are significantly related and decrease at increasing distances from the zone most affected by minespoil and by air which is still vented from mine shafts. On the basis of these results and of Al analysis, it seems likely that anomalous Hg content in Mt. Amiata lichens is mainly due to the out-gassing of volatile Hg from soil, from vegetation and, in the most heavily polluted zone, to the air from mine shafts.  相似文献   

12.
The accumulation of phenolic acids in soil is one of the main problems associated with continuous cropping of peanut. Although laccases secreted by fungi can efficiently transform phenolic acids, there are few reports on the use of these enzymes to bioremediate continuous cropping soil. Food waste and wheat straw are waste products; however, they could be used productively as resources for laccase production by the endophytic fungus Phomopsis liquidambari B3. We cultured Phomopsis liquidambari B3 in medium containing food waste as the main nitrogen source and wheat straw as the main carbon source. In order to study the effects of fermentation liquid on phenolic acid degradation, rhizosphere soil microbial communities and peanut seedling growth, the fermentation product, which had high laccase activity, was added to continuously cropped soil of peanut. The concentration of 4-hydroxybenzoic acid, vanillic acid, and coumaric acid in soil had decreased by 57.4, 52.5, and 49.4%, respectively, compared with no-treatment control during 28 days. Analysis of denaturing gradient gel electrophoresis profiles showed that the bacterial and fungal community structures in rhizosphere soil were affected by changes in the phenolic acids concentration. The biomass of peanut plants and the number of root nodules were increased 68.3% and 5.9-fold, respectively. These results showed that the laccase product reduced the accumulation of phenolic acids in soil, the decrease in phenolic acids concentration and the increase in certain dominant microorganisms promoted peanut seedling growth and nodulation. This technology provides a new strategy for bioremediation of continuous cropping soil, while simultaneously reducing waste and protecting the environment.  相似文献   

13.
Kemmitt et al. (Kemmitt, S.J., Lanyon, C.V., Waite, I.S., Wen, Q., Addiscott, T.M., Bird, N.R.A., O'Donnell, A.G., Brookes, P.C., 2008. Mineralization of native soil organic matter is not regulated by the size, activity or composition of the soil microbial biomass - a new perspective. Soil Biology & Biochemistry 40, 61-73) recently proposed the “Regulatory Gate” hypothesis, which states that decomposition of soil organic matter (SOM) is regulated solely by abiotic factors. Without studying the mechanisms of such regulation, Kemmitt with coauthors challenged the classical Winogradsky theory of soil microbiology and questioned the concept of autochtonous and zymogenous microbial populations. In this letter, we revive the significance of microbial activity for SOM decomposition especially for the short-term (hours to weeks) processes and show that the “Regulatory Gate” is (micro)biologically driven.We explain the results of the three experiments in Kemmitt et al. (2008) from a microbiological point of view and suggest that SOM decomposition is mainly regulated by exoenzymes. We criticize the abiotic Regulatory Gate hypothesis based on bottleneck processes and pools limiting the SOM decomposition rate, comparison of constant and changing environmental conditions, as well as the connection between community structure and functions. We explain the results of Kemmitt et al. (2008) according to the properties of soil microbial community: functional redundancy and inconsistency between the excessive (but largely inactive) pool of total microbial biomass and the real mineralization activity. Finally, we suggest that to gain new perspectives on SOM decomposition and many other biochemical processes, future studies should focus on hot spots of (micro)biological activity (i.e., the rhizosphere, drillosphere, detritosphere, biopores, etc.) rather than on the bulk soil.  相似文献   

14.
In the New Jersey Pinelands, canopy gaps in the pine-dominated forest support patches of lichens, mosses, and caespitose grasses. We tested the hypotheses that non-vascular plants and lichens can affect nutrient cycling processes and that mosses and lichens would differ from each other. We predicted that (1) lichen tissues would decompose more slowly than pine or moss tissues, (2) all plant materials would decompose more slowly beneath lichens than beneath mosses, and (3) soil enzyme activities would be higher under lichens than under mosses or grasses, reflecting greater nutrient limitation. We compared rates of decomposition of the litter of Pinus rigida and moss and lichen tissues, and measured soil enzyme activities responsible for nutrient mineralization from litter (acid and alkaline phosphatases, chitinase, β-glucosidase, aminopeptidase, and phenol oxidase) under three types of groundcover (lichens, mosses, and grasses) and unvegetated soil at two sites. While groundcover affected enzyme activities, the patterns of enzyme activities differed markedly between the two sites. In general, the enzyme activities were uniformly low. Decomposition rates were more strongly affected by the groundcover than by litter materials. While all litters tended to decompose more slowly under lichens than under mosses, supporting one of our initial hypotheses, the rates of decomposition were markedly different between the two sites. These results suggest that while mosses and lichens create patches of different soil function in both sites, the differences between the sites in unknown factors cause the enzyme activities and decomposition rates to differ.  相似文献   

15.
Lichens are prominent components of many biological soil crusts. Owing to their persistence, lichen thalli create microhabitats for other microbes. Here, the structure of bacterial communities at the thallus–soil interface in lichen soil crusts was studied by using fluorescence in situ hybridization (FISH), confocal laser scanning microscopy (CLSM) and 3D image reconstruction. Terricolous lichen thalli above the tree-line in open habitats of the Austrian Alps were sampled. We selected six lichen species associated with green algal photobionts: Arthrorhaphis citrinella, Baeomyces placophyllus, B. rufus, Icmadophila ericetorum, Psora decipiens and Trapeliopsis granulosa. Alphaproteobacteria and Acidobacteria are predominant in these soil crust lichens, where the latter are frequently present in the lower part of lichen thalli and in the hypothallosphere. In the inconspicuous thallus structures of Arthrorhaphis citrinella, Baeomyces rufus, Icmadophila ericetorum and Trapeliopsis granulosa we observed association of bacteria with algal cells in soil particles and on the outer surface of the mycobiont–photobiont aggregates. We found bacterial cells intermixed with photobiont cells in the lower part of the lichen thalli and as small colonies on the surface of the squamules of Baeomyces placophyllus and Psora decipiens. Moreover, technical issues of performing FISH and confocal microscopy with biological soil crusts are discussed.  相似文献   

16.
《Geoderma》1987,39(3):235-247
Two humic acids of different origin (peat and soil) were degraded with a 5% sodium perborate solution (140°C). This degradation process consists mainly of a stoichiometric production of hydrogen peroxide while the perborate is reacting with carboxyl groups of the oxidized polymers. A single perborate treatment degraded more than 40% of the humic acids to soluble products, but a 5-step oxidation was necessary for total degradation, the sample being transformed into soluble oligomers with properties similar to those of fulvic acids. The oligomeric fractions with lowest molecular weights, including individual molecules (soluble in ethyl acetate), were purified by adsorption chromatography and studied by GC-MS after methylation. The higher molecular weight fractions of oligomers were recovered over polyvinylpyrrolidone, eluted by alkali, and purified by ion-exchange chromatography (47% peat HA; 25% soil HA).Degradation products included alkanes, fatty acids and dicarboxylic acids. Aromatic compounds (mainly phenolic, benzenecarboxylic and cinnamic acids), amounted to 24–50% of the total volatile degradation products. There were striking differences between peat and soil humic acids, the former yielding typical lignin degradation products. Independently checked, the perborate degradation products were not the same as those obtained by mild treatment with hydrogen peroxide under alkaline conditions.  相似文献   

17.
Fungal oxidative exo-enzymes lacking substrate specificity play a central role in the cycling of soil organic matter. Due to their broad ecological impact and available knowledge of their gene structure, laccases appeared to be appropriate markers to monitor fungi with this kind of oxidative potential in soils. A degenerate PCR-primer pair Cu1F/Cu2R, specific for basidiomycetes, was designed to assess directly the diversity of laccase genes in soils. PCR amplification of mycelial cultures and fruit-bodies of a wide spectrum of basidiomycetes, covering all functional groups (saprophytes, symbionts, and pathogens), produced multiple DNA fragments around 200 bp. A neighbor-joining tree analysis of the PCR-amplified laccase sequences showed a clear species-specificity, but also revealed that most fungal taxa possess several laccase genes showing a large sequence divergence. This sequence diversity precluded the systematic attribution of amplified laccase of unknown origin to specific taxa. Amplification of laccase sequences from DNA, extracted from a brown (moder) forest soil, showed a specific distribution of laccase genes and of the corresponding fungal species in the various soil horizons (Oh, Ah, Bv). The most organic Oh-horizon displayed the highest gene diversity. Saprophytic fungi appeared to be less widespread through the soil horizons and displayed a higher diversity of laccase genes than the mycorrhizal ones.  相似文献   

18.
The source of N2O in terrestrial ecosystems has long been debated. Both nitrification and denitrification produce N2O but their relative importance remains uncertain. Here we apply site preference, SP (the difference in δ15N between the central and outer N atom in N2O), to estimate the relative importance of bacterial denitrification (including nitrifier denitrification) to total N2O production from soil. We measured SP over a diurnal cycle following the third year of tillage of a previously uncultivated grassland soil at the Kellogg Biological Station (KBS) in southwestern Michigan. Fluxes of N2O in our study ranged between 7.8 and 12.1 g N2O-N ha−1 d−1 and were approximately 3 and 10 times greater than fluxes observed in managed agricultural and successional fields, respectively, at KBS. Consequently, our study captured a period of high flux resulting from the cultivation of a historically never-tilled soil. Concentration weighted SP values decreased from 12.9‰ in the morning to a minimum value of −0.1‰ in the afternoon.Based on SP values reported for bacterial denitrification (−5 to 0‰; Toyoda et al., 2005; Sutka et al., 2006), hydroxylamine oxidation (nitrification) and fungal denitrification (33-37‰; Sutka et al., 2006) we found that production attributable to bacterial denitrification increased from between 52.9 and 60.9% in the morning to between 87.5 and 100% in the afternoon. Further, we observed diurnal variation in flux and SP that is consistent with increased production from bacterial denitrification associated with temperature-driven increases in respiration.  相似文献   

19.
Proteinases in the humus-feeding larva of Pachnoda ephippiata were partially purified and characterized. Proteinase activity from the midgut was alkali-stable and its pH optimum for activity was about pH 12. Nine proteolytic bands were visible on zymogram gels containing gelatin; one band of 19 kDa was dominant. P. ephippiata mainly employed serine proteinases for digestive proteolysis. The combination of strong midgut alkalinity and midgut proteinases with pronounced alkali stability, a high proteolytic activity on model humic acids, and a large tolerance to high humic acid concentrations would enable the P. ephippiata to gain nutrients from soil by digesting the proteinaceous component of soil humic substances.  相似文献   

20.
《CATENA》2004,55(1):1-15
The terricolous lichen communities occurring under a temperate sub-arid to sub-humid climate (mean annual rainfall about 750 mm) on Pliocene clay soils of southern Tuscany (central Italy) are similar to those reported for arid or sub-arid areas, with mean annual rainfall around 200 mm. The distribution of these communities is influenced by the availability of bare soil and percentage cover of vascular plants. Where vascular communities are more important and pedogenetic processes lead to the development of more structured and evolved soils, pioneer lichen communities of the Toninio-Psoretum decipientis are replaced by communities such as that of Cladonietum convolutae, which are more capable of competing for light and nutrients with dense communities of tall grasses such as Bromus erectus. The distribution patterns of Artemisia cretacea and B. erectus among vascular plants, and Fulgensia fulgens and Cladonia rangiformis among lichens, account for most of the variability in vascular and lichen communities, respectively.  相似文献   

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