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1.
Mecoprop-p [(R)-2-(4-chloro-2-methylphenoxy) propanoic acid) is widely used in agriculture and poses an environmental concern because of its susceptibility to leach from soil to water. We investigated the effect of soil depth on mecoprop-p biodegradation and its relationship with the number and diversity of tfdA related genes, which are the most widely known genes involved in degradation of the phenoxyalkanoic acid group of herbicides by bacteria. Mecoprop-p half-life (DT50) was approximately 12 days in soil sampled from <30 cm depth, and increased progressively with soil depth, reaching over 84 days at 70-80 cm. In sub-soil there was a lag period of between 23 and 34 days prior to a phase of rapid degradation. No lag phase occurred in top-soil samples prior to the onset of degradation. The maximum degradation rate was the same in top-soil and sub-soil samples. Although diverse tfdAα and tfdA genes were present prior to mecoprop-p degradation, real time PCR revealed that degradation was associated with proliferation of tfdA genes. The number of tfdA genes and the most probable number of mecoprop-p degrading organisms in soil prior to mecoprop-p addition were below the limit of quantification and detection respectively. Melting curves from the real time PCR analysis showed that prior to mecoprop-p degradation both class I and class III tfdA genes were present in top- and sub-soil samples. However at all soil depths only tfdA class III genes proliferated during degradation. Denaturing gradient gel electrophoresis confirmed that class III tfdA genes were associated with mecoprop-p degradation. Degradation was not associated with the induction of novel tfdA genes in top- or sub-soil samples, and there were no apparent differences in tfdA gene diversity with soil depth prior to or following degradation.  相似文献   

2.
The impact of exotic plant invasions on soil communities and nutrient cycling processes has received an increasing attention in recent years. To test whether the exotic plant invasions affect nematode communities through altering litter quality, we compared mass loss and nematode colonization during the stem litter decomposition of invasive Spartina alterniflora and native Phragmites australis in salt marshes of the Yangtze River estuary, China. Plastic drinking straws were synchronously used as controls. The addition of plant residues was found stimulating the growth of nematodes, particularly bacterial feeders on day 16 after burial. A top-down control of bacterivous nematodes by carnivores existed in nematode succession during the litter decomposition. With higher nitrogen content and lower C:N ratio, stem litter of the invasive S. alterniflora decayed faster and supported more abundant nematodes than the native P. australis. The greater nematode abundance in S. alterniflora was mainly due to two dominant genera of bacterial nematodes, namely Diplolaimelloides and Diplolaimella. Lower values of maturity index and structure index in S. alterniflora than in P. australis litter indicate that a more degraded food web condition resulted from the faster litter decay. A considerable difference in nematode community structures between two litter types only occurred in a certain period of the decomposition (from 8 to 32 days after burial), suggesting that the changes in faunal community structure are time dependent. In summary, this study confirmed the hypothesis that the invasion of S. alterniflora stimulates the growth of bacterial nematodes by producing higher quality of litter than the native P. australis. The results obtained here suggest that the invasion of exotic plant is likely to alter ecosystem functions indirectly through exerting its effect on soil decomposer communities such as nematodes.  相似文献   

3.
Litter decomposing basidiomycetous fungi produce ligninolytic oxidases and peroxidases which are involved in the transformation of lignin, as well as humic and fulvic acids. The aim of this work was to evaluate their importance in lignin transformation in forest litter. Two litter decomposing basidiomycete species differing in their abilities to degrade lignin - Hypholoma fasciculare, and Gymnopus erythropus - were cultured on sterile or non-sterile oak litter and their transformation of a 14C-labelled synthetic lignin (dehydrogenation polymer 14C-DHP) was compared with that of the indigenous litter microflora. Both in sterile and non-sterile litter, colonisation by basidiomycetes led to higher titres of lignocellulose-degrading enzymes, in particular of laccase and Mn-peroxidase (MnP). The titres of the latter were 6 to 40-fold increased in the presence of basidiomycetes compared to non-sterile litter. During 10 weeks, G. erythropus mineralised over 31% of 14C-DHP in sterile litter and 23% in non-sterile litter compared to 14% in the non-sterile control. Lignin mineralization by H. fasciculare was comparable to the non-sterile control, 12% in sterile litter and 16% in the non-sterile litter. The largest part of 14C from 14C-DHP was transformed into humic compounds during litter treatment with both fungi as well as in the control. In addition to the fast lignin mineralization, microcosms containing G. erythropus also showed a lower final content of unaltered lignin and 23-28% of the lignin was converted into water-soluble compounds with relatively low molecular mass (<5 kDa). Both G. erythropus and H. fasciculare were also able to further mineralise humic compounds. During a 10-week fungal treatment of an artificial 14C-humic acid (14C-HA) supplemented to the natural humic material of a forest soil, the fungi mineralised 42% and 19% of the labelled material, respectively, under sterile conditions. The 14C-HA mineralization by introduced basidiomycetes in microcosms containing non-sterile humic material, however, did not significantly differ from that of a non-sterile control and was around 12%. Altogether the results show that saprobic basidiomycetes can considerably differ in their rates of lignin and humic substance conversion. Furthermore, lignin degradation in forest soil can rather slow down by interspecific competition than it is accelerated by cooperation of different microorganisms occupying specific nutritional niches. Therefore, the overall contribution of saprobic basidiomycetes depends on their particular eco-physiological status and the competitive pressure, and may be often lower than initially expected. Significant lignin transformation including partial mineralization is seemingly not exclusively dependent on exceptional high titres of ligninolytic enzymes but also on so far unknown factors. Higher endocellulase production and subsequent weight loss was found in microcosms where saprobic basidiomycetes were combined with indigenous microbes. Potentially, lignin degradation by the basidiomycetes may have increased cellulose availability to the indigenous microbes.  相似文献   

4.
The objectives of this study were to evaluate the contribution of arbuscular mycorrhizal (AM) fungal hyphae to 15N uptake from vineyard cover crop litter (Medicago polymorpha), and to examine the soil microbial community under the influence of mycorrhizal roots and extraradical hyphae. Mycorrhizal grapevines (Vitis vinifera) were grown in specially designed containers, within which a polyvinyl chloride (PVC) mesh core was inserted. Different sizes of mesh allowed mycorrhizal roots (mycorrhizosphere treatment) or extraradical hyphae (hyphosphere treatment) to access dual labeled 15N and 13C cover crop litter that was placed inside the cores after 4 months of grapevine growth. Mesh cores in the bulk soil treatment, which served as a negative control, had the same mesh size as the hyphosphere treatment, but frequent rotation prevented extraradical hyphae from accessing the litter. Grapevines and soils were harvested 0, 7, 14, and 28 days after addition of the cover crop litter and examined for the presence of 15N. Soil microbial biomass and the soil microbial community inside the mesh cores were examined using phospholipid fatty acid analysis. 15N concentrations in grapevines in the hyphosphere treatment were twice that of grapevines in the bulk soil treatment, suggesting that extraradical hyphae extending from mycorrhizal grapevine roots may have a role in nutrient utilization from decomposing vineyard cover crops in the field. Nonetheless, grapevines in the mycorrhizosphere treatment had the highest 15N concentrations, thus highlighting the importance of a healthy grapevine root system in nutrient uptake. We detected similar peaks in soil microbial biomass in the mycorrhizosphere and hyphosphere treatments after addition of the litter, despite significantly lower microbial biomass in the hyphosphere treatment initially. Our results suggest that although grapevine roots play a dominant role in the uptake of nutrients from a decomposing cover crop, AM hyphae may have a more important role in maintaining soil microbial communities associated with nutrient cycling.  相似文献   

5.
Due to the production of lignocellulose-degrading enzymes, saprotrophic basidiomycetes can significantly contribute to the turnover of soil organic matter. The production of lignin- and polysaccharide-degrading enzymes and changes of the chemical composition of litter were studied with three isolates from a Quercus petraea forest. These isolates were capable of fresh litter degradation and were identified as Gymnopus sp., Hypholoma fasciculare and Rhodocollybia butyracea. Within 12 weeks of incubation, H. fasciculare decomposed 23%, R. butyracea 32% and Gymnopus sp. 38% of the substrate dry mass. All fungi produced laccase and Mn-peroxidase (MnP) and none of them produced lignin peroxidase or other Mn-independent peroxidases. There was a clear distinction in the enzyme production pattern between R. butyracea or H. fasciculare compared to Gymnopus sp. The two former species caused the fastest mass loss during the initial phase of litter degradation, accompanied by the temporary production of laccase (and MnP in H. fasciculare) and also high production of hydrolytic enzymes that later decreased. In contrast, Gymnopus sp. showed a stable rate of litter mass loss over the whole incubation period with a later onset of ligninolytic enzyme production and a longer lasting production of both lignin and cellulose-degrading enzymes. The activity of endo-cleaving polysaccharide hydrolases in this fungus was relatively low but it produced the most cellobiose hydrolase. All fungi decreased the C/N ratio of the litter from 24 to 15-19 and Gymnopus sp. also caused a substantial decrease in the lignin content. Analytical pyrolysis mass spectrometry of litter decomposed by this fungus showed changes in the litter composition similar to those caused by white-rot fungi during wood decay. These changes were less pronounced in the case of H. fasciculare and R. butyracea. All fungi also changed the mean masses of humic acid and fulvic acid fractions isolated from degraded litter. The humic acid fraction after degradation by all three fungi contained more lignin and less carbohydrates. Compared to the decomposition by saprotrophic basidiomycetes, litter degradation in situ on the site of fungal isolation resulted in the relative enrichment of lignin and differences in lignin composition revealed by analytical pyrolysis. It can most probably be explained by the participation of non-basidiomycetous fungi and bacteria during natural litter decomposition.  相似文献   

6.
Cutover peatlands are often rapidly colonised by pioneer plant species, which have the potential to affect key ecosystem processes such as carbon (C) turnover. The aim of this study was to investigate how plant cover and litter type affect fungal community structure and litter decomposition in a cutover peatland. Intact cores containing Eriophorum vaginatum, Eriophorum angustifolium, Calluna vulgaris and bare soil were removed and a mesh bag with litter from only one of each of these species or fragments of the moss Sphagnum auriculatum was added to each core in a factorial design. The presence or absence of live plants, regardless of the species, had no effect on mass loss, C, nitrogen (N) or phosphorus (P) concentrations of the litter following 12 months of incubation. However, there was a very strong effect of litter type on mass loss and concentrations of C, N and P between most combinations of litter. Similarly, plant species did not affect fungal community structure but litter type had a strong effect, with significant differences between most pairs of litter types. The data suggest that labile C inputs via rhizodeposition from a range of plant functional types that have colonised cutover bogs for 10-15 years have little direct effect on nutrient turnover from plant litter and in shaping litter fungal community structure. In contrast, the chemistry of the litter they produce has much stronger and varied effects on decomposition and fungal community composition. Thus it appears that there is distinct niche differentiation between the fungal communities involved in turnover of litter versus rhizodeposits in the early phases of plant succession on regenerating cutover peatlands.  相似文献   

7.
The chemical composition and quantity of plant inputs to soil are primary factors controlling the size and structure of the soil microbial community. Little is known about how changes in the composition of the soil microbial community affect decomposition rates and other ecosystem functions. This study examined the degradation of universally 13C-labeled glucose, glutamate, oxalate, and phenol in soil from an old-growth Douglas-fir (Pseudotsuga menziesii)—western hemlock (Tsuga heterophylla) forest in the Oregon Cascades that has experienced 7 y of chronic C input manipulation. The soils used in this experiment were part of a larger Detritus Input and Removal Treatment experiment and have received normal C inputs (control), doubled wood inputs, or root and litter input exclusion (no inputs). Soil from the doubled wood treatment had a higher fungal:bacterial ratio, and soil from the no inputs treatment had a lower fungal:bacterial ratio, than the control soil. Differences in the utilization of the compounds added to the field-manipulated soils were assessed by following the 13C tracer into microbial biomass and respiration. In addition, 13C-phospholipid fatty acids (PLFA) analysis was used to examine differential microbial utilization of the added substrates. Glucose and glutamate were metabolized similarly in soils of all three litter treatments. In contrast, the microbial community in the double wood soil respired more added phenol and oxalate, whereas microbes in the no inputs soil respired less added phenol and oxalate, than the control soil. Phenol was incorporated primarily into fungal PLFA, especially in soil of the double wood treatment. The addition of all four substrates led to enhanced degradation of soil organic matter (priming) in soils of all three litter treatments, and was greater following the addition of phenol and oxalate as compared to glucose and glutamate. Priming was greater in the no inputs soil as compared to the control or doubled wood soils. These results demonstrate that altering plant inputs to soil can lead to changes in microbial utilization of C compounds. It appears that many of these changes are the result of alteration in the size and composition of the microbial community.  相似文献   

8.
We compare forest floor microbial communities in pure plots of four tree species (Thuja plicata, Tsuga heterophylla, Pseudotsuga menziesii, and Picea sitchensis) replicated at three sites on Vancouver Island. Microbial communities were characterised through community level physiological profiles (CLPP), and profiling of phospholipid fatty acids (PLFA).Microbial communities from cedar forest floors had higher potential C utilisation than the other species. The F layer of the forest floor under cedar contained significantly higher bacterial biomass (PLFA) than the F layer under the other three tree species. There were differences in microbial communities among the three sites: Upper Klanawa had the highest bacterial biomass and potential C utilisation; this site also had the highest N availability in the forest floors. Forest floor H layers under hemlock and Douglas-fir contained greater biomass of Gram positive, Gram negative bacteria and actinomycetes than F layers based on PLFA, and H layers under spruce contained greater biomass of Gram negative bacteria than F layers. There were no significant differences in bacterial biomass between forest floor layers under cedar. Fungal biomass displayed opposite trends to bacteria and actinomycetes, being lowest in cedar forest floors, and highest in the F layer and at the site with lowest N availability. There were also differences in community composition among species and sites, with cedar forest floors having a much lower fungal:bacterial ratio than spruce, hemlock and Douglas-fir. The least fertile Sarita Lake site had a much greater fungal:bacterial ratio than the more fertile San Juan and Upper Klanawa sites. Forest floor layer had the greatest effect on microbial community structure and potential function, followed by site, and tree species. The similarity in trends among measures of N availability and microbial communities is further evidence that these techniques provide information on microbial communities that is relevant to N cycling processes in the forest floor.  相似文献   

9.
Peatlands represent massive global C pools and sinks. Carbon accumulation depends on the ratio between net primary production and decomposition, both of which can change under projected increases of atmospheric CO2 and N deposition. The decomposition of litter is influenced by 1) the quality of the litter, and 2) the microenvironmental conditions in which the litter decomposes. This study aims at experimentally testing the effects of these two drivers in the context of global change. We studied the in situ litter decomposition from three common peatland species (Eriophorum vaginatum, Polytrichum strictum and Sphagnum fallax) collected after one year of litter production under pre-treatment conditions (elevated CO2: 560 ppm or enhanced N: 3 g m−2 y−1 NH4NO3) and decomposed the following year under treatment conditions (same as pre-treatment). By considering the cross-effects between pre-treatments and treatments, we distinguished between the effects on mass loss of 1) the pre-treatment-induced litter quality and 2) the treatment conditions under which the litters were decomposing. The combination between CO2 pre-treatment and CO2 treatment reduced Polytrichum decomposition by −24% and this can be explained by litter quality-driven decomposition changes brought by the pre-treatment. CO2 pre-treatment reduced Eriophorum litter quality, although this was not sufficient to predict decomposition. The N addition pre-treatment reduced the decomposition of Eriophorum, due to enhanced lignin and soluble phenols concentrations in the initial litter, and reduced litter-driven losses of starch and enhanced litter-driven losses of soluble phenols. While decomposition indices based on initial litter quality provide a broad explanation of quantitative and qualitative decomposition, they can only be taken as first approximations. Indeed, the microbial ATP activity, the litter N loss and resulting litter quality, were strongly altered irrespective of the compounds' initial concentration and by means of processes that occurred independently of the initial litter-qualitative changes. The experimental design was valuable to assess litter- and ecosystem-driven decomposition pathways simultaneously or independently. The ability to separate these two drivers makes it possible to attest the presence of litter-qualitative changes even without any litter biochemical determinations, and shows the screening potential of this approach for future experiments dealing with multiple plant species.  相似文献   

10.
Cellulose and lignin degradation dynamics was monitored during the leaf litter decomposition of three typical species of the Mediterranean area, Cistus incanus L., Myrtus communis L. and Quercus ilex L., using the litter bag method. Total N and its distribution among lignin, cellulose and acid-detergent-soluble fractions were measured and related to the overall decay process. The litter organic substance of Cistus and Myrtus decomposed more rapidly than that of Quercus. The decay constants were 0.47 year−1, 0.75 year−1 and 0.30 year−1 for Cistus, Myrtus and Quercus, respectively. Lignin and cellulose contents were different as were their relative amounts (34 and 18%, 15 and 37%, 37 and 39% of the overall litter organic matter before exposure, for Cistus, Myrtus and Quercus, respectively). Lignin began to decrease after 6 and 8 months of exposure in Cistus and Myrtus, respectively, while it did not change significantly during the entire study period in Quercus. The holocellulose, in contrast, began to decompose in Cistus after 1 year, while in Quercus and Myrtus immediately. Nitrogen was strongly immobilized in all the litters in the early period of decay. Its release began after the first year in Cistus and Myrtus and after 2 years of decomposition in Quercus. These litters still contained about 60, 20 and 90% of the initial nitrogen at the end of the experiment (3 years). Prior to litter exposure nitrogen associated with the lignin fraction was 65, 54 and 37% in Cistus, Myrtus and Quercus, while that associated with the cellulose fraction was 30, 24 and 28%. Although most of the nitrogen was not lost from litters, its distribution among the litter components changed significantly during decomposition. In Cistus and Myrtus the nitrogen associated with lignin began to decrease just 4 months after exposure. In Quercus this process was slowed and after 3 years of decomposition 8% of the nitrogen remained associated with lignin or lignin-like substances. The nitrogen associated with cellulose or cellulose-like substances, in contrast, began to decrease from the beginning of cellulose decomposition in all three species. At the end of the study period most of the nitrogen was not associated to the lignocellulose fraction but to the acid-detergent-soluble substance (87, 88 and 84% of the remaining litter nitrogen).  相似文献   

11.
The palatability to isopods and microbes of a broad range of hardwood leaf litter, derived from three field CO2-enrichment experiments in the USA, was investigated, using δ13C, to trace the C flow from litter to isopods and to CO2 respired by microbial decomposition. Leaf litter grown under elevated CO2 had δ13C values ranging from −39 to −45‰, which were significantly different from ambient litter δ13C values of around −30‰. Litter palatability to isopods of the Porcellio sp. was tested by incubating ambient- and elevated-CO2 litter, and a mixture of the two, in the presence of isopods for 14 days, under environmentally controlled conditions; δ13C was measured on litter and isopods' body before and after incubation. In an additional experiment, litter was incubated in the absence of fauna for 30 days, and on five occasions the δ13C of the CO2 respired from litter was measured. The 13C label was clearly carried from the litter source to the isopods' bodies, and their faeces. For microbial-respired CO2, δ13C was significantly higher than that of the litter source, suggesting preferential degradation of substrates enriched in 13C as compared to those in the overall litter. With the exception of Quercus myrtifolia leaf litter, elevated CO2 did not affect the palatability to isopods nor the microbial degradation of any of the litters, possibly as a result of unaltered litter N concentration. However, significant differences in litter palatability and decay rates were observed among the different species. With this study, the use of isotopically labelled litter material was confirmed as a key methodology that can significantly contribute to the advancement of the understanding of litter decomposition and of the quantification of C fluxes in the process.  相似文献   

12.
Real-time quantitative PCR assays, targeting part of the ammonia monooxygenase (amoA), nitrous oxide reductase (nosZ), and 16S rRNA genes were coupled with 15N pool dilution techniques to investigate the effects of long-term agricultural management practices on potential gross N mineralization and nitrification rates, as well as ammonia-oxidizing bacteria (AOB), denitrifier, and total bacterial community sizes within different soil microenvironments. Three soil microenvironments [coarse particulate organic matter (cPOM; >250 μm), microaggregate (53-250 μm), and silt-and-clay fraction (<53 μm)] were physically isolated from soil samples collected across the cropping season from conventional, low-input, and organic maize-tomato systems (Zea mays L.-Lycopersicum esculentum L.). We hypothesized that (i) the higher N inputs and soil N content of the organic system foster larger AOB and denitrifier communities than in the conventional and low-input systems, (ii) differences in potential gross N mineralization and nitrification rates across the systems correspond with AOB and denitrifier abundances, and (iii) amoA, nosZ, and 16S rRNA gene abundances are higher in the microaggregates than in the cPOM and silt-and-clay microenvironments. Despite 13 years of different soil management and greater soil C and N content in the organic compared to the conventional and low-input systems, total bacterial communities within the whole soil were similar in size across the three systems (∼5.15 × 108 copies g−1 soil). However, amoA gene densities were ∼2 times higher in the organic (1.75 × 108 copies g−1 soil) than the other systems at the start of the season and nosZ gene abundances were ∼2 times greater in the conventional (7.65 × 107 copies g−1 soil) than in the other systems by the end of the season. Because organic management did not consistently lead to larger AOB and denitrifier communities than the other two systems, our first hypothesis was not corroborated. Our second hypothesis was also not corroborated because canonical correspondence analyses revealed that AOB and denitrifier abundances were decoupled from potential gross N mineralization and nitrification rates and from inorganic N concentrations. Our third hypothesis was supported by the overall larger nitrifier, denitrifier, and total bacterial communities measured in the soil microaggregates compared to the cPOM and silt-and-clay. These results suggest that the microaggregates are microenvironments that preferentially stabilize C, and concomitantly promote the growth of nitrifier and denitrifier communities, thereby serving as potential hotspots for N2O losses.  相似文献   

13.
Condensed tannins (CT) can strongly affect litter decomposition, but their fate during the decomposition process, in particular as influenced by detritivore consumption, is not well understood. We tested the hypothesis that litter CT are reduced by the gut passage of two functionally distinct detritivores of Mediterranean forests, the millipede Glomeris marginata, and the land snail Pomatias elegans, as a fixed proportion of initial litter CT, but more so in Pomatias since snails are known to have a more efficient enzymatic capacity. Contrary to our hypothesis, both detritivore species reduced litter CT to near zero in their faecal pellets irrespective of the wide range in initial leaf litter CT concentrations of 9-188 mg g−1 d m among three Mediterranean tree species (Pistacia terebinthus, Quercus ilex, Alnus glutinosa) and different decomposition stages of their litter. The almost complete disappearance of CT even from some litter types highly concentrated in CT, due to either degradation by gut microorganism or complexation of CT into insoluble high molecular weight structures, suggests a high “de-tanning” efficiency across functionally distinct detritivore species. The transformation of CT-rich litter into virtually CT-free faecal pellets by detritivores might be highly relevant for the subsequent decomposition process in ecosystems with a high macrofauna abundance and CT-rich plant species such as Mediterranean forests.  相似文献   

14.
The relative importance of specific plant properties versus soil characteristics in shaping the bacterial community structure of the rhizosphere is a topic of considerable debate. Here, we report the results of a study on the bacterial composition of the rhizosphere of the wild plant Carex arenaria (sand sedge) growing at 10 natural sites in The Netherlands. The soil properties of the sandy soils at these sites were highly disparate, most notably in pH, chloride and organic matter content. Rhizosphere and bulk soil bacterial communities were examined by culture-independent means, namely, 16S rDNA-directed PCR-DGGE profiling. Large differences were observed between the bacterial communities of the different sites for both bulk and rhizosphere soil. Cluster analysis of bacterial profiles revealed that the rhizosphere community of each site was generally more closely related to the bulk soil community of that site rather than to rhizosphere communities of other sites. Hence, bacterial community structure within the rhizosphere of C. arenaria appeared to be determined to a large extent by the bulk soil community composition. This conclusion was supported by a reciprocal planting experiment, where C. arenaria shoots of different sites yielded highly similar rhizosphere communities when planted in the same soil.  相似文献   

15.
The phenoxyalkanoic acid herbicides constitute a group of chemically related molecules that have been widely used for over 50 years. A range of bacteria have been selected from various locations for their ability to degrade these compounds. Previously reported strains able to utilise 2,4-dichlorophenoxyacetic acid (2,4-D) include, Ralstonia eutropha JMP134, Burkholderia sp. RASC and Variovorax paradoxus TV1 and Sphingomonas sp. AW5 able to utilise 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). In addition a novel set of mecoprop-degrading strains including Alcaligenes denitrificans, Alcaligenes sp. CS1 and Ralstonia sp. CS2 are here described. It has been reported recently that TfdA enzymes, initially reported to have a role in 2,4-D catabolism are also involved in the first-step cleavage of related phenoxyalkanoate herbicides. However, a diversity of tfdA gene sequences have been reported. We relate the tfdA gene type to the metabolic ability of these strains. The tfdA-like genes were investigated by polymerase chain reaction amplification using a set of specific tfdA primers. Degradation ability was observed via phenol production from a range of unsubstituted and substituted phenoxyalkanoics including, 2,4-D, 2-methyl 4-chlorophenoxyacetic acid (MCPA), racemic mecoprop, (R)-mecoprop, 2-(2,4-dichlorophenoxy) propionic acid (racemic 2,4-DP), 2,4,5-T, 2,4-dichlorophenoxybutyric acid (2,4-DB), 4-chloro-2-methylphenoxybutyric acid (MCPB) and phenoxyacetate. Mecoprop-degrading strains showed partial tfdA sequences identical to the one described for V. paradoxus TV1 (a strain isolated on 2,4-D). However, substrate specificity was not identical as V. paradoxus exhibited greatest activity towards 2,4-D and MCPA only, whereas the mecoprop-degrading strains showed intense activity towards 2,4-D, MCPA, racemic mecoprop and (R)-mecoprop as substrates. However, Sphingomonas sp. AW5 which has been shown to carry a very different tfdA-like gene was the only strain to utilise the phenoxybutyric acid MCPB as a sole carbon source. In this study, we thus demonstrate that sequence diversity is not related to substrate specificity within the tfdA-like gene family. However, phylogenetically unrelated sequences may govern substrate specific activity.  相似文献   

16.
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17.
As part of a study of the processes involved in litter biodegradation, we considered the variations over 1 year of the phosphatase activities in sclerophyllous evergreen oak litter (Quercus ilex L.). Evergreen oak is representative of tree species in the forests of the French Mediterranean area. Acid (E.C. 3.1.3.2.) and alkaline (E.C. 3.1.3.1.) phosphatases, were measured over 13 months in the forest litter, along with several biotic and abiotic variables, potentially involved in the regulation of these enzymes. These comprised moisture, temperature, pH, water-extractable inorganic P (PI), fungi, culturable heterotrophic bacteria and protein concentrations. Moisture considerably affected the production of proteins and acid phosphatases, probably formed by litter microorganisms. This result corroborated the study of Criquet et al. [Soil Biology and Biochemistry 34 (2002) 1111] which indicated that rainfall was the most important factor regulating the production and the activity of numerous enzymes in sclerophyllous forest litter. However, it appeared that moisture cannot alone predict all of the variations in phosphatase activities and the mineralisation rate of organic P (PO). Indeed, principal component analyses (PCA) and multiple regressions showed that temperature and bacterial communities were also implicated in phosphatase dynamics and PO mineralisation. Acid phosphatases were negatively correlated with the temperature, whilst alkaline phosphatases were positively correlated with this variable. The significant correlation obtained between bacteria and PI concentrations, and the lack of correlation between bacteria and both acid and alkaline phosphomonoesterases, suggest that other important phosphatase types, such as phosphodiesterases, must be strongly implicated in PO mineralisation of the litter and in the regulation of P microbial metabolism.  相似文献   

18.
Seven most efficient phytase and phosphatases producing fungi were isolated from the soils of arid and semi-arid regions of India and tested for their efficiency on hydrolysis of two important organic P compounds: phytin and glycerophosphate. The native soil organic P may be exploited after using these organisms as seed inoculants, to help attain higher P nutrition of plants. The identified organisms belong to the three genera: Aspergillus, Emmericella and Penicillium. Penicillium rubrum released the most acid into the medium during growth. Aspergillus niger isolates were found to accumulate biomass the fastest. A significant negative correlation (r=−0.593,n=21, p<0.01) was observed between the development of fungal mat and pH of the media. The extracellular (E) phosphatases released by different fungi were less than their intracellular (I) counterpart, but the trend was reversed in case of phytase production. The E:I ratio of different fungi ranged from 0.39 to 0.86 for acid phosphatase, 0.29 to 0.41 for alkaline phosphatases and 9.4 to 19.9 for phytase. The efficiency of hydrolysis of different organic P compounds of different fungi varied from 2.12-4.85 μg min−1 g−1 for glycerophosphate to 0.92-2.10 μg min−1 g−1 for phytin. The trend of efficiency was as follows: Aspergillus sp.>Emmericella sp.>Penicillium sp. The results indicated that the identified fungi have enough potential to exploit native organic phosphorus to benefit plant nutrition.  相似文献   

19.
In the present study, the temporal and spatial variation of the abundance of the alkane monooxygenase gene alkB and 16S rRNA genes in different soil compartments was analysed in the presence or absence of 2-methyl-4-chlorophenoxyacetic acid (MCPA) after the addition of pea litter to soil in a microcosm study. Samples were analysed shortly after litter addition (T0) and 1?week (T1), 3?weeks (T3) and 6?weeks (T6) after the addition of litter. In addition also, the quantity and quality of litter-derived alkanes was analysed and measured. The results revealed a fast and complete degradation of MCPA in all compartments throughout the experiment. Nevertheless, significant changes in the distribution patterns of short- and middle-chained alkanes suggest an interaction of MCPA and alkane degradation. alkB gene copy numbers were highly influenced by the time point of analysis and by the investigated soil compartment. Overall, an increase in alkB gene copy numbers from T0 to T3 was visible in the upper soil compartments whereas a decrease compared to T0 was measured in the deeper soil compartments. MCPA addition resulted in an increase of alkB abundance at T6. Gene copy numbers of 16S rRNA were not influenced by sampling time and soil compartment. In contrast to the control treatments, a slight increase in 16S rRNA gene copy numbers was visible at T1 and T3 compared to T0 in all soil compartments.  相似文献   

20.
The effect of endogeic earthworms (Octolasion tyrtaeum (Savigny)) on the translocation of litter-derived carbon into the upper layer of a mineral soil by fungi was investigated in a microcosm experiment. Arable soil with and without O. tyrtaeum was incubated with 13C/15N-labelled rye leaves placed on plastic rings with gaze (64 μm mesh size) to avoid incorporation of leaves by earthworms. The plastic rings were positioned either on or 3 cm above the soil surface, to distinguish between biotic and chemical/physical translocation of nutrients by fungi and leaching.Contact of leaves to the soil increased 13C translocation, whereas presence of O. tyrtaeum reduced the incorporation of 13C into the mineral soil in all treatments. Although biomass of O. tyrtaeum decreased during the experiment, more 13C and 15N was incorporated into earthworm tissue in treatments with contact of leaves to the soil. Contact of leaves to the soil and the presence of O. tyrtaeum increased cumulative 13CO2-C production by 18.2% and 14.1%, respectively.The concentration of the fungal bio-indicator ergosterol in the soil tended to be increased and that of the fungal-specific phospholipid fatty acid 18:2ω6 was significantly increased in treatments with contact of leaves to the soil. Earthworms reduced the concentration of ergosterol and 18:2ω6 in the soil by 14.0% and 43.2%, respectively. Total bacterial PLFAs in soil were also reduced in presence of O. tyrtaeum, but did not respond to the addition of the rye leaves. In addition, the bacterial community in treatments with O. tyrtaeum differed from that without earthworms and shifted towards an increased dominance of Gram-negative bacteria.The results indicate that litter-decomposing fungi translocate litter-derived carbon via their mycelial network in to the upper mineral soil. Endogeic earthworms decrease fungal biomass by grazing and disruption of fungal hyphae thereby counteracting the fungal-mediated translocation of carbon in soils.  相似文献   

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