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1.
Afforestation and deforestation are key land-use changes across the world, and are considered to be dominant factors controlling ecosystem functioning and biodiversity. However, the responses of soil microbial communities to these land-use changes are not well understood. Because changes in soil microbial abundance and community structure have consequences for nutrient cycling, C-sequestration and long-term sustainability, we investigated impacts of land-use change, age of stand and soil physico-chemical properties on fungal and bacterial communities and their metabolic activities. This study was carried out at four sites in two geographical locations that were afforested on long-established pastures with Pinus radiata D. Don (pine). Two of the sites were on volcanic soils and two on non-volcanic soils and stand age ranged from 5 to 20 y. Microbial communities were analysed by biochemical (phospho-lipid fatty acids; PLFA) and molecular (multiplex-terminal restriction fragment length polymorphism; M-TRFLP) approaches. Both site and stand age influenced microbial properties, with changes being least detectable in the 5-y-old stand. Land use was a key factor influencing soil metabolic activities as measured by physiological profiling using MicroResp. Pasture soils had higher microbial biomass (P < 0.001), and metabolic activities (P < 0.001), and basal respiration rates were up to 2.8-times higher than in the pine soils. Microbial abundance analysis by PLFA showed that the fungal to bacterial ratio was higher in the pine soils (P < 0.01). Community analysis suggested that soil bacterial communities were more responsive to site (principal component 1; P < 0.001) than to land use (principal component 5; P < 0.001). In contrast, the fungal community was more affected by land-use change (principal component 1; P < 0.001) than by site, although site still had some influence on fungal community structure (principal component 2; P < 0.001). Redundancy analysis also suggested that bacterial and fungal communities responded differently to various soil abiotic properties, land-use change and location of sites. Overall, our results indicate that the change in land use from pasture to P. radiata stands had a direct impact on soil fungal communities but an indirect effect, through its effects on soil abiotic properties, on bacterial communities. Most of the changes in bacterial communities could be explained by altered soil physico-chemical properties associated with afforestation of pastures.  相似文献   

2.
Long-term impacts of metal contamination derived from sewage sludge on soil microbial communities have been widely evaluated, but confounding effects have made it difficult to draw firm conclusions and thus to advise on safe metal limits. Here we used Multiplex-terminal restriction length fragment polymorphism (M-TRFLP) to assess the long-term impact of sludge-borne Zn and Cu contamination on the structure of bacterial, fungal and archaeal communities across seven different soils at metal levels relevant to current guideline limits. Despite strong effects of site on microbial community structure, analysis of similarity (ANOSIM) demonstrated a small but significant effect of Zn on bacteria (P < 0.001), archaea (P < 0.001), and fungi (P < 0.001). Significant effects of Cu on bacteria (P < 0.001), archaea (P < 0.001) and fungi (P < 0.001) were also observed. Several bacterial and fungal T-RFs were identified as responding to Zn or Cu. For example the bacterial T-RF 72 was negatively correlated with Zn and Cu, and T-RF 259 was positively correlated with Zn. Attempts to identify these bacterial markers of Zn and Cu contamination suggest a negative impact of Cu on Acidobacteria in arable soils. These results demonstrate for the first time, that despite a strong influence of site on microbial community structure, effects of Zn and Cu derived from sewage sludge can be detected as shifts in bacterial, fungal and archaeal communities indicating a common response more than 11 years after sludge addition.  相似文献   

3.
Reactive forms of nitrogen (Nr) are accumulating at local, regional and global levels largely due to human activities, particularly N-fertilizer production and use as well as fossil fuel combustion. This has resulted in a change in the nitrogen (N) cycle and excess Nr in the environment, which has negative environmental effects. Therefore, characterizing denitrification and the edaphic variables controlling denitrification and its products is the first step in predicting the long-term effects of Nr accumulation. In the present study, six forest soil types in different climatic zones were collected from East China and evaluated for denitrification products following a K15NO3 amendment and subsequent incubation. The results showed that denitrification, indicated by production of nitric oxide (NO), nitrous oxide (N2O) and dinitrogen (N2), was higher in the studied temperate forest soils than in the studied subtropical and tropical forest soils and was negatively correlated with soil redox potential at the beginning of incubation (r = −0.94, P < 0.01), but not with soil pH. The ratios of NO/total N gas and N2O/total N gas produced during denitrification varied among the soils, and were generally higher in the subtropical and tropical soils. Spearman's correlation analysis showed that the NO ratio was positively correlated with soil oxidation capacity (OXC) (r = 0.94, P < 0.01) and redox potential at the beginning of incubation (r = 0.86, P < 0.05), but negatively correlated with soil pH (r = −0.83, P < 0.05). The N2O ratio was not significantly correlated with these edaphic variables, but showed a significant correlation to NO ratio (r = 0.83, P < 0.05). These results suggested that the OXC value might be the key factor affecting denitrification rates in soils. One possible explanation for these effects is that large OXC values would result in a higher level soil redox potential, thus suppressing denitrification and enhancing NO and N2O ratios during denitrification.  相似文献   

4.
Organism succession during ecosystem development has been researched for aboveground plant communities, however, the associated patterns of change in below-ground microbial communities are less described. In 2008, a study was initiated along a developmental sand-dune soil chronosequence bordering northern Lake Michigan near Wilderness Park (WP). It was hypothesized that soil bacterial communities would follow a pattern of change that is associated with soil, plant, and ecosystem development. This study included 5 replicate sites along 9 soils (n = 45) ranging in age from ∼105 to 4010 years since deposition. Soil bacterial community composition and diversity were studied using bacterial tag-encoded FLX amplicon pyrosequencing of the 16S rRNA gene. Bray–Curtis ordination indicated that bacterial community assembly changed along the developmental soil and plant gradient. The changes were not affected by seasonal differences, despite likely differences in plant root C (e.g. exudates), temperature, and water availability in soil. Soil base cations (Ca, Mg) and pH declined, showing log-linear correlations with soil age (r ∼ 0.83, 0.84 and 0.81; P < 0.01). Bacterial diversity (Simpson's 1/D) declined rapidly during the initial stages of soil development (∼105–450 y) and thereafter (>450 y) did not change. Turnover of plant taxa was also more rapid early during ecosystem development and correlated with bacterial community structural change (P < 0.000001; r = 0.56). It is hypothesized that plants help to drive pedogenic change during early (<450 y) soil development (e.g. pH decline, cation leaching) which drive selection of soil bacterial communities. In mature soils (∼450–4000 y), resilient and stable soil bacterial community structures developed, mimicking steady-state climax communities that were observed during latter stages of primary plant succession. These relationships point to possible feedbacks between plant and bacterial communities during ecosystem development.  相似文献   

5.
Monomethyl-mercury is one of the most toxic compounds. Methylation of Hg usually appears under anoxic conditions. In Swiss forest soils, methyl-Hg concentrations of up to 3 μg kg−1 soil dw have been observed, but the impact of methyl-Hg on soil microorganisms have rarely been examined so far. In this study, we investigated the effect of increasing concentrations of methyl-Hg (0, 5, 20, 90 μg kg−1 soil dw) on the microbial communities in various forest soils differing in their physico-chemical properties. Experiments were conducted in microcosms under controlled conditions and the basal respiration (BR), the microbial biomass carbon (MBC) and the bacterial and fungal community structures using T-RFLP-profiling were investigated. BR was significantly affected by methyl-Hg. In general, the BR increased with increasing methyl-Hg concentrations, whereas the MBC was significantly reduced. Bacterial communities were more sensitive to methyl-Hg than fungal communities. In five out of seven soils, the bacterial community structures differed significantly between the treatments whereas the fungal communities did not. The impact of methyl-Hg on the soil bacterial communities was site specific. In one soil, a methyl-Hg concentration of already 5 μg kg−1 soil dw significantly affected the relative abundance of 13% bacterial operational taxonomic units (OTU), whereas in other soils concentrations of even 90 μg kg−1 soil dw rarely affected the abundance of OTUs. In this study, for the first time, the impact of methyl-Hg on soil bacterial and fungal communities in forest soils was assessed. We showed that its impact strongly depends on the physico-chemical conditions of the soil and that bacterial communities were more sensitive to methyl-Hg than fungi.  相似文献   

6.
Like other N-fixing invasive species in Hawaii, Falcataria moluccana dramatically alters forest structure, litterfall quality and quantity, and nutrient dynamics. We hypothesized that these biogeochemical changes would also affect the soil microbial community and the extracellular enzymes responsible for carbon and nutrient mineralization. Across three sites differing in substrate texture and age (50-300 years old), we measured soil enzyme activities and microbial community parameters in native-dominated and Falcataria-invaded plots. Falcataria invasion increased acid phosphatase (AP) activities to >90 μmol g−1 soil h−1 compared to 30-60 μmol g−1 soil h−1 in native-dominated stands. Extracellular enzymes that mineralize carbon and nitrogen also increased significantly under Falcataria on the younger substrates. By contrast, total microbial biomass and mycorrhizal abundance changed little with invasion or substrate. However, fungal:bacterial ratios declined dramatically with invasion, from 2.69 and 1.35 to <0.89 on the 50- and 200-year-old substrates, respectively. These results suggest that Falcataria invasion alters the composition and function of belowground soil communities in addition to forest structure and biogeochemistry. The increased activities of AP and other enzymes that we observed are consistent with a shift toward phosphorus limitation and rapid microbial processing of litterfall C and N following Falcataria invasion.  相似文献   

7.
Soil samples taken from a sewage irrigation area, a partial sewage irrigation area and a ground water irrigation area (control area) were studied with the methods of Biolog and FAME. It was found that the microbial utilization of carbon sources in sewage irrigation areas was much higher than that of control area (P < 0.05). With the increasing of the amount of sewage irrigation, microbial functional diversity slightly increased by the Biolog analysis; however, the amount of epiphyte decreased by the FAME analysis. The results also showed that the Cr, Zn contents were positively correlated with the values of AWCD and the microbial diversity, while Hg content showed negative correlation with the microbial parameters (AWCD of 72 h and Shannon index). Our studies suggested that sewage irrigation resulted in an obvious increase of heavy metals content in soil (P < 0.05), although the maximum heavy metals concentrations were much lower than the current standard of China. Other soil basic characteristics such as cation exchange capacity (CEC), total nitrogen (Nt) and organic matter in sewage irrigation areas obviously increased (P < 0.05). Therefore, it is demonstrated that long-term sewage irrigation had influenced soil microorganisms and soil quality in the studied soils. As a result, it is important to monitor the changes in agricultural soils. Furthermore, our results also confirmed that the methods of Biolog and FAME are effective tools for the assessment of soil microbial structure/function and soil health.  相似文献   

8.
不同类型水稻土微生物群落结构特征及其影响因素   总被引：5，自引：1，他引：4  
选取基于我国土壤地理发生分类的不同类型土壤发育的四种水稻土,利用15N2气体示踪法测定生物固氮速率,采用实时荧光定量PCR（Real-time PCR）技术测定细菌丰度,通过16S rRNA基因高通量测序分析微生物群落组成和多样性。结果表明：变形菌门（Proteobacteria）、酸杆菌门（Acidobacteria）、绿弯菌门（Chloroflexi）和蓝藻门（Cyanobacteria）是水稻土中优势微生物类群。四种类型土壤发育的水稻土细菌群落结构差异显著（Stress<0.001）,群落结构分异（NMDS1）与土壤pH存在极显著正相关关系（P<0.01）。土壤有机碳和碱解氮含量显著影响水稻土中细菌丰度和群落多样性（P<0.01）。红壤发育的水稻土细菌16S rRNA基因拷贝数显著高于其他三种类型水稻土,但OTU数量、Chao1指数和PD指数均低于其他三种类型水稻土。土壤pH对水稻土生物固氮速率有显著影响（P<0.01）,紫色土发育的水稻土具有最高的生物固氮速率（3.2±0.7 mg×kg-1×d-1）,其中优势类群细鞘丝藻属（Leptolyngbya）可能是生物固氮的主要贡献者。研究结果丰富了对水稻土微生物多样性的认识,为通过调控土壤pH和微生物群落组成来提高稻田生物固氮潜力提供了理论依据。  相似文献   

9.
Microcalorimetric technique was used to investigate the effects of balanced versus nutrient-deficiency fertilization on soil microbial activity in a long-term (19-year) fertilizer experiment. The number of microorganisms in soils was measured by viable cell count, and the power-time curves were recorded for soil samples supplemented with glucose and ammonium sulphate, also with or without sodium dihydrogen phosphate for P-deficiency fertilization. Both the bacterial and the fungal populations were significantly higher (P < 0.05) under balanced fertilization than under nutrient-deficiency fertilization. The microbial activity presented by heat dissipation per cell unit indicated that microorganisms under balanced fertilizer treatments had more efficient metabolism, while decreased microbial activity under nutrient-deficiency treatments was firstly due to soil available P, followed by N and K (P < 0.05). In addition, microbial growth in soils under P-deficiency fertilization was stimulated by adding available P, while the lower growth rate, less peak heat, and longer peak time all indicated the low activity of soil microorganisms. We emphasize the importance of balanced fertilization, as well as the role of available P, in maintaining and promoting soil microbial activity.  相似文献   

10.
Soil N fertilization stimulates the activity of the soil bacterial species specialized in performing the different steps of the denitrification processes. Different responses of these bacterial denitrifiers to soil N management could alter the efficiency of reduction of the greenhouse gas N2O into N2 gas in cultivated fields. We used next generation sequencing to show how raising the soil N fertility of Canadian canola fields differentially modifies the diversity and composition of nitrite reductase (nirK and nirS) and nitrous oxide reductase (nosZ) gene-carrying denitrifying bacterial communities, based on a randomized complete blocks field experiment. Raising soil N levels increased up to 60% the ratio of the nirK to nirS genes, the two nitrite reductase coding genes, in the Brown soil and up to 300% in the Black soil, but this ratio was unaffected in the Dark Brown soil. Raising soil N levels also increased the diversity of the bacteria carrying the nitrite reductase gene nirK (Simpson index, P = 0.0417 and Shannon index, 0.0181), and changed the proportions of the six dominant phyla hosting nirK, nirS, and nosZ gene-carrying bacteria. The level of soil copper (Cu) and the abundance of nirK gene, which codes for a Cu-dependent nitrite reductase, were positively related in the Brown (P = 0.0060, R2 = 0.48) and Dark Brown (0.0199, R2 = 0.59) soils, but not in the Black soil. The level of total diversity of the denitrifying communities tended to remain constant as N fertilization induced shifts in the composition of these denitrifying communities. Together, our results indicate that higher N fertilizer rate increases the potential risk of nitrous oxide (N2O) emission from canola fields by promoting the proliferation of the mostly adaptive N2O-producing over the less adaptive N2O-reducing bacterial community.  相似文献   

11.
Isothermal microcalorimetry measures the thermal flows occurring in systems with very high precision and may be used to quantify carbon (C) assimilation and resource-use efficiencies in soils. We determined the thermodynamic efficiency of soil microbial communities located in soils which had received contrasting long-term management regimes (53 y) with respect to organic matter and nitrogen (N) inputs, viz. farmyard manure, sewage sludge, straw and calcium nitrate, calcium nitrate only, or ammonium sulphate. Two thermodynamic efficiency indices were considered: (i) total thermodynamic efficiency of soil microbial communities (ηeff), i.e. general heat production released following substrate addition, per unit heat energy input to the soil system, and (ii) a specific thermodynamic efficiency index of energy retained in the soil system (ηsoil). The latter index provides quantitative data on how much C is assimilated and energy retained in the soil system. Further, we derived a ‘substrate-induced heat production’ (SIHP) index, which adjusts for size of the microbial biomass. Optimised concentrations of water or glucose plus water were added to the soil samples and resultant thermal signatures and C mineralisation were determined over a 48-h incubation period at 25 °C. The thermal signatures were further related to the microbial community profiles of the soils. The phenotypic structural and functional diversity profiles of the microbial communities in soils were assessed by phospholipid fatty acid and multi-substrate induced respiration methods at the start of the experiment, confirming significant differences between all five treatments in community composition and functional capabilities. Both the total and specific thermodynamic efficiency indices of the soil microbial communities exposed to long-term stress by heavy metal toxicity (sewage sludge) and low pH ((NH4)2SO4) were significantly smaller in magnitude than those under the three conventional (i.e. Ca(NO3)2, Straw + Ca(NO3)2, farmyard manure) input regimes (P < 0.05). The SIHP index however, was highest in the treatments receiving long-term inorganic inputs, indicating more heat production per unit biomass, than that found in all three organic input regimes. These differences in efficiencies were reflected in both the phenotypic and functional profiles of the communities. These indices may provide quantification of C assimilation and resource-use efficiency under different land-use and management scenarios, and potentially allow evaluation of the role of soils in governing the terrestrial C balance by studying the fate and regulation of C in soil systems.  相似文献   

12.
Key physicochemical factors associated with microbial community composition and functions in Australian agricultural soils were identified. Soils from seven field sites, with varying long-term agricultural management regimes, were characterised physicochemically, on the basis of their bacterial and fungal community structures (using PCR-DGGE), and by assessing potential catabolic functions (MicroResp?). Soil type, rather than agricultural management practice, was the key determinant of microbial community structure and catabolic function (P<0.05). Following multivariate analysis, soil pH was identified as the key habitat-selective physicochemical soil property associated with variation in biological diversity and profiles of organic substrate utilisation. In particular, the capacity of soils to catabolise different C-substrates was closely correlated (ρ=0.604, P=0.001) to pH. With decreasing pH, the catabolism of common low molecular weight organic compounds (especially cysteine and aspartic acid) declined, however catabolism of two others (lysine and arginine) increased. Shifts in the capacity of soil microbiota to cycle common organic compounds have implications for overall geochemical cycling of C and N in acidifying soils. The genetic structure of the bacterial communities in soil strongly correlated with pH (ρ=0.722; P=0.001) and that of soil fungi with pH and % sand (ρ=0.323; P=0.006). Catabolic function was more closely associated with the structure of the bacterial than fungal communities. This work has shown that soil pH is a primary driver of microbial diversity and function in soil. Agricultural management practices thereby act to selectively shift populations and functions against this background.  相似文献   

13.
Boreal wetlands are characterized by a mosaic of plant communities, including forests, shrublands, grasslands, and fens, which are structured largely by changes in topography and water table position. The soil associated with these plant communities contain quantitatively and qualitatively different forms of soil organic matter (SOM) and nutrient availability that drive changes in biogeochemical cycling rates. Therefore different boreal plant communities likely contain different soil biotic communities which in turn affect rates of organic matter decomposition. We examined relationships between plant communities, microbial communities, enchytraeids, and soil C turnover in near-surface soils along a shallow topographic soil moisture and vegetation gradient in interior Alaska. We tested the hypothesis that as soil moisture increases along the gradient, surface soils would become increasingly dominated by bacteria and mesofauna and have more rapid rates of C turnover. We utilized bomb radiocarbon techniques to infer rates of C turnover and the 13C isotopic composition of SOM and respired CO2 to infer the degree of soil humification. Soil phenol oxidase and peroxidase enzyme activities were generally higher in the rich fen compared with the forest and bog birch sites. Results indicated greater C fluxes and more rapid C turnover in the surface soils of the fen sites compared to the wetland forest and shrub sites. Quantitative PCR analyses of soil bacteria and archaea, combined with enchytraeid counts, indicated that surface soils from the lowland fen ecosystems had higher abundances of these microbial and mesofaunal groups. Fungal abundance was highly variable and not significantly different among sites. Microbial data was utilized in a food web model that confirmed that rapidly cycling systems are dominated by bacterial activity and enchytraeid grazing. However, our results also suggest that oxidative enzymes play an important role in the C mineralization process in saturated systems, which has been often ignored.  相似文献   

14.
Soil microbes in urban ecosystems are affected by a variety of abiotic and biotic factors resulting from changes in land use. However, the influence of different types of land use on soil microbial properties and soil quality in urban areas remains largely unknown. Here, by comparing five types of land use: natural forest, park, agriculture, street green and roadside trees, we examined the effects of different land uses on soil microbial biomass and microbial functional diversity in Beijing, China. We found that soil properties varied with land uses in urban environments. Compared to natural forest, soil nutrients under the other four types of urban land use were markedly depleted, and accumulation of Cu, Zn, Pb and Cd was apparent. Importantly, under these four types of land use, there was less microbial biomass, but it had greater functional diversity, particularly in the roadside‐tree soils. Furthermore, there were significant correlations between the microbial characteristics and physicochemical properties, such as organic matter, total nitrogen and total phosphorus (P < 0.05), suggesting that lack of nutrients was the major reason for the decrease in microbial biomass. In addition, the larger C/N ratio, Ni concentration and pool of organic matter together with a higher pH contributed to the increase in microbial functional diversity in urban soils. We concluded that different land uses have indirect effects on soil microbial biomass and microbial community functional diversity through their influence on soil physicochemical properties, especially nutrient availability and heavy metal content.  相似文献   

15.
Fungal and bacterial numbers and their enzymes activities in terms of enzymes, namely cellulase, amylase and invertase were estimated in two forest stands of alder (open and closed forest). The fungal and bacterial population numbers were higher in the closed forest than in the open ones. Consequently, the different enzyme activities were also greater in the closed forest. A correlation coefficient was calculated between fungal population numbers, bacterial population numbers, moisture content, pH, total nitrogen, weight loss, cellulose and total sugars and the enzymes activities. Invertase activity showed a positive correlation (P < 0.05) with litter soluble sugars and total nitrogen but negatively with weight loss. Amylase and cellulase activities were correlated significantly with fungi and bacteria and moisture content of litter. Cellulase also correlated significantly but negatively with the cellulose  (P < 0.01). The results of the investigation indicated that changes in forest canopy has an effect on fungal and bacterial population numbers and microbial enzymes activities.  相似文献   

16.
To clarify the variation in soil microbial respiration (SMR) in Jiuduansha wetland during different succession stages, the SMR of five typical zones was evaluated. The results showed that the SMR during different successional stages of vegetation varied significantly (P < 0.05), with the SMR of the Spartina alterniflora zone (0.43 mg CO2 g−1 d−1) being the highest. These findings implied that S. alterniflora could enhance the SMR. Based on both the SMR and input of organic matter from plant decomposition, the Phragmites australis community likely possesses a higher organic carbon accumulation capability. In addition, the results of the present study implied that the difference in microbial characteristics among the wetland soils may be the primary reason for their different SMR. Path analysis indicated that the correlation between soil bacterial diversity and SMR was especially strong. Moreover, phylogenetic analysis showed that the bacterial community structure along the successional stages varied. Specifically, microbial species such as Acidobacteria, δ-Proteobacteria and Cytophaga belonging to Bacteroidetes, which have special heterotrophic metabolic capabilities or the ability to degrade cellulose, were the dominant soil bacterial flora in the S. alterniflora zone, which ultimately strengthened the SMR. Different elevations and vegetation types leading to a change in the wetland soil characteristics such as waterlogging time and inorganic nitrogen may be important factors resulting in the differences in soil microbial characteristics of different successional stages in Jiuduansha wetland.  相似文献   

17.
Here, we examine soil-borne microbial biogeography as a function of the features that define an American Viticultural Area (AVA), a geographically delimited American wine grape-growing region, defined for its distinguishing features of climate, geology, soils, physical features (topography and water), and elevation. In doing so, we lay a foundation upon which to link the terroir of wine back to the soil-borne microbial communities. The objective of this study is to elucidate the hierarchy of drivers of soil bacterial community structure in wine grape vineyards in Napa Valley, California. We measured differences in the soil bacterial and archaeal community composition and diversity by sequencing the fourth variable region of the small subunit ribosomal RNA gene (16S V4 rDNA). Soil bacterial communities were structured with respect to soil properties and AVA, demonstrating the complexity of soil microbial biogeography at the landscape scale and within the single land-use type. Location and edaphic variables that distinguish AVAs were the strongest explanatory factors for soil microbial community structure. Notably, the relationship with TC and TN of the <53 μm and 53–250 μm soil fractions offers support for the role of bacterial community structure rather than individual taxa on fine soil organic matter content. We reason that AVA, climate, and topography each affect soil microbial communities through their suite of impacts on soil properties. The identification of distinctive soil microbial communities associated with a given AVA lends support to the idea that soil microbial communities form a key in linking wine terroir back to the biotic components of the soil environment, suggesting that the relationship between soil microbial communities and wine terroir should be examined further.  相似文献   

18.
The 1980 eruption of Mount St. Helens created a unique opportunity to study microbial communities in a developing soil ecosystem containing little total carbon (C) or total nitrogen (N). We collected surface samples (0-5 cm) from areas near Mount St. Helens National Volcanic Monument 17 years after the eruption. The samples were from bare soil with no plant development, soil under living prairie lupine (Lupinus lepidus) and dead prairie lupine in the pyroclastic plain near Spirit Lake, Washington. We also collected soil from a nearby forested area. Phospholipid fatty acids (PLFAs) from pyroclastic materials were analyzed to determine changes in soil microbial composition. Total bacterial DNA was also extracted from the soils and denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes and DNA sequence analysis of cloned 16S rRNA gene libraries were used to determine the influence of plants on microbial development. Both principal components analysis (PCA) of PLFA fingerprints and non-metric multidimensional scaling (NMS) of DGGE fingerprints distinguished the four soils. Lupine plants influenced the PLFA and DGGE fingerprints depending on the distance of the samples from the plant. DGGE and PLFA profiles from the forest soil were significantly different (P=0.001, based on Monte Carlo permutation test) from those of the bare soil and soil with live lupine. Bacterial clone libraries were constructed, and 800 clones were analyzed by amplified ribosomal DNA restriction analysis (ARDRA) and grouped into operational taxonomic units (OTUs). A total of 51, 77, 58, and 42 different OTUs were obtained from forest soil, soil with live and dead lupine, and bare soil, respectively. Phylogenetic analysis revealed that 62% of the 228 OTUs were classified as Proteobacteria, Actinobacteria, Acidobacterium, Verrucomicrobia, Bacteroides, Cyanobacteria, Planctomycetes, and candidate divisions TM7 and OP10. Members of Proteobacteria represented 29% of the OTUs. Thirty-eight percent of the OTUs could not be classified into known bacterial divisions. This study emphasized the role of prairie lupine in the establishment of pioneering microbial communities and the subsequent roles the biotic components played in improving the quality of pyroclastic soil.  相似文献   

19.
In gold mining regions, the risk of soil pollution by mercury is a major environmental hazard, especially in tropical areas where soil microflora plays a major part in soil functioning, major bio-geochemical cycles and carbon turn-over. The impact of mercury pollution on soil microflora should thus be carefully assessed in such environments while taking into consideration the specificities of tropical soils. The aim of this study was to compare the effects of mercury (0, 1 and 20 μg of inorganic mercury per gram of soil) on the functional diversity and genetic structure of microbial communities in a tropical soil. We investigated the effects of mercury on tropical soil microflora using soil microcosms spiked with mercury and incubated at 28 °C for 1 month. Microcosm flora, its biomass and its activity, as well as its functional and genetic structure, were followed by cultural methods, measures of respiration, ECOLOG plates, and DGGE (denaturing gel gradient electrophoresis), respectively. Fate of total and bioavailable mercury was estimated by CVAFS (cold vapor atomic fluorescence spectrometry). Results obtained for the microcosms enriched with only 1 μg g?1 mercury were indistinguishable from controls. Conversely, in the presence of high mercury contents (20 μg g(1), an immediate effect was measured on soil respiration, functional diversity (ECOLOG plates) and genetic structure (DGGE), although no significant effect was observed on plate counts or microbial biomass. In addition, whereas microbial activities (respiration and functional diversity) rapidly regained control values, a lasting effect of the high mercury concentration was observed on the genetic structure of the soil microbial community. These modifications took place during the first week of incubation when total mercury concentration was declining and bioavailable mercury was at its highest.This multiple approach study is one of the first attempts at investigating the effects of mercury on soil microbial communities in tropical soils. Our results demonstrate that in the tropical soil under study, mercury affects the soil microbial communities in a different manner than was previously reported in temperate soils. Furthermore, mercury toxicity on soil microbes may be modulated by typical tropical soil characteristics.  相似文献   

20.
Although understory vegetation is known to play an important role in driving the processes and functions of forest ecosystems, little is known about how understory vegetation affects the composition and function of soil microbial communities in forest ecosystems, especially in subtropical and tropical forests. This study used the experimental removal of understory fern (Dicranopteris dichotoma) to investigate the effect of the fern on substrate utilization patterns of culturable soil bacterial communities in two subtropical Eucalyptus plantations. One year after treatment, the removal of understory fern significantly increased soil temperature by 2–3 °C and retarded litter decomposition by 5.6–23.1%. However, understory fern removal did not affect the substrate utilization pattern of soil bacterial communities. Our study provides evidence that, although understory fern removal significantly alters soil temperature and litter decomposition rate, the disturbance caused by understory removal one year after treatment is too weak to cause detectable changes in substrate utilization pattern of culturable soil bacterial communities in subtropical Eucalyptus plantations.  相似文献   

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