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1.
Prosopis laevigata and Parkinsonia praecox are the most abundant perennial shrubs in the Tehuacán Desert, forming ’islands of fertility’ that dominate the alluvial terraces. Both species exhibit very similar phenology, with the timing of litter foliage being the only difference between them. P. praecox litter occurs shortly after the rains, while P. laevigata maintains its leaves until the next wet season. As degradable organic matter (OM) is one of the leading factors determining soil biota composition and activity, because of the OM provided by littering, we expected that the vertical distribution of the microbial community in the vicinity of the root zone of P. praecox would be higher in comparison to P. laevigata. One soil sampling was performed; during the rainy season in August, soil samples were collected from a 0–50-cm depth at 10-cm intervals, in the vicinity of the root canopy of four individual plants of each species and the interspaces between them. Soil moisture, organic matter, and counts of bacteria and fungi under shrubs were found to decrease from the upper to deeper layers. Respiratory activity was higher in the deeper layers (p < 0.01) in all three sampling sites. Total bacterial, fungal, and heterotrophic diazotrophs were found to be significantly (p < 0.001) more numerous under shrubs than in the interspace soil. No nitrogen-fixing bacteria were isolated from interplant soils in comparison to the soil samples collected beneath the shrubs. Heterotrophic diazotrophs significantly (p < 0.01) reduced more acetylene under P. praecox (29.0 nmol/g soil) than under P. laevigata (20.1 nmol/g soil). Although the microbial numbers were unaffected by differences in plant phenology, greater nitrogenase activity under P. praecox may influence nitrogen distribution in this arid environment. Due to the fact that only one sampling was undertaken, this study elucidates the differences in the microbial community between the two shrubs, but the dynamics in the above community could not be shown.  相似文献   

2.
The ultimate goal of soil remediation is to restore soil health. Soil microbial parameters are considered to be effective indicators of soil health. The aim of this study was to determine the effects of phytoextraction on microbial properties through the measurement of soil microbial biomass carbon, soil basal respiration and enzyme activities. For this purpose, a pre-stratified rhizobox experiment was conducted with the Cd hyperaccumulator Sedum alfredii H. for phytoextraction Cd from an artificial contaminated soil (15.81 mg kg−1) under greenhouse conditions. The plant and soil samples were collected after growing the plant for three and six months with three replications. The results indicated that the ecotype of S. alfredii H. originating from an ancient silver mining site was a Cd-hyperaccumulator as it showed high tolerance to Cd stress, the shoot Cd concentration were as high as 922.6 mg kg−1 and 581.9 mg kg−1 at the two samplings, and it also showed high BF (58.4 and 36.8 after 3 and 6 months growth), and TF (5.8 and 5.1 after 3 and 6 months growth). The amounts of Cd accumulated in the shoots of S. alfredii reached to an average of 1206 μg plant−1 after 6 months growth. Basal respiration, invertase and acid phosphatase activities of the rhizosphere soil separated by the shaking method were significantly higher (P < 0.01) than that of the near-rhizosphere soil and the unplanted soil after 3 months growth, so were microbial biomass carbon, urease, invertase and acid phosphatase activities of the rhizosphere soil after 6 months growth. Acid phosphatase activity of the 0–2 mm sub-layer rhizosphere soil collected by the pre-stratified method after 3 months growth was significantly higher (P < 0.05) than that of other sub-layer rhizosphere soils and bulk soil, and so were microbial biomass carbon, basal respiration, urease, invertase and acid phosphatase activities of the 0–2 mm sub-layer rhizosphere soil after 6 months growth. It was concluded that phytoextraction by S. alfredii could improve soil microbial properties, especially in rhizosphere, and this plant poses a great potential for the remediation of Cd contaminated soil.  相似文献   

3.
In order to understand the impact of human activities on soil microbial diversity, we investigated bacterial communities in samples recovered from four New Caledonia environments that have been disturbed by varying degrees of nickel mining associated activities: an undisturbed area with natural soil (characterized by pristine vegetation), a mine spoil (devoid of vegetation), two revegetated mine spoils by endemic plants. For each sample, total DNA was extracted and 16S rDNA clone library were constructed. 442 clones were sequenced and analyzed. Using these clones, diversity was estimated not only in terms of species richness (non-parametric estimators) and evenness (Reciprocal of Simpson's index), but also in terms of phylogenetic diversity (LIBSHUFF program). Statistically significant differences were detected in phylogenetic composition between mine spoils and natural soil (p = 0.001), between revegetated soils and natural soil (p = 0.001), and between revegetated soils and mine spoils (p = 0.001). On the other hand, no significant differences in species richness were observed between the different environmental samples.These findings provide insights into the response of bacterial community following environmental perturbations caused by nickel-mining activities and revegetation efforts.  相似文献   

4.
The aim of this study was to investigate the response of soil microbial biomass and organic matter fractions during the transition from conventional to organic farming in a tropical soil. Soil samples were collected from three different plots planted with Malpighia glaba: conventional plot with 10 years (CON); transitional plot with 2 years under organic farming system (TRA); organic plot with 5 years under organic farming system (ORG). A plot under native vegetation (NV) was used as a reference. Soil microbial biomass C (MBC) and N (MBN), soil organic carbon (SOC) and total N (TN), soil organic matter fractioning and microbial indices were evaluated in soil samples collected at 0–5, 5–10, 10–20 and 20–40 cm depth. SOC and fulvic acids fraction contents were higher in the ORG system at 0–5 cm and 5–10 cm depths. Soil MBC was highest in the ORG, in all depths, than in others plots. Soil MBN was similar between ORG, TRA and NV in the surface layer. The lowest values for soil MBC and MBN were observed in CON plot. Soil microbial biomass increased gradually from conventional to organic farming, leading to consistent and distinct differences from the conventional control by the end of the second year.  相似文献   

5.
Allelopathic rice releases allelochemicals from its roots to paddy soils at early growth stages to inhibit neighboring weeds. However, little is currently known about the effects of allelochemicals on soil microbes. In this study, we show that allelopathic rice can have great impact on the population and community structure of soil microbes. Allelopathic rice PI312777 seedlings reduced the culturable microbial population and total PLFA when compared to non-allelopathic rice Liaojing-9. Similar results were observed when, instead of growing seedlings, soils were incubated with plant root exudates. This result demonstrates that the composition of root exudates from the rice varieties tested contributes to the soil microbial community. Further experiments showed that the microbial community was affected by the allelochemical 5,4′-dihydroxy-3′,5′-dimethoxy-7-O-β-glucopyranosylflavone exuded from allelopathic rice roots, through immediately hydrolyzing glucose with stimulation on soil bacteria and aglycone (5,7,4′-trihydroxy-3′,5′-dimethoxyflavone) with inhibition on soil fungi. This result indicates that the flavone O-glycoside can provide carbon and interact with soil microbes. PC analysis of the fatty acid data clearly separated the allelopathic PI312777 and the non-allelopathic Liaojing-9 variety (PC1 = 46.4%, PC2 = 20.3%). Similarly, the first principal component (PC1 = 37.4%) together with the second principal component (PC2 = 17.3%) explained 54.7% of the variation between the allelopathic and non-allelopathic root exudates. Furthermore, the canonical correlation between allelopathic root exudates and the flavone O-glycoside was statistically significant (Canonical R = 0.889, χ2 (25) = 69.72, p = 0.0041). Although the data generated in this study were not completely consistent between culturable microbes and PLFA profile, it is a fact that variation in soil microbial populations and community structures could be distinguished by the allelopathic and non-allelopathic rice varieties tested. Our results suggest that individual components of rice root exudates, such as allelochemicals from allelopathic rice, can modify the soil microbial community.  相似文献   

6.
Napropamide is one of the most commonly used herbicide in agricultural practice and can exhibit toxic effect to soil microorganisms. Therefore, the main objective of this study was to examine the genetic and functional diversity of microbial communities in soil treated with napropamide at field rate (FR, 2.25 mg kg−1 of soil) and 10 times the FR (10 × FR, 22.5 mg kg−1 of soil) by the denaturing gradient gel electrophoresis (DGGE) and the community level physiological profile (CLPP) methods. In addition, the r/K-strategy approach was used to evaluate the effect of this herbicide on the community structure of the culturable soil bacteria. DGGE patterns revealed that napropamide affected the structure of microbial community; however, the richness (S) and genetic diversity (H) values indicated that the FR dosage of napropamide experienced non-significant changes. In turn, the 10 × FR dosage of herbicide caused significant changes in the S and H values of dominant soil bacteria. DGGE profiles suggest an evolution of bacteria capable of degrading napropamide among indigenous microflora. Analysis of the CLPPs indicated that the catabolic activity of microbial community expressed as AWCD (average well-color development) was temporary positively affected after napropamide application and resulted in an increase of the substrate richness (SR) as well as functional biodiversity (H) values. Analysis of the bacterial growth strategy revealed that napropamide affected the r- or K-type bacterial classes (ecotypes). In treated-soil samples K-strategists dominated the population, as indicated by the decreased ecophysiological (EP) index. Napropamide significantly affected the physiological state of culturable bacteria and caused a reduction in the rate of colony formation as well as a prolonged time of growth rate. Obtained results indicate that application of napropamide may poses a potential risk for soil functioning.  相似文献   

7.
Microbial biomass (MB) is the key factor in nutrient dynamics in soil, but no information exists how clearing of vegetation to cultivate maize in the central highlands of Mexico might affect it. Soil MB was measured with the chloroform fumigation incubation (CFI) and fumigation extraction (CFE) techniques and the substrate-induced respiration (SIR) method in soil sampled under or outside the canopy of mesquite (Prosopis laevigata) and huisache (Acacia tortuoso), N2 fixing shrubs, and from fields cultivated with maize. Microbial biomass C as measured with the CFI technique ranged from 122 mg C kg−1 in agricultural soil to 373 mg C kg−1 in soil sampled under mesquite shrubs. Microbial biomass N as measured with the CFI technique ranged from 11 mg N kg−1 in agricultural soil to 116 mg N kg−1 in soil sampled under mesquite shrub. The ratio of microbial biomass C as measured with CFI related to the ninhydrin-positive compounds (NPC) was 12.23 after 1 day and 8.43 after 10 days while the relationship with extractable C was 3.15 and 2.96, respectively. The metabolic quotient (qCO2) decreased in the order OUTSIDE > MESQUITE > HUIZACHE > AGRICULTURE, and the microbial biomass:soil organic C ratio decreased in the order MESQUITE > HUIZACHE > OUTSIDE > AGRICULTURE using SIR to determine the microbial biomass. It was found that converting soil under natural vegetation to arable soil was not only detrimental for soil quality, but might be unsustainable as organic matter input is limited.  相似文献   

8.
Changes in soil microbial biomass, enzyme activities, microbial community structure and nitrogen (N) dynamics resulting from organic matter amendments were determined in soils with different management histories to gain better understanding of the effects of long- and short-term management practices on soil microbial properties and key soil processes. Two soils that had been under either long-term organic or conventional management and that varied in microbial biomass and enzyme activity levels but had similar fertility levels were amended with organic material (dried lupin residue, Lupinus angustifolius L.) at amounts equivalent to 0, 4 and 8 t dry matter lupin ha?1. Microbial biomass C and N, arginine deaminase activity, fluorescein diacetate hydrolysis, dehydrogenase enzyme activity and gross N mineralisation were measured in intervals over an 81-day period. The community structure of eubacteria and actinomycetes was examined using PCR–DGGE of 16S rDNA fragments. Results suggested that no direct relationships existed between microbial community structure, enzyme activities and N mineralisation. Microbial biomass and activity changed as a result of lupin amendment whereas the microbial community structure was more strongly influenced by farm management history. The addition of 4 t ha?1 of lupin was sufficient to stimulate the microbial community in both soils, resulting in microbial biomass growth and increased enzyme activities and N mineralisation regardless of past management. Amendment with 8 t lupin ha?1 did not result in an increase proportional to the extra amount added; levels of soil microbial properties were only 1.1–1.7 times higher than in the 4 t ha?1 treatment. Microbial community structure differed significantly between the two soils, while no changes were detected in response to lupin amendment at either level during the short-term incubation. Correlation analyses for each treatment separately, however, revealed differences that were inconsistent with results obtained for soil biological properties suggesting that differences might exist in the structure or physiological properties of a microbial component that was not assessed in this study.  相似文献   

9.
《Pedobiologia》2014,57(4-6):277-284
Assimilating atmospheric carbon (C) into terrestrial ecosystems is recognized as a primary measure to mitigate global warming. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) is the dominant enzyme by which terrestrial autotrophic bacteria and plants fix CO2. To investigate the possibility of using RubisCO activity as an indicator of microbial CO2 fixation potential, a valid and efficient method for extracting soil proteins is needed. We examined three methods commonly used for total soil protein extraction. A simple sonication method for extracting soil protein was more efficient than bead beating or freeze–thaw methods. Total soil protein, RubisCO activity, and microbial fixation of CO2 in different agricultural soils were quantified in an incubation experiment using 14C-CO2 as a tracer. The soil samples showed significant differences in protein content and RubisCO activity, defined as nmol CO2 fixed g−1 soil min−1. RubisCO activities ranged from 10.68 to 68.07 nmol CO2 kg−1 soil min−1, which were closely related to the abundance of cbbL genes (r = 0.900, P = 0.0140) and the rates of microbial CO2 assimilation (r = 0.949, P = 0.0038). This suggests that RubisCO activity can be used as an indicator of soil microbial assimilation of atmospheric CO2.  相似文献   

10.
With the advent of glyphosate [N-(phosphonomethyl)glycine] tolerant crops, soils have now been receiving repeated applications of the herbicide for over 10 years in the Midwestern USA. There is evidence that long-term use of glyphosate can cause micronutrient deficiency but little is known about plant potassium (K) uptake interactions with glyphosate. The repeated use of glyphosate may create a selection pressure in soil microbial communities that could affect soil K dynamics and ultimately K availability for crops. Therefore, the objectives of this study were to characterize the effect of foliar glyphosate applied to GR (glyphosate resistant) soybeans on: (1) rhizosphere microbial community profiles using ester linked fatty acid methyl ester (EL-FAME) biomarkers, (2) exchangeable, non-exchangeable, and microbial K in the rhizosphere soil, and (3) concentrations of soybean leaf K. A greenhouse study was conducted in a 2 × 2 × 3 factorial design with two soil treatments (with or without long-term field applications of glyphosate), two plant treatments (presence and absence of soybean plants), and three rates of glyphosate treatments (0×, 1× at 0.87, and 2× at 1.74 kg ae ha?1, the recommended field rate). After each glyphosate application, rhizosphere soils were sampled and analyzed for microbial community structure using ester linked fatty acid methyl ester biomarkers (EL-FAME), and exchangeable, plant tissue and microbial biomass K. Glyphosate application caused a significant decrease in the total microbial biomass in soybean rhizosphere soil that had no previous exposure to glyphosate, at 7 days after glyphosate application. However, no significant changes were observed in the overall microbial community structure. In conclusion, the glyphosate application lowered the total microbial biomass in the GR soybean rhizosphere soil that had no previous exposure to glyphosate, at 7 days after glyphosate application; caused no changes in the microbial community structure; and did not reduce the plant available K (soil exchangeable or plant tissue K).  相似文献   

11.
Paclobutrazol is a plant growth regulator largely utilized in mango cultivation and usually applied directly to soil. The aim of this study was to examine the effect of paclobutrazol on soil microbial biomass, soil respiration and cellulose decomposition in Brazilian soils under laboratory conditions. Soil samples were collected from fields with and without a reported history of paclobutrazol application. A solution of paclobutrazol (8 mg of active ingredient kg?1 of soil) was added to soils, which were then incubated at 28 °C for 30 days. Paclobutrazol decreased soil microbial biomass, soil respiration and cellulose decomposition in soil with and without a report of paclobutrazol application, while significant increase was observed in the respiratory quotient (qCO2). Our results show that the soil microbiological attributes were negatively affected by paclobutrazol in short-term experiment.  相似文献   

12.
This study investigates how carbon sources of soil microbial communities vary with soil depth. Microbial phospholipid fatty acids (PLFA) were extracted from 0–20, 20–40 and 40–60 cm depth intervals from agricultural soils and analysed for their stable carbon isotopes (δ13C values). The soils had been subjected to a vegetation change from C3 (δ13C≈?29.3‰) to C4 plants (δ13C≈?12.5‰) 40 years previously, which allowed us to trace the carbon flow from plant-derived input (litter, roots, and root exudates) into microbial PLFA. While bulk soil organic matter (SOM) reflected ≈12% of the C4-derived carbon in top soil (0–20 cm) and 3% in deeper soil (40–60 cm), the PLFA had a much higher contribution of C4 carbon of about 64% in 0–20 cm and 34% in 40–60 cm. This implies a much faster turnover time of carbon in the microbial biomass compared to bulk SOM. The isotopic signature of bulk SOM and PLFA from C4 cultivated soil decreases with increasing soil depth (?23.7‰ to ?25.0‰ for bulk SOM and ?18.3‰ to ?23.3‰ for PLFA), which demonstrates decreasing influence of the isotopic signature of the new C4 vegetation with soil depth. In terms of soil microbial carbon sources this clearly shows a high percentage of C4 labelled and thus young plant carbon as microbial carbon source in topsoils. With increasing soil depth this percentage decreases and SOM is increasingly used as microbial carbon source. Among all PLFA that were associated to different microbial groups it could be observed that (a) depended on availability, Gram-negative and Gram-positive bacteria prefer plant-derived carbon as carbon source, however, (b) Gram-positive bacteria use more SOM-derived carbon sources while Gram-negative bacteria use more plant biomass. This tendency was observed in all three-depth intervals. However, our results also show that microorganisms maintain their preferred carbon sources independent on soil depth with an isotopic shift of 3–4‰ from 0–20 to 40–60 cm soil depth.  相似文献   

13.
The incorporation of organic amendments from pruning waste into soil may help to mitigate soil degradation and to improve soil fertility in semiarid ecosystems. However, the effects of pruning wastes on the biomass, structure and activity of the soil microbial community are not fully known. In this study, we evaluate the response of the microbial community of a semiarid soil to fresh and composted vegetal wastes that were added as organic amendments at different doses (150 and 300 t ha−1) five years ago. The effects on the soil microbial community were evaluated through a suite of different chemical, microbiological and biochemical indicators, including enzyme activities, community-level physiological profiles (CLPPs) and phospholipid fatty acid analysis (PLFA). Our results evidenced a long-term legacy of the added materials in terms of soil microbial biomass and enzyme activity. For instance, cellulase activity reached 633 μg and 283 μg glucose g−1 h−1 in the soils amended with fresh and composted waste, respectively. Similarly, bacterial biomass reached 116 nmol g−1 in the soil treated with a high dose of fresh waste, while it reached just 66 nmol g−1 in the soil amended with a high dose of composted waste. Organic amendments produced a long-term increase in microbiological activity and a change in the structure of the microbial community, which was largely dependent on the stabilization level of the pruning waste but not on the applied dose. Ultimately, the addition of fresh pruning waste was more effective than the application of composted waste for improving the microbiological soil quality in semiarid soils.  相似文献   

14.
In recent decades, perennial rhizomatous grasses have been introduced in the Po Valley (Northern Italy), not only to produce bioenergy, but also to face the loss of soil organic carbon due to intensive crop management. Given the dual purpose of perennial energy crops, this work was intended to evaluate changes induced by the introduction of these crops on soil microbial community structure and on soil functionality. We compared a 9 year-old land conversion to two perennial energy crops, giant Miscanthus (Miscanthus sinensis × giganteus) and giant reed (Arundo donax L.), with two 40-year old annual arable systems, continuous wheat and maize/wheat rotation. The structure of the bacterial community was studied by the fingerprinting method of denaturing gradient gel electrophoresis (PCR-DGGE) amplifying 16S rRNA fragments, while the functional aspects of soil were investigated through the determination of three soil enzyme activities involved in soil carbon, nitrogen, and phosphorous cycles (β-glucosidase, urease, and alkaline phosphatase, respectively). Introduction of perennial energy crops positively stimulated the three soil enzymes, especially in the shallow soil layer (0–0.15 m), where accumulation of carbon and nitrogen was stronger. Enzyme activities were also positively correlated with organic carbon, apart from β-glucosidase. A significant but weaker correlation was also observed between enzyme activities and total nitrogen. The DGGE profiles revealed the relationship between crop types and soil microbial communities. Community richness was higher in perennial than in annual crops, but no effect of soil depth was observed. In opposition, Shannon index of diversity was not influenced by crop type, but only by soil depth with a 32% increase in the shallow layer. We conclude that the introduction of perennial energy crops in a South European soil increases both soil biochemical activity and microbial diversity, related to the ability of these crops to stabilize organic matter in soil. It is thereby evidenced that perennial rhizomatous grasses for energy uses could represent a sustainable choice for the recovery of soils depleted by intensive agricultural management.  相似文献   

15.
《Applied soil ecology》2007,35(2-3):125-139
The toxic effect of chromate on soil microbial communities is not well documented, although microorganisms control biogeochemical cycling, contribute to formation of soil structure, regulate the fate of organic matter applied to soil. In this study the effects of short- and middle-term chromate on the soil microbial community were investigated. The shifts in the size and in the diversity of culturable heterotrophic bacterial community, the resistance to Cr(VI) of heterotrophic bacteria, the presence of cyanobacteria, the activity of 19 enzymes, and the ATP content were monitored over time (120 days) in soil microcosms artificially contaminated with three concentrations of chromate (50, 250 and 1000 mg kg−1 soil). The chromate contamination affected the structure and the diversity of the soil bacterial community. Bacterial strains isolated from the microcosm contaminated with the highest concentration of chromate were identified by 16S rDNA gene sequencing. All isolates belonged to the genus Pseudomonas, were able to reduce Cr(VI), and showed a high resistance to chromate. To our knowledge, this is the first report that shows Pseudomonas strains having the capability to resist up to 40 mM of Cr(VI) on minimal medium. The cyanobacterial group was more sensitive to chromate contamination than culturable heterotrophic bacteria. No cyanobacterial growth was detected in enrichment cultures from the soil polluted with the highest chromate concentration. Some enzymes were inhibited by high concentrations of chromate, whereas others were stimulated. The ATP content in microcosms was strongly affected by chromate. We conclude that the soil microbial community responds to chromate pollution through changes in community structure, in metabolic activity, and in selection for Cr(VI)-resistance.  相似文献   

16.
We examined the effect of chronic soil warming on microbial biomass, functional capacity, and community structure in soil samples collected from the Soil Warming Study located at the Harvard Forest Long-term Ecological Research (LTER) site. Twelve years of chronic soil warming at 5 °C above the ambient temperature resulted in a significant reduction in microbial biomass and the utilization of a suite of C substrates which included amino acids, carbohydrates, and carboxylic acids. Heating significantly reduced the abundance of fungal biomarkers. There was also a shift in the mineral soil microbial community towards gram positive bacteria and actinomycetes.  相似文献   

17.
Biochar’s role on greenhouse gas emission and plant growth has been well addressed. However, there have been few studies on changes in soil microbial community and activities with biochar soil amendment (BSA) in croplands. In a field experiment, biochar was amended at rates of 0, 20 and 40 t ha−1 (C0, C1 and C2, respectively) in May 2010 before rice transplantation in a rice paddy from Sichuan, China. Topsoil (0–15 cm) was collected from the rice paddy while rice harvest in late October 2011. Soil physico-chemical properties and microbial biomass carbon (MBC) and nitrogen (MBN) as well as selected soil enzyme activities were determined. Based on 16S rRNA and 18S rRNA gene, bacterial and fungal community structure and abundance were characterized using terminal-restriction fragment length polymorphism (T-RFLP) combined with clone library analysis, denaturing gradient gel electrophoresis (DGGE) and quantitative real-time PCR assay (qPCR). Contents of SOC and total N and soil pH were increased but bulk density decreased significantly. While no changes in MBC and MBN, gene copy numbers of bacterial 16S rRNA was shown significantly increased by 28% and 64% and that of fungal 18S rRNA significantly decreased by 35% and 46% under BSA at 20 and 40 t ha−1 respectively over control. Moreover, there was a significant decrease by 70% in abundance of Methylophilaceae and of Hydrogenophilaceae with an increase by 45% in Anaerolineae abundance under BSA at 40 t ha−1 over control. Whereas, using sequencing DGGE bands of fungal 18S rRNA gene, some bands affiliated with Ascomycota and Glomeromycota were shown inhibited by BSA at rate of 40 t ha−1. Significant increases in activities of dehydrogenase, alkaline phosphatases while decreased β-glucosidase were also observed under BSA. The results here indicated a shift toward a bacterial dominated microbial community in the rice paddy with BSA.  相似文献   

18.
Cover crops have traditionally been used to reduce soil erosion and build soil quality, but more recently cover crops are being used as an effective tool in organic weed management. Many studies have demonstrated microbial community response to individual cover crop species, but the effects of mixed species cover crop communities have received less attention. Moreover, the relationship between arable weeds and soil microbial communities is not well understood. The objective of this study was to determine the relative influence of cover crop diversity, early-season weed communities, and tillage on soil microbial community structure in an organic cropping system through the extraction of fatty acid methyl esters (FAMEs). A field experiment was conducted between 2009 and 2011 near Mead, NE where spring-sown mixtures of zero (control), two, and eight cover crop species were included in a sunflower–soybean–corn crop rotation. A mixture of four weed species was planted in all experimental units (excluding the no-cover control), and also included as an individual treatment. Cover crops and weeds were planted in late-March, then terminated in late-May using a field disk or sweep plow undercutter, and main crops were planted within one week of termination. Three (2009) or four (2010–11) soil cores were taken to a depth of 20 cm in all experimental units at 45, 32, and 25 days following cover crop termination in 2009, 2010, and 2011, respectively. Total FAMEs pooled across 2009 and 2010 were greatest in the two species mixture–undercutter treatment combination (140.8 ± 3.9 nmol g−1) followed by the eight species mixture–undercutter treatment combination (132.4 ± 3.9 nmol g−1). Abundance of five (2009 and 2010) and seventeen (2011) FAME biomarkers was reduced in the weedy treatment relative to both cover-cropped treatments and the no-cover control. In 2009 and 2010, termination with the undercutter reduced abundance of most actinomycete biomarkers while termination with the field disk reduced abundance of C18:1(cis11) and iC16:0. Canonical discriminant analysis of the microbial community successfully segregated most cover crop mixture by termination method treatment combinations in 2009 and 2010. Microbial communities were most strongly influenced by the presence and type of early-spring plant communities, as weeds exerted a strong negative influence on abundance of many key microbial biomarkers, including the AMF markers C16:1(cis11) and C18:1(cis11). Weeds may alter soil microbial community structure as a means of increasing competitive success in arable soils, but this relationship requires further investigation.  相似文献   

19.
Anaerobic digestion of organic materials generates residues of differing chemical composition compared to undigested animal manures, which may affect the soil microbial ecosystem differently when used as fertilizers. This study investigated the effects of two biogas residues (BR-A and BR-B) and cattle slurry (CS) applied at rates corresponding to 70 kg NH4+-N ha−1 on bacterial community structure and microbial activity in three soils of different texture (a sandy, a clay and an organic clay soil). 16S rRNA genes were targeted in PCR reactions and bacterial community profiles visualized using terminal restriction fragment length polymorphism. General microbial activity was measured as basal respiration (B-resp), substrate-induced respiration (SIR), specific growth rate (μSIR), metabolic quotient (qCO2) and nitrogen mineralization capacity (NMC). Non-metric multidimensional scaling analysis visualized shifts in bacterial community structure related to microbial functions. There were significant differences in bacterial community structure after 120 days of incubation (+20 °C at 70% of WHC) between non-amended (control) and amended soils, especially in the sandy soil, where CS caused a more pronounced shift than biogas residues. Terminal-restriction fragment (TRF) 307, the predominant peak in CS-amended sandy soil, was identified as possibly Bacillus or Streptococcus. TRF 226, the dominant peak in organic soil amended with BR-B, was classified as Rhodopseudomonas. B-resp significantly increased and SIR decreased in all amendments to organic soil compared with the control, potentially indicating decreased efficiency of heterotrophic microorganisms to convert organic carbon into microbial biomass. This was also reflected in an elevated qCO2 in the organic soil. The μSIR level was higher in the sandy soil amended with BR-A than with BR-B or CS, indicating a shift toward species capable of rapidly utilizing glucose. NMC was significantly elevated in the clay and organic soils amended with BR-A and BR-B and in the sandy soil amended with BR-B and CS. Thus, biogas residues and cattle slurry had different effects on the bacterial community structure and microbial activity in the three soils. However, the effects of biogas residues on microbial activities were comparable in magnitude to those of cattle slurry and the bacterial community structure was less affected. Therefore, we do not see any reason not to recommend using biogas residues as fertilizers based on the results presented.  相似文献   

20.
Elevated copper (Cu) concentrations have been shown to decrease the microbial activity in soils. Plants can have beneficial effects on the biological activity of soils mainly through their root exudates. In this study we investigated the impact of various plant species with different Cu tolerance levels on the microbial activity in two soils with low (10 mg/kg) and high (180 mg/kg) copper concentrations. The soil was a Kahangi Sandy Loam. Three different plants, Agrostis capillaris ‘Parys’ tolerant for Cu, Agrostis capillaris ‘Highland’ non-tolerant and Helianthus annuus tolerant and a hyper-accumulator for Cu were used. To increase the Cu availability to plants, EDTA was added to some of the pots 20 days after sowing. The effect of Cu contamination on the biological activity of soil in the presence and absence of plant growth was evaluated by measuring the dehydrogenase activity, the microbial biomass, the basal respiration, and the potential nitrification.Results show that plants increased the microbial activity in the low Cu soil. In the high Cu soil the microbial activity seemed to be related to the plant health. With the Cu-tolerant Agrostis capillaris ‘Parys’, the microbial activity increased faster than with the other plant species. Up to 50 days after sowing, the tolerant grass Agrostis capillaris ‘Parys’ had a higher plant biomass and was much healthier than the non-tolerant grass. Later on the growth of the non-tolerant Agrostis capillaris ‘Highland’ recovered, and the microbial activity of the soil reached close to those recorded for the soil treatments with the Cu-tolerant plant species. The addition of EDTA delayed the increase in microbial activity even further. The proportion of microbial biomass carbon in the organic fraction was higher in the low Cu soil than in the high Cu soil, with ratios ranging from 1.3 to 3.3 and from 0.5 to 1.7 respectively. The basal respiration rate in the original soil was significantly lower in the high Cu soil than in the low Cu soil, and was generally increased by the presence of plants.  相似文献   

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