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1.
Laboratory experiments were carried out to investigate the fate of bacteria during and after passage through the intestinal tract of detritivore earthworms. Earthworms (Lumbricus spp.) were fed with cattle dung inoculated 7 days previously with one of five different Gram-negative bacteria. Bacterial concentrations were determined 2 days later in dung and soil, and in gut material from different parts of the earthworm intestinal tract. A high percentage (28–82%) of the total bacteria (epifluorescence direct counts) in the earthworm gut content was culturable. The concentration of total heterotrophic aerobic bacteria did not vary significantly among the five different bacterial additions and the non-inoculated control. In earthworm casts the number of total heterotrophs per gram dry matter (2.1×109) was higher than in soil (1.7×108), but lower than in the dung (1.5×1010). The test-bacteria, however, showed different survival patterns along the earthworm intestinal tract. The concentrations of Escherichia coli BJ 18 and Pseudomonas putida MM 1 and MM 11 in earthworm casts were lower than in the ingested dung, while concentrations of Enterobacter cloacae A 107 and Aeromonas hydrophila DMU 115 in dung and casts were similar. Ent. cloacae, and to aminor extent E. coli, were reduced in numbers by several orders of magnitude in the pharynx and/or crop. In the hind gut, however, the concentration of Ent. cloacae had increased to the same level as in the ingested dung, while the concentration of E. coli remained low. Our observations indicate that the bacterial flora of ingested food materials changes qualitatively and quantitatively during gut transit.  相似文献   

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

3.
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   

4.
Glucosinolate profiles differ among plant species and their isothiocyanate (ITC) derivatives differ in toxicity to nematodes. Successful management of plant-parasitic nematodes by ITCs requires the incorporation of appropriate amounts of glucosinolate-containing biomass. Plant materials, containing glucosinolate-precursors of the ITCs most toxic to nematodes, were selected and applied to soil based upon ITC lethal concentration (LC) values. This provided a reliable and repeatable basis for application rates for suppression of Meloidogyne javanica and Tylenchulus semipenetrans by Brassica hirta and M. javanica by B. juncea. Sufficient biomass of B. hirta to potentially yield 0.03-0.12 μmol ml−1 of glucotropeolin reduced nematode survival compared to similar amounts of broccoli (Brassica oleraceae var. botrytis). At biomass levels providing >0.37 μmol ml−1 of glucotropeolin, mortality of M. javanica was 100% with B. hirta. Biomass of B. juncea potentially yielding 2.82 μmol ml−1 of sinigrin reduced M. javanica survival 65% below that obtained by a similar amount of broccoli. Rates of B. juncea to yield lethal levels of allyl ITC to reduce T. semipenetrans survival underestimated the glucosinolate application rates for this amendment. Application of plant biomass to soil >2.9% w/w reduced M. javanica survival regardless of the glucosinolate concentration of the amendment material. Application of brassicaceous amendments to soil initiates complex and dynamic biological and chemical processes. Despite the inherent complexity, we find that brassicaceous amendments can be applied to achieve consistent and repeatable nematode suppression when based upon the chemistry of the incorporated material.  相似文献   

5.
White-tailed deer (Odocoileus virginianus) overbrowsing has altered plant species diversity throughout deciduous forest understories in eastern North America. Here we report on a landscape-level (306 km2) project in Pennsylvania, USA that tracked the herbaceous community response to deer herd reductions. From 2001 to 2007, we estimated deer densities, browse impact on woody seedlings, and censused the herbaceous flora in permanent plots throughout the area. We assessed herb layer species richness, abundance, and dominance and measured three known phytoindicators of deer impact: Trillium spp., Maianthemum canadense, and Medeola virginiana. We predicted that browse-sensitive taxa would increase in abundance, size, and flowering as would overall species diversity following deer culls and browse impact that declined by an order of magnitude by 2007. Following intensified deer harvests, we observed a limited recovery of the herbaceous community. Trillium spp. abundance, height, and flowering; M. canadense cover; and M. virginiana height all increased following herd reductions. Similarly, forb and shrub cover increased by 130% and 300%, respectively. Nevertheless, species diversity (i.e., richness and dominance) did not vary. Our work demonstrates that reducing deer densities can provide rapid morphological and population-level benefits to palatable species without a concomitant recovery in diversity. We suggest that decreasing deer populations alone may not promote plant diversity in overbrowsed, depauperate forests without additional restoration strategies to mitigate a browse-legacy layer dominated by browse-resistant species.  相似文献   

6.
A 49-day incubation experiment was carried out with the addition of field-grown maize stem and leaf residues to soil at three different temperatures (5, 15, and 25 °C). The aim was to study the effects of two transgenic Bt-maize varieties in comparison to their two parental non-Bt varieties on the mineralization of the residues, on their incorporation into the microbial biomass and on changes in the microbial community structure. The stem and leaf residues of Novelis-Bt contained 3.9 μg g−1 dry weight of the Bt toxin Cry1Ab and those of Valmont-Bt only 0.8 μg g−1. The residues of the two parental non-Bt varieties Nobilis and Prelude contained higher concentrations of ergosterol (+220%) and glucosamine (+190%) and had a larger fungal C-to-bacterial C ratio (+240%) than the two Bt varieties. After adding the Bt residues, an initial peak in respiration of an extra 700 μg CO2-C g−1 soil or 4% of the added amount was observed in comparison to the two non-Bt varieties at all three temperatures. On average of the four varieties, 19-38% of the maize C added was mineralized during the 49-day incubation at the three different temperatures. The overall mean increase in total maize-derived CO2 evolution corresponded to a Q10 value of 1.4 for both temperature steps, i.e. from 5 to 15 °C and from 15 to 25 °C. The addition of maize residues led to a strong increase in all microbial properties analyzed. The highest contents were always measured at 5 °C and the lowest at 25 °C. The variety-specific contents of microbial biomass C, biomass N, ATP and adenylates increased in the order Novelis-Bt ? Prelude<Valmont-Bt ? Nobilis. The mineralization of Novelis-Bt residues with the highest Bt concentration and lowest N concentration and their incorporation into the microbial biomass was significantly reduced compared to the parental non-Bt variety Nobilis. These negative effects increased considerably from 5 to 25 °C. The transgenic Bt variety Valmont did not show further significant effects except for the initial peak in respiration at any temperature.  相似文献   

7.
Metal rich fly ash dumps may serve as repository of ecologically useful multi-functional rhizobacteria having potential use in the development of vegetation at the dumps. Therefore, in the present study bacteria from the rhizosphere of a wild perennial grass colonizing Indraprastha and Badarpur fly ash dumps of Delhi region were purified, identified and functionally characterized. The fly ash had low levels of nutrients, moisture and organic matter coupled with toxic levels of heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn). Both the dumps were mostly barren except for a few patches of Saccharum ravennae and some weedy species. Sixty five dominant, morphologically distinct rhizobacteria were purified, which belonged to 18 genera and 38 species. Gram-positive bacteria were dominating in the fly ash environment. Bacillus spp. and Paenibacillus spp. were common at both the dumps. Multi-metal tolerance was shown by diverse bacterial taxa. The minimum inhibitory concentration (MIC) was highest for As (12.5-20.0 mM) and Pb (7.5-10.0 mM), although many rhizobacteria also possessed significant tolerance to Cr, Zn, Ni, Cu, Co and Cd. The tolerance profiles of rhizobacteria to different metals may be ranked in the decreasing order as As > Pb > Cr > Zn > Ni > Cu > Co > Cd > Hg. Majority of rhizobacteria showed good siderophore activity. Multiple-metal tolerance was also coupled with high siderophore production in some of the isolates (Microbacterium barkeri IPSr74, Serratia marcescens IPSr90 and IPSr82, Enterococcus casseliflavus BPSr32, Bacillus sp. IPSr80, Pseudomonas aeruginosa BPSr43 and Brochothrix campestris BPSr3). Most of the bacteria could grow on nitrogen-deficient medium. However, the dominant nitrogen-fixers reported from the rhizosphere of other Saccharum species were not detected. S. marcescens IPSr90 was the only rhizobacterium, which showed ACC-deaminase (ACCD) activity. Proportion of phosphate-solubilizing bacteria was high. Considerable improvement in the seedling establishment, plant weight and shoot length in rhizobacterial inoculated plants of S. ravennae in fly ash environment indicated the significance of rhizobacteria in its colonization and spread to the dumps. Representative rhizobacteria, with high MIC (for most of the metals) and good plant growth promoting (PGP) traits comparable to commercially useful bacterial inoculants were identified as S. marcescens IPSr82 and IPSr90, P. aeruginosa BPSr43, Paenibacillus larvae BPSr106, Arthrobacter ureafaciens BPSr55, Paenibacillus azotofixans BPSr107 and E. casseliflavus BPSr32. S. ravennae and some of these rhizobacteria may be potentially useful for the development of inoculation technologies for conversion of barren fly ash dumps into ecologically and economically productive habitats.  相似文献   

8.
Glomalin concentrations of extra-radical arbuscular mycorrhizal (AM) hyphae were estimated by deploying hyphal in-growth cores containing glomalin-free sand in field soils in a tropical forest and in pot cultures. In field soils, glomalin was 0.044±0.013 μg m−1 hyphae. In pot cultures glomalin concentrations were lower (range 0.0068-0.036 μg m−1), and varied significantly among species. Using this technique, preliminary estimates of extraradical AM hyphal production on Inceptisols were 1.91 Mg ha−1yr−1 and on Oxisol were 1.47 Mg ha−1 yr−1, but they could range between 0.9-5.7 Mg ha−1 yr−1. These rates of hyphal production are approximately 10% (range 5-33%) of estimated above ground primary production of the forest.  相似文献   

9.
Scanty information on long-term soil organic carbon (SOC) dynamics hampers validation of SOC models in the tropics. We observed SOC content changes in a 16-year continuously cropped agroforestry experiment in Ibadan, south-western Nigeria. SOC levels declined in all treatments. The decline was most pronounced in the no-tree control treatments with continuous maize and cowpea cropping, where SOC levels dropped from the initial 15.4 to 7.3-8.0 Mg C ha−1 in the 0-12 cm topsoil in 16 years. In the two continuously cropped alley cropping (AC) systems, one with Leucaena leucocephala and one with Senna siamea trees, SOC levels dropped to 10.7-13.2 Mg C ha−1. Compared to the no-tree control treatments, an annual application of an additional 8.5 Mg ha−1 (dry matter) of plant residues, mainly tree prunings, led to an extra 3.5 Mg C ha−1 (∼0.2% C) in the 0-12 cm top soil after 11 years, and 4.1 Mg C ha−1 after 16 years. The addition of NPK fertilizer had little effect on the quantities of above-ground plant residues returned to the soil, and there was no evidence that the fertilizer affected the rate of SOC decomposition. The fact that both C3 and C4 plants returned organic matter to the soil in all cropping systems, but in contrasting proportions, led to clear contrasts in the 13C abundance in the SOC. This 13C information, together with the measured SOC contents, was used to test the ROTHC model. Decomposition was very fast, illustrated by the fact that we had to double all decomposition rate constants in the model in order to simulate the measured contrasts in SOC contents and δ13C between the AC treatments and the no-tree controls. We hypothesized (1) that the pruning materials from the legume trees and/or the extra rhizodeposition from the tree roots in the AC treatments accelerated the decomposition of the SOC present at the start of the experiment (true C-priming), and/or (2) that the physical protection of microbial biomass and metabolites by the clay fraction on this site, having a sandy top soil in which clay minerals are mainly of the 1:1 type, is lower than assumed by the model.  相似文献   

10.
Fatty acid (FA) analysis is a promising tool to study trophic relationships in soil food webs. We determined FA biomarkers to trace bacterial food sources (Bacillus megaterium, Pseudomonas putida, Enterobacter aerogenes) of Collembola (Heteromurus nitidus, Protaphorura fimata, Folsomia candida). In addition, δ15N, δ13C, C/N ratio, body weight and NLFA/PLFA ratio (neutral lipid/phospholipid fatty acids) of Collembola were assessed. These measures indicated that P. putida ranked first, B. megaterium second and E. aerogenes third in food quality. FAs specific for bacteria were found in the NLFAs of the Collembola reflecting the respective bacterial diet. Biomarker FAs for gram-positive bacteria were methyl branched i14:0, i15:0, a15:0 and i17:0. Consumption of gram-negative bacteria was reflected by the cyclic form cy17:0 (E. aerogenes, P. putida) and by 16:1ω5 (P. putida).  相似文献   

11.
Earthworms are known to be important regulators of soil structure and soil organic matter (SOM) dynamics, however, quantifying their influence on carbon (C) and nitrogen (N) stabilization in agroecosystems remains a pertinent task. We manipulated population densities of the earthworm Aporrectodea rosea in three maize-tomato cropping systems [conventional (i.e., mineral fertilizer), organic (i.e., composted manure and legume cover crop), and an intermediate low-input system (i.e., alternating years of legume cover crop and mineral fertilizer)] to examine their influence on C and N incorporation into soil aggregates. Two treatments, no-earthworm versus the addition of five A. rosea adults, were established in paired microcosms using electro-shocking. A 13C and 15N labeled cover crop was incorporated into the soil of the organic and low-input systems, while 15N mineral fertilizer was applied in the conventional system. Soil samples were collected during the growing season and wet-sieved to obtain three aggregate size classes: macroaggregates (>250 μm), microaggregates (53-250 μm) and silt and clay fraction (<53 μm). Macroaggregates were further separated into coarse particulate organic matter (cPOM), microaggregates and the silt and clay fraction. Total C, 13C, total N and 15N were measured for all fractions and the bulk soil. Significant earthworm influences were restricted to the low-input and conventional systems on the final sampling date. In the low-input system, earthworms increased the incorporation of new C into microaggregates within macroaggregates by 35% (2.8 g m−2 increase; P=0.03), compared to the no-earthworm treatment. Within this same cropping system, earthworms increased new N in the cPOM and the silt and clay fractions within macroaggregates, by 49% (0.21 g m−2; P<0.01) and 38% (0.19 g m−2; P=0.02), respectively. In the conventional system, earthworms appeared to decrease the incorporation of new N into free microaggregates and macroaggregates by 49% (1.38 g m−2; P=0.04) and 41% (0.51 g m−2; P=0.057), respectively. These results indicate that earthworms can play an important role in C and N dynamics and that agroecosystem management greatly influences the magnitude and direction of their effect.  相似文献   

12.
Enzyme activities and microbial biomass in coastal soils of India   总被引：1，自引：0，他引：1  
Soil salinity is a serious problem for agriculture in coastal regions, wherein salinity is temporal in nature. We studied the effect of salinity, in summer, monsoon and winter seasons, on microbial biomass carbon (MBC) and enzyme activities (EAs) of the salt-affected soils of the coastal region of the Bay of Bengal, Sundarbans, India. The average pH of soils collected from different sites, during different seasons varied from 4.8 to 7.8. The average organic C (OC) and total N (TN) content of the soils ranged between 5.2-14.1 and 0.6-1.4 g kg−1, respectively. The electrical conductivity of the saturation extract (ECe) of soils, averaged over season, varied from 2.2 to 16.3 dSm−1. The ECe of the soils increased five fold during the summer season (13.8 dSm−1) than the monsoon season (2.7 dSm−1). The major cation and anion detected were Na+ and Cl−, respectively. Seasonality exerted considerable effects on MBC and soil EAs, with the lowest values recorded during the summer season. The activities of β-glucosidase, urease, acid phosphatase and alkaline phosphatase were similar during the winter and monsoon season. The dehydrogenase activity of soils was higher in monsoon than in winter. Average MBC, dehydrogenase, β-glucosidase, urease, acid phosphatase and alkaline phosphatase activities of the saline soils ranged from 125 to 346 mg kg−1 oven dry soil, 6-9.9 mg triphenyl formazan (TPF) kg−1 oven dry soil h−1, 18-53 mg p-nitro phenol (PNP) kg−1 oven dry soil h−1, 38-86 mg urea hydrolyzed kg−1 oven dry soil h−1, 213-584 mg PNP kg−1 oven dry soil h−1 and 176-362 mg PNP g−1 oven dry soil h−1, respectively. The same for the non-saline soils were 274-446 mg kg−1 oven dry soil, 8.8-14.4 mg TPF kg−1 oven dry soil h−1, 41-80 mg PNP kg−1 oven dry soil h−1, 89-134 mg urea hydrolyzed kg−1 oven dry soil h−1, 219-287 mg PNP kg−1 oven dry soil h−1 and 407-417 mg PNP kg−1 oven dry soil h−1, respectively. About 48%, 82%, 48%, 63%, 40% and 48% variation in MBC, dehydrogenase activity, β-glucosidase activity, urease activity, acid phosphatase activity and alkaline phosphatase activity, respectively, could be explained by the variation in ECe of saline soils. Suppression of EAs of the coastal soils during summer due to salinity rise is of immense agronomic significance and needs suitable interventions for sustainable crop production.  相似文献   

13.
Carbon isotopic composition of soils subjected to C3-C4 vegetation change is a suitable tool for the estimation of C turnover in soil organic matter (SOM) pools. We hypothesized that the biological availability of SOM pools is inversely proportional to their thermal stability. Soil samples from a field plot with 10.5 years of cultivation of the C4 plant Miscanthus×gigantheus and from a reference plot under C3 grassland vegetation were analysed by thermogravimetry coupled with differential scanning calorimetry (TG-DSC). According to differential weight losses (dTG) and energy release or consumption (DSC), five SOM pools with increasing thermal stability were distinguished: (I) 20-190 °C, (II) 190-310 °C, (III) 310-390 °C, (IV) 390-480 °C, and (V) 480-1000 °C. Their δ13C values were analysed by EA-IRMS. The weight losses in pool I were connected with water evaporation, since no significant C losses were measured and δ13C values remained unchanged. The δ13C of pools II and III in soil samples under Miscanthus were closer to the δ13C of the Miscanthus plant tissues (−11.8‰) compared to the thermally stable SOM pool V (−19.5‰). The portion of the Miscanthus-derived C4-C in total SOM in 0-5 cm reached 55.4% in the 10.5 years. The C4-C contribution in pool II was 60% and decreased down to 6% in pool V. The mean residence times (MRT) of SOM pools II, III, and IV were similar (11.6, 12.2, and 15.4 years, respectively), while pool V had a MRT of 163 years. Therefore, we concluded that the biological availability of thermal labile SOM pools (<480 °C) was higher, than that of the thermal stable pool decomposed above 480 °C. However, the increase of SOM stability with rising temperature was not gradual. Therefore, the applicability of the TG-DSC for the separation of SOM pools with different biological availability is limited.  相似文献   

14.
Here we present results from a field experiment in a sub-arctic wetland near Abisko, northern Sweden, where the permafrost is currently disintegrating with significant vegetation changes as a result. During one growing season we investigated the fluxes of CO2 and CH4 and how they were affected by ecosystem properties, i.e., composition of species that are currently expanding in the area (Carex rotundata, Eriophorum vaginatum and Eriophorum angustifolium), dissolved CH4 in the pore water, substrate availability for methane producing bacteria, water table depth, active layer, temperature, etc. We found that the measured gas fluxes over the season ranged between: CH4 0.2 and 36.1 mg CH4 m−2 h−1, Net Ecosystem Exchange (NEE) −1000 and 1250 mg CO2 m−2 h−1 (negative values meaning a sink of atmospheric CO2) and dark respiration 110 and 1700 mg CO2 m−2 h−1. We found that NEE, photosynthetic rate and CH4 emission were affected by the species composition. Multiple stepwise regressions indicated that the primary explanatory variables for NEE was photosynthetic rate and for respiration and photosynthesis biomass of green leaves. The primary explanatory variables for CH4 emissions were depth of the water table, concentration of organic acid carbon and biomass of green leaves. The negative correlations between pore water concentration and emission of CH4 and the concentrations of organic acid, amino acid and carbohydrate carbon indicated that these compounds or their fermentation by-products were substrates for CH4 formation. Furthermore, calculation of the radiative forcing of the species expanding in the area as a direct result of permafrost degradation and a change in hydrology indicate that the studied mire may act as an increasing source of radiative forcing in future.  相似文献   

15.
Several sites that are contaminated with isomers of the chlorinated insecticide hexachlorocyclohexane (HCH) are present across the globe and cause toxicity. For their bioremediation, we studied the degradation of HCH-isomers in contaminated soils by an isolate Pseudomonas aeruginosa ITRC-5. The degradation is optimal at 2 mg technical-HCH (t-HCH)/g soil, 15% water content, pH 8.0, temperature 28 °C and inoculum density 106 colony forming unit/g soil. Under these conditions, from 5 kg soil, >98% α- and γ-HCH, 17% β-HCH and 76% δ-HCH are degraded after 15 days of incubation, which is accompanied with the release of 600 μg chloride/mg t-HCH. Concomitant to the degradation, a four-fold reduction in the toxicity of HCH-isomers to earthworm, Eisenia foetida, is also observed. Addition of ITRC-5 enhanced the degradation of soil-applied HCH-isomers in ‘open field’ conditions as well, and 97%, 43%, 94% and 77% of α-, β-, γ- and δ-HCH, respectively, are degraded after 12 weeks of incubation. Thus, the bacterium causes microbial degradation and detoxification of HCH-isomers, and can be used for the bioremediation of contaminated soils.  相似文献   

16.
Sclerotia are the primary over wintering inoculum of Sclerotinia sclerotiorum (Lib.) de Bary. The effects of tillage on the primary inoculum are not well understood. The purpose of this research was to study sclerotial viability over time and between burial depths in soil, to identify bacteria colonizing and degrading the sclerotia, and determine whether these bacteria may be utilized as biological control agents. Correlation analysis indicated that a significant negative relationship existed between sclerotial viability and elapsed temporal factors (R2=−0.68, P<0.0001), and depth of burial (R2=−0.58, P<0.0001). After twelve months, sclerotia on the soil surface had the highest viability (57.5%), followed by those at the 5 cm depth (12.5%), and only 2.5% of those placed at the 10 cm depth remained viable. A significant negative relationship between sclerotial viability and bacterial populations also existed (R2=−0.60, P<0.0001). Two hundred and sixty-eight bacteria were isolated from sclerotia, 29 of which showed strong in vitro antagonism to the mycelial growth of S. sclerotiorum. Biodiversity of the inhibitory bacterial isolates was minimal on sclerotia from the soil surface and within all depths sampled at three months (i.e. in January). All burial depths within the April and July sampling dates produced bacterial diversities that were distinct from each other.  相似文献   

17.
Plants of the Brassicaceae contain glucosinolates, the hydrolysis products of which inhibit the growth of many soil-borne fungi that cause plant disease. However, amending soil with green manures of these plants gives inconsistent control of several soil-borne diseases, including those caused by Rhizoctonia solani. To identify factors that contribute to this inconsistency we investigated, in the laboratory and in pot experiments in the glasshouse, the saprophytic behaviour of R. solani AG2-1 (ZG5) in a sandy soil amended with various green manures. Fresh material from either Brassica napus var. Karoo, B. napus B1, B. napus B2, B. nigra, Diplotaxis tenuifolia (a brassicaceous weed) and the non-Brassicaceae species, oat (Avena sativa) or lupin (Lupinus angustifolius) was used at 10 or 100 g of fresh material kg−1 of dry soil in Lancelin sand. At 100 g kg−1 the volatiles of all green manures reduced the hyphal growth of R. solani, except for B. napus B1. D. tenuifolia at 100 g kg−1 inhibited the growth and sclerotial formation of R. solani. Most green manures at 10 g kg−1, and at 40% water holding capacity, stimulated the growth of R. solani for up to 3 months and increased the activity of other microbes. R. solani infected the brassicaceous plants when growing and colonized the residues mixed with soil at 10 g kg−1. This inoculum increased the severity of damping-off in canola, by 27%. Disease was particularly severe when the green manure species, except D. tenuifolia and oat, were grown in situ and residues returned to the pot from which they came, before sowing canola. There is a potential hazard in applying green manures of Brassica species as their residues can, under certain conditions, support the saprophytic activity of R. solani which increases damping-off in canola sown in the amended soils.  相似文献   

18.
Soil microorganisms contribute to the formation of non-living soil organic matter (SOM) by metabolic transformation of plant-derived material. After cell death, their biomass components with a specific molecular character become incorporated into SOM imprinting its chemical properties, although this process has not yet been quantified. In order to elucidate the contribution to SOM formation, we investigated the fate of gram-negative bacterial model biomass (Escherichia coli usually introduced into soil with manure or feces) during incubation of soil with isotopically (13C) and genetically (lux gene) labeled cells. The decline of living cells was monitored by the loss of bioluminescence. The carbon turnover and mineralization was balanced by bulk soil stable isotope analysis, and the persistence of nucleic acids was investigated by PCR amplification of the lux gene. During incubation, the number of viable E. coli cells decreased rapidly (99.9% within the first 42 d) serving as substrate for other microorganisms or for the formation of SOM, and bioluminescent cells could only be detected during the first 56 d. However, the lux gene was still detected after 224 d, which indicates stabilization of DNA in SOM. Although the survival of E. coli in soil is limited, only about 65% of the added labeled biomass carbon was mineralized to 13CO2 and 51% remained in soil after 224 d with an average 13C recovery of 117%. The amount of 13C found in the PLFA representative of living cells had decreased to 25% of the initial value, suggesting a proportional decrease of the 13C in the soil microbial biomass. The extent of this decrease is higher than the mineralization of the bulk E. coli C and thus the difference of around 25% has to be stabilized as metabolites, or in non-living SOM. The data provide evidence that the genetic information and a considerable part of the carbon from dying bacterial biomass were retained in both the soil microbial food web and in non-living SOM.  相似文献   

19.
Phosphorus deficiency and aluminium toxicity in weathered soils can be amended by applying organic residues. Nitrogen mineralization, changes in P-availability and changes in salt-extractable Al following the incorporation of residues of various green manures (Flemingia congesta, Mucuna pruriens, Pueraria phaseoloides, Tithonia diversifolia) were quantified in a field core incubation experiment. Dried residues were added at an application rate of 45 kg P ha−1 to two soils representative for the main soil groups of the South Vietnamese uplands, set up in incubation cores in an experimental field near Ho Chi Minh City, Vietnam.Decomposition of the residues proceeded at high rates. Mineralized nitrogen from the residues was recovered mainly as ammonium during the first 2 weeks of incubation. Nitrogen release from Tithonia residues with the highest lignin content and lignin:N ratio occurred more gradually compared to the three legumes. Resin-extractable P was significantly increased by residue treatments. Largest and sustained increases in resin-extractable P (0.67 and 2.06 mg P kg−1 in the two soils) were observed in samples amended with Tithonia, which was related to the large P-content (0.37%) and small C:P ratio (110) of the residues. The P-concentration in the residues, rather than the total amount of P applied through the residues, affected the increase in P-availability. The increase in resin-extractable P was correlated to the P-content (R=0.64) and C:P ratio (R=−0.65) of the residues. Salt-extractable Al-concentrations were considerably reduced by the organic amendments, up to 70 and 50% in the two soils. At the rate of 45 kg P ha−1, no significant differences between the residue treatments to reduce soil acidity were observed.As such, the application of high quality residues that are rich in P, in particular T. diversifolia, may enhance crop production by creating favourable soil conditions during the initial stages of plant development of the main crop.  相似文献   

20.
The transport of the spores of Pasteuria penetrans was studied in three contrasted textured soils (a sandy, a sandy-clay and a clay soils), cultivated with tomato, inoculated with juveniles of Meloidogyne javanica and watered with 25 or 150 mm day−1. One month after inoculation of the nematodes, 53% of the spores inoculated were leached by water flow in the sandy soil but only 14% in the sandy-clay soil and 0.1% in the clay soil. No nematodes survived in the clay soil, while the population was multiplied both in the sandy and in the sandy-clay soils. But juveniles of M. javanica were more infected by P. penetrans in the sandy-clay soil than in the sandy soil. Comparing different combinations of bare soils containing 1.1-57% of clay showed that the best spore percolation and retention balance occurred in soils amended with 10-30% clay. However, the spore recoveries decreased when the soil was enriched with more than 30% clay. The role of clay particles on the extractability of spores and on their availability to attach to the nematode cuticle in the soil is discussed.  相似文献   

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