On the concentration of acetic acid in straw and soil

Summary Freshly harvested wheat straw contained 0.096 g water g^–1 dry straw and 180 mM acetic acid. The straw absorbed water more rapidly from wet soil. The concentration of acetic acid fell to about 10 mM within 6 h of incorporation of straw in the soil and then remained relatively constant for a period of 12 days, irrespective of soil moisture content. In soil at its maximum water holding capacity after gravitational drainage, the decline in acetic acid concentration (c) with distance (d) from wheat or barley straw was exponential, with c=c_o e^–nd where c_o is the concentration of acetic acid at the straw surface and n is a constant (0.46 for barley and 0.42 for wheat straw). The presence of acetic acid seems to be a major cause of poor establishment and growth when seeds and seedling roots come into contact with straw.     

Rapid Method of Determining Factors Limiting Bacterial Growth in Soil

A technique to determine which nutrients limit bacterial growth in soil was developed. The method was based on measuring the thymidine incorporation rate of bacteria after the addition of C, N, and P in different combinations to soil samples. First, the thymidine incorporation method was tested in two different soils: an agricultural soil and a forest humus soil. Carbon (as glucose) was found to be the limiting substance for bacterial growth in both of these soils. The effect of adding different amounts of nutrients was studied, and tests were performed to determine whether the additions affected the soil pH and subsequent bacterial activity. The incubation time required to detect bacterial growth after adding substrate to the soil was also evaluated. Second, the method was used in experiments in which three different size fractions of straw (1 to 2, 0.25 to 1, and <0.25 mm) were mixed into the agricultural soil in order to induce N limitation for bacterial growth. When the straw fraction was small enough (<0.25 mm), N became the limiting nutrient for bacterial growth after about 3 weeks. After the addition of the larger straw fractions (1 to 2 and 0.25 to 1 mm), the soil bacteria were C limited throughout the incubation period (10 weeks), although an increase in the thymidine incorporation rate after the addition of C and N together compared with adding them separately was seen in the sample containing the size fraction from 0.25 to 1 mm. Third, soils from high-pH, limestone-rich areas were examined. P limitation was observed in one of these soils, while tendencies toward P limitation were seen in some of the other soils.     

Fungal and bacterial growth in soil with plant materials of different C/N ratios

Fungal (acetate-in-ergosterol incorporation) and bacterial (leucine/thymidine incorporation) growth resulting from alfalfa (C/N=15) and barley straw (C/N=75) addition was studied in soil microcosms for 64 days. Nitrogen amendments were used to compensate for the C/N difference between the substrates. Fungal growth increased to a maximum after 3–7 days, at five to eight times the controls, following the addition of straw, and three to four times the controls following the addition of alfalfa. After 20–30 days, the fungal growth rate converged with the controls, resulting in a cumulative fungal growth two to three times the controls following straw addition and about 20% higher than the controls following alfalfa addition. The bacterial growth rate reached rates five times the controls following alfalfa addition and twice that of the controls following straw addition after 3–7 days. It remained elevated after 64 days. The cumulative bacterial growth was two and four times the controls following straw and alfalfa addition, respectively. A negative correlation was found between N addition and bacterial growth, while N stimulated fungal growth. Thus, the C/N ratio of the additions (substrate and extra N) could not entirely explain the different results regarding fungal and bacterial growths. Respiration was not always related to the combined growth of the microorganisms, emphasizing the requirement for a better understanding of growth efficiencies of fungi and bacteria.     

Genotypic characterization of soil bacteria in the Umm Al-Namil Island,Kuwait

Microflora is an integral part of soil ecosystem, in which bacteria are the largest group of soil microbes. This is a pioneer study for establishing baseline data on the diversity of soil bacteria among different regions in Kuwait. The aim is to understand biodiversity in different settings, how bacteria adapt to different niches in the environment as well as in different hosts. The identification of bacterial 16S rRNA molecules from environmental soil samples was investigated. Genomic Deoxyribonucleic acid DNA was extracted from 25 soil samples derived from five different test regions in the Umm Al-Namil Island, Kuwait. After amplification of bacterial 16S rRNA molecules by the Polymerase chain reaction PCR, the products were characterized and complex band patterns were obtained, indicating high bacterial diversity. A sample of the 16 s rRNA amplicons were sequenced in order to identify the species. The spatial distribution of bacterial taxa in the different soil samples was homogeneous, suggesting a stable and widespread community. Forty-nine isolates from Umm Al-Namil island were identified by comparative analysis of partial 16S rRNA gene sequences. Phylogenetic analysis was carried out in order to study the connection between the isolates to identify species. A large proportion of these isolates represent correspond to known or novel species within the Pseudomonus and Bacillus genera, which are common soil bacteria. Our results provided a reference for future studies to facilitate bacterial identification and ecological research in Kuwait.     

II. Cereal disease: the interplay between resistance and pathogenicity: Inheritance of pathogenicity in Gaeumannomyces graminis var. tritici

Variation in host response of isolates of the eyespot pathogen from different sources was examined over a number of years. Pathogen types were found in intensively-cropped couch-infested cereal sites that were almost as virulent on Agropyron repens (couch) as on wheat or barley. The commonly occurring wheat (W) type isolates from couch-free cereal crops were virulent on wheat and barley but avirulent on couch. Couch (C) types were isolated not only from couch but also from wheat, barley and oat crops with couch infestation. In pathogenicity tests on rye, C. types did not differ in virulence from the more commonly occurring W types. Aegilops ventricosa was equally resistant to both types. W type isolates from wheat and barley were examined to assess differential pathogenicity on wheat and barley. Sequential cropping with single cereal crops was used to separate out possible specific types. Isolates from fourth wheat and fourth barley crops were more pathogenic on the original than on the alternative host. When comparisons were made between isolates from third and fifth consecutive wheat and barley crops only those from barley showed a preference for the original host. An experiment comparing isolates from third and seventh consecutive wheat and barley crops showed a decline in virulence from the short to the longer sequences on the alternative but not on the original host.     

The effect of ammoniation on the intake and nutritive value of straw

Studies were conducted to compare the increases in dry matter digestibility (DMD) in vitro and in vivo and to determine the metabolisable energy (ME) value of straw ammoniated at ambient temperature. Two stacks of straw sealed with polyethylene were allowed to react with 3% (w/w) anhydrous NH₃ for 30 and 56 days, respectively. Both DMD in vitro and nitrogen tests were carried out over an eight-week period subsequent to opening the stacks. Digestibility in vivo was measured with 12 wether lambs. The non-treated and ammoniated straws were given ad libitum, with a supplement of either ground barley or a lamb concentrate which contained 16% crude protein (CP).There was a mean increase of 15 percentage units in DMD in vitro for the ammoniated straw irrespective of whether it was treated for 30 or 56 days. The corresponding increase in mean DMD in vivo was 14.2 units. The CP content of the straw was increased from 3.1 to 7.6%. The increase in DMD in vitro and total N content was maintained throughout the sampling period. Approximately 58% of the anhydrous NH₃ added to the straw appeared to have been irreversibly “bound” to the straw. The ME values for the ammoniated straw were 6.78 and 7.49 MJ/kg when the straw was supplemented with either barley or the lamb concentrate, respectively. Straw ammoniation had a marked effect on intake. The overall increase in intake was 70% for the treated compared with the non-treated material.     

Interactions between rumen bacteria and ciliate protozoa in their attachment to barley straw

The attachment of ¹⁴C-choline-labelled mixed rumen protozoa to barley straw in vitro was not significantly affected when bacteria prepared from rumen fluid were added to the incubation mixture. There was similarly little effect on protozoal attachment when the straw had already been colonized by a bacterial population for 24 h. In contrast, it was deduced from measurements of enzyme activities associated with straw that bacterial attachment was reduced if protozoa were present. Bacteria that had colonized the straw for 25 h beforehand were less susceptible to predation by protozoa.     

Influence of fungal-bacterial interactions on bacterial conjugation in the residuesphere

Conjugal gene transfer among bacteria in the residuesphere (area between decaying plant material and soil) of leaves of barley straw was studied. The residuesphere was shown to be a hot-spot for conjugal gene transfer compared to conjugation in sterile sand and non-sterile bulk soil. Impact of fungal colonisation of the residuesphere on bacterial colonisation and conjugation was also investigated. The inhibition of fungal colonisation, due to the application of an eukaryotic inhibitor, increased bacterial colonisation of the residuesphere in soil microcosms compared to non-treated leaves. This treatment also had a transient, positive effect on conjugation. Bacterial conjugation in the residuesphere of leaves subjected to 17 days of fungal colonisation was significantly lower than in the residuesphere of non-colonised leaves. Fungal biomass, as measured by chitinase activity, was inversely related to the conjugation efficiency.     

应用16S rDNA克隆文库技术研究长期稻草还田对水稻土细菌多样性的影响

利用中国科学院桃源农业生态试验站施肥制度长期定位试验田对照(CK)和稻草还田(OM)施肥处理的土壤样品,应用16S rDNA克隆文库技术直接提取土壤微生物总DNA,分别构建细菌16S rDNA克隆文库,并进行序列测定和分析。结果表明,与对照(CK)相比,稻草还田(OM)后土壤细菌群落结构发生了显著改变,土壤细菌多样性和均匀度均有所降低。对照(CK)和稻草还田(OM)两个施肥处理的优势种群均为变形菌,酸杆菌次之;稻草还田减少了变形菌、疣微菌、绿弯菌和绿菌的分布,而增加了硝化螺旋菌的分布。16S rDNA系统发育分析则表明,稻草还田对酸杆菌群落结构影响最大,其次是疣微菌和δ-变形菌。     

Belowground carbon input and translocation potential of fodder radish cover-crop

We compared the soil C input potential of a common catch-crop (fodder radish) established in 6-year-old direct-drilled (DD) plots with adjacent conventionally tilled (CT) plots on a Danish sandy loam soil by use of ¹⁴C-isotope labelling techniques. Intact monoliths of soil with actively growing fodder radish seedlings were extracted in Autumn of 2008 from DD and CT field plots and labelled with ¹⁴CO₂ at different time intervals during fodder radish growth. Labelled monoliths were then sampled 6 and 100 days after termination of labelling by clipping above-ground biomass at soil level and separating below-ground components into macro-roots and macro-root-free soil at 0?C10, 10?C25 and 25?C45 cm soil depth. Using fodder radish ¹⁴C data and the preceding spring barley biomass yield data we estimated C input from the spring barley-fodder radish cycle in addition to evaluating the effect of the removal of spring barley harvestable straw on soil C input. Potential soil C input under straw removal scenarios with and without an established fodder radish crop was also evaluated. Relative to other depths, over 70% of labelled below-ground C was found in the 0?C10 cm soil depth in both DD and CT treatments for each of the two samplings. For both macro-root and macro-root-free soil and in both tillage treatments, labelled C decreased significantly with depth (P?<?0.05). A decline of labeled C in macro-root but an increase of labeled C in macro-root-free soil was observed from day 6 to day 100 for both tillage treatments. Over the autumn-winter growing period, total below-ground C input by fodder radish within the 0?C45 cm soil depth was approximately 1.0 and 1.2 Mg C ha^?1 for CT and DD, respectively. We used data from 100 days after labelling, which coincided with the incorporation of the field fodder radish biomass, to estimate that the total fodder radish contribution to below-ground C after biomass incorporation would range between 1.6 and 1.7 Mg C ha^?1 for DD and CT, respectively. The figures for spring barley straw removal with fodder radish establishment would be between 4.9 and 5.1 Mg C ha^?1, while with no fodder radish establishment, C input to the soil would range between 3.2 Mg C ha^?1 and 3.4 Mg C ha^?1, which is approximately 0.6 Mg C ha^?1 lower than the 4 Mg C ha^?1 biomass C input required to maintain long-term soil organic C. In comparison, under straw retention and fodder radish catch-crop establishment the total spring barley and fodder radish C input would be approximately 6.1 and 6.5 Mg C ha^?1 for DD and CT, respectively. We conclude that fodder radish catch-crops have a potential for mitigating against soil C depletion resulting from export of cereal straw to other uses.     

温室条件下条形柄锈菌体细胞重组的分子确证

为了获得温室条件下条形柄锈菌发生体细胞重组而导致毒性变异的直接证据,本研究选取7个美国条形柄锈菌小麦专化型菌系和2个美国条形柄锈菌大麦专化型菌系按照夏孢子颜色和专化型与毒性差异组成9对菌系组合,对于室内混合接种产生的子代菌系用具有不同抗性的小麦或大麦品种进行筛选,采用毒性分析及SSR分子标记技术对条形柄锈菌体细胞重组现象进行了研究。对获取的413个单孢子代菌系进行的毒性分析结果显示,有84个单孢子代菌系的毒性谱表现与亲本菌系不同,初步证明体细胞重组过程的存在。SSR标记分析结果显示,11对SSR引物中有6对引物在5对菌系组合的28个毒性谱不同的单孢子代菌系中,检测发现3个单孢菌系的扩增条带与其亲本菌系不同,且表现为亲本菌系扩增条带的重组,为体细胞重组菌系。这一结果从分子水平上证明了条形柄锈菌在室内接种条件下可以通过体细胞重组产生新小种而导致毒性变异。     

Conjugative plasmids in multi-resistant bacterial isolates from Indian soil

Aims:  Determination of heavy metal and antibiotic resistance and presence of conjugative plasmids in bacteria isolated from soil irrigated with wastewater.
Methods and Results:  Composite soil samples were collected from Ghaziabad, Uttar Pradesh, India. Forty different bacteria were selected from nutrient agar and characterized by morphological, cultural and biochemical tests. All the isolates were tested for their resistance to different heavy metals and antibiotics. The DNA derived from multiple metal and antibiotic-resistant bacterial isolates was PCR amplified and plasmid-specific sequences (IncP, IncN, IncW, IncQ and pMV158-type) were analysed by dot blot hybridization. All isolates gave PCR products with trfA2 and oriT primers of the IncP group. These PCR products also hybridized with the RP4-derived probes. However, the samples were negative for all the other investigated plasmids as proved by PCR and dot blots.
Conclusions:  The presence of conjugative/mobilizable IncP plasmids in the isolates indicates that these bacteria have gene-mobilizing capacity with implications for potential dissemination of introduced recombinant DNA.
Significance and Impact of the Study:  The detection of IncP plasmids in all the bacterial isolates is another proof for the prevalence of these plasmids. We propose that IncP plasmids are mainly responsible for the spread of multi-resistant bacteria in these soils.     

Virulence of Septoria nodorum as Affected by Passage Through Detached Leaves of Wheat and Barley Cultivars1

Abstract Three genetically marked, single–spore isolates of Septoria nodorum from wheat were passed through detached leaves of wheat cvs Blueboy and Coker 747 and the barley cv. Boone to produce three sub–isolates per original isolate. Each sub–isolate was cultured for three pycnidiospore generations on its respective host. Virulence of each sub–isolate on detached leaves of Blueboy, Caldwell, Coker 747, and NK81W701 wheat, and Boone and Surry barley was compared with that of the original single–spore isolate from which it was derived. In most cases, sub–isolates passed through wheat were significantly more virulent than the originals on wheat cultivars. They also were more virulent to barley than the original isolates but they were less virulent to barley than to wheat cultivars. Isolate × cultivar interactions were statistically significant (P < .0001) for isolates passed through wheat or barley and were greater than isolate × cultivar interactions among the original isolates. In seven of eight isolates passed through wheat or barley, only the original genetic marker was recovered after three generations, indicating that cross–contamination could not account for the observed change of virulence. In the single case of apparent contamination, of a sub–isolate, virulence declined.     

Cereal supplementation modified the fibrolytic activity but not the structure of the cellulolytic bacterial community associated with rumen solid digesta

4 ruminally cannulated cows were fed a forage diet (93% hay + 7% straw) and a mixed diet (33 % hay + 7% straw + 40% barley) in a 2 x 2 crossover experimental design. In sacco degradation of forage, fibrolytic activities (polysaccharidases and glycosidases) of the solid-associated bacteria (SAB), and distribution of the 3 main cellulolytic bacterial species (Fibrobacter succinogenes, Ruminococcus albus, Ruminococcus flavefaciens) were determined for both diets. Barley supplementation decreased the hay degradation rate and mainly the polysaccharidase activities of the SAB (30% on average). The sum of rRNA of the 3 cellulolytic bacterial species represented on average 17% of the total bacterial signal and R. albus was the dominant cellulolytic bacterial species of the 3 studied. Barley supplementation did not modify the proportion of the 3 cellulolytic bacteria attached to plant particles. The negative effect of barley on the ruminal hay degradation rate is due to a decrease in fibrolytic activity of the SAB, and not to a modification of the balance of the three cellulolytic bacterial species examined.     

The transformation of nitrogen and carbon in the soil during humification of straw labelled with N15

Summary Laboratory tests were made on the effect of NaNO₃ or (NH₄)₂CO₃ on the dynamics of humification in the soil of oat straw tagged with N¹⁵. The mixture was incubated for 112 days, at constant temperature and moisture conditions. It was found that NH₄-N accelerated the straw humifications more than NO₃-N. Humification started directly after the straw was introduced into the soil. N¹⁵ derived from straw consituted a part of the forming humic compounds. Already after 14 days of incubation, the N¹⁵ of straw was found in all fractions of humic compounds. Mineralization accompanied humification. The added inorganic-N accelerated not only straw humification, but also the mineralization of forming humic compounds. This is why the added inorganic-N had no influence on the content of humic compounds. The decisive factor in the increase of humic and fulvic acids in the soil, was the straw. The inorganic N added to the straw, had no influence on the quality of humic acids formed in the soil.     

Plasmids of Azospirillum brasilense

The cells from natural isolates of A. Brasilense were found to harbour 1 to 4 plasmids with the molecular masses within the 27-300 Md range. 100 Md plasmids are specific for this bacterial species. Strains isolated from the roots of cereals (wheat, maize, barley) have more heterogeneous plasmid composition as compared to the strains isolated from soil.     

Ammonia-treated barley straw and rolled barley offered either together, in a mixed ration, or successively to beef steers

Barley straw treated with anhydrous ammonia at a rate of 40 g per kg of straw dry matter (DM) and rolled barley were offered to 20 steers weighing initially 350 kg. Each steer was offered in total approximately 600 kg of straw DM and approximately 525 kg of barley DM. Ten steers were offered the straw alone in the long form at the beginning of the trial followed by the rolled barley alone. The remaining 10 steers were offered straw which had been ground through a 40-mm screen and mixed with the rolled barley in a complete diet. Dry matter digestibility coefficients of the ammonia-treated straw and the mixed straw plus barley diet were 0.52 and 0.57 ± 0.026, respectively. The DM digestibility coefficient of rolled grain in the mixed diet was predicted from the digestibility of starch to be 0.78 and the DM digestibility of straw in the mixed diet, determined by difference, was 0.39. Although steers offered the straw followed by rolled barley took on average 39 days longer to consume their total food allowance, cold dressed carcass weights of the two groups were not significantly different nor was there any difference in the carcass composition of the two groups of steers as determined by specific gravity measurements. Maintenance energy requirements were calculated for the two groups of steers and although the same amount of food was consumed by both groups and the energy required for maintenance was higher in the group offered straw followed by barley, the depression in the energy available from straw offered in a mixed diet caused the same total amount of metabolizable energy to be available for carcass gain to both groups.     

Soil conditions and the take-all disease of wheat; control of the disease under continuous cultivation of a spring-sown cereal

In a field experiment on the control of take-all at the Woburn Experimental Station, winter wheat was followed by two consecutive crops of spring-sown barley. Samples of the barley crop were taken from the forty-eight plots of the experiment in 1945 and 1946, for estimation of root Disease Rating, and grain yields were also recorded. A comparison of six autumn treatments of the stubble has shown that treatments affecting the available nitrogen content of the soil exercised a predominant effect upon incidence of take-all in the following crop. Two effects of nitrogen applied in autumn have been distinguished: (1) an immediate effect, in assisting survival of Ophiobolus graminis in infected root and stubble residues; (2) a deferred effect, in promoting disease escape of the following crop. The ploughing in of straw in autumn was found to increase the incidence of take-all, presumably because the adverse deferred effect of decomposing straw in locking up available nitrogen and withholding it from the following crop. outweighed its beneficial immediate effect in helping to starve out O. graminis , by depriving the fungus of nitrogen. The autumn growth of undersown trefoil ( Medicago lupulina ) on the stubble land seenled to be entirely beneficial; active growth of the legume appeared to assist in starving out O. graminis , and nitrogen was released by decomposition of the trefoil in the soil after spring ploughing in time to benefit the barley crop immediately following.     

Comparative identification by fatty acid analysis of soil,rhizosphere, and geocarposphere bacteria of peanut (Arachis hypogaea L.)

Bacterial isolates were collected from the geocarposphere, rhizosphere, and root-free soil of field grown peanut (Arachis hypogaea L.) at three sample dates, and the isolates were identified by analysis of fatty acid methyl-esters to determine if qualitative differences exist among the bacterial microflora of these zones. Five bacterial genera were associated with isolates from soil, while pod and root isolates constituted 16 and 13 genera, respectively, indicating that bacterial diversity was higher in the rhizosphere and geocarposphere than in soil. The dominant (most frequently identified) genus across all three samples dates was Flavobacterium, for pods, Pseudomonas for roots, and Bacillus, for root-free soil. Sixteen bacterial taxa were only isolated from the geocarposphere, 7 only from the rhizosphere, and 5 only from soil. These results show that specific bacterial taxa are preferentially adapted to colonization of the geocarposphere and suggest that the soil, rhizosphere, and geocarposphere constitute three distinct ecological niches. Bacteria which colonize the geocarposphere should be examined as potential biological control agents for pod-invading fungi such as the toxigenic strains of Aspergillus flavus and A. parasiticus.     

Variations in soil culturable bacteria communities and biochemical characteristics in the Dongkemadi glacier forefield along a chronosequence

The variations in the soil culturable bacterial communities and biochemical parameters of early successional soils from a receding glacier in the Tanggula Mountain were investigated. We examined low organic carbon (C) and nitrogen (N) contents and enzymatic activity, correlated with fewer bacterial groups and numbers in the glacier forefield soils. The soil pH values decreased, but the soil water content, organic C and total N significantly increased, along the chronosequence. The soil C/N ratio decreased in the early development soils and increased in the late development soils and it did not correlate with the soil age since deglaciation. The activities of soil urease, sucrase, protease, polyphenol oxidase, catalase, and dehydrogenase increased along the chronosequence. The numbers of culturable bacteria in the soils increased as cultured at 25°C while decreased at 4°C from younger soils to older soils. Total numbers of culturable bacteria in the soils cultured at 25°C were significantly positively correlated to the soil total N, organic C, and soil water content, as well as the activities of soil urease, sucrase, dehydrogenase, catalase, and polyphenol oxidase. We have obtained 224 isolates from the glacier forefield soils. The isolates were clustered into 28 groups by amplified ribosomal DNA restriction analysis (ARDRA). Among them, 27 groups and 25 groups were obtained from the soils at 25°C and at 4°C incubation temperatures, respectively. These groups are affiliated with 18 genera that belong to six taxa, viz, Actinobacteria, Gammaproteobacteria, Bacteroidetes, Firmicutes, Alphaproteobacteria, and Betaproteobacteria. The dominant taxa were Actinobacteria, Gammaproteobacteria, and Bacteroidetes in all the samples. The abundance and the diversity of the genera isolated at 25°C incubation temperature were greater than that at 4°C.