Glyphosate and Previous Crop Residue Effect on Deleterious and Beneficial Soil-borne Fungi from a Peanut–Corn–Soybean Rotations

Bean seedlings (Phaseolus vulgaris L.) were transplanted to soil with corn previous crop residue, peanut previous crop residue and no agricultural soil, and treated with a range of glyphosate concentrations. Trichoderma, Gliocladium, Fusarium and Pythium soil‐borne fungi populations were monitored during 24 days after glyphosate treatment to study the glyphosate and previous crop residue effects on these populations. In addition, those genera of soil‐borne fungi were tested to study in vitro toxicity to glyphosate. Independently of glyphosate concentration, the highest population of Trichoderma spp. and Gliocladium spp. were registered on soil with previous corn residue. Fusarium and Pythium populations increased proportionally to the increment of glyphosate concentration. No effect of glyphosate was founded on Trichoderma and Gliocladium populations. The in vitro study results indicated an inhibitory effect of glyphosate on mycelial grown of the most studied soil‐borne fungi.     

Quantification of Monosporascuscannonballus Ascospores in Muskmelon Fields in Eastern Spain

The populations of Monosporascuscannonballus ascospores in the soils of 14 muskmelon fields throughout muskmelon production areas of Comunidad Valenciana (eastern Spain) were quantified from 2002 to 2003. The fields were surveyed in July, at the end of the cropping season, when plants approached maturity and symptoms of vine decline in the canopy appeared as patches of wilted or dead plants. Ascospores were recovered from all muskmelon fields surveyed. The average soil populations ranged from 1.54 to 6.33 per g of soil and the number of ascospores within a soil sample ranged from 0.50 to 16.20 ascospores/g of soil. This is the first detailed report on ascospore populations of M. cannonballus in muskmelon fields from a cucurbit‐growing area in Spain and the Mediterranean basin.     

Changes in populations of soil microorganisms,nematodes, and enzyme activity associated with application of powdered pine bark

Evaluation of enzyme activities in combination with taxonomic analyses may help define the mechanisms involved in microbial decomposition of orgaic amendments and biological control of soilborne pathogens. In this study, powdered pine bark was added to nematode-infested soil at rates of 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 g kg^–1. Total fungal populations did not differ among treatments immediately after application of pine bark. After 7 days, fungal populations were positively correlated with increasing levels of pine bark. This increase was sustained through 14 and 21 days.Penicillium chrysogenum andPaecilomves variotii were the predominant fungal species isolated from soil amended with pine bark. Total bacterial populations did not change with addition of pine bark at 0, 7, and 14 days after treatment. At 21 and 63 days, total bacterial populations declined in soil receiving the highest rates of pine bark. Addition of pine bark powder to soil caused a shift in predominant bacterial genera fromBacillus spp. in nonamended soil, toPseudomonas spp. in amended soil. Soil enzyme activities were positively correlated with pine bark rate at all sampling times. Trehalase activity was positively correlated with total fungal populations and with predominant fungal species, but was not related to bacterial populations. The number of non-parasitic (non-stylet bearing) nematodes andMeloidogyne arenaria in soil and roots were not correlated with pine bark rate. However,Heterodera glycines juveniles in roots, and the number of cysts g^–1 root, declined with increasing levels of pine bark.Journal Series Series No. 18-933598 Alabama Agricultural Experiment Station     

Inbreeding and soil conditions affect dispersal and components of performance of two plant species in fragmented landscapes

During habitat fragmentation, plant populations become smaller and more isolated from each other, resulting in increasing inbreeding rates within populations. Furthermore, fragmentation is often accompanied by a progressive deterioration of soil conditions. Overall, high inbreeding rates and poor soil conditions decrease plant performance and so increase the probability of extinction of fragmented plant populations. The goal of this study was to investigate the effects of inbreeding and soil acidification on seed and offspring traits of Succisa pratensis and Hypochaeris radicata, two plant species differing in mating system, lifespan and dispersal ability. For each species, plants from four populations of different sizes were hand-pollinated. The selfed and outcrossed progeny were grown at two soil pH levels. Overall, results showed that the dispersal potential of H. radicata was reduced by selfing, indicating that dispersal capacity is not independent from the genetic erosion process. Variation among seed families and its interactions with pollination treatments indicate that dispersal capacity may have a genetic basis. The performance of both species decreased sharply as soil conditions became more acidic, but inbreeding did not aggravate the process. These results suggest that S. pratensis and H. radicata populations may decline in the long term; however, family level variation suggests a potential for adaptation to new conditions.     

Changes in the populations of microorganisms associated with the application of soil amendments to control Sclerotium rolfsii Sacc.

Populations of microorganisms from soil treated with guanidine thiocyanate, guanylurea sulfate, thiourea, or furfural were compared with those of untreated soil. The materials effected quantitative and/or qualitative changes in composition of the soil microflora depending on the compound used. Guanidine thiocyanate (Gt) significantly (p0.05) increased total fungal populations relative to populations of other treatments. Populations of Penicillium purpurogenum were markedly higher in Gt-treated soil. Gt also increased total bacterial populations, and was the only compound that increased actinomycete populations. The relative percentage of Trichoderma harzianum was significantly higher in soil treated with thiourea than in the other treatments. Furfural increased the percentage of P. purpurogenum with respect to total fungi, and was as effective as guanylurea sulfate in increasing chitinolytic bacteria and those in the Pseudomonas cepacia-group. Thiourea most effectively promoted proliferation of coryneform bacteria. Chitinolytic fungi increased synergistically when Gt and guanylurea sulfate were applied in combination.     

线虫和蚯蚓对土壤微量气体排放的影响

线虫和蚯蚓是农业中广泛存在的土壤动物,由于它们与微生物的相互作用及对土壤生态系统能量传递和养分转化的影响,可能影响土壤微量气体代谢和温室气体的排放.通过在不同土壤线虫密度下接种蚯蚓的15d培养试验结果表明,土壤动物对土壤微量气体(CO2和N2O)代谢有显著促进作用.与灭线土相比,高密度线虫土壤处理与高密度线虫土壤加蚯蚓的处理导致CO2排放量分别增加了4.3倍和5.2倍,相应的N2O排放量增加了1.8倍和2.7倍.与低密度线虫土壤处理比较时,高密度线虫土壤处理导致CO2和N2O排放量分别增加了19%和21%.接种蚯蚓在高密度线虫土中较接种在低密度线虫土壤中的CO2和N2O排放量分别增加了12%和27%.5个处理中,除了低密度线虫加蚯蚓的处理和高密度线虫处理间差异不显著外,其余各处理间均达到极显著差异(P<0.01).两种气体的排放速率呈极显著正相关(R2=0.9414).高密度线虫土壤较低密度线虫土壤显著提高了土壤的DOC含量,不同线虫密度土壤中DOC显著性的差异与CO2和N2O排放密切相关(P<0.05).     

Soil populations of Thielaviopsis basicola associated with cherry rootstocks in relation to effects of the pathogen on their growth

Large differences were found between populations of Thielaviopsis basicola in soils from nursery layer-beds of different cherry rootsock clones. The soils were classified primarily into those with small (< 700 propagules/g) and those with large (3600–45000 propagules/g) populations, although significant differences occurred between soil populations in the latter group. Clones associated with small soil populations (Prunus pseudocerasus, and P. avium×P. pseudocerasus hybrids) were highly resistant to T. basicola root rot; clones associated with large soil populations (selections and intraspecific crosses of P. avium, and hybrids of P. avium × P. incisa) were susceptible. The results indicated that severe pathogenesis was associated with varying levels of parasitism in different clones, but not that extensive parasitism of cherry species occurred without pathogenesis. Resistance to T. basicola in the P. pseudocerasus hybrids is an important asset to these potential cherry rootsocks.     

Absence of a role for lytic microorganisms in the decline of bacteria andSaccharomyces introduced into soil

The populations ofKlebsieila pneumoniae, Escherichia coli, Enterobacter aerogenes, andPseudomonas sp. fell following their addition to soil, but species lysing these gram-negative bacteria were not detected. The numbers ofStaphylococcus aureus andMicrococcus flavus fell by more than four orders of magnitude and ofSaccharomyces cerevisiae by more than two orders after their addition to soil. Organisms lysing these gram-positive bacteria were present in soil, but their numbers did not increase as a result of the additions. Lytic activity againstS. aureus was detected in soil filtrates, but this activity was not enhanced by inoculation of soil with the bacterium. Addition of cycloheximide to soil suspensions delayed the fall in abundance ofM. flavus but did not suppress the lytic populations. We conclude that lysis is not responsible for the decline of bacteria orS. cerevisiae added to soil.     

Sex expression, skewed sex ratios, and microhabitat distribution in the dioecious desert moss Syntrichia caninervis (Pottiaceae)

The moss Syntrichia caninervis is the dominant soil bryophyte in a blackbrush (Coleogyne ramosissima) community in the southern Nevada Mojave Desert, with a mean cover of 6.3%. A survey of the 10-ha study site revealed an expressed ramet sex ratio of 14♀ : 1♂ (N = 890), with 85% of ramets not expressing sex over their life span, and an expressed population sex ratio of 40♀ : 2♂ : 1♀♂ (female : male : mixed-sex, N = 89), with 52% of populations not expressing sex. A greater incidence of sex expression was associated with shaded microsites, higher soil moisture content, and taller ramets. Shaded microsites had higher surface soil moisture levels than exposed microsites. In the exposed microhabitat, surface soil moisture was positively correlated with ramet height but not with sex expression. Male ramets and populations were restricted to shaded microhabitats, whereas female ramets and populations were found in both shaded and exposed microhabitats, suggesting gender specialization. The rarity of mature sporophytes, found in 0% of the ramets sampled and in only 3% of the populations, is probably due to the rarity of mixed-sex populations. We hypothesize that mixed-sex populations are rare because of factors relating to male rarity and that the differential cost of sex expression reduces the clonal growth capacity of male individuals.     

Effect of green manure on Pythium spp. population and microbial communities in intensive cropping systems

Saprophytic soil-borne pathogens can be either actively suppressed by organic amendments or enhanced, depending on soil health conditions. This can be deleterious in the event of selection of a soil-borne population by previous soil management and short crop rotation. Trials were performed in the open field and in pots, using naturally infected soil from intensive crop systems, i.e., soil from fields with 8 years of strawberry cultivation. The aim was to study short-term response of Pythium and soil microbial populations to green manure. The use of green manure in these naturally infested soils, 3–10 weeks after fresh tissue incorporation, caused Pythium populations to increase concurrent with an increase in soil microbial populations, and did not result in the suppression of the pathogen. A more elaborate trial was performed under controlled conditions, amending soil with fresh wheat plant material, air-dried wheat plant material and an organic fertilizer with a high level of humic substances. Although compared to the original soil, all amendments caused a similar increase in organic matter content and small differences in soil respiration, incorporation of fresh, not decomposed, plant material strongly increased Pythium, while the organic fertilizer did not affect the original level of the pathogen population. The increase in total number of fungi and bacteria did not have any suppressive effect on the Pythium population in naturally infested soil used for this study.     

ZINC-TOLERANT ECOTYPES IN MELILOTUS ALBA (LEGUMINOSAE)

Melilotus alba (Leguminosae) populations from mine sites in southwestern Wisconsin were shown to be ecotypically adapted to high levels of zinc in the soil. In greenhouse experiments using high-zinc soil and high levels of zinc in sand culture, seedlings from mine populations grew better and suffered less mortality than did seedlings from roadside populations.     

Characterization of Depth-Related Changes in Bacterial Communities Involved in Mineral Weathering Along a Mineral-Rich Soil Profile

In this study, we used denaturing gradient gel electrophoresis (DGGE) and culture-dependent methodology to characterize bacterial populations and mineral-dissolving bacteria in a mineral-rich soil profile. DGGE and sequencing revealed 13 known bacterial families and 7 unknown populations for the soil profile. Seventy-one isolates could solubilize feldspar. Weathering effectiveness and pattern of the isolates differed among the horizons. The 71 mineral-dissolving isolates were affiliated with 32 bacterial species within 14 genera, among which Bacillus, Burkholderia, and Arthrobacter were dominant. Distinct mineral-dissolving populations were observed between the surface and subsurface horizons. Notably, the deepest horizon showed maximum diversity of the mineral-dissolving bacteria. Furthermore, a significantly higher proportion of the high efficiency mineral-dissolving bacteria was observed in the deeper horizons than in the upper horizons. The results suggested that the soil profile harboured diverse mineral-dissolving populations and the dissolving potential and pattern and the community of the mineral-dissolving bacteria changed with depth.     

Molecular diagnostics and chemical analysis for assessing biodegradation of polychlorinated biphenyls in contaminated soils

Summary The microbial populations in PCB-contaminated electric power substation capacitor bank soil (TVA soil) and from another PCB-contaminated site (New England soil) were compared to determine their potential to degrade PCB. Known biphenyl operon genes were used as gene probes in colony hybridizations and in dot blots of DNA extracted from the soil to monitor the presence of PCB-degrading organisms in the soils. The microbial populations in the two soils differed in that the population in New England soil was enriched by the addition of 1000 p.p.m. 2-chlorobiphenyl (2-CB) whereas the population in the TVA capacitor bank soil was not affected. PCB degradative activity in the New England soil was indicated by a 50% PCB disappearance (gas chromatography), accumulation of chlorobenzoates (HPLC), and¹⁴CO₂ evolution from¹⁴C-2CB. The PCB-degrading bacteria in the New England soil could be identified by their positive hybridization to thebph gene probes, their ability to produce the yellowmeta-cleavage product from 2,3-dihydroxybiphenyl (2,3-DHB), and the degradation of specific PCB congeners by individual isolates in resting cell assays. Although the TVA capacitor bank soil lacked effective PCB-degrading populations, addition of a PCB-degrading organism and 10 000 p.p.m. biphenyl resulted in a >50% reduction of PCB levels. Molecular characterization of soil microbial populations in laboratory scale treatments is expected to be valuable in the design of process monitoring and performance verification approaches for full scale bioremediation.     

Competitiveness of indigenous populations of Bradyrhizobium japonicum serocluster 123 as determined using a root-tip marking procedure in growth pouches

Soil Bradyrhizobium populations limit nodule occupancy of soybean by symbiotically-superior inoculant strains throughout much of the American midwest. In this study, the competitiveness of indigenous populations of B. japonicum serocluster 123 from Waukegan and Webster soils was evaluated in growth pouches using a root-tip marking procedure. The native rhizobia were from soils incubated 0–8 h in soybean root exudate (SRE) or plant nutrient solution (PNS) prior to inoculation. Populations of serocluster 123 strains in soil and nodule occupancy by these strains were assessed using fluorescent antibodies prepared against B. japonicum USDA 123. There were no significant differences in populations that came from SRE or PNS incubated soils: both populations increased in number over the incubation period. Nodule occupancy by both populations in growth pouches was similar to that previously encountered in field studies with these two soils. With the Waukegan soil, the serocluster 123 population dominated nodulation forming 69 and 62% of taproot nodules above and below the root tip mark, respectively. However, for the more alkaline Webster soil, serocluster 123 strains were much less competitive, producing only 9 and 13%, respectively, of the nodules formed above and below the root tip mark. In growth pouches, soil populations of bradyrhizobia from the Webster soil produced significantly more nodules than those from the Waukegan soil, but both strains and a pure culture of USDA 110 had a similar distribution of nodules.     

Community Structure of Actively Growing Bacterial Populations in Plant Pathogen Suppressive Soil

The bacterial community in soil was screened by using various molecular approaches for bacterial populations that were activated upon addition of different supplements. Plasmodiophora brassicae spores, chitin, sodium acetate, and cabbage plants were added to activate specific bacterial populations as an aid in screening for novel antagonists to plant pathogens. DNA from growing bacteria was specifically extracted from the soil by bromodeoxyuridine immunocapture. The captured DNA was fingerprinted by terminal restriction fragment length polymorphism (T-RFLP). The composition of the dominant bacterial community was also analyzed directly by T-RFLP and by denaturing gradient gel electrophoresis (DGGE). After chitin addition to the soil, some bacterial populations increased dramatically and became dominant both in the total and in the actively growing community. Some of the emerging bands on DGGE gels from chitin-amended soil were sequenced and found to be similar to known chitin-degrading genera such as Oerskovia, Kitasatospora, and Streptomyces species. Some of these sequences could be matched to specific terminal restriction fragments on the T-RFLP output. After addition of Plasmodiophora spores, an increase in specific Pseudomonads could be observed with Pseudomonas-specific primers for DGGE. These results demonstrate the utility of microbiomics, or a combination of molecular approaches, for investigating the composition of complex microbial communities in soil.     

Indigenous Populations of Three Closely Related <Emphasis Type="Italic">Lysobacter</Emphasis> spp. in Agricultural Soils Using Real-Time PCR

Previous research had shown that three closely related species of Lysobacter, i.e., Lysobacter antibioticus, Lysobacter capsici, and Lysobacter gummosus, were present in different Rhizoctonia-suppressive soils. However, the population dynamics of these three Lysobacter spp. in different habitats remains unknown. Therefore, a specific primer–probe combination was designed for the combined quantification of these three Lysobacter spp. using TaqMan. Strains of the three target species were efficiently detected with TaqMan, whereas related non-target strains of Lysobacter enzymogenes and Xanthomonas campestris were not or only weakly amplified. Indigenous Lysobacter populations were analyzed in soils of 10 organic farms in the Netherlands during three subsequent years with TaqMan. These soils differed in soil characteristics and crop rotation. Additionally, Lysobacter populations in rhizosphere and bulk soil of different crops on one of these farms were studied. In acid sandy soils low Lysobacter populations were present, whereas pH neutral clay soils contained high populations (respectively, <4.0–5.87 and 6.22–6.95 log gene copy numbers g⁻¹ soil). Clay content, pH and C/N ratio, but not organic matter content in soil, correlated with higher Lysobacter populations. Unexpectedly, different crops did not significantly influence population size of the three Lysobacter spp. and their populations were barely higher in rhizosphere than in bulk soil.     

Mechanisms of salt tolerance in transgenic Arabidopsis thaliana constitutively overexpressing the tomato 14-3-3 protein TFT7

A hydroponics experiment was conducted to investigate the effects of iron plaque on root surfaces with respect to selenite uptake and translocation within the seedlings of two cultivars of rice (Oryza sativa L. cv Xiushui48 and Bing9652). Different amounts of iron plaque were formed by adding 0, 10, 30, 50, 70 mg Fe l⁻¹ in the nutrient solution. After 24 h of growth, the amount of iron plaque was positively correlated with the Fe²⁺ addition to the nutrient solution. These concentrations of Fe, inducing plaque, had no significant effect on the shoot and root growth of rice plants in 50 μg Se l⁻¹ nutrient solution. The amount of Se accumulated in iron plaque was positively correlated to the amount of iron plaque. Increasing iron plaque decreased the selenium concentration in shoots and in roots. At the same time, the translocation of Se from roots to shoots was reduced with increasing amounts of iron plaque. At both the shorter and longer exposure times, the ratio of root- to-shoot selenium was higher than in the controls. More Se stayed in the roots at the longer exposure time than at the shorter time. The concentration of selenium in the xylem sap was sharply decreased with increasing amount of iron plaque on the rice roots. The DCB (dithionite-citrate-bicarbonate)-extracted Se was up to 89.9–91.1% of the total Se when roots with iron plaque (Fe 70) were incubated in 50 μg Se l⁻¹ solution for 30 min. This DCB-extracted Se, however, accounted for only 21.9–28.7% of total Se when roots with iron plaque were incubated in the same solution for 3 days. Se adsorbed in iron plaque can be desorbed by low-molecular-weight organic acids, similar to the desorption of Se from ferrihydrite. These results suggest that iron plaque might act as a ‘buffer’ for Se in the rhizosphere.     

Leaf traits of natural populations of <Emphasis Type="Italic">Adiantum reniforme</Emphasis> var. <Emphasis Type="Italic">sinensis</Emphasis>, endemic to the Three Gorges region in China

Leaf mass per unit area (LMA), carbon and nitrogen contents, leaf construction cost, and photosynthetic capacity (P _max) of Adiantum reniforme var. sinensis, an endangered fern endemic to the Three Gorges region in southwest China, were compared in five populations differing in habitat such as soil moisture and irradiance. The low soil moisture and high irradiance habitat population exhibited significantly higher LMA, area-based leaf construction (CC_A), and carbon content (C_A), but lower leaf nitrogen content per unit dry mass (N_M) than the other habitat populations. The high soil moisture and low irradiance habitat populations had the lowest CC_A, but their cost/benefic ratios of CCA/P _max were similar to the medium soil moisture and irradiance habitat population due to their lower leaf P _max. Hence A. reniforme var. sinensis prefers partially shaded, moist but well-drained, slope habitats. Due to human activities, however, its main habitats now are cliffs or steeply sloped bare rocks with poor and thin soil. The relatively high energy requirements and low photosynthetic capacity in these habitats could limit the capability of the species in extending population or interspecific competition and hence increase its endangerment.     

The distribution of an intertidal aphid,Pemphigus trehernei foster,on marine saltmarshes

Summary The intertidal aphid, Pemphigus trehernei, is restricted to aster plants (Aster tripolium) growing near the edges of creeks and salt pans in low areas on tidal saltmarshes. Aphid populations in mid-marsh areas do not show an equivalent edge effect. In low-marshes the edge soil generally has more surface cracks and cavities which can accommodate aphids and a higher % air space than soil from regions away from edges. Adults and 1st instars can penetrate edge soil more readily than non-edge soil. Aphid abundance is positively correlated with % air space in low-marsh regions. Aphid populations established on potted asters were destroyed or reduced to very low levels when transferred to non-edge regions of low-marsh areas. It is suggested that aphid distribution is primarily limited by soil conditions, especially the extent of soil drainage.     

Rhizosphere and root-infecting fungi and the design of ecological field experiments

As part of a wider study into the role of soil fungi in the ecology of the winter annual grass, Vulpia ciliata ssp. ambigua (Le Gall) Stace & Auquier, we applied the fungicides benomyl and prochloraz to three natural populations of the grass growing in East anglia, United Kingdom. The rhizosphere and rootinfecting fungi associated with the three populations were analysed each month between February and May 1992 when plants set seed. There were marked differences between the fungal floras associated with each of the three populations of V. ciliata, despite the fact that associated plant species and soil nutrient status were broadly similar between sites. This was attributed to wide differences in soil pH between the three populations. Prochloraz did not affect fungal abundance, but benomyl decreased the isolation frequencies of Fusarium oxysporum from roots and the frequencies of Penicillium and Trichoderma spp. isolated from rhizosphere soil, and increased the frequency of isolation of Mucor hiemalis from the rhizosphere of V. ciliata. There were also significant increases in the isolation frequencies of F. oxysporum from roots and M. hiemalis, Trichoderma spp. and Phoma fimeti from the rhizosphere of V. ciliata as plants matured. The significance of these results for the design of ecological field experiments are discussed in light of a previous study which has shown that asymptomatic root-infecting fungi can affect plant fecundity and hence abundance in natural populations of V. ciliata. We propose that differences in microbial communities between sites, controlled in part by soil chemistry, are a major factor determining plant performance under field conditions.