Influence of organic and inorganic soil amendments on plant growth in crude oil-contaminated soil

Phytoremediation can be a viable alternative to traditional, more costly remediation techniques. Three greenhouse studies were conducted to evaluate plant growth with different soil amendments in crude oil-contaminated soil. Growth of alfalfa (Medicago sativa L., cultivar: Riley), bermudagrass (Cynodon dactylon L., cultivar: Common), crabgrass (Digitaria sanguinalis, cultivar: Large), fescue (Lolium arundinaceum Schreb., cultivar: Kentucky 31), and ryegrass (Lolium multiflorum Lam., cultivar: Marshall) was determined in crude oil-contaminated soil amended with either inorganic fertilizer, hardwood sawdust, papermill sludge, broiler litter or unamended (control). In the first study, the addition of broiler litter reduced seed germination for ryegrass, fescue, and alfalfa. In the second study, bermudagrass grown in broiler litter-amended soil produced the most shoot biomass, bermudagrass produced the most root biomass, and crabgrass and bermudagrass produced the most root length. In the third study, soil amended with broiler litter resulted in the greatest reduction in gravimetric total petroleum hydrocarbon (TPH) levels across the six plant treatments following the 14-wk study. Ryegrass produced more root biomass than any other species when grown in inorganic fertilizer- or hardwood sawdust + inorganic fertilizer-amended soil. The studies demonstrated that soil amendments and plant species selection were important considerations for phytoremediation of crude oil-contaminated soil.     

化肥和有机肥长期施用对红壤酶活性的影响

选择长期定位试验中的不施肥对照(CK)、单施化肥(NPK)、单施有机肥(OM)及化肥有机肥配施(NPKM)4种处理,研究了长期化肥和有机肥互作对旱地红壤酶活性的影响及酶活性与土壤理化性质、微生物生物量的关系。结果表明,施肥特别是化肥和有机肥的交互作用能不同程度促进参与碳、氮循环的总体酶活性增加;其中,OM对酶活性的促进作用强于NPK,NPKM的酶活性最高。与CK相比,施用有机肥的处理(即OM和NPKM)会降低参与碳循环酶和参与氮循环酶的比值,而NPK不影响该比值。OM处理的单位微生物量碳酶活性和单位有机碳酶活性均显著低于其他处理,而在NPK处理中这两项指标最高,OM和NPKM处理则提高了单位微生物量氮酶活性。一方面说明有机肥可以缓解土壤微生物的碳限制,但是供氮能力相对不足,而与化肥配施缓解了氮素的限制状况;另一方面暗示有机肥可以提高土壤生物的生态效率。总之,化肥和有机肥配施能够在碳氮资源的生物有效性上形成互补关系,能够同时促进土壤生物和作物生长,从而满足土壤生态系统服务功能持续发挥的需要。     

Influence of soil fauna on fungal plant pathogens in agricultural and horticultural systems

An understanding of the ecology of plant pathogens is crucial for the development of agricultural and horticultural growing systems that enhance plant health. One important group of organisms that influences plant pathogen survival and dispersal is the soil fauna. This review deals with known and possible interactions between soil animals and different groups of fungal plant pathogens. It is suggested that facultative saprophytes may be affected considerably by mycelial grazing by soil animals, while obligate pathogens may be more influenced by animals that ingest spores and other types of propagules. Both types of pathogens can also be influenced by indirect interactions with the soil fauna. Manipulating the soil environment for enhancement of beneficial soil animals that consume pathogens seems to be a realistic possibility for sustainable agriculture and horticulture.     

Predators mediate the effects of a fungal pathogen on prey: an experiment with grasshoppers,wolf spiders,and fungal pathogens

1. Prey interact with multiple kinds of enemies such as predators, parasites, and pathogens. Interactions among enemies can alter prey dynamics but they are often studied separately. 2. During the summers of 2005–2006, we conducted a field experiment to examine interactions among grasshoppers, spider predators, and a lethal fungal pathogen of grasshoppers. Grasshopper nymphs were stocked into field enclosures. Predation was manipulated by adding spiders to enclosures on day 1, day 5, or day 10 of the experiment, or no spiders were added. We monitored grasshopper survival and grasshopper mortality from fungal pathogens for 4 weeks. 3. Fungal pathogens were abundant in 2005 but not in 2006, probably because of favourable weather conditions in 2005. When fungal pathogens were abundant, spider presence reduced grasshopper mortality from fungal pathogens, but only when spiders were present early in the experiment (added on day 1 or day 5). 4. The outcome of predator–prey interactions varied between years, probably as a result of differences in pathogen prevalence. In 2005, spider presence reduced the number of deaths from the pathogen, leading to a slight trend of increased grasshopper density. However, in 2006, when pathogens were not an important source of mortality, spider predation was compensatory.     

The role of organic amendments to soil for crop protection: Induction of suppression of soilborne pathogens

Application of external organic inputs to soils can be considered as one of the most ancient strategies in agriculture, and it has been commonly used since the very beginning of human-based agricultural practices. During all this time, application of several organic matters to agricultural soils has demonstrated their benefit to plants and soils. Organic amendments have proved to be useful in recovering soil properties, improving soil quality and, in some cases, can be directly involved in providing beneficial effects to plants. All these obtained effects finally lead to an increase in crop protection and sustainability. One most expected effect caused by the application of organic amendments, is the suppression of a wide range of soilborne pathogens (mainly bacterial and fungal pathogens) due to the induction of physicochemical and biological changes in soils. In order to get insight into the nature of the induced soil suppression of soilborne plant pathogens, the analysis of the physical, chemical and the microbial changes, pointed to the key role of beneficial activities produced by soil microorganisms finally adapted to the environmental changes produced by the influence of organic amendments. As shown in the case studies reported here, participation of soil microbes specifically selected after organic amendment is crucial in the control of fungal soilborne diseases. Moreover, the development of “omics” approaches allowed these recent studies to go one step further, revealing the main actors involved in the induced soil suppressiveness and their activities. Thus “omics” techniques will help to understand the soil and its microbiome as a whole system, and to assign the important roles of its biological components.     

Long-term effects of organic amendments on the recovery of plant and soil microbial communities following disturbance in the Canadian boreal forest

Background and Aims

Ecosystem recovery following disturbance requires the reestablishment of key soil biogeochemical processes. This long-term 7 year study describes effects of organic material, moisture, and vegetation on soil microbial community development in the Athabasca Oil Sands Region of Western Canada.

Methods

Phospholipid fatty acid analysis was used to characterize and compare soil microbial community composition and development on reclaimed and natural forest sites. Additionally, we conducted a laboratory moisture manipulation experiment.

Results

The use of forest floor material as an organic amendment resulted in a greater percent cover of upland vegetation and placed the soil microbial community on a faster trajectory towards ecosystem recovery than did the use of a peat amendment. The soil microbial composition within the reclaimed sites exhibited a greater response to changes in moisture than did the soil microbial communities from natural sites.

Conclusion

Our research shows that the use of native organic amendment (forest floor) on reclaimed sites, and the associated establishment of native vegetation promote the development of soil microbial communities more similar to those found on natural forest sites. Additionally, soil microbial communities from natural sites may be more resistant to changes in soil moisture than those found on reclaimed sites.     

Mechanisms of survival of necrotrophic fungal plant pathogens in hosts expressing the hypersensitive response

The hypersensitive response (HR), elicited when resistant hosts are infected by incompatible races of biotrophic fungi, has been researched extensively. New studies on host responses to necrotrophic fungi are beginning to show that when the HR occurs in hosts colonized by necrotrophs, fungal growth is accelerated rather than retarded. We review current knowledge about how necrotrophs survive in host plants in which the HR is expressed. We discuss how necrotrophs cope with the environmental factors formed as a result of the HR. Necrotrophs contain an array of enzymes, which can help in exploiting the hostile environment in order to colonize the host and to remove or inactivate active oxygen species (AOS). Among this array of enzymes are superoxide dismutase (SOD), peroxidases, catalase, and perhaps laccases and polyphenol oxidases. Of these, only SOD and catalase have been studied in any detail. The precise significance of SOD and catalase in host invasion and fungal resistance is still not adequately known. The importance of different peroxidases is also still far from clear. We speculate that AOS species may trigger the response of necrotrophs to the host environment.     

Effect of organic amendment on soil fertility and plant nutrients in a post-fire Mediterranean ecosystem

Backgrounds and aims

In Mediterranean frequently burnt areas, the decrease of soil fertility leads to regressive vegetation dynamics. Organic amendments could help to accelerate post-fire ecosystem resilience, by improving soil properties and plant nutrition. This study was conducted to assess the potential of a composted biosolid to restore an early post-fire shrubland.

Methods

About 50 Mg.ha^?1 of fresh co-composted sewage sludge and green wastes were surface applied 7 months after fire on a silty-clayey soil. We monitored over a 2-year period organic matter and nutrient transfers to soil, nutrient responses of dominant plant species, and ecosystem contamination by potentially toxic trace elements.

Results

Over the experimental survey, compost rapidly and durably improved soil P₂O₅, MgO and K₂O content, and temporarily increased N-(NO₃ ^? + NO₂ ^?) content. Plant nutrition was improved more or less durably depending species. The most positive compost effect was on plant and soil phosphorus content. Plant nutrient storage was not improved 2 years after amendment, suggesting luxury consumption. No contamination by trace elements was detected in soil and plant.

Conclusions

The use of compost after fire could help for rapidly restoring soil fertility and improving plant nutrition. The increase of soil nutrient pools after amendment emphazised the diversity of plant nutritional traits. Eutrophication risk could occur from high compost and soil P₂O₅ content.     

植物篱对紫色土区坡耕地水土流失及土壤肥力的影响

植物篱的水土保持效果已得到广泛的认可,并在世界很多地方推广应用,然而,到目前为止,植物篱对坡耕地土壤肥力的影响规律研究却很少。利用长期定位小区试验,研究了植物篱对坡耕地土壤肥力的影响规律,旨在弄清植物篱提高土壤肥力的作用与效果,不断完善植物篱技术。研究发现,坡耕地在建立植物篱后,土壤粘粒在篱前富积,篱下加剧侵蚀,粘粒的富积与侵蚀沿等高线成水平带状分布;土壤有机质、N、P等主要营养元素出现与土壤颗粒相同的分布规律;对K来说,其分布不受植物篱的影响,表现出较为均一分布的特点。从土壤养分的绝对数量来看,P呈高度富积,而有机质和K则是高度耗竭。因此,坡耕地施肥时可以适当减少P的施用量,增加有机物和K的施用量。针对植物篱带对坡耕地肥力影响的特点,即篱前肥力升高,篱下肥力下降,在坡耕地管理上应特别加强篱下土壤带的培肥,以提高坡面整体生产能力。     

Earthworm effects on plant growth do not necessarily decrease with soil fertility

Earthworms are known to generally increase plant growth. However, because plant-earthworm interactions are potentially mediated by soil characteristics the response of plants to earthworms should depend on the soil type. In a greenhouse microcosm experiment, the responsiveness of plants (Veronica persica, Trifolium dubium and Poa annua) to two earthworm species (in combination or not) belonging to different functional groups (Aporrectodea. caliginosa an endogeic species, Lumbricus terrestris an anecic species) was measured in term of biomass accumulation. This responsiveness was compared in two soils (nutrient rich and nutrient poor) and two mineral fertilization treatments (with and without). The main significant effects on plant growth were due to the anecic earthworm species. L. terrestris increased the shoot biomass and the total biomass of T. dubium only in the rich soil. It increased also the total biomass of P. annua without mineral fertilization but had the opposite effect with fertilization. Mineral fertilization, in the presence of L. terrestris, also reduced the total biomass of V. persica. L. terrestris did not only affect plant growth. In P. annua and V. persica A. caliginosa and L. terrestris also affected the shoot/root ratio and this effect depended on soil type. Finally, few significant interactions were found between the anecic and the endogeic earthworms and these interactions did not depend on the soil type. A general idea would be that earthworms mostly increase plant growth through the enhancement of mineralization and that earthworm effects should decrease in nutrient-rich soils or with mineral fertilization. However, our results show that this view does not hold and that other mechanisms are influential.     

有机肥对石灰性土壤肥力属性的长期影响

用常规化学分析和差热分析方法研究了长期不同施肥模式下有机肥对土壤生态肥力的影响。结果表明,长期施用有机肥(厩肥、高秸处理)可显著提高土壤有机碳含量,其水散性G0复合体减少;水稳性G1、G2复合体增加,3种胶散复合体的有机碳含量提高,重组复合体中活性强的松结合态腐殖质较多。施入有机肥不仅可提高土壤有机无机复合体的总能量水平,而且也能提高复合体中松结态、稳结态、紧结态腐殖质的能态。高秸、厩肥处理的原土、重组、稳紧态复合体、紧结态复合体和3种胶散复合体焓变值较高,具有较高能态。施用有机肥的土壤全氮、全磷、重组磷及C/N比均呈提高趋势,pH值降低,其原土和重组复合体的阳离子交换量较高。     

Infection structures of biotrophic and hemibiotrophic fungal plant pathogens

Biotrophic plant pathogenic fungi are one of the major causes of crop losses. The infection processes they exhibit are typified by infected host plant cells remaining alive for several days. This requires the development of specialized infection structures such as haustoria which are produced by obligate biotrophs, and intracellular hyphae which are produced by many hemibiotrophs. These infection hyphae are surrounded by the host plant plasma membrane, and in the case of haustoria the extrahaustorial membrane differs biochemically and structurally from the normal membrane. An interfacial matrix separates haustoria and intracellular hyphae from the invaginated membrane and this seems to be characteristic of biotrophic interactions. There is clear evidence for molecular differentiation of the haustorial plasma membrane in powdery mildews and rusts in comparison with the other fungal membranes. Relatively few pathogenicity genes related to biotrophy, and the switch from biotrophy to necrotrophy in hemibiotrophs, have been identified.     

Metabolites of rhizobacteria antagonistic towards fungal plant pathogens

Biological control of insect, plant pathogens and weeds is the only major alternative to the use of pesticides in agriculture and forestry. A double-layer technique was used for isolation of antagonistic bacteria from rhizosphere against plant pathogenic fungi. Four potential rhizobacteria was selected in dual culture plate method based on their antifungal activity against several soil-borne fungal plant pathogens. The selected rhizobacteria, identified based on their morphological, biochemical and molecular traits, belong to the species of fluorescentPseudomonas (SAB8, GM4) andBacillus (A555, GF23). The active antifungal metabolites produced by these strains in culture filtrates were tested for the growth inhibition ofFusarium semitectum used as test fungus. The active fraction of antifungal metabolite/(s) from fluorescentPseudomonas (SAB8, GM4) and their effects on hyphal growth were observed under microscope. Two kinds of alterations were detected: inhibition of hyphal tip elongation and an extensive branching of hyphae with closer septa.     

Isolation and characterization of soil Streptomyces species as potential biological control agents against fungal plant pathogens

The use of antagonist microorganisms against fungal plant pathogens is an attractive and ecologically alternative to the use of chemical pesticides. Streptomyces are beneficial soil bacteria and potential candidates for biocontrol agents. This study reports the isolation, characterization and antagonist activity of soil streptomycetes from the Los Petenes Biosphere Reserve, a Natural protected area in Campeche, Mexico. The results showed morphological, physiological and biochemical characterization of six actinomycetes and their inhibitory activity against Curvularia sp., Aspergillus niger, Helminthosporium sp. and Fusarium sp. One isolate, identified as Streptomyces sp. CACIS-1.16CA showed the potential to inhibit additional pathogens as Alternaria sp., Phytophthora capsici, Colletotrichum sp. and Rhizoctonia sp. with percentages ranging from 47 to 90 %. This study identified a streptomycete strain with a broad antagonist activity that could be used for biocontrol of plant pathogenic fungi.     

Application of different organic amendments in a gasoline contaminated soil: effect on soil microbial properties

The effects of four organic wastes, including cotton gin crushed compost (CC), poultry manure (PM), sewage sludge (SS) and organic municipal solid waste (MSW) on some biological properties of a Xerollic Calciorthid soil polluted with gasoline at two loading rates (5% and 10%) were studied in an incubation experiment. Three hundred grams of sieved soil (<2mm) were polluted with gasoline and mixed with PM at a rate of 10%, CC at a rate of 17.2%, SS at a rate of 23.1%, or MSW at a rate of 13.1%, applying to the soil the same amount of organic matter with each organic amendment. An unamended soil, non polluted (C) and polluted with gasoline at 5% (G1) and 10% (G2) rate were used as reference. Soil samples were collected after 1, 30, 60, 90, 120, 180 and 270 d of incubation and analyzed for microbial biomass carbon, respiration and dehydrogenase, urease, beta-glucosidase, phosphatase and arylsulfatase activities. At the end of the incubation period, soil biological properties were higher in organic amended soils than in C, G1 and G2 treatments. In particular, soil microbial biomass carbon and dehydrogenase, urease, beta-glucosidase, phosphatase and arylsulfatase activities increased 87.1%, 92.9%, 88.7%, 93.2%, 78.2% and 85.3%, respectively for CC-amended soils respect to G2, 85.7%, 82.3%, 87.3%, 92.2%, 76.7% and 83.6%, respectively for PM-amended soils; 82%, 90%, 84.8%, 89.9%, 74.1% and 80%, respectively for SS-amended soils; and 71.3%, 78.3% 26.2%, 38.2%, 79.7% and 88.6%, respectively for MSW-amended soils. Since the adsorption capacity of gasoline was higher in CC than the PM, SS and MSW-amended soils, it can be concluded that the addition of organic wastes with higher humic acid concentration is more beneficial for remediation of soils polluted with gasoline.     

Resource heterogeneity, soil fertility, and species diversity: effects of clonal species on plant communities

Spatial heterogeneity in soil resources is widely thought to promote plant species coexistence, and this mechanism figures prominently in resource-ratio models of competition. However, most experimental studies have found that nutrient enhancements depress diversity regardless of whether nutrients are uniformly or heterogeneously applied. This mismatch between theory and empirical pattern is potentially due to an interaction between plant size and the scale of resource heterogeneity. Clonal plants that spread vegetatively via rhizomes or stolons can grow large and may integrate across resource patches, thus reducing the positive effect of small-scale resource heterogeneity on plant species richness. Many rhizomatous clonal species respond strongly to increased soil fertility, and they have been hypothesized to drive the descending arm of the hump-shaped productivity-diversity relationship in grasslands. We tested whether clonals reduce species richness in a grassland community by manipulating nutrient heterogeneity, soil fertility, and the presence of rhizomatous clonal species in a 6-year field experiment. We found strong and consistent negative effects of clonals on species richness. These effects were greatest at high fertility and when soil resources were applied at a scale at which rhizomatous clonals could integrate across resource patches. Thus, we find support for the hypothesis that plant size and resource heterogeneity interact to determine species diversity.     

Epigenetic regulation of development and pathogenesis in fungal plant pathogens

Evidently, epigenetics is at forefront in explaining the mechanisms underlying the success of human pathogens and in the identification of pathogen‐induced modifications within host plants. However, there is a lack of studies highlighting the role of epigenetics in the modulation of the growth and pathogenicity of fungal plant pathogens. In this review, we attempt to highlight and discuss the role of epigenetics in the regulation of the growth and pathogenicity of fungal phytopathogens using Magnaporthe oryzae, a devastating fungal plant pathogen, as a model system. With the perspective of wide application in the understanding of the development, pathogenesis and control of other fungal pathogens, we attempt to provide a synthesized view of the epigenetic studies conducted on M. oryzae to date. First, we discuss the mechanisms of epigenetic modifications in M. oryzae and their impact on fungal development and pathogenicity. Second, we highlight the unexplored epigenetic mechanisms and areas of research that should be considered in the near future to construct a holistic view of epigenetic functioning in M. oryzae and other fungal plant pathogens. Importantly, the development of a complete understanding of the modulation of epigenetic regulation in fungal pathogens can help in the identification of target points to combat fungal pathogenesis.