Effect of certain chemicals on soil fungistasis

Summary Fungistatic property of soil sample amended with certain chemicals has been studied. The fungistatic property was found to be highest in soil samples amended with potassium permanganate and copper sulphate. The remaining chemicals also caused different levels of fungistasis. Thus presence of various chemicals in the microbial products seems to be the possible cause of soil fungistasis.     

Germination of conidia ofVerticillium dahliae in soil

Summary A study was made of the effect of soil fungistasis on the germination of conidia ofVerticillium dahliae Kleb. Conidia germinated on steam or propylene oxide sterilized soil, but not on unsterilized soil of six types tested. Peptone (0.5 per cent) nullified fungistasis. Glucose (0.5 per cent) had no effect on fungistasis. Wheat straw or lignin amended to unsterilized soil had no effect on spore germination after sterilization. Fungistasis was restored to sterilized soil by incorporating natural soil at various ratios or by lowering the soil pH. Fungistasis was also restored by incubating various micro-organisms in sterile soil. The fungistasis so obtained was nullified by incorporation of nutrients or by sterilization. The results suggest that nutrient deficiency as well as inhibitory substances of microbial origin might play a role in soil fungistasis. 5012 plant and soil     

Studies on soil fungistasis: Effect of certain physical and biological factors

Summary The effect of different physical and biological factors like soil sterilization, incubation period of soil, spore age, amendment of certain fungal species and their metabolites on soil fungistasis has been investigated.Different degree of sterilization affected the fugistasis differently. Soil heating above 80°C completely annulled the fungistasis. No fungistasis was recorded in soil samples steamed for 15 mts in an autoclave.Incubation of soil samples to longer duration resulted in increased fungistasis. Maximum fungistatic value was noted in samples incubated for 15 days at 25±1°C.Spore age also played important role in fungistasis. A positive relation was noted in the spore age and fungistasis upto 30 days of age and thereafter the increase in fungistasis was not well marked.Varying inhibitory effect was noted on the spore germination of the test fungi in relation to amendment of certain fungi individually and in different combinations to the soil.Aspergillus flavus alone and in combination ofAspergillus niger proved most inhibitory. The filtrate of the different fungi also induced fungistasis in soil. In this case alsoA. flavus was most effective.     

土壤抑真菌作用与细菌群落结构的关系

自然清洁土壤所具有的抑真菌作用,是健康土壤的一种自然属性,也是土壤质量的重要指标之一,对控制农作物土传病原真菌的爆发具有积极的生态学意义.本试验以中国科学院沈阳生态实验站近10年未受农药和肥料影响的撂荒地土壤作为自然清洁土壤样品,通过高温（对照、100 ℃、110 ℃、121 ℃）处理得到具有不同抑真菌作用的土壤模型,采用PCR DGGE(变性梯度凝胶电泳)方法对上述土壤样品的细菌群落结构进行分析.结果表明：土壤抑真菌作用与土壤细菌群落结构紧密相关;对照清洁土壤抑真菌作用最强,处理后土壤细菌群落结构偏离自然清洁土壤愈远,土壤抑真菌能力愈差;DGGE特异性条带切胶测序结果表明,Sphingomonas asaccharolytica、Nitrospira sp.、Hyphomicrobiaceae sp.、Bacillus megaterium和Micrococcus sp.可能与土壤抑真菌作用密切相关.     

Fungal diversity increases soil fungistasis and resistance to microbial invasion by a non resident species

Biodiversity decline is a major concern for ecosystem functioning. Recent research efforts have been mostly focused on terrestrial plants, while, despite their importance in both natural and artificial ecosystems, little is known about soil microbial communities. This work aims at investigating the effects of fungal species richness on soil invasion by non resident microbes. Synthetic fungal communities with a species diversity ranging from 1 to 8 were assembled in laboratory microcosms and used in three factorial experiments to assess the effect of diversity on soil fungistasis, microbial invasion of soil amended with plant litter and of plant rhizosphere. The capability of different microbes to colonize environments characterized by different resident microbial communities was measured. The number of microbial species in the microcosms positively affected soil fungistasis that was also induced more rapidly in presence of synthetic communities with more species. Moreover, the increase of resident fungal diversity dramatically reduced the invasibility of both soil and plant rhizosphere. We found lower variability of soil fungistasis and invasibility in microcosms with higher species richness of microbial communities. Our study pointed out the existence of negative relationships between fungal diversity and soil invasibility by non resident microbes. Therefore, the loss of microbial species may adversely affect ecosystem functionality under specific environmental conditions.     

蝉棒束孢内菌核、菌膜及其生境土壤真菌群落结构及生态功能分析

通过分析蝉棒束孢Isaria cicadae内菌核、菌膜及其生境土壤的真菌群落结构与核心真菌组的生态功能,初步探索蝉棒束孢自然生长过程中内环境真菌与其周围环境中真菌的关系。本研究利用高通量测序技术检测6株采自贵阳大将山和贵阳森林公园的蝉棒束孢及土壤样本,结果表明,蝉棒束孢内菌核共检测到43个真菌属,菌膜检测到58个真菌属,菌际土检测到260个真菌属,且内菌核和菌膜真菌群落结构相似。而两地生境土的真菌群落结构有差异,大将山以棒束孢属Isaria、被孢霉属Mortierella和一分类地位未知属占优势,而贵阳森林公园以被孢霉属、隐球酵母属Cryptococcus、红菇属Russula、棒束孢属占优势,且两地菌际土中棒束孢属的丰度均显著高于其他土样。核心真菌组检测分析显示,内菌核的核心真菌组有10个OTUs,菌膜的核心真菌组有5个OTUs,菌际土的核心真菌组有20个OTUs,3种样本的核心真菌组的生态功能群均检测到有与植物相关的功能群,内菌核中检测到外生菌根真菌群,菌膜中检测到植物病原真菌群,菌际土中检测到丛枝菌根真菌群和植物病原菌群。     

Biological and mathematical description of the growth pattern of Fusarium oxysporum in a sterilized soil

Abstract The population dynamics of 4 F. oxysporum strains incubated in sterilized soil have been studied for 35 days. Enumeration of fungal propagules was carried out by the soil dilution plate technique. The qualitative variations of the populations were viewed by epifluorescent microscopy after staining the fungal propagules in soil with Calcofluor. A logistic model was used to describe population dynamic parameters. The predominant mode of growth of F. oxysporum in sterilized soil involved abundant production of conidia during the exponential phase. The increase of the propagules resulting from mycelial development during the lag phase was not taken into account by the logistic model. By determining the density of the population at the end of the lag phase, growth parameters of different F. oxysporum strains have been identified allowing the saprophytic competence of each strain to be characterized.     

西双版纳热带森林土壤种子库的季节变化

通过萌发实验法对西双版纳地区的一类热带季节雨林 (番龙眼、千果榄仁 )和 2类次生林(白背桐林、中平树林 )的土壤种子库的季节变化进行了探讨。结果表明 :该地区的土壤种子库动态具有明显的季节性。季节雨林的土壤种子库储量相对稳定 ,土壤上层 ( 0～ 2 cm )的种子储量在雨季末期较大。2类次生林土壤种子库的变化则相反 ,土壤种子库中的种子种类在旱季末期较雨季末期多 ,土壤上层的种子储量在旱季末期较大。各样地均有一些种类只出现在旱季末期或雨季末期。种子在土壤种子库的动态与植物的繁殖物候和所处的环境紧密相关 ,不同种类植物的土壤种子库由于植物本身的生物学特性、传播方式和所处环境的影响而表现出不同的动态模式     

The role of rock-phosphate-solubilizing fungi and vesicular–arbusular-mycorrhiza (VAM) in growth of wheat plants fertilized with rock phosphate

A total of 36 fungal species isolated from soil were tested for their ability to solubilize rock phosphate (RP) in agar plates. Most of these fungi were non-rock phosphate solubilizers, but two isolates, Aspergillus niger and Penicillium citrinum, had high activity. Liquid culture experiments revealed that both fungi caused a remarkable drop in pH of culture media and solubilized considerable amounts of phosphate. The effects on wheat of inoculation with vesicular–arbuscular mycorrhizal fungi and rock-phosphate-solubilizing fungi and fertilization with rock phosphate were studied in sterilized pot soils, nonsterilized pot trials and in field plot soils. Rock phosphate fertilization and inoculation with Glomus constrictum and rock-phosphate-solubilizing fungi (A. niger and P. citrinum) significantly increased dry matter yield of wheat plants under all experimental conditions. However, the effect was more evident in non- sterilized pot soils and in the field than in sterilized pots. Rock phosphate had no significant effect on the total phosphorus content of plants grown under pot conditions but it was significantly increased in field plots; the effect of inoculation with fungi (G. constrictum, A. niger and P. citrinum) on plant phosphorus was closely related to this in dry matter production. The greatest positive effect on growth and phosphorus contents of wheat plants was recorded in the treatments that received rock phosphate and were inoculated with a mixed inoculum of the three microorganisms used, followed by dual inoculation treatments of G. constrictum plus either A. niger or P. citrinum.     

Inhibition of growth,and effects on nutrient uptake of arctic graminoids by leaf extracts — allelopathy or resource competition between plants and microbes?

Previous research has shown that plant extracts, e.g. from boreal dwarf shrubs and trees, can cause reduced growth of neighbouring plants: an effect known as allelopathy. To examine whether arctic and subarctic plants could also be affected by leaching of phytochemicals, we added extracts from the commonly occurring arctic dwarf shrubs Cassiope tetragona and Empetrum hermaphroditum, and from mountain birch, Betula pubescens ssp. tortuosa to three graminoid species, Carex bigelowii, Festuca vivipara and Luzula arcuata, grown in previously sterilized or non-sterilized arctic soils. The graminoids in non-sterilized soil grew more slowly than those in sterilized soil. Excised roots of the plants in non-sterilized soil had higher uptake rate of labelled P than those in sterilized soil, demonstrating larger nutrient deficiency. The difference in growth rate was probably caused by higher nutrient availability for plants in soils in which the microbial biomass was killed after soil sterilization. The dwarf shrub extracts contained low amounts of inorganic N and P and medium high amounts of carbohydrates. Betula extracts contained somewhat higher levels of N and much higher levels of P and carbohydrates. Addition of leaf extracts to the strongly nutrient limited graminoids in non-sterilized soil tended to reduce growth, whereas in the less nutrient limited sterilized soil it caused strong growth decline. Furthermore, the N and P uptake by excised roots of plants grown in both types of soil was high if extracts from the dwarf shrubs (with low P and N concentrations) had been added, whereas the P uptake declined but the N uptake increased after addition of the P-rich Betula extract. In contrast to the adverse extract effects on plants, soil microbial respiration and soil fungal biomass (ergosterol) was generally stimulated, most strongly after addition of the Betula extract. Although we cannot exclude the possibility that the reduced plant growth and the concomitant stimulation of microbial activity were caused by phytochemicals, we believe that this was more likely due to labile carbon in the extracts which stimulated microbial biomass and activity. As a result microbial uptake increased, thereby depleting the plant available pool of N and P, or, for the P-rich Betula extract, depleting soil inorganic N alone, to the extent of reducing plant growth. This chain of events is supported by the negative correlation between plant growth and sugar content in the three added extracts, and the positive correlation between microbial activity, fungal biomass production and sugar content, and are known reactions when labile carbon is added to nutrient deficient soils.     

FUNGISTASIS IN SOILS

1. Fungistasis in soil is a widespread phenomenon affecting most fungal propagules, though some are insensitive. In most instances, it is coexistent with the presence of living microorganisms, and is annulled by energy-yielding nutrients. Fungistasis with characteristics similar to that in soil may also occur on leaves of plants. 2. Germination and growth of bacteria and actinomycetes is also restricted in soils. The characteristics of their inhibition appear to be the same as those for fungi. Therefore, the concept of a widespread microbial inhibition in soil can be applied to all three groups of microorganisms. 3. Fungistasis can be detected by various direct methods, or indirectly by methods involving the use of porous or permeable carriers. It may be expressed as a restriction on the final amount of germination (the usual parameter), germination rate (with time), and rate of germ-tube or hyphal growth. Since the expression of fungistasis is often complete in soil, titration with nutrients may be required to distinguish between the sensitivities of different fungi. 4. Fungistasis generally is expressed most strongly at soil moisture contents somewhat less than saturation. Its expression usually is maximal in neutral or slightly alkaline soils. In acidic conditions fungistasis may be lessened because of suppression of bacterial and actinomycete activity. Increased sensitivity of some fungi in soils of pH > 7.0 may be caused by a directly unfavourable effect of pH on the fungus. 5. Fungal species with small spores tend to be highly sensitive to fungistasis. These spores tend to germinate slowly and to require exogenous nutrients for germination. By contrast, species with larger spores and sclerotia often do not require exogenous nutrients for germination. The larger spores tend to germinate rapidly and to exhibit low sensitivity, as compared with small spores. A few nutrient-independent spores are insensitive to fungistasis. At least a part of the difference in sensitivity is related to germination time; spores which germinate slowly compete poorly with the soil micro-flora for their nutrients. 6. Fungistasis is often temporarily annulled by enriching the soil with energy-yielding nutrients. Usually, complex materials such as plant residues are most effective. A few weeks after such treatment, the level of fungistasis may, however, be increased. Annulment of fungistasis by compounds not utilized as energy sources has not yet been demonstrated. 7. Several soils naturally suppressive to Fusarium wilt diseases were more fungistatic to Fusarium than soils conducive to wilt. Potential means by which fungistasis may be manipulated to control root-infecting fungi are (a) through stimulation of germination with nutrients, thus exposing the germ tube to lysis, and (b) by increasing the fungistatic level of soil through appropriate amendments. 8. Volatile substances identified in soils, some of which are potentially inhibitory to fungi include (a) ammonia, which apparently is evolved from ammonium salts in some arid soils of high pH, (b) ethylene, which has been identified in some soils of pH < 7.0 (though high levels of this gas seem to be tolerated by most fungi), (c) allyl alcohol, and (d) other unidentified substances. Non-volatile inhibitors include high molecular weight substances revealed by molecular sieve chromatography of soil extracts. Microbial metabolites such as those present in staled fungal cultures also have been proposed to account for fungistasis. In a few soils fungistasis persists after sterilization because of the presence of inhibitory concentrations of calcium carbonate, iron or aluminium. Inherent in the proposition that inhibitory substances provide the primary mechanism of fungistasis is the concept of a highly complex phenomenon, involving various highly specific inhibitory and counteracting stimulatory substances, with the outcome for the fungus depending on the kinds and relative amounts of each present. 9. By the nutrient-deficiency hypothesis, the level of available nutrients in soil is insufficient to support germination of nutrient-dependent propagules, except in nutrient-rich microsites. Inhibition of nutrient-independent propagules is explained by loss of endogenous nutrients required for germination, through microbial nutrient competition. Evidence for this hypothesis is (a) the imposition of fungistasis on numerous nutrient-independent propagules during incubation on leaching model systems designed to simulate microbial nutrient competition in soil, (b) similar losses of endogenous nutrients occurring on soil and the leaching system, and (c) the fact that soils are chronically deficient in energy in relation to the microbial populations present, with the consequence that enforced inactivity is imposed upon most of the population at any given time for this reason alone, regardless of the presence or absence of fungistatic substances. Journal series article no. 7747 from the Michigan Agricultural Experiment Station.     

神农架国家公园林线过渡带土壤真菌多样性

林线过渡带是陆地生态系统对气候变化响应的敏感区域,研究林线过渡带土壤真菌的群落结构和形成机制,对于预测气候变化对土壤养分循环和维持陆地生态系统功能的影响具有重要意义。利用Illumina高通量测序技术分析了神农架国家公园林线上下的灌木林和针叶林的土壤真菌群落结构和多样性。结果表明,在真菌物种组成上,两种植被类型的土壤优势菌门、属和种类不同,针叶林和灌木林的优势菌门分别是担子菌门(Basidiomycota)和接合菌门(Zygomycota)。除趋势对应分析(DCA)和不相似性检验(Dissimilarity test)表明两种林型的土壤真菌群落结构组成存在显著差异,且针叶林土壤真菌Shannon指数、Chao值和Richness指数均显著(P0.05)高于灌木林。典范对应分析(CCA)和Mantel检验显示土壤真菌群落结构与土壤p H、植物多样性、土壤温度和土壤湿度存在显著相关性。因此,林线过渡带上下的土壤真菌群落结构和多样性存在显著差异,土壤p H、植物多样性、土壤湿度和土壤温度可能是影响土壤真菌群落结构的重要因素。     

Microbial community composition affects soil fungistasis

Most soils inhibit fungal germination and growth to a certain extent, a phenomenon known as soil fungistasis. Previous observations have implicated microorganisms as the causal agents of fungistasis, with their action mediated either by available carbon limitation (nutrient deprivation hypothesis) or production of antifungal compounds (antibiosis hypothesis). To obtain evidence for either of these hypotheses, we measured soil respiration and microbial numbers (as indicators of nutrient stress) and bacterial community composition (as an indicator of potential differences in the composition of antifungal components) during the development of fungistasis. This was done for two fungistatic dune soils in which fungistasis was initially fully or partly relieved by partial sterilization treatment or nutrient addition. Fungistasis development was measured as restriction of the ability of the fungi Chaetomium globosum, Fusarium culmorum, Fusarium oxysporum, and Trichoderma harzianum to colonize soils. Fungistasis did not always reappear after soil treatments despite intense competition for carbon, suggesting that microbial community composition is important in the development of fungistasis. Both microbial community analysis and in vitro antagonism tests indicated that the presence of pseudomonads might be essential for the development of fungistasis. Overall, the results lend support to the antibiosis hypothesis.     

Microbial Community Composition Affects Soil Fungistasis

Most soils inhibit fungal germination and growth to a certain extent, a phenomenon known as soil fungistasis. Previous observations have implicated microorganisms as the causal agents of fungistasis, with their action mediated either by available carbon limitation (nutrient deprivation hypothesis) or production of antifungal compounds (antibiosis hypothesis). To obtain evidence for either of these hypotheses, we measured soil respiration and microbial numbers (as indicators of nutrient stress) and bacterial community composition (as an indicator of potential differences in the composition of antifungal components) during the development of fungistasis. This was done for two fungistatic dune soils in which fungistasis was initially fully or partly relieved by partial sterilization treatment or nutrient addition. Fungistasis development was measured as restriction of the ability of the fungi Chaetomium globosum, Fusarium culmorum, Fusarium oxysporum, and Trichoderma harzianum to colonize soils. Fungistasis did not always reappear after soil treatments despite intense competition for carbon, suggesting that microbial community composition is important in the development of fungistasis. Both microbial community analysis and in vitro antagonism tests indicated that the presence of pseudomonads might be essential for the development of fungistasis. Overall, the results lend support to the antibiosis hypothesis.     

Stress tolerance of soil fungal communities from native Atlantic forests,reforestations, and a sand mining degraded area

Microorganisms are essential to the functionality of the soil, particularly in organic matter decomposition and nutrient cycling, which regulate plant productivity and shape the soil structure. However, biotic and abiotic stresses greatly disrupt soil fungal communities and, thereby, disturb the ecosystem. This study quantified seasonal tolerances to UV-B radiation and heat of fungal communities, which could be cultured, found in soil from two native Atlantic forest fragments called F1 and F2, five reforested areas (RA) planted in 1994, 1997, 2004, 2007, and 2009 with native species of the Atlantic forest, and one sand mining degraded soil (SMDS). The cold activity of the soil fungal communities (FC) from the eight different areas was also studied. Higher tolerance to UV-B radiation and heat was found in the FC from the SMDS and the 2009RA, where the incidence of heat and UV radiation from sun was more intense, which caused selection for fungal taxa that were more UV-B and heat tolerant in those areas. Conversely, the FC from the native forests and older reforested sites were very susceptible to heat and UV-B radiation. The cold activity of the soil FC from different areas of the study showed an erratic pattern of responses among the sampling sites. Little difference in tolerance to UV-B radiation and heat was found among the FC of soil samples collected in different seasons; in general soil FC collected in winter were less tolerant to UV-B radiation, but not for heat. In conclusion, FC from SMDS soil that receive intense heat and UV radiation, as well as with low nutrient availability, were more tolerant to both UV-B radiation and heat.     

The role of rock-phosphate-solubilizing fungi and vesicular–arbusular-mycorrhiza (VAM) in growth of wheat plants fertilized with rock phosphate

A total of 36 fungal species isolated from soil were tested for their ability to solubilize rock phosphate (RP) in agar plates. Most of these fungi were non-rock phosphate solubilizers, but two isolates, Aspergillus niger and Penicillium citrinum, had high activity. Liquid culture experiments revealed that both fungi caused a remarkable drop in pH of culture media and solubilized considerable amounts of phosphate. The effects on wheat of inoculation with vesicular–arbuscular mycorrhizal fungi and rock-phosphate-solubilizing fungi and fertilization with rock phosphate were studied in sterilized pot soils, nonsterilized pot trials and in field plot soils. Rock phosphate fertilization and inoculation with Glomus constrictum and rock-phosphate-solubilizing fungi (A. niger and P. citrinum) significantly increased dry matter yield of wheat plants under all experimental conditions. However, the effect was more evident in non- sterilized pot soils and in the field than in sterilized pots. Rock phosphate had no significant effect on the total phosphorus content of plants grown under pot conditions but it was significantly increased in field plots; the effect of inoculation with fungi (G. constrictum, A. niger and P. citrinum) on plant phosphorus was closely related to this in dry matter production. The greatest positive effect on growth and phosphorus contents of wheat plants was recorded in the treatments that received rock phosphate and were inoculated with a mixed inoculum of the three microorganisms used, followed by dual inoculation treatments of G. constrictum plus either A. niger or P. citrinum.     

Sugar for my honey: carbohydrate partitioning in ectomycorrhizal symbiosis

Simple, readily utilizable carbohydrates, necessary for growth and maintenance of large numbers of microbes are rare in forest soils. Among other types of mutualistic interactions, the formation of ectomycorrhizas, a symbiosis between tree roots and certain soil fungi, is a way to overcome nutrient and carbohydrate limitations typical for many forest ecosystems. Ectomycorrhiza formation is typical for trees in boreal and temperate forests of the northern hemisphere and alpine regions world-wide. The main function of this symbiosis is the exchange of fungus-derived nutrients for plant-derived carbohydrates, enabling the colonization of mineral nutrient-poor environments. In ectomycorrhizal symbiosis up to 1/3 of plant photoassimilates could be transferred toward the fungal partner. The creation of such a strong sink is directly related to the efficiency of fungal hexose uptake at the plant/fungus interface, a modulated fungal carbohydrate metabolism in the ectomycorrhiza, and the export of carbohydrates towards soil growing hyphae. However, not only the fungus but also the plant partner increase its expression of hexose importer genes at the plant/fungus interface. This increase in hexose uptake capacity of plant roots in combination with an increase in photosynthesis may explain how the plant deals with the growing fungal carbohydrate demand in symbiosis and how it can restrict this loss of carbohydrates under certain conditions to avoid fungal parasitism.     

Mycorrhiza of plants in different vegetation types in tropical ecosystems of Xishuangbanna,southwest China

We examined plants growing in four tropical vegetation types (primary forest, secondary forest, limestone forest and a slash and burn field) in Xishuangbanna, southwest China for mycorrhizal associations. Of the 103 plant species examined (belonging to 47 families), 81 had arbuscular mycorrhizal (AM) associations, while three species possessed orchid mycorrhiza. AM colonization levels ranged between 6% and 91% and spore numbers ranged between 1.36 spores and 25.71 spores per 10 g soil. Mean AM colonization level was higher in primary and secondary forest species than in plant species from limestone forests and a slash and burn field. In contrast, mean AM fungal spore numbers of the primary and limestone forest were lower than in the secondary forest or the slash and burn field. AM fungal spores belonging to Glomus and Acaulospora were the most frequent in soils of Xishuangbanna. AM fungal colonization and spore numbers were significantly correlated to each other and were significantly influenced by vegetation type.     

Volatile-mediated antagonism of soil bacterial communities against fungi

Competition is a major type of interaction between fungi and bacteria in soil and is also an important factor in suppression of plant diseases caused by soil-borne fungal pathogens. There is increasing attention for the possible role of volatiles in competitive interactions between bacteria and fungi. However, knowledge on the actual role of bacterial volatiles in interactions with fungi within soil microbial communities is lacking. Here, we examined colonization of sterile agricultural soils by fungi and bacteria from non-sterile soil inoculums during exposure to volatiles emitted by soil-derived bacterial communities. We found that colonization of soil by fungi was negatively affected by exposure to volatiles emitted by bacterial communities whereas that of bacteria was barely changed. Furthermore, there were strong effects of bacterial community volatiles on the assembly of fungal soil colonizers. Identification of volatile composition produced by bacterial communities revealed several compounds with known fungistatic activity. Our results are the first to reveal a collective volatile-mediated antagonism of soil bacteria against fungi. Given the better exploration abilities of filamentous fungi in unsaturated soils, this may be an important strategy for bacteria to defend occupied nutrient patches against invading fungi. Another implication of our research is that bacterial volatiles in soil atmospheres can have a major contribution to soil fungistasis.     

Colonization-competition tradeoffs as a mechanism driving successional dynamics in ectomycorrhizal fungal communities

Colonization-competition tradeoffs have been shown to be important determinants of succession in plant and animal communities, but their role in ectomycorrhizal (ECM) fungal communities is not well understood. To experimentally examine whether strong spore-based competitors remain dominant on plant root tips as competition shifts to mycelial-based interactions, we investigated the mycelial competitive interactions among three naturally co-occurring ECM species (Rhizopogon occidentalis, R. salebrosus, and Suillus pungens). Each species was grown alone and in all pair-wise combinations on P. muricata seedlings in experimental microcosms and culture assays. Competitive outcomes were assessed from ECM root tip colonization, soil mycelial abundance, and mycelial growth in culture. In the microcosm experiment, we observed a clear competitive hierarchy of R. salebrosus>R. occidentalis>S. pungens. Competitive effects were also apparent in the culture assays, however, no similar hierarchy was present. These results contrast with our previous findings from spore-based competition, suggesting that ECM competitive outcomes can be life-stage dependent. The differing competitive abilities observed here also showed general correspondence with patterns of ECM succession in Pinus muricata forests, indicating that competitive interactions may significantly influence temporal patterns of ECM community structure.