Ectomycorrhiza of Kobresia myosuroides at a primary successional glacier forefront

The bog sedge Kobresia myosuroides is among the first ectomycorrhizal (EM) plants forming dense pads on receding glacier forefronts of the Austrian Alps. This is the only Cyperaceae species known to form EM. To date, little is known about fungal species involved in these EM associations. Therefore, the main aim of this study was to detect EM fungal communities of K. myosuroides (1) by describing mycorrhizal morphotypes (MT) and (2) by identifying the mycobionts by rDNA internal transcribed spacer (ITS) sequencing. Furthermore, seasonal dynamics of Kobresia mycobionts were investigated. Sampling was performed in all four seasons (also under snow cover) during the years 2005 and 2006 at the Rotmoos glacier forefront, a well-characterized alpine primary successional habitat in the Austrian alps (2,300 m above sea level). The degree of EM infection of K. myosuroides roots was high (95%). Ten MTs were described and sequences of 18 fungal taxa were obtained. This was the highest mycobiont diversity ever reported for this plant. Cenococcum geophilum was the most abundant mycobiont (37-46%) and shared dominancy with Sebacina incrustans (16-44%) and Tomentella spp. (7-37%). Tomentella (including Thelephora) was the most species-rich mycobiont genus with five taxa, followed by Cortinarius, Inocybe, and Sebacina with two taxa each and one Hebeloma species. Other ascomycete mycobionts beside C. geophilum were Helvella sp., Lecythophora sp., and one Pezizales species. Due to high interannual differences in the EM fungal community, no significant seasonal changes could be detected. The importance of fungal mycobionts in alpine habitats is discussed.     

<Emphasis Type="Italic">Polygonum viviparum</Emphasis> mycobionts on an alpine primary successional glacier forefront

Polygonum viviparum is one of the first ectomycorrhizal (EM) plant species colonising primary successional sites at the Rotmoos glacier forefront (Tyrolean Alps, Austria). On a site with soil development of about 150 years (2,400 m above sea level), mycobionts of P. viviparum were identified by morphotyping and fungal ribosomal deoxyribonucleic acid internal transcribed spacer sequencing. For studying seasonal dynamics and spatial heterogeneity, ectomycorrhizae were sampled on five plots during all seasons. P. viviparum root tips were always EM. In total, 18 mycobiont taxa of the following genera were identified: Cenococcum (1), Cortinarius (2), Helvella (1), Inocybe (3), Russula (1), Sebacina (2), Thelephora (2) and Tomentella (6). All were non-specific EM partners of EM plants. As early as 2 weeks after spring snow melt, EM were well developed, vital and showed high mycobiont diversity. The relative abundance of senescent root tips was lowest in spring and increased throughout the year, with a maximum in winter (frozen soil). Thus, mycobiont growth and physiological activity obviously start when soil is still under snow cover: We speculate that water availability is one important initiation factor for mycorrhizal development under snow cover, when temperatures still range around the freezing point. Irrespectively of the season, most abundant mycobionts at this primary successional site belonged to the genera Tomentella, Sebacina and Cenococcum, also in frozen soil. Spatial heterogeneity was high when considering species composition and diversity indices. Overall mycobionts species richness was restricted at this site, probably because of the limited availability of fungal partners. We regard the presence/absence of fungal partner and limiting abiotic impacts of the environment as key factors for the symbiotic status of P. viviparum. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

<Emphasis Type="Italic">Piriformospora indica</Emphasis> and <Emphasis Type="Italic">Sebacina vermifera</Emphasis> increase growth performance at the expense of herbivore resistance in <Emphasis Type="Italic">Nicotiana attenuata</Emphasis>

A Sebacinales species was recovered from a clone library made from a pooled rhizosphere sample of Nicotiana attenuata plants from 14 native populations. Axenic cultures of the related species, Piriformospora indica and Sebacina vermifera, were used to examine their effects on plant performance. Inoculation of N. attenuata seeds with either fungus species stimulated seed germination and increased growth and stalk elongation. S. vermifera inoculated plants flowered earlier, produced more flowers and matured more seed capsules than did non-inoculated plants. Jasmonate treatment during rosette-stage growth, which slows growth and elicits herbivore resistance traits, erased differences in vegetative, but not reproductive performance resulting from S. vermifera inoculation. Total nitrogen and phosphorous contents did not differ between inoculated and control plants, suggesting that the performance benefits of fungal inoculation did not result from improvements in nutritional status. Since the expression of trypsin proteinase inhibitors (TPI), defensive proteins which confer resistance to attack from Manduca sexta larvae, incur significant growth and fitness costs for the plant, we examined the effect of S. vermifera inoculation on herbivore resistance and TPI activity. After 10 days of feeding on S. vermifera-inoculated plants, larval mass was 46% higher and TPI activity was 48% lower than that on non-inoculated plants. These results suggest that Sebacina spp. may interfere with defense signaling and allow plants to increase growth rates at the expense of herbivore resistance mediated by TPIs.     

Species richness and community composition of mat-forming ectomycorrhizal fungi in old- and second-growth Douglas-fir forests of the HJ Andrews Experimental Forest,Oregon, USA

We investigated the species identity of mat-forming ectomycorrhizal (EM) fungi associated with old- and second-growth Douglas-fir stands. Using molecular analyses of rhizomorphs and EM root tips, we characterized 28 unique internal transcribed spacer sequences and considered them proxies for mat-forming EM species. In both stand age classes, one Athelioid species in the genus Piloderma dominated our sample of the mat-forming fungal community. In second-growth stands, the second most frequently encountered mat-forming EM species belonged to the genus Hysterangium. In old-growth stands, several Ramaria species were associated with a frequently encountered mat morphology but no species dominated the community. After using rarefaction analysis to standardize sampling effort, the total species richness did not differ statistically between old- and second-growth habitats. Both an abundance of infrequently encountered species and incomplete sampling of the mat-forming EM community may have limited our ability to detect potential differences in species richness. Several frequently encountered Piloderma species appear to have broad (holarctic) distributions and diverse host associations and their potential importance in forest ecosystems warrants further study.     

Host preferences and differential contributions of deciduous tree species shape mycorrhizal species richness in a mixed Central European forest

Mycorrhizal species richness and host ranges were investigated in mixed deciduous stands composed of Fagus sylvatica, Tilia spp., Carpinus betulus, Acer spp., and Fraxinus excelsior. Acer and Fraxinus were colonized by arbuscular mycorrhizas and contributed 5% to total stand mycorrhizal fungal species richness. Tilia hosted similar and Carpinus half the number of ectomycorrhizal (EM) fungal taxa compared with Fagus (75 putative taxa). The relative abundance of the host tree the EM fungal richness decreased in the order Fagus > Tilia >> Carpinus. After correction for similar sampling intensities, EM fungal species richness of Carpinus was still about 30–40% lower than that of Fagus and Tilia. About 10% of the mycorrhizal species were shared among the EM forming trees; 29% were associated with two host tree species and 61% with only one of the hosts. The latter group consisted mainly of rare EM fungal species colonizing about 20% of the root tips and included known specialists but also putative non-host associations such as conifer or shrub mycorrhizas. Our data indicate that EM fungal species richness was associated with tree identity and suggest that Fagus secures EM fungal diversity in an ecosystem since it shared more common EM fungi with Tilia and Carpinus than the latter two among each other.     

Changes in species richness and composition in European acidic grasslands over the past 70 years: the contribution of cumulative atmospheric nitrogen deposition

Our study investigates the negative impact of nitrogen (N) deposition on species richness in acidic grasslands, based on a temporal comparison of vegetation data spanning a period of almost 70 years. We compiled a large data base of plots assigned to the Violion caninae grassland type, composed of managed, but unfertilized semi-natural grasslands on nutrient-poor, acidic soils. In total 1114 plots, mainly from Great Britain, the Netherlands and Germany, were compiled, dating back to 1939. Environmental site information included geographical and soil (mean Ellenberg values) variables as well as estimates of cumulative N and sulphur (S) deposition since 1939. Statistical analyses were carried out separately for the data subsets from the three regions. In all regions, the vegetation differentiation was mainly related to soil acidity and nutrient availability, as well as to the year of sampling and the cumulative amounts of N and S deposition. Plot-species richness of vascular plants and bryophytes (analysed for Great Britain only) decreased with time and analyses suggest these are affected by various factors, notably soil pH, but also latitude and cumulative N deposition. The latter explained more of the variation in species number than the year of sampling and cumulative S deposition, which supports the interpretation that the decline in species richness is mainly caused by increasing N availability and less by altered management and soil acidification. For Great Britain and Germany, cumulative N deposition showed a strong negative relationship with several biodiversity measures, especially the proportion of dicots, whereas it was positively related to the proportion of grass species. In general, our results give temporal evidence for the negative effect of N deposition on species richness in semi-natural vegetation.     

Host plant richness explains diversity of ectomycorrhizal fungi: Response to the comment of Tedersoo et al. (2014)

Exploring the relationships between the biodiversity of groups of interacting organisms yields insight into ecosystem stability and function (Hooper et al. 2000 ; Wardle 2006 ). We demonstrated positive relationships between host plant richness and ectomycorrhizal (EM) fungal diversity both in a field study in subtropical China (Gutianshan) and in a meta‐analysis of temperate and tropical studies (Gao et al. 2013 ). However, based on re‐evaluation of our data sets, Tedersoo et al. ( 2014 ) argue that the observed positive correlation between EM fungal richness and EM plant richness at Gutianshan and also in our metastudies was based mainly from (i) a sampling design with inconsistent species pool and (ii) poor data compilation for the meta‐analysis. Accordingly, we checked our data sets and repeated the analysis performed by Tedersoo et al. ( 2014 ). In contrast to Tedersoo et al. ( 2014 ), our re‐analysis still confirms a positive effect of plant richness on EM fungal diversity in Gutianshan, temperate and tropical ecosystems, respectively.     

Habitat Invasibility and Dominance by Alien Annual Plants in the Western Mojave Desert

Patterns of habitat invasibility and alien dominance, respectively measured as species richness and biomass of alien annual plants, were evaluated in association with four habitat factors at the Desert Tortoise Research Natural Area (DTNA) in the western Mojave Desert, USA. Habitat factors varied in levels of disturbance outside (high) and inside (low) the DTNA, and in levels of soil nutrients in washlet (high) and hummock (low) topographic positions, in Larrea-north (high), Larrea-south (medium), and interspace (low) microhabitats near creosote bushes (Larrea tridentata), and during 1995 when rainfall was 207% (high) and 1994 when rainfall was 52% (low) of the long-term average. Dominant alien plants included the annual grasses Bromus rubens, Bromus trinii, and Schismus spp., and the forb Erodium cicutarium. Species richness and dominance of alien annual plants were slightly higher where disturbance was high, and much higher where soil nutrients were high. B. rubens and B. trinii were most dominant in washlets and in the Larrea-north microhabitats during both years. These two species evolved in mesic ecosystems, and appeared to be particularly limited by soil nutrients at this site. Schismus spp. and E. cicutarium were also most dominant in washlets, but their dominance varied between interspaces in 1994 and the Larrea-south microhabitat in 1995. Monitoring to detect the invasion of new annual plants should focus on regions of high rainfall and nitrogen deposition and on washes and beneath-canopy microhabitats. The ecological range of each alien species should be evaluated separately, because their evolutionary origins may greatly affect their patterns of invasion and dominance in the Mojave Desert. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fungal colonization of shrub willow roots at the forefront of a receding glacier

Shrub willows (Salix spp.) form associations with arbuscular mycorrhizal (AM), ectomycorrhizal (EM) and dark septate endophytic (DSE) fungi. Willow root colonization by these three types of fungi was studied on a deglaciated forefront of Lyman Glacier, Washington, USA. Root colonization was low; less than 1% of the root length was colonized by AM and 25.6% by DSE. EM colonized 25% of the root tips and 19.4% of the root length. AM and DSE colonization were not related to distance from the present glacier terminus or to canopy cover. EM colonization increased with distance from the glacier terminus based on gridline intercept data but not on root tip frequency data. Availability of propagules in the substrate was low, but numbers of propagules increased with distance from the glacier terminus. The EM communities were dominated by three ascomycetes showing affinity to Sordariaceae in BLAST analyses. Other frequent taxa on the glacier forefront included species of Cortinariaceae, Pezizaceae, Russulaceae, Thelephoraceae and Tricholomataceae. When occurrence of individual taxa was used as a response variable to canopy cover, distance from the glacier terminus, and their interaction, four different fungal guilds were identified: 1) fungi that did not respond to these environmental variables; 2) fungi that occurred mainly in intercanopy areas and decreased with distance from the glacier terminus; 3) fungi that were insensitive to canopy cover but increased with distance from the glacier terminus; 4) fungi that occurred mainly under willow canopies and increased with distance from the glacier terminus. We suggest that fungal colonization is mainly limited by fungal propagule availability. Environmental conditions may also limit successful establishment of plant-fungus associations. We propose that the four EM guilds partly explain successional dynamics. The initial EM community comprises fungi that tolerate low organic matter and nitrogen environment (first and second guilds above). During later community development, these fungi are replaced by those that benefit from an increased organic matter and nitrogen environment (third and fourth guilds above).     

Wild bee community change over a 26‐year chronosequence of restored tallgrass prairie

Restoration efforts often focus on plants, but additionally require the establishment and long‐term persistence of diverse groups of nontarget organisms, such as bees, for important ecosystem functions and meeting restoration goals. We investigated long‐term patterns in the response of bees to habitat restoration by sampling bee communities along a 26‐year chronosequence of restored tallgrass prairie in north‐central Illinois, U.S.A. Specifically, we examined how bee communities changed over time since restoration in terms of (1) abundance and richness, (2) community composition, and (3) the two components of beta diversity, one‐to‐one species replacement, and changes in species richness. Bee abundance and raw richness increased with restoration age from the low level of the pre‐restoration (agricultural) sites to the target level of the remnant prairie within the first 2–3 years after restoration, and these high levels were maintained throughout the entire restoration chronosequence. Bee community composition of the youngest restored sites differed from that of prairie remnants, but 5–7 years post‐restoration the community composition of restored prairie converged with that of remnants. Landscape context, particularly nearby wooded land, was found to affect abundance, rarefied richness, and community composition. Partitioning overall beta diversity between sites into species replacement and richness effects revealed that the main driver of community change over time was the gradual accumulation of species, rather than one‐to‐one species replacement. At the spatial and temporal scales we studied, we conclude that prairie restoration efforts targeting plants also successfully restore bee communities.     

The Rengen Grassland Experiment: Effect of Soil Chemical Properties on Biomass Production, Plant Species Composition and Species Richness

The Rengen Grassland Experiment (RGE), set up on a Nardus grassland in 1941, consists of a control and five fertilizer treatments (Ca, CaN, CaNP, CaNP-KCl and CaNP-K₂SO₄). In 2005, soil chemical properties were analyzed to investigate the effect of soil variables on biomass production, plant species composition and species richness of vascular plants. Further, the effect of sampling scale (from 0.02 to 5.76 m²) on species richness was investigated. Soil properties (plant-available contents of K, P, C:N ratio, and pH) and biomass production were found to be strictly dependent on the fertilizers applied. Diversification of soil P content between treatments with and without P application is still in progress. Biomass production was most positively affected by P and K soil contents under N application. Furthermore, pH had a small positive effect on biomass production, and C:N ratio a moderately negative one. Two types of nutrient limitation were recognized: (1) limitation of total biomass production and (2) limitation of individual plant species. Long-term addition of a limiting nutrient affected the grassland ecosystem in three ways: (1) causing a change in plant species composition without significant increase in total biomass production, (2) causing no change in species composition but with significant increase in total biomass production, and (3) causing substantial change in plant species composition accompanied by significant increase in total biomass production. The explanatory power of all measured soil properties on plant species composition was almost the same as the power of the treatment effect (61.7% versus 62% of explained variability in RDA). The most powerful predictors of plant species composition were soil P, K and Mg contents, pH, and biomass production. The soil P content and biomass production were the only variables leading to a significant negative effect on species richness. An almost parallel increase in species richness with increasing sampling area was detected in all treatments. Constant differences among treatments were independent of sampling area.     

Promiscuous arbuscular mycorrhizal symbiosis of yam (Dioscorea spp.), a key staple crop in West Africa

Yam (Dioscorea spp.) is a tuberous staple food crop of major importance in the sub-Saharan savannas of West Africa. Optimal yields commonly are obtained only in the first year following slash-and-burn in the shifting cultivation systems. It appears that the yield decline in subsequent years is not merely caused by soil nutrient depletion but might be due to a loss of the beneficial soil microflora, including arbuscular mycorrhizal fungi (AMF), associated with tropical “tree-aspect” savannas and dry forests that are the natural habitats of the wild relatives of yam. Our objective was to study the AMF communities of natural savannas and adjacent yam fields in the Southern Guinea savanna of Benin. AMF were identified by morphotyping spores in the soil from the field sites and in AMF trap cultures with Sorghum bicolor and yam (Dioscorea rotundata and Dioscorea cayenensis) as bait plants. AMF species richness was higher in the savanna than in the yam-field soils (18–25 vs. 11–16 spp.), but similar for both ecosystems (29–36 spp.) according to the observations in trap cultures. Inoculation of trap cultures with soil sampled during the dry season led to high AMF root colonization, spore production, and species richness (overall 45 spp.) whereas inoculation with wet-season soil was inefficient (two spp. only). The use of D. cayenensis and D. rotundata as baits yielded 28 and 29 AMF species, respectively, and S. bicolor 37 species. AMF root colonization, however, was higher in yam than in sorghum (70–95 vs. 11–20%). After 8 months of trap culturing, the mycorrhizal yam had a higher tuber biomass than the nonmycorrhizal controls. The AMF actually colonizing D. rotundata roots in the field were also studied using a novel field sampling procedure for molecular analyses. Multiple phylotaxa were detected that corresponded with the spore morphotypes observed. It is, therefore, likely that the legacy of indigenous AMF from the natural savanna plays a crucial role for yam productivity, particularly in the low-input traditional farming systems prevailing in West Africa.     

The mid-domain effect in ectomycorrhizal fungi: range overlap along an elevation gradient on Mount Fuji,Japan

Mid-domain effect (MDE) models predict that the random placement of species'' ranges within a bounded geographical area leads to increased range overlap and species richness in the center of the bounded area. These models are frequently applied to study species-richness patterns of macroorganisms, but the MDE in relation to microorganisms is poorly understood. In this study, we examined the characteristics of the MDE in richness patterns of ectomycorrhizal (EM) fungi, an ecologically important group of soil symbionts. We conducted intensive soil sampling to investigate overlap among species ranges and the applicability of the MDE to EM fungi in four temperate forest stands along an elevation gradient on Mount Fuji, Japan. Molecular analyses using direct sequencing revealed 302 EM fungal species. Of 73 EM fungal species found in multiple stands, 72 inhabited a continuous range along the elevation gradient. The maximum overlap in species range and the highest species richness occurred at elevations in the middle of the gradient. The observed richness pattern also fit within the 95% confidence interval of the mid-domain null model, supporting the role of the MDE in EM fungal richness. Deviation in observed richness from the mean of the mid-domain null estimation was negatively correlated with some environmental factors, including precipitation and soil C/N, indicating that unexplained richness patterns could be driven by these environmental factors. Our results clearly support the existence of microbial species'' ranges along environmental gradients and the potential applicability of the MDE to better understand microbial diversity patterns.     

三峡水库初次蓄水后干流库区枝角类的空间分布与季节变化

为了阐明三峡水库初次蓄水后干流库区枝角类的时空分布规律, 2004年4月至2005年1月, 在600余公里干流库区设置10个样点, 定性和定量采集枝角类标本。本次调查共采到9种枝角类, 其中春季8种, 夏季5种, 秋季2种, 冬季3种。枝角类种类组成的空间分布差异明显, 河流状态的江段有4种, 水库状态的江段有7种, 水库状态的江段距大坝越近, 枝角类种类越丰富。枝角类的密度和生物量的空间分布和季节变化规律一致, 季节间差异极显著(P<0.01), 春季最高, 夏季次之, 秋季和冬季较低; 空间分布上表现为在干流库区的纵向分布上差异极显著(P<0.01), 河流状态样点远低于水库状态的样点, 水库上游江段又低于下游坝前段。结果显示三峡水库的枝角类具有明显的纵向分布和季节变化特征。     

龙脑香科植物对丛枝菌根真菌的影响

在天然林地和温室盆栽条件下,比较研究了龙脑香科植物对丛枝菌根(Arbuscular mycorrhizas,AM)真菌孢子密度、相对多度、频度、属的组成、丰度和侵染状况等方面的影响.结果表明,用坡垒作盆栽寄主加富培养后,菌根侵染率、泡囊、丛枝和侵入点都低于原采样植物,以原坡垒土壤中栽植苗木的侵染率为最高,可达20.3%;而以望天树根围土壤栽植的苗木为最低,仅为10.6%;坡垒还不同程度地改变了原采样植物根围土壤中AM真菌孢子的密度、相对多度、频度、属的组成、丰度等.在4种土壤中,栽植坡垒苗木后,AM真菌的孢子密度都有不同程度的增长.采用与原采样相同种类的植物作为AM真菌加富培养的寄主更有利于促进AM真菌的生长发育、保持AM的多样性.     

Enteric bacteria isolated from acute diarrheal patients in the Republic of Korea between the year 2004 and 2006

In an epidemiological survey of human enterobacterial infections in the Republic of Korea during three years from 2004 to 2006, we isolated 1,784 (6.2%, isolation rate of enteropathogens from stool samples) in 2004, 2,547 (9.5%) in 2005 and 3,506 bacteria (12.3%) from people who visited clinics. Among the isolated bacteria, pathogenic Escherichia coli, especially, EAEC was the most frequently identified pathogen in both urban and rural regions followed by Staphylococcus aureus, Salmonella species, Bacillus cereus, Vibrio parahaemolyticus, Campylobacter jejuni, Clostridium perfringens, and Shigella species. Distinct seasonality was found in V. parahaemolyticus species, while this pathogen showed no age-specific patterns. However, other bacteria, i.e., pathogenic E. coli, S. aureus, Salmonella spp., and B. cereus showed similar seasonality throughout the year, showing a slight increase in the infection rate during the summer months and high prevalence among children under 10 years of age and elder-age people. The antibiotic susceptibility patterns of pathogenic E. coli, Salmonella spp., and S. aureus showed high resistance to penicillins. However, both pathogenic E. coli and Salmonella spp. were susceptible to several cephems, imipenem, and amikacin. Moreover, S. aureus strains resistant to vancomycin were not found. In conclusion, these surveillances can play an important role for the control and prevention to the diseases originated by enteritis bacteria.     

Ecosystem development in short‐term postglacial chronosequences: N and P limitation in glacier forelands from Santa Inés Island,Magellan Strait

Glacier foreland moraines provide an ideal model to examine the patterns of ecosystem development and the evolution of nitrogen and phosphorous limitation over successional time. In this paper, we focus on a 400‐year soil chronosequence in the glacier forelands of Santa Inés Island in the Magellan Strait, southern Chile by examining forest development on phosphorus (P)‐poor substrates in a uniquely unpolluted region of the world. Results show a steady increase in tree basal area and a humped trend in tree species richness over four centuries of stand development. The increase in basal area suggests that the late successional tree species were more efficient nutrient users than earlier successional ones. Total contents of carbon (C) and nitrogen (N) in soils increased during the chronosequence, reaching an asymptote in late succession. The net increases in soil C : N, C : P and N : P ratios observed over successional time suggest that nutrient limitation is maximal in 400‐year‐old substrates. Foliar C : N and C : P ratios also increased over time to reach an asymptote in old‐growth stages, following soil stoichiometric relationships; however the foliar N‐to‐P ratio remained constant throughout the chronosequence. Biological N fixation was greater in early postglacial succession, associated with the presence of the symbiotic N‐fixer Gunnera magellanica. Declining trends of δ¹⁵N in surface soils through the 400‐year chronosequence are evidence of decreasing N losses in old‐growth forests. In synthesis, glacier foreland chronosequences at this high South American latitude provide evidence for increasing efficiency of N and P use in the ecosystem, with the replacement of shade‐intolerant pioneers by more efficient, shade‐tolerant tree species. This pattern of ecosystem development produces a constant foliar N : P ratio, regardless of variation in soil N‐to‐P ratio over four centuries.     

Strong differences in Quercus robur-associated ectomycorrhizal fungal communities along a forest-city soil sealing gradient

Ectomycorrhizal fungi (EM) that associate with tree roots in a symbiotic relationship may be crucial in mediating tree health in urban environments, but research on the effects of urbanization on EM communities is very limited so far. Here, we compared EM communities of adult pedunculate oaks (Quercus robur) between urban and forest environments, and assessed the effect of soil sealing around the trees on their EM community composition and EM diversity. We sampled 32 oak individuals across 4 sampling classes (Street, Lane, Park and Forest), and we characterized their EM communities using 454 amplicon pyrosequencing. The EM communities were not nested but they were significantly different between all sampling classes, with a very strong community differentiation between forest and urban trees. There were indications that EM richness declined with increasing sealed soil surface, with a significant effect of sampling class on estimated EM richness and diversity. We also identified indicator EM of the different sampling classes. The most important soil factor affecting EM community composition was pH, followed by plant available phosphorus, total nitrogen content and organic matter. Our results may have important implications when developing EM inocula for managing tree health in urban environments.     

Mite (Acari; Arachnida) diversity of two native plants in fragments of a semideciduous seasonal forest in Brazil

Studies to determine mite species richness in natural environments are still scarce, and have been conducted mainly in tropical ecosystems. The aim of this study was to determine the species richness of mites on two common native plants in fragments of the semideciduous seasonal forest in the Northwest of São Paulo State, Brazil. In each of eight fragments, 10 specimens of Actinostemon communis (Euphorbiaceae) and 10 of Trichilia casaretti (Meliaceae) were selected and marked. In total, 124 species of mites belonging to 21 families were found on the two plants. Tarsonemidae had the highest diversity (34 species), followed by Phytoseiidae (31), Tetranychidae (9) and Tenuipalpidae (8). Species accumulation curves for the two sampled plants did not reach an asymptote, even with the large sampling effort. Hence, it is estimated that a greater sampling effort may lead to an increase in species richness compared with what was found in this study. The richness of this mite fauna suggests that preservation of these plant species is important to maintain the mite diversity in these forest fragments.     

Fungal occurrence,disease incidence and severity,and yield of maize symptomatic for seedling disease in Mississippi

A study was conducted in Mississippi from 1995 to 1997 comparing soil rhizosphere fungi isolated from Pioneer 3167 hybrid maize (Zea mays L.) planted on Brooksville silty clay and Memphis silt loam soils. Maize seedlings were collected over four sampling dates from conventional and no-tillage plots. Eleven fungal genera consisting of nineteen species were isolated from these plants; Trichoderma spp. were most frequently isolated, followed by Fusarium spp. The highest disease incidence occurred in tilled plots of the latest planting date on Brooksville silty clay when samples were collected 17 days after planting. Root disease was most severe in 1996 from seedlings planted on the last planting date in tilled plots sampled 17 days after planting. Yields were significantly (P ≤ 0.05) higher on Brooksville silty clay soil than on Memphis silt loam in both 1995 and 1996. Yields were highest from no-tillage plots and from maize planted on the earliest date. There was a significant correlation between incidence of root infection and disease severity. There was no correlation between the incidence of root infection and yield or between disease severity and yield at either location. This revised version was published online in June 2006 with corrections to the Cover Date.