Soil Inoculum Potential Research Articles

Mycorrhizal Fungal Inoculum Potential in Crop Rotation Soil With Different Levels of Irrigation

Research indicates arbuscular mycorrhizal fungi (AMF) inoculum potential and AMF biomass production in agricultural soil are strongly influenced by both soil moisture availability and crop rotation (CR) strategies. We hypothesized that AMF biomass production in and inoculum potential of Wyoming semiarid agricultural soil would increase when managed using CR and irrigation. To test this hypothesis, we examined AMF activity (AMF biomarker fatty acid, and AMF infection of roots) in two differently managed soils (no-CR soil and two-year CR soil) in a field experiment. Furthermore, in a greenhouse experiment, we examined AMF activity in the same two CR treatment soils under different irrigation regimes (wet, irrigated to 60% field capacity, and dry, irrigated to 15% field capacity). Notably, the two-year CR soil had greater amounts of AMF biomarker fatty acid and greater inoculum potential, and higher percentage of AMF root colonization compared to no-CR soil. Despite the fact that the CR soil had more AMF propagules, it was less than the undisturbed non-agricultural native sage-grassland soils previously reported. Overall, the findings suggest that high levels of irrigation can inhibit the activity of AMF adapted to semiarid soil conditions and CR can increase activity of AMF in soils from semiarid regions.

Selective logging and shifting cultivation practices significantly reduce ectomycorrhizal inoculum potential of humid forest soils of South Cameroon

Selective logging and shifting cultivation practices significantly reduce ectomycorrhizal inoculum potential of humid forest soils of South Cameroon

Selective logging and shifting cultivation practices significantly reduce ectomycorrhizal inoculum potential of humid forest soils of South Cameroon

Selective logging and shifting cultivation practices significantly reduce ectomycorrhizal inoculum potential of humid forest soils of South Cameroon

Effect of Soil Microbiome from Church Forest in the Northwest Ethiopian Highlands on the Growth of Olea europaea and Albizia gummifera Seedlings under Glasshouse Conditions

Loss of beneficial microbes and lack of native inoculum have hindered reforestation efforts in the severely-degraded lands worldwide. This is a particularly pressing problem for Ethiopia owing to centuries-old unsustainable agricultural practices. This study aimed to evaluate the inoculum potential of soils from church forest in the northwest highlands of Ethiopia and its effect on seedling growth of two selected native tree species (Olea europaea and Albizia gummifera) under a glasshouse environment. Seedlings germinated in a seed chamber were transplanted into pots containing sterilized and/or non-sterilized soils collected from under the canopy of three dominant church forest trees: Albizia gummifera (AG), Croton macrostachyus (CM), and Juniperus procera (JP) as well as from adjacent degraded land (DL). A total of 128 pots (2 plant species × 4 soil origins × 2 soil treatments × 8 replicates) were arranged in a factorial design. Overall, seedlings grown in AG, CM, and JP soils showed a higher plant performance and survival rate, as a result of higher soil microbial abundance and diversity, than those grown in DL soils. The results showed significantly higher plant height, root collar diameter, shoot, and total mass for seedlings grown in non-sterilized forest soils than those grown in sterilized soils. Furthermore, the bacterial relative abundance of Acidobacteria, Actinobacteria, and Nitrospirae was significantly higher in the non-sterilized forest soils AG, CM, and JP (r2 = 0.6–0.8, p < 0.001). Soil pH had a strong effect on abundance of the bacterial community in the church forest soils. More specifically, this study further demonstrated that the effect of soil microbiome was noticeable on the performance of Olea seedlings grown in the soil from CM. This suggests that the soils from remnant church forests, particularly from the canopy under CM, can serve as a good soil origin, which possibly would promote the native tree seedling growth and survival in degraded lands.

Plasticity in root symbioses following shifts in soil nutrient availability during long‐term ecosystem development

Abstract The vast majority of terrestrial plants form root symbioses with arbuscular mycorrhizal (AM) fungi to enhance nutrient (particularly phosphorus, P) acquisition. However, some plant species also form dual symbioses involving ectomycorrhizal (ECM) fungi, with a subset of those also forming triple symbioses also involving dinitrogen (N2)‐fixing bacteria. It has been suggested that these plants show plasticity in root symbioses to optimise nutrient acquisition depending on the type and strength of soil nutrient limitation (e.g., N vs. P), yet empirical evidence remains limited. Alternatively, the degree of investment or “preference” in particular root symbioses might simply reflect differences in inoculum potential among soils of contrasting nutrient availability, reflecting adaptations of root symbionts to different edaphic conditions. Here, we grew two co‐occurring plant species forming triple (AM/ECM/N2‐fixing; Acacia rostellifera) or dual (AM/ECM; Melaleuca systena) symbioses in soils of increasing age and contrasting nutrient availability from an Australian long‐term soil chronosequence to disentangle the relative importance of abiotic factors (e.g., soil nutrient availability and stoichiometry) and biotic factors (e.g., soil inoculum potential) in determining root colonisation patterns and functional outcomes of these multiple root symbioses. For both plant species, we found clear hump‐shaped plant growth patterns along the pedogenesis‐driven gradient in soil nutrient availability, with peak growth in intermediate‐aged soils, while high levels of mycorrhizal colonisation by the “preferred” root symbionts were maintained across all soils. We found large increases (540%) in foliar manganese concentrations with increasing soil age and declining P availability, suggesting that plants may be relying on the release of carboxylates to help acquire P in the most P‐impoverished soils. Finally, we found that soil abiotic properties, such as strong differences in soil nutrient availability, are generally more important than soil inoculum potential in explaining these shifts in our plant and root responses. Synthesis. Our study suggests that plants capable of forming multiple root symbioses show plasticity in their nutrient‐acquisition strategies following shifts in soil nutrients during long‐term ecosystem development, yet maintain a preference for certain root symbionts despite changes in soil microbial inoculum.

Effect of Sugar Beet Variety and Nonhost Plant on Rhizoctonia solani AG2-2IIIB Soil Inoculum Potential Measured in Soil DNA Extracts

A direct soil DNA extraction method from soil samples (250 g) was applied for detection of the soilborne sugar-beet-infecting pathogen Rhizoctonia solani anastomosis group (AG) 2-2IIIB using a newly developed real-time polymerase chain reaction assay that showed specificity to AG2-2IIIB when tested against various R. solani AG. The assay showed a good relation between cycle threshold and amount of AG2-2IIIB sclerotia detected in three spiked field soils and was also able to detect the pathogen in naturally infested field soil samples. A field trial was conducted to quantify R. solani AG2-2IIIB soil inoculum potential (IP) before and after growing a susceptible and a resistant sugar beet variety as well as after subsequent growth of an expected nonhost winter rye. Plants of the susceptible sugar beet variety displayed a higher disease severity. A more than sixfold increase of the R. solani AG2-2IIIB soil IP was observed in contrast to the resistant variety that resulted in a constant IP. Growing winter rye significantly reduced soil IP to the initial level at sowing. Further research is required to better understand the interaction between disease occurrence and soil IP as well as the environmental influence on IP development.

The distribution and colonization of soybean by Rhizoctonia solani AG11 in fields rotated with rice

From 2009 to 2012, a spatial study was conducted on soybean fields undergoing rice and soybean rotations to determine the distribution and importance of Rhizoctonia spp. Fields were sampled for soil populations by toothpick-baiting and plants were collected at growth stage V3 from GPS sampling points placed on either side of the rice levee system from the previous rice cropping year. Anastomosis group 11 (AG11) of Rhizoctonia solani, a group not recognized as causing any plant diseases on rice or soybean, was the most prevalent Rhizoctonia spp. recovered from soil and soybeans in fields assayed from 2009 to 2012. The mean recovery from the soil was 7.1 (0–94.4) and 12.2 (0–79.7) propagules/kg from fields with 48 and >96 GPS points, respectively, while the mean number of plants colonized by the fungus was 114.3 (24%) for fields with 48 GPS points and 153.8 (16%) for fields with >96 points. In 2012, all three fields assayed indicated aggregation of the soil inoculum potential of the fungus and two of the three fields indicated aggregation from the plants colonized by R. solani AG11. In all years, semi-variogram models indicated 15 measured major ranges exceeded 50 m and 11 exceeded 100 m with most of the nugget values (error) less than 5 m indicating that there is a contiguous population across space with little microstructure below the measured major range at these distances. For the three fields examined in 2012, recovery of AG11 from plants was negatively correlated with soil volumetric water content suggesting dryer areas of the field favored infection of plants. Plant stands from soil obtained for GPS locations grown under a controlled environment found a positive correlation for two of the three locations between plant stand and colonization by AG11. These studies suggest that R. solani AG11 is the dominate Rhizoctonia group in rice soybean rotations in Arkansas in the United States. R. solani AG11 opportunistically colonizes soybean and is associated with greater plant stands across fields suggesting a positive rather than a negative pathogenic role for this fungus and the host plant.

Occurrence and Structure of Arbuscular Mycorrhizal Fungal Communities in Cassava after Cultivation of Cover Crops as Observed by the “PCR-DGGE” Technique

ABSTRACT Cassava (Manihot esculenta Crantz) is a highly mycotrophic crop, and prior soil cover may affect the density of arbuscular mycorrhizal fungi (AMFs), as well as the composition of the AMFs community in the soil. The aim of this study was to evaluate the occurrence and the structure of AMFs communities in cassava grown after different cover crops, and the effect of the cover crop on mineral nutrition and cassava yield under an organic farming system. The occurrence and structure of the AMFs community was evaluated through polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE). A randomized block experimental design was used with four replications. Six different cover crop management systems before cassava were evaluated: black oats, vetch, oilseed radish, intercropped oats + vetch, intercropped oats + vetch + oilseed radish, plus a control (fallow) treatment mowed every 15 days. Oats as a single crop or oats intercropped with vetch or with oilseed radish increased AMFs inoculum potential in soil with a low number of propagules, thus benefiting mycorrhizal colonization of cassava root. The treatments did not affect the structure of AMFs communities in the soil since the AMFs communities were similar in cassava roots in succession to different cover crops. AMFs colonization was high despite high P availability in the soil. The cassava crop yield was above the regional average, and P levels in the leaves were adequate, regardless of which cover crop treatments were used. One cover crop cycle prior to the cassava crop was not enough to observe a significant response in variables, P in plant tissue, crop yield, and occurrence and structure of AMFs communities in the soil. In the cassava roots in succession, the plant developmental stage affected the groupings of the structure of the AMF community.

An Experimental Test of Epi- and Endozoochory of Arbuscular Mycorrhizal Fungi Spores by Small Mammals in a Maryland Forest

Small mammals have been proposed as important dispersers of the spores of arbuscular mycorrhizal fungi (AMF), yet few data exist to support this hypothesis. We experimentally tested 2 models of small-mammal dispersal of AMF spores by quantifying their impact on the mycorrhizal inoculum potential of sterile soil flats in a northeast mesophytic forest in Maryland. Epizoochory did not provide a mechanism for spore dispersal in our study. However, our data demonstrated that endozoochory by several small-mammal species can be an effective dispersal mode for AMF. In the field experiment, inoculum potential of soil from plots that were accessible to Peromyscus leucopus (White-footed Mouse) was significantly higher than in control plots, which excluded small mammals. This study provides experimental evidence that White-footed Mice disperse AMF spores.

A Sensitive Assay for Rapid Detection and Quantification of Aphanomyces euteiches in Soil.

Aphanomyces euteiches is a widespread oomycete pathogen causing root rot in a wide range of leguminous crops. Losses can reach up to 100% for pea culture and there is currently no registered pesticide for its control. Crop management remains the most efficient tool to control root rot, and avoidance of infested soil seems to be the optimal solution. A test was developed to identify fields suitable for pea crops, consisting of the determination of the inoculum potential of soil using baiting plants. A new rapid, specific, and sensitive molecular method is described allowing the quantification of less than 10 oospores per gram of soil. This challenge is achieved by a real-time polymerase chain reaction procedure targeting internal transcribed spacer 1 from the ribosomal DNA operons. A preliminary study based on typical soils from northwestern France demonstrated that the A. euteiches oospore density in soil is related to the inoculum potential. Furthermore, this method has proved sensitive enough to accurately study the influence of biotic factors that may govern the actual emergence of root rot.

Quantitative methods for assessment of the impact of different crops on the inoculum density of Rhizoctonia solani AG2-2IIIB in soil

Rhizoctonia solani AG2-2IIIB is the causal agent of late crown and root rot in sugar beet. In a 4-year field study we analyzed the impact of different plant residue management systems of sugar beet and maize as well as of growing wheat (non-host) and different maize varieties on the soil inoculum density of R. solani. Sugar beet remains were either tilled or removed from the field; maize was then grown during the two following years and also tilled or removed. The soil inoculum potential of R. solani was studied using three different on- and off-site monitoring systems. A monthly assessment of root damage indices of maize and sugar beet and broad bean as an indicator plant was carried out. In addition, an indirect quantitative real-time PCR assay using quinoa seed baits was developed to analyze field soil samples for R. solani AG2-2 soil concentration at the end of each year. The results show that the non-host wheat as a pre-crop to sugar beet reduced the Rhizoctonia inoculum potential in the soil significantly. Additionally, the incorporation of host plant debris (sugar beet + maize) into the soil increased the Rhizoctonia soil inoculum potential and the incidence of sugar beet rot. Although the maize genotypes’ susceptibility to R. solani differed, their plant debris did not significantly influence growth and survival of R. solani in the soil. This work describes methods that allow elucidating the effect of agricultural practice on Rhizoctonia levels in the soil and on disease development in the field.

Ectomycorrhizal inoculum potential of northeastern US forest soils for American chestnut restoration: results from field and laboratory bioassays

American chestnut (Castanea dentata) was once a dominant overstory tree in eastern USA but was decimated by chestnut blight (Cryphonectria parasitica). Blight-resistant chestnut is being developed as part of a concerted restoration effort to bring this heritage tree back. Here, we evaluate the potential of field soils in the northern portion of the chestnut's former range to provide ectomycorrhizal (EM) fungus inoculum for American chestnut. In our first study, chestnut seedlings were grown in a growth chamber using soil collected from three sites dominated by red oak (Quercus rubra) as inoculum and harvested after 5months. Of the 14 EM fungi recovered on these seedlings, four species dominated in soils from all three sites: Laccaria laccata, a Tuber sp., Cenococcum geophilum, and a thelephoroid type. Seedlings grown in the nonsterilized soils were smaller than those growing in sterilized soils. In the second study, chestnut seedlings were grown from seed planted directly into soils at the same three sites. Seedlings with intermingling roots of established trees of various species were harvested after 5months. Seventy-one EM fungi were found on the root tips of the hosts, with 38 occurring on chestnut seedlings. Multiple versus single host EM fungi were significantly more abundant and frequently encountered. The fungi observed dominating on seedlings in the laboratory bioassay were not frequently encountered in the field bioassay, suggesting that they may not have been active in mycelial networks in the field setting but were in the soils as resistant propagules that became active in the bioassay. These results show that soil from red oak stands can be used to inoculate American chestnut with locally adapted ectomycorrhizal fungi prior to outplanting, a relatively cost effective approach for restoration efforts.

Successive legumes tested in a greenhouse crop rotation experiment modify the inoculum potential of soils naturally infested by Aphanomyces euteiches

The consequence of 10 successive monocultural cycles involving different legume species/cultivars on the inoculum potential (IP) of soils naturally infested by Aphanomyces euteiches was investigated under greenhouse conditions. The results showed that the IP of a soil naturally infested by A. euteiches can be significantly modified not only by the non‐host or host status of crop species but also by the level of resistance of the cultivar. Susceptible species/cultivars (pea, lentil and susceptible cultivars of vetch and faba bean) are very favourable to pathogen multiplication, and continuous cultivation of each of these increased the IP values of a soil with a moderate initial IP (from 1·9 to 3·5 after 10 cycles). Conversely, non‐host species and resistant cultivars of vetch or faba bean contributed to reducing the IP values of soils irrespective of the initial IP (from 1·9 to 0·5 and from 4 to 2, respectively, after 10 cycles). Aphanomyces root rot severity values on the resistant legume species/cultivars were not affected by the successive cultural cycles. This study, which showed that the IP of A. euteiches in soil can be reduced by planting appropriate legume species and cultivars in greenhouse conditions, will be useful for defining better crop successions for legumes.

The abundance and diversity of legume-nodulating rhizobia and arbuscular mycorrhizal fungal communities in soil samples from deforested and man-made forest systems in a semiarid Sahel region in Senegal

Exotic and native tree species have been widely used in the West Africa to reverse the tendency of land degradation. Although benefic effects have been reported on soil stabilization, a lack of information about their impact on soil symbiotic microorganisms still remains. This investigation has been carried out in a semiarid Sahel region and aimed to survey the abundance and diversity of natural legume-nodulating rhizobia (LNR) and arbuscular mycorrhizal (AM) fungal communities in soil samples from deforested and man-made forest systems. A genetically diverse LNR population is supported by the phylogenetic analysis, which clustered the isolates into three genera: Bradyrhizobium, Mesorhizobium and Sinorhizobium. The results showed that the man-made forest systems increased the LNR abundance and genetic diversity as well as the soil phosphorus and nitrogen contents. By contrast, strong modifications have been recorded in the characteristics of the AM fungal communities. The number of AM fungus taxa as well as the mycorrhizal inoculum potential (MIP) of soils decreased drastically in the man-made forest systems in comparison with the deforested land. In addition, the larger-spored AM fungi (Scutellospora and Gigaspora) were specifically found in soil samples from the deforested land. The displacement of larger-spored species was associated with a concomitant proliferation of small spored (Glomus) species. We conclude that man-made forestry can modify the soil symbiotic microorganisms and the results support the need for further adoption of management practices that could improve or sustain the development of herbaceous layers to promote the soil AM fungal communities.

Arbuscular mycorrhizal root colonization and soil P availability are positively related to agrodiversity in Mexican maize polycultures

In Los Tuxtlas, Mexico, the local Popoluca people maintain the traditional management of their maize agroecosystems. However, it is not known whether the loss of agrodiversity over recent decades has affected mycorrhizal populations, nutrient availability, and crop productivity. This study utilized linear mixed effect models to analyze the relationship between agrodiversity (three, six, and greater than or equal to eight cultivated species) and (a) arbuscular mycorrhizal fungi (AMF) inoculum potential, measured as the most probable number (MPN) of propagules and colonization level, (b) nutrient availability, and (c) aboveground maize productivity. We also investigated the relationship between soil nutrient content and inoculum potential. Soil samples were taken before planting, and during flowering, in the 2009 maize cycle. We found that AMF colonization level of maize roots and P availability increased with planted species richness, but that this effect only occurred at the flowering sampling date. Plots with a higher MPN of propagules presented increased C and NO3− contents and lower C/N ratio than those with lower MPN of propagules, regardless of agrodiversity. Soils that produced the highest maize root colonization level also featured high P availability and N content. We conclude that decreased agrodiversity in these traditional systems does not significantly affect the soil MPN of propagules, but may have a negative impact on the ability of the mycorrhizal community to colonize maize roots, as well as reducing the availability of P, which is often the most limiting nutrient in tropical soils.

Arbuscular mycorrhizal soil infectivity and spores distribution across plantations of tropical, subtropical and exotic tree species: a case study from the forest reserve of Bandia, Senegal

AbstractSeveral fast‐growing and multipurpose trees such as exotic and valuable native species have been widely used in West Africa to reverse the tendency of massive degradation of plant cover and restore soil productivity. Although benefic effects have been reported on soil stabilization, a lack of information about their impact on soil symbiotic microorganisms still remains. This investigation has been carried out in field trees of 28 years old in a forest reserve at Bandia. To determine the mycorrhizal inoculum potential (MIP) of soils, a mycorrhizal bioassay was conducted using seedlings of Zea mays L. Spores concentration, arbuscular mycorrhizal (AM) fungi morphotypes and mycorrhizal colonization of field plants were examined. Results showed that fungal communities were dominated in all samples by the genus Glomus. Nevertheless, the others genera Gigaspora and Scutellospora occurred preferentially out of the plantations. The number and richness of spores as well as the MIP of soils were decreased in the tree plantations. Accordingly, the amount of annual herbaceous plants kept out of the tree plantations was much greater than those under the tree plantations. The colonization was higher in field root systems of herb plants in comparison with that of the tree plants. Comparisons allowed us to conclude that vegetation type modifies the AM fungal communities, and the results suggest further adoption of management practices that could improve or sustain the development of herbaceous layers and thus promote the AM fungal communities.

Fall cover cropping can increase arbuscular mycorrhizae in soils supporting intensive agricultural production

Intensive agricultural practices, such as tillage, monocropping, seasonal fallow periods, and inorganic nutrient application have been shown to reduce arbuscular mycorrrhizal fungi (AMF) populations and thus may reduce benefits frequently provided to crops by AMF, such as nutrient acquisition, disease resistance and drought tolerance. We have evaluated the ability of different cover crops to elevate the native mycorrhizal inoculum potential of soils under soil–climatic conditions typical of the upper Midwest U.S. production agricultural region. We measured the number of soil AMF propagules at three sites in the late fall following cover crops that were seeded into summer-harvested small grains within a no-till rotation. At all three sites, soil AMF propagule numbers were generally low (≤1propaguleg−1). Fall cover crops significantly increased the mycorrhizal inoculum potential of the soils. Forage oats (Avena sativa (L.) Hausskn.), by itself or in mixtures, was most effective at both sites where it was planted. At the third site, a cover crop mixture doubled the inoculum potential of these soils. The effect of cover crop treatments on AMF propagules was corroborated at one site over two seasons by measuring AMF biomass with the neutral lipid fatty acid mycorrhizal biomarker, C16:1cis11. Identification of AMF-promoting cover crops for inclusion in diversified, no till cropping rotations in the upper Midwest U.S. will provide opportunity for reduced inorganic nutrient application with economic and environmental benefit.

Morphological Enumeration of Resting Spores in Sporosori of the Plant Pathogen Spongospora subterranean

Plasmodiophorid sporosori (aggregations of resting spores) reach their most complex form in Spongospora subterranea f. sp. subterranea, the biotrophic plant pathogen which causes the economically important disease powdery scab of potato ( Solanum tuberosum ). Resting spores are the perennation life cycle stage of plasmodiophorids, allowing them to survive for long periods and infect subsequent host generations. Light microscopy was used to measure resting spores and sporosori of Sp. subterrane a, and enumerate resting spores in individual sporosori. Mean resting spore diameters differed for two sporosorus collections, being 4.0 μm (from New Zealand) and 4.3 μm (from Switzerland). Counts of resting spores in 4 μm thick serial sections of sporosori from one collection gave a mean of 667 (range 155 to 1,526) resting spores per sporosorus. Number of resting spores per sporosorus was closely related to sporosorus volume, and could be accurately estimated using the formula; number of resting spores = 0.0081 × sporosorus volume (assuming sporosori to be spheroids). Using this formula, mean numbers of resting spores in sporosori from 37 Sp. subterranea collections from field-grown potato tubers from 13 countries were determined to range from 199 to 713. Differences in numbers of resting spores between the collections were statistically significant (P < 0.05), and independent of country or host cultivar of origin, indicating that enumeration should be carried out for individual sporosorus collections to accurately quantify inoculum. Morphology, using scanning electron microscopy, also showed that between 2 and 51% (average 20%) of resting spores released zoospores after exposure to roots of host plants. The formula for resting spore enumeration validated in this study can be used to standardise Sp. subterranea resting spore inoculum for plant pathology studies, and possibly to assist determination of soil inoculum potential for disease risk evaluations.

Crescimento e micorrização de genótipos de milho em casa de vegetação

O trabalho foi desenvolvido em casa de vegetação com o objetivo de comparar o crescimento e a micorrização por fungos micorrízicos arbusculares (FMA) em nove genótipos de milho, além de verificar o potencial de inóculo de FMA do solo. Coletado de uma área de cerrado sensu stricto ocupada por pastagem degradada, o solo foi adubado, misturado com areia de rio, fumigado e colocado em sacos plásticos (3 kg). Foram semeadas cinco sementes de cada genótipo de milho em 20 sacos, mas apenas 10 receberam cerca de 300 esporos de FMA, coletados do solo de pastagem. Cada saco constituiu-se em uma repetição, com apenas uma planta. As avaliações de altura e diâmetro do caule foram realizadas aos 15, 30, 45 e 60 dias após a emergência, além de massa seca do sistema radicular (MSR) e parte aérea (MSPA), colonização micorrízica (COL) e dependência micorrízica (DM). Concomitantemente, um segundo experimento foi realizado para avaliar o potencial de inóculo de FMA do solo de pastagem, o qual passou por uma diluição seriada de 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% e 10%, incluindo apenas o solo não esterilizado (100%) e somente solo esterilizado (0%), em sacos plásticos, semeado o híbrido Tractor. Após 60 dias, as raízes foram colhidas para quantificar a colonização micorrízica. A inoculação de FMA acarretou incrementos na produção de matéria seca de forma diferenciada entre genótipos; com Condá, F0, D1 e F8 exibindo os maiores valores de MSPA, enquanto Tractor e D7 os menores valores de MSR. Os genótipos não responsivos ou pouco responsivos quanto à dependência micorrízica tiveram comportamento diferente quanto à COL, com Condá, Sol da Manhã, F0 e D1 proporcionando média de 60%. Verificou-se que a área de pastagem, mesmo degradada, propiciou alto potencial de inóculo, revelado pela alta porcentagem de colonização das raízes por FMA.

Waiting for fungi: the ectomycorrhizal invasion of lowland heathlands

Summary 1. In England, the loss of lowland heathland, a habitat of global conservation importance, is primarily due to the invasion of birch and pine. This encroachment has been researched in depth from a plant perspective but little is known about the role of mycorrhizal fungi. In lowland heathlands the resident dwarf shrubs form ericoid mycorrhizas whereas invading trees form ectomycorrhizas. Therefore, tree encroachment into heathlands can be regarded as the replacement of a resident mycorrhizal community by an invading one. 2. This study examined how fungi form mycorrhizas with Betula and Pinus in lowland heathlands. We addressed the question of whether there are mycorrhizal fungi that mediate invasion using a molecular ecology approach to compare the mycorrhizal inoculum potential of soil at three levels of invasion (uninvaded heathland, invaded heathland and woodland) and the fungi forming mycorrhizas on tree seedlings and trees across diverse sites. 3. We show that in lowland heathlands: (i) seedlings have severely limited access to ectomycorrhizal fungi relative to woodlands, (ii) there are few keystone spore‐dispersed ectomycorrhizal fungi that can mediate tree invasion, (iii) tree seedlings can remain non‐mycorrhizal for at least one year when no inoculum is present, even near saplings, and (iv) mycorrhizal seedlings achieve greater biomass than non‐mycorrhizal seedlings. Within uninvaded heathland we detected only Rhizopogon luteolus, Suillus variegatus, S. bovinus (Pinus symbionts) and Laccaria proxima (primarily a Betula symbiont). 4. Synthesis. Overall, ectomycorrhizal inoculum in lowland heathlands is rare; most tree seedlings growing in heathland soil are not mycorrhizal due to limited spore dispersal, poorly developed spore banks and weak common mycorrhizal networks. These seedlings can persist awaiting mycorrhization to boost their growth.