Fungal Root Colonization Research Articles

Ontogenetic transition from specialized root hairs to specific root-fungus symbiosis in the dominant Mediterranean seagrass Posidonia oceanica

Terrestrial plants typically take up nutrients through roots or mycorrhizae while freshwater plants additionally utilize leaves. Their nutrient uptake may be enhanced by root hairs whose occurrence is often negatively correlated with mycorrhizal colonization. Seagrasses utilize both leaves and roots and often form root hairs, but seem to be devoid of mycorrhizae. The Mediterranean seagrass Posidonia oceanica is an exception: its adults commonly lack root hairs and regularly form a specific association with a single pleosporalean fungus. Here we show that at two sites in the southern Adriatic, all its seedlings possessed abundant root hairs with peculiar morphology (swollen terminal parts) and anatomy (spirally formed cell walls) as apparent adaptations for better attachment to the substrate and increase of breaking strain. Later on, their roots became colonized by dark septate mycelium while root hairs were reduced. In adults, most of terminal fine roots possessed the specific fungal association while root hairs were absent. These observations indicate for the first time that processes regulating transition from root hairs to root fungal colonization exist also in some seagrasses. This ontogenetic shift in root traits may suggests an involvement of the specific root symbiosis in the nutrient uptake by the dominant Mediterranean seagrass.

Xylariales): Physiological characterization and structural features of its association with wheat.

: Plant roots can be colonized by asymptomatic fungal strains belonging to several taxa, among them, the group defined as Dark Septate Endophytes (DSE). Microdochium bolleyi commonly colonizes wheat roots and other crops. It is considered a weak pathogen or even a non-pathogenic fungal species, which has also been considered as a potential biocontrol agent against aggressive soil-borne pathogens in cereal crops. We isolated a strain of M. bolleyi from wheat roots sampled in a crop field in Argentina, and characterized its abilities to grow in different carbon and nitrogen sources, to produce indole and to solubilize phosphorus; also several enzymatic activities were evaluated. In addition, resynthesis was performed under controlled conditions in order to characterize root fungal colonization under both, optical and transmission microscopy. The strain 22-1 colonized wheat root parenchymal tissue, forming chlamysdospores inside parenchymal cells and root hairs, and poorly grew in carbon and nitrogen sources. This fungus also synthesized indoles in in vitro culture, but it cannot solubilize phosphorus. Only amylase activity was detected out of seven enzymatic activity measured. Microdochium bolleyi (strain 22-1) colonized the roots, it formed typical DSE fungal structures and behaved like a “true endophyte”; however further studies are necessary to elucidate its role in the association with wheat.

Availability of Phosphorus after Long-term Whole and Separated Slurry Application to Perennial Grass prior to Corn Silage.

Removing solids from whole dairy slurry (WS) can reduce P loading on fields. This study investigated the effects of 11 yr of applications of WS, separated liquid fraction (LF), commercial fertilizer, WS plus fertilizer, and a control on total and extractable (Kelowna) soil P in perennial grass ( Schreb.) and two subsequent silage corn ( L.) crops. Plots received 200 kg N ha with or without 40 kg P ha. Shoot biomass, P uptake, arbuscular mycorrhizal fungi root colonization, and soil microbial P were determined for corn at six leaves. Whole-crop and grain yield, P uptake, dry matter, and grain content were determined at maturity. The LF treatment received 30% less manure P than WS, had lower extractable soil P at 0 to 15 and 15 to 30 cm, and had lower total P at 0 to 15 cm. Historical treatments had no effect on soil microbial P or arbuscular mycorrhizal fungi colonization. At six leaves, corn shoot biomass, P concentration, and P uptake were related to historical P rates in Year 2, but the relationship was not apparent in Year 1. Starter P fertilizer increased shoot yield and P uptake for all treatments in both years. At maturity, most yield parameters for WS and LF were similar in Year 1, but in Year 2, there was a significant response to starter P fertilizer and a positive relationship between historical P rate and corn performance. This study shows that long-term LF treatments reduced the risk of P pollution with relatively little effect on the P response of subsequent corn crops.

Glyphosate decreases mycorrhizal colonization and affects plant-soil feedback

Our aim was to study the effects of glyphosate, tilling practice and cultivation history on mycorrhizal colonization and growth of target (weeds) and non-target (crops) plants. Glyphosate, the world's most widely used pesticide, inhibits an enzyme found in plants but also in microbes. We examined the effects of glyphosate treatment applied in the preceding fall on growth of a perennial weed, Elymus repens (target plant) and a forage grass, Festuca pratensis (non-target plant) and their arbuscular mycorrhizal fungal (AMF) root colonization in a field pot experiment. Non-target plants were sown in the following spring. Furthermore, we tested if glyphosate effects depend on tillage or soil properties modulated by long cultivation history of endophyte symbiotic grass (E+ grass). AMF root colonization, plant establishment and growth, glyphosate residues in plants, and soil chemistry were measured. Glyphosate reduced the mycorrhizal colonization and growth of both target and non-target grasses. The magnitude of reduction depended on tillage and soil properties due to cultivation history of E+ grass. We detected glyphosate residues in weeds and crop plants in the growing season following the glyphosate treatment. Residues were higher in plants growing in no-till pots compared to conspecifics in tilled pots. These results demonstrate negative effects of glyphosate on non-target organisms in agricultural environments and grassland ecosystems.

Intensified dryland crop rotations support greater grain production with fewer inputs

Rising use and costs of agri-chemical inputs to support agricultural production have placed an economic burden on farmers while contributing to environmental and human health issues. Ecologically based nutrient and weed management – the use of ecological processes to replace external chemical inputs – may represent a strategy to support crop growth while achieving positive environmental and economic outcomes. In dryland agroecosystems around the world, farmers are increasingly transitioning toward no-till and intensified cropping systems, in which unvegetated fallow periods are replaced with crops. This study seeks to determine if cropping system intensification represents an ecologically based strategy for managing nutrients and weeds relative to traditional crop-fallow systems, and to understand the implications for crop production and profitability. We quantified total and potentially mineralizable nitrogen (N), arbuscular mycorrhizal fungal (AMF) colonization of wheat roots and implications for plant phosphorus (P) uptake, 6 years of crop yields, fertilizer and herbicide use, and net operating income across dryland, no-till cropping systems in the semi-arid High Plains, USA. Three levels of cropping system intensity were represented ranging from wheat-fallow (unvegetated fallow every other year) to continuous cropping (no fallow years). After accounting for variability due to environment and site characteristics, total and potentially mineralizable N were 12% and 30% greater in continuous rotations relative to wheat-fallow, respectively. Mid-intensity (fallow every 2 or 3 years) and continuous rotations had roughly 2 and 3 times more AMF colonization than wheat-fallow, respectively, and AMF colonization was positively correlated with wheat plant P concentration. Farmers practicing continuous cropping applied 22 and 34 kg ha−1 less N fertilizer per crop compared to wheat-fallow and mid-intensity, respectively, despite similar and 60% greater annualized crop production than mid-intensity and wheat-fallow rotations, respectively. Additionally, farmers who practiced continuous cropping used less than half the total herbicide used by wheat-fallow farmers. Net operating incomes of continuous and mid-intensity rotations were an estimated 47 USD ha−1 yr−1 (80%) and 42 USD ha−1 yr−1 (70%) more than wheat-fallow, respectively. These results suggest that cropping system intensification, and especially continuous cropping, represents an opportunity to achieve more grain production while managing weeds and nutrients with fewer agri-chemical inputs, leading to greater profitability and improved environmental outcomes in no-till agroecosystems.

Mixture of Salix Genotypes Promotes Root Colonization With Dark Septate Endophytes and Changes P Cycling in the Mycorrhizosphere.

The roots of Salix spp. can be colonized by two types of mycorrhizal fungi (ectomycorrhizal and arbuscular) and furthermore by dark-septate endophytes. The fungal root colonization is affected by the plant genotype, soil properties and their interactions. However, the impact of host diversity accomplished by mixing different Salix genotypes within the site on root-associated fungi and P-mobilization in the field is not known. It can be hypothesized that mixing of genotypes with strong eco-physiological differences changes the diversity and abundance of root-associated fungi and P-mobilization in the mycorrhizosphere based on different root characteristics. To test this hypothesis, we have studied the mixture of two fundamentally eco-physiologically different Salix genotypes (S. dasyclados cv. ‘Loden’ and S. schwerinii × S. viminalis cv. ‘Tora’) compared to plots with pure genotypes in a randomized block design in a field experiment in Northern Germany. We assessed the abundance of mycorrhizal colonization, fungal diversity, fine root density in the soil and activities of hydrolytic enzymes involved in P-mobilization in the mycorrhizosphere in autumn and following spring after three vegetation periods. Mycorrhizal and endophytic diversity was low under all Salix treatments with Laccaria tortilis being the dominating ectomyorrhizal fungal species, and Cadophora and Paraphaeosphaeria spp. being the most common endophytic fungi. Interspecific root competition increased richness and root colonization by endophytic fungi (four taxa in the mixture vs. one found in the pure host genotype cultures) more than by ectomycorrhizal fungi and increased the activities of hydrolytic soil enzymes involved in the P-mineralization (acid phosphatase and β-glucosidase) in mixed stands. The data suggest selective promotion of endophytic root colonization and changed competition for nutrients by mixture of Salix genotypes.

Assessment of Arbuscular Mycorrhizal (AM) fungi of Glyphochloa santapaui: Vulnerable and endemic grass species of Maharashtra, India.

Glyphochloa santapaui (S.K. Jain & Deshp.) Clayton santapaui is endemic to Maharashtra state restricted to Ferricrete-Lateritic rocky plateaus at Sindhudurg and Ratnagiri district. Due to ongoing anthropogenic threats this species is rated as Vulnerable under IUCN Red List of Threatened Species and hence attention is needed toward its conservation.The lateritic plant-soil interactions in different taxa is dependent to their microbial or mycorrhizal associates. So far endemic grass species - Arbuscular mycorrhizal associations on Lateritic rocky plateaus are poorly investigated. In present paper critical assessment of AM fungal colonization in roots of vulnerable- endemic grass Glyphochloa santapaui is interpreted. Overall colonization percentage was 71.80%. Moreover, root segments of some samples were commonly co-colonized by dark septate hyphae (dsh) of other fungal endophytes (Ofe) and AM fungi. In present assessment, four Glomeromycota families viz., Acaulosporaceae, Diversisporaceae, Gigasporaceae and Glomeraceae were recorded comprising 18 species under 6 genera. These AM fungal species are viz., Acaulospora elegans, A. rehmii, A. scrobiculata, A. tuberculata, A. appendicula; Diversispora epigaea; Gigaspora albida, G. gigantea, G. margarita, G. rosea; Scutellospora calospora S. dipurpusescrns; Glomus gerdemanni, G. hoi, G. occultum, G. versiforme, G. warcuppi and Sclerocystis sinuosa. On the basis of analysis of spore density and relative abundance, two dominanting species of AM fungi viz., Diversispora epigaea and Gigaspora gigantea were recognized.

Effect of community-based soil and water conservation practices on arbuscular mycorrhizal fungi types, spore densities, root colonization, and soil nutrients in the northern highlands of Ethiopia

BackgroundSoil and water conservation measures (SWC) have a great practical significance to the restoration of arbuscular mycorrhiza (AMF). The objective of this study was to quantify the effect of decades long community-based soil and water conservation practices on arbuscular mycorrhiza fungi spore density, woody plant root colonization, and soil nutrients.MethodsThe SWC measures considered were stone terraces, exclosures + stone terraces, exclosures alone, and adjacent non-conserved open communal grazing lands. Soil and root samples were collected from the rhizosphere of matured woody plant species using systematic sampling from 10 m × 10 m plot based on slope positions. Spores were isolated using wet sieving and decanting method, while AMF fungal root colonization was done using the gridline intersection method.ResultsThe study revealed that five major genera of AMF, including Glomus, Acaulospora, Gigaspora, Scutellospora, and Entrophospora were identified. Glomus was found to be the most abundant genera, which accounted for (52%) of the total spore density, followed by Acaulospora (18%). Besides, exclosures had the highest total spore density (60%) being followed by stone terraces (23%), whereas the lowest (17%) spore density was recorded in the open communal grazing lands. Total root colonization among the treatments ranged from 48.6% in the open communal grazing lands to 68.7% in the exclosure with terraces. Hyphal colonization was higher than arbuscular and vesicular colonization. The total colonization was in the order of exclosure with terraces > exclosure alone > terraces > non-conserved communal grazing lands.ConclusionsRehabilitating the communal grazing lands with terraces and exclosure is an important approach for restoring AMF and regenerating the degraded lands.

Arbuscular mycorrhizal fungal communities associated with two dominant species differ in their responses to long‐term nitrogen addition in temperate grasslands

Abstract Arbuscular mycorrhizal (AM) fungi are important components of grassland ecosystems and are sensitive to enhanced atmospheric nitrogen (N) deposition. Enhanced N deposition has been widely reported to reduce species richness and alter species composition across different types of grasslands world‐wide. Despite extensive studies on effects of N deposition on AM fungal communities of grasslands, few studies have specifically focused on effects of N deposition on AM fungi associated with dominant species in grasslands. We investigated long‐term (12‐year) effects of N addition (80 kg ha−1 year−1) on AM fungal community richness in roots and rhizosphere biomass of two dominant plant species (forb Artemisia frigida and grass Stipa krylovii) in temperate steppes of northern China. We found that AM fungi associated with the two dominant plant species differed in their responses to N addition. Nitrogen addition led to a significant reduction in AM fungal richness colonized in roots, and biomass in the rhizosphere of A. frigida, while N addition had little impacts on AM fungi colonized in roots and rhizosphere of S. krylovii. Nitrogen addition significantly reduced AM fungal colonization in roots and AM fungal spore density in the rhizosphere soils of A. frigida. In contrast, N addition had no effect on AM fungal colonization in roots and spore density in the rhizosphere of S. krylovii. Nitrogen addition markedly suppressed photosynthetic rates in A. frigida due to excessive foliar accumulation of manganese. The N‐induced reduction in photosynthetic rates reduced allocation of C into roots in A. frigida, leading to a lower root/shoot ratio, and suppression of AM fungal community associated with A. frigida. The inhibition of AM fungi would render A. frigida less competitive in terms of acquisition of mineral nutrients in soils, thus contributing to its loss in the steppe community under conditions of elevated N deposition. These findings provide a mechanistic explanation for N‐evoked differential responses of AM fungal communities associated with A. frigida and S. krylovii by linking soil properties and host plants to AM fungal communities. A plain language summary is available for this article.

Ericoid plant species and Pinus sylvestris shape fungal communities in their roots and surrounding soil.

Root-colonizing fungi can form mycorrhizal or endophytic associations with plant roots, the type of association depending on the host. We investigated the differences and similarities of the fungal communities of three boreal ericoid plants and one coniferous tree, and identified the community structure of fungi utilizing photosynthates from the plants studied. The fungal communities of roots and soils of Vaccinium myrtillus, Vaccinium vitis-idaea, Calluna vulgaris and Pinus sylvestris were studied in an 18-month-long experiment where the plants were grown individually in natural substrate. Photosynthates utilizing fungi were detected with DNA stable-isotope probing using 13 CO2 (13 C-DNA-SIP). The results indicated that the plants studied provide different ecological niches preferred by different fungal species. Those fungi which dominated the community in washed roots had also the highest 13 C-uptake. In addition, a common root endophyte without confirmed mycorrhizal status also obtained 13 C from all the plants, indicating close plant-association of this fungal species. We detect several fungal species inhabiting the roots of both ericoid mycorrhizal and ectomycorrhizal plants. Our results highlight that the ecological role of co-occurrence of fungi with different life styles (e.g. mycorrhizal or endophytic) in plant root systems should be further investigated.

Beneficial effect of arbuscular mycorrhizal fungus, Glomus fasciculatum on plant growth and nutrient uptake in tomato

In the present study arbuscular mycorrhizal fungus (AMF), Glomus fasciculatum was used as bio-inoculant in three different cultivars viz., PKM-1, Gaurav and Monarch of tomato to assess the efficacy of AMF on the extent of root colonization, plant growth parameters and plant N, P, K status in pot experiments under greenhouse conditions. The three tomato cultivars showed positive response to AM fungal inoculation. The per cent AM fungal root colonization ranged from 26.4 to 36.0% in 30 days and 40.2 to 47.0% in 60 days old plants. Per cent root colonization was maximum (47.0%) in PKM-1 and minimum 40.2% in cultivar Monarch. Glomus fasciculatum treated plants resulted in significant increase in plant height, shoot and root fresh and their dry weights over control plants recording maximum in Monarch cultivar. The shoot and root dry weights in 30 days crop of AM inoculated plants in Monarch cultivar increased to more than four and threefolds, respectively over control. In 60 days crop the shoot dry weights of AM inoculated plants were increased to 56.04% and root dry weight to 125.32% over control. Plant N, P and K content was significantly increased in G. fasciculatum inoculated plants indicating that these three elements were efficiently transported in mycorrhizal plants. Biomass, and dry matter production was maximum in cultivar Gaurav. N and K content of AM inoculated PKM-1 plants was increased to 132.54 and 26.38% respectively over control. However, P was recorded maximum in cultivar Monarch that increased to 114.68% over control. The results of our experiment proved G. fasciculatum as a biofertilizer in three cultivars of tomato.

Contrasting communities of arbuscule-forming root symbionts change external critical phosphorus requirements of some annual pasture legumes

Annual pasture legumes with a superior ability to acquire soil phosphorus (P) and a low external critical P requirement could reduce the need for P fertiliser. Roots of pasture legumes grown in field soil will commonly be colonised by arbuscular mycorrhizal fungi (AMF). However, recent research suggests a second community of arbuscule-forming root-colonising fungi may be present: fine root endophytes (FRE). AMF are known to enhance P acquisition by plants under certain conditions, whereas very little is known about FRE and their impact on plant P status. We, therefore, grew plants at seven levels of P supply to determine and compare the external critical P requirements of two species of Ornithopus and two cultivars of Trifolium subterraneum when colonised predominantly by FRE (FRE-dominant treatment) or both FRE and AMF (mixed treatment). As expected from previous studies, the Ornithopus species had a lower critical P requirement than the T. subterraneum cultivars. However, for the Ornithopus species only, the FRE-dominant community had a significantly lower external critical P requirement (24–31 mg P kg−1 soil) than the mixed community (50–58 mg P kg−1 soil). Moreover, at low-P supply (≤15 mg applied P kg−1 soil), Ornithopus species in the FRE-dominant treatment had longer specific root length, smaller average root diameter, 45–128% greater total root length, and lower shoot and root P concentration than in the mixed treatment. We concluded that comparisons among experiments of root morphological traits and external critical P requirements can be affected by the presence of different communities of arbuscule-forming root-colonising fungi and that these effects may vary among plant species.

A Poly(A) Ribonuclease Controls the Cellotriose-Based Interaction between Piriformospora indica and Its Host Arabidopsis.

Piriformospora indica, an endophytic root-colonizing fungus, efficiently promotes plant growth and induces resistance to abiotic stress and biotic diseases. P. indica fungal cell wall extract induces cytoplasmic calcium elevation in host plant roots. Here, we show that cellotriose (CT) is an elicitor-active cell wall moiety released by P. indica into the medium. CT induces a mild defense-like response, including the production of reactive oxygen species, changes in membrane potential, and the expression of genes involved in growth regulation and root development. CT-based cytoplasmic calcium elevation in Arabidopsis (Arabidopsis thaliana) roots does not require the BAK1 coreceptor or the putative Ca2+ channels TPC1, GLR3.3, GLR2.4, and GLR2.5 and operates synergistically with the elicitor chitin. We identified an ethyl methanesulfonate-induced mutant (cytoplasmiccalcium elevation mutant) impaired in the response to CT and various other cellooligomers (n = 2-7), but not to chitooligomers (n = 4-8), in roots. The mutant contains a single nucleotide exchange in the gene encoding a poly(A) ribonuclease (AtPARN; At1g55870) that degrades the poly(A) tails of specific mRNAs. The wild-type PARN cDNA, expressed under the control of a 35S promoter, complements the mutant phenotype. Our identification of cellotriose as a novel chemical mediator casts light on the complex P. indica-plant mutualistic relationship.

Experimentation on Degradation of Petroleum in Contaminated Soils in the Root Zone of Maize (Zea Mays L.) Inoculated with Piriformospora Indica

ABSTRACTPlant-based methods such as rhizodegradation are very promising for the remediation of petroleum-contaminated soils. Associations of plants with endophytes can further enhance their phytoremediation potential. In this study, a rhizobox experiment was conducted to investigate whether inoculation with the root-colonizing fungus Piriformospora indica could further enhance the degradation of petroleum hydrocarbons in the root zone of maize (Zea mays L.). The rhizoboxes were subdivided into compartments in accordance with distance from the plants. After filling the boxes with soil from a petroleum-contaminated site, seedlings that had either been inoculated with P. indica or not were grown in the middle compartments of the rhizoboxes and grown for 64 days. A plant-free treatment was included for control. The presence of roots strongly increased the counts of total and petroleum-degrading soil bacteria, respiration, dehydrogenase activity, water-soluble phenols and petroleum degradation. All these effects were also found in the soil adjacent to the middle compartments of the rhizoboxes, but strongly decreased further away from it. Inoculation with P. indica further enhanced all the recorded parameters without changing the spatial pattern of the effects. Inoculated plants also produced around 40% more root and shoot biomass than noninoculated plants and had greener leaves. Together, the results indicate that the treatment effects on the recorded soil microbial and biochemical parameters including petroleum hydrocarbon degradation were primarily due to increased root exudation. Irrespectively of this, they show that maize can be used to accelerate the rhizodegradation of petroleum hydrocarbons in soil and that inoculation with P. indica can substantially enhance the phytoremediation performance of maize.

Effects of Organic and Chemical Agriculture Systems on Arbuscular Mycorrhizal Fungi and Green Tomato Production in Calakmul, Mexico

Organic agriculture is increasingly used as an alternative to conventional agriculture due to its positive impact on the health of ecosystems and agroecosystems. However, the outcome of organic agriculture in terms of the production of various crops remains uncertain due to the influence of many variables, rising questions about its advantages over conventional agriculture. This study assessed the impacts of organic agricultural system on arbuscular mycorrhizal (AM) fungi diversity in soil and green tomato (Physalis ixocarpa Brot. ex Horn) crop production. A field experiment was conducted using a random block design with five repetitions of the following treatments: a) Control (no fertilization, NF); b) Vermicompost use (OTV); c) OTV with vermicompost leaching (OTH); and d) Inorganic fertilization (CST). Throughout the crop cycle, soil samples were analyzed chemically, the relative growth rate (RGR) of the plants was measured, and the colonization and diversity of AM fungi were quantified in roots and soil; finally, above-ground, root biomass, and fruit production were measured. Organic fertilization (OTV, OTH) increased (p p > 0.05). It is concluded that organic agriculture management is essential to promote a greater AM fungi diversity and fungi root colonization. Plant-AM fungi interaction increases growth rates and it allows a similar tomato production compared with conventional agriculture.

Staining and microscopy of mycorrhizal fungal colonization in preserved ericoid plant roots

Staining and microscopy of mycorrhizal fungal colonization in preserved ericoid plant roots

Interactive effects of co-inoculation of Bradyrhizobium japonicum strains and mycorrhiza species on soybean growth and nutrient contents in plant

ABSTRACTThe main objective of this study was to investigate the effects of co-inoculation with different strains of Bradyrhizobium japonicum (i.e. Helinitro, Rizoking, and Nitragin) and arbuscular mycorrhizal fungi (AMF) species (i.e. Glomus fasciculatum, Glomus versiforme, Glomus intraradices, Glomus mosseae, and Glomus etunicatum) on soybean growth, fungal root colonization, and nutrient uptake of nitrogen (N), phosphorus (P), zinc (Zn), iron (Fe), and copper (Cu). Co-inoculation with various AMF species and rhizobia significantly (p<0.01) increased the soybean biomass production as compared to the non-inoculated controls. Furthermore, AMF colonization of roots of soybean plants increased by 79, 70.1, 67, 63, 57.5, and 50.1% in the presence of G. fasciculatum (GF), G. versiforme (GV), G. intraradices (GI), G. mosseae (GM), and G. etunicatum (GE), and Gmix (a mixed culture of fungi), respectively. Higher nutrient contents were observed in plants co-inoculated with Helinitro and GF. More insight into these results will enable optimization of the effective use of AM fungi in combination with their bacterial partners as a tool for increasing soybean yields in Iran; however, its general analytical framework could be applied to other parts of the world.

Mineral phosphorus fertilization modulates interactions between maize, rhizosphere yeasts and arbuscular mycorrhizal fungi

Yeasts are abundant and diverse in rhizosphere soil, but information about their importance in agroecosystems is limited. Here we examined maize plant growth response to inoculation with the native maize rhizosphere yeasts Cryptococcus flavus and Candida railenensis in non-mycorrhizal and mycorrhizal maize without and with mineral P fertilization as KH2PO4. Maize plant growth promotion and suppression was observed after inoculation with a native community of arbuscular mycorrhizal (AM) fungi with and without mineral P fertilization, respectively. Inoculation with Cr. flavus reduced shoot biomass of maize plants irrespective of the mycorrhizal status, but only without P fertilization. AM fungal root colonization was increased by C. railenensis without P fertilization, but was reduced by Cr. flavus in combination with mineral P fertilization. In conclusion, our results show that mineral P fertilization strongly modulates interactions between maize, rhizosphere yeasts and AM fungi, which are important to take into account when integrating such root associated microorganisms as biofertilizers in agroecosystems.

Long-term belowground effects of grassland management: the key role of liming.

The functioning of human-managed grassland ecosystems strongly depends on how common management practices will affect grassland "belowground compartment" including soil biogeochemistry and plant roots. Key questions remain about how animal grazing, liming (e.g., the addition of CaCO3 to soils), and nutrient fertilization might affect, in the long-term, soil nutrient cycling and multiple root traits. Here we focus on a mesotrophic grassland located in Berkshire, UK, where contrasting levels of rabbit grazing, liming, and different inorganic fertilizers have been applied since 1991. We ask how (1) soil nitrogen (N) availability and cycling, (2) total root mass, (3) root mass decomposition, and (4) arbuscular mycorrhizal fungal (AMF) root colonization might respond to 22years of very different management. We found that liming strongly affected total root mass, root decomposition, root AMF colonization as well as soil N availability and cycling and that these effects were mainly driven by liming-induced increases in soil pH. Increases in soil pH were associated with significant (1) decreases in root mass, (2) increases in root mass decomposability and in the mineralization of N in decomposing root detritus, and (3) increases in AMF infection. Soil pH was also significantly related to greater N availability (i.e., soil NO3 levels) and to lower δ15 N natural abundance, which suggests more efficient N uptake by plants in limed soils as we found in our study. The application of multiple nutrients (N, P, K, Mg) also reduced total root mass, while N-only fertilization was associated with greater AMF infection. Surprisingly the long-term impact of grazing was generally weak and not significant on most plant and soil parameters. Despite soil pH affecting most belowground variables, changes in soil pH were not associated with any change in soil C and N stocks. Because liming can improve nutrient cycling (and benefits soil pH and grass yields) without negatively affecting soil C sequestration, we suggest that regular liming applications may provide management solutions for increasing the long-term sustainability of permanent grassland.

Vegetative Composition, Arbuscular Mycorrhizal Fungi Root Colonization, and Biological Nitrogen Fixation Distinguish Organic and Conventional Perennial Forage Systems

Core Ideas Conventional and organic forage fields did not differ in total forage yield. Legume content was more than two times greater under organic management. Total forage biological nitrogen fixation was greater under organic management. Arbuscular mycorrhizal fungi root colonization was greater under organic management. Arbuscular mycorrhizal fungi root colonization was inversely related to soil test P concentrations. Low concentrations of Olsen soil test phosphorus (STP) on organic dairy farms in Canada have been reported, however, the resulting impact on crop productivity is unclear. This study evaluated mixed forage (alfalfa [Medicago sativa L.]/timothy [Phleum pratense L.]) productivity, nutrient uptake, and related soil biological and biochemical properties on organic and conventional dairy farms in Ontario, Canada. Despite a lower STP concentration, mean organic forage yield (8.0 Mg DM ha−1) did not significantly differ from conventional (9.5 Mg DM ha−1). The proportion of N derived from biological nitrogen fixation (BNF) in alfalfa did not differ by management system, however the total forage BNF‐N was greater in the organic fields due to a twofold increase in legume proportions. Alfalfa tissue P concentrations, above the suggested critical value of 2.0 g kg−1 in all systems, were positively correlated with STP (r = 0.82, P = &lt; 0.0001) and significantly greater in conventional (3.3 g kg−1) than organic (2.4 g kg−1). Mean arbuscular mycorrhizal fungi (AMF) root colonization of alfalfa was greater in organic systems (37 vs. 23%) and was negatively correlated with STP (P = 0.0006). Management systems did not differ in soil alkaline and acid phosphatase activity, or phytase‐labile P. It was concluded that legume‐based forages can produce acceptable yields at low STP concentrations (&lt;10 mg kg−1) and supports the importance of legumes, legume BNF, and biological processes linked to soil P cycling in maintaining productivity in organic dairy farming systems.