How does the Fungal Endophyte Neotyphodium coenophialum Affect Tall Fescue (Festuca arundinacea) Rhizodeposition and Soil Microorganisms?

The goal of our study was to investigate the impact of fungal endophytes in tall fescue (Festuca arundinacea) on rhizodeposition and in turn, the soil microbial community. Sand-based, aseptic microlysimeter units were constructed for the collection of rhizodeposit solutions for chemical analyses from the roots of endophyte-free (E−) and endophyte-infected (E+) tall fescue plants. E+ plants were infected with Neotyphodium coenophialum, the most common endophyte found in tall fescue. Rhizodeposit solutions collected over nine weeks from E+ grass contained more organic carbon and carbohydrates than E−. These solutions were allowed to percolate through columns of plant-free soils to assess the response of the soil microbial communities. Soils to which solutions from E+ grass were applied had significantly higher respiration rates than those receiving solutions from E− grass, suggesting that microbial activity was stimulated by changes in the rhizodeposits. Culture-based assays of the soil microbial community (plate counts and community-level physiological profiling) suggest that the basic structure of the microbial community was not affected by application of rhizodeposit solutions from E+ plants as compared to E−. Our results indicate that the presence of a fungal endophyte may enhance rhizodeposition by tall fescue and could consequently influence microbial mineralization processes in the soil. In grasslands where nutrients may be limiting, hosting a fungal endophyte has the potential to enhance plant nutrient supply indirectly via a stimulatory effect on the soil microbial biomass. Megan M. Van Hecke and Amy M. Treonis - Both authors contributed equally to this work.     

Endophytic fungi (Neotyphodium coenophialum) affect the growth and mineral uptake, transport and efficiency ratios in tall fescue (Festuca arundinacea)

Neotyphodium coenophialuminteracts mutualistically with its host grasses. Tall fescue (Festuca arundinacea Schreb.) plants infected by the fungal endophyte,Neotyphodium coenophialum(Morgan-Jones and Gams) Glenn, Bacon and Hanlin, often perform better than non-infected plants, especially in limited resource environments. However, there is a scarcity of information about endophyte-grass ecotypes interaction in Andisols of temperate regions. Clones of three tall fescue ecotypes (Fukaura, Koiwai and Showa) either infected with N. coenophialum (E+) or noninfected (E–) were grown in Andisols (Black Andisol: naturally low content of phosphorus, high in other nutrients; Red Andisol: naturally high content of phosphorus, low in other nutrients) for 133 days in a controlled environment. Cumulative shoot dry weight, daily regrowth rates (tiller number, plant height and shoot dry matter) after clippings and nutrient uptake, transport and efficiency ratios were measured. In Black Andisol, E+ plants had significantly higher cumulative shoot dry weight as well as daily regrowth rates than E– plants, while in Red Andisol the reverse was true. Among the ecotypes studied, Showa had the highest shoot growth. Significantly higher phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) uptake as well as transport were identified in E+ vs. E– plants grown in Black Andisol. With few exceptions, values for nutrient efficiency ratios were not significantly different between E+ and E– plants grown in both soils. Significant three-way interaction (endophyte × ecotype × soil) for cumulative shoot dry weight and regrowth rate revealed that the ecotype specific regrowth responses to endophyte infection were depended on soil nutrient conditions. Vegetative growth and nutrient acquisition in tall fescue varied with ecotype and were modified by abiotic (soil fertility status) as well as biotic (endophyte infection) factors.     

Leaf endophyte Neotyphodium coenophialum modifies mineral uptake in tall fescue

Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon and Hanlin, a fungal endophyte found primarily in shoots of tall fescue (Festuca arundinacea Shreb.), can modify rhizosphere activity in response to phosphorus (P) deficiency. In a controlled environment experiment, two cloned tall fescue genotypes (DN2 and DN4) free (E-) and infected (E+) with their naturally occurring endophyte strains were grown in nutrient solutions at low P (3.1 ppm) or high P (31 ppm) concentrations for 21 d. Endophyte infection increased root dry matter (DM) of DN4 by 21% but did not affect root DM of DN2. Under P deficiency, shoot and total DM were not affected by endophyte but relative growth rate was greater in E+ than E- plants. In high P nutrient solution, E+ plants produced 13% less (DN2) or 29% more (DN4) shoot DM than E- plants. Endophyte affected mineral concentrations in roots more than in shoots. Regardless of P concentration in nutrient solution, E+ DN2 accumulated more P, Ca, Zn and Cu but less K in roots than E- plants. When grown in high P nutrient solution, concentrations of Fe and B in roots of E+ DN2 plants were reduced compared with those of E- plants. Concentrations of P, Ca and Cu in roots of DN4 were less, but K was greater in E+ than E- plants. In shoots, E+ DN2 had greater concentrations of Fe and Cu than E- DN2, regardless of P concentration in nutrient solution. Genotype DN4 responded to endophyte infection by reducing B concentration in shoots. Nutrient uptake rates were affected by endophyte infection in plants grown in low P nutrient solution. A greater uptake rate of most nutrients and their transport to shoots was observed in DN2, but responses of DN4 were not consistent. Results suggest that endophyte may elicit different modes of tall fescue adaptation to P deficiency. This revised version was published online in June 2006 with corrections to the Cover Date.     

Low allelopathic potential of an invasive forage grass on native grassland plants: a cause for encouragement?

Tall fescue (Festuca arundinacea Schreb.), a highly competitive European grass that invades US grasslands, is reportedly allelopathic to many agronomic plants, but its ability to inhibit the germination or growth of native grassland plants is unknown. In three factorial glasshouse experiments, we tested the potential allelopathic effects of endophyte-infected (E+) and uninfected (E−) tall fescue on native grasses and forbs from Midwestern tallgrass prairies. Relative to a water control, at least one extract made from ground seed, or ground whole plant tissue of E+ or E− tall fescue reduced the germination of 10 of 11 species in petri dishes. In addition, the emergence of two native grasses in potting soil was lower when sown with E+ and E− tall fescue seedlings than when sown with seeds of conspecifics or tall fescue. However, when seeds of 13 prairie species were sown in sterilized, field-collected soil and given water or one of the four tall fescue extracts daily, seedling emergence was lower in one extract relative to water for only one species, and subsequent height growth did not differ among treatments for any species. We conclude that if tall fescue is allelopathic, its inhibitory effects on the germination and seedling growth of native prairie plants are limited, irrespective of endophyte infection. On the other hand, the apparent inability of these plants to detect tall fescue in field soil could hinder prairie restoration efforts if germination near this strong competitor confers fitness consequences. We propose that lack of chemical recognition may be common among resident and recently introduced non-indigenous plants because of temporally limited ecological interactions, and offer a view that challenges the existing allelopathy paradigm. Lastly, we suggest that tall fescue removal will have immediate benefits to the establishment of native grassland plants.     

Neotyphodium Coenophialum-Infected Tall Fescue and Its Potential Application in the Phytoremediation of Saline Soils

The growth response of endophyte-infected (EI) and endophyte-free (EF) tall fescue to salt stress was investigated under two growing systems (hydroponic and soil in pots). The hydroponic experiment showed that endophyte infection significantly increased tiller and leaf number, which led to an increase in the total biomass of the host grass. Endophyte infection enhanced Na accumulation in the host grass and improved Na transport from the roots to the shoots. With a 15 g l^?1 NaCl treatment, the phytoextraction efficiency of EI tall fescue was 2.34-fold higher than EF plants. When the plants were grown in saline soils, endophyte infection also significantly increased tiller number, shoot height and the total biomass of the host grass. Although EI tall fescue cannot accumulate Na to a level high enough for it to be termed a halophyte, the increased biomass production and stress tolerance suggested that endophyte / plant associations had the potential to be a model for endophyte-assisted phytoextraction in saline soils.     

Assessing short-term responses of prokaryotic communities in bulk and rhizosphere soils to tall fescue endophyte infection

In contrast to endophyte-free (E−) tall fescue, endophyte-infected (E+) tall fescue pastures appear to enhance soil carbon sequestration. A hypothetical mechanism that may account for the enhanced carbon sequestration is that the E+ tall fescue affects the soil microbial community or components of it that are involved in organic carbon turnover. A 60-week mesocosm study with a factorial arrangement of soil type, loamy sand (LS) and clay loam (CL), and E+ and E− tall fescue was conducted to determine if the soil microbial communities were affected by the presence of the endophyte. Bulk and rhizosphere soil samples were fixed in paraformaldehyde, and prepared for total direct microbial counts, and with a combination of one of a domain or subdivision fluorescent oligonucleotide probe for enumerating metabolically active Eubacteria, bacterial subdivisions, and Archaea. E+ tall fescue suppressed the archaeal and high G+C gram-positive bacterial communities of the bulk CL, the delta-proteobacterial community in the rhizosphere CL, and the Planctomycetes community of the rhizosphere LS. In the long-term, suppression of these microbial communities may be a factor in enhanced soil carbon sequestration associated with E+ tall fescue.     

Variation in Nitrogen Utilization in Acremonium coenophialum Isolates

Acremonium coenophialum, a fungal endosymbiont in tall fescue, is responsible for the production of alkaloid toxins. Animals grazing endophyte-infected tall fescue often show toxicosis. In marginal environments, the endophyte is important for long-term survival of tall fescue. Few differences in endophyte isolates from individual tall fescue plants have been reported. To aid development of a toxicosis-free tall fescue, it is important to identify differences in endophyte isolates. This report describes variation in nitrogen utilization in a defined culture medium by endophyte isolates from Kentucky-31 tall fescue. Overall, the best nitrogen sources for dry weight production of mycelium were proline and potassium nitrate. Thirty-four isolates grown on agar-solidified defined media with single nitrogen sources showed variation in nitrogen utilization. Fifty percent of the isolates were unable to utilize two or more amino acids. Manipulation of endophyte variation could lead to development of a toxicosis-free tall fescue cultivar.     

Endophytic fungus improves growth and metal uptake of Lolium arundinaceum Darbyshire ex. Schreb

The effect of endophyte infection on plant growth, cadmium (Cd) uptake, and Cd translocation was investigated using tall fescue (Lolium arundinaceum) grown in greenhouses in contaminated solution. Endophyte infection significantly increased tiller number and biomass of the host grass under both control and Cd-stress conditions. Endophyte infection not only enhanced Cd accumulation in tall fescue, but also improved Cd transport from the root to the shoot. Under 20 mg L(-1) Cd stress, the phytoextraction efficiency of endophyte-infected (EI) tall fescue was 2.41-fold higher than endophyte-free plants. Although the total Cd accumulation in EI tall fescue was insufficient for practical phytoextraction applications, the observed high biomass production and tolerance of stress from abiotic factors including heavy metals, gives endophyte/plant associations the potential to be a model for endophyte-assisted phytoremediation of metal-polluted soils.     

Effects of the endophyte Epichloë coenophiala on the root microbial community and growth performance of tall fescue in different saline-alkali soils

Soil salinization is detrimental to plant growth and yield in agroecosystems worldwide. Epichloë endophytes, a class of clavicipitaceous fungi, enhance the resistance of host plants to saline-alkali stress. This study explored the effects of the systemic fungal endophyte Epichloë coenophiala on the root microbial community and growth performance of tall fescue (Lolium arundinaceum) growing under different saline-alkali stress conditions. Structural equation modeling (SEM) was conducted to analyze the direct and indirect effects (mediated by root microbial community diversity and soil properties) of the endophyte on the growth of tall fescue under saline-alkali stress. The endophyte-infected plants produced higher shoot and root biomass compared to endophyte-free plants under saline-alkali stress (200 and 400 mM). Endophyte infection increased the fungal community diversity and altered its composition in the roots, decreasing the relative abundance of Ascomycota and increasing that of Glomeromycota. Furthermore, endophyte infection decreased the bacterial community diversity and the relative abundance of dominant Proteobacteria. SEM showed that endophyte infection increased the shoot and root biomass under saline-alkali stress (200 and 400 mM) by increasing the arbuscular mycorrhizal fungal diversity in the roots, and soil total nitrogen and phosphorus concentrations. Therefore, it is important to examine aboveground microbes as factors influencing plant growth in saline-alkali stress by affecting belowground microbes and soil chemical properties.     

Shoot specific fungal endophytes alter soil phosphorus (P) fractions and potential acid phosphatase activity but do not increase P uptake in tall fescue

Aims

An experiment was performed to test how different fungal endophyte strains influenced tall fescue’s ability to access P from four P sources varying in solubility.

Methods

Novel endophyte infected (AR542E+ or AR584E+), common toxic endophyte infected (CTE+), or endophyte-free (E-) tall fescues were grown for 90 days in acidic soils amended with 30 mg kg^?1 P of potassium dihydrogen phosphate (KH₂PO₄), iron phosphate (FePO₄), aluminum phosphate (AlPO₄), or tricalcium phosphate ((Ca₃(PO₄)₂), respectively.

Results

Phosphorus form strongly influenced plant biomass, P acquisition, agronomic P use efficiency, microbial communities, P fractions. P uptake and vegetative biomass were similar for plants grown with AlPO₄, Ca₃(PO₄)₂, and KH₂PO₄ but greater than in control and FePO₄ soils. Infection with AR542E+ resulted in significantly less shoot biomass than CTE+ and E- varieties; there was no influence of endophyte on root biomass. The biomarker for arbuscular mycorrhizal fungi (AM fungi, 16:1ω5c) was selected as an effective predictor of variations in P uptake and tall fescue biomass. Potential acid phosphatase activity was strongly influenced by endophyte x P form interaction.

Conclusions

Endophyte infection in tall fescue significantly affected the NaOH-extractable inorganic P fraction, but had little detectable influence on soil microbial community structure, root biomass, or P uptake.

     

不同浓度和形态磷处理下内生真菌感染对高羊茅的影响

以感染内生真菌(endophyte-infected,EI)和不感染内生真菌(endophyte-free,EF)的高羊茅(Festuca arundinacea Schreb.)为材料,在温室沙培条件下研究内生真菌对高羊茅适应缺磷及利用不同形态磷肥的影响。结果表明,1)缺磷条件下,高羊茅EI和EF植株生长差异不显著;正常供磷条件下,高羊茅EI植株拥有更多分蘖数和绿叶数。说明正常供磷条件下内生真菌改善了宿主高羊茅的生长。2)与水溶性磷相比,高羊茅根有机酸和酸性磷酸酶(acid phosphatase,APase)活性在难溶性磷条件下显著增加,而根总酚含量无显著变化。在水溶性磷条件下,高羊茅EI植株根总酚含量显著高于EF植株,此时EI植株比EF植株拥有更多分蘖数和绿叶数,说明在水溶性磷条件下内生真菌对宿主地上部生长具有一定贡献。在难溶性磷条件下,虽然高羊茅EI植株根总酚含量仍然高于EF植株,但同时EI植株根有机酸含量显著低于EF植株,因此内生真菌感染只是增大了宿主植物的根冠比,而对分蘖数和绿叶数等无显著影响,说明内生真菌对宿主利用难溶性磷贡献不大。可见,内生真菌对宿主植物的生长在水溶性磷条件下更有利。     

Are endophyte-mediated effects on herbivores conditional on soil nutrients?

Neotyphodium endophytes are assumed to have mutualistic relationship with their grass hosts, mainly resulting from mycotoxin production increasing plant resistance to herbivores by the fungus that subsists on the plant. To study importance of often ignored environmental effects on these associations, we performed a greenhouse experiment to examine the significance of endophyte infection and nutrient availability for bird-cherry aphid (Rhopalosiphum padi) performance on meadow fescue (Lolium pratense). Naturally endophyte-infected (E+), uninfected (E–), or manipulatively endophyte-free (ME–) half-sib families of meadow fescue were grown on two soil nutrient levels. Endophyte infection reduced aphid performance in general. However, to our knowledge, this is the first study to demonstrate experimentally that herbivore performance decreases on E+ host plants with increasing availability of nutrients in soils. Potential improvement in herbivore performance in high nutrient soils and decreased plant performance in low nutrient soils in ME– plants, compared to E– and E+ plants, suggests that loss of endophyte infection after long coevolutionary relationship may be critical to plant fitness.     

The Effects of Endophytes on Seed Production and Seed Predation of Tall Fescue and Meadow Fescue

Fungal endophytes of grasses are often included in agricultural management and in ecological studies of natural grass populations. In European agriculture and ecological studies, however, grass endophytes are largely ignored. In this study, we determined endophyte infection frequencies of 13 European cultivars and 49 wild tall fescue (Schedonorus phoenix) populations in Northern Europe. We then examined seed production and seed predation of endophyte-infected (E+) and endophyte-free (E?) tall fescue (in wild grass populations and in a field experiment) and meadow fescue (Schedonorus pratensis; in a field experiment only). Endophytes were detected in only one of the 13 cultivars. In contrast, >90% of wild tall fescue plants harbored endophytes in 45 wild populations but were absent in three inland populations in Estonia. In three wild tall fescue study sites, 17%, 22%, and 56% of the seeds were preyed upon by the cocksfoot moth. Endophyte infection did not affect seed mass of tall fescue in the field experiment. However, seed predation was lower in E+ than E? grasses in the two tall fescue populations with higher predation rates. For meadow fescue, the mean number of seeds from E+ plants was higher than E? plants, but E? and E+ seeds had equal rates of predation by the moth. Our results suggest that the effects of grass endophytes on seed production and cocksfoot moth seed predation vary considerably among grass species, and the effects may depend on herbivore pressure and other environmental conditions.     

Temporal and spatial patterns of soil water following wildfire-induced changes in plant communities in the Great Basin in Nevada,USA

Infection of tall fescue (Festuca arundinacea Schreb.) with its endemicNeotyphodium coenophialum-endophyte (Morgan-Jones and Gams) Glenn, Bacon and Hanlin appears to reduce copper (Cu) concentrations in forage and serum of grazing animals, contributing to a range of immune-related disorders. A greenhouse experiment was conducted to identify effects of novel endophyte strains on Cu acquisition by tall fescue (Festuca arundinacea Schreb.) varieties Grasslands Flecha and Jesup infected with a novel, non ergot producing endophyte strain AR542, and two perennial ryegrass (Lolium perenne L.) varieties Aries and Quartet infected with a novel, non lolitrem B producing strain AR1, and their noninfected (E−) forms. Individual endophyte/grass associations were cultivated in nutrient solutions at 1.0 (P+) and 0.0 mM (P−) phosphorus concentrations. The Cu²⁺-binding activity of extracellular root exudates, and concentrations of Cu and other heavy metals in roots and shoots were measured. Extracellular root exudates of AR542-infected vs. E− tall fescue had higher Cu²⁺-binding activity only in P− nutrient solution as shown by lower concentration of free Cu²⁺ (0.096 vs. 0.188 mmol Cu²⁺ g⁻¹ root DM, respectively). The Cu²⁺-binding activity by root exudates of perennial ryegrass was not affected by endophyte infection, but was higher (i.e., lower concentration of free Cu²⁺) in P− vs. P+ nutrient solution (0.068 vs. 0.114 mmol Cu²⁺ g⁻¹ root DM). In this hydroponic experiment, Cu concentrations in shoots of both grasses were not a function of Cu²⁺-binding activity and endophyte effects on heavy metal concentrations in shoots and roots were specific for each variety. The Cu²⁺-binding activity of extracellular root exudates may affect Cu accumulation by field-grown, endophyte-infected tall fescue under P-limiting growth conditions and warrants verification by more specific methods.     

Evidence for chemical changes on the root surface of tall fescue in response to infection with the fungal endophyte Neotyphodium coenophialum

Endophyte-infected (E+) tall fescue (Festuca arundinacea Schreb.) plants grown in phosphorus (P) deficient soils accumulate more P in roots and shoots than noninfected isolines. In a growth chamber experiment, four tall fescue genotypes DN2, DN4, DN7, and DN11, infected with their naturally occurring strains of Neotyphodium coenophialum (Morgan-Jones & Gams) Glenn, Bacon & Hanlin, and their noninfected isolines (E-), were cultivated in nutrient solution at two P levels: 31 ppm (P+) and 0 ppm (P-) for 4 wk. The Fe³⁺ reducing activity of extracellular reductants and intact root tissues, and total phenolic concentration in roots and shoots were measured. Endophyte infection significantly increased Fe³⁺ reducing activity rate of extracellular reductants (9.6 × 10^-3 mol Fe³⁺ h-1 g-1 root FW) when compared to E- plants (3.9 × 10^-3) and Fe³⁺ reduction rate of intact root tissues (6.16 and 4.48 mol Fe³⁺ h-1 g-1 root FW, respectively for E+ and E- plants). In response to P deficiency, Fe³⁺ reduction rate of intact root tissues increased in E+ plants by 375% when compared to E- plants, whereas no significant differences were observed when P was provided. Total phenolic concentration was 20% greater in shoots of E+ plants than in E- plants. In response to P deficiency, total phenolic concentration significantly increased in roots of E+ plants by 7%, and decreased in roots of E- plants by 10%. The most active Fe³⁺ reducing zones were located along branching of secondary and tertiary roots. The Fe³⁺ reducing activity on the root surface and total phenolic concentration in roots and shoots increased dramatically in response to endophyte infection, especially under P limiting conditions.Visiting Scientist sponsored by the Fulbright Program No. 21133     

Defoliation and Leaf Age Influence on Ergot Alkaloids in Tall Fescue

A controlled environment experiment was conducted to determinethe influence of defoliation on the regrowth and developmentof two tall fescue (Festuca arundinacea Schreb.) host-endophyte(Neotyphodium coenophialum Morgan-Jones and Gams (Glenn, Bacon,Price and Hanlincomb. nov. ) associations (DN2 and DN11), knownto differ in morphology and alkaloid production capacity. Defoliationtreatments included an uncut control, and clipping to a 5- or10-cm residue height. In a separate experiment, leaf age effectswere determined on an uncut plant canopy. Ergot alkaloid concentrationwas greatest in pseudostem and least in harvested leaf. Non-infectedplants were devoid of alkaloid. Alkaloid production (expressedas a function of dry matter) and yield were greater in uncutthan clipped plants, and were greater in DN11 than DN2 plants.Alkaloid production increased with increasing N concentrationin both associations; however, the rate of production was influencedby concentration of non-structural carbohydrate. Leaf age influencedleaf mass and alkaloid concentration and yield. Oldest leaves(>6 weeks after appearance) of DN2 and DN11 had the lowestconcentrations of ergot alkaloid, while leaves that were 2 to4 weeks old had the greatest alkaloid concentration and yield(alkaloid concentrationxleaf mass). Repeated defoliation reducedthe production of alkaloids, but did so as a function of non-structuralcarbohydrate. Our data suggest that alkaloid production canbe modified by defoliation as well as by host-endophyte association. Neotyphodium coenophialum ; Festuca arundinacea ; N; non-structural carbohydrate     

Measures of leaf-level water-use efficiency in drought stressed endophyte infected and non-infected tall fescue grasses

Neotyphodium coenophialum [Morgan-Jones and Gams], grows in the above-ground parts of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.]. It is an asexual fungus that is transmitted through seed of its host plant. This grass/endophyte association is enhanced by the protection of the host from herbivory and improved drought stress. We investigated how a decline in leaf-level stomatal conductance impacts the instantaneous water-use efficiency (WUE), in endophyte-infected (E+) versus non-infected (E?) Kentucky-31 tall fescue grasses grown in a controlled environmental chamber over a 10-week period. Grasses were cut at 6 weeks after germination and allowed to regrow under high and low soil moisture availability. One week after cutting, soil moisture was allowed to decline in the low water treatment for 2 weeks until severe stress was demonstrated through a decline in stomatal conductance to less than 100 mmol m^?2 s^?1. We found no differences in WUE between E+ and E? plants when water was not limiting while higher WUE was exhibited in E+ plants relative to E? plants under severe drought stress. The E? plants showed an 18-fold reduction in mean WUE and a 70-fold reduction in photosynthesis under drought stress, while there was no change in WUE and only a fourfold decline in photosynthesis between well-watered and drought stressed E+ plants at 21 days. While there were no differences in the rates of transpiration between E+ and E? plants under severe drought stress, differences in WUE can be attributed mainly to higher photosynthetic rates of E+ than E? plants. The difference in photosynthetic rates between E+ and E? plants under drought conditions could not be explained by differences in stomatal conductance and Rubisco (EC 4.1.1.39) activities.     

The effect ofAcremonium coenophialum on the growth and nematode infestation of tall fescue

The presence of the endophytic fungusAcremonium coenophialum Morgan-Jones et Gams in tall fescue (Festuca arundinacea Schreb.) induces toxicity when this grass is grazed by cattle; however, there is evidence that removing the endophyte reduces the stand vigor and longevity of fescue. A field trial was conducted to determine the effects of water supply and the presence of the endophytic fungus on plant growth, drought tolerance, and soil nematode populations in Kentucky 31 tall fescue. The design included two factors, level of endophyte infection (0 and 75%) and irrigation regime (none, low, and high). Where water deficits occurred, herbage yield and leaf area were lower, and percentage dead tissue and canopy minus air temperature were greater in endophyte-free compared with endophyte-infected fescue. Soil populations ofPratylenchus scribneri andTylenchorhynchus acutus were substantially higher in the noninfected than in the endophyte-infected plots. The endophyte apparently confers drought tolerance to Kentucky 31 tall fescue, and this effect may be at least partially mediated through enhanced resistance to soil-borne nematodes.Published with the approval of the Director of the Ark. Agric. Exp. Stn.     

Connecting plant–microbial interactions above and belowground: a fungal endophyte affects decomposition

Mutualisms can strongly affect the structure of communities, but their influence on ecosystem processes is not well resolved. Here we show that a plant–microbial mutualism affects the rate of leaf litter decomposition using the widespread interaction between tall fescue grass (Lolium arundinaceum) and the fungal endophyte Neotyphodium coenophialum. In grasses, fungal endophytes live symbiotically in the aboveground tissues, where the fungi gain protection and nutrients from their host and often protect host plants from biotic and abiotic stress. In a field experiment, decomposition rate depended on a complex interaction between the litter source (collected from endophyte-infected or endophyte-free plots), the decomposition microenvironment (endophyte-infected or endophyte-free plots), and the presence of mesoinvertebrates (manipulated by the mesh size of litter bags). Over all treatments, decomposition was slower for endophyte-infected fescue litter than for endophyte-free litter. When mesoinvertebrates were excluded using fine mesh and litter was placed in a microenvironment with the endophyte, the difference between endophyte-infected and endophyte-free litter was strongest. In the presence of mesoinvertebrates, endophyte-infected litter decomposed faster in microenvironments with the endophyte than in microenvironments lacking the endophyte, suggesting that plots differ in the detritivore assemblage. Indeed, the presence of the endophyte in plots shifted the composition of Collembola, with more Hypogastruridae in the presence of the endophyte and more Isotomidae in endophyte-free plots. In a separate outdoor pot experiment, we did not find strong effects of the litter source or the soil microbial/microinvertebrate community on decomposition, which may reflect differences between pot and field conditions or other differences in methodology. Our work is among the first to demonstrate an effect of plant–endophyte mutualisms on ecosystem processes under field conditions.     

Genotypic and chemotypic diversity of Neotyphodium endophytes in tall fescue from Greece

Epichloid endophytes provide protection from a variety of biotic and abiotic stresses for cool-season grasses, including tall fescue. A collection of 85 tall fescue lines from 15 locations in Greece, including both Continental and Mediterranean germplasm, was screened for the presence of native endophytes. A total of 37 endophyte-infected lines from 10 locations were identified, and the endophytes were classified into five distinct groups (G1 to G5) based on physical characteristics such as colony morphology, growth rate, and conidial morphology. These classifications were supported by phylogenetic analyses of housekeeping genes tefA and tubB, and the endophytes were further categorized as Neotyphodium coenophialum isolates (G1, G4, and G5) or Neotyphodium sp. FaTG-2 (Festuca arundinacea taxonomic group 2 isolates (G2 and G3). Analyses of the tall fescue matK chloroplast genes indicated a population-wide, host-specific association between N. coenophialum and Continental tall fescue and between FaTG-2 and Mediterranean tall fescue that was also reflected by differences in colonization of host tillers by the native endophytes. Genotypic analyses of alkaloid gene loci combined with chemotypic (chemical phenotype) profiles provided insight into the genetic basis of chemotype diversity. Variation in alkaloid gene content, specifically the presence and absence of genes, and copy number of gene clusters explained the alkaloid diversity observed in the endophyte-infected tall fescue, with one exception. The results from this study provide insight into endophyte germplasm diversity present in living tall fescue populations.