Insect oviposition preference between Epichloë‐symbiotic and Epichloë‐free grasses does not necessarily reflect larval performance

Variation in plant communities is likely to modulate the feeding and oviposition behavior of herbivorous insects, and plant‐associated microbes are largely ignored in this context. Here, we take into account that insects feeding on grasses commonly encounter systemic and vertically transmitted (via seeds) fungal Epichloë endophytes, which are regarded as defensive grass mutualists. Defensive mutualism is primarily attributable to alkaloids of fungal origin. To study the effects of Epichloë on insect behavior and performance, we selected wild tall fescue (Festuca arundinacea) and red fescue (Festuca rubra) as grass–endophyte models. The plants used either harbored the systemic endophyte (E+) or were endophyte‐free (E?). As a model herbivore, we selected the Coenonympha hero butterfly feeding on grasses as larvae. We examined both oviposition and feeding preferences of the herbivore as well as larval performance in relation to the presence of Epichloë endophytes in the plants. Our findings did not clearly support the female's oviposition preference to reflect the performance of her offspring. First, the preference responses depended greatly on the grass–endophyte symbiotum. In F. arundinacea, C. hero females preferred E+ individuals in oviposition‐choice tests, whereas in F. rubra, the endophytes may decrease exploitation, as both C. hero adults and larvae preferred E? grasses. Second, the endophytes had no effect on larval performance. Overall, F. arundinacea was an inferior host for C. hero larvae. However, the attraction of C. hero females to E+ may not be maladaptive if these plants constitute a favorable oviposition substrate for reasons other than the plants' nutritional quality. For example, rougher surface of E+ plant may physically facilitate the attachment of eggs, or the plants offer greater protection from natural enemies. Our results highlight the importance of considering the preference of herbivorous insects in studies involving the endophyte‐symbiotic grasses as host plants.     

Endophyte species influence the biomass production of the native grass Achnatherum sibiricum (L.) Keng under high nitrogen availability

Research on the interaction of endophytes and native grasses normally takes infection status into account, but less often considers the species of endophyte involved in the interaction. Here, we examined the effect of endophyte infection, endophyte species, nitrogen availability, and plant maternal genotype on the performance of a wild grass, Achnatherum sibiricum. Six different Epichloë‐infected maternal lines of A. sibiricum were used in the study; three lines harbored Epichloë gansuensis (Eg), while three lines harbored Epichloë sibirica (Es). These endophytes are vertically transmitted, while Eg also occasionally produces stromata on host tillers. We experimentally removed the endophyte from some ramets of the six lines, with the infected (E+) and uninfected (E?) plants grown under varying levels of nitrogen availability. Eg hosts produced more aboveground biomass than Es hosts only under high nitrogen supply. Endophyte species did not show any influence on the maximum net photosynthetic rate (P_max), photosynthetic nitrogen use efficiency, or total phenolics of A. sibiricum under all nitrogen conditions. However, the plant maternal genotype did influence the P_max and shoot biomass of A. sibiricum. Our results show that endophyte species influenced the shoot biomass of A. sibiricum, and this effect was dependent on nitrogen supply. As with most coevolutionary interactions, A. sibiricum that harbored Eg and Es may show pronounced geographic variation in natural habitats with increased nitrogen deposition. In addition, stroma‐bearing endophyte (Eg) provides positive effects (e.g., higher biomass production) to A. sibiricum plants during the vegetative growth stage.     

Direct and indirect effects of the fungal endophyte <Emphasis Type="Italic">Epichloë uncinatum</Emphasis> on litter decomposition of the host grass, <Emphasis Type="Italic">Schedonorus pratensis</Emphasis>

Microbial plant symbionts have been suggested to mediate plant-soil feedback and affect ecosystem functions. Systemic Epichloë fungal endophytes of grasses are found to mediate litter decomposition. These effects are often linked to alkaloids produced by Epichloë species, which are hypothesized to negatively affect decomposers. Although endophytes have been found to affect plant community and soil biota, direct (through litter quality) and indirect (through the environment) effects of fungal endophytes on litter decomposition have been scarcely scrutinized. We placed litterbags with endophyte-symbiotic (E+) and non-symbiotic (E?) Schedonorus pratensis plant litter in plots dominated by E+ or E? plants of the same species, and followed the dynamics of mass losses over time. We predicted the endophyte would hinder decomposition through changes in litter quality and that both types of litter would decompose faster in home environments. E+ litter decomposed faster in both environments. The mean difference between decomposition rate of E+ and E? litter tended to be higher in E? plots. Nitrogen and phosphorus, two elements usually associated with high decomposition rates, were significantly lower in E+ litter. We also detected a higher proportion of C in the cellulose form in E+ litter. Contrary to the general assumption, we found that symbiosis with Epichloë fungal endophytes can be associated with higher decomposition of plant litter. Since direct effects of Epichloë fungi were still stronger than indirect effects, it is suggested that besides the alkaloids, other changes in plant biomass would explain in a context-dependent manner, the endophyte effects on the litter decomposition.     

Epichloë endophyte affects the root colonization pattern of belowground symbionts in a wild grass

Plants host multiple symbionts that interact with each other affecting plant performance and regulating their establishment. Here, we analyzed how the association with Epichloë endophytes affects belowground colonization by Dark Septate Endophytes (DSE) and arbuscular mycorrhizal fungi (AMF) in the grass Bromus auleticus. Epichloë-symbiotic (E+) and Epichloë-non symbiotic (E−) plants were sampled from a long-term experimental plot and colonization structures were analyzed in the roots. We also examined the influence of Epichloë exudates on the in vitro growth of DSE Microdochium bolleyi isolated from roots. Epichloë symbiosis increased AMF colonization, although differences were not significant. Despite the lack of differences in total DSE colonization, in concordance with in vitro findings, a higher significant abundance of microsclerotia was observed in E+ plants. A negative correlation between total mycorrhizal and DSE was found. Our findings show a more uniform root colonization pattern in E+ plants, suggesting a root symbiosis modulating role.     

A foliar endophyte increases the diversity of phosphorus-solubilizing rhizospheric fungi and mycorrhizal colonization in the wild grass Bromus auleticus

Asexual Epichloë endophytes establish mutualistic symbioses with grasses, improve fitness of their hosts and modify the surrounding environment. To test the hypothesis that this symbiotic association increases the abundance and diversity of phosphate-solubilizing fungi (PSF), a pot experiment was conducted combining two endophytic statuses: Epichloë-infected (E+) and non-infected (E−) Bromus auleticus plants, and two soil types collected from agricultural (A) and non-agricultural (NA) fields. Soil fungi were isolated at the beginning of the experiment and 12 months after the introduction of B. auleticus, and tested for their inorganic P (Pi)-solubilizing capability. Arbuscular mycorrhizal colonization in B. auleticus roots of E+ and E− plants was also analyzed. PSF abundance was affected by the endophytic status and by the type of soil; the highest value was detected in the E−NA treatment, followed by the E+A treatment. PSF diversity was higher in NA than in A soils and higher in soils treated with E+ than in those treated with E−. Arbuscular mycorrhizal fungi colonization was higher in E+ plants. We hypothesize that the positive association between Epichloë endophytes and mycorrhizal fungi with an increase in the PSF diversity would generate an increase in the phosphorus (P) available to plants.     

Variable effects of endophytic fungus on seedling establishment of fine fescues

Seedborne systemic endophytic fungi of grasses are thought to be plant mutualists, because they have been shown to improve their host’s resistance against biotic and abiotic stresses. The interactions in plant–endophyte associations vary from mutualistic to parasitic with environmental conditions and the genotypes of interacting species. The possible pros and cons of endophytic fungi are expected to be most evident during the seedling establishment, where host fitness is most directly affected. If this holds true, endophytes may play a focal role in local adaptation of hosts to different environments. We examined if endophyte-infected and uninfected seeds and seedlings of two native grass species, Festuca rubra and F. ovina, differ in seed germination and seedling growth rates under greenhouse conditions. The germination of F. rubra seeds was also studied in the field. This is the first time that the effects of Epichloë endophyte on seedling establishment of fine fescues from natural populations have been experimentally evaluated. Mother plant (seed family) had a marked effect on many response variables in both grass species. Length and mean biomass of tillers of endophyte-infected (E+) F. ovina seedlings were lower, but root:shoot ratios were higher than in endophyte-free (E?) seedlings. In F. rubra, the effects of the endophyte were dependent on the habitat where the seeds were collected. The E+ seeds from river banks germinated faster than E+ seeds from meadows, and E+ seedlings from the river banks produced fewer but taller and heavier tillers than the other seedlings. Our data suggest that the effects of the endophyte infection on the seedling stage of fine fescues are dependent the species of grass, host genetic background and mother plant habitat. The germination strategy and growth form of E+ red fescue seedlings from river banks may be beneficial to surviving in the harsh conditions of that habitat.     

Fungal endophyte infection changes growth attributes in Lolium multiflorum Lam

Abstract Lolium multiflorum is a successful invader of postagricultural succession in the Inland Pampa grasslands in Argentina, becoming a dominant species in the plant community. Individual plants of this annual species are naturally highly infected with fungal endophytes (Neotyphodium sp.) from early successional stages. We assessed the effect of Neotyphodium infection on the biology of L. multiflorum. We evaluated growth attributes between endophyte infected (E+) and uninfected (E–) plants under non‐competitive conditions during the normal growing season. E+ plants produced significantly more vegetative tillers and allocated more biomass to roots and seeds. Although seed germination rates were greater in endophyte free plants, the rate of emergence and the final proportion of emerged seedlings were similar between the biotypes. The greater production of vegetative tillers, and the greater resource allocation to roots and seeds are likely to confer an ecological advantage to E+ plants, thus enabling their dominance over the E– individuals in natural grasslands.     

Infection with the fungal endophyte Epichloë festucae may alter the allelopathic potential of red fescue

Red fescue (Festuca rubra) is a perennial grass used as both forage and turfgrass. Asymptomatic plants of this species are systemically infected by the fungal endophyte Epichloë festucae, which has a beneficial effect on the infected plants. The aim of this study was to determine the effect of the endophyte Epichloë festucae on the allelopathic potential of F. rubra against four associated pasture species that are also considered as weeds in lawns, Trifolium pratense, Trifolium repens, Lotus corniculatus and Plantago lanceolata. Two experiments were designed to evaluate the allelopathic effect of extracts from the roots and leaves of endophyte‐infected (E+) and non‐infected (E?) plants on the germination and seedling growth of the four target species. Regardless of the endophyte status of the host plant, leaf extracts elicited a stronger reduction in germination and seedling growth than root extracts. Extracts from E+ plants reduced the speed of germination index of Trifolium spp. to a greater extent than those from E? plants. Radicle length of the target species was the parameter most affected by the presence of the endophyte in F. rubra. Root extracts from E+ plants had a greater inhibitory effect on the radicle growth of the target species than did root extracts from E? plants. A greater concentration in total phenolic compounds was found in the roots of E+ plants than of E?; however, this difference was not observed in the leaves. Thus, the allelopathic potential of F. rubra is altered in infected plants.     

Root discoloration and shoot symptoms in silver birch after Phytophthora infection in vitro

• There are no records of established plant pathogenic Phytophthora species in Finnish forests, but they are likely in the future. Therefore, the effects of Phytophthora inoculations on young, ca. 2‐month‐old silver birch (Betula pendula) seedling roots and shoots were investigated.
• Visual inspection of dark discoloration, direct PCR and re‐isolation, and detailed root morphology analyses were used to evaluate the effects of Phytophthora inoculation on roots. Symptoms in leaves and stems were also recorded.
• Phytophthora was successfully re‐isolated from 67% of the surface‐sterilized roots of inoculated seedlings, but not from the non‐inoculated control seedlings. Dark discolorations were found more often in the root segments of inoculated seedlings than in control seedlings. In the Phytophthora‐treated seedlings, discoloured root segments were usually linked and found primarily in the main root or lateral roots attached to it, whereas in the control seedlings a few single discoloured root segments were scattered throughout the root systems. The number of root segments was lower in the inoculated than in the control seedlings, indicating root loss after Phytophthora inoculation. In the shoots of inoculated birches, leaf and shoot wilting was observed.
• The appearance of wilting in shoots without visible dark discoloration in the base of stems indicated that symptoms originated from roots inoculated with Phytophthora.

     

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.     

Molecular evidence for host-adapted races of the fungal endophyte Epichloë bromicola after presumed host shifts

Abstract.— Host shifts of plant‐feeding insects and parasites promote adaptational changes that may result in the formation of host races, an assumed intermediate stage in sympatric speciation. Here, we report on genetically differentiated and host‐adapted races of the fungal endophyte Epichloë bromicola, which presumably emerged after a shift from the grass Bromus erectus to other Bromus hosts. Fungi of the genus Epichloë (Ascomycota) and related anamorphs of Neotyphodium are widespread endophytes of cool‐season grasses. Sexually reproducing strains sterilize the host by formation of external fruiting structures (stromata), whereas asexual strains are asymptomatic and transmitted via seeds. In E. bromicola, strains infecting B. erectus are sexual, and strains from two woodland species, B. benekenii and B. ramosus, are asexual and seed transmitted. Analyses of amplified fragment length polymorphism fingerprinting and of intron sequences of the tub2 and tef1 genes of 26 isolates from the three Bromus hosts collected at natural sites in Switzerland and nearby France demonstrated that isolates are genetically differentiated according to their host, indicating that E. bromicola does not form a single, randomly mating population. Phylogenetic analyses of sequence data did not unambiguously resolve the exact origin of asexual E. bromicola strains, but it is likely they arose from within sexual populations on B. erectus. Incongruence of trees derived from different genes may have resulted from recombination at some time in the recent history of host strains. Reciprocal inoculations of host plant seedlings showed that asexual isolates from B. benekenii and B. ramosus were incapable of infecting B. erectus, whereas the sexual isolates from B. erectus retained the assumed ancestral trait of broad compatibility with Bromus host seedlings. Because all isolates were interfertile in experimental crosses, asexual strains may not be considered independent biological species. We suggest that isolates infecting B. benekenii and B. ramosus represent long‐standing host races or incipient species that emerged after host shifts and that may evolve through host‐mediated reproductive isolation toward independent species.     

An ecological framework for understanding the roles of Epichloë endophytes on plant defenses against fungal diseases

Plants harbor a wide diversity of microorganisms in their tissues. Some of them have a long co-evolutionary history with their hosts, likely playing a pivotal role in regulating the plant interaction with other microbes such as pathogens. Some cool-season grasses are symbiotic with Epichloë fungal endophytes that grow symptomless and systemically in aboveground tissues. Among the many benefits that have been ascribed to endophytes, their role in mediating plant interactions with pathogens has been scarcely developed. Here, we explored the effects of Epichloë fungal endophytes on the interaction of host grasses with fungal pathogens. We made a meta-analysis that covered a total of 18 host grass species, 11 fungal endophyte species, and 22 fungal pathogen species. We observed endophyte-mediated negative effects on pathogens in vitro and in planta. Endophyte negative effects on pathogens were apparent not only in laboratory but also in greenhouse and field experiments. Epichloë fungal endophytes had negative effects on pathogen growth and spores' germination. On living plants, endophytes reduced both severity and incidence of the disease as well as colonization and subsequent infection of seeds. Symbiosis with endophytes showed an inhibitory effect on debilitator and killer pathogens, but not on castrators, and this effect did not differ among biotrophic or necrotrophic lifestyles. We found that this protection can be direct through the production of fungistatic compounds, the competition for a common resource, or the induction of plant defenses, and indirect associated with endophyte-generated changes in the abiotic or the biotic environment. Several mechanisms operate simultaneously and contribute differentially to the reduction of disease within grass populations.     

<Emphasis Type="Italic">Epichloë</Emphasis> exudates promote in vitro and in vivo arbuscular mycorrhizal fungi development and plant growth

Background and aims

We studied, through exudates employment, the effect of Epichloë (endophytic fungi), both independently and in association with Bromus auleticus (grass), on arbuscular mycorrhizal fungi (AMF) colonization, host and neighbouring plants biomass production and soil changes.

Methods

Through in vitro and greenhouse experiments, Epichloë endophytes effect on AMF development was evaluated. In vitro studies of exudates effect on Gigaspora rosea and Rhizophagus intraradices were performed using root or endophyte exudates. A 6-month greenhouse experiment was conducted to determine Bromus auleticus endophytic status effect and endophyte exudates role in biomass production, neighbouring plants mycorrhizal colonization and soil properties.

Results

Endophyte exudates and E+ plant root exudates promoted in vitro AMF development in the pre-infective stage of G. rosea and in carrot root culture mycelium of R. intraradices in a dose-response relationship, while control media and E- plants exudates had no effect. R. intraradices colonization and plant growth was clearly increased by endophytes and their exudates.

Conclusions

This is the first work evidencing the direct effect of Epichloë endophytes and infected plants root exudates on AMF extramatrical development. While higher levels of AMF colonization were observed in E+ plants, no clear effect was detected in neighbouring plants colonization, plant biomass or soil properties.

     

Population studies of native grass-endophyte symbioses provide clues for the roles of host jumps and hybridization in driving their evolution

Fungal endophytes in the genera Epichloë and Neotyphodium, collectively termed the epichloae, have fascinated biologists for decades. These intriguing fungi, also referred to as ‘class 1 or clavicipitaceous endophytes’, spend the large majority, or even their entire life cycle, within the tissues of their cool‐season grass hosts without eliciting any symptoms of infection. While all epichloae reside within the intercellular spaces of aboveground vegetative grass tissues, the species at the symbiotic extreme are known as Neotyphodium, and the intimacy of their interaction extends to the reproductive (flowering) stage. At this point, fungal filaments (hyphae) nondestructively invade the developing ovaries of their host and are incorporated into perfectly viable, healthy seeds. Thus, these endophytes live solely within the tissues of their host plants and are transmitted maternally from generation to generation. A second life history characteristic of interest is that while all Epichloë and some Neotyphodium species are haploid, a great many of the strictly seed‐transmitted Neotyphodium spp. are interspecific hybrids. This phenomenon may be critical for the success of these symbioses over longer spans of evolutionary time and will be discussed in greater detail below. A third characteristic, and one of the primary reasons these grass endophytes have received so much attention over the last three decades, is the strong mutualistic nature these relationships often exhibit. In exchange for photosynthetically derived carbon, the endophytes protect their cool‐season grass hosts from grazing herbivores and a variety of abiotic stresses. It has been hypothesized that these three biological phenomena are related ( Schardl & Craven 2003 ), perhaps with the former two driving the third, and it is here that the recent article in Molecular Ecology entitled ‘Genetic diversity in epichloid endophytes of Hordelymus europaeus suggests repeated host jumps and interspecific hybridizations’, by Oberhofer & Leuchtmann (2012) , provides critical clues to linking these traits together. While the large majority of studies have focused on documenting the ever‐increasing list of mutualistic qualities attributed to these fungi, very few have taken an exhaustive population‐level approach to document plant and endophyte genotypes within a naturally occurring system ( Faeth et al. 2010 ; Jani et al. 2010 ; Tintjer & Rudgers 2006 ). Such information is crucial to more fully elucidate the factors shaping grass‐endophyte symbioses and those often driving these relationships to mutualistic extremes.     

Comment arising from a paper by Wittmer et al.: hypothesis testing for top-down and bottom-up effects in woodland caribou population dynamics

Asexual fungal endophytes, which do not produce reproductive structures, spread in host populations only vertically via the propagules of their hosts. With such a close relationship between the fitness of the asexual endophyte and that of the host, the relationship is traditionally thought to be mutualistic. Here we present data showing that the positive effect of asexual endophytes may concern only a short period of the host’s life and that its lifetime reproductive success may be reduced. We followed 180 individuals of a perennial grass, Puccinellia distans, for the first 3 years of their growth both in the field and in a common garden experiment. In the first 2 years, infected individuals produced more generative shoots with longer inflorescences. Three-year-old individuals produced significantly fewer generative shoots with shorter inflorescences when infected with the fungus Epichloë typhina. Moreover, the dry mass of above- and belowground parts after three seasons was significantly lower in infected individuals. We suggest that if the endophyte retains control over plant reproduction and if shorter generation time is more crucial for the fungus than for the perennial host, then the fungus should stimulate plant reproduction early in life even though infection incurs a future cost. This reasoning suggests that discovering an endophyte’s beneficial effect on its perennial host in one season provides insufficient grounds for concluding that a mutualistic relationship exists.     

Rock-degrading endophytic bacteria in cacti

A plant–bacterium association of the cardon cactus (Pachycereus pringlei) and endophytic bacteria promotes establishment of seedlings and growth on igneous rocks without soil. These bacteria weather several rock types and minerals, unbind significant amounts of useful minerals for plants from the rocks, fix in vitro N₂, produce volatile and non-volatile organic acids, and reduce rock particle size to form mineral soil. This study revealed the presence of large populations of culturable endophytic bacteria inside the seeds extracted from wild plants, from seeds extracted from the guano of bats feeding on cactus fruit, in seedlings growing from these seeds, in the pulp of fruit, and in small, mature wild plants, and are comparable in size to populations of endophytic populations in some agricultural crops. The dominant culturable endophytes were isolates of the genera Bacillus spp., Klebsiella spp., Staphylococcus spp., and Pseudomonas spp. Based on partial sequencing of the 16s rRNA gene, the isolated strains had low similarity to known strains in these genera. However, these strains have higher molecular similarity among endophytes obtained from seeds, endophytes from roots, and some bacterial strains from the rhizoplane. Seedlings developed from seeds with endophytes contain the similar species of endophytes in their shoots, possibly derived from the seeds. This study shows the involvement of endophytic bacteria in rock weathering by cacti in a hot, subtropical desert and their possible contribution to primary colonization of barren rock. This study proposes that cacti capable of acquiring diverse populations of endophytes may give them an evolutionary advantage to gain a foothold on highly uncompromising terrain.     

Effects of the Epichloë fungal endophyte symbiosis with Schedonorus pratensis on host grass invasiveness

Initial studies of grass–endophyte mutualisms using Schedonorus arundinaceus cultivar Kentucky‐31 infected with the vertically transmitted endophyte Epichloë coenophiala found strong, positive endophyte effects on host‐grass invasion success. However, more recent work using different cultivars of S. arundinaceus has cast doubt on the ubiquity of this effect, at least as it pertains to S. arundinaceus–E. coenophiala. We investigated the generality of previous work on vertically transmitted Epichloë‐associated grass invasiveness by studying a pair of very closely related species: S. pratensis and E. uncinata. Seven cultivars of S. pratensis and two cultivars of S. arundinaceus that were developed with high‐ or low‐endophyte infection rate were broadcast seeded into 2 × 2‐m plots in a tilled, old‐field grassland community in a completely randomized block design. Schedonorus abundance, endophyte infection rate, and co‐occurring vegetation were sampled 3, 4, 5, and 6 years after establishment, and the aboveground invertebrate community was sampled in S. pratensis plots 3 and 4 years after establishment. Endophyte infection did not enable the host grass to achieve high abundance in the plant community. Contrary to expectations, high‐endophyte S. pratensis increased plant richness relative to low‐endophyte cultivars. However, as expected, high‐endophyte S. pratensis marginally decreased invertebrate taxon richness. Endophyte effects on vegetation and invertebrate community composition were inconsistent among cultivars and were weaker than temporal effects. The effect of the grass–Epichloë symbiosis on diversity is not generalizable, but rather specific to species, cultivar, infection, and potentially site. Examining grass–endophyte systems using multiple cultivars and species replicated among sites will be important to determine the range of conditions in which endophyte associations benefit host grass performance and have subsequent effects on co‐occurring biotic communities.     

Plant–fungal symbiosis affects litter decomposition during primary succession

Microbial symbionts of plants can affect decomposition by altering the quality or quantity of host plant tissue (substrate) or the micro‐environment where decomposition occurs (conditioning). In C₃ grasses, foliar fungal endophytes (Clavicipitaceae) can increase plant resistance to drought and/or produce alkaloids that reduce herbivory – effects that may also influence host litter composition and subsequent litter decomposition. We studied the effect of the endophyte Epichloë sp. on litter decomposition in the Great Lakes dunes (USA) using a reciprocal design altering endophyte presence/absence in both American beachgrass Ammophila breviligulata substrate (litter bags) and its conditioning of the decomposition microenvironment. Symbiont treatments were crossed with rain‐out shelters that altered growing season precipitation. The first year of decomposition, senesced leaf substrate from A. breviligulata with Epichloë decomposed 21% faster than endophyte‐free substrate. By the third year, conditioning by live symbiotic plants reduced cumulative decomposition by 33% compared to plots planted with endophyte‐free plants. Of the traits we examined – litter quantity, C:N ratio, mineral composition, fungal colonization, and carbon chemistry – increased litter quantity via greater tiller production was the primary trait shift associated with endophyte symbiosis. Epichloë in A. breviligulata litter also altered litter nitrogen decomposition dynamics, as evidenced by lower nitrogen and protein content in decomposed tissue from plants that hosted the endophyte. Differences in initial litter quality and subsequent colonization by saprotrophic fungi were ruled out as key drivers. Altered precipitation had negligible effects on decomposing processes in the dunes. Grass–Epichloë symbiosis altered nutrient cycling through increasing the rate of litter decomposition when present in the litter and through reducing litter decomposition by conditioning the decomposition microenvironment. Epichloë are widespread symbionts of grasses. Thus, their effects on decomposition could be an important, but often overlooked, driver of nutrient cycling in grass‐dominated ecosystems.     

Consequences of simultaneous interactions of fungal endophytes and arbuscular mycorrhizal fungi with a shared host grass

Plants simultaneously associate with multiple microbial symbionts throughout their lifetimes. To address the question of whether the effects of simultaneous symbionts are contingent on the specific identities, we conducted a greenhouse experiment manipulating the presence and identities of arbuscular mycorrhizal fungi (AMF) and fungal endophytes on the shared host grass Elymus hystrix. Each plant host was inoculated with one of two AMF species having varying effects on host growth, or a sterile soil control. Further, we used naturally occurring endophyte‐infected (E+) and uninfected (E–) individuals from two populations of the endophyte Epichloë elymi that varied in their interaction with E. hystrix. We then measured responses of plants, AMF, and fungal endophytes. Overall, we found that the combined effects of AMF and fungal endophytes on plant growth were additive, reflecting the mutualistic quality of each symbiont independently interacting with host plants. However, fungal endophyte infection differentially altered hyphal colonization of the two AMF species and the identity of the coinfecting AMF species affected fungal endophyte fitness traits. The results of this study demonstrate that the outcome of interspecific symbiotic interactions varies with partner identity such that the effects of simultaneous symbioses can not be generalized.     

An endophytic fungus reduces herbivory in its recently colonised grass host: a food-choice experiment on common voles, weeping alkaligrass and Epichlo? typhina

The interactions of endophytes with plants are believed to evolve over time from parasitic to mutualistic, and in the seed-transmitted fungal endophytes, these interactions are conventionally treated as mutualistic. The weeping alkaligrass Puccinellia distans has recently dispersed to new habitats in Europe, where it was colonised by the seed-transmitted fungus Epichlo? typhina. The E. typhina-infected weeping alkaligrass has a fertility advantage over -uninfected plants, but this advantage is held only over shorter time scales. We assess the antiherbivore value of E. typhina in mature weeping alkaligrass against common voles Microtus arvalis, a herbivore naturally co-occurring with weeping alkaligrass. In two consecutive food-choice tests conducted in a lab, we examined feeding by na?ve voles on E. typhina-infected (E+) and -uninfected grass (E?) originating from Central Europe. In the first test, all voles consumed comparable amounts of E+ biomass and E? biomass. In the subsequent test, the voles reduced their feeding rates by 57?%, but E+ food was avoided twice as frequently as E? food (75 vs. 33?% reduction). This result suggests that toxins produced by E. typhina repel herbivores soon after the first contact. We show that in addition to its direct fitness consequences, endophyte-mediated resistance to herbivory increases the fertility advantage of E. typhina-infected weeping alkaligrass. This effect can increase the ability of weeping alkaligrass to invade habitats with intense herbivory.