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     

Influence of phosphorus on the growth and ergot alkaloid content of Neotyphodium coenophialum-infected tall fescue (Festuca arundinacea Schreb.)

Tall fescue (Festuca arundinacea Schreb.) plants infected by the fungal endophyte Neotyphodium coenophialum (Morgan-Jones & Gams) (Glenn et al., 1996) often perform better than noninfected plants, especially in marginal resource environments. There is a lack of information about endophyte related effects on the rhizosphere of grasses. In a greenhouse experiment, four endophyte-infected (E+) tall fescue clones (DN2, DN4, DN7, DN11) and their endophyte-free (E–) forms were grown in limed (pH 6.3) Porter soil (low fertility, acidic, high aluminum and low phosphorus content, coarse-loamy mixed mesic Umbric Dystrochrept) at three soil P levels (17, 50, and 96 mg P kg^-1 soil) for five months. Excluding the genotype effect, endophyte infection significantly increased cumulative herbage DM yield by 8% at 17 mg P kg^-1 soil but reduced cumulative herbage DM yield by 12% at 96 mg P kg^-1 soil. With increased P availability in the soil, shoot and root DM, and root/shoot ratio in E+ plants were significantly less when compared to E– plants. Endophyte infection increased specific root length at 17 and 50 mg P kg^-1soil. At soil P level of 17 mg P kg^-1soil, E+ plants had significantly higher P concentrations both in roots and shoots. Similar relationships were found for Mg and Ca. E+ plants had significantly higher Zn, Fe, and Al concentration in roots, and lower Mn and Al concentration in shoots when compared to E– plants. Ergot alkaloid concentration and content in shoot of E+ plants increased with increasing P availability in the soil from 17 to 50 mg P kg^-1 but declined again at 96 mg P kg^-1 soil. Ergot alkaloid accumulation in roots increased linearly with P availability in the soil. Results suggest that endophyte infection affects uptake of phosphorus and other mineral nutrients and may benefit tall fescue grown on P-deficient soils. Phosphorus seems also to be involved in ergot alkaloid accumulation in endophyte-infected tall fescue.     

Effects of elevated CO2, nitrogen and fungal endophyte-infection on tall fescue: growth, photosynthesis, chemical composition and digestibility

Rising global carbon dioxide levels may lead to profound changes in plant composition, regardless of the degree of global warming that may result from the accumulation of this greenhouse gas. We studied the interaction of a CO₂ doubling and two levels of nitrogen fertilizer on the growth and chemical composition of tall fescue (Festuca arundinacea Schreber cv. KY‐31) when infected and uninfected with the mutualistic fungal endophyte Neotyphodium coenophialum Morgan‐Jones and Gams. Two‐year‐old plants were harvested to 5 cm every 4 weeks, and after 12 weeks of growth plants grown in twice ambient CO₂ concentrations: photosynthesized 15% more; produced tillers at a faster rate; produced 53% more dry matter (DM) yield under low N conditions and 61% more DM under high N conditions; the % organic matter (OM) was little changed except under elevated CO₂ and high N when %OM increased by 3%; lignin decreased by 14%; crude protein (CP) concentrations (as %DM) declined by 21%; the soluble CP fraction (as %CP) increased by 13%; the acid detergent insoluble CP fraction (as %CP) increased by 12%, and in vitro neutral detergent fiber digestibility declined by 5% under high N conditions but not under low N. Plants infected with the endophytic fungus: photosynthesized 16% faster in high N compared with under low N; flowered earlier than uninfected plants; had 28% less lignin in high N compared with under low N; and had much smaller reductions in CP concentration (as %DM) and smaller increases in the soluble CP fraction (as %CP) and the acid detergent insoluble CP fraction (as %CP) under elevated CO₂. Such large and varied changes in plant quality are likely to have large and significant effects on the herbivore populations that feed from these plants.     

Prescribed Fire and Herbicide Effects on Soil Processes During Barrens Restoration

Prescribed fire has become a common tool of natural area managers for removal of non‐indigenous invasive species and maintenance of barrens plant communities. Certain non‐native species, such as tall fescue (Festuca arundinacea), tolerate fire and may require additional removal treatments. We studied changes in soil N and C dynamics after prescribed fire and herbicide application in remnant barrens in west central Kentucky. The effects of a single spring burn post‐emergence herbicide, combined fire and herbicide treatments, and an unburned no‐herbicide control were compared on five replicate blocks. In fire‐plus‐herbicide plots, fescue averaged 8% at the end of the growing season compared with 46% fescue cover in control plots. The extent of bare soil increased from near 0 in control to 11% in burned plots and 25% in fire‐plus‐herbicide plots. Over the course of the growing season, fire had little effect on soil N pools or processes. Fire caused a decline in soil CO₂ flux in parallel to decreased soil moisture. When applied alone, herbicide increased plant‐available soil N slightly but had no effect on soil respiration, moisture, or temperature. Fire‐plus‐herbicide significantly increased plant‐available soil N and net N transformation rates; soil respiration declined by 33%. Removal of non‐native plants modified the chemical, physical, and biological soil conditions that control availability of plant nutrients and influence plant species performance and community composition.     

Phloem phytochemistry and aphid responses to elevated CO2, nitrogen fertilization and endophyte infection

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Influence of genetic variation in the fungal endophyte of a grass on an herbivore and its parasitoid

Neotyphodium coenophialum (Glenn, Bacon, Price & Hanlin) (Ascomycota: Clavicipitaceae) is an endophytic fungus that lives symbiotically within grasses and produces alkaloids that can help protect its hosts from some insect pests. We used laboratory‐based experiments to investigate whether fungal genotype influences an herbivore and its parasitoid. We tested whether variation in novel isolates, plus a control lacking fungal infection, affected preference by fall armyworm, Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae: Amphipyrini), and growth and survival of Euplectrus comstockii Howard (Hymenoptera: Eulophidae: Euplectrini), a parasitoid of fall armyworm. Caterpillars preferred leaf blades in choice experiments from uninfected tall fescue [Lolium arundinaceum (Schreb.) Darbysh., cultivar Jesup (Poaceae)] and tended to avoid blades from plants containing fungal isolates AR502, AR542, or the most common strain from pastures in Georgia, USA, in tall fescue. However, caterpillars fed as much on leaf blades from plants containing isolate AR502 as from those lacking infection. Parasitoid pupal mass was not influenced by fungal isolate, yet fungal isolate did influence parasitoid survival. Survival was higher than expected for parasitoids reared from hosts fed plants lacking fungal infection, but was lower than expected for those reared from hosts fed plants infected with the common strain or AR542 isolates. In contrast, parasitoids reared from hosts fed plants infected with isolate AR502 did not experience higher mortality than expected by chance. Our results show that N. coenophialum can modify bottom‐up trophic cascades through direct effects on herbivores, as well as indirect effects on a natural enemy of the herbivores and that the fungus may influence the tritrophic interaction in ways that counterbalance herbivore protection provided by the symbiont. Our work also shows that these effects are influenced by fungal genotype. As attempts are made to produce forage cultivars with strains of fungal endophyte that lack negative influences on livestock, it will be prudent for investigators to assess the multi‐trophic effects of these novel associations within agroecosystems.     

Influence of endophyte infection, plant age and harvest interval on Rhopalosiphum padi survival and its relation to quantity of N-formyl and N-acetyl loline in tall fescue

Rhopalosiphum padi L. (Homoptera: Aphididae) is sensitive to loline alkaloids present in tall fescue, Festuca arundinacea Shreb., infected with the endophytic fungus, Acremonium coenophialum Morgan-Jones & Gams. Aphid survival was higher on endophyte-free plants regardless of plant age after germination or age of regrowth tissue after clipping. Survival of aphids on endophyte-infected grass was lower on young tissue but increased as plants aged, although it never reached the same level on endophyte-free plants. Both N-formyl and N-acetyl loline increased as uncut or regrowth tissue aged; however, this was influenced by the age of the plant at the initial cut and the clipping frequency. Although even small amounts of loline cause high aphid mortality, the aphids are able to survive on endophyte-infected plants if the tillers have senescing leaves which contain lower amounts of loline. Preference for senescing leaves may help R. padi avoid plant parts containing high amounts of toxic allelochemicals, thus contributing to higher numbers of aphids on older, endophyte-infected plants.     

Unusually high‐quality soil seed banks in a Midwestern U.S. oak savanna region: variation with land use history,habitat restoration,and soil properties

An overarching conclusion in the literature is that soil seed banks rarely contain many restoration‐target species and are often liabilities rather than assets to restoration. Our objective was to evaluate composition and spatial variation of seed banks and their potential contributions to restoration, including restoration‐target species such as rare species and those characterizing historical habitats. On 64 sites in a Midwestern U.S. oak savanna landscape, we sampled soil seed banks in seven habitat types (restored oak savannas, oak woodlands, and mesic prairies; unmanaged upland oak and mesic forests; and unmanaged and managed pine plantations). The germinable seed bank was exceptionally rich in restoration‐target species. In total for the 64 sites, seedlings of 127 species emerged from seed bank samples. Of the 101 native species, 56 were restoration‐target species, an unusually high number among seed bank studies. Restoration‐target species in seed banks included 13 threatened or endangered species, in addition to 43 other specialist species associated with high‐quality native habitats or on a floral list thought to characterize historical ecosystems. When analyzed across the 64‐site gradient, seed banks differed among the seven habitat types and varied with historical (1939) land use, recent management activities that restored open‐structured habitats, and biophysical gradients of tree density, soil drainage, and soil texture. While not all restoration‐target species were detected in the seed bank, the unusually high‐quality seed bank is a potential asset to restoration and was partly structured along environmental gradients across the landscape.