Jim A. Nelson

Effects of multiple climate change factors on the tall fescue–fungal endophyte symbiosis: infection frequency and tissue chemistry

• Climate change (altered CO(2) , warming, and precipitation) may affect plant-microbial interactions, such as the Lolium arundinaceum-Neotyphodium coenophialum symbiosis, to alter future ecosystem structure and function. • To assess this possibility, tall fescue tillers were collected from an existing climate manipulation experiment in a constructed old-field community in Tennessee (USA). Endophyte infection frequency (EIF) was determined, and infected (E+) and uninfected (E-) tillers were analysed for tissue chemistry. • The EIF of tall fescue was higher under elevated CO(2) (91% infected) than with ambient CO(2) (81%) but was not affected by warming or precipitation treatments. Within E+ tillers, elevated CO(2) decreased alkaloid concentrations of both ergovaline and loline, by c. 30%; whereas warming increased loline concentrations 28% but had no effect on ergovaline. Independent of endophyte infection, elevated CO(2) reduced concentrations of nitrogen, cellulose, hemicellulose, and lignin. • These results suggest that elevated CO(2) , more than changes in temperature or precipitation, may promote this grass-fungal symbiosis, leading to higher EIF in tall fescue in old-field communities. However, as all three climate factors are likely to change in the future, predicting the symbiotic response and resulting ecological consequences may be difficult and dependent on the specific atmospheric and climatic conditions encountered.

Warming reduces tall fescue abundance but stimulates toxic alkaloid concentrations in transition zone pastures of the U.S.

Tall fescue pastures cover extensive acreage in the eastern half of the United States and contribute to important ecosystem services, including the provisioning of forage for grazing livestock. Yet little is known concerning how these pastures will respond to climate change. Tall fescues ability to persist and provide forage under a warmer and wetter environment, as is predicted for much of this region as a result of climate change, will likely depend on a symbiotic relationship the plant can form with the fungal endophyte, Epichloë coenophiala. While this symbiosis can confer environmental stress tolerance to the plant, the endophyte also produces alkaloids toxic to insects (e.g., lolines) and mammals (ergots; which can cause “fescue toxicosis” in grazing animals). The negative animal health and economic consequences of fescue toxicosis make understanding the response of the tall fescue symbiosis to climate change critical for the region. We experimentally increased temperature (+3°C) and growing season precipitation (+30% of the long-term mean) from 2009–2013 in a mixed species pasture, that included a tall fescue population that was 40% endophyte-infected. Warming reduced the relative abundance of tall fescue within the plant community, and additional precipitation did not ameliorate this effect. Warming did not alter the incidence of endophyte infection within the tall fescue population; however, warming significantly increased concentrations of ergot alkaloids (by 30–40%) in fall-harvested endophyte-infected individuals. Warming alone did not affect loline alkaloid concentrations, but when combined with additional precipitation, levels increased in fall-harvested material. Although future warming may reduce the dominance of tall fescue in eastern U.S. pastures and have limited effect on the incidence of endophyte infection, persisting endophyte-infected tall fescue will have higher concentrations of toxic alkaloids which may exacerbate fescue toxicosis.

Fungal endophyte presence and genotype affect plant diversity and soil-to-atmosphere trace gas fluxes

AimsNovel fungal endophyte (Neotyphodium coenophialum; Latch, Christensen and Samuels; Glenn, Bacon, and Hanlin) genotypes in symbiosis with tall fescue (Lolium arundinaceum; Schreb. Darbysh.) have been recently introduced to agricultural seed markets. These novel endophytes do not produce the full suite of toxins that the ‘common toxic’ form does, and therefore, may not have the same consequences on plant and soil processes. Here, we evaluated the effects of endophyte presence and genotype on ecosystem processes of tall fescue stands.MethodsWe quantified the effects of the presence of the common toxic endophyte (CT), two novel endophyte genotypes (AR-542, AR-584), no endophyte (endophyte free, E-), and a mixture of all endophyte statuses (mix) within a single genotype of tall fescue (PDF) on various soil and plant parameters.ResultsEndophyte presence and genotype affected tall fescue cover and plant species diversity: cover—CT, AR-542, AR -584, mix > E- and species diversity—E- > AR-542, AR -584 > CT, mix. Most measured soil parameters had significant endophyte effects. For example, higher fluxes of soil CO2 and N2O were measured from stands of AR-542 than from the other endophyte treatments.ConclusionsThese results indicate that endophyte presence and genetic identity are important in understanding the ecosystem-scale effects of this agronomically important grass-fungal symbiosis.

Variation in Vegetation and Microbial Linkages with Slope Aspect in a Montane Temperate Hardwood Forest

Plant ecologists have long been interested in aspect-related contrasts of montane forests. Few studies have assessed correlation (linkage) among vegetation strata; fewer have included soil microbial communities. This study assessed contrasts in overstory, spring herbaceous, and soil microbial communities between northeast (NE) - and southwest (SW) -facing slopes in a second-growth West Virginia hardwood forest. We addressed three questions: (1) how do soil microbial, herbaceous layer, and overstory communities vary with slope aspect? (2) do forest vegetation strata and soil microbial communities exhibit linkage? (3) do biotic relationships and linkage vary with slope aspect? Moisture, organic matter, pH, soil NO3−, and net nitrification were significantly higher in NE soils; soil NH4+ was significantly higher in SW soils, and net N mineralization was virtually identical between aspects. Vegetation communities markedly differed between the slopes. Overall, 29 tree and 118 herbaceous species were encountere...

Ecosystem function differs between Old World bluestem invaded and native coastal prairie in South Texas

Exotic Old World bluestem grasses (OWBG) are invading prairie and savanna ecosystems of the southern Great Plains USA, yet little is known about whether or how this invasion alters ecosystem processes. We conducted a study in a south Texas coastal prairie to address the following questions: (1) Does litter production, quality, decomposition rates, and soil nutrient dynamics differ significantly between areas dominated by OWBG versus native prairie?; and, (2) Does soil texture influence the effects of OWBG dominance on ecosystem processes? Ecosystem parameters were measured in adjacent patches of native and OWBG invaded coastal prairie on two soil textures, sandy loam and clay. Our findings indicate that ecosystem function differed between OWBG and native prairie dominated areas, but these results were not consistent across soil textures. On sandy loam soil, the soil microclimate differed substantially between OWBG and native prairie, and areas dominated by OWBG had higher aboveground plant production, soil organic C and total N pools, soil inorganic N concentrations and mineralization rates, and litter decomposition rates than native prairie. In contrast, on clay soils, these ecosystem properties often varied little between OWBG and native prairie. Dominance of OWBG appears to have altered native ecosystem function; yet, in this study the directionality and extent of these OWBG effects were strongly soil texture dependent, suggesting that local edaphic factors will likely interact with OWBG dominance in determining ecosystem properties. Consideration of these results may be valuable for managing OWBG such that control or restoration efforts on coarse-textured soils may be given priority over finer-textured soils.

Compositional Differences in Simulated Root Exudates Elicit a Limited Functional and Compositional Response in Soil Microbial Communities

Inputs of low molecular weight carbon (LMW-C) to soil – primarily via root exudates– are expected to be a major driver of microbial activity and source of stable soil organic carbon. It is expected that variation in the type and composition of LMW-C entering soil will influence microbial community composition and function. If this is the case then short-term changes in LMW-C inputs may alter processes regulated by these communities. To determine if change in the composition of LMW-C inputs influences microbial community function and composition, we conducted a 90 day microcosm experiment whereby soils sourced from three different land covers (meadows, deciduous forests, and white pine stands) were amended, at low concentrations, with one of eight simulated root exudate treatments. Treatments included no addition of LMW-C, and the full factorial combination of glucose, glycine, and oxalic acid. After 90 days, we conducted a functional response assay and determined microbial composition via phospholipid fatty acid analysis. Whereas we noted a statistically significant effect of exudate treatments, this only accounted for ∼3% of the variation observed in function. In comparison, land cover and site explained ∼46 and ∼41% of the variation, respectively. This suggests that exudate composition has little influence on function compared to site/land cover specific factors. Supporting the finding that exudate effects were minor, we found that an absence of LMW-C elicited the greatest difference in function compared to those treatments receiving any LMW-C. Additionally, exudate treatments did not alter microbial community composition and observable differences were instead due to land cover. These results confirm the strong effects of land cover/site legacies on soil microbial communities. In contrast, short-term changes in exudate composition, at meaningful concentrations, may have little impact on microbial function and composition.

Fungal endophyte symbiosis alters nitrogen source of tall fescue host, but not nitrogen fixation in co-occurring red clover

Background and aimsInfection of tall fescue with the common toxic fungal endophyte Epichloë coenophiala harms livestock via toxic alkaloid production; therefore, non-toxic ‘novel’ strains of the endophyte have been developed and released. How different endophyte strains impact biological nitrogen fixation (BNF) in mixed species pastures is unknown. We asked whether novel endophyte or common toxic endophyte-infected (NE+; CTE+) tall fescue affects symbiotic and non-symbiotic BNF, and utilization of biologically-fixed nitrogen in tall fescue.MethodsTall fescue was planted either endophyte-free (E-), infected with CTE, two non-toxic strains AR542 NE, AR584 NE, or a blend of endophyte treatments. We measured natural abundance of 15 N in plant and soil samples, and conducted soil acetylene reduction assays.ResultsEndophyte presence and strain significantly affected the δ15N of tall fescue. Near red clover, CTE+ and AR584 NE+ tall fescue were most 15 N-depleted; but away, E- tall fescue was most 15 N-depleted. Endophyte strain significantly influenced N concentration in red clover, but not symbiotic or non-symbiotic BNF.ConclusionsEndophyte strains produce different effects on tall fescue’s competitive ability and nitrogen utilization. In mixed pastures, deployment of NE strains for decreased alkaloid toxicity will differentially impact use of biologically fixed nitrogen in tall fescue and nitrogen concentration in red clover.