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

Abstract

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 fescue's 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.

Metabolomics of fescue toxicosis in grazing beef steers

“…This is expected, however, as warming increases E+ alkaloid content (McCulley et al, 2014). Total urinary EA concentration increased after 1 day of grazing, peaked on day 14, and remained elevated.…”

Enhanced aphid abundance in spring desynchronizes predator–prey and plant–microorganism interactions

“…We chose to simulate 2 weeks, as it represents an aphid shift with an increasing spring temperature by ~2 °C which represents a range between the SRES climate change predictions for 2099 (IPCC WG III 2000; Harrington and Clark 2010). We are aware that climate warming can also change endophyte and host grass growth (Vega-Frutis et al 2014; McCulley et al 2014), but the focus of our study was to uncover effects of increased aphid abundances in spring on interacting trophic levels.…”

Ecophysiological Responses of Tall Fescue Genotypes to Fungal Endophyte Infection, Elevated Temperature, and Precipitation

“…Although studies evaluating the effects of nontoxic endophyte symbioses are relatively scarce, a large body of work demonstrates that CTE+ and CTE– tall fescue plants respond differently to environmental stressors such as drought and high temperatures (Malinowski and Belesky, 2000; Assuero et al, 2006). Endophyte presence can alter physiological processes, such as photosynthesis and leaf water potential, in ways that may enhance plant tolerance and recovery from drought and heat stress (Marks and Clay, 1996; Richardson et al, 1993). The mechanisms contributing to these responses are complex and not fully known but appear to involve biochemical, physiological, and overall plant growth responses that are influenced by the presence of the endophyte and the surrounding environment (Elmi and West, 2006; Cheplick and Faeth, 2009).…”