Tall fescue (Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.) can form a symbiosis with the fungal endophyte Epichloë coenophiala, whose presence often benefits the plant, depending on plant and fungal genetics and the prevailing environmental conditions. Despite this symbiosis having agricultural, economic, and ecological importance, relatively little is known regarding its response to predicted global climate change. We quantified the ecophysiological responses of four tall fescue genetic clone pairs, where each pair consisted of one endophyte‐infected (E+) and one endophyte‐free clone, to climate change factors of annually elevated temperature and seasonally increased precipitation. Endophyte presence increased fescue tillering and biomass production in the elevated temperature treatment and greatly enhanced the ability of two of the fescue clones to recover from the hot and unusually dry summer. Surprisingly, endophyte infection also stimulated biomass production and photosynthesis rates (for one clone) in the most mesic treatment (additional precipitation). Toxic ergot alkaloid concentrations increased in E+ individuals exposed to elevated temperatures, particularly in the fall, but the strength of the response varied across E+ genotypes. Overall, this study suggests that choice of plant and endophyte genetic material will be important in determining the productivity, toxicity, and resilience of tall fescue pastures under future climate conditions.

The frequency and intensity of extreme weather years, characterized by abnormal precipitation and temperature, are increasing. In isolation, these years have disproportionately large effects on environmental N losses. However, the sequence of extreme weather years (e.g., wet-dry vs. dry-wet) may affect cumulative N losses.We calibrated and validated the DAYCENT ecosystem process model with a comprehensive set of biogeophysical measurements from a corn-soybean rotation managed at three N fertilizer inputs with and without a winter cover crop in Iowa, USA.Our objectives were to determine: (i) how 2-year sequences of extreme weather affect 2-year cumulative N losses across the crop rotation, and (ii) if N fertilizer management and the inclusion of a winter cover crop between corn and soybean mitigate the effect of extreme weather on N losses. Using historical weather (1951-2013), we created nine 2-year scenarios with all possible combinations of the driest ("dry"), wettest ("wet"), and average ("normal") weather years. We analyzed the effects of these scenarios following several consecutive years of relatively normal weather. Compared with the normal-normal 2-year weather scenario, 2-year extreme weather scenarios affected 2-year cumulative NO 3 À leaching (range: À93 to +290%) more than N 2 O emissions (range: À49 to +18%). The 2-year weather scenarios had nonadditive effects on N losses: compared with the normal-normal scenario, the dry-wet sequence decreased 2-year cumulative N 2 O emissions while the wet-dry sequence increased 2-year cumulative N 2 O emissions. Although dry weather decreased NO 3 À leaching and N 2 O emissions in isolation, 2-year cumulative N losses from the wet-dry scenario were greater than the dry-wet scenario. Cover crops reduced the effects of extreme weather on NO 3 À leaching but had a lesser effect on N 2 O emissions. As the frequency of extreme weather is expected to increase, these data suggest that the sequence of interannual weather patterns can be used to develop short-term mitigation strategies that manipulate N fertilizer and crop rotation to maximize crop N uptake while reducing environmental N losses. K E Y W O R D Sclimate change, crop phase, crop system, extreme precipitation, nitrate, nitrous oxide

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