Environmental conditions and plant diversity show little effect on mycotoxin occurrence in European grasslands used for horse husbandry

In light of ongoing threats to European grasslands, grazing by livestock such as horses can contribute to biodiversity conservation. An emerging field of research relevant to both grassland ecosystems and animal husbandry has focused on grass-endophyte symbioses between Epichloe fungi and grasses of the genera Festuca, Lolium, and Schedonorus. These endophytes produce toxic alkaloids and have been associated with certain fitness benefits to host grasses, possibly leading to diminished grassland diversity. However, these grass-endophyte symbioses have rarely been studied in (semi-) natural settings. In this study we explored the prevalence of mycotoxins produced by fungal endophytes in temperate European grasslands, testing for possible links between mycotoxin occurrence and eco- logical conditions or land use. We sampled 310 vegetation plots of 10 m2 at seven horse sanctuaries (“sites”) in France, Germany, Austria, and Hungary. In a subset of 204 plots, we collected and tested 372 samples of the target grass genera for the mycotoxins ergovaline and lolitrem B using ultra-performance liquid chromatography– mass spectrometry (UPLC-MS). For all plots, we calculated plant diversity measures and mean Ecological Indicator Values for Europe (EIVEs). Differences in the vegetation and mycotoxin preva- lence were tested using linear mixed-effects models. To explore ecological effects on mycotoxin preva- lence, we calculated generalized mixed models at plot and sample level. 364Plant diversity was similar to averages for the countries studied, with maxima and Red List species occurring in dryer and wetter conditions. Mycotoxins occurred at all sites under a broad range of environmental conditions. Mycotoxin occurrence was comparable to endophyte infection rates from the literature. Festuca rubra aggr. tested positive at rates exceeding twice that of Lolium perenne and Schedonorus arundinaceus. Infection was associated with higher soil moisture and lower nitrogen EIVEs, in contrast to the literature showing benefits to hosts primarily in dry and nutrient-rich conditions. Grass cover and host dominance showed contrasting effects on mycotoxin prevalence in host species. There was no relationship between mycotoxin prevalence and temperature, biodiversity, or land-use type. From our results, we conclude that endophyte infection is common in semi-natural grasslands in temperate Europe but appears to currently present only a limited risk to livestock. We find no strong or consistent relationships between mycotoxin occurrence and ecological conditions or plant diversity. This is consistent with evidence that the effects of infection on hosts are context-dependent and complex. Species-rich grasslands may provide a protective effect against endophyte toxicosis in livestock by diluting mycotoxin concentrations where endophyte infection occurs.