Fungal endophytes of a forage grass reduce faecal degradation rates

Abstract

Mutualisms between fungal endophytes and forage grasses can exert broad-reaching effects on grassland communities and ecosystem processes. We hypothesised that endophytes of grasses would retard the process of faecal degradation since grazing animals consume primarily live plant material and excrete a large portion of the herbage they consume as faeces. We examined the degradation rates of faeces from sheep that had consumed pure swards of perennial ryegrass containing a range of unique strains (AR1, AR37, or Wild type) of the fungal endophyte, Neotyphodium lolii, or no endophyte. Ultimately, the presence of endophytes in perennial ryegrass resulted in slower faecal decay rates compared to the nil endophyte treatment, although only consistently for the C concentration decay rates that were approximately 2× to 4× slower in the endophyte-derived faecal matter. The decay rate of dry matter content was significantly slower (ca. 1.5×) in the novel endophyte-derived faeces (AR1 and AR37) compared to the nil endophyte-derived faeces. The N decay rates differed significantly only in the AR1 treatment that was approximately 4× slower than the nil endophyte group. The reduced decay rates are attributed to the presence of endophyte-derived alkaloids in the faeces, and a greater proportion of more easily degraded hemicellulose in faeces from sheep that consumed the endophyte-free grass. There were no significant differences in the faecal carbon and nitrogen decay rates among the three endophyte strain treatments. This suggests that all the strain-specific alkaloids might have similar effects, or that N. lolii has a general effect that is not strain-specific, such as altered fibre composition, as reported here. This is the first report of a fungal endophyte affecting the rate of faecal degradation, and the first report of the alkaloids peramine, lolitrem B and epoxy–janthitrems in faecal matter. This study shows that a common agronomic grass–endophyte mutualism can have effects on ecosystem processes that have not previously been considered.