Strictly vertically transmitted (hereditary) Epichloë spp. fungal endophytes are symbionts with cool-season pooid host grasses. Such endophytes may increase host invasiveness in the non-native, introduced ranges. However, because costs and benefits for the host can vary with the growing conditions, the endophyte may become locally or temporally extinct when costs outweigh benefits. Our long-term field experiment involved the introduction of seven Schedonorus pratensis (meadow fescue) cultivars hosting Epichloë uncinata endophyte, which represent host-grass populations differing in genetic backgrounds and Epichloë infection frequencies, to an unmanaged old field. In the first 6 years, the host grasses persisted but did not become invasive in the plant community, regardless of their endophyte infection frequency. Subsequently, we hypothesized that increasing nutrient availability would decrease endophyte costs and thus increase the host’s success and abundance. We fertilized half of the plots for four additional years and re-examined S. pratensis invasiveness. We predicted that increased nutrient availability would increase S. pratensis abundance and E. uncinata frequency and concentration, as well as decrease plant community diversity, relative to unfertilized plots. Fertilization increased endophyte concentrations in three low-endophyte host populations. However, E. uncinata did not enable S. pratensis populations to achieve high abundance or to reduce plant community diversity in the old field, with or without fertilization. Thus, nutrient availabililty and host invasiveness appear to be decoupled in this study system.

严格垂直传播的（世袭的）Epichloëspp。真菌内生菌与凉爽的类泊寄主草共生。这样的内生菌可以在非天然的引入范围内增加宿主的侵袭性。但是，由于寄主的成本和收益会随生长条件的变化而变化，因此当成本超过收益时，内生菌可能会局部或暂时灭绝。我们的长期野外试验涉及引入七个内生附生内生Epichloëuncinata内生菌的Schedonorus pratensis（草甸羊茅）品种，这些品种代表了遗传背景和Epichloë不同的寄主草种群。感染的频率，到一个不受管理的旧领域。在最初的6年中，无论其内生菌感染的频率如何，寄主草都可以持久存在，但并未对植物群落造成侵害。随后，我们假设增加养分的利用率将降低内生菌的成本，从而增加寄主的成功率和丰度。我们将一半的土地施肥了四年，然后重新检查了鼠尾草的入侵性。我们预测，相对于未施肥的地块，增加的养分利用率将增加沙棘的丰度和沙棘的频率和浓度，并降低植物群落的多样性。施肥增加了三个低内生菌宿主种群中的内生菌浓度。然而，在有或没有施肥的情况下，E。uncinata不能使S. pratensis种群获得高丰度或减少旧田的植物群落多样性。因此，在该研究系统中，养分的利用率和宿主的侵袭性似乎是分离的。