Forest succession suppressed by an introduced plant-fungal symbiosis.

Microbial symbionts can affect plant nutrition, defensive chemistry, and biodiversity. Here we test the hypothesis that symbionts alter the speed and direction of plant succession in communities that are shifting from grasslands to forests. A widespread C3 grass introduced to the United States, Lolium arundinaceum (tall fescue), hosts a fungal endophyte that is toxic to herbivores.