It's Not Always a Bed of Roses

Abstract

ECOLOGY Many plants maintain mutualisms with systemic fungi (endophytes): The fungi gain nutrients and the plants gain resistance via fungal alkaloids against stress, pathogens, and herbivores. But the benefit/cost equation can be pulled from mutualism toward antagonism by the effects of other variables in the community. Lehtonen et al. found that when a hemiparasite, in this case yellow rattle, enters a grass/endophyte system, the yellow rattle becomes more successful at deterring aphid attack. Ultimately, the endophyte-positive grass suffered more from parasitism and grew less than similarly parasitized but endophyte-free grass. What seems to be happening is that the yellow rattle is not only taking nutrients from the grass but also obtaining the fungal alkaloids, which then repel the aphids. So together the yellow rattle and the fungus are sapping nutrients from the host grass, and the fungus no longer supplies as much protective benefit to its grass host. — CA Ecol. Lett. 8 , 1256 (2005).