Effects of endophyte status of tall fescue tissues on the earthworm (Eisenia fetida)

Abstract

A cryptic fungal endophyte, Neotyphodium coenophialum, infects most tall fescue (Festuca arundinacea) pastures in the United States. Cattle, sheep, and horses that consume the endophyte-infected grass can suffer fescue toxicosis caused by toxic alkaloids in the infected plants. The effects of the endophyte on mammalian herbivores have been well documented, but less is known regarding the quality of the grass (infected vs noninfected) as a food material for soil invertebrates. We conducted 21-d tests with earthworms (Eisenia fetida) to determine the nutritional quality of endophyte-infected and noninfected tall fescue leaf and root tissues. Earthworm survival, growth, and reproduction were measured in each treatment combination of tissue type and infection status. Earthworm survival was 100% in all treatments. Tall fescue tissue type (leaf vs root) and infection status (present or absent) both significantly affected E. fetida growth and reproduction. The earthworms grew and had moderate levels of reproduction in replicates containing tall fescue leaf tissue as the sole food source regardless of the endophyte-infection status, but earthworms lost weight and had less reproduction in replicates where tall fescue root tissue was the sole food source. An unexpected effect of infection status on earthworm growth in the tall fescue leaf-tissue treatments was also evident: mean growth of E. fetida with access to endophyte-infected leaf tissue as the sole food source was 3.6-fold greater than mean growth of E. fetida with access to noninfected leaf tissue as the sole food source. Knowledge regarding the relative effects of endophyte status of tall fescue on soil organisms may allow the development of more effective environmental management strategies at sites where tall fescue is being considered for use in phytoremediation or for vegetative cover. Investigators working with tall fescue should be alert to the possibility of endophyte-mediated effects of tall fescue on other organisms and, at a minimum, should provide information regarding the grass's infection status when reporting the results of studies that involve use of tall fescue.