Fungal endophyte symbiosis alters nitrogen source of tall fescue host, but not nitrogen fixation in co-occurring red clover

Abstract

Background and aims Infection of tall fescue with the common toxic fungal endophyte Epichloë coenophiala harms livestock via toxic alkaloid production; therefore, non-toxic 'novel' strains of the endophyte have been developed and released. How different endophyte strains impact biological nitrogen fixation (BNF) in mixed species pastures is unknown. We asked whether novel endophyte or common toxic endophyte-infected (NE+; CTE+) tall fescue affects symbiotic and nonsymbiotic BNF, and utilization of biologically-fixed nitrogen in tall fescue. Methods Tall fescue was planted either endophyte-free (E-), infected with CTE, two non-toxic strains AR542 NE, AR584 NE, or a blend of endophyte treatments. We measured natural abundance of 15 N in plant and soil samples, and conducted soil acetylene reduction assays. Results Endophyte presence and strain significantly affected the δ 15 N of tall fescue. Near red clover, CTE+ and AR584 NE+ tall fescue were most 15 N-depleted; but away, E-tall fescue was most 15 N-depleted. Endophyte strain significantly influenced N concentration in red clover, but not symbiotic or non-symbiotic BNF.Conclusions Endophyte strains produce different effects on tall fescue's competitive ability and nitrogen utilization. In mixed pastures, deployment of NE strains for decreased alkaloid toxicity will differentially impact use of biologically fixed nitrogen in tall fescue and nitrogen concentration in red clover. Abbreviations CTE+common toxic endophyte-infected Eendophyte-free BNF biological nitrogen fixation NE+ novel endophyte-infected EMix equal mix of E-, CTE+, AR542 NE+, and AR584 NE+ treatments within plot PDF pasture demonstration farm RC red clover TF(+RC) tall fescue plant located close to red clover TF(-RC) tall fescue plant located away from red clover CF-IRMS continuous flow isotope ratio mass spectrometer ARA acetylene reduction assay Plant Soil

Fungal endophyte infection increases tall fescue's survival, growth, and flowering in a reconstructed prairie

“…These results are consistent with previous work demonstrating the benefits of endophyte infection for tall fescue in diverse plant communities (e.g. Clay & Holah ; Bouton et al ; Rudgers et al ; Rudgers & Clay ; Slaughter et al ). However, our observed lack of endophyte infection effects on the species diversity or richness of the surrounding, developing plant community contradicts our second hypothesis and prior findings (Clay & Holah ; Rudgers et al ; Rudgers & Clay ).…”

“…Domestic livestock grazing is also present within tallgrass prairie restorations where tall fescue invasion is problematic in the United States, though tall fescue's influence on fire behavior has also been invoked as a mechanism driving invasion there (McGranahan et al 2012a). Endophyte infection may also increase the competitive ability of tall fescue relative to other plants (Clay & Holah 1999;Rudgers et al 2005;Slaughter et al 2016), although we found that the effects of endophyte infection on tall fescue did not affect the surrounding plant community. Perhaps the endophyte-associated effects on tall fescue and the surrounding plant community might have been more dramatic had domestic livestock grazing occurred in our prairie reconstruction.…”

“…This species has invaded prairie fragments in the Great Plains (Clay & Holah ; Cully et al ; Rudgers et al ), reducing species richness (McGranahan et al ) and altering fire behavior (McGranahan et al , ). Endophyte presence has been found to increase tall fescue's invasiveness and competitiveness including negative impacts on other plants shown in both greenhouse (Rudgers et al ) and field studies, though not in a restoration context (Clay & Holah ; Rudgers & Clay ; Slaughter et al ).…”

Editorial special issue: soil, plants and endophytes

“…However, whether new endophytic strains have an impact on biological N 2 fixation in mixed species pastures is unknown. The results by Slaughter et al (2016) showed that endophytic strains produce different effects on tall fescue and nitrogen utilization. In mixed pastures, the deployment of novel endophytic strains to decrease alkaloid toxicity will differentially impact the use of biologically fixed N 2 in tall fescue and nitrogen concentration in red clover.…”

“…The following five papers of this Special Issue emphasize the complexity of these interactions, and strongly suggest that the integrated knowledge of the role of endophytes in the aboveground food webs and nutrient cycling are very much in need to understand ecosystem functions. Slaughter et al (2016) examined whether novel endophyte or common toxic endophyte-infected tall fescue could affect symbiotic and non-symbiotic biological N 2 fixation, and utilization of biologically-fixed N 2 in tall fescue. Infection of tall fescue with the common toxic fungal endophyte Epichloë coenophiala is known as harming livestock via toxic alkaloid production, and the need of new non-toxic strains of the endophyte has been recently pointed out Kauppinen et al 2016;Saikkonen et al 2016).…”