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United States Department of Agriculture

Agricultural Research Service

Research Project: FORAGE SYSTEMS FOR SUSTAINABLE ANIMAL PRODUCTION IN THE MID-SOUTH Title: Alkaloids May Not be Responsible for Endophyte Associated Reductions in Tall Fescue Decomposition Rates

Authors
item Siegrist, Jacob -
item Mcculley, Rebecca -
item Bush, Lowell -
item Phillips, Time -

Submitted to: Functional Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 2, 2009
Publication Date: January 1, 2010
Citation: Siegrist, J.A., Mcculley, R.L., Bush, L.P., Phillips, T.D. 2010. Alkaloids May Not be Responsible for Endophyte Associated Reductions in Tall Fescue Decomposition Rates. Functional Ecology 2010. 24:460-468.

Interpretive Summary: 1. Fungal endophyte - grass symbioses can have dramatic ecological effects, altering individual plant physiology, plant and animal community structure and function, and ecosystem processes such as litter decomposition and nutrient cycling. 2. Within the tall fescue (Schedonorus arundinaceus) - fungal endophyte (Neotyphodium coeno¬phialum) symbiosis, fungal produced alkaloids are often invoked as the putative mechanism driv¬ing these ecological responses. Yet few measurements of alkaloids exist in the ecological literature. In this study, we quantified alkaloid levels in live, standing dead and decomposing endophyte-infected (E+) and -free (E-) plant material and simultaneously evaluated the direct and indirect effects of endophyte presence on tall fescue decomposition. 3. Loline and ergot alkaloid levels were consistently high in live E+ (common toxic strain of N. coenophialum) tall fescue biomass throughout the sampling period (May-November 2007), whereas, E- live and standing dead material had non-detectable alkaloid concentrations. Stand¬ing dead E+ biomass had significantly reduced alkaloid levels (6-19x lower than the levels mea¬sured in the corresponding live E + biomass) that were equivalent to E- live and dead for loline but were still somewhat higher than E- material for ergots. 4. In an effort to test the role of alkaloids in directly inhibiting decomposition, as has been sug-gested by previous studies, we conducted a litter bag experiment using green, alkaloid-laden E + and alkaloid-free E- tall fescue plant material. We incubated E + and E- litter bags in both E+ and E- tall fescue stands for 170 days, and measured mass loss, carbon and nitrogen con¬tent, and ergot and loline alkaloid concentrations over the incubation period. 5. Consistent with previous reports, both direct and indirect effects of endophyte presence on litter decomposition were observed: endophyte presence in the litter and surrounding micro-environment significantly reduced decomposition rates. Surprisingly, despite large differences in alkaloid content between E+ and E- litter from Day 0-Day 21 of the incubation, direct effects of the endophyte on litter decomposition, while significant, were relatively small (differences in mass loss between E+ and E- litter were never > 3%). Alkaloids were gone from E+ material by day 56. 6. We propose that results from this study indicating alkaloids are largely absent in standing dead material (the typical input to the decomposition process), and that despite being present in our litter bag experiment, failed to produce large differences in mass loss between E+ and E- material questions the supposition that fungal produced alkaloids directly inhibit decomposi¬tion. Additional studies exploring the mechanisms behind the direct and indirect effects of endo¬phytes on this ecosystem process are needed.

Technical Abstract: 1. Fungal endophyte - grass symbioses can have dramatic ecological effects, altering individual plant physiology, plant and animal community structure and function, and ecosystem processes such as litter decomposition and nutrient cycling. 2. Within the tall fescue (Schedonorus arundinaceus) - fungal endophyte (Neotyphodium coeno¬phialum) symbiosis, fungal produced alkaloids are often invoked as the putative mechanism driv¬ing these ecological responses. Yet few measurements of alkaloids exist in the ecological literature. In this study, we quantified alkaloid levels in live, standing dead and decomposing endophyte-infected (E+) and -free (E-) plant material and simultaneously evaluated the direct and indirect effects of endophyte presence on tall fescue decomposition. 3. Loline and ergot alkaloid levels were consistently high in live E+ (common toxic strain of N. coenophialum) tall fescue biomass throughout the sampling period (May-November 2007), whereas, E- live and standing dead material had non-detectable alkaloid concentrations. Stand¬ing dead E+ biomass had significantly reduced alkaloid levels (6-19x lower than the levels mea¬sured in the corresponding live E + biomass) that were equivalent to E- live and dead for loline but were still somewhat higher than E- material for ergots. 4. In an effort to test the role of alkaloids in directly inhibiting decomposition, as has been sug-gested by previous studies, we conducted a litter bag experiment using green, alkaloid-laden E + and alkaloid-free E- tall fescue plant material. We incubated E + and E- litter bags in both E+ and E- tall fescue stands for 170 days, and measured mass loss, carbon and nitrogen con¬tent, and ergot and loline alkaloid concentrations over the incubation period. 5. Consistent with previous reports, both direct and indirect effects of endophyte presence on litter decomposition were observed: endophyte presence in the litter and surrounding micro-environment significantly reduced decomposition rates. Surprisingly, despite large differences in alkaloid content between E+ and E- litter from Day 0-Day 21 of the incubation, direct effects of the endophyte on litter decomposition, while significant, were relatively small (differences in mass loss between E+ and E- litter were never > 3%). Alkaloids were gone from E+ material by day 56. 6. We propose that results from this study indicating alkaloids are largely absent in standing dead material (the typical input to the decomposition process), and that despite being present in our litter bag experiment, failed to produce large differences in mass loss between E+ and E- material questions the supposition that fungal produced alkaloids directly inhibit decomposi¬tion. Additional studies exploring the mechanisms behind the direct and indirect effects of endo¬phytes on this ecosystem process are needed.

Last Modified: 12/22/2014
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