Global change factors interact with fungal endophyte symbiosis to determine tall fescue litter chemistry

Background/Question/Methods

Neotyphodium coenophialum is an endophytic fungus of tall fescue (Schedonorus phoenix) capable of producing alkaloids which can alter plant resource allocation, drought tolerance, resistance to herbivory, and litter chemistry.  The objectives of this study were to: 1) evaluate whether global climate change factors affect the frequency of endophyte infection within tall fescue communities, and 2) determine the direct and interactive effects of global climate change and endophyte infection on tall fescue litter chemistry. Tall fescue tillers were collected from a (6 year) multi-factor manipulation experiment in a constructed “old field” community at the Oak Ridge National Laboratory in eastern Tennessee.  The community, comprised of C3 and C4 grasses, forbs, and legumes, was exposed in open-top chambers to combinations of ambient or elevated [CO₂], ambient or elevated air temperature, and high or low soil moisture.   

Results/Conclusions

Endophyte infection frequency of tall fescue was higher under elevated CO₂ compared to ambient (91% vs. 81% infected for elevated and ambient CO₂, respectively; p<0.02) but was not impacted by warming or moisture.  Within endophyte infected tillers, elevated CO₂ decreased alkaloid concentrations, both ergovaline and loline, by ~30% (P<0.05).  Warming had no effect on ergovaline concentrations, but increased loline concentrations 28% (P<0.01).  In this study, uninfected tall fescue had higher %C than infected tall fescue (P<0.01); however there were no significant differences in %N, C:N, or acid-detergent fiber (ADF) between endophyte-infected and -free tall fescue tillers.  Elevated CO₂ increased litter C:N compared to ambient CO₂ (P=0.02) , while warming and moisture had no effect on this parameter.  ADF decreased 9% (P<0.001) under elevated CO₂ compared to ambient and increased 5% in wet relative to dry conditions (P<0.02).  Warming had no effect on ADF.  Taken together, these results suggest elevated CO₂ may interact with the plant-fungal symbiosis and lead to increased endophyte infection frequency and altered litter quality in tall fescue, more so than warming and changes in moisture.  Understanding the ecological significance of these alterations in endophyte prevalence and litter chemistry will require further study.