ARS | Publication request: SHORT-TERM RESPONSES OF SOIL C AND N FRACTIONS TO TALL FESCUE ENDOPHYTE INFECTION

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 28, 2005
Publication Date: June 22, 2006
Citation: Franzluebbers, A.J. 2006. Short-term responses of soil c and n fractions to tall fescue endophyte infection. Plant and Soil Journal. 282:153-164.

Interpretive Summary: Tall fescue plants are naturally infected with a fungus that offers host-plant resistance to environmental and biological stresses, but through its production of toxic chemical compounds causes a variety of health disorders in grazing animals. One of the beneficial ecological consequences of fungus infection is the accumulation of soil organic matter, either through enhanced plant production and/or through reduced soil microbial activity. A USDA-ARS scientist in Watkinsville GA conducted an experiment to determine the changes in soil organic carbon and nitrogen during the first year of growth of tall fescue either infected or not with the fungus, Neotyphodium. Soil organic carbon and nitrogen accumulated throughout the experiment in response to the large input from growing and dying roots. However, there were no consistent indications that the forms of organic carbon and nitrogen in soil were altered by the presence of the plant fungus. Tall fescue forage accumulation was greater with than without the fungus, confirming previous results that fungus infection confers greater fitness.

Technical Abstract: Tall fescue (Festuca arundinacea Schreb.) is naturally infected with a fungal endophyte, Neotyphodium coenophialum, which produces toxic ergot alkaloids that negatively affect herbivores and that may alter soil organic matter dynamics. A 60-week mesocosm study with a factorial arrangement of soil type (clay loam and loamy sand) and endophyte infection (with and without) was conducted to determine potential changes in soil C and N fractions. Forage and root dry-matter production were greater with than without endophyte infection, while forage C and N concentrations were unaffected. Total, particulate, mineralizable, and aggregate-associated C and N fractions increased several fold during the course of the experiment due to large rhizosphere inputs in all treatments. The fraction of total C and N in water-stable macroaggregates (>0.25 mm) was initially 0.43 + 0.10 and 0.46 + 0.16, respectively, and increased during the course of the experiment to 0.68 + 0.06 and 0.56 + 0.15 when averaged across soil type and endophyte infection level as a result of organic matter cycling and deposition in this active biophysical fraction. Changes in soil C and N fractions due to endophyte infection were minimal. The lack of detectable changes in soil C and N fractions due to endophyte infection may have been a result of the overwhelming input of C from roots and/or the relatively short-term nature of this study. Greater plant productivity of endophyte-infected tall fescue is likely a contributing mechanism for eventual changes in total and active C and N fractions that have been observed in long-term pastures.