Alteration of Carbon and Nitrogen Pools in Bulk and Rhizosphere Soil in Response to Tall Fescue Cultivar and Endophyte Status.

Tall fescue (Lolium arundinaceum (Schreb.) is a cool-season perennial grass within which can live a fungal endophyte (Neotyphodium coenophialum) thought to provide enhanced edaphic and climactic stress tolerance to the host compared to non-infected neighbors. Our prior research demonstrated that a variety of root exudate compounds released from tall fescue were differentially affected by tall fescue cultivar, endophyte genotype and their interaction. Changes in root exudates could influence soil processes, including carbon and nitrogen pools. To test this, we collected rhizosphere and bulk soil samples from six year old field plots located in Lexington, KY planted with two different tall fescue cultivars (PDF and 97TF1), each containing four endophyte treatments [endophyte-free (E-) or infected with one of three strains of Neotyphodium (common toxic, novel AR542 and novel AR584)]. The influence of fescue cultivar, endophyte presence and strain, and soil sample location were assessed for soil organic carbon, soil total nitrogen, particulate and non-particulate organic matter (POM and n-POM, respectively) - C and – N, and dissolved organic carbon and nitrogen (DOC, DON) pools. Soil functional aspects were evaluated by measuring soil respiration using a unique oxygen sensitive microtiter plate method, as well as the activity of seven different soil enzymes related to C, N and P cycling. As expected, significant differences were found between rhizosphere and bulk soils in POM, n-POM, DOC, DON and enzyme activity; however, contrary to expectations, little discernible differences related to fescue cultivar or endophtye were found within either rhizosphere or bulk soils. These results suggest that the impact of endophyte presence and fescue cultivar on soil nutrient pools may not be detectable within a six year time period. It is also possible that the site-specific conditions, such as climate, hydrology, soil type, nutrient availability, or management, which reduced endophyte and cultivar effects on soil nutrient pools.