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Title:   Author  item
                                            Belesky, Daviditem
                                            Halvorson, Jonathanitem
                                            Ruckle, Joyce
  Submitted to: Ecological Society of America Abstracts
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 4/13/2009
                                    Publication  Date: N/A
                                    Citation: N/AInterpretive Summary:
                                Technical Abstract: The value of tall fescue [Lolium arundinaceum, Schreb. S. J. Darbyshire] in terms of productivity and persistence in agro-ecosystems arises in part from association with Neotyphodium coenophialum (Morgan-Jones and Gams, Glenn, Bacon, and Hanlin) endophyte.  The influence of novel, non-ergogenic endophytes on photosynthate partitioning and nutritive value of tall fescue is unclear, especially when simultaneous stresses (e.g., defoliation and shading) are imposed on the association.  We conducted a field experiment, in shaded and open sites, using container-grown tall fescue (cultivar Jesup) plants that were host to either a native or a novel non-ergogenic fungal endophyte (MaxQTM), or that were devoid of endophyte.  Our data suggest that carbon isotope discrimination (Delta) is an indicator of response to light, since Delta increased as the relative amount of shading from co-occurring trees increased.  This trend was observed throughout the growing season and was consistent whether Delta was expressed relative to potential evapotranspiration (ETo), leaf dry matter content (LDMC) or the nutritive value index of herbage energy relative to herbage crude protein (TDN:CP).  Carbon isotope discrimination decreased as photosynthetic nitrogen use efficiency increased, with the response associated with microsite.  No simple explanation for trends can be offered because of the numerous complex interactions of physiology with management and micro-environment conditions.  The trend we observed correlated to multiple simultaneous stresses, including defoliation, occurred and agrees with previous observations on Delta response to light gradients.  The discrimination index might be useful for identifying shade tolerant perennial grasses for use in silvopasture.


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