Monday, November 13, 2006 - 1:30 PM

Remobilization of Leaf Nitrogen in Stockpiled Tall Fescue.

Melissa A. Remley, University of Missouri-Columbia, 1-31 Agriculture Building, Columbia, MO 65211 and Dale Blevins, "Agronomy Dep., 1-87 Agric.Bldg", University of Missouri, University of Missouri, Columbia, MO 65211, United States of America.

Leaf concentrations of phloem mobile macronutrient elements, including nitrogen (N), decline in stockpiled tall fescue (Festuca arundinacea) during winter months.  It has not, however, been determined whether this decline is caused by the remobilization of these nutrients to other plant tissues or by leaching of the aboveground biomass.  The objective of this field study was to determine if nitrogen in stockpiled tall fescue leaves is remobilized during the winter months.  15N labeling of leaves of stockpiled tall fescue was conducted in late autumn to monitor leaf nitrogen mobilization to other plant structures throughout the stockpiling period.  Above and belowground tissues were harvested monthly throughout the winter and early spring.  Atom%15N of the separated tissues was determined by continuous flow isotope ratio mass spectrometry.  15N-label was found in all of the tall fescue tissues throughout the winter months.  Excluding the 15N-treated leaf tissue, the majority of 15N was found in newly developed aboveground tissues.  These tissues included new leaves on the treated tillers that had formed post-treatment and new underground tillers arising from rhizomes that eventually become new aboveground tillers.  An increase in 15N abundance was also found in newly developed fine roots, whose growth proliferated in mid-winter.  These results suggest that tall fescue remobilizes N from leaves to all underground structures and utilizes this N for both new root and shoot growth in late winter and early spring.