245-33
Nitrogen Concentrations in Legumes Respond Differently to Defoliation and Ontogenesis.

Poster Number 706

Tuesday, November 5, 2013
Tampa Convention Center, East Hall, Third Floor

Caitlyn E. Cooper1, Harley D. Naumann2, Barry D. Lambert3 and James P. Muir3, (1)Environmental and Agricultural Management, Tarleton State University, Stephenville, TX
(2)Soil and Crop Sciences, Texas A&M University, College Station, TX
(3)Texas A&M AgriLife Research-Stephenville, Stephenville, TX
The nutrients a plant allocates to vegetative tissue are determined by costs and benefits.  We determined how N concentrations in leaves of two warm-season perennial herbaceous legumes were affected by simulated herbivory and plant maturity.  Desmodium paniculatum (panicled tick-clover; PTC) and Lespedeza cuneata (sericea lespedeza; SL) were reared in a greenhouse and subjected to one of four treatments: previously un-defoliated plants and three repeated defoliations of the upper 50, 75, and 100% of herbage regrowth at 145, 181 , and 222  d after seeding, approximately equivalent to vegetative, early reproductive and seed set stages.  The two species responded differently to simulated herbivory.  All PTC treatment groups experienced stable or increased (P≤0.05) N concentration from vegetative to flowering stage, and all treatments underwent a decrease (P≤0.05) in N between flowering and seeding.  Ontogenesis and defoliation treatment did not affect SL N concentration.  Results suggest PTC might have experienced nutrient stress after the second defoliation and was unable to compensate in subsequent leaf development for N lost to defoliation.  Seeds usually contain the greatest proportion of legume N, and in a N-stressed situation, PTC might have mobilized N from vegetative tissue to reproductive organs to meet N demands for seed fill.  By maintaining stable leaf N concentrations across multiple defoliation events, SL appears to be able to utilize N resources more efficiently than PTC at seed set when demands for N are high.  Regenerated PTC leaves with lower nutrient concentrations may be less attractive to herbivores. Different nutrient allocation strategies provide varying challenges and opportunities that are legume species specific.
See more from this Division: C06 Forage and Grazinglands
See more from this Session: General Forage and Grazinglands: II

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