Cunningham, Suzanne M. , Chang, Shyh-Rong , Volenec, Jeffrey J. .
Impact of taproot N pools on shoot growth of defoliated alfalfa (Medicago sativa L.) differing in nodule effectiveness.
Taproot N and C reserves are thought to influence shoot regrowth of defoliated alfalfa (Medicago sativa L.) plants, but the relative impact of these reserves is not clear. Our objective was to determine if variation in taproot C and N pools impacts herbage regrowth of alfalfa after defoliation. Ineffective- and effective-nodulating populations of ‘Saranac’ alfalfa were seeded in pots, inoculated with Rhizobium melitoti, and provided complete Hoagland’s nutrient every five days for 129 days in order to facilitate establishment. Contrasting N pool levels were created in taproots of ineffective Saranac plants by replacing complete Hoagland’s solution with minus-N Hoagland’s solution for one-half of the plants thus creating the variation in taproot N pools necessary to test the relationship between taproot pool N and shoot regrowth. Plants were sampled during the three weeks of contrasting N nutrition, defoliated, roots and crowns transplanted into N-free sand, and all plants were provided minus-N Hoagland’s for the remainder of the study. As expected, growth and taproot N pools of effectively nodulating Saranac were not influenced by N treatment. At transplanting ineffective Saranac+N taproots had higher protein and lower starch concentrations than taproots of ineffective Saranac-N plants. At transplanting taproot sugar concentrations were highest in ineffective Saranac plants and declined 28% by Day 7 in ineffective Saranac+N plants to levels observed in effectively nodulated Saranac. Taproot protein and amino-N concentrations in ineffective Saranac+N plants declined by Day 14 to levels found in ineffective Saranac-N plants. After 29 days regrowth in N, herbage yield was greater in ineffective Saranac+N than in ineffective Saranac-N plants. These observations support the hypothesis that the quantity of taproot N influences herbage regrowth of defoliated alfalfa.
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1 - Purdue University, Agronomy, 915 West State Street, West Lafayette, IN, 47907-2054, USA
2 - Taiwan Livestock Research Institute, Forage Crops
3 - Purdue University, Agronomy
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM