Influence of Phosphorus and Potassium on Alfalfa Yield, Taproot C and N Pools, and Transcript Levels of Key Genes after Defoliation

• Published in: Crop science 2009-05, Vol.49 (3), p.974-982
• Main Authors: Berg, W.K, Cunningham, S.M, Brouder, S.M, Joern, B.C, Johnson, K.D, Volenec, J.J
• Format: Article
• Language: English
• Subjects: Alfalfa; beta-amylase; carbon; crop yield; Defoliation; Detection limits; Fertility; forage crops; Gene expression; genes; Medicago sativa; messenger RNA; Molecular weight; nitrogen; nutrient availability; nutrient reserves; phosphorus; plant nutrition; potassium; roots; seasonal variation; storage proteins; Studies; Sucrose; sucrose synthase; translocation (plant physiology); yield components
• ISSN: 0011-183X; 1435-0653
• DOI: 10.2135/cropsci2008.07.0395

Fertilization with K and P impacts alfalfa (Medicago sativa L.) yield, but how these nutrients influence taproot reserves and gene expression is unknown. Our objectives were to determine how P and K impact (i) alfalfa yield and yield components, (ii) accumulation and use of taproot carbon (C) and nitrogen (N) pools, and (iii) transcript levels for β-amylase, sucrose synthase, and the high molecular weight vegetative storage protein in alfalfa taproots. Yield and yield components were determined at 30-d intervals beginning in late May. Roots were sampled after the late June harvest (Day 0) and 1, 3, 6, 10, 14, 21, and 30 d thereafter. Addition of P and K increased forage yield by enhancing mass per shoot. High P resulted in rapid starch use, while taproots of plants fertilized with K had low sugar concentrations. Transcripts decline by Day 6 and by Day 10 were below detection limits. Transcripts for β-amylase and sucrose synthase accumulated rapidly after Day 10 in taproots of plants fertilized with both P and K. Balanced P and K nutrition resulted in the accumulation and effective utilization of C and N reserves and in improved alfalfa adaptation to defoliation.