Poster: Mineral nutrition

Abs # 193: The impact of P and K nutrition on alfalfa (Medicago sativa L.) taproot carbon and nitrogen pools during cold acclimation and spring regrowth.

Presenter:	Berg, William K., bergw@purdue.edu
Authors	Berg, William K. (A)   Cunningham, Suzanne M. (A)   Brouder, Sylvie M. (A)   Joern, Brad C. (A)   Johnson, Keith D. (A)   Volenec, Jeffrey J. (A)
Affiliations:	(A): Agronomy Dept., Purdue University

Proper phosphorus (P) and potassium (K) nutrition is essential for optimum alfalfa growth and plant survival. Our objective was to understand the role of P and K in stress tolerance and shoot growth in spring by examining changes in biochemical and molecular mechanisms known to impact alfalfa growth and winter survival. A factorial arrangement of P (0 and 75 kg/ha) and K (0 and 400 kg/ha) treatments was replicated four times in the field. Roots were sampled following defoliation in mid September, and 7, 14, 21, 28, 42, 56, 70, and 84 days after shoot removal until plants were dormant in early December. Roots also were sampled at the initiation of shoot growth in spring and weekly thereafter until plants were defoliated in late May. The influence of P and K fertilization on concentrations of sugars, starch, buffer-soluble protein, and amino nitrogen pools, as well as gene expression patterns for a P transporter and vegetative storage proteins in taproots were analyzed. During cold acclimation in fall and throughout spring regrowth, application of K increased root starch concentrations and decreased sugar levels. Across all harvesting dates, root N pools were consistently lowest in alfalfa roots never fertilized with P and K. At both the fall and spring sampling dates, application of K without P increased gene expression of taproot VSPs.