SEASONAL-CHANGES IN NONSTRUCTURAL CARBOHYDRATES, PROTEIN, AND MACRONUTRIENTS IN ROOTS OF ALFALFA, RED-CLOVER, SWEETCLOVER, AND BIRDSFOOT-TREFOIL

Root total nonstructural carbohydrate (TNC) has been studied, but litt le is known about seasonal trends in proteins and other macronutrients in legume roots. Our objectives were to determine how winter hardenin g and resumption of growth in spring influence (i) concentrations of s ugars and starch, and activities of amylases; and (ii) protein concent ration and composition, and abundance of N, P, and K. Alfalfa (Medicag o sativa L.), red clover (Trifolium pratense L.), birdsfoot trefoil (L otus corniculatus L.), and biennial sweetclover (Melilotus officinalis L.) were seeded in rows in the held in May and roots were sampled at approximately monthly intervals in autumn and biweekly in spring. All species accumulated high root TNC and starch concentrations in autumn. Starch and TNC concentrations declined throughout winter, but increas ed in roots of alfalfa and red clover in May. Starch accumulation and degradation patterns in spring were correlated with root endoamylase a ctivity. Root sugar concentrations increased threefold from October to November. Root N and soluble protein concentrations increased 50% bet ween September and December, and declined between March and May. Speci fic proteins accumulated to high concentrations in alfalfa roots durin g autumn. Root P increased 50% between October and April and was assoc iated with an increase in root phytate. Proteins, N, P, and phytate ac cumulated during winter hardening in autumn in roots of these forage l egume species that, in conjuction with TNC, may supply nutrients to re growing shoots in spring.