SEASONAL MARCH OF CARBOHYDRATES IN ELYMUS AMBIGUUS AND MUHLENBERGIA GRACILIS, AND THEIR REACTION UNDER MODERATE GRAZING USE

In a study of the western wheat grass, Agropyron smwithii, the seasonal march of the total concentration of the sugar and starch fractions was found to vary inversely with the rate of growth of the herbage. The storage of these carbohydrates occurred during the declining phasof herbage growth, near the close of the annual growth cycle (2). A subse4ent study of the seasonal march of the carbohydrates of the needle grass, Stipa pulcra, showed inverse proportionality between the rate of herbage growth and the total concenitration of the sugar and starch fractions, in both the herbage and the stem bases and roots of the plant. Carbohydrate storage was also delayed until the closing phase of the annual growth cycle (5). In each of these grasses, one clipping treatment, applied at the onset of the interval of carbohydrate storage, resulted in a maximum diminution in these food materials in the stem bases and roots of the plant, at tlle close of the growing season. In view of the economic importance of these facts in the management of range lands, it is obviously desirable to extend these studies to other grass species. The object of the present study therefore, was to determine: (1) the normal progress of the carbohydrate foods in the herbage and in the subterranean organs of the plant; (2) the period of food accumulation; and (3) the effect of a single harvest made at various stages of the annual growth upon the accumulation of carbohydrate food in the perennial organs of the plant. The experimental plots were located at Ruxton, on the eastern slope of Pike's Peak, in Colorado. The immediate area was a grass covered hillside situated at the upper limit of the transition life zone, and with a gentle slope to the southeast. The soil was relatively deep on the slope, showing some rock outcrop and a loose admixture of gravel. The grasses studied were wild rye, Elymus ambiguus Vasey and Scribn., and a dropseed, Muhlenbergia gracilis Trin. These grasses were predominant on the area although there were other grasses and a sparse population of low herbs present. At weekly intervals height growth data were secured by measuring 50 shoots, selected at random over the area. The dry weight increment was determined by drying the shoots in a ventilated oven at 650 C. (table I). Upon plotting these data, cumulative curves, sigmoid in character, were 727