CARBOHYDRATE AND NITROGEN TRENDS IN BLUEBUNCH WHEATGRASS, AGROPYRON SPICATUM, WITH SPECIAL REFERENCE TO GRAZING INFLUENCES

Abstract

Undisturbed A. spicatum plants were collected, near Bozeman. Montana, at 2-week intervals from snow disappearance in the spring to late fall; in addition clipped plants were taken to simulate early spring grazing. The content of the reducing sugars, sucrose, reserve polysaccharides, total carbo-hydrates total N, and amide N were detd. for roots and herbage. Available carbohydrate reserves were stored in the lower internodes, as well as in the roots. Minimum normal reserve depletion occurred in the middle of the vegetative phase which was considered the vulnerable point in seasonal development. Shortly after the appearance of the first flower stalks max. seasonal carbohydrate content occurred in the herbage and total N declined rapidly. Two months later the peak was reached in root storage. N appeared to be an important reserve. Reducing sugars were associated with vegetative growth, sucrose with differentiation, and reserve polysaccharides with the brief rest period. Four clippings taken during 8 weeks of early spring reduced reserves below the normal minimum although C/N ratios remained essentially the same. Prolongation of the vulnerable point is of concern since the plant must develop reserves prior to the normal mid-summer drought.