Diurnal Variations of Nonstructural Carbohydrates in the Individual Parts of Switchgrass Shoots at Anthesis

Abstract

Switchgrass (Panicum virgatum L.) was harvested at early anthesis in the field at Madison, Wisconsin, during 1972. Shoots were separated into the inflorescence, individual green leaf blades, green leaf sheaths, and internodes at 6 am, 12 noon, 6 pm, and 12 midnight during 3 days: All tissues were analyzed for percentages (dry wt) of reducing and nonreducing sugars, total sugars, starch, and total nonstructural carbohydrates (TNC). Diurnal trends were clearest in the inflorescence, leaf blades, and the upper sheaths and internodes, but they were not always statistically significant. The trend was an increase of nonreducing sugar, total sugar, and starch percentages from 6 am to 6 pm and then a decrease to 12 midnight. Diurnal change in reducing sugar percentage was small in all plant parts. Basal sheaths and internodes tended to increase in percentage of starch and TNC from 6 am to 12 midnight. These are storage parts, and presumably carbohydrates were being translocated continuously from upper parts to these lower sinks for storage, especially after 6 pm. These data indicate that pasturing in the evening might provide advantages insofar as energy concentration in herbage is concerned. The highest content of energy occurred in the inflorescence of all the individual shoot parts. Diurnal trends of elemental concentrations in the shoot parts also were determined and were found to be largely nonsignificant.