Grazing Effects on the Total Nonstructural Carbohydrate Pools in Caucasian Bluestem1

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AbstractTotal nonstructural carbohydrates (TNC) may be overemphasized relative to other factors governing plant survival in pastures. A grazing study was conducted on established 1‐ha pastures of Caucasian bluestem [Bothriochloa caucasica (Trin.) C.E. Hubb.] during 1983–1984 at the Forage and Livestock Research Laboratory, 2 km west of El Reno, OK. The objective was to compare allocation of TNC to leaf, stem (plus sheath), stem base, and dead components of heavily or lightly grazed Caucasian bluestem. Soils were fine‐silty Pachic Haplustolls of the Dale Series. Put‐and‐take stocking was used to maintain high and low grazing pressures from mid‐May to late September both years. Pastures were sampled four times in 1983 and three times in 1984 by excavating representative plants, separating them into plant parts, and analyzing for TNC. Heavy grazing pressure initially decreased (P<0.1) concentrations of TNC in all living tissues. However, no differences in TNC concentration due to grazing pressure were found the second year. On six of seven sampling dates over 2 yr, grazing pressure did not affect (P>0.1) the amount of TNC located in stem bases. Stem bases contained more than half the total shoot TNC in heavily grazed plants; however, lightly grazed plants contained much more total shoot TNC (as much as seven times greater) compared to heavily grazed plants, due to light utilization by animals. A densely appressed physical arrangement of stem bases provided sites for tiller initiation and protection from grazing. Crown architecture in Caucasian bluestem, together with physiological and morphological adjustments, ensured a nongrazeable mass of stem bases containing sufficient quantities of TNC to sustain plants under heavy grazing.