Grazing effects on shoot and root dynamics and above- and below-ground non-structural carbohydrate in Caucasian bluestem

The objective of this study was to characterize changes in morphology and shoot/root total nonstructural carbohydrate (TNC) relationships in Caucasian bluestem (Bothriochloa caucasica) under grazing. Pastures were continuously grazed by steers weighing about 225 kg from mid-May to late September of 1983 and 1984. Heavily grazed (H) swards produced more tillers m⁻¹ than lightly grazed (L) swards. Number of tillers declined in both treatments during the midsummer drought period; however, the reduction was much less in H than in L swards. Above normal precipitation in August 1983 allowed number of tillers to rapidly recover (by approximately 4000 and 8000 m⁻¹ for L and H treatments, respectively) reaching 10 700 and 17 800 tillers m⁻¹ respectively, in late September. After 2 years of grazing, H swards initiated twice as many roots on an area basis; however, ability to penetrate soil to lower depths may have been reduced. Heavily grazed Caucasian bluestem had lower concentrations of total non-structural carbohydrate (TNC) in shoots ( P < 0.04) in both years, but had higher (28% at the end of 1984) TNC concentration in roots compared to lightly grazed ( P = 001) plants. Greater root mass was found in lightly grazed swards; therefore, we suggest that root growth and TNC concentration tend to be inversely related. Total amount of TNC was higher in L swards, but during the course of the study total above and below-ground TNC in H swards remained stable. Total above-ground TNC pools are subject to short-term variation and dilution from senescent herbage, thus TNC pools in individual plant parts may be a better indication of plant response.