raLi and Forage Science (1988) Volume 43, 111-119 Grazing effects on shoot and root dynamics and above- and below-ground non-structural carbohydrate in Caucasian bluestem S. CHRISTIANSEN AND T . SVEJCAR Forage and Livestock Re.fearch Laboratory, El Reno, Oklahoma. USA Abstract The objective of this study was to characterize changes in morphology and shoot/root total non- structural carbohydrate (TNC) relationships in Caucasian bluestem {Boihriochloa 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" ^ 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"^ for L and H treatments, respectively) reach- ing 10 700 and 17 800 tillers m ^ 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 (/'<0 04) in both years, but had higher (28% at the end of 1984) TNC concentration in roots compared to lightly grazed (/*=00I) plants. Greater root mass was found in lightly grazed swards; therefore, we suggest that root growth and TNC concentration tend to be inver- sely related. Total amount of TNC was higher in L swards, but during the course ofthe study total above- and below-ground TNC in H swards Correspondence; Dr Scoll Chrisliansen, USDA-ARS, For- age and Livestock Research Laboratory, P.O. Box i|99. El Reno. OK 73036, USA. 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. Introduction Caucasian bluestem (Bothriochloa caucasica) was introduced to the United States as a single plant introduction (PI 78758) from the Botanic Gar- den, Tiflis, Caucasus, USSR on 4 February 1929 (Harlan, 1952), with intended use for revege- tation of depleted range and marginal cropland. The use of Caucasian bluestem in forage-live- stock production systems in the Southern Great Plains has expanded following evidence oflong- term adaptability (Eck and Sims, 1984) and beef production greater than that possible with most native range species (Sims and Dewald, 1982). Caucasian bluestem is generally considered graz- ing tolerant, but grazing response of this C4 grass remains undocumented. Tillering ability is an important characteristic in the selection of species which will persist under heavy grazing. Well-grazed swards ofthe grazing tolerant species Lolium perenne develop high population densities of small tillers (Jones et al., 1982; Grant et a!., 1983; Grant and King, 1983; Parsons etal., 1984). The release of meristems and subsequent increase in tillering with heavy graz- ing has been attributed to increased light intensity (Grant and King, 1983) and altered light quality (Deregibuser fl/., 1985) reaching the plant crown. Control of tillering by light intensity and/or quality might aid in balancing population levels with available resources. To support high levels of tillering under intense defoliation, grazing tolerant plants must allocate carbon to active meristems. Richards and Cald- II