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

Abstract

Abstract 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.