Seasonal variation of total non-structural carbohydrate (TNC) levels in "Bromus tomentellus" under moderate and heavy grazing in Semirom

One of the problems of rangelands in Iran is the early grazing which threatens the regeneration and persistence of many palatable species. Non-structural carbohydrate reserves are considered to be very important for primary growth and also for regrowth of range plants after defoliation. Bromus tomentellus is one of the important and wide spread species in mountainous rangelands of Iran. This palatable species is intensively grazed by livestock. This study aimed to determine the variation of non-structural carbohydrate of this species in three phenological stages for estimating the best time of grazing in Shahid Hamzavi research station in Semirom, Isfahan province. Two rangeland sites with heavy and light grazing histories under three phonological stages (early growth stage (3-4 leaves), panicle emergence and seed ripening) were preferred. Six individual plant were selected randomly in each phonological stage and then the reserves of non-structural carbohydrate were measured in shoot (stem base) and root. According to AOAC, Sheffer-Somogy (1940) method, the total amounts of non-structural carbohydrates were determined. Results indicated that in seed ripening stage the TNC in both shoot and root under light grazing was 2.23 mg/g and significantly higher than that under heavy grazing (1.25 mg/g). Roots contained significantly higher levels of TNC than Stems. TNC levels were minimum in early growth stage but maximum in panicle emergence stage. These results emphasized the degrading effect of early grazing while panicle emergence stage found to be the proper time for the beginning of grazing.