ABSTRACT
Summary Seasonal changes in amount, composition, and digestibility of fiber in vegetative tissues of forage grasses are usually associated with advancing tissue maturity. Our objective was to determine the relative effects of maturity and environment on amount and composition of hemicellulose in field-grown tall fescue (Festuca arundinacea Schreb.). Regrowth of identical chronological age was sampled weekly at different times during the growing season. Leaf samples were extracted with neutral detergent solution to isolate cell walls (NDF). The NDF was treated with 1.0 H2SO4 to remove and hydrolize hemicellulose. The hydrolyzates were analyzed for concentrations of xylose and arabinose, using high performance liquid chromatography. Hemicellulose concentration decreased during regrowth in early summer, remained about the same during midsummer, and increased in late summer. Conversely, xylose concentration in hemicellulose increased during early summer and decreased during late summer, while arabinose concentration remained about the same throughout the season. These results indicate that the effect of time of season was greater than that of tissue age and imply that environment influenced the composition of the cell wall. Using growth data, weekly changes in hemicellulose composition of new growth were calculated. Differences due to season were greater than indicated by the whole-plant data, suggesting that composition of the newly synthesized cell wall changed considerably during the growing season, conforming more closely to trends in photoperiod than in temperature.
