Nonstructural Carbohydrates in Stem Base Components of Tall Fescue During Regrowth1

Abstract

Nonstructural carbohydrates in stem bases are important for regrowth of tall fescue (Festuca arundinacea Schreb.). The objectives of this study were to i) examine changes in concentration of nonstructural carbohydrates in individuals tem base tissues during regrowth; ii) evaluate the relationship between leaf elongation rate (LER) and concentration of nonstructural carbohydrates; and iii) estimate the degree of polymerization (DP) fructans in tissues during regrowth. Plants were grown in a controlled environment chamber at 23°C with a photosynthetic photon flux density of 650 µmol m−2 s−1 during a 14‐h photoperiod. Plants were sampled immediately following defoliation and 2, 4, 7, 10, 14, 17, 21, and 24 days later. Reducing sugars, nonreducing sugars, starch, and fructan in intact stem bases declined to approximately 50% of initial concentrations by Day 4, and returned to original concentrations by Day 24. Initial concentrations of starch and fructan were higher in younger (inner) sheaths,when compared to older sheaths.Concentrations of nonreducing sugars in all sheaths declined following defoliation, while concentrations of reducing sugars and starch did not change markedly. Fructan concentrations on Day 24 were 19 and 77% of initial concentrations in the oldest and youngest sheaths, respectively. Nonstructural carbohydrates accumulated in newly formed sheaths and were not restored in older sheaths. Nonreducing sugars and fructan in elongating leaf bases declined to approximately 30% of initial concentrations by Day4. Maximum LER of 16 mm day−1 occurred between Days 2 and 7, which indicates that carbohydrates may not normally limit LER. The DP of fructan in old sheaths initially averaged 19 and decreased during regrowth, while the DP of 15 of young sheaths remained constant. The DP of fructan in bases of elongating leaves was less than 6 during rapid growth. Bases of elongating leaves may be more appropriate than intact stem bases as indicators of the availability of nonstructural carbohydrates for regrowth because of their responsiveness to defoliation.