Respiration, Carbohydrate Content, and Leaf Growth of Tall Fescue1

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Abstract
Tall fescue (Festuca arundinacea Schreb.) was grown in controlled environment chambers with a 14‐hour photoperiod, and then kept in darkness for 8 days in one experiment and 20 days in another. The objectives were to determine concentrations of total nonstructural carbohydrates (TNC) and relate them to leaf elongation rates (LER) and to rates of dark respiration (RD). After various times in darkness, leaf terminal meristems in vegetative tillers, root tips, and center‐sections of collared leaf blades were excised, and oxygen consumption was measured.Oxygen consumption was generally highest in terminal meristems, intermediate in root tips, and lowest in mature leaf blades. For the first 6 days the daily LER was greater in plants growing in darkness compared with those in 14‐hour photoperiods. From 6 to 12 days of darkness, LER was similar on both sets of plants. After 12 days the dark‐grown plants had lower LER. By extrapolation of the LER/RD, relationship to zero LER, maintenance respiration of leaf terminal meristems was estimated to be about 0.95 μ1 02‐mg structural dry weight (SDW)‐1.hour‐1, which represented 24% of the oxygen consumed. Collared leaf segments approached maintenance levels of RD after 2 days of darkness and root tips after 8 days. However, terminal meristems had a high TNC concentration and continued to support leaf growth actively for up to 16 days of darkness. The RD, TNC, and LER were all directly associated. Maximum RD in terminal meristems occurred at 35% TNC while LER remained similar when TNC levels were higher than 28%. In mature leaf tissue about 60% of the oxygen consumption was associated with maintenance respiration.