Respiration, Carbohydrate Content, and Leaf Growth of Tall Fescue

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 (R,). 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 meristerns, 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 LERIR, relationship to zero LER, maintenance respiration of leaf terminal meristems was estimated to be about 0.95 p1 Ol.mg structural dry weight (SDW)-'. hour-', which represented 24 % of the oxygen consumed. Collared leaf segments approached maintenance levels of R, 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 R,, TNC, and LER were all directly associated. 'Contribution from the Dep. of Agronomy, Univ. of MissouriColumbia, Columbia, M O 65211. Approved for publication by the Director of the Missouri Agric. Exp. Stn. as Research Paper No. 8780. Received 5 May 1981. 2Professor of agronomy, Univ. of Nebraska-Lincoln, graduate assistant and professor, Dep. of Agronomy, Univ. of Missouri-Columbia, respectively. This research was conducted while the senior author was on sabbatic leave at the Univ. of Missouri-Columbia. The authors would like to express sincere appreciation to Mr. John Coutts for valuable technical assistance. Maximum R, 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. Additional index words: Maintenance respiration, Growth respiration, Leaf elongation, Festuca arundinacea Schreb. I DENTIFICATION of physiological and morphological characteristics of forage grasses related to dry matter production may assist plant breeders in their efforts to improve forage yield. In tall fescue (Festuca arundinacea Schreb.), a poor correlation exists between CO, exchange rate of single leaves and forage yield (Nelson et al., 1975). Horst et al. (1978) determined that leaf elongation rate (LER) was positively correlated with forage yield. Wilhelm and Nelson (1978) suggested that preferential utilization of assimilate for leaf growth during the first 16 days of regrowth was in part responsible for the rapid LER observed. Physiological processes such as partitioning and utilization of photosynthate may be more important in influencing yield of tall fescue than is the rate of carbon assimilation of single leaves. Relationships between dark respiration (R,) and whole plant growth rates have been examined assuming two components of R, (Thornley, 1970; McCree, 1970). The maintenance component is proportional to plant biomass and appears to be independent of substrate concentration (Penning de Vries, 1974). Several methods of determining the components of RD have been suggested, both experimental (McCree, 1970; Yokoi et al., 1978) and empirical (Thornley, 1970, 1977; Penning de Vries, 1975). Variation in R, components exists between species (McCree, 1974; Ryle et al., 1976; Yokoi et al., 1978; Kimura et al., 1978; Lambers, 1979), and between plant parts of the same species (Hansen and Jensen, 1977; Hansen, 1978; Jones and Nelson, 1979; Lambers et al., 1979). Plant age (Lambers, 1979) and mineral nutrition (Hansen, 1979; Lambers, 1979) also influence respiration