Growth Morphology of Reed Canarygrass (Phalaris arundinacea L.) Tillers under Sward Conditions

Trends of formation and senescence of leaves, length of successive component organs (leaf blades, leaf sheaths and internodes), and total length of reed canarygrass (Phalaris arundinacea L.) tillers in swards with different cutting frequency and nutrient level were investigated during growing seasons in 1987. the leaf appearance on each growing tiller (16 tillers per treatment were examined in every growth period of swards) was rather rapid and regular with the rate of around 6-7 days/leaf during the first half period of each primary and aftermath growth, irrespective of cutting frequency and nutrient level (Fig. 1, Table 2). The death of 1st leaf was observed in the beginning of May in primary canopy or in ca. 20 days after previous cutting in aftermaths, and the leaf death gradually extended upwards. The rate of leaf senescence proceeded much more slowly than that of the leaf formation, resulting gradual increment of living leaf numbers per tiller during each growth period. The increase of tiller length was most abundant in the latter half period of primary growth and was suppressed a little in autumn, however, the difference in length increment of tillers was rather small among seasons (Fig. 2). The pattern of tiller elongation fairly resembled under different managements and seasons, that is, the first rapid growth of tillers continued until they attained ca. 30 cm height, being followed by short rest period of elongation, and thereafter quicker increment in tiller length was resumed. Leaf blade length of tillers in each period increased successively until leaf blade attained maximal size at 6th to 7th phytomer which was counted acropetally from the first blade-bearing leaf, and subsequently it got shorter size (Fig. 3). During the course of growth in primary canopy, lower internodes which attached to the same phytomer units of first few successive leaf blades remained very short in length, whereas 4th or much higher-positioned internodes got successively longer size, terminating at 9th to 10th phytomer because of ear formation. Although elongation was short in first 2 to 3 nodes, successive internodes elongated rather longer inspite of vegetative growth in aftermath canopies, resulting higher C/F ratio in swards with longer regrowing pariod (Table 3). The estimation of total length of internode elongation at each leaf age by finding the remainder of tiller length and uppermost expanded leaf length (leaf blade + leaf sheath) suggested that abrupt internode elongation would occur at the beginning of May (ca. 30-35 days after sprouting in early spring) or about 25 days after each cutting, when the 2nd rapid increase of tiller length began (Fig. 4). Highly positive correlation between DM yield of swards and C/F ration (Fig. 5) indicates that the internode elongation of each shoot component in swards may perform the most important part for high and seasonally-balanced DM production in reed canarygrass. This high shoot growth rate should be derived partly from the regular diversion of the growth distribution pattern from the initial leaf formation to the preferential internode elongation which prepares a new active sink for dry matter accumulation in the shoot.