Cell division in meristematic tissues, followed by cell expansion, is responsible for plant growth and development. The most important meristematic region is the crown. Crowns form as shoots develop from the embryo of germinating seeds, from terminal buds of rhizomes (and/or stolons in some species), and from axillary buds on the crown that develop into tillers. Like leaves, tillers grow upward within sheaths of enclosing leaves.
The crown is an unelongated stem located at the base of the plant at or below the soil surface, and it includes an upper stem apex with bud meristems from which new shoots grow, unelongated internodes, and lower meristematic nodes from which new adventitious roots are initiated. All leaves originate from ridge-like, subapical meristems that form just below the crown apex. An intercalary meristem produces new cells at the base of each emerging leaf (Hull, 2003). Photomicrographs of these structures can be seen in Chapter 14. The leaf tip is pushed upward inside the sheath of the previously formed leaf as these cells enlarge. Cell division usually stops by the time the leaf tip emerges from the enclosing leaf sheath. As the leaf grows, a second intercalary meristem forms above the crown and below the first intercalary meristem. This meristem produces cells that contribute to the growth of the leaf sheath. Leaf sheath cells usually continue to divide and expand for some time after the leaf blade is fully developed. The growth of leaves is synchronized. As the tip of one leaf moves upward within the shoot, the sheath of the next oldest leaf begins to grow. Newly emerging leaves often use more carbohydrates than they produce. Young, fully expanded leaves have the highest photosynthetic rate and contribute photoassimilates to other plant parts. As older leaves approach senescence, they contribute very little energy to the rest of the plant (Hull, 2003). Improved, turf-type tall fescue cultivars are classified by growth type as forage/early standard, standard, semidwarf, and dwarf.
Rhizomes are underground lateral shoots arising extravaginally from crowns. A rhizome contains leaves arranged in an alternate pattern, nodes, internodes, and axillary buds. Unlike aerial shoots, a rhizome has scalelike leaves, elongated internodes and a small, conical leaf enclosing the tip. Buds in the axil of each leaf may produce aerial shoots, roots, or branch rhizomes.
Rooting characteristics vary among turfgrass species and tall fescue cultivars. In a 2-yr greenhouse study, ‘Mustang' tall fescue had a total root length in the 0- to 120-cm depth (0-47 in depth) soil partition from 180 to 270% greater than that of ‘Midlawn' bermudagrass (Cynodon dactylon (L.) Pers. ´ C. transvaalensis Burtt Davy), ‘Prairie' buffalograss [Buchloë dactyloides (Nutt.) Engelm.], and ‘Meyer' zoysia (Zoysia japonica Steud.) (Qian et al., 1997). Tall fescue was mowed once weekly at a height of 6.4 cm (2.5 in) and bermudagrass, buffalograss, and zoysia were mowed twice weekly at 4.5 cm (1.75 in). Maximum root extension of the tall fescue cultivar was 33 to 60% deeper than that of the warm-season turfgrasses. Results of a study indicated that harvested roots of the perennial ryegrass cultivars Manhattan II, Rodeo, and Stallion were much heavier than those of Arid, ‘Falcon', and Rebel tall fescues (Han et al., 1992). Under greenhouse conditions, Arid had a higher primary root length density at a soil depth of 25 to 100 cm (10-40 in) and greater total root length than Bonsai, a dwarf, turf-type tall fescue (White et al., 1993). Similarly, a rhizotron imaging system revealed that Rebel exhibited less drought stress and had a more even distribution of roots throughout the soil profile than other standard, dwarf, and semidwarf cultivars (Watkins et al., 2002). A rhizotron is a clear-walled chamber through which roots can be monitored as they grow. The dwarf, turf-type cultivar Matador had the majority of living roots at a soil depth from 0 to 25 cm (0-10 in) and showed the greatest amount of drought stress.
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