Agriculture Reference
In-Depth Information
The basic patterns of shoot growth are also reflected in contrasting degrees of
development of the embryonic shoot within the bud. In determinate species, leaves
in the bud are unexpanded but already nearly completely developed before budburst,
and all the leaves appear simultaneously as a flush associated with rapid stem elon-
gation; this type of simultaneous shoot growth is always associated with fully
preformed shoots (Hallé 1978). Expansion of the embryonic leaves in a preformed
shoot may be arrested after their initial development for weeks or even years before
budburst (Foster 1929, 1931; Garrison 1949a,b, 1955; Barthélémy and Caraglio
2007). In species with indeterminate shoot growth, in contrast, single leaves appear
successively along a slowly growing shoot (Kikuzawa 1978, 2003). Leaves of
species with successive, indeterminate shoot growth may be either preformed in the
bud (Kikuzawa 1982) or newly produced (neoformed) during the growing season.
Some trees, such as species in the genus
Betula
, have both determinate “short
shoots” and indeterminate “long shoots” within their canopy (Kikuzawa 1983).
Leaves on the short shoots and the initial leaves on long shoots are preformed in the
overwintering bud, and later leaves on the extending long shoots are formed only
in the season they emerge (Macdonald and Mothersill 1983; Macdonald et al. 1984;
Caesar and Macdonald 1984). These patterns of simultaneous leaf emergence in
species with determinate shoot growth and successive leafing in species with
indeterminate shoot growth, as well as the combination of the two shoot growth
syndromes in some species, are found in evergreen trees in temperate regions (Nitta
and Ohsawa 1997), herbaceous plants (Yoshie and Yoshida 1989; Kikuzawa 2003),
and tropical trees (Lowman 1992; Kikuzawa 1978; Miyazawa et al. 2006).
There also is some relationship between the structure of buds and the nature of
shoot growth and leaf emergence in deciduous broad-leaved trees (Kikuzawa 1983,
1984, 1986). Species that have buds covered by well-developed, distinct bud scales
inevitably have determinate shoot growth (flushing with simultaneous leafing), but
not all species with determinate shoot growth necessarily have true bud scales. For
example,
Styrax obassia
has a naked bud, but it also has determinate shoot growth.
The incipient shoot forming within the bud of any species with true bud scales is
referred to as heteronomous (Fig.
2.3
) because the shoot contains two types of meta-
meric units: one forms the bud scales themselves and the other forms true leaves
(Kikuzawa 1983, 1986). On the other hand, species with indeterminate shoot growth
(successive leafing) generally lack true bud scales and are referred to as homono-
mous: all the metameric units comprising the shoot are basically identical, producing
leaves that may or may not have stipules or other ancillary structures derived from
the leaf lamina functioning as bud scales in the outermost metameric whorl. In
Alnus
hirsuta
, for example, the stipules of the outermost leaf function as scales enveloping
the bud as opposed to the distinct bud scales in
Ulmus davidiana
(see Fig.
2.3
).
In the Aceraceae there is a morphological series suggesting the evolutionary transition
from homonomous to heteronomous buds (Sakai 1990).
Dipteronia
, the closest and
more primitive relative of
Acer
, is homonomous, lacking bud scales entirely
(Fig.
2.4
). In
Acer
species with determinate shoot growth the distinction between
normal leaves and bud scales is clear - the bud is fully heteronomous. In
Acer
spe-
cies with indeterminate shoot growth, however, the distinction between heteronomy
