Agriculture Reference
In-Depth Information
temperate deciduous broad-leaved forests, where the leaf longevity of species with
determinate shoot growth such as
Fagus crenata
,
Quercus crispula
, and
Carpinus
cordata
was 160-180 days, whereas leaf longevity in
Alnus hirsuta
with indetermi-
nate shoot growth was 80-90 days (Kikuzawa 1983, 1988). Because there is no limi-
tation set by the length of the growing period in aseasonal tropical forests, the same
expectation need not apply, but in fact the leaf longevity of species with indeterminate
shoot growth still tends to be less than those with determinate shoot growth. Leaf
longevity was 1-4 months in
Heliocarpus appendiculatus
(Ackerly and Bazzaz 1995)
with indeterminate shoot growth. Leaf longevity of
Dendrocnide excelsa
, a species in
subtropical and cool temperate rainforests with indeterminate shoot growth, was
about 7 months compared to 20 months in species such as
Doryphora sassafras
,
Ceratopetalum apetalum
, and
Nothofagus moorei
with determinate shoot growth
(Lowman 1992). There is clearly endogenous organization of the timing of shoot
growth and leaf turnover.
In species with indeterminate shoot growth, the birth rate of a leaf (
r
) is given
by the ratio of standing leaf number (
N
) on a shoot and leaf longevity (
L
) from (4.6)
(Ackerly 1996).
rNL
=
/
(7.1)
Designating 1/
r
=
P
,
P
represents the interval between emergence of leaves,
which is called the plastochron interval (Maxsymowych 1959). Using
P
, we can
rewrite (7.1) as
L N
=
ยท
(7.2)
Leaf longevity thus can be estimated as the product of number of leaves and the
plastochron interval. Ackerly (1996) compared species with leaf longevity from 32
to 5,200 days and standing leaf number per shoot ranging from 3 to 45 (Fig.
7.1
).
For species with indeterminate shoot growth, leaf longevity largely depends on the
rate of leaf turnover, with the oldest leaf being lost as a new leaf emerges. If the
growth rate and loss rate of leaves are equivalent, the canopy will be in steady state.
Moreover, if photosynthetic capacity is determined by the position of leaves as
expected in (4.13), then the canopy photosynthesis at any time should be equivalent
to the photosynthetic gain of a single leaf throughout its life: in other words, there
appears to be an ergodic character to the functional relationships between
the leaf and canopy levels (Kikuzawa et al. 2009). Leaf longevity in this steady-
state condition then is determined by the appearance rate of leaves, which will
reflect the shoot growth rate.
Plant Growth Rates and Leaf Longevity
A negative correlation between the relative growth rate of plants and leaf longevity
is expected when a tree canopy is in a stable state with new leaves produced at the
same rate as leaves dropping; then, leaf longevity is determined simply by the inverse
