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lived leaves, there is a more gradual linear decline of photosynthetic rate with age
(Matsumoto 1984; Koike et al. 1994). The general tendency is for photosynthetic
capacity to decrease with leaf age, but the rate of decrease lessens as leaf longevity
becomes greater (Fig.
2.11
).
There are two hypotheses to explain the decline of photosynthetic capacity
with time: (1) acclimation to the changing light regime of individual leaves as
the canopy develops (Hikosaka 1998; Gan and Amasino 1997) and (2) dimin-
ished function resulting from age-related changes and senescence of foliar
tissues (Guarente et al. 1998; Warren 2006). The two hypotheses are not mutu-
ally exclusive. Reduced insolation can induce translocation of nitrogen from a
shaded, older leaf to a younger sunlit leaf (Hemminga et al. 1999), with conse-
quent degradation of photosynthetic function in the older leaf. Even if the
microenvironment around a leaf is stable over its lifetime, cumulative damage
and reduced internal conductance of CO
2
(Hensel et al. 1993; Guarente et al.
1998; Nooden 2004; Warren 2006) can lead to gradually lower photosynthetic
capacity in older leaves.
Ha
10
Ki02
Ps
Po
As
Ki02
1
Am
Ah
Bp
Ki97
Ki97
Fc
Ki97
0.1
Ki97
Ki97
0.01
10
100
1000
Leaf Longevity days
Fig. 2.11
Relationship between the rate of decline in photosynthetic capacity with time and leaf
longevity. Data are for
Acer mono
(Am, Kikuzawa and Ackerly 1999),
Alnus hirsuta
(Ah, Kikuzawa
and Ackerly 1999),
Alnus sieboldiana
(As, Kikuzawa 2003), five tropical tree species (Ki97,
Kitajima et al. 1997), two tropical pioneer tree species (Ki02, Kitajima et al. 2002),
Betula platy-
phylla
(Bp, Kikuzawa and Ackerly 1999),
Fagus crenata
(Fc, Kikuzawa 2003),
Heliocarpus
appendiculatus
(Ha, Ackerly and Bazzaz 1995),
Polygonatum odoratum
(Po, Kikuzawa 2003),
and
Polygonum sachalinensis
(Ps, Kikuzawa 2003)
