Agriculture Reference
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axes of variation in foliar design (Wright et al. 2004) and, more generally, is an
important index of plant strategies at the whole-plant level as well (Westoby 1998;
Westoby et al. 2002).
Specific leaf area, the inverse of leaf mass per area, was considered a key
element in studies of plant productivity beginning in the early twentieth century
(Blackman 1919; Clifford 1972). It was, however, only in the 1970s when tradi-
tional methods of growth analysis began to be superseded by direct measures of
photosynthesis using infrared gas analysis techniques (Šesták et al. 1971) that the
positive correlation between
A
max
and LMA (Fig.
6.1
) gradually came into explicit
discussion, through the interests first of plant breeders (Gifford and Evans 1981;
Marini and Barden 1981) and then of ecologists (Oren et al. 1986; Koike 1988;
Reich et al. 1991). Physiological ecologists were quick to recognize how
anatomical variation in leaves contributed to differences in LMA and could in
turn influence photosynthetic function (Nobel et al. 1975; Koike 1988). For
example,
Populus maximowiczii
with a high LMA has relatively thick palisade
and spongy mesophyll layers (Fig.
6.2
), which facilitate high
A
max
in its sunny,
early successional environment (Koike 1988; Hanba et al. 1999; Terashima
2003). Conversely,
Acer palmatum
is a species of shaded forest understory envi-
ronments with a low LMA and a thin leaf lacking extensive internal air space and
having low
A
max
(Koike 1988). These sort of investigations firmly cemented LMA
(or specific leaf weight, SLW, or its inverse, specific leaf area, SLA) as part of a
growing constellation of traits critically associated with the photosynthetic capac-
ity of leaves.
MAY 25
JULY 16
24
20
16
12
Peripheral
Interiors
8
Y=6.0+1.6x
Y=
−
5.0+2.5x
r=.70*
4
r=.83
*
0
4
8
12
4
8
12
SLW (mg cm
−
2
)
Fig. 6.1
Relationship between photosynthetic capacity (
Pn
) and leaf mass per unit area (LMA)
(here,
SLW
) for individual leaves in the interior or peripheral canopy of orchard-grown apple trees
just after leaf maturation (May 25) and in midsummer (July 16). (Redrawn from Marini and
Barden 1981)
