Agriculture Reference
In-Depth Information
Leaf N or A
max
Fig. 6.4
Interrelationships among daily photosynthetic capacity (
A
day
), maximum photosynthetic
capacity
(A
max
), and foliar nitrogen (
N
). The relationship between
A
day
and
A
max
is linear (
dashed
line
);
A
day
increases asymptotically with foliar
N
dependent on evolutionarily constrained
responses to the ambient environment of the leaf. The three asymptotic curves are examples of
possible
A
day
-
N
relationships, in each case with the optimal allocation of
N
when the tangent lines
to the curves are equivalent. When tangent lines correspond to lines originating at the origin,
nitrogen use efficiency (NUE) is optimum. Because
Leaf N
is proportional to
A
max
, this relationship
can be taken as a surrogate for the
A
day
-
A
max
relationship reported by Zots and Winter (1996)
b
a
1000
1000
100
100
63
63
10
1000
10
21
21
1000
100
100
7
7
10
10
Herbs
Pioneers
Broad-leaved deciduous
Broad-leaved evergreen (leaf life-span > 1 year)
Needle-leaved evergreen
Fig. 6.5
Consistent relationships among three key elements of foliar function for 111 species
from six biomes (
a
) and for 170 species reported in the literature (
b
). (From Reich et al. 1997)
Photosynthetic Function and Leaf Longevity
Reich and his colleagues (Reich et al. 1991, 1992) also had been investigating the
relationship between
A
max
and leaf longevity, as had others (Gower et al. 1993;
Yamamoto 1994). Their 1997 paper (Reich et al. 1997) documented not only the
