Agriculture Reference
In-Depth Information
Fig. 6.2
Cross sections of leaves:
left
,
Populus maximowiczii
(
Pm
);
right
,
Acer palmatum
(
Ap
).
(From Koike 1988)
Photosynthesis and Foliar Nitrogen Content
The relationship between photosynthetic capacity and foliar nitrogen content was
brought into sharp focus in the collation by Field and Mooney (1986) of data on
wild plants (Fig.
6.3
) and the associated development of a theory for maximizing
photosynthetic return on allocation of foliar nitrogen (Mooney and Gulmon 1979;
Field 1983). Chlorophyll and photosynthetic enzymes account for the large part of
foliar
N
(Evans 1989), so it is not surprising that photosynthetic capacity is
positively correlated with foliar nitrogen content. Field's (1983) theory for optimal
allocation of nitrogen builds on the leaf-level correlation between
A
max
and foliar
N
(Fig.
6.3
) to address the question of allocation of nitrogen across all the leaves on
the plant. Field argued that the photosynthetic return on nitrogen investments is
maximized when all leaves have the same slope [
a
in (6.2)] of the line tangent to
the graph of daily photosynthetic gains on foliar nitrogen:
(6.2)
aAN
=∂ ∂
/
day
Although the optimization is scaled in terms of daily photosynthetic gains, there is
a connection to the leaf-level relationship between
A
max
and foliar
N
(Field and
Mooney 1986) through the linear relationship between
A
day
and
A
max
for a given leaf
(Field 1991; Zots and Winter 1996; Rosati and DeJong 2003). Daily photosynthetic
gain increases asymptotically with foliar
N
for a family of curves that originate in
