Agriculture Reference
In-Depth Information
availability often limited plant productivity in terrestrial ecosystems, considerable
attention subsequently has been devoted to the optimal distribution of nitrogen
across canopy strata (Field 1983; Hirose and Werger 1987a,b). Most of this litera-
ture tracing back to Monsi and Saeki (1953) has taken a static view of the plant
canopy, but recently Hikosaka (2003a,b, 2005) has turned the focus toward the
dynamics of leaf turnover in the context of optimizing a stratified plant canopy. He
considers that leaves are produced from the products of canopy photosynthesis and
that after the canopy reaches a stable state older leaves will be shed in proportion
to the production of new leaves. Simulations using Hikosaka's model revealed the
negative trends of leaf longevity on canopy light environment and on availability of
soil nitrogen that have been documented in studies at the canopy level. Hikosaka's
model also showed a positive correlation between leaf longevity and leaf mass per
leaf area (LMA), which is consistent with both models and observations (Fig.
4.4
).
a
b
200
26
150
24
100
22
50
20
0
0
0123456
Nitrogen uptake rate (mmol m
-2
d
-1
)
500
1000
1500
2000
Noon PFD (
µ
mol m
-2
d
-1
)
c
d
30
120
N uptake rate
= 0.4
N uptake rate = 0.4
25
80
20
N uptake rate = 4
N uptake rate
= max.
40
0
15
0
0.1
0.2
0.3
0 0
100
150
200
250
Leaf mass per area (g m
-2
)
Slope of P
max
−
n
L
relationship
(mmol m
-1
s
-1
)
Fig. 4.4
Relationships between leaf longevity and (
a
) nitrogen uptake rate from soil, (
b
) irradiance,
(
c
) relationship between photosynthetic capacity and foliar nitrogen, and (
d
) leaf mass per area.
(From Hikosaka 2003a, b)
