Agriculture Reference
In-Depth Information
Box 4.3
The Monsi-Saeki Model and Its Implications
Masami Monsi and Toshiro Saeki (1953) were pioneers in the development of
models for ecosystem productivity. They presented a canopy photosynthesis
model in which (1) light intensity decreased exponentially with accumulating
leaf area and (2) canopy photosynthetic rate increased asymptotically with
light intensity. Thus, in a given light regime there should be a depth in the
canopy where photosynthetic gains are just balanced by respiratory losses;
any deeper into the canopy respiratory losses surpass photosynthetic gains.
Monsi and Saeki predicted that in a given light regime there should be an
optimum leaf area index (LAI, the area or biomass of leaves per unit ground
area), although they recognized that the optimal LAI might also depend on
interactions among leaf angle, leaf size, and branching architecture that influ-
enced light interception in different species and plant communities. Monsi
and Saeki's pioneering work stimulated many studies to see how LAI varied
after canopy closure within and among diverse plant community types. For
example, Tadaki and Hachiya (1968) reported that the LAI in terms of leaf
weight per unit land area was consistently about 3.0 ton ha
−1
for temperate
deciduous forests, 8.6 ton ha
−1
for evergreen broad-leaved forests, and
16 ton ha
−1
for evergreen coniferous forests.
Although Monsi and Saeki developed their model for plant communities,
it has implications for individual plant canopies as well. If leaf biomass in
a community or in the canopy of an individual plant is constant, then any new
leaf production must be associated with the fall of a corresponding amount
of old leaves. Light captured by a new leaf in the upper canopy will reduce the
light penetrating to the deepest level of the canopy, thus tipping the balance
of photosynthetic gains to respiratory losses in the most shaded leaves and
(continued)
