100 Influential Papers - page 24

Monteith, J.L. (1972)
Solar radiation and productivity in tropical ecosystems.
Journal of
Applied Ecology, 9, 747-766.
The elegant concept developed by John Monteith was that plant productivity could
be determined from the proportion of incident radiation absorbed, and converted into
dry matter, by a crop canopy. Deriving this conversion efficiency was fundamental and
far-sighted; this approach is now the basis for determining the annual productivity
of crops and natural vegetation. Applications using ‘radiation use efficiency’ now
include harvest index calculations for horticulture or agricultural crops; estimates of
productivity and turnover in forest savannas, tropical forests, and boreal peatlands, as
well as global biomass inventories. This concept is now incorporated into large-scale
models from canopies to ecosystems, via eddy covariance and satellite remote sensing.
Monteith (1972) also compared productivities of crops which we now recognize as
C3 (rice, soybeans, groundnuts) or C4 (maize, millet, sorghum) as a function of light
energy conversion. A schematic defining C3 and C4 energy
conversion is now commonly used to define future
agricultural demand. Although published in 1972,
25% of citations have occurred in the past three
years! Given the current pressures on food
production, carbon sequestration by natural
vegetation and the need to predict and scale
such processes for the future, the relevance of
Monteith’s logical insights, and the legacy of
this paper, will endure.
Howard Griffiths
Hellkvist, J., Richards, G.P. & Jarvis, P.G. (1974)
Vertical gradients of water potential and tissue water relations in Sitka
spruce trees measured with the pressure chamber.
Journal of Applied
Ecology, 11, 637-667.
The paper by Paul Jarvis and colleagues has endured as a field-based study which
married theoretical considerations of water-relations components in a quantitative,
practical fashion. Gradients in water and solute potential, and the bulk modulus of
cellular elasticity, were coupled to diurnal variations in evaporative demand within
a Sitka spruce stand. Developing the theoretical considerations of Scholander and
Tyree, the paper provided a robust confirmation of theory with some exquisite data
and insightful analysis. Many subsequent studies building on these approaches now
recognize that the hydraulic conductance of roots, stems and leaves form an equally
important contribution to maintaining sap flow, together with chemical and hydraulic
signals, in part regulated by aquaporins. Limitations imposed by water transport in
the tallest redwoods or eucalypts can be viewed in the context of recent insights into
the frequency of cavitation and associated dynamic repair processes. The hydraulic
pathway in leaves is now seen to be an equivalent limitation to that imposed by stomata
in regulating water fluxes to the atmosphere. Most recently, the notion that the turgor
loss point, derived from P-V curves, serves as a drought tolerance index, has re-
emphasised the fundamental importance of the work initiated by Hellkvist
et al
. (1974).
Howard Griffiths
S ECT I ON F I VE
PHYS I OLOG I CA L ECOLOGY
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5
Clymo, R.S. (1973)
Growth of
Sphagnum
: some effects
of environment.
Journal of Ecology,
61, 849-869.
Dicky Clymo has contributed more to our
knowledge of
Sphagnum
than perhaps
anyone else and, as he reminds us, it is
important because there is a lot of it, its
ecology and physiology are distinctive,
and peat bogs are largely comprised of its
remains. In this substantial study Clymo
combines experimental manipulations in
the laboratory with observations in the
field to understand the ways in which
physical factors (water table height and
light) and chemical factors (H
+
and Ca
2+
ions) influence the growth and niche
separation of twelve species of
Sphagnum
,
which are characteristic of a range of
mire communities. The study elegantly
demonstrates the importance of interacting
factors and shows that variables cannot
be simply combined in an additive way.
Clymo elucidates the mechanistic basis
of the species-specific responses to
water table height and demonstrates that
ecological and physiological optima do not
necessarily coincide. Further, data from
experimental perturbations are used to
explain community level patterns in the
field. On a personal note, the clarity and
novelty of Clymo’s research was reflected in
his brilliant teaching, which inspired me to
pursue my chosen career path.
Malcolm Press
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