influence stomatal behavior and regulate leaf initi-
Gas-exchange Processes
ation, leaf expansion, and other development pro-
Growth Processes
cesses.
Death Processes
LITERATURE CITED
Allmaras, R.R., W .W . Nelson and W .B. Voorhees
(1975) Soybean and corn rooting in southwestern
Minnesota. II. Root distribution and related water
Mechanistic
inflow. Soil Science Society of America Proceedings,
Semimechanistic
39: 771777.
Amoozegar-Fard, A., D.R. Nielsen and A.W . War-
rick (1982) Soil solute concentration distributions
Flux
for spatially varying pore water velocities and ap-
parent diffusion coefficients. Soil Science Society of
Budget
America Journal, 46: 38.
Atkin, R.K., G.E. Barton and D.K. Robinson (1973)
Low
High
Effect of root-growing temperature on growth sub-
Degree of Mechanism
stances in xylem exudate of Zea mays. Journal of
Figure 12. Types of arctic plant growth models based
Experimental Botany, 24: 475487.
on relative degree of comprehensiveness and mecha-
Barber, S.A. (1978) Growth and nutrient uptake of
nism. Comprehensiveness refers to the number of pro-
soybean roots under field conditions. Agronomy
cesses considered (e.g., gas exchange, growth, and
Journal, 70: 457461.
death), whereas mechanism refers to the level of detail at
Barber, S.A. and J.H. Cushman (1981) Nitrogen up-
which each of these processes is treated (after Reynolds
take model for agronomic crops. In Modeling
and Leadley 1992).
Wastewater Renovation-Land Treatment (I.K. Iskan-
cal modeling. Mechanistic models are based on
dar, Ed.). New York: Wiley-Interscience, p. 382
the high mechanism and comprehensiveness that
409.
provide very detailed information. Flux models
Barber, S.A. and M. Silberbush (1984) Plant root
are a special kind of semimechanistic model. The
morphology and nutrient uptake. In Roots, Nutri-
models contain a high degree of mechanism and
ent and Water Influx and Plant Growth (D.M. Kral,
comprehensiveness in terms of gas exchange per
Ed.). American Society of Agronomy, Madison,
se, but tend to have low overall comprehensiveness
Wisconsin, ASA Special Pub. No. 49, p. 6587.
in terms of other plant growth processes.
Barber, S.A., A.D. Mackay, R.O. Kuchenbuch and
It is evident from the literature reviewed that
P.B. Barraclough (1989) Effects of soil temperature
whole plant models combine mechanistic princi-
and water on maize root growth. Developments in
ples with empirical observations to predict mass
Plant Soil Science, 36: 231233.
as a function of various edaphic factors. Root up-
Barley, K.P. (1970) The configuration of the root
take is usually treated in a highly simplified sub-
system in relation to nutrient uptake. Advances in
model, the root system acting as a zero-sink for
Agronomy, 22: 159201.
nutrients, and the uptake is controlled by soil wa-
Barraclough, P.B. (1989) Root growth, macro-
ter potential and transpiration rate or by diffu-
nutrient uptake dynamics and soil fertility require-
sion flux rate.
ments of a high-yielding winter oilseed rape crop.
Plant Soil, 119: 5970.
Barraclough, P.B., H. Kuhlmann and A.H. Weir
CONCLUSIONS
(1989) The effects of prolonged drought and nitro-
Our understanding of the fundamental as-
gen fertilizer on root and shoot growth and water
pects of growth and proliferation of plant roots
uptake by winter wheat. Journal of Agronomy and
within the temperate soil environment is incom-
Crop Science, 163: 352360.
plete. During the last seven or eight years, con-
Barraclough, P.B., A.H. Weir and H. Kuhlmann
cepts of plant-water relations in dry soil have
(1991) Factors affecting the growth and distribu-
changed and consider the roots rather than the
tion of winter wheat roots under UK field condi-
shoots to regulate plant growth and develop-
tions. In Plant Roots and Their Environment. Proceed-
ment. Recent evidence suggests that root signals
ings of the International Society of Root Research
17
Previous Page
