Some Aspects of the Water Relations of two Mahogany Species
Date
1971-12
Authors
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Journal ISSN
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Publisher
Univeristy of Ghana
Abstract
The general distribution, growth form and economic importance of
Khaya senegalensis (Desr) A. Juss. and Khaya ivorensis A. Chev. are
described. Some aspects of the water relations of seedlings of these
two species, the former a savanna species and the latter a forest species
were studied with the view of ascertaining whether moisture plays an
important role in determining the pattern of their distribution.
Growth of seedlings under four soil watering regimes namely -
-0.3 (A), -0,4 (B), -0.8 (C), and -4.5 (D) bars; and under culture
solution and culture solution to which polyethylene glycol was added
to give the following osmotic potentials (bars): -0.3 (A), -2.8 (B),
-5.3 (C), aid -10.3 (D) was studied. The experiment was done in the
greenhouse . Growth of K. Senegalensis was more sensitive to moderate
moisture stress and less sensitive to high moisture stress. K, ivorensis
on the other hand showed less sensitivity to moderate stress but high sensitivity
to severe stress. However when soil moisture stress was -0.3 bars,
growth of K. ivorensis was very poor. This was attributed to a reduction
in root permeability due to poor aeration as a result of more permanent near
saturation of the soil.
Studies of diurnal patterns of plant water status were carried out
by examining leaf relative water content, (R.W.C.) leaf water potential
(L.W.P.) and stem diameter variation, in relation to soil moisture stress.
R.W.C. was overall higher in seedlings of K. senegalensis than in those of
K. ivorensis. L.W.P. on the other hand was lower for IC. senegalensis than
for K. ivorensis seedlings. Stem shrinkage decreased with decrease of soil
moisture content from 100 to about 50%, field capacity. The decrease in
K. senegalensis was greater than in K. ivorensis-. However at 27% field
capacity, shrinkage in K. senegalensis was consistently reduced more than in
K. ivorensis. This may indicate better water conservation by the former
species.
Transpiration was also studied in relation to the soil moisture
treatments, both in the greenhouse aid in the research room, the latter
being a semi-controlled environment where temperature, relative humidity
and light intensity were precisely known. The transpiration of seedlings
growing in osmotic solution was also studied in the greenhouse, employing
stresses of -0.3 and -10.3 bars. Transpiration generally decreased with
moisture stress in the root medium. In the research room transpiration of
K. senegalensis was higher than that of IC. ivorensis under all soil
treatments. In the greenhouse, however, similar higher transpiration rates
were recorded for K. senegalensis seedlings than for K. ivorensis seedlings
when stress was from -0.3 to -0.8 bars, but at severer stresses (-4.5 and
-10.3 bars) transpiration of K. senegalensis was reduced more than that of
K. ivorensis.
Infiltration of leaves of K. senegalensis and K. ivorensis with
mixtures of liquid paraffin and commercial Kerosene showed that stomatal
conductivity of K. senegalensis leaves was greater than that of
K. ivorensis leaves at low moisture stress. At more severe stress
(-4.5 bars) conductivity of leaves of both species was low.
The desorption curve for K. senegalensis seedlings was above that
for K. ivorensis seedlings. Curves of leaves for adult trees of both
species were however similar. K. senegalensis leaves could tolerate
desiccation better than K. ivorensis leaves.
Stomata of K. senegalensis leaves close at higher relative water
content values than those of K. ivorensis leaves.
The results are discussed in relation to the distribution of these
species and to the general ecological problem of the control of plant distribution
between forest and savanna in West Africa.
Description
Thesis (MSc.)-University of Ghana, 1971