170 D.W. Lucero et al. European Journal of Agronomy 11 1999 167–177
clover and 12 ryegrass plants were harvested for each interaction treatment and soil water deficit
level.
2.5. Morphological measurements Non-destructive measurements [stolon length,
internode length, primary leaf appearance rate LAR and secondary LAR] were carried out on
two randomly selected stolons from two white clover plants per replication 72 plants in total,
eight plants per interaction and soil water deficit level . Measurements for time zero were taken at
the establishment of water stress day 66 and thereafter on days 77, 88, 96 and 102. Primary and
secondary LARs were determined according to criteria established by Carlson 1966, and total
leaf index was a combination of both primary and secondary LARs [see Fig. 2a–c]. Primary leaves
were defined as those leaves growing from the primary stolon axis and secondary leaves were
defined as those leaves developing on stolons initi- ated from the main axis of selected stolons. The
relative growth rate RGR of stolons and leaves was a function of growth divided by time
[Figs. 1c, 2a–c]. At each measurement, stolon length, from one internode to another, was
recorded and average internodal length was a
Fig. 1. Stolon length, stolon internodal length and stolon rela-
function of the lengths of all internodes summed
tive growth rate RGR of white clover plants grown individu-
and divided by the number of internodes.
ally, in shoot+root interaction, or just shoot interaction with ryegrass and subjected to three levels of water deficit. Error
bars on observed data indicate ±1 standard deviation.
2.6. Statistical analysis The effect of treatments was obtained from
highest root DM yield, and plants grown in shoot+root interaction the lowest root DM yield.
analyses of variance. Mean separations were per- formed by an LSD procedure where the F values
For ryegrass grown in no interaction, an increase in soil water deficit from no to moderate reduced
were significant at the 0.05 probability level SAS Institute, 1990.
root DM yield by over 50 and an additional
increase to severe soil water deficit further reduced root DM yield by 36
.
3. Results
3.2. Above-ground dry matter yield 3.1. Below-ground dry matter yield
Shoot DM yield decreased as soil water deficit increased Table 1. Plants grown in no interaction
Root DM yield tended to decrease as soil water deficit increased Table 1. Ryegrass produced
at no soil water deficit had the highest shoot DM yields. At no and moderate soil water deficit,
more root DM than white clover at each soil water deficit level. Plants grown in no interaction had the
plants grown in shoot+root interaction had higher
171 D.W. Lucero et al. European Journal of Agronomy 11 1999 167–177
ilar. Ryegrass grown in shoot+root interaction had, respectively, 19
and 25 higher DM yields
at no and moderate soil water deficit than ryegrass grown in just shoot interaction. An increase in soil
water deficit from no to moderate level decreased white clover shoot DM yield by on average 35
; however, for white clover grown in shoot+root
interaction this decrease was less 26 compared
with 40 and 38
, respectively for white clover plants grown in no interaction or in shoot inter-
action. On the other hand, an increase in soil water deficit from no to moderate level reduced
ryegrass shoot DM yield by on average only 24
range 20 to 29 . As soil water deficit level
increased, the differences in DM yield observed between the different interaction treatments tended
to decrease. However, this relationship was not true for plants grown in shoot+root interaction,
where an increase in soil water deficit from moder- ate to severe level significantly increased the reduc-
tion in white clover shoot DM yield. Though shoot DM yield was higher for ryegrass grown in
shoot+root interaction compared with shoot inter- action, an increase in soil water deficit from moder-
ate to severe level decreased ryegrass shoot DM yield by 32
in shoot+root interaction but only 20
in shoot interaction.
Fig. 2. Primary, secondary and total leaf appearance rate LAR of white clover plants grown individually, in shoot+root
3.3. White clover leaf and stolon growth
interaction, or just shoot interaction with ryegrass and subjected to three levels of water deficit. Error bars on observed data
indicate ±1 standard deviation.
At no and moderate soil water deficit white clover grown in shoot+root interaction had sig-
nificantly higher leaf DM yield than white clover shoot DM yield than plants grown in shoot inter-
action. At moderate soil water deficit ryegrass had grown in shoot interaction Table 2. This increase
in total leaf DM yield was in the form of petioles higher shoot DM yield than white clover, whereas
at severe soil water deficit ryegrass had higher as leaf lamina DM yield was similar for white
clover grown in shoot+root interaction or shoot shoot DM yield than white clover only when
grown in shoot+root interaction. At severe soil interaction. Both leaf and stolon DM yields
decreased as soil water deficit increased. At no and water deficit the white clover grown in no inter-
action and in shoot interaction had, respectively, moderate soil water deficit, white clover grown in
shoot+root interaction had a higher percentage of 107
and 57 more shoot DM yield than
white clover grown in shoot+root interaction. shoot DM in the form of leaf tissue than did white
clover grown in shoot interaction 69 and 68.5 Conversely, at no and moderate soil water deficit,
white clover grown in shoot+root interaction had, compared with 62 and 63
, respectively. At mod- erate soil water deficit, white clover grown in
respectively, 11 and 32
more shoot DM yield than white clover grown in shoot interaction and
shoot+root interaction had 20 and 40
more leaf DM yield than white clover grown in either
the shoot DM yields of white clover grown in no interaction and shoot+root interaction were sim-
no interaction or in shoot interaction, respectively.
172 D.W. Lucero et al. European Journal of Agronomy 11 1999 167–177
Table 1 Dry matter yield and rootshoot ratio of white clover and ryegrass plants grown either individually, with shoot interaction or with
both shoot+root interaction in the greenhouse and subjected to three levels of soil water deficit Treatment
Dry matter yield a g plant−1
Assoc.water stress level Below-ground
Above-ground Total
Rootshoot ratio WC
RG WC
RG WC
RG WC
RG Individual0.0 MPa
0.91 cde b
3.52 a 6.84 ab
7.42 a 7.75 b
10.94 a 0.13 cd
0.48 e Individual−0.5 MPa
0.71 efgh 1.66 b
4.07 e 5.27 c
4.78 fgh 6.93 bcd
0.17 de 0.31 de
Individual−1.0 MPa 0.57 ghi
1.05 cd 3.30 fg
3.75 ef 3.87 ij
4.80 fgh 0.17 de
0.28 d Shoot0.0 MPa
0.60 fghi 1.12 c
5.17 cd 5.39 cd
5.67 def 6.51 cde
0.12 bc 0.21 cd
Shoot−0.5 MPa 0.64 fghi
1.02 cd 3.19 fg
4.09 e 3.83 hij
5.11 efg 0.20 e
0.25 cd Shoot−1.0 MPa
0.45 hij 0.81 defg
2.50 g 3.28 fg
2.95 jk 4.09 ghij
0.18 e 0.25 d
Shoot+root0.0 MPa 0.44 ij
0.86 def 5.75 b
6.40 ab 6.19 cde
7.26 bc 0.08 a
0.15 a Shoot+root−0.5 MPa
0.45 hij 0.84 def
4.21 e 5.11 cd
4.66 ghi 5.95 def
0.11 b 0.16 b
Shoot+root−1.0 MPa 0.29 j
0.65 fghi 1.59 h
3.50 efg 1.88 k
4.15 ghij 0.18 e
0.19 bc a Both WC and RG treatments compared within below-, above-ground, total and rootshoot ratio columns.
b LSD followed by different letters are significantly different P≤0.05. Table 2
White clover leaf, stolon and flower dry matter and percentage of above-ground yield from plants grown in the greenhouse individually, with shoot interaction or with both shoot+root interaction with ryegrass and subjected to three levels of soil water deficit
Treatment Final harvest dry matter yield
Assoc.water stress Petiole
ag Leaf g
Leaf g Leaf
Stolon g Stolon
Total leaf Flower
Individual0.0 MPa 2.05 a
b 2.18 a
4.33 a 63.3
2.20 a 34.1
97.4 2.6
Individual−0.5 MPa 1.08 cd
1.32 c 2.40 c
59.0 1.43 cd
35.1 94.1
5.9 Individual−1.0 MPa
0.83 de 1.00 de
1.83 d 55.4
1.17 de 35.5
90.9 9.1
Shoot0.0 MPa 1.56 b
1.64 b 3.20 b
61.9 1.82 b
35.2 97.1
2.9 Shoot−0.5 MPa
0.98 cd 1.04 de
2.01 d 63.0
1.11 de 34.8
97.8 2.2
Shoot−1.0 MPa 0.72 de
0.83 ef 1.55 de
62.0 0.89 e
35.6 97.5
2.4 Shoot+root0.0 MPa
2.18 a 1.79 b
3.97 a 69.0
1.61 bc 28.0
97.0 3.0
Shoot+root−0.5 MPa 1.66 b
1.22 cd 2.88 c
68.5 1.30 cde
31.0 99.5
0.5 Shoot+root−1.0 MPa
0.39 e 0.58 f
0.97 f 61.0
0.61 f 38.4
99.4 0.6
a Treatments compared only within columns. b LSD column means followed by different letters are significantly different P≤0.05.
Conversely, at severe soil water deficit, white clover leaf decreased and flower increased as a percen-
tage of shoot DM yield as soil water deficit grown in no interaction or in shoot interaction had
90 and 45
higher leaf DM yields, respectively increased.
than white clover grown in shoot+root interaction. Stolon as a percentage of shoot DM yield increased
3.4. Root and shoot ratios as soil water deficit increased for white clover
grown in shoot+root interaction, and at severe soil Rootshoot ratios were highly variable for all
treatments Table 1. For white clover, roots water deficit made up almost 40
of above-ground DM yield compared with 28
and 31 at no and
tended to increase in proportion to shoots as soil water deficit level increased. This effect was most
moderate soil water deficit, respectively. For white clover grown in no interaction, the percentage of
noted in white clover grown in shoot+root inter-
173 D.W. Lucero et al. European Journal of Agronomy 11 1999 167–177
action, but was due more to a decrease in shoot Increasing soil water deficit had a much greater
effect on secondary LAR than on primary LAR growth than to an increase in root growth, as soil
volume in this experiment was restricted. [Fig. 2b]. White clover subjected to no soil water
deficit and grown in no interaction had twice as high a secondary LAR as the other two interaction
3.5. Stolon growth and relative growth rate treatments. Total LAR was highest for white clover
grown in no interaction at no soil water deficit, Average stolon and stolon internodal length
decreased as soil water deficit increased [Fig. 1a almost twice as much as the other interaction
treatments and soil water deficits [Fig. 2c]. At and b]. At no and moderate soil water deficit,
average stolon and stolon internodal length was moderate soil water deficit a similar total LAR
was observed for each interaction treatment; how- highest in white clover grown in shoot+root inter-
action, followed by plants grown in no interaction ever, the total LAR of white clover grown in
shoot+root interaction was the most severely and then by plants grown in shoot interaction. At
severe soil water deficit, white clover grown in reduced when soil water deficit was severe.
shoot+root interaction had shorter stolons than white clover grown in either no interaction or in
shoot interaction. For average stolon internodal
4. Discussion
