Annals of Botany 96: 269–278, 2005
doi:10.1093/aob/mci175, available online at www.aob.oupjournals.org
Comparison of Early Development of Three Grasses: Lolium perenne,
Agrostis stolonifera and Poa pratensis
J O E L L E F U S T E C 1,*, J O E L L E G U I L L E U X 2, J O S I A N E L E C O R F F 2 and J E A N - P A U L M A I T R E 2
1
Laboratoire d’Ecophysiologie Végétale et Agroécologie, Ecole Supérieure d’Agriculture, 55 rue Rabelais,
BP 30748, 49007 Angers cedex 01, France and 2Unité Mixte de Recherche Sciences Agronomiques Appliquées
à l’Horticulture A-462, 42 rue Georges Morel, BP 60057, 49071 Beaucouzé cedex, France
Received: 8 December 2004 Returned for revision: 10 February 2005 Accepted: 25 April 2005 Published electronically: 2 June 2005
Background and Aims To improve the management of grass communities, early plant development was compared
in three species with contrasting growth forms, a caespitose (Lolium perenne), a rhizomatous (Poa pratensis) and
a caespitose–stoloniferous species (Agrostis stolonifera).
Methods Isolated seedlings were grown in a glasshouse without trophic constraints for 37 d (761 Cd). The
appearance of leaves and their location on tillers were recorded. Leaf appearance rate (LAR) on the tillers and
site-filling were calculated. Tillering was modelled based on the assumption that tiller number increases with the
number of leaves produced on the seedling main stem. Above- and below-ground parts were harvested to compare
biomass.
Key Results Lolium perenne and A. stolonifera expressed similar bunch-type developments. However, root
biomass was approx. 30 % lower in A. stolonifera than in L. perenne. Poa pratensis was rhizomatous. Nevertheless,
the ratio of above-ground : below-ground biomass of P. pratensis was similar to that of L. perenne. LAR was
approximately equal to 030 leaf d 1 in L. perenne, and on the main stem and first primary tillers of A. stolonifera.
LAR on the other tillers of A. stolonifera was 30 % higher than on L. perenne. For P. pratensis, LAR was 30 % lower
than on L. perenne, but the interval between the appearance of two successive shoots from rhizomes was 30 % higher
than the interval between two successive leaf stages on the main stem. Above-ground parts of P. pratensis first grew
slower than in the other species to the benefit of the rhizomes, whose development enhanced tiller production.
Conclusions Lolium perenne had the fastest tiller production at the earliest stages of seedling development.
Agrostis stolonifera and P. pratensis compensated almost completely for the delay due to higher LAR on tillers or
ramets compared with L. perenne. This study provides a basis for modelling plant development.
Key words: Lolium perenne, perennial ryegrass, Agrostis stolonifera, creeping bentgrass, Poa pratensis, Kentucky
bluegrass, space colonization, Gramineae, morphogenesis, tillering model, growth strategy, site-filling.
INTRODUCTION
Perennial grass communities such as natural meadows or
turves, are usually a mixture of different species. To keep
compact long-lasting canopies, their management requires
the relationships between growth strategies, environmental
constraints, interplant competition and cultural practices
to be taken into account. However, Graminae are clonal
plants with a modular structure, composed of tillers or
ramets that may express contrasting growth forms (Harper,
1977; Moulia et al., 1999a). First, bunch or caespitose types
are highly branched with closely packed tillers, and ramets
are formed close to the older shoots. Tiller emergence
is intravaginal, i.e. tillers arise through the entire length
of the sheath (Cattani and Struik, 2001). Secondly, many
Gramineae species can grow from rooting plagiotropic
shoots like rhizomes or stolons that arise through the sheath
tissue by extravaginal emergence. These plants are able to
spread radially to form large, clonal stands (Harper, 1977).
Grasses with different growth forms respond differently
to interplant competition, environmental constraints and
human practices, and their presence in mixtures makes it
hard to control canopy cover. Consequently, to improve
the management of plurispecific communities, a greater
* For correspondence. E-mail [email protected]
knowledge of growth patterns encountered in grasses is
required.
Some studies mainly conducted by agronomists have
looked at the development of isolated plants. They have
focused on a small number of Gramineae species of agronomic importance, such as maize (Moulia et al., 1999a, b),
wheat (Triticum aestivum; Masle-Meynard and Sébillotte,
1981a, b), barley (Hordeum sativum; Fletcher and Dale,
1977; Kirby et al., 1985), Festuca spp. (Sugiyama, 1995)
or perennial ryegrass (Lolium perenne; Richards et al.,
1988; Neuteboom and Lantinga, 1989; Yang et al., 1998;
Gautier et al., 1999). Plant development is described and
quantified using the phyllochron, i.e. the number of growing
degree days between the emergence of leaf number n and
leaf number n + 1 (Klepper et al., 1982; Frank and Bauer,
1995). Thus, tillering models (also called ‘tillering patterns’)
have been built either from the phyllochron of the main stem
(MS), i.e. the first shoot emerged from the seed, or from the
values of the leaf emergence rate (Masle-Meynard and
Sébillotte, 1981a; Kirby et al., 1985; Bos and Neuteboom,
1998). These models are based on the assumption that tiller
number increases with the successive leaf stages of
the seedling MS. They may be used either to represent
the theoretical maximal development of a plant, or the structure of the typical ‘mean’ individual. Furthermore, as leaf
ª The Author 2005. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.
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270
Fustec et al. — Morphogenesis of Three Growth Forms of Grasses
appearance rate (LAR) is related to the production rate of
axillary buds, it determines the production rate of potential
tillering sites. Thus, more recently, plant development has
been described using the LAR and the site-filling ratio (Fs),
which is a measure of tiller bud activity and occupancy
of existing tillering sites (Davies, 1974; Neuteboom and
Lantinga, 1989). Tillering activity has also been measured
as site use (Skinner and Nelson, 1992) or nodal probability
(Matthew et al., 1998).
The development patterns of isolated plants provide the
first key elements towards a better understanding of tillering
response of different growth forms of grasses to environmental conditions, interplant interactions and cultural practices. The description of growth patterns provides basic
information to model isolated plants and also plurispecific
canopies. Most relevant information is on caespitose types.
Few attempts have been made to investigate the development of stoloniferous and rhizomatous types. Some studies
on stolon development have been conducted, mainly with
creeping bentgrass (Mueller and Richards, 1986; Cattani
and Struik, 2001; Cattani et al. 2002). Therefore, it was
intended to compare early development, particularly tillering dynamics of rhizome and stolon types with that of bunch
types. For this purpose, three grass species likely to be
found together in the same canopies, and known to express
different growth strategies, were chosen for the study: the
caespitose perennial ryegrass L. perenne, the caespitose–
stoloniferous creeping bentgrass Agrostis stolonifera and
the rhizomatous kentucky bluegrass Poa pratensis.
MATERIALS AND METHODS
Plant material and growth conditions
Species were selected based on their contrasting growth
strategies and on the similarity of their ecological requirements. Thus, they could be grown under the same conditions. Three turfgrass cultivars were considered: Lolium
perenne L. ‘Rival’, Agrostis stolonifera L. ‘Penneagle’ and
Poa pratensis L. ‘Entopper’. Caryopses were sown in
February on a moist artificial substrate (50 % sand and
50 % white peat), in a warmed glasshouse in Angers
(033 E, 4728 N, France). On average, air temperature was
189 6 09 C and relative humidity was around 60 6 66 %.
Twenty days after sowing, plants had formed their coleoptile and three leaves without any primary tiller. Twelve
individuals of each cultivar were then selected, based
on their homogeneous development, for a 37-d experiment
(beginning mid-March). Each isolated plant was randomly
pricked out in the middle of one of 36 culture trays
placed on the tables described below. From the beginning
until the end of the experiment, day length increased
from 12 h to 135 h.
Transplanted seedlings were grown on two sub-irrigation
tables (2 m · 4 m), in the glasshouse described earlier.
Each table was covered with an absorbent felt cloth
(Aquanappe1) to water and feed the plants by capillarity.
The felt tablecloth was flooded three times a day, for 15 min,
with a nutrient solution mixed in a 300-dm3 tank (Sevital1
solution: N-P-K 12 : 4 : 6; 1 % NO3 ; 11 % urea; dilution
05 % during the first fortnight, and then 1 %, renewed
weekly). After watering, the excess of solution percolated
into a plastic gutter located in the middle of the table and
back into the tank. The Aquanappe1 was covered with a
black plastic film punched with small holes, to limit solution
evaporation and avoid algal development. Thirty-six bottomless culture trays made of a rectangular plastic frame
(polyvinyl chloride, 60 cm long, 40 cm wide and 10 cm
high), were laid out in rows on the sub-irrigation tables.
Each table could support two rows of nine trays. Within
a row, trays were adjacent by their longest edges. As a
consequence, plants were 40 cm from their neighbours
and 140 cm from seedlings of the other row; there was
no above- nor below-ground interplant competition. Each
tray was filled with 21 dm3 of substrate (sand, white peat
and pouzzolana in equal proportions; pH 675 adjusted
with CaCO3 Recalcit1). Glasshouse conditions (nutrient
solution, water, increasing photoperiod, temperature) were
designed to enhance growth and to minimize stress.
Data collection
Tillering was monitored 5 d per week up to 37 days after
transplanting (DAT). Leaf emergence was recorded as follows: a new leaf was scored when its tip had appeared above
the level of the next older leaf sheath. After ligule development, a leaf was considered as fully emerged and was
marked with a thin plastic ring bearing a code giving its
location on the plant, and the location of its ‘parent’ phytomer. The seedling stem was called the MS. The first leaf to
emerge on the MS (coleoptile), and the first leaf on a tiller
(called the prophyll) were numbered 0. Ramifications on the
MS (tillers) were named after their ‘parent’ leaf; e.g. T31
was the secondary tiller arising at the axil of the 1st true
leaf of the primary tiller, itself borne at the axil of the
3rd true leaf on MS (Fig. 1). When present, above-ground
plagiotropic shoots (stolons, St) and below-ground shoots
(rhizomes, Rh) can produce new rooted orthotropic shoots
called S and R, respectively. Ramifications of S and R were
also named after their ‘parent’ leaf; for example, R12 was
the primary tiller borne at the axil of leaf 2 of R1, which was
itself the first orthotropic shoot on a rhizome.
At 38 DAT, plant height was measured above the substrate surface. Horizontal spread of each plant was estimated
by placing a wired fence with a 4-cm mesh over the tray, and
by counting the number of threads crossed by the aboveground organs. Six of the 12 plants of each cultivar were
harvested (remaining plants were kept for another experiment). Each plant was sorted into different samples: (a) MS
pooled with R and S shoots when present, (b) primary tillers
including St; (c) secondary tillers; (d) tertiary tillers;
(e) roots; and (f) rhizomes. Each sample was dried up to
constant weight in a forced-air drier at 60 C, before biomass measurements.
Data analysis
The numbers of leaves (or phytomers) and tillers produced per plant were calculated as a function of thermal
time (i.e. growing degree days, Cd, base temperature 0 C;
Fustec et al. — Morphogenesis of Three Growth Forms of Grasses
T31 MS
271
MS
MS
T3
R1
S1
S12
R12
Rh
A
B
St
C
F I G . 1. Different growth strategies in grasses: (A) bunch-type, (B) rhizomatous-type, and (C) stoloniferous-type. MS indicates seedling main stem,
T, seedling ramifications; S, orthotropic shoots on stolon (St); R, shoots on rhizomes (Rh). Coleoptile leaf on the MS (closed circles) and prophylls
(small open circles) are called leaf 0 on tillers. True leaves are large open circles. Code used for tillers: e.g. T3 is the primary tiller arising at the axil of the 3rd
true leaf of MS, T31 is the secondary tiller arising at the axil of the 1st true leaf on T3.
T A B L E 1. Spatial development of isolated plants of L. perenne, A. stolonifera and P. pratensis grown in a greenhouse for 38 DAT
Plant height (cm)
Colonized threads (%)
L. perenne
A. stolonifera
P. pratensis
P rows
5.4 6 0.3b
49.1 6 4.4b
4.5 6 0.5c
59.6 6 6.1a
7.8 6 0.5a
24.1 6 3.1c
0.0030
0.0033
Data are means 6 standard error of six plants.
P values are given according to Kruskal–Wallis. Letters abc indicate significant differences among species in rows.
‘Colonized threads’ expresses the percentage of threads of a wired fence placed over the culture trays, crossed by above-ground parts of the plants at 38 DAT.
McMaster and Wilhem, 1997). The phyllochron of the MS
was estimated as the inverse of the slope of the regression of
the MS phytomer number on thermal time. The number of
fully emerged leaves on ‘parent’ tillers was counted when
the first ‘daughter’ tiller emerged (Kirby et al., 1985). The
rate of leaf appearance, i.e. the number of leaves per tiller
per day was calculated for each order of tiller in each species. For this calculation, only true leaves were considered
because prophylls expressed different behaviours, either
appearing at the same time as the first true leaf or later.
Site-filling (Fs) was obtained at successive leaf stages of
MS, from the natural logarithm of the increase in tiller
number during each leaf appearance interval (Neuteboom
and Lantinga, 1989). The ratio of the number of new leaves
and new tillers (DL/DT ) at successive leaf stages of MS was
also calculated. So as not to underestimate tillering potential, coleoptile leaves and prophylls were taken into account
in the site-filling calculation (Neuteboom and Lantinga,
1989). Biomass of tillers, below-ground parts (roots and
Rh), and the ratios of above-ground : below-ground parts
and above-ground parts : roots were also compared among
species.
Statistical analyses were performed with Systat 10 software (Systat 10, 2000). As standard deviations were not
equal across samples, non-parametric Kruskal–Wallis and
unpaired Mann–Whitney tests, based on median equality,
were used to compare species. Equations of regressions
were compared from Jerrold (1998). Tillering models
(i.e. the structure of a typical ‘mean’ individual) combined
the present experimental results and models given by MasleMeynard and Sébillotte (1981a) and Kirby et al. (1985).
RESULTS
Spatial colonization and branching
During the course of the experiment, no plant or leaf died
except coleoptiles. Plant height was significantly larger for
P. pratensis with a mean height of 78 cm, compared with
L. perenne (54 cm) and A. stolonifera (45 cm; P < 001,
Table 1). However, P. pratensis clearly produced fewer
leaves (around 29) than L. perenne (around 106) and
A. stolonifera (around 86; Fig. 2A and B), and some of
the phytomers were produced by new tillers on rhizomes
(Fig. 2B). Horizontal spread was less important for
P. pratensis; at the end of the experiment, 24 % of the
trays were occupied, while L. perenne and A. stolonifera
colonized 49 % and 60 % of the available area, respectively
(Table 1). Growth patterns were as expected with one exception regarding A. stolonifera; L. perenne was caespitose and
P. pratensis was rhizomatous with three to five R tillers per
plant. Unfortunately, no S and only one extravaginal St was
observed for A. stolonifera. In that species, some primary
tillers with intravaginal development began to express a
plagiotropic development. As they were not orthotropic,
they were not considered as St for A. stolonifera.
Generally, above-ground parts of L. perenne and
A. stolonifera expressed the same development patterns
with very few differences over the 37 DAT. First, in both
species, the exponential curves that fitted the increase in leaf
number on thermal time differed only by their constants
(Fig. 2A). After log transformation, the y-axis intercepts
of the regression lines were found to be significantly different (P < 00001), while the slopes were not (P > 005).
Fustec et al. — Morphogenesis of Three Growth Forms of Grasses
272
phytomer (or leaf) numbers across time (Fig. 3D and E), and
at the end of the experiment, no statistical difference could
be found between the numbers of phytomers on primary
(around 45), secondary (around 32) and tertiary tillers
(around 5). In contrast, the number of phytomers per plant
of P. pratensis remained low (Fig. 3F).
Phytomer number on MS
Total number of phytomers
Total number of phytomers
140
A
120
N, L. perenne
N, A. stolonifera
100
80
60
40
Biomass partitioning
20
0
50
45
40
35
30
25
20
15
10
5
0
12
B
N, P. pratensis
N, R of P. pratensis
C
10
8
6
N, L. perenne
N, A. stolonifera
N, P. pratensis
4
2
0
0
100
200
300
400
500
Thermal time (°Cd)
600
700
F I G . 2. Evolution of the leaf number (N) as a function of thermal time (Tth)
in L. perenne (open triangles), A. stolonifera (open squares), P. pratensis
(open circles) and R of P. pratensis (closed circles). (A) Whole plants of
L. perenne and A. stolonifera, (B) whole plants of P. pratensis; (C) only the
MS for the three species. Data are from 12 plants grown in a greenhouse for
37 DAT. Equations: (A) NL. perenne = 36045e00048Tth (R2 = 094) and
NA. stolonifera = 24659e00048Tth (R2 = 089); (B) NP. pratensis =
33026e00032Tth (R2 = 088), NR. P. pratensis = 00123Tth – 13295 (R2 =
066); (C) NMS L. perenne = 00106Tth + 40997 (R2 = 092),
NMS A. stolonifera = 0011Tth + 32443 (R2 = 094), NMS P. pratensis =
00086Tth + 35643 (R2 = 093).
Secondly, there was no significant difference between the
slopes of the regression lines modelling MS leaf number on
thermal time for the two bunch species (P > 005; Fig. 2C).
This result indicates MS phyllochron similarity, with
943 Cd leaf 1 for L. perenne and 909 Cd leaf 1 for
A. stolonifera. Thirdly, both species were characterized
by a similar increase of the numbers of primary and
secondary tillers with about 12 tillers at 761 Cd (Fig. 3A,
and B). Their development differed markedly from that of
P. pratensis, in which primary tillers occurred at approx.
345 Cd (i.e. about 150 Cd later than in the two other
species), and their number did not exceed 6 at 37 DAT
(Fig. 3C). Tertiary tillers appeared at about 478 Cd in
L. perenne and only at about 618 Cd in A. stolonifera.
Nevertheless, the two species showed similar increases in
Dry weights of above-ground samples were not significantly different between L. perenne and A. stolonifera
(P > 005) except for primary tillers, which had a larger
biomass in L. perenne (P = 00126; Fig. 4A). In both species, there was approx. 70–80 % less dry matter by tiller
for secondary and tertiary tillers compared with MS and
primary tillers (P < 0001; Table 2). Furthermore, dry matter
allocated by tiller to MS, primary, secondary and tertiary
ramifications was not different between the two species
(P > 005; Table 2). In contrast, biomass of primary and
secondary tillers was significantly lower in P. pratensis than
in the other two species (P < 00001; Fig. 4A). Biomass
by tiller was also clearly lower in P. pratensis than in
the other species for primary shoots (P < 00001) as well
as for samples in which MS and R were pooled (P < 0005;
Table 2).
Lolium perenne allocated significantly more biomass to
below-ground parts than the other two grasses (P < 00001;
Fig. 4B). Despite an efficient branching, the ratio of aboveground parts/roots was clearly lower in L. perenne (25) than
in A. stolonifera (53) and P. pratensis (46; P < 0001;
Fig. 4C). In the rhizomatous P. pratensis, below-ground
biomass was distributed between rhizomes and roots
(Fig. 4B). Unexpectedly, when rhizomes were taken into
account, no difference could be found between L. perenne
and P. pratensis in the ratio of above-ground : below-ground
biomass (P > 005; Fig. 4C).
Leaf appearance rate, tiller location and site-filling
Across all species and tillers, between 014 and 043 leaf
emerged per day (Table 3). In L. perenne, the LAR reached
029 leaf d 1 on MS, and there was no significant difference
among the different ramifications (P > 005; Table 3). In
P. pratensis, there was no significant difference among the
LAR on MS, T2, T3 and T4. However, LAR on R was about
30–50 % higher than on the other shoots (P < 005; Table 3).
In A. stolonifera, LAR on T5 and on secondary tillers was
almost 30 % higher than on MS and on all other primary
tillers (P < 005; Table 3). Leaf emergence rate on MS
did not differ significantly between L. perenne and
A. stolonifera, while in P. pratensis, it was approx. 30 %
lower (P < 005; Table 3).
In the three grass species, MS began to produce primary
tillers after the appearance of five leaves (with the coleoptile
included; Table 4). In L. perenne, T1 was the first primary
tiller to emerge in 667 % of the seedlings, and T2 in the
others (results not presented). In A. stolonifera, T1 was the
first primary tiller to appear in 583 % of the plants, and T2 in
the others. In both species, secondary and tertiary tillers
emerged at the axil of leaf 1 and appeared when the ‘parent’
273
Fustec et al. — Morphogenesis of Three Growth Forms of Grasses
20
60
Number of phytomers
Number of tillers
A
15
10
5
40
30
20
10
0
60
0
20
15
10
5
E
50
Number of phytomers
Number of tillers
B
40
30
20
10
0
60
0
20
Number of phytomers
C
Number of tillers
D
50
15
10
5
F
50
40
30
20
10
0
0
62
206
345
478
Thermal time (˚Cd)
618
62
761
163
226
306 365 443 497
Thermal time (˚Cd)
580
656 761
F I G . 3. Increase in the number of tillers and phytomers in relation to thermal time. Evolution of the number of MS and new shoots on rhizomes (closed
circles), primary (open circles), secondary (filled squares) and tertiary tillers (open triangles) in (A) L. perenne, (B) A. stolonifera and (C) P. pratensis.
Numbers of phytomers on primary (open circles), secondary (filled squares) and tertiary tillers (open triangles) in (D) L. perenne, (E) A. stolonifera and
(F) P. pratensis. Data are means and standard errors from 12 plants grown in a greenhouse for 37 DAT.
2500
Dry matter weight (mg)
7
1200
A
B
6
1000
2000
5
800
1500
4
600
3
1000
400
500
0
C
2
200
MS + Rn
TI
T II
Above-ground parts
T III
Total
0
1
Roots
Rh.
Total
Below-ground parts
0
Ab./Roots
Ab./Bel.
Ratios
F I G . 4. Biomass of (A) above-ground parts, (B) below-ground parts and (C) ratio of above-ground : below-ground parts (Ab./(Bel.) in L. perenne (open
columns), A. stolonifera (grey columns) and P. pratensis (black columns), sampled after 37 DAT. MS indicates the seedling main stem, T is used for seedling
ramifications (primary, T I- tillers; secondary, -T II- tillers; tertiary, -T III-tillers), and R is used for shoots from rhizomes (Rh). Below-ground parts include
roots and rhizomes. Means and standard error are given for six plants.
Fustec et al. — Morphogenesis of Three Growth Forms of Grasses
274
T A B L E 2. Mean dry weight (mg) allocated by tiller in L. perenne, A. stolonifera and P. pratensis
Kinds of tillers
MS + R
TI
T II
T III
P columns
L. perenne
159.83 6
143.55 6
51.92 6
20.20 6
0.0006
A. stolonifera
20.62aA
12.24aA
4.52bA
1.87cA
126.33 6
118.28 6
32.12 6
15.30 6
0.0007
22.51aA
11.35aA
5.04bAB
2.34cA
P. pratensis
P rows
64.42 6 11.84aB
41.91 6 7.20aB
33.00 6 4.42aB
–
n.s.
0.0043
<0.0001
0.0072
n.s.
MS, Seedling main stem; R, shoots from rhizome; T I, primary, T II, secondary and T III, tertiary tillers.
Data are means 6 standard error of six plants grown in a greenhouse for 37 DAT. A, B and C indicate significant differences between medians in rows
and a, b and c significant differences between medians in columns. P values are given according to Kruskal–Wallis test. n.s., Non-significant (P > 005).
T A B L E 3. Mean leaf appearance rate on tillers (leaf d 1) in L. perenne, A. stolonifera and P. pratensis (prophylls excluded)
Shoot location
MS
Primary tiller emerged at:
leaf 1 axil on MS (T1)
leaf 2 axil on MS (T2)
leaf 3 axil on MS (T3)
leaf 4 axil on MS (T4)
leaf 5 axil on MS (T5)
Secondary tillers
R
P columns
P MS and R
L. perenne
A. stolonifera
P. pratensis
P rows
0.29 6 0.01aA
0.30 6 0.02aA
0.20 6 0.02aB
0.0042
6 0.04aA
6 0.03aA
6 0.04abA
6 0.01aB
6 0.01bcB
6 0.03cB
–
0.0185
–
–
0.16 6 0.01aB
0.16 6 0.02aB
0.14 6 0.03aC
n.s.
0.0013
0.0030
<0.0001
0.0043
0.0253
–
0.29
0.26
0.24
0.27
0.33
0.31
6 0.05aA
6 0.03aA
6 0.04aA
6 0.03aA
6 0.02aA
6 0.04aA
–
0.29
0.30
0.33
0.35
0.40
0.43
n.s.
–
–
0.28 6 0.02c
0.0020
0.0405
MS, Seedling main stem; R, shoots from rhizome.
Data are means 6 standard error of 12 plants grown in a greenhouse during 37 DAT.
A, B, C indicate significant differences between medians in rows and a, b, c significant differences between medians in columns. P values are given
according to Kruskal–Wallis test. n.s., Non-significant (P > 005).
T A B L E 4. Leaf number on a ‘parent’ shoot when the first
‘daughter’ tiller emerged in L. perenne, A. stolonifera and
P. pratensis (coleoptile leaves and prophylls included)
Phytomer number on the ‘parent’
shoot at first ‘daughter’ tiller emergence
L. perenne
Leaf number on MS at growth of:
1st T I
5.7 6 0.2a
R1
–
R2
–
R3
–
R4
–
R5
–
Leaf number on T I at growth of:
4.7 6 0.2b
1st T II on T1
4.3 6 0.1b
1st T II on T2
1st T II on T3
4.1 6 0.1b
1st T II on T4
4.0 6 0.2b
4.3 6 0.3b
1st T II on T5
Leaf number on T II at 4.5 6 0.3b
growth of 1st TIII
P columns
<0.0001
A. stolonifera
P. pratensis
5.3 6 0.1a
–
–
–
–
–
5.8
6.3
6.7
7.4
8.2
9.3
0.2b
0.1b
0.3ab
0.3ab
–
4.5 6 0.8ab
–
4.0 6 0f
4.0 6 0f
–
–
–
<0.0001
<0.0001
4.1
4.2
4.6
4.5
6
6
6
6
6
6
6
6
6
6
0.2a
0.3b
0.3bc
0.3c
0.2d
0.2e
MS, Seedling main stem; R, shoots from rhizome; T I, primary, T II,
secondary and T III, tertiary tillers.
Data are means 6 standard error of 12 plants grown in a greenhouse for
37 DAT.
P values are given according to Kruskal–Wallis. a, b and c indicate
significant differences between medians in columns.
tiller showed four leaves (with the prophyll included;
Table 4). In contrast, in P. pratensis, T2 was always the
first primary tiller. ‘Daughter’ tillers began to emerge when
‘parent’ tillers had four leaves (with the prophyll included;
Table 4). In P. pratensis, R1 appeared when MS had a
mean of 63 6 03 leaves (Table 4). The interval between
two successive R emerging was approx, 33 % higher than
the interval between two successive leaf stages on MS
(DMS = 2/3 DR; Table 4).
In the present study, no primary tiller emerged from the
coleoptile. Only 3–5 % of the buds at the axil of a prophyll
developed. There was no significant difference among species in the increase in total tiller numbers at the successive
leaf stages (values were between 145 and 176; P > 005;
Table 5), nor in the ratio of number of new leaves over
number of new tillers (approximately four for all the species; P > 0º05; Table 5). As a consequence, site-filling did
not differ significantly among the three species, and was
between 0523 and 0606 tiller tiller 1 LAR 1 (P > 005;
Table 5).
Tillering models
Tillering models were constructed for each species based
on (a) mean LAR on the different tillers, as presented in
Table 3, (b) mean leaf number on ‘parent’ tiller when either
the first ‘daughter’ tiller or the first R emerged, as shown in
275
Fustec et al. — Morphogenesis of Three Growth Forms of Grasses
T A B L E 5. Increase in the total number of tillers (T), site-filling (Fs) and ratio of the number of new leaves over the number of new
tillers (dL/dT) at the successive leaf stages of the main stem in L. perenne, A. stolonifera and P. pratensis
Increase in T (= exp Fs)
Case 1
Case 2
Site-filling (Fs)
Case 1
Case 2
dL/dT
Case 1
Case 2
L. perenne
A. stolonifera
P. pratensis
P (rows)
1.62 6 0.06
1.76 6 0.11
1.63 6 0.16
1.64 6 0.06
–
1.45 6 0.66
n.s.
n.s.
0.523 6 0.02
0.557 6 0.02
0.545 6 0.02
0.598 6 0.02
–
0.606 6 0.04
n.s.
n.s.
3.42 6 0.18
3.47 6 0.27
4.00 6 0.18
4.24 6 0.33
–
4.30 6 0.34
n.s.
n.s.
Values are means 6 standard error of 12 seedlings grown in a greenhouse for 37 DAT.
In case 1, the first tiller emerged at the axil of leaf 1. In case 2, the first tiller appeared at the axil of leaf 2.
n.s., Non-significant according to Kruskal–Wallis test (P > 005).
Table 4 and (c) location of the first ‘daughter’ tiller on the
‘parent’ tiller, as observed in a majority of experimental
plants for each species. Thus, equal values for LAR were
assumed on all tillers in L. perenne, and on most shoots of
A. stolonifera (except for T5 and secondary tillers). It was
also considered that leaf 1 and the prophyll (leaf 0) emerged
at the same time on tillers. In P. pratensis, the LAR on MS
was one-third lower than on L. perenne. For L. perenne
and A. stolonifera, it was decided that the first primary
tiller would appear at the axil of leaf 1, and of leaf 2 for
P. pratensis. R appearance rate in P. pratensis was chosen
to be one-third higher than the LAR of MS of L. perenne.
LAR on R was also considered to be one-third higher than
on ‘mother plant’ tillers.
The values obtained from the tillering models were close
to the observed data. In the diagrams, when the MS presents
11 leaves, the number of shoots reaches 31 in L. perenne
and 27 in A. stolonifera (Table 6A and B). After 37 DAT,
2917 6 26 s.e.) shoot plant 1 were obtained experimentally when there were 107 6 02 (standard error) leaves on
MS for L. perenne, and 2025 6 429 shoot plant 1 when the
MS had 112 6 04 leaves for A. stolonifera. Poa pratensis
produced 85 6 089 leaves on the MS during the experiment and on average 75 6 063 shoots plant 1 while the
tillering model gives a theoretical amount of 12 tillers when
MS has eight leaves. From extrapolation, the theoretical
number of tillers produced by a plant of P. pratensis at
stage 11 leaves on MS is approx. 30 and 50 % higher
than the shoot number obtained at the same plant stage
in A. stolonifera and L. perenne, respectively.
DISCUSSION
Previous studies have described tiller dynamics in Lolium
perenne (Mitchell, 1953; Richards et al., 1988; Neuteboom
and Lantinga, 1989; Yang et al., 1998; Gautier et al., 1999).
The present results on phyllochron value and total number
of tillers at 37 DAT are consistent with those of Gautier et al.
(1999). Taking into account the tiller prophyll in their
model, Neuteboom and Lantinga (1989) obtained a maximum value for site-filling equal to 0693; in that case, total
tiller number would double at successive leaf stages. In the
present experiment, all primary tillers emerged from the bud
located immediately above the previous tiller. However, the
plants showed a consistent lack of tiller emergence at the
axil of the coleoptile and an irregular development of tillers
at the axil of the prophylls. As a consequence, the site-filling
value for L. perenne (and for the other species studied)
seems low for isolated plants grown without trophic constraints. Nevertheless, the site-filling values were higher
than 0481, the maximum site-filling value expected for
L. perenne when neither coleoptile nor prophyll tillers
are produced (Davies, 1974).
The site-filling found was close to the value obtained by
Bahmani et al. (2000) who studied seedlings within a population and demonstrated that shade drastically reduced the
number of tillers produced by plants of L. perenne, with no
change of the phyllochron. Cattani and Struick (2001), who
conducted a similar short experiment with creeping bentgrass under long days (16 h) at 20 C/15 C, did not observe
either the stolons they expected under low light intensity.
Several authors have shown that a decrease of the red : far
red ratio or an increase in blue radiation have the same
effects (Deregibus et al., 1983; Casal et al., 1986; Warringa
and Kreuzer, 1996; Gautier et al., 1999). On the other hand,
in barley, Fletcher and Dale (1977) demonstrated that LAR
(and phyllochron) was unaffected by shading.
In Angers, mean light intensity tends to increase
from 430 mmol m 2 s 1 at the beginning of March to
690 mmol m 2 s 1 in mid-April (data collected over
25 years by INRA). It is likely that in the present experiment, tillering was reduced by a low level of photosynthetic
active radiation, while warm temperatures enhanced
leaf and bud productions. From the results published by
Cao and Mos (1989) in wheat and barley, it appears that
12–135 h day length is not short enough to have a major
effect on phyllochron. A longer day length (16 h)
would have certainly enhanced initiation of the coleoptile
tiller (Kirby et al., 1985), as has also been reported for
A. stolonifera (Cattani et al., 2002). This may explain
why the values of DL/DT were about 20 % greater than
those obtained by Neuteboom and Lantinga (1989).
Fustec et al. — Morphogenesis of Three Growth Forms of Grasses
276
T A B L E 6. Emergence pattern of the successive tillers in (A) L. perenne, (B) A. stolonifera and (C) P. pratensis
NpLp
Ramification emergence
Shoot number
(A) Lolium perenne when the 1st primary tiller emerges at the axil of leaf 1
1
MS
5
T1
6
T2
7
T3 – T11
8
T4 – T12 – T21
9
T5 – T13 – T22 – T31 – T111
10
T6 – T14 – T23 – T32 – T41 – T112 – T211
11
T7 – T15 – T24 – T33 – T42 – T51 – T113 – T212 – T221 – T311 – T1111
End of observations
12
T8 – T16 – T25 – T34 – T43 – T52 – T61 – T114 – T213 – T222 – T231 – T312 – T321 –
T411 – T1112 – T1121 – T2111
13
T9 – T17 – T26 – T35 – T44 – T53 – T62 – T71 – T115 – T214 – T223 – T232 – T241 – T313 – T322 –
T331 – T412 – T421– T511 – T1113 – T1122 – T1221 – T2113 – T2211 – T3111 – T11111 – T21111
NpLp
NpAs
Ramification emergence
NpPp
48
75
Shoot number
(B) Agrostis stolonifera when the 1st primary tiller emerges at the axil of leaf 1
1
1
MS
5
5
T1
6
6
T2
7
7
T3 – T11
8
8
T4 – T12 – T21
9
9
T5 – T13 – T22 – T31
10
10
T6 – T14 – T23 – T32 – T41 – T111
11
11
T7 – T15 – T24 – T33 – T42 – T51 – T112 – T121 – T211
End of observations
12
12
T8 – T16 – T25 – T34 – T43 – T52 – T61 – T113 – T114 – T122 – T212 – T311 – T321 – T1111
13
13
T9 – T17 – T26 – T35 – T44 – T53 – T54 – T62 – T71 – T115 – T123 – T124 – T112 –
T213 – T214 – T312 – T322– T411 – T511 – T1112 – T1121 – T1211 – T2111
NpLp
1
2
3
5
8
13
20
31
Ramification emergence
1
2
3
5
8
12
18
27
41
64
Shoot number
(C) Poa pratensis when the 1st primary tiller emerges at the axil of leaf 2
1
1
MS
6
4
–
5
T2
9
6
T3 – R1
–
7
T4 – T22 – R2 – R3
12
8
T5 – T23 – T32 – R4
End of observations
–
9
T6 – T24 – T33 – T42 – T222 – R13 – R5 – R6
15
10
T7 – T25 – T34 – T43 – T52- T223 – T232 – T322 – R7 – R14 – R15 – R23 – R33
–
11
T8 – T26 – T35 – T44 – T53 – T62 – T224 – T233 – T323 – T332 – T422 –
T2222 – R8 – R9 – R16 – R24 – R25 – R34 – R35 – R43 – R133
1
2
4
8
12
20
33
54
MS, Seedling main stem; T, seedling ramifications; R, shoots from rhizomes.
Np gives the number of phyllochrons on the MS, for L. perenne (NpLp), A. stolonifera (NpAs) and P. pratensis (NpPp). For an easier comparison between
the three grasses, NpLp is presented as reference, left of the values of NpAs in (B) and left of the values of NpPp in (C). Subscripts indicate ‘parent’ leaves
of tillers. Tillering models were calculated from values given in Tables 3 and 4.
As had been observed in ryegrass by Mitchell (1953), the
LAR in L. perenne was similar among all tillers, so that the
tillering models of Masle-Meynard and Sébillotte (1981b)
and Kirby et al. (1985) for wheat and barley were easy to
transpose to this species. Kirby et al. (1985) proposed a
model where the first primary shoot emerges at the axil
of the coleptile leaf when the MS presents three fully expanded leaves (coleoptile included). In Masle-Meynard and
Sébillote’s experiments (Masle-Meynard and Sébillote,
1981b), T1 was the first primary shoot and appeared
when the MS had five fully expanded leaves. It was
observed that in L. perenne and A. stolonifera, T1 was
the first primary shoot in most cases. On about 35 % of
the plants of each species, the first primary shoot emerged
at the axil of leaf 2. In the three species, primary and
secondary first ‘daughter’ tillers emerged one bud earlier
than on the MS. The variability was greater in A. stolonifera
than in L. perenne and this might be partly due to the fact that
A. stolonifera is an obligate outcrosser (Cattani et al., 2002).
Above-ground parts of L. perenne and A. stolonifera
expressed similar bunch-type behaviours with the same
MS phyllochron values. Their development was difficult
to discriminate statistically. In the two species, the number
of shoots increased exponentially with time. They both
reached the fourth level of ramification at 37 DAT, and
allocated similar amounts of dry matter to the different
ramifications. Even though tiller dynamics and distribution
appeared globally similar in both species, the production of
the first ‘daughter’ tiller in A. stolonifera was delayed by one
leaf interval on secondary axes and on the upper primary
Fustec et al. — Morphogenesis of Three Growth Forms of Grasses
axes compared with L. perenne. By extrapolation from the
tillering models, the highest LAR found on secondary tillers
compared with the MS and primary tillers would not compensate for the delay in phytomer production. These differences are important to discriminate growth strategies of the
two bunch types. They might be linked to the morphology
of the phytomers; L. perenne is known to form compact
tussocks with large numbers of long leaf blades, while
A. stolonifera produces shorter leaf blades with larger
and longer internodes useful for horizontal creeping (around
1 cm longer than in L. perenne). Because the production of
few large tillers requires more carbon available within the
plant than the production of many small tillers (Sugiyama,
1995), these morphological differences might partly explain
the higher shoot : root ratio measured in A. stolonifera
compared with L. perenne (50 % higher). Lolium perenne
is a compact plant that actually colonizes both soil and
air vertically, and new ramets are produced very close to
the MS (Grime et al., 1988). By contrast, stolons of
A. stolonifera provide large amounts of nitrogen and soluble
carbohydrates to new ramets rooting at substantial distances
from the seedling MS, especially in the later stages of plant
development.
Olff et al. (1990) stressed that the combination of light
intensity and nutrient supply is important for shoot : root
ratios in several grasses. The present values seem to be in
agreement with results obtained with L. perenne in comparable nutrient, light intensity and temperature conditions
(Olff et al., 1990). Lolium perenne is known to be a good
competitor for both light and nutrients. Lolium perenne is
also known to contain large amounts of nitrogen compounds
and water-soluble carbohydrates useful to support ramification (Ourry et al., 1988; Warringa and Kreuzer, 1996;
Santos et al., 2002). Surprisingly, despite its intense root
development, previous authors have shown that L. perenne
has less ability to use N for regrowth of laminae after defoliation than other growth forms, even when N is supplied.
Sink/source relationships in grasses have been described
under successive defoliations in L. perenne (Ourry et al.
1988), and in different growth forms such as the caespitose–
rhizomatous Poa trivialis, the caespitose–stoloniferous
Agrostis castellana, and the rhizomatous Festuca rubra
(Thornton et al., 1994).
In P. pratensis, biomass allocation to MS (+ R), primary
and secondary tillers was much lower than in the other
species. Rhizome growth seemed to be favoured compared
with above-ground development. In this species, rhizomes
are important sinks of nutrients for new ramets (rooted R
and ramifications). However, on the MS and tillers, LAR as
well as the biomass allocated to above-ground parts were
60 % lower in P. pratensis than in L. perenne. As a consequence, root : shoot ratios were similar between the two
species even though they expressed opposite growth strategies. For example, >75 % of below-ground parts in
P. pratensis were rhizomes, i.e. storage organs useful for
the production of ramets far from the MS (Grime et al.,
1988). While MS development was 30 % slower in
P. pratensis than in the other species, the interval between
the emergence of two successive rhizomes was approximately equal to a phyllochron on the MS of L. perenne and
277
A. stolonifera. In addition, these new shoots had similar
LAR than the rate observed on the MS of the other two
species.
In conclusion, even though L. perenne had the fastest
tiller production at the earliest stages of seedling development, A. stolonifera and P. pratensis compensated almost
completely for the delay. No significant differences were
observed in the rate of emergence of the successive tillers
and in site-filling values on the MS of the three species,
despite their contrasted growth forms. This study provides a
basis for modelling plant development. However, changes
in morphogenesis of these species with contrasting growth
tactics are expected under different growth conditions,
such as interplant competition, and longer studies on the
development of rhizomes in P. pratensis and of stolons in
A. stolonifera are required.
ACKNOWLEDGEMENTS
We thank Dr Bruno Moulia, Dr Vern S. Baron and two
anonymous referees for helpful comments that improved
the manuscript. We also thank the Groupement National
Interprofessionnel des Semences (GNIS) from Angers for
providing the caryopses.
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