Biologia, Bratislava, 61/4: 441—447, 2006
Section Botany
DOI: 10.2478/s11756-006-0074-0
Seasonal dynamics of dry weight, growth rate and root/shoot ratio
in different aged seedlings of Salix caprea
Jiří Dušek1* & Jan Květ1,2
1
Department of Ecology and Hydrobiology, Faculty of Biological Sciences, University of South Bohemia, Branišovská 31,
CZ-37005 České Budějovice, Czech Republic; e-mail: [email protected]
2
Academy of Sciences of the ČR, Institute of Botany, Dukelská 135, CZ-37982 Třeboň, Czech Republic
Abstract: Willows (e.g. Salix caprea L.) are deciduous and richly branched shrubs or small trees. Salix caprea shows a
high adaptability to different habitat conditions. One way of evaluating this adaptability is to measure willow biomass and
production. Young plants of S. caprea were sampled from the bottom of an artificial lagoon in which sediments removed from
the local Vajgar fishpond were deposited. The bottom of the lagoon was overgrown by vegetation dominated by seedlings
of the willows S. caprea and S. aurita. Willows grew in the lagoon at average density of 58 plants per m2 . The biomass
production and growth of S. caprea were determined for 15 samples (collected from 315 individuals) during the growing
season. Annual net dry matter production in the whole community was estimated for 2.7 kg m−2 . Willows are generally
considered to be fast-growing plants. The highest RGR of willows recorded by us was 0.03 to 0.04 g g−1 d−1 both in the
stems and roots. This value was often recorded from July to August.
Key words: biomass, RGR, willows, production, fishpond deposit, Salix
Introduction
Willows (Salix caprea L.) are deciduous and richly
branched shrubs or small trees predominantly occurring in the temperate zone. Salix caprea often grows on
sunny sites (willows are not adapted to shade) (Hejný
& Slavík, 1990). Mature plants mostly form bushes
or open scrub on wasteland, spoil or in mires, and are
more frequent as canopy species in scrub than in woodlands (Grime et al., 1989). Salix caprea shows a high
adaptability to different habitat conditions and fast
growth in different conditions. One way of evaluating
this adaptability is by measuring willow biomass and
production. Salix caprea is also a pioneer tree species,
which fills gaps in tree stands arising as a result of disturbance (Faliński, 1997; Kuzovkina & Quigley,
2005). Stands of S. caprea, together with other species
of genus Salix, can be used for the recovery of heavily
disturbed natural sites (e. g., mines, gravel pits, spoilheaps of lignite mines, waste sites) by increasing the
ecological complexity (Kuzovkina & Quigley, 2005).
The amount of biomass produced and the ratio
between aboveground and belowground biomass characterise plants growth traits as well as the conditions
site. Most species respond to different conditions by
changing their ratio between belowground (R) and
aboveground (S) biomass (R/S ratio). The responses to
changing conditions observed as differences in the R/S
ratio reflect the general ecological characteristics of the
current species (van Hees & Clerkx, 2003). Growth
differences can be also found in diferent clones of one
species (Salix sp., Populus sp.) (Tharakan et al., 2005;
Labrecque & Teodorescu, 2005). In general fast
growing species have low R/S ratios and slow growing
species high R/S ratios (Lambers & Poorter, 1992).
High irradiance can increase photosynthetic rate
and, following allocation of starch into the root systém (May until October in S. caprea L.), belowground biomass, resulting in higher R/S ratios (Sauter
& Wellenkamp, 1998). Irradiance indirectly affects
biomass production and R/S ratio also through increasing soil temperature. The effect of soil temperature on biomass production and the R/S ratio in
beech seedlings was reported by Lyr & Garbe (1995).
Shading can have no effect on the biomass distribution within the root systém, but can reduce the R/S
ratio, leading to increased by growth of aboveground
plant parts (van Hees & Clerkx, 2003). The effect
of soil nutrient contents related to irradiance and soil
moisture levels (Minotta & Pinzauti, 1996). Madsen (1994) reported a decrease of the R/S ratio with
irradiance in well watered beech seedlings. In dry and
nutrient-poor habitats, belowground biomass increases
and the R/S ratio is usually greater than 1, as plants
* Corresponding author
c 2006 Institute of Botany, Slovak Academy of Sciences
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442
form extensive root systems. The R/S ratio is often
less than 1 (more biomass allocated to aboveground
plant parts) in stands which are sufficiently supplied
with water and nutrients. The R/S ratio also changes
during the plant life cycle. The mass of belowground organs increases from the juvenile to the generative stage
and decreases during the senile stage. The R/S ratio
usually increases with advancing development of established seedlings (Lambers & Poorter, 1992).
Data on the growth, biomass and R/S ratio in
woody plants (trees and shrubs), even young ones, are
important for knowledge about responses of trees to
changing conditions, both at the local and global scales.
Information about S. caprea L. growth can be used for
various environmental projects considered to improve
the environment. The results of willow growth of this
paper are based on 15 samples collected during growth
season. These samples represent cca 315 collected individuals of Salix caprea L. In this article, the biomass,
growth rate (RGR) and R/S ratio were studied. The
aim of the study was to record in detail how fast willows
grow in an artificial site and how biomass production
and the R/S ratio changed in differently aged willow
stands.
Site description and plant material
The lagoon was situated about 1 km from the edge of
Jindřichův Hradec in South Bohemia, Czech Republic. The
removal of sediments was a crucial part of the restoration
of the Vajgar fishpond, actually an artificial lake filled with
water since the 13th century (POKORNÝ & HAUSER, 1994).
Rifts appeared in the deposited sediment during its drying. On 15 October 1994, four sediment samples (to 20 cm
depth) were taken at random for chemical analyses. For soil
chemical analysis were used standard analytical methods
(KLUTE, 1996). The sediment had a relatively high calcium
content, but low pH (pH(H2 O) 4.18 and pH(KCl) 4.13). The
sediment had a high sulphate content (6 to 7 g kg−1 of dry
weight, POKORNÝ & HAUSER, 1994), but most was precipitated as calcium sulphate and did not affect the pH of the
soil. The alkalinity of the pore water was low: 0.7 mmol L−1
(POKORNÝ & HAUSER, 1994). Available and total phosphorus were 14.5 mg kg−1 , 2.48 g kg−1 , respectively (Tab. 1).
Individuals of Salix caprea were sampled in 1994 and
1995 from the bottom of a lagoon in which fishpond sediments had been deposited in 1992–93. The bottom of the
lagoon was overgrown mostly by seedlings of the willows S.
caprea (average density: 48 individuals per m−2 ) and S. aurita (average density: 10 individuals per m−2 ). The age of S.
caprea was one (14 individuals per m2 ), two (24 individuals
per m2 ) and three (10 individuals per m2 ) years. Colonization by the two Salix species occurred because of favourable
conditions in the bottom of the lagoon. These conditions
were: 1) sufficient amount of seeds from the surroundings; 2)
the availability of moisture for seed germination (soil moisture is less important after seedling establishment); 3) the
absence of competitors; 4) the availability of full irradiance
and; 5) the nutrient availability in the sediment.
J. Dušek & J. Květ
Table 1. Nutrient contents in the upper soil layer of a lagoon in
which fishpond sediments had been deposited. Mean ± standard
deviation.
Mean ± SD
Characteristics
(KCl)
(H2 O)
pH
4.13 ± 0.09
4.18 ± 0.08
±
±
±
±
Available nutrients [mg kg−1 ]
P
K
Mg
Ca
14.5
156
441
1590
Organic matter
[%]
15.2 ± 0.8
N-NO3
N-NH4
6.1 ± 3.6
71.9 ± 5.2
P
K
Ca
2.48 ± 0.22
11.0 ± 0.71
3.13 ± 0.34
Nitrogen [mg kg−1 ]
Total nutrients [g kg−1 ]
0.9
30
25
90
Methods
Whole S. caprea plants were sampled 15 times during one
growing season. On each sampling date 21 individuals were
sampled, for a total of 315 individuals overall. The following
parameters were recorded for each plant: stem length, basal
stem diameter, width of the root system and rooting depth,
dry weight of aboveground organs (leaves and stems were
weighed separately) and roots. Individuals of S. caprea were
separated into three groups according to age, i. e., one, two
and three – year trees, based on the number of rings, stems
height, basal diameter and the number of branches. Plant
samples were dried at 80 ◦C in a drying oven with air circulation. Leaf area was estimated with a standard computer
scanner (Helwett-Packard scanner, software Area made by
V. Hauser (unpublished)). Leaf samples, consisting of leaves
from 12 willow individuals, and dry weight and area of these
leaves were then determined separately for each willow. The
values of resulting leaf area and leaf dry weight were then
used to calculate specific leaf area (SLA) (KVĚT & MARSHALL, 1971)
Seasonal and overall changes in the dry weight of
stems, leaves and roots were fitted to curves by the “loess
smoother” method (CLEVELAND, 1979, 1994). Values from
these curves were used for calculating RGR’s (Relative
growth rates) of stems, leaves and roots, using the formula:
RGR = (ln W2 − ln W1 )/(t2 − t1 ) (KVĚT et al., 1971; HUNT,
1978, 1982). Fitting of the RGR curves was also made by
the “loess smoother” method (CLEVELAND, 1979, 1994).
Results
Dry weight data
Figure 1 presents the dry weight dynamics of the willow stems, leaves and roots in all three study years.
The maximum dry weight of each organ type, and of
the whole plant was attained from August to September in all three age groups. There was a notable difference between the last (autumn) dry weight value for
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Seasonal dynamics of dry weight, growth rate and root/shoot ratio in Salix caprea
443
Fig. 1. Dry weight of Salix caprea roots, leaves, stems and whole plants for one- to three-year old willows.
Table 2. Estimation of annual net dry weight production (g m−2 ) in the Salix caprea willow scrub. n – average number of plant per
m2 .
Age of willows
n
Stems
Leaves
Roots
Aboveground
Total
One – Year
Two – Year
Three – Year
14
24
10
112 a
569 b
591 c
31 a
187 b
242 c
39 a
240 b
237 c
143 a
756 b
833 c
182 a
996 b
1070 c
Total
48
460
516
Kruskal-Wallis test
DF = 2, N = 323
1272
H = 129.2
p < 0.001
H = 78.8
p < 0.001
two-year stems and the first (spring) value for threeyear stems (Fig. 1). Average stem height and diameter
of the two-year willows were 115.5 ± 3.4 cm (mean ±
standard error) and 8.4 ± 0.2 mm respectively. For oneyear old seedlings, these values were 82.8 ± 4.6 cm and
5.3 ± 0.3 mm respectively. In the stand dominated twoyear willow individuals. It was estimated that grazing
by roe deer (Capreolus capreolus L.) removed 10 % of
intact aboveground biomass mainly in the two-year willows.
Each of the curves of leaf dry weight for one to
three-year willows showed a decrease after the summer maximum (August – September). The fluctuations
around the maximum leaf dry weight showed the widely
fluctuating summer values, while the “loess smoother”
method accounted for these values in fitting the curves.
Root dry weight also differed seasonally, with maxima
H = 169.3
p < 0.001
1732
H = 143.0
p < 0.001
2248
H = 159.2
p < 0.001
for the different year classes occurring in August or
September (Fig. 1).
Root/Shoot ratio and annual dry mass production
The R/S ratio was greater than 1 at the beginning of
the growing season and decreased to 0.2 by summer
(Fig. 2). There was only a small difference in R/S ratio
between the three age groups. The difference between
the R/S ratio expressed either as dry or fresh weight
decreased as the willows grew and the proportion of
tissues in their aboveground biomass increased.
Total annual net production for S. caprea was
about 2.2 kg m−2 (Tab. 2). This value was calculated
from measuring 48 individuals of S. caprea. However,
S. aurita also grew in the lagoon at a density of 10 individuals m−2 . If it is assumed that S. aurita has the
same net production and the same age composition as
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444
J. Dušek & J. Květ
Fig. 2. Seasonal variation of RGR (Relative Growth Rate) and Root/Shoot ratio of one, two and three year old plants of Salix caprea.
RGR was calculated from the fitted lines of dry weight (see Fig. 1).
Table 3. Leaf dry weight and characteristics per individual of willows (Salix caprea L.) sampled on August 7, 1995. Mean ± standard
deviation, results of Kruskal-Wallis test, DF = 2; N = 36.
Characteristics of leaves
Average leaf area per indiv.[cm2 ]
Average dry weight per indiv. [g]
Specific leaf area [leaf area/dry leaf weight]
One – year
Two – year
Three – year
Kruskal-Wallis test
467.0 ± 80.3 a
2.6 ± 0.5 a
177.8 ± 10.5 a
532.4 ± 73.3 a
3.4 ± 0.6 b
159.1 ± 13.7 b
485.0 ± 89.3a
3.2 ± 0.7 b
155.0 ± 8.7 b
H = 3.3 p = 0.18
H = 8.8 p = 0.01
H = 16.3 p < 0.001
S. caprea, then the total net dry weight production in
the whole community would be about 2.7 kg m−2 .
Growth rate data
Figure 2 presents the growth rate dynamics of willow
stems, leaves and roots for the three age classes. The
growth rate of each organ and for of the whole plant
were calculated from dry weight data. The maximum
growth rate of stems was attained during May to August. Stem RGR differed between the age groups. The
stem RGR of one-year willows had two maxima, with
the decline during June to July probably being due
to herbivory. The second peak corresponded with expansion (branching and thickening) of the stems. The
two-and three-year old willows showed only one seasonal maximum of stem RGR, but the maximum lasted
longer in the two-year willows, which were forming
branches at that time.
All curves of leaf growth are similar for all three age
groups of willows, with maximum growth rates recorded
in March and April (Fig. 2). The leaf growth rate was
around zero during May to September. The several os-
cillations occurring during this time were caused by
leave loss (grazing by roe-deer, etc.).
Table 3 summarises the characteristics of S. caprea
leaves. Average leaf area was greatest in two-year willows, probably due to their having a high number of
leaves. Three-year willows formed fewer, but thicker
leaves.
Root RGR differed among the three age classes
(Fig. 2). The roots of one-year willows grew quickly
during June and July. The older willows formed new
roots and “repaired” their root systems after the winter period. Two- and three-year willows formed new
roots in May to July. A decrease in root dry weight was
observed before then.
Root system morphology in Salix caprea
Willows created fibrous roots with the majority of fineroots found in the upper 20–30 cm of the soil profile.
Two types of roots were formed (Figs 3 a,b). The first
type comprised surface roots forming branches only on
one side of the root system. The other type penetrated
deeper and formed more branches than did the roots of
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445
Fig. 3. Salix caprea root system (a) which comprised surface roots forming branches only on one side, root system which penetrated
deeper and formed more branches (b).
the first type. Gradual drying of the sediment resulted
in the formation of cracks, which split the sediment
surface into polygons. Plants with the first type of roots
often grew at the edges of the polygons, while those
with the other type of roots were often found at the
polygon centers.
Discussion
The chemical composition of deposited sediments
(Tab. 1) corresponded to the chemical composition of
littoral sediments of other fishponds in the Czech Republic (Dykyjová & Úlehlová, 1978; Prach et al.,
1987). The organic matter content in the Vajgar sediment is comparable with that in the accumulation zones
of fishpond littorals (Dykyjová & Úlehlová, 1978).
The pH of the sediment was low however the sediment
contains relatively high calcium content. The effect of
calcium was eliminated by calcium precipitation as calcium sulphate (Pokorný & Hauser, 1994).
The sediments from Vajgar pond were gradually
dried and the upper layer oxidized, but the lower layer
was less oxidized, with being ammonia the main form of
available nitrogen. The content of nitrate nitrogen was
markedly low. The high content of ammonia nitrogen
was caused by less oxidation in the lower sediment layer
and also by the production of ammonia nitrogen due to
organic decomposition. Nitrate nitrogen is more mobile
than ammonia nitrogen in sediment and can be flushed
by water (effect of drainage).
Willows grew in the lagoon at a density of 58 individuals per m2 . The annual net dry matter production in the whole community was 2.7 kg m−2 . This
level of production is comparable with that of intensive wood culture systems producing biomass for energy (Kopp et al., 1993, 1996 and 1997). Labreckue
& Teodorescu (2005) reported aboveground biomass
yield of Salix clones SX64 and clone SX61 to be 6.75
kg m−2 and 62.34 kg m−2 , respectively after 4 growing seasons. The shoot density in this study was similar to that (about 46-49 trees per m2 ) in experiments
investigating biomass production of willow clones in
fertilized and non-fertilized treatments (Kopp et al.,
1996). The aboveground biomass of the SP3 clone
(Salix purpurea L.) ranged from 0.2 to 1.7 kg m−2
in fertilized stands and 0.15 to 1.1 kg m−2 in nonfertilized stands. Fertilization increased aboveground
biomass production during each of the first three growing seasons, had little effect during the fourth growing season, and reduced production during the fifth
season (Kopp et al., 1996). These values of annual
aboveground biomass in two- and three-year willows are
slightly below those measured in this study. (Tab. 2).
This may be due to the higher shoot density of the willows in this study. Thereafter, the willow stand in the
Vajgar site was not a monoculture (seedlings of Salix
aurita) and higher production may be the result of the
willow stand being composed of different age cohorts.
It was assumed that the level of intraspecfic competition in a differently aged stand is more intense than
in an even-aged stand (no increase in root dry weight
is assumed to occur during winter are most probably
caused by competition in the rhizosphere). However,
the use of light and nutrient sources can be more efficient in a differently aged stand than for an evenaged stand. The SLA of the one-year willows was different in comparison with older willows, other hand
the leaf area was the same (Tab. 3). The young willows formed smaller, but more leaves and old willows
formed less large leaves. The current situation is a result of strong competitions about space and optimal
irradiance.
The maximum dry weight of each organ type and of
the whole plant was attained during August to September. There was a notable difference between the last
(autumn) dry weight value for two-years stems and the
first (spring) value for three-year stems (Fig. 1). A possible explanation is as follows: a the age of two years
(in the previous year), the population of the current
year’s three-year willows was more vigorous (with a
higher dry weight per individual willow) than the current year’s population of two-year willows which were
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446
under a stronger competitive pressure by their older
neighbours. Another possible explanation may be also
grazing by herbivores. Roe-deer (Capreolus capreolus
L.) were observed to graze on the willow stand. Deer
are selective herbivores and preferred bunches of S.
caprea L. at stem heights between 85 and 115 cm (Renand et al., 2003). Willows are preferred by deer over
birch (Bergman et al., 2005). The level of grazing is
influenced by the surrounding vegetation, structure of
saplings and stand density. The effect of grazing was the
highest in two-year willows. The average height of the
two-year willows was 115.5 ± 3.4 cm (mean ± standard
error), with stem diameter of 8.4 ± 0.2 mm, while the
average height of the one-year willows was 82.8 ± 4.6
cm with a stem diameter of 5.3 ± 0.3 mm. Two-year
willows were dominate in the stand. It is likely that the
two-year willows were preferred over the one and three
year willows.
Willows are generally considered to be fast-growing
trees together with Populus species, but biomass production is higher in willow plantations than for poplar
(Grime et al., 1989). The highest RGR of willows
recorded in the lagoon of Vajgar site was 0.03 to 0.04
g g−1 d−1 both for stems and roots. This value was
often recorded in July and August at the time the
stems were elongating and, especially in the three-year
willows, branches were forming. Martinková (1976)
recorded the growth of new shoots of several Salix
species (S. alba, S. interior, S. muscina, S. purpurea
and S. repens) from stem cuttings. The RGR of new
shoots growing from the cuttings was about 0.07 to
0.09 d−1 in May, while it was only about 0.02 during
July and August. At this time, Martinková (1976) observed many differences between willow species. In general, RGR is dependent on both plant species and climatic conditions. RGR of the other trees species ranged
from 0.049 to 0.112 g g−1 d−1 (Castro-Díez et. al.
2003), with willows species is at the higher end of this
range.
RGR is a parameter showing the actual changes
of growth under natural conditions. Growth rate is low
when conditions are unfavourable, but when conditions
change, the growth rate changes at once. The RGR
recorded in the lagoon population showed that the conditions were favourable for willow growth. Irradiance
and nutrient levels were sufficient for seedlings. Competition within the willow stand allowed for the formation of a very dense and vigorous willow stand. This
helped to dryout and oxidizes the deposited sediment
from the Vajgar fishpond, which could then be used for
agricultural purposes.
Acknowledgements
The authors thank Dr. Tomáš PICEK for a critical review of
this manuscript and Dr. Keith EDWARDS for his linguistic
assistance.
J. Dušek & J. Květ
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Received Sept. 15, 2005
Accepted May 4, 2006
Unauthenticated
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