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Relation between moisture content and early growth in stem cuttings of selected fast-growing willow clones
Biomass and Bioenergy Vol. 4, No. 4. pp. 249-253. 1993 Printed in Great Britain. All rights reserved
0961-9534/93 $6.00+ 0.00 ‘Q 1993Pergamon Press Ltd
RELATION BETWEEN MOISTURE CONTENT AND EARLY GROWTH IN STEM CUTTINGS OF SELECTED FAST-GROWING WILLOW CLONES L. SENNERBY-FORSSE, B. TELENIUS and H. A. VON FIRCKS Swedish
University
of Agricultural
Section
of Short
Sciences, Department of Ecology and Environmental Rotation Forestry, Box 7072, S-750 07 Uppsala, Sweden
(Received 13 July 1992: recked receioed I9 December
1992; accepted 22 December
Research,
1992)
Abstract-Short rotation biomass plantations with Mix spp. are established with stem cuttings prepared from one- to two-year-old dormant coppice shoots. The quality and physiological condition of cuttings are critical for survival and establishment of plantations. Provided that the stems used for cuttings are healthy and dormant at the time of harvesting, the main risk of deterioration is from the storage conditions. Moisture loss during storage is regarded as the most critical factor to rooting and survival of woody cuttings. Cuttings of nine selected clones of Salix uiminalis, S. da&ados and S. daphnoides were left to dry for different time intervals in controlled conditions and the survival rate and early growth response at different moisture levels were recorded. The ability to withstand lower moisture content varied significantly between species and clones. Two different types of response were demonstrated among the willows. S. dusyclados and S. daphnoides clones tended to resist drying better, while S. uiminalis clones showed variation and generally tolerated moisture loss better than clones of other species tested. Sprouting was more affected by low moisture content than rooting in all clones. The sensitivity in some of the clones to even moderate moisture loss suggests that recommendations to water soak Salk cuttings before planting should be a standard procedure in the establishment of biomass plantations with willows. Keywords-Biomass rooting, Mix.
plantations,
cutting,
drought
resistance,
performance,
moisture
content.
of the most critical factors to rooting,‘-9 very little is known about the effects of moisture loss from cuttings on establishment success and growth in different genotypes of willow. The main purpose of this study was to assess the drying rate and the effect of decreasing moisture content on rooting, sprouting and early biomass production in dormant stem cuttings of selected Salix spp.
1. INTRODUCTION
Short rotation biomass plantations with willows (S&ix spp.) are established with stem cuttings.’ The cuttings are prepared from one- to twoyear-old coppice shoots that are harvested in a dormant condition, from November to March.2 To achieve successful establishment, the cutting material must be in good physiological condition when planted. Most willows used in biomass plantations root readily through adventitious roots developing from preformed root primordia in the stems.3 Provided that the stems are dormant and not affected by disease or other damage at the time of harvesting, the main risk of deterioration is therefore the conditions under which the cuttings are stored. External factors, such as temperature, humidity and light, are closely connected with the survival rate of woody cuttings.4-6 Ideally, dormant willow cuttings should be stored at -4°C wrapped in plastic bags to prevent moisture loss.* However, these conditions are not always achieved or maintained and cuttings can be severely damaged, especially by drying. Although moisture is regarded as one JBB 414-c
growth
2. MATERIALS
AND METHODS
2.1. Materials
Clones with a high rooting ability and a normal survival rate of at least 98% were used for the study. Six clones of S. viminalis and two clones of S. dasyclados, frequently used in practical willow plantations in Sweden, were chosen. As a comparison, one clone of S. daphnoides was included in the study (Table 1). The stems of the latter species are covered by a thick wax layer indicating a certain ability to withstand dry conditions. The clones were cultivated in stool beds in the middle part of Sweden (lat. 59”49’N, long. 18”40’E, altitude 15 m above sea level). One249
250
L. SENNERBY-FORSSE Ed al.
year-old shoots, 1.5-3.5 m in height, without visible damage were harvested from four-yearold stools in the end of February and beginning of March 1988 (i.e. dormant condition). The shoots were immediately cut into 20-cm long cuttings with a diameter of 0.5-1.8 cm. The length and diameter of the cuttings were standardized in order to minimize size effects on the results (Table 1). Two hundred cuttings per clone were stored in an upright position in plastic bags at -4°C for about two months before the experiment started in May 1989. 2.2. Drying treatment Ten cuttings of each clone were taken from storage and immediately placed in a growth chamber without illumination. They were placed horizontally on a rib and left uncovered to dry. The duration of the drought treatment in the chamber varied from 5 to 384 h, with a minimum difference of 5 h between treatments, in order to obtain different moisture levels in the cuttings. Ten cuttings per clone were excluded from drought treatment in order to achieve the moisture content immediately after storage. In total, 1530 cuttings were used in the experiments. The temperature was set to +25”C, relative humidity fluctuated between 3040% and the air flow was 0.2 m ss ’in the growth chambers. After this drying treatment, each cutting was divided into two IO-cm long pieces. The basal half was used for calculation of moisture content and dried to constant weight (48 h at + 105C). Moisture content was expressed on a fresh weight basis. The upper half of each cutting was cultured in tap water (+ 24°C) in greenhouse conditions in HIKO 50 containers (normally used for seedling cultivation). The containers consisted of separate, cylindrical units 78 mm deep, 32 mm in diameter and 35 mm apart from each Table I. Species, clones and average diameter (mm) and standard deviation (SD) of the cuttings used in the experiment Species
Clone
S. viminalis viminalis viminalis viminalis viminalis viminalis absyclados aksyclados daphnoides
78112 78183 78021 78101 78102 78198
S. S. S. S. S. S. S. S.
Diameter SD (mm)
77056
9.5 9.2 8.9 9.9 9.8 9.4 10.9 9.4
1.9 1.6 1.2 1.8 1.6 1.8 2.3 2.1
78139
9.5
1.6
81090
other. Cuttings were placed with 7 cm (70%) of the stem submerged in water. The temperature in the greenhouse was +24”C during the day and + 18°C during the night. Periodically higher temperatures were recorded due to exceptionally sunny and warm weather conditions. The time required for visible roots to develop and for buds to sprout was recorded for each cutting on a daily basis. When no visible life signs were observed after day 14, the cuttings were regarded as non-viable. After 14 days in hydroculture, the total dry matter production of roots and shoots was measured. 2.3. Data treatment After drying treatment, cuttings were classified according to their moisture content in classes from 55 to 30% moisture. Each moisture class ranged 5%, and the cuttings in each class were represented by the class middle value of all cuttings within the given range. To correlate moisture content to time of drying exposure, linear least square regression lines were determined for each clone from the experimental data and presented by the calculated clonal intercept and slope coefficient. Clonal differences in biomass production (gDM roots and shoots total) in different moisture classes were analyzed by using one-way analysis of variance. All given statistical significances were based on P < 0.05.
3. RESULTS
3.1. Resistance to drying Prior to the drying treatment the mean moisture content varied from 49 to 56% across the clones, with an average value of 52%. During the first 168 h of drying the moisture content decreased linearly with time (Fig. 1). Within this interval a linear regression was fitted to each clone with a mean R* value of 0.89. Significant variation existed between all clones with respect to the initial moisture content as well as the moisture loss per unit time (Table 2). The highest rate of moisture loss was found in S. viminalis clone 78021 and the lowest in S. daphnoides clone 78 139. The median slope for all clones corresponded to an average decrease in moisture content of 4 percentage points per 24 h. The maximum difference in moisture content reduction between clones was 1.6 percentage points per 24 h. After 150 h of drying, cuttings of clone 78139
Moisture content and early growth in stem cuttings 06
0.0
,
1 0
I
/
1
I
I
100
200 Hours
300
I
3.3. Sprouting and rooting
I
The time required for sprouting and rooting increased with decreasing moisture content, sprouting being more affected than rooting (Table 3). In the highest moisture classes (5045%) it generally took 46 days before sprouts and roots had emerged in all clones. Delayed sprouting was first observed in moisture class 40% in the S. dasyclados clones and in one of the S. viminalis clones (78021). Rooting was little affected at this level in most clones. At 35% moisture the S. viminalis clones (except 78021) were still sprouting and rooting within a week, while in the other clones growth start took 10 days or more. The time interval between rooting and sprouting increased with decreasing moisture content. In moisture class 30% both sprouting and rooting were delayed in all clones.
400
of drying
Fig. 1. Decrease in moisture content over time (h) in nine clones of S. viminalis, S. dasyclados and S. daphnoides. Each value represents an average of minimum 10 cuttings per clone.
had moisture contents 515% other clones.
higher than all
3.4. Biomass production
3.2. Tolerance to moisture loss Survival rate was considered an index of a clone’s tolerance to moisture loss, i.e. the ability to sprout and root at decreasing moisture content. A significant variation in this respect was observed among the clones. Clone 78112, S. viminalis, was the most tolerant clone with a 90% survival rate after a reduction of the initial 50% moisture content to 30% moisture (Table 2). The two S. dasyclados clones 81090 and 77056, together with S. viminafis clone 78021, showed the least tolerance to moisture loss. Cuttings of these clones could not maintain a 90% survival rate in moisture classes below 40% (Table 2).
Table 2. Relation between relative moisture content (RMC) and time intervals (T, h of drying at +25’(Y).* Initial moisture content (MC, %) is shown Initial MC (%)
Slope (rel h-‘) x 10-r
Clone
a
b
78112 78183 78021 78101 78102 78198 81090 77056 78139
0.499 0.523 0.567 0.479 0.506 0.489 0.491 0.495 0.540
-1.80 - I .68 -1.92 -1.89 -1.59 - 1.54 -1.34 - I .28 -1.24
*The model used (mean R2 = 0.89).
251
was RMC =
a + bT
There was little variation in biomass production between clones in moisture classes 45% or higher. One exception was clone 78112, S. viminalis, which produced significantly more biomass than other clones in all moisture classes (Table 4). The first response to moisture loss in terms of decreased biomass production was observed in the two S. dasyclados clones 81090 and 77056 and in S. viminalis clone 7802 1. The production in these clones was reduced to less than half in moisture class 40% compared to the production at 5045% moisture. At 30% moisture the biomass production was significantly reduced in all clones. 4. DISCUSSION
Clonal differences in moisture content of current coppice shoots of willow and poplars have been reported previously.“*” However, the influence of site conditions, variation between years, and the phenological stage of shoots at the time of sampling makes it difficult to separate phenotypic and genotypic effects on the water content. In this study the response to moisture loss differed among the species and clones. Most S. viminalis clones, and especially clone 78112, showed a low resistance to moisture loss, but had a higher tolerance as shown in the large amount of biomass produced even with a low moisture content. The resistance to drying was generally higher in the S. dasyclados clones and in the S. daphnoides clone 78 139. The latter clone, with a thick waxy cuticula, differed
252
L. SENNERBY-FOKSSE Tutul. Table 3. Growth start of cuttings in different moisture class, shown as average number of days before visible sprouting (S) and emergence of roots (R), i.e. S,‘R. and standard deviation (SD) in different moisture classes (%), in nine clones of S. GGudis, S. dusyclados and S daphnoides (N = 10 cuttings per clone and class)* 50?‘0
Moisture class 40%
45%
Clone
SIR
SD (SIR)
S/R
SD (S,‘R)
SiR
78112 78183 7802 I 78101 78102 78198 81090 77056 78139
4/S 412 5:4 414 4!4 414 5;s S/6 S/5
I,!1 2’1 1’2 III I:1 0;’I 3.‘l I:2 l/l
3/4 3:3 512 4i4 4i4 414 4i5 5/6 5.‘3
I:‘1 I;‘1 2;‘l I;‘1
3,‘2 4,2 714 4,3 5i2 3!3 8,;5 8,:l 5j3
I ,‘2 l& 3.3 1’2 2:2
*Cuttings without sign of sprouting regarded as dead (0)
and/or
SD (S’R,
rooting
from all other clones through a pronounced ability to avoid drying. The results thus suggest that some willow species may be more adapted to dry conditions than others. Sprouting proved to be more sensitive to moisture loss than rooting in the willows studied. Sprouting and rooting generally occurred close in time, until the moisture content was below 45%. The larger effect on sprouting compared to rooting suggests that water was first lost from bud tissue or tissue connected to bud growth. When roots emerged and water transport started, the buds eventually responded by bursting. The rooting ability in most cuttings was not seriously affected until below 35% moisture. In general, S. oiminalis clones tended to start growth processes more rapidly in all moisture classes and were less influenced by lower moisture content than clones of S. dasyclados and S. daphnoides.
The biomass production was closely related to sprouting/rooting behaviour of the cuttings.
I !o* IL1 4,s II
I I I I 6~2 4,6 2: 1
30%
3i”~<,
S R
SD (S/R)
4:3 73 I?:4 52 h,4 4,J
1’1 ?‘I 7 2 2 I 5:Z 2, I 6.‘6 5;8 6’7
!I 7 II!9 10;7
S:R
.SD t.S RI
lx3
: 1 -iI 1,: t!‘4
I13 0’ 7 13’7 12>6 IO:4 oo* o* I3 o*‘ll
on day 14 after start of hydroculture
‘;+ 41 4x 5 :h 4jx
were
The decrease in biomass production in cuttings with a reduced moisture content was partly a reflection of the increasing amount of time required for sprouting and rooting. Under the present experimental conditions, plants with an early onset of shoot and root growth had a longer growing period than plants with a later onset of growth. The highest production was achieved in plants where sprouting and rooting were close in time. The relationship between roots and shoots in a cutting is not fully understood, but several studies point towards a mutual dependence. A positive relationship between the number of roots and axillary bud growth was reported by Hansen and Kristensen” who suggested this to be a common phenomenon. Studies have shown that the presence of growing buds is necessary for the formation of roots in cuttings of Popufus robusta,“.14 suggesting a stimulatory effect of buds on root development. Healthy axillary buds, as opposed to absent or inferior buds, gave the best results in terms of survival and
Table 4. Early biomass production (gDM) and standard error (SE) of cuttings of nine S. Gmnalis, S. dasycludos and S. duphnoides clones with different moisture content (moisture classes, %). Letters indicate significant differences in biomass production between clones (P z 0.05)
Clone
gDM
SE
78112 78183 78021 78101 78102 78198 81090 77056 78139
0.224 0.139 0.119 0.149 0.136 0.122 0.124 0.125 0.102
0.009 0.014 0.010 0.016 0.012 0.011 0.012 0.008 0.005
Moisture class 40%
45%
50% P
DM
SE
a b b,c b b b,c b,c b,c c
0.245 0.148 0.122 0.127 0.150 0.129 0.151 0.112 0.101
0.013 0.010 0.020 0.008 0.011 0.007 0.011 0.007 0.011
P a b b,c b,c b b,c b c c
35%
30%
DM
SE
P
DM
SE
P
DM
SE
P
0.381 0.123 0.044 0.117 0.129 0.158 0.069 0.058 0.092
0.044 0.015 0.011 0.011 0.011 0.011 0.015 0.013 0.009
a b c b b b c c c
0.225 0.068 0.030 0.054 0.121 0.101 0.042 0.033 0.044
0.022 0.008 0.015 0.030 0.015 0.011 0.011 0.008 0.011
a c c c b b c c c
0.078 0.028 0.007 0.009 0.023 0.041 0.004 0.003 0.003
0.018 0.009 0.004 0.003 0.008 0.014 0.003 0.001 0.002
a b c c h b c ‘ c
Moisture
content
and early growth
growth for cuttings of cottonwoods” and willows (Sennerby-Forsse, unpublished). Cutting size and/or part of the shoot used for the cutting, i.e. ontogenetical differences, might influence drying sensitivity. To avoid size influences, which can be very significant for survival and production,‘6 cutting dimensions were standardized in this study. It is also possible that ontogenetical differences between the apical and basal portions of the shoots had some influence on the results. However, cuttings should theoretically contain a similar mixture of stem parts and different clones should therefore be comparable in this respect. It can be speculated that the hydroculture used in the experiment to evaluate survival of cuttings had a positive effect on growth as the cuttings were able to compensate for the lost moisture to a certain degree. In a field situation, without water soaking before planting, the survival rate would probably have been lower even after moderate drying stress. As shown by Swingle,7 the rooting ability of willow cuttings improved considerably with increased soaking time and Peterson and Phipps17 confirmed a positive effect of water soaking on survival rate in poplar cuttings. We therefore advise that water soaking of woody cuttings before planting should be a recommended procedure in the establishment of biomass plantations.
5.
CONCLUSIONS
The results showed that the ability to withstand decreasing moisture content varied significantly between species and clones. Two different types of response were demonstrated in that clones of S. dasyclados and S. daphnoides resisted drying better, while S. viminalis clones generally showed a higher tolerance to moisture loss. Clones of the latter species generally had superior survival rates, were faster in sprouting and rooting and showed higher biomass production in the lower moisture classes. The differences seemed to be mainly species specific. However, the least tolerant as well as the most tolerant clone were found within S. viminalis. The result thus suggests both inter- and intraspecific differences in drought response, indicating a potential for selecting suitable genotypes for coppice plantations on sites with different moisture conditions. Acknowledgements-This study help of funds from the National
was carried out with the Board ot tnergy, Sweden
in stem cuttings
253
The authors would like to thank Dr W. A. Kenney and Prof. L. Zsuffa, University of Toronto, Faculty of Forestry for constructive criticism of the manuscript.
REFERENCES 1. G. Siren, L. Sennerby-Forsse and S. Ledin, Energy plantations-short rotation forestry in Sweden. In Biomass (D. 0. Hall and R. P. Overend. Eds), pp. 119-143. John Wiley & Sons Ltd. England (1987). 2. L. Sennerby-Forsse Handbook for Energy (Ed.), Forestry. Swedish Univ. Agric. Sci., Dept. of Ecol. and Environ. Res., Uppsala, Sweden (1986). 3. I. Fjell, Preformation of root primordia in shoots and root morphogenesis in Salix oiminalis. Nerd. J. Bof. 5, 357-376 (I 985). 4. S. Shapiro, The role of light in the growth of root primordia in the stem of the Lombardy poplar. In The Ed.), Physiology of Forest Trees (K. V. Thimann, pp. 445465. Ronald Press (1958). 5. E. Vieitez and J. Pena, Seasonal rhythm of rooting of Salix atrocinerea cuttings. Phys. Plant. 21, 544-555 (1968). of cottonwood by 6. L. Zsuffa, Vegetative propagation rooting cuttings. In Proceedings from “Symposium on Eastern Cottonwood and Related Species” (B. A. Thielges and S. B. Land, Eds), Greeniille, Mississippi, Sept 28%Oct 2, 1976. Louisiana State University, Division of Continuing Education, Baton Rouge, LA 70803 (1976). study of rooting and I. F. Swingle, A physiological callusing in apple and willow. J. Agr. Res. 39, 81.- 128 (1929). Overwinter storage 8. W. H. Cram and H. Lindquist, of Walker poplar cuttings. For. Chron. 58, 175- 177 (1982). 9. H. M. Phipps, E. A. Hansen and A. S. Fege, Preplant soaking of dormant Populus hardwood cuttings. US Forestry Service Research paper NC-241. US For. Ser. Res. Rep (1983). Clonal variation of wood specific 10. L. Sennerby-Forsse, gravity, moisture content and stem bark percentage in l-year-old shoots of 20 fast-growing Salix clones. Can. J.-For. Res. 15, 531-534 (1985). and P. Layton, II. W. A. Kennev. L. Sennerbv-Forsse A review of -biomass quality research relevant to the use of poplar and willows. Bornas. 17, 21. 37 (1990). Axillary bud growth in 12. J. Hansen and K. Kristensen, relation to adventitious root formation in cuttings. Physiol. Plant 79, 39-44 (1990). 13. P. F. Wareing and N. G. Smith, Physiological studies on the rooting of cuttings. Rep. For. Res. 47, 118-121 (1963). of 14. N. G. Smith and P. F. Wareing. The distribution latent root primordia in stems of Populus robusta and factors affecting the emergence of preformed roots from cuttings. Foresrr?; 18, 197-266 (1972). 15. M. A. Radwan, J. M. Kraft and D. S. DeBelI. Bud characteristics of unrooted stem cuttings affect establishment success of cottonwood. Research Nore PNWRN-461. Forest Service, Pacific Northwest Research Station (1987). and L. Roy, The 16 D. Burgess, 0. Q. Hendrickson importance of initial cutting size for improving the growth performance of Sa1i.xalba. L. Stand. J. For. Res. 5, 2 15- 224 (I 990). 17 L. A. Peterson and H. M. Phipps. Water soaking pretreatment improves rooting and early survival of hardwood cuttings of some Populus clones. Tree Planters Notes 27(I). 12-22 (1976).
0961-9534/93 $6.00+ 0.00 ‘Q 1993Pergamon Press Ltd
RELATION BETWEEN MOISTURE CONTENT AND EARLY GROWTH IN STEM CUTTINGS OF SELECTED FAST-GROWING WILLOW CLONES L. SENNERBY-FORSSE, B. TELENIUS and H. A. VON FIRCKS Swedish
University
of Agricultural
Section
of Short
Sciences, Department of Ecology and Environmental Rotation Forestry, Box 7072, S-750 07 Uppsala, Sweden
(Received 13 July 1992: recked receioed I9 December
1992; accepted 22 December
Research,
1992)
Abstract-Short rotation biomass plantations with Mix spp. are established with stem cuttings prepared from one- to two-year-old dormant coppice shoots. The quality and physiological condition of cuttings are critical for survival and establishment of plantations. Provided that the stems used for cuttings are healthy and dormant at the time of harvesting, the main risk of deterioration is from the storage conditions. Moisture loss during storage is regarded as the most critical factor to rooting and survival of woody cuttings. Cuttings of nine selected clones of Salix uiminalis, S. da&ados and S. daphnoides were left to dry for different time intervals in controlled conditions and the survival rate and early growth response at different moisture levels were recorded. The ability to withstand lower moisture content varied significantly between species and clones. Two different types of response were demonstrated among the willows. S. dusyclados and S. daphnoides clones tended to resist drying better, while S. uiminalis clones showed variation and generally tolerated moisture loss better than clones of other species tested. Sprouting was more affected by low moisture content than rooting in all clones. The sensitivity in some of the clones to even moderate moisture loss suggests that recommendations to water soak Salk cuttings before planting should be a standard procedure in the establishment of biomass plantations with willows. Keywords-Biomass rooting, Mix.
plantations,
cutting,
drought
resistance,
performance,
moisture
content.
of the most critical factors to rooting,‘-9 very little is known about the effects of moisture loss from cuttings on establishment success and growth in different genotypes of willow. The main purpose of this study was to assess the drying rate and the effect of decreasing moisture content on rooting, sprouting and early biomass production in dormant stem cuttings of selected Salix spp.
1. INTRODUCTION
Short rotation biomass plantations with willows (S&ix spp.) are established with stem cuttings.’ The cuttings are prepared from one- to twoyear-old coppice shoots that are harvested in a dormant condition, from November to March.2 To achieve successful establishment, the cutting material must be in good physiological condition when planted. Most willows used in biomass plantations root readily through adventitious roots developing from preformed root primordia in the stems.3 Provided that the stems are dormant and not affected by disease or other damage at the time of harvesting, the main risk of deterioration is therefore the conditions under which the cuttings are stored. External factors, such as temperature, humidity and light, are closely connected with the survival rate of woody cuttings.4-6 Ideally, dormant willow cuttings should be stored at -4°C wrapped in plastic bags to prevent moisture loss.* However, these conditions are not always achieved or maintained and cuttings can be severely damaged, especially by drying. Although moisture is regarded as one JBB 414-c
growth
2. MATERIALS
AND METHODS
2.1. Materials
Clones with a high rooting ability and a normal survival rate of at least 98% were used for the study. Six clones of S. viminalis and two clones of S. dasyclados, frequently used in practical willow plantations in Sweden, were chosen. As a comparison, one clone of S. daphnoides was included in the study (Table 1). The stems of the latter species are covered by a thick wax layer indicating a certain ability to withstand dry conditions. The clones were cultivated in stool beds in the middle part of Sweden (lat. 59”49’N, long. 18”40’E, altitude 15 m above sea level). One249
250
L. SENNERBY-FORSSE Ed al.
year-old shoots, 1.5-3.5 m in height, without visible damage were harvested from four-yearold stools in the end of February and beginning of March 1988 (i.e. dormant condition). The shoots were immediately cut into 20-cm long cuttings with a diameter of 0.5-1.8 cm. The length and diameter of the cuttings were standardized in order to minimize size effects on the results (Table 1). Two hundred cuttings per clone were stored in an upright position in plastic bags at -4°C for about two months before the experiment started in May 1989. 2.2. Drying treatment Ten cuttings of each clone were taken from storage and immediately placed in a growth chamber without illumination. They were placed horizontally on a rib and left uncovered to dry. The duration of the drought treatment in the chamber varied from 5 to 384 h, with a minimum difference of 5 h between treatments, in order to obtain different moisture levels in the cuttings. Ten cuttings per clone were excluded from drought treatment in order to achieve the moisture content immediately after storage. In total, 1530 cuttings were used in the experiments. The temperature was set to +25”C, relative humidity fluctuated between 3040% and the air flow was 0.2 m ss ’in the growth chambers. After this drying treatment, each cutting was divided into two IO-cm long pieces. The basal half was used for calculation of moisture content and dried to constant weight (48 h at + 105C). Moisture content was expressed on a fresh weight basis. The upper half of each cutting was cultured in tap water (+ 24°C) in greenhouse conditions in HIKO 50 containers (normally used for seedling cultivation). The containers consisted of separate, cylindrical units 78 mm deep, 32 mm in diameter and 35 mm apart from each Table I. Species, clones and average diameter (mm) and standard deviation (SD) of the cuttings used in the experiment Species
Clone
S. viminalis viminalis viminalis viminalis viminalis viminalis absyclados aksyclados daphnoides
78112 78183 78021 78101 78102 78198
S. S. S. S. S. S. S. S.
Diameter SD (mm)
77056
9.5 9.2 8.9 9.9 9.8 9.4 10.9 9.4
1.9 1.6 1.2 1.8 1.6 1.8 2.3 2.1
78139
9.5
1.6
81090
other. Cuttings were placed with 7 cm (70%) of the stem submerged in water. The temperature in the greenhouse was +24”C during the day and + 18°C during the night. Periodically higher temperatures were recorded due to exceptionally sunny and warm weather conditions. The time required for visible roots to develop and for buds to sprout was recorded for each cutting on a daily basis. When no visible life signs were observed after day 14, the cuttings were regarded as non-viable. After 14 days in hydroculture, the total dry matter production of roots and shoots was measured. 2.3. Data treatment After drying treatment, cuttings were classified according to their moisture content in classes from 55 to 30% moisture. Each moisture class ranged 5%, and the cuttings in each class were represented by the class middle value of all cuttings within the given range. To correlate moisture content to time of drying exposure, linear least square regression lines were determined for each clone from the experimental data and presented by the calculated clonal intercept and slope coefficient. Clonal differences in biomass production (gDM roots and shoots total) in different moisture classes were analyzed by using one-way analysis of variance. All given statistical significances were based on P < 0.05.
3. RESULTS
3.1. Resistance to drying Prior to the drying treatment the mean moisture content varied from 49 to 56% across the clones, with an average value of 52%. During the first 168 h of drying the moisture content decreased linearly with time (Fig. 1). Within this interval a linear regression was fitted to each clone with a mean R* value of 0.89. Significant variation existed between all clones with respect to the initial moisture content as well as the moisture loss per unit time (Table 2). The highest rate of moisture loss was found in S. viminalis clone 78021 and the lowest in S. daphnoides clone 78 139. The median slope for all clones corresponded to an average decrease in moisture content of 4 percentage points per 24 h. The maximum difference in moisture content reduction between clones was 1.6 percentage points per 24 h. After 150 h of drying, cuttings of clone 78139
Moisture content and early growth in stem cuttings 06
0.0
,
1 0
I
/
1
I
I
100
200 Hours
300
I
3.3. Sprouting and rooting
I
The time required for sprouting and rooting increased with decreasing moisture content, sprouting being more affected than rooting (Table 3). In the highest moisture classes (5045%) it generally took 46 days before sprouts and roots had emerged in all clones. Delayed sprouting was first observed in moisture class 40% in the S. dasyclados clones and in one of the S. viminalis clones (78021). Rooting was little affected at this level in most clones. At 35% moisture the S. viminalis clones (except 78021) were still sprouting and rooting within a week, while in the other clones growth start took 10 days or more. The time interval between rooting and sprouting increased with decreasing moisture content. In moisture class 30% both sprouting and rooting were delayed in all clones.
400
of drying
Fig. 1. Decrease in moisture content over time (h) in nine clones of S. viminalis, S. dasyclados and S. daphnoides. Each value represents an average of minimum 10 cuttings per clone.
had moisture contents 515% other clones.
higher than all
3.4. Biomass production
3.2. Tolerance to moisture loss Survival rate was considered an index of a clone’s tolerance to moisture loss, i.e. the ability to sprout and root at decreasing moisture content. A significant variation in this respect was observed among the clones. Clone 78112, S. viminalis, was the most tolerant clone with a 90% survival rate after a reduction of the initial 50% moisture content to 30% moisture (Table 2). The two S. dasyclados clones 81090 and 77056, together with S. viminafis clone 78021, showed the least tolerance to moisture loss. Cuttings of these clones could not maintain a 90% survival rate in moisture classes below 40% (Table 2).
Table 2. Relation between relative moisture content (RMC) and time intervals (T, h of drying at +25’(Y).* Initial moisture content (MC, %) is shown Initial MC (%)
Slope (rel h-‘) x 10-r
Clone
a
b
78112 78183 78021 78101 78102 78198 81090 77056 78139
0.499 0.523 0.567 0.479 0.506 0.489 0.491 0.495 0.540
-1.80 - I .68 -1.92 -1.89 -1.59 - 1.54 -1.34 - I .28 -1.24
*The model used (mean R2 = 0.89).
251
was RMC =
a + bT
There was little variation in biomass production between clones in moisture classes 45% or higher. One exception was clone 78112, S. viminalis, which produced significantly more biomass than other clones in all moisture classes (Table 4). The first response to moisture loss in terms of decreased biomass production was observed in the two S. dasyclados clones 81090 and 77056 and in S. viminalis clone 7802 1. The production in these clones was reduced to less than half in moisture class 40% compared to the production at 5045% moisture. At 30% moisture the biomass production was significantly reduced in all clones. 4. DISCUSSION
Clonal differences in moisture content of current coppice shoots of willow and poplars have been reported previously.“*” However, the influence of site conditions, variation between years, and the phenological stage of shoots at the time of sampling makes it difficult to separate phenotypic and genotypic effects on the water content. In this study the response to moisture loss differed among the species and clones. Most S. viminalis clones, and especially clone 78112, showed a low resistance to moisture loss, but had a higher tolerance as shown in the large amount of biomass produced even with a low moisture content. The resistance to drying was generally higher in the S. dasyclados clones and in the S. daphnoides clone 78 139. The latter clone, with a thick waxy cuticula, differed
252
L. SENNERBY-FOKSSE Tutul. Table 3. Growth start of cuttings in different moisture class, shown as average number of days before visible sprouting (S) and emergence of roots (R), i.e. S,‘R. and standard deviation (SD) in different moisture classes (%), in nine clones of S. GGudis, S. dusyclados and S daphnoides (N = 10 cuttings per clone and class)* 50?‘0
Moisture class 40%
45%
Clone
SIR
SD (SIR)
S/R
SD (S,‘R)
SiR
78112 78183 7802 I 78101 78102 78198 81090 77056 78139
4/S 412 5:4 414 4!4 414 5;s S/6 S/5
I,!1 2’1 1’2 III I:1 0;’I 3.‘l I:2 l/l
3/4 3:3 512 4i4 4i4 414 4i5 5/6 5.‘3
I:‘1 I;‘1 2;‘l I;‘1
3,‘2 4,2 714 4,3 5i2 3!3 8,;5 8,:l 5j3
I ,‘2 l& 3.3 1’2 2:2
*Cuttings without sign of sprouting regarded as dead (0)
and/or
SD (S’R,
rooting
from all other clones through a pronounced ability to avoid drying. The results thus suggest that some willow species may be more adapted to dry conditions than others. Sprouting proved to be more sensitive to moisture loss than rooting in the willows studied. Sprouting and rooting generally occurred close in time, until the moisture content was below 45%. The larger effect on sprouting compared to rooting suggests that water was first lost from bud tissue or tissue connected to bud growth. When roots emerged and water transport started, the buds eventually responded by bursting. The rooting ability in most cuttings was not seriously affected until below 35% moisture. In general, S. oiminalis clones tended to start growth processes more rapidly in all moisture classes and were less influenced by lower moisture content than clones of S. dasyclados and S. daphnoides.
The biomass production was closely related to sprouting/rooting behaviour of the cuttings.
I !o* IL1 4,s II
I I I I 6~2 4,6 2: 1
30%
3i”~<,
S R
SD (S/R)
4:3 73 I?:4 52 h,4 4,J
1’1 ?‘I 7 2 2 I 5:Z 2, I 6.‘6 5;8 6’7
!I 7 II!9 10;7
S:R
.SD t.S RI
lx3
: 1 -iI 1,: t!‘4
I13 0’ 7 13’7 12>6 IO:4 oo* o* I3 o*‘ll
on day 14 after start of hydroculture
‘;+ 41 4x 5 :h 4jx
were
The decrease in biomass production in cuttings with a reduced moisture content was partly a reflection of the increasing amount of time required for sprouting and rooting. Under the present experimental conditions, plants with an early onset of shoot and root growth had a longer growing period than plants with a later onset of growth. The highest production was achieved in plants where sprouting and rooting were close in time. The relationship between roots and shoots in a cutting is not fully understood, but several studies point towards a mutual dependence. A positive relationship between the number of roots and axillary bud growth was reported by Hansen and Kristensen” who suggested this to be a common phenomenon. Studies have shown that the presence of growing buds is necessary for the formation of roots in cuttings of Popufus robusta,“.14 suggesting a stimulatory effect of buds on root development. Healthy axillary buds, as opposed to absent or inferior buds, gave the best results in terms of survival and
Table 4. Early biomass production (gDM) and standard error (SE) of cuttings of nine S. Gmnalis, S. dasycludos and S. duphnoides clones with different moisture content (moisture classes, %). Letters indicate significant differences in biomass production between clones (P z 0.05)
Clone
gDM
SE
78112 78183 78021 78101 78102 78198 81090 77056 78139
0.224 0.139 0.119 0.149 0.136 0.122 0.124 0.125 0.102
0.009 0.014 0.010 0.016 0.012 0.011 0.012 0.008 0.005
Moisture class 40%
45%
50% P
DM
SE
a b b,c b b b,c b,c b,c c
0.245 0.148 0.122 0.127 0.150 0.129 0.151 0.112 0.101
0.013 0.010 0.020 0.008 0.011 0.007 0.011 0.007 0.011
P a b b,c b,c b b,c b c c
35%
30%
DM
SE
P
DM
SE
P
DM
SE
P
0.381 0.123 0.044 0.117 0.129 0.158 0.069 0.058 0.092
0.044 0.015 0.011 0.011 0.011 0.011 0.015 0.013 0.009
a b c b b b c c c
0.225 0.068 0.030 0.054 0.121 0.101 0.042 0.033 0.044
0.022 0.008 0.015 0.030 0.015 0.011 0.011 0.008 0.011
a c c c b b c c c
0.078 0.028 0.007 0.009 0.023 0.041 0.004 0.003 0.003
0.018 0.009 0.004 0.003 0.008 0.014 0.003 0.001 0.002
a b c c h b c ‘ c
Moisture
content
and early growth
growth for cuttings of cottonwoods” and willows (Sennerby-Forsse, unpublished). Cutting size and/or part of the shoot used for the cutting, i.e. ontogenetical differences, might influence drying sensitivity. To avoid size influences, which can be very significant for survival and production,‘6 cutting dimensions were standardized in this study. It is also possible that ontogenetical differences between the apical and basal portions of the shoots had some influence on the results. However, cuttings should theoretically contain a similar mixture of stem parts and different clones should therefore be comparable in this respect. It can be speculated that the hydroculture used in the experiment to evaluate survival of cuttings had a positive effect on growth as the cuttings were able to compensate for the lost moisture to a certain degree. In a field situation, without water soaking before planting, the survival rate would probably have been lower even after moderate drying stress. As shown by Swingle,7 the rooting ability of willow cuttings improved considerably with increased soaking time and Peterson and Phipps17 confirmed a positive effect of water soaking on survival rate in poplar cuttings. We therefore advise that water soaking of woody cuttings before planting should be a recommended procedure in the establishment of biomass plantations.
5.
CONCLUSIONS
The results showed that the ability to withstand decreasing moisture content varied significantly between species and clones. Two different types of response were demonstrated in that clones of S. dasyclados and S. daphnoides resisted drying better, while S. viminalis clones generally showed a higher tolerance to moisture loss. Clones of the latter species generally had superior survival rates, were faster in sprouting and rooting and showed higher biomass production in the lower moisture classes. The differences seemed to be mainly species specific. However, the least tolerant as well as the most tolerant clone were found within S. viminalis. The result thus suggests both inter- and intraspecific differences in drought response, indicating a potential for selecting suitable genotypes for coppice plantations on sites with different moisture conditions. Acknowledgements-This study help of funds from the National
was carried out with the Board ot tnergy, Sweden
in stem cuttings
253
The authors would like to thank Dr W. A. Kenney and Prof. L. Zsuffa, University of Toronto, Faculty of Forestry for constructive criticism of the manuscript.
REFERENCES 1. G. Siren, L. Sennerby-Forsse and S. Ledin, Energy plantations-short rotation forestry in Sweden. In Biomass (D. 0. Hall and R. P. Overend. Eds), pp. 119-143. John Wiley & Sons Ltd. England (1987). 2. L. Sennerby-Forsse Handbook for Energy (Ed.), Forestry. Swedish Univ. Agric. Sci., Dept. of Ecol. and Environ. Res., Uppsala, Sweden (1986). 3. I. Fjell, Preformation of root primordia in shoots and root morphogenesis in Salix oiminalis. Nerd. J. Bof. 5, 357-376 (I 985). 4. S. Shapiro, The role of light in the growth of root primordia in the stem of the Lombardy poplar. In The Ed.), Physiology of Forest Trees (K. V. Thimann, pp. 445465. Ronald Press (1958). 5. E. Vieitez and J. Pena, Seasonal rhythm of rooting of Salix atrocinerea cuttings. Phys. Plant. 21, 544-555 (1968). of cottonwood by 6. L. Zsuffa, Vegetative propagation rooting cuttings. In Proceedings from “Symposium on Eastern Cottonwood and Related Species” (B. A. Thielges and S. B. Land, Eds), Greeniille, Mississippi, Sept 28%Oct 2, 1976. Louisiana State University, Division of Continuing Education, Baton Rouge, LA 70803 (1976). study of rooting and I. F. Swingle, A physiological callusing in apple and willow. J. Agr. Res. 39, 81.- 128 (1929). Overwinter storage 8. W. H. Cram and H. Lindquist, of Walker poplar cuttings. For. Chron. 58, 175- 177 (1982). 9. H. M. Phipps, E. A. Hansen and A. S. Fege, Preplant soaking of dormant Populus hardwood cuttings. US Forestry Service Research paper NC-241. US For. Ser. Res. Rep (1983). Clonal variation of wood specific 10. L. Sennerby-Forsse, gravity, moisture content and stem bark percentage in l-year-old shoots of 20 fast-growing Salix clones. Can. J.-For. Res. 15, 531-534 (1985). and P. Layton, II. W. A. Kennev. L. Sennerbv-Forsse A review of -biomass quality research relevant to the use of poplar and willows. Bornas. 17, 21. 37 (1990). Axillary bud growth in 12. J. Hansen and K. Kristensen, relation to adventitious root formation in cuttings. Physiol. Plant 79, 39-44 (1990). 13. P. F. Wareing and N. G. Smith, Physiological studies on the rooting of cuttings. Rep. For. Res. 47, 118-121 (1963). of 14. N. G. Smith and P. F. Wareing. The distribution latent root primordia in stems of Populus robusta and factors affecting the emergence of preformed roots from cuttings. Foresrr?; 18, 197-266 (1972). 15. M. A. Radwan, J. M. Kraft and D. S. DeBelI. Bud characteristics of unrooted stem cuttings affect establishment success of cottonwood. Research Nore PNWRN-461. Forest Service, Pacific Northwest Research Station (1987). and L. Roy, The 16 D. Burgess, 0. Q. Hendrickson importance of initial cutting size for improving the growth performance of Sa1i.xalba. L. Stand. J. For. Res. 5, 2 15- 224 (I 990). 17 L. A. Peterson and H. M. Phipps. Water soaking pretreatment improves rooting and early survival of hardwood cuttings of some Populus clones. Tree Planters Notes 27(I). 12-22 (1976).