Researches on Populus in Korea for Various Purposes

Jour. Korean For. Soc. Vol. 98, No. 5, pp. 513~523 (2009)

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Researches on Populus in Korea for Various Purposes Chul-Woo Kim

, Du-Song Cha

, Yong-Eui Choi

, Yeong-Bon Koo

,

Wan-Yong Choi

, Jae-Heon Oh

and Jae-Seon Yi

1

Department of Forestry, Graduate School, Kangwon National University, Chuncheon, Korea 200-701

2

College of Forest & Environmental Sciences, Kangwon National University, Chuncheon, Korea 200-701

3

Korea Forest Research Institute, Seoul, Korea 130-712

Abstract :

Many species, cultivars, and hybrids in Populus have been introduced and developed by the scientists of Department of Forest Genetic Resources, Korea Forest Research Institute in Korea. P. alba

glandulosa , P. euramericana , P. nigra

maximowiczii , P. koreana

P. nigra var . italica , and P. davidiana have been studied from many aspects, i.e., genetics, breeding, physiology, propagation, silviculture, biomass production, biotechnology and phytoremediation. These precedent results will provide a sound basis for a newly-arising research on short-rotation coppice as one of renewable resources and phytoremediation plants. It was found that there were many promising varieties and clones for these purposes. However, minute analysis on specific gravity and caloric values for those plants should be followed under several silvicultural and rotational systems.

Key words :

biomass, short rotation coppice (SRC), bioenergy, phytoremediaiton, Populus

Introduction

The Korean Government released the various policies on the new and renewable energy source including forest biomass. Among the policies, “National Basic Plan for the Development of Resource and Technology for Energy 2006-2015” is finally presented to the public May 18, 2006 (http://www.nstc.go.kr). It focuses on the develop- ment of 5 core technologies, that is, energy proficiency, reduction of green-house gas, new/renewable energy, electric power, and resources survey/management. Five percent of the whole energy, according to the Plan, will be supplied by the new/renewable energy in 2011. To increase its ratio from 2.2% in 2005 to 5% in 2011, US$

1.58 trillion (about 20.44% of the whole investment for five core technologies) is necessary.

More than 80% of the Gangwon province, where Kangwon Nat'l University is located, is covered by for- est and its Provincial Government will supply 10% of the energy consumption from the new/renewable source in 2015.

Some research projects, based on national and regional energy plan mentioned above, were started this year to supply energy using forest biomass. Such projects include estimation of forest biomass, technique development of

chip or pellet production, new boiler or stove develop- ment, short-rotation coppice (SRC) establishment, and so on. In SRC, poplars and willows were considered at first (FAO, 2005). Few researches are found on willows in Korea except several taxonomic reports. Many research works were carried out on poplars, while there were a small number of findings aiming at the biomass produc- tion for energy.

SRC consists of densely planted, high-yielding variet- ies of either willow or poplar, harvested on a 2-5 years cycle, although commonly every 3 years (DEFRA, 2002).

A plantation could be viable for up to 30 years before re-planting becomes necessary, although this depends on the productivity of the stools. Even the people in forest science and forestry are not familiar with SRC, the term itself, in Korea. They regard it simply as fuel forest.

However, it is more than that. Poplar is one of the important species as material for biotechnology (Choi and Park, 1993; Marchadier and Sigaud, 2005) and phy- toremediation (Licht and Isebrands, 2005; Yeo et al ., 2001).

Some research works dealing with poplars since 1960s in Korea were reviewed to start a new SRC project for biomass energy. They will include biomass, genetics and breeding, propagation, silviculture, biotechnology, phy- toremediation, and fuel-related study. This review aims at providing a wide range of information to those who like to start a new project especially on bioenergy using

*Corresponding author

E-mail: [email protected]

poplars in Korea.

Background

Poplar studies in Korea can not be explained without mentioning introduction and hybridization (Noh et al ., 1984). Italian hybrid poplars, I-476 (male) and I-214 (female), were encouraged to be planted on alluvial deposits along the rivers and low lands from 1962 by the Government. They were selected from a total of 330 varieties of poplars by the scientists led by the late Dr.

Hyun of Korea Forest Genetics Research Institute (now, it is Department of Forest Resources Devlopment, Korea Forest Research Institute). The Italian poplars were so popular that the total of planting area reached 740,000 ha by 1995. However, since then its new plantation was restrained by law because the poplars planted on the river banks and basins could prevent the flow of exces- sive water during rainy season. P. alba

glandulosa was planted from 1973 on the lower parts of middle slope where hybrids clones did perform better than introduced poplars. Up to 1986, these three hybrids were supplied by the Government and some private propagators. From 1987 P. nigra

P. maximowiczii was started to be sup- plied; and from 1989 P. koreana

P. nigra var. italica . There are 5 native species (Koo et al ., 1992) in Korea.

In Leuce section there are P. davidana and P. glandu- losa ; and in Tacamahaca section there are P. maximow-

iczii , P. koreana , and P. simonii . P. galndulosa was thought to be native to Korea. However, a recent study revealed that P. glandulosa might be originated by the saltational speciation caused by the hybridization between P. alba and P. davidiana in nature (Hong et al ., 1998).

More than 350 species and cultivars were introduced.

The most heavily studied ones are P. alba , P. nigra , P.

nigra var. italica , and P. deltoides . P. alba is supposed to be introduced as female from the late 1800's to the early 1900's from southern part of France by the missionary.

Among hybrids studied heavily are P. alba

P. glandu- losa , P. euramericana , P. nigra

P. maximowiczii (Fig- ure 1), and P. koreana

P. nigra var. italica .

From the first energy crisis in 1973, it was noticed that poplars are important for the bioenergy resource together with timber.

Biomass and Growth

In P. alba

glandulosa standing crop, the terrestrial parts of 6-year-old plantation (693 trees/ha) was 18.11 ton/ha and that of 9-year-old one (527 or 625 trees/ha) was 47.3 and 38.8 ton/ha, respectively. The stem wood volume of 6-year-old plantation was 31.3 m

/ha and that of 9-year-old was 83.9 and 68.8 m

/ha, respectively (Kim et al ., 1977). Compared with one of important oak species in Korea, this hybrid showed higher biomass (Choi and Park, 1993). Aboveground total biomass of Quercus variabilis forest (20-year-old) was 31,275 kg/

ha, and that of P. alba

glandulosa plantation (17-year- old) was 55,581 kg/ha in southern part of Korea.

The average width of annual ring growth was reported on 9 species and varieties, when they were 15 to 20 years (Noh et al ., 1984). ‘I-214’, ‘I-476’, P. deltoides , P.

nigra var. italica and P. alba showed growth over 10 mm, but P. maximowiczii , P. koreana , and P. davidiana growth of 4.0 to 4.4 mm. Several physical properties were investigated for 9 species. They were moisture con- tent, specific gravity, bulk density, and shrinkage ratio.

Three highly informative reports were found on poplar biomass research.

Biomass production of a plantation at 1-year, 2-year, and 3-year rotation on both low (2,500 trees/ha) and upper hills (2,000 trees/ha) was studied for 12 species: Lespedeza cyr- tobotrya , Amorpha fruticosa , Robinia pseudoacacia , Acer saccharinum , Platanus orientalis , P. alba

glan- dulosa F

, Salix alba , Pinus rigida , Alnus hirsuta var.

sibirica , Alnus inokumai , Alnus glutinosa , and Alnus incana (Hyun et al ., 1982). In one-year rotation, Lespe- deza cyrtobotrya produced the largest amount of biom- ass (2.6 t/ha/yr, fresh weight) and P. alba x glandulosa F

the second largest (2.2 t/ha/yr) on low hill. In two- year rotation, the latter produced the largest amount (4.8

Figure 1. Hybrid poplar stand (

P. nigra

maximowiczii

Researches on Populus in Korea for Various Purposes 515

t/ha/yr) and Alnus hirsuta var. sibirica the second largest (2.8 t/ha/yr) on low hill. In three-year rotation, the larg- est weight (11.2 t/ha/yr) was produced by Robinia pseudoacacia and the second largest (6.2 t/ha/yr) by Alnus hirsuta var. sibirica on low hill. Amorpha fruti- cosa , Acer saccharinum , Platanus orientalis , and Salix alba were not suitable for biomass or fuelwood produc- tion due to poor growth. Biomass yield on upper hill was reduced considerably for all twelve species. For maximum biomass production, a three-year rotation with coppice is preferred to one-year and two-year rotation.

The recommendable regime appeared to be a three-year rotation with Robinia pseudoacacia and Alnus hirsuta var. sibirica on low hill.

Two test plantations were established in spring, 1980 with the density of 20,000 and 40,000 trees/ha in the nursery (Lee et al ., 1982). There were two harvesting regimes, that is, annual harvest and biennial harvest (Figure 2). The results were based on one harvest under both systems. In P. alba

glandulosa plantation, when established with the density of 20,000 and 40,000 trees/

ha, annual rotation could produce 8.84 and 12.65 ton/ha/

yr in stem-branch dry weight; biennial rotation 10.33 and 18.8 ton/ha/yr, respectively. In P. nigra

maximow- iczii plantation, when established with the density of 20,000 and 40,000 trees/ha, annual rotation could pro- duce 8.87 and 10.87 ton/ha/yr in stem-branch dry weight;

biennial rotation 11.26 and 18.01 ton/ha/yr, respectively.

For both species, biennial harvest was recommendable at both densities. However, it was not easy which species is better for short-rotation system. In height and basal diameter growth there were no significant differences among clones and planting density for both species; but, there were significant differences in biomass among clones and planting density.

Fourteen clones of 3 hybrid poplars ( P. alba

glan-

dulosa , P. koreana

P. nigra var. italica , and P. nigra

maximowiczii ) were established with the density of 10,000 trees/ha and raised for up to 6 years to select superior clones for biomass production under three rota- tion systems (Kim et al ., 1977). Biomass production var- ied with clones as well as rotation years. All 5 clones of P. alba

glandulosa produced more biomass than the others in annual rotation plot, while one clone showed high consistent biomass under 3 rotation regimes, that is 7.59 to 10.45 MT/ha/yr. Stems were the main source of biomass comprising 54 to 63%; branches 15 to 20%;

and the leaves 23 to 31%. Whereas the average stem- branch dry weights of all the clones at annual, biannual, and 3-year rotation were 9.60, 6.53 and 9.06 MT/ha/yr.

In annual rotation regime, the biomass increased with years. The difference by harvesting plot and year seemed that expansion of trees was highly correlated with age.

For P. alba

glandulosa 72-16 clone produced average 11.5 MT/ha/yr, but 4.20 for the first year, 10.37 for the 2nd year, 12.37 for the 3rd year, and 16.88 for the 4th year. There also seemed to be interaction between clone and rotation period.

Genetics and Breeding

Hybridization of poplars commenced since 1953. P.

alba

glandulosa appeared as the best combination out of crosses among 30 varieties. It showed significant hybrid vigor on acid and poor slopes and surpassed I- 476 in height and diameter at breast height when they were 4 or 5 years old. Also its rootability of stem cut- tings was intermediate between both parental species (Hyun et al ., 1967). However, specific gravity was influ- enced by the pollen tree (Son and Chung, 1972).

P. alba

glandulosa clone No. 3, showing better growth than clone No. 1, was selected from No. 1 clones. From No. 2 clones, No. 4 clones were selected. Clone 3 is a single clone, while No. 4 clones consist of 4 different clones by stability analysis. A hybrid between P. kore- ana and P. nigra var. italica showed much wider range of adaptation than the hybrid, P. nigra

maximowiczii . And this was released to the forest owners in 1984.

Compared with I-476 and I-214, P. euramericana ‘Eco 28’ and P. deltoides ‘Lux’ were selected for Marssonina brunnea and Melampsora larici-populina disease resis- tance and growth (Noh et al ., 1984).

In P. alba

glandulosa F

, combined heritabilities for two clones in a broad sense were observed 68.5% for stem straightness, 62.1% for number of root primordia, 58.0% for total number of clusters, 55.4% for bark color, 52.3% for total number of branches, and 40.5% for num- ber of adventitious branches (Noh et al ., 1985). Genetic gains, depending on the selection intensity, were pre- Figure 2.

plantation for biomass

test.

dicted as 15.9 to 14.8% for stem straightness; 8.3 to 12.4% for total number of clusters; 12.6 to 16.7% for total number of branches.

Growth yield of P. alba

glandulosa clones could be estimated from either leaf area per tree or leaf chloro- phyll content per tree and both of them were suggested as criteria to select superior clones in early growth (Kim and Lee, 1983).

A total of 175 superior aspen, P. davidana , were selected to develop a new variety for high mountain regions (Noh et al ., 1989). The plus trees were, in height, diameter at breast height and growth rate, superior to some conifers, but inferior to other poplars such as euramerican clones and P. alba

glandulosa . Genetic gain would be at least 16.9% in annual diameter increment, 20.9% in annual height growth, and 42.3% in annual volume growth, when the best clones are re-selected from the first selec- tions. The broad sense heritability of height in P.

davidana was estimated from 4-year-old clones as H

= 0.883 (Noh, 1982). If we select the best one clone, the genetic gain of 35.3%, equal to 1.02 m, is expected; and if we select the best two clones, the genetic gain is 25.6%, equal to 0.74 m.

Five species and 11 clones of P. alba

glandulosa were investigated for genetic relationships on RAPD marker analysis (Hong et al ., 1998). The close genetic relationship between P. glandulosa and P. davidiana was ascertained by the principal component analysis. It was deduced that P. glandulosa might be originated by the saltational speciation caused by the hybridization between P.

alba and P. davidiana in nature.

There were 50 species of insects harmful to the pop- lars (Noh et al ., 1984). However, their control methods were provided. Among more than 5 kinds of disease, two severe diseases are Marssonina brunnea and Melampsora larici-populina disease, but their control method was developed. Two varieties were selected against them.

Propagation

While the rooting ability of clones of P. alba

glan- dulosa hybrid varied much, most of the cuttings showed the highest rooting ratio at the rooting bed of 20°C (Kim et al ., 1978). Rooting ratio of each clone in nursery showed the same order at a rooting bed and in air lay- ering. There were no significant difference in rooting ratio between autumn and spring cuttings of P. alba v glandulosa and P. nigra var. italica

P. maximowiczii (Noh et al ., 1980). 40 cm-long cuttings were desirable for autumn and 30-cm-long ones for spring in the former hybrid. In the latter hybrid, 50 cm was adequate for autumn and 40 cm for spring.

Usually 1/1 cuttings were used for plantation and 1/2 cuttings were raised per m

with 37.5 cm

25.0 cm in the nursery (Noh et al ., 1984). For P. alba

glandulosa the recommended spacing is 25.0 cm

25.0 cm to produce 16 cuttings per m

. In dry months cuttings are placed into soil in spacing of 20 cm between trees and 60 cm between rows. By this way, survival and growth of cuttings could be improved in nursery with less soil moisture content.

There were two fertilizations with the mixture of 20 kg of urea, 30 kg of phosphate and 10-20 kg of potassium chlo- ride per 1,000 m

in mid-June and mid-July.

The growth of P. koreana

P. nigra var. italica cut- tings was greatly affected by cutting diameter (Koo et al ., 1986). Cuttings ranging from 6~10 mm in basal diameter developed rooted cuttings with the basal diam- eter of 16.4 mm; and cuttings 11~15 mm the basal diam- eter 19.3 mm. Cuttings ranging from 6~10 mm in basal diameter developed rooted cuttings with the height growth of 274 cm; and cuttings 11~15 mm the height growth 320 cm. There was no significant difference in rooting ratio (all above 90%) between two kinds of basal diameter of cuttings. However, the larger was the basal diameter of cuttings, the straighter was the rooted cut- ting. There was no difference in height and basal diam- eter growth between main stem and lateral stem cuttings.

For hydroponic rooting of greenwood cuttings, the nutrient solution and growth regulators were not always necessary for clones of P. alba

glandulosa and P. nigra

maximowiczii (Noh et al ., 1983). The most important factor was temperature and the optimum one was 20- 25°C. In plain underground water the former showed up to 85% rooting ratio; and the latter 100%. In the former clones, the upper part of one shoot showed higher root- ing ratio (95 to 100%) than the lower part (60%). The latter one showed the same pattern. This rooting trend in greenwood cutting was opposite to the trend in hard- wood cutting, which showed more rooting ratio in the lower part of the branches. As this softwood cutting can be repeated about 7 times from May to September every 20 days, propagation can be speeded up in comparison with hardwood cutting.

Two production systems of rooted cuttings were stud- ied. Monoclonal and multi-clonal nursery plots were established with eight clones of P. nigra

maximowiczii and a clone of P. koreana

P. nigra var. italica and their growth was investigated in autumn (Lee et al ., 1986).

Multi-clonal plots showed better growth both in basal

diameter and height than monoclonal plots. Diameter

ranged from 17.9 to 22.0 mm; and height ranged from

274 to 338 cm. Height is more influenced by multi-

clonal system than basal diameter. It is beneficial to raise

multi-clonal nursery because it is more resistant to dis-

ease and insects. As growth of both traits seems to be

Researches on Populus in Korea for Various Purposes 517

stimulated by multi-clonal system, it was not possible to select the competent clones for nursery.

The leaf-flushing started within one to three weeks when the stem cuttings were planted in the end of March (Koo et al ., 1991). Leaf-flushing started first in Taca- mahaca section, and followed by hybrid, Leuce and Aigeros in order. For rooted cutting production, a single clone cultivation from a single section would show bet- ter growth than a clone mixture originated from the dif- ferent sections in nursery. Almost all the clones except aspen clones accomplished more than 90% of their height and diameter growth at the end of August.

Silviculture

P. alba

glandulosa showed higher volume growth (2.5 times) than P. euramericana ‘I-476’ in clay soil of hillside, while P. euramericana ‘I-476’ and P. koreana

nigra showed good volume growth in sandy loam at the age of 10 (Son and Chung, 1972). P. koreana x nigra showing higher specific gravity is recommended for Gangwon Province. For P. nigra

maximowiczii , the evaluation of growth performance of the hybrid poplar seems to be made at least 7 years after planting (Son, 1974). The hybrids seemed to have high adaptability to the poor soil condition and high rooting capacity com- pared to P. euramericana .

A regression equation was suggested to evaluate the site for P. alba

glandulosa plantation except the site including pan within 60 cm in depth, because the hybrid does not grow well on poorly drained soil (Noh, 1982).

The clones were evaluated for stability to select the ade- quate plantation sites (Noh and Lee, 1983). There were 3 groups; i.e., good performance for all sites, maximum potential in good sites, and good performance on poor sites. This analysis method can be applied to select opti- mum clone for the place to be established. Some clones should be released upon the request for the special envi- ronment.

In a trial using 8- and 6-year-old plantation, P. nigra

maximowiczii hybrids outgrow P. euramericana ‘I-476’

on both flat and up lands with low pH value (Noh et al ., 1984). The hybrid shows average annual height growth of 1.4 m and average annual increment of 1.4 cm for diameter at breast height. The volume growth of 5-year- old hybrid showed strong relationship with available phosphorous (P

O

) content in soil. It showed a strong coppice ability which may be useful for short rotation cultivation.

For timber production of poplars when planted 5 m

5 m, but P. alba x glandulosa when planted 3.5 m

3.5 m, they were fertilized at the planting time with a mix- ture of 20 g of urea, 20 g of superphosphate and 5 g of

KCl per tree (Noh et al ., 1984). 300 g of this mixture ratio was fertilized every year during the first 3 years. 6 to 7 years after planting, the first thinning removed about half of the trees for pulp and the remained ones for saw or veneer logs.

Biotechnology

1. Multiplication

Adventitious shoots, originated in vitro from buds of P. alba

glandulosa , rooted in vitro easily on GD, MS and WPM media (Kim et al ., 1982). These plants, after transferred to pots, needed 4- to 6-week hardening in green house for out-planting. To secure the sterile explants from 8 to 15 year old mature trees of P. alba x glandulosa and P. euramericana , buds of main, current- year shoots were more adequate than those of lateral shoots (Kim et al ., 1982). However, buds of one-year- old root sprouts were more preferred to branch buds.

The production of multiple shoots varied with clones on MS medium with 0.2 mg/L BAP. Three to nine shoots per bud were established in P. alba

glandulosa and 10 to 18 shoots in P. euramericana ‘I 476’. Differentiating buds were subcultured every 30 days and could be mul- tiplied 10 to 20 times a month. Rooting was most suc- cessful on GD media with 0.2 mg/L IBA.

Clonal variation was observed in callus induction fre- quency, color, relatively growth and texture in P. alba

glandulosa (Moon et al ., 1987). Root and shoot initia- tion varied much with clones from 7.7 to 50.0% and 0 to 63.6%, respectively. However, no difference was observed in rooting of shoots established in vitro. No chromo- somal aberration (2n = 38) was observed in plantlet cells originated from callus of internodal tissue of P. alba

glandulosa (Kim et al ., 1986).

Stems including one or two axillary buds were cul- tured in vitro on 12 different media to overcome diffi- culties in poor sexual and asexual reproduction of P.

davidana (Cheong and Yi, 1997). More than 9 propagules were obtained per explant cultured in 0.2 mg/L BAP for a period of 5 weeks.

Effect of thidiazuron on shoot proliferation of P. kore- ana

trichocarpa , which always shows open stomata, was observed in half-strength MS media with the con- centrations of 0.01 and 0.02 mg/L (Kong et al ., 2004).

The highest shooting rates were achieved to 83.3% and 47.6% by axillary bud and leaf cultures, respectively.

Dormant buds and callus of P. koreana

P. nigra var.

italica could survive freezing in liquid nitrogen for 60

days, after being treated with DMSO or glycerin, and

grow in vitro and also in pot cutting (Chung et al .,

1989). Cryopreseration of Populus germplasm may be

possible for in vitro propagation and future tree improve-

ment.

2. Genetic transformation

The petiole and leaf segments of P. davidiana were transformed successfully by Agrobacterium rhizogenes for hairy root production (Lee et al ., 1989). When hairy roots with their growth enhanced on a-quarter-strength MS media were culture on MS media with 0.5 to 1.0 mg/L zeatin, a few of them established shoots effec- tively, which rooted easily in vitro showing heavy root development.

In the transformation study of P. koreana

P. nigra , the gene is transcriptionally active only in young tissue even though it is attached to a constituitive promotor (Noh et al ., 2004). Therefore, the expression of foreign gene in poplar plants seemed to be affected by the met- abolic state of the cells and thus vary greatly with the developmental stages and the age of tissue.

Phytoremediation

To develop a clone resistant to aluminum from the cal- lus of P. koreana

P. nigra var. italica , the selection test for callus was recommended using MS media with 1,200 ppm AlCl

.6H

O at pH 4.5 (Choi et al ., 1987). In in vitro culture system, P. davidiana was most resistant to aluminium than P. maximowiczii , P. nigra , P. alba

glandulosa , and P. nigra

P. maximowiczii and showed stimulated shoot and root growth at the low levels of Al like 0.1 to 0.2 mM concentration. P. nigra

P. maxi- mowiczii exhibited significantly higher aluminium toler- ance than its parents (Chung and Chun, 1990).

In vitro salt tolerance test was tried to buds of P. alba

×

glandulosa , P. nigra

maximowiczii , and P. koreana

P. nigra var. italica by bridge culture on the various media containing 10, 20, 30, 50% of artificial saltwater (ASW) (Lee et al ., 1986). All explants stopped growing on 50% of ASW. At least 5-week culture period was necessary to reach the conclusion. It was recommended to select the resistant clone(s) showing good growth by the comparison of growth rate according to each treat- ment from the beginning than the comparison of relative tolerance index. Although two clones were recommend- able by in vitro test, another actual field practice test is necessary.

The 2-month-old rooted cuttings of P. alba

glandu- losa , P. nigra

maximowiczii , P. euramericana , P. del- toides , P. koreana

P. nigra var. italica were cultivated at different salt concentrations (0.0, 0.1, 0.5 and 1.0%

NaCl) for 60 days (Yeo et al ., 1999). The survival rate of 5 poplar tree species reached 70% at 0.1% NaCl treat- ment, but most of all the poplars died with serious vis- ible injury at 0.5 and 1.0% NaCl treatments during the

period of the treatment. Consequently, poplars seemed to survive at the lower concentrations of 0.1% of NaCl. As P. deltoides showed the increased height growth and dry mass at 0.1% NaCl, it may be more resistant to salt than other species.

In a study on sensitivity of five clones of P. alba

glandulosa cuttings to ozone exposure, it was found that fast-growing cultivar was more sensitive to ozone than slow-growing cultivar (Kim et al ., 2000). Thus sensitiv- ity of trees to ozone exposure is closely related to their growth rate.

Rooted cuttings of P. alba

glandulosa and seedlings of Betula schmidtii were planted in pots and irrigated with Pb-containing water for 60 days and observed showing growth inhibition at the concentration of 800 mg/L and above (Yeo et al ., 2001). Most Pb was accu- mulated in plant roots and only a small portion was transported to the shoots. In general, Betula schmiditii showed more tolerance, but the highest tolerance to Pb was observed in one clone of P. alba

glandulosa , which showed the applicability for phytoesxtraction together with biomass production and easy large-scale cultivation.

P. alba

glandulosa was the most effective species among the four poplar species, i.e. P. koreana

nigra var. italica , P. nigra

maximowiczii , and P. eurameri- cana , in Cd absorption from contaminated soil (Han et al ., 2001). But P. euramericana instead effectively absorbed Pb. Mycorrhizal inoculation by Pisolithus tinctorius increased the Cd accumulation in the tissues by four times in P. alba

glandulosa and also increased Pb accumulation by two times in P. koreana

nigra var.

italica , with leaves being the major sites of metal accu- mulation.

Landfill leachate solution, whether mixed with water or not, was applied for 3 months to the one-year rooted cuttings of P. euramericana and Betula platyphylla var.

japonica (Woo et al ., 2001). Seedlings were stimulated for height, diameter at root collar and biomass produc- tion. Poplars, P. alba

glandulosa , grown in waste land- fills showed lower photosynthetic enzymes and reduced photosynthetic rates (Kim et al ., 2002). Adaptability of P. alba

glandulosa to the water relations in waste land- fills was proved (Kim et al ., 2002). Poplar trees grown in waste landfills maintained smaller leaf area, denser leaf hairs, and higher specific leaf dry mass. They also showed the lower stomatal conductance and stomata clo- sure at lower CO

concentration, which implies that trees in the landfills had more sensitive stomatal response.

Increased leaf boundary layer and stomatal resistance of landfill poplars allowed more efficient water use and higher water retentivity.

The two-month-old rooted-cuttings of P. alba

glan-

R e s e a r c h e s o n P o p u l u s i n K o r e a f o r V a r i o u s P u r p o s e s 5 1 9

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Choi and Pa rk 199 3 biom ass, net product ion, natur al Quer cus variabili s for est , Pop ulus alba

P. gl andulosa plantation Journal of Kor ean For est S ociety 82 (2) : 18 8-194 Hyun et al. 198 2 wood biom ass pr oduction, tw elve coppi ce plant ati ons, 1, 2 or 3- year rotat ions Journal of Kor ean For est So ciety 55 : 30- 36 Kim et a l . 197 7 productive s tru ctur e, pro ductivity , Populus alb a

gla ndulosa pl an tation Journal of Kor ean For est S ociety 35:9- 14 Ki m et al. 200 2 photosy nthet ic r esp on ses, Populus alb a

P. gl andulosa , adaptati on, waste l andfil ls Journal of Kor ean For est S ociety 91(1) :79- 87 Lee et al . 198 2 biom ass gr owth, pr oduction, Popul us hy brids Re search Report, Institu te of Fo rest Ge ne tics , Korea 18:9- 16. Noh et al . 1984 poplar s, breeding, cultivati on, exploi tation, ut ilizatio n Re search Report, Institu te of Fo rest Ge ne tics , Korea 20:16- 45 Ge ne tics and Breeding

Hon g et al . 199 8 genetic rel ati onships, s ecti on Le uc e (G en us Popu lus ), RAPD ma rker Journal of Kor ean For est S ociety 87(2) :153- 163 Hyun et al. 196 7 gro wth pe rfor ma nce, P. al ba

glandulosa Re search Report, Institu te of Fo rest Ge ne tics , Korea 5:53- 60 Kim an d L ee 198 3 selection, Populus alba

glandulosa F

clones , phy siological character s Journal of Kor ean For est So ciety 59:15- 30 Noh 198 2 site e va luation, Populus alba

Populu s glandul os a F

clones, path analy sis Re search Report, Institu te of Fo rest Ge ne tics , Korea 18:1 13-1 56 Noh et al . 198 4 poplar , br eeding, cul tivation, exploitat ion, uti lization Re search Report, Institu te of Fo rest Ge ne tics , Korea 20:16- 45 Noh et al . 198 5 repeat ab ility , genetic gain, char acters, Populus alb a x glandul os a F

clo nes Re search Report, Institu te of Fo rest Ge ne tics , Korea 21:27- 36 No h et al. 198 9 grow th pa tte rn, va riat ion, ec on om ic ch arac ter ist ics, Ko rea n as pe n ( Popu lus dav idiana Dod e) Re search Report, Institu te of Fo rest Ge ne tics , Korea 25:1 1-29 Son and Chung 197 2 gro wth p erf orm ance, specifi c gr avity , hy bri d popl ar Re search Report, Institu te of Fo rest Ge ne tics , Korea 9:9-1 6 Pr op ag ati on

Kim et a l. 197 8 roo ting ability , clone, Populus alba

glandulosa hy brid Journal of Kor ean For est S ociety 38:19-2 6 Ko o et al . 198 6 type and diam eter of cutt ing, gr owth, topo phy sis , rooted cuttin g, Suwon poplar ( P. kor eana

P. n igr a var . italica ) Re search Report, Institu te of Fo rest Ge ne tics , Korea 22:15- 20 Ko o et al . 199 1 gro wth pe rfor ma nce, rooted cutting, poplar clones, nur ser y Re search Report, Institu te of Fo rest Ge ne tics , Korea 27:24- 29 Lee et al. 198 6 inter genoty pic com petit ion, P. ni gr a

maximowicz ii F

clones, nursery gr owth Re search Report, Institu te of Fo rest Ge ne tics , Korea 22:26- 29 No h et al. 198 0 growth, surviv al, cuttin g seas on, cutting lengt h, Popu lus alba

glandu los a F

, Populus ni gr a var . it alica

maximowicz ii F

Re search Report, Institu te of Fo rest Ge ne tics , Korea 16:68- 77 No h et al. 198 3 hy droponic root ing, gr ee nw ood cut ting, popl ar clones Re search Report, Institu te of Fo rest Ge ne tics , Korea 19:36- 45 No h et al. 1984 poplar , br eeding, cul tivation, exploitat ion, uti lization Re search Report, Institu te of Fo rest Ge ne tics , Korea 20:16- 45 Sil vicultur e

Noh 198 2 site ev aluation, Populus alba

Populu s glandul os a F

clones, path analy sis Re search Report, Institu te of Fo rest Ge ne tics , Korea 18:1 13-1 56 Noh and Lee 198 3 reselection , Popul us alba

glandul os a F

clo nes , stabil ity analy sis Re search Report, Institu te of Fo rest Ge ne tics , Korea 19:28- 35 No h et al. 198 4 poplar , br eeding, cul tivation, exploitat ion, uti lization Re search Report, Institu te of Fo rest Ge ne tics , Korea 20:16- 45 No h et al. 198 4 gro wth, adequate s ite, Po pulus nig ra

P. maximowicz ii F

cones Re search Report, Institu te of Fo rest Ge ne tics , Korea 20:46- 51 Son 197 4 gro wth pe rfor ma nce, Populus ni gr a

maximowiczii F

Re search Report, Institu te of Fo rest Ge ne tics , Korea 1 1:61-67 Son and Chung 197 2 gro wth p erf orm ance, specifi c gr avity , hy bri d popl ar Re search Report, Institu te of Fo rest Ge ne tics , Korea 9:9-1 6 M oon et al. 198 7 clonal vari ation, call us cultur e, Po pulus alb a

P. gl andulosa Re search Report, Institu te of Fo rest Ge ne tics , Korea 23:149- 155

Table 1. Continued.

Re search T opic Autho r(s) Yea r Key words Jour nal Bi otechnology

Cheong and Y i 1997 in vitr o, plant m ult iplicatio n, axillar y bud, Po pulus david ana Dode Journal of Kor ean F orest Society 86 :128-1 34 Ch ung et al. 1989 freezing preservati on, dor ma nt bu d, callus, Populus kor eana

P. nigra var . italica Res ear ch Repor t, In sti tute of Forest Genetics, Korea 25:142- 148 Kang et al. 2004 TDZ (T hidiazuron ), shoot pro lifer ation, pea ce poplar Kor ean Journ al of Pl ant Bi otechnology 31(1 ):45- 53 Kim et a l. 1982 ma ss propagat ion, bud cultur e, Populus al ba

Populus glandulosa F

Res ear ch Repor t, In sti tute of Forest Genetics, Korea 17:57- 63 Kim et a l. 1982 ma ss produ ction, popl ar clone, bud cultur e Res ear ch Repor t, In sti tute of Forest Genetics, Korea 18:80- 85. Kim et a l. 1986 plantl et regeneratio n, callus, inter nodal tiss ue , Popul us alba

P. glandu los a Res ear ch Repor t, In sti tute of Forest Genetics, Korea 22:122- 127 Lee et a l. 1989 tra ns form ati on, Populus david iana , Ag robact er ium r hiz ogenes Res ear ch Repor t, In sti tute of Forest Genetics, Korea 25:149- 153 Moon et a l. 1987 clonal vari ation, callu s cultur e, Pop ulus alba

P. gla ndulosa Res ear ch Repor t, In sti tute of Forest Genetics, Korea 23:149- 155 Noh et al. 2004 dif ferent ial exp ress ion , chim eric nos-n pt II gene, Populus kor eana

P. nigra Kor ean Journ al of Pl ant Bi otechnology 6(1) :15- 19 Phy tor em e- diati on

Choi et al. 1987 alu mi niu m, gr ow th, Po pu lus kor ean a

P. ni gra va r. ital ica , c ell an d c all us cu ltu re Res ear ch Repor t, In sti tute of Forest Genetics, Korea 23:132- 136 Chung a nd Chun 1990 va ria tio n, a lum ini um to ler an ce, in vi tro cu lture d Pop ulu s Journal of Kor ean F orest Society 79(1 ):26- 32 Han et al. 2001 Cd, Pb, accum ula tion, tis sue, rooted cu tting, Populus pecies , ecom ycor rhizal fungi ( Pi so lithus tinctorius ) Journal of Kor ean F orest Society 90(4 ):495- 504. Kim et a l. 2000 Pop ulus alba

P. gla ndulosa cut tings, ozone expos ure, cham ber , gr owth rate Journal of Kor ean F orest Society 89(1 ):105- 11 5 Kim et a l. 2002 photosy ntheti c r esponse, Populus alba

P. glandulosa , a da pta tio n, waste l andfil ls Journal of Kor ean F orest Society 91(1 ):79- 87 Kim et a l . 2002 adaptabili ty, water relation s, Populus alba

P. glandulo sa , w aste landfi lls Journal of Kor ean F orest Society 91(3 ):279- 286 Lee et a l. 1986 vari ation, salt toler ance, hy bri d pop lars, in vitr o cul ture Res ear ch Repor t, In sti tute of Forest Genetics, Korea 22:139- 144 W oo et a l. 2001 was te leachate, irr igation, Populu s eur americana , Betula plat yphyllka var . japo nica , seedlings Journal of Kor ean F orest Society 90(1 ):55- 63 Ye o et al. 1999 NaC l, growt h, cation accum ulation , poplar species Journal of Forest Science, Kor ea Fo rest R esearch In sti tute, Kor ea. 61 :9-17 Ye o et al . 2001 uptake, to lerance, le ad, Popul us alba

P. glandu los a , Betul a schmidti i Journal of Kor ean F orest Society 90(5 ):600- 607 Ye o et al. 2001 gro wt h r esp on se, absor ption capacity , poplars, lives tock waste water Journal of Kor ean F orest Society 90(6 ):734- 741 Ye o et al. 2002 absorpti on abil ity , tolerance, livestock waste water , poplar species and clones Journal of Korean S olid W ast es E ngineer ing So ciety 19( 8): 912- 92 0 Fuel-r elated Rese arches

Han and C hoi 2002 densified f uels fr om poplar s Journal of Kor ean Fo rest Engineer ing Society 21( 3):59- 65 Hy un et al. 1982 wood biom ass pro duction, tw elve coppi ce species , plantation, 1, 2 or 3- year rot ations Journal of Kor ean F orest Society 55:30- 36 Lee and Hy un 1980 woody biom ass , product, ener gy sour ce Res ear ch Repor t, In sti tute of Forest Genetics, Korea 16:78- 86. Noh et al. 1984 poplar , br eeding, cult ivation, exploitati on, util ization Res ear ch Repor t, In sti tute of Forest Genetics, Korea 20:16- 45. Son an d C hun g 1972 gro wt h per for ma nce, specific gr avity , hy brid popl ar Res ear ch Repor t, In sti tute of Forest Genetics, Korea 9:9- 16.

Researches on Populus in Korea for Various Purposes 521

dulosa , P. euramericana and P. nigra

maximowiczii clones were exposed to livestock waste water (LWW) and ground water (Yeo et al ., 2001). The height growth was better in LWW treatment than in ground water, while the best one was observed in P. alba

glandulosa , which showed no significant difference among clones in height growth. Aboveground biomass of all the species increased, like chlorophyll content in leaf, in the LWW treatment, while root dry weight decreased. P. alba

glandulosa showed the best absorption capacity of LWW, while the absorption amount of LWW was less than that of ground water. Among all the clones one clone of P. alba

glandulosa was promising for the selection for absorption capacity.

Five one-year-old clones of each P. alba

glandulosa , P. nigra

maximowiczii , and P. euramericana were irri- gated with LWW (Yeo et al ., 2002). P. alba

glandu- losa showed the highest performance in dry weight, total amount of nitrogen absorbed per tree, and water-use effi- ciency. At the age of three, one tree of P. alba

glan- dulosa could absorb 604 liter of LWW during one growing season.

Fuel-related Researches

In caloric values per gram, P. euramericana ‘I-476’

showed the highest value, 4,327 cal/g among 30 kinds of trees, which is higher than those of non-poplar species such as Betula , Pinus and Alnus (Lee and Hyun, 1980).

Caloric values ranged from 4,485 cal/g for Salix alba to 5,150 cal/g for Alnus glutinosa (Hyun et al ., 1982). The difference in caloric values between 1-year rotation and 2-year rotation woods was very small (< 100 cal/g) for the same species.

Variation in specific gravity was so high among indi- viduals as well as among localities. It was mentioned that it is necessary to study interaction of genotype and environment for specific gravity investigation (Son and Chung, 1972). Specific gravity of aspen hybrid was high (ex., P. alba

glandulosa : 0.41), while Tacamahaca or Aigeiros hybrids showed relatively low specific gravity (ex., P. euramericana ‘I-476’: 0.375).

Specific gravity of one-year-old branches was inves- tigated for 30 species and varieties, including many pop- lars, Pinus , Quercus , and Alnus species (Lee and Hyun, 1980). P. euramericana ‘I-476’ showed the lowest spe- cific gravity (0.29), while Quercus acutissima has the highest value (0.83). Almost all Populus species showed values ranging from 0.33 to 0.45. Three-year-old Salix koreensis branch showed 0.49.

P. euramericana ‘I-214’ showed the lowest specific gravity, 0.32; and P. davidiana the highest one, 0.48 (Noh et al. , 1984).

From untreated sawdust, poplar hybrids showed the highest yield of ethanol in a peracetic acid treatment and 4 days incubation, ranging from 0.93% to 1.21%, which were higher values in 4% NaOH or alkaline-butanol treatement (Lee and Hyun, 1980). However, the yield from wood saw could be increased up to 6% if the delig- nification is improved.

From P. tomenti

glandulosa and P. davidiana , com- paction of sawdust wase studied (Han and Choi, 2002).

And with various processing, densified fuels can be pro- duced with fines less than 5%.

Suggestions and Prospects

Many researches on Populus in Korea have focused on breeding, propagation, and silviculture so far to refor- est the denuded land and to meet the timber demand.

However, a lot of information obtained from those stud- ies will give a sound basis of the research for the new use of Populus trees. It includes the renewable energy source and phytoremediation tool.

From this point of view, many researches should be done on SRC development and management including disease/insect control; planting/harvest machine develop- ment; woody biomass harvest/collection; bio-fuel pro- duction; and heating apparatuses for wood fuel.

In addition, scientists in many fields such as genetics, physiology, soil science, microbiology and ecology should be engaged in cooperative research to enhance the phy- toremediation function of Populus .

To help find out references for each topic, the impor- tant researches are described in Table 1.

Acknowledgement

This study was supported to corresponding author by Korea Forest Service and Kangwon National University Research Foundation.

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(Received June 22, 2009; Accepted September 1, 2009)