Promoting seedling stress resistance through nursery techniques in China

Abstract

Plantation forestry is one of the most important approaches to restoring forest cover in China. Of the remaining sites suitable for afforestation in China, 52 % are considered harsh and only 13 % considered good, which indicates that successfully establishing a plantation in the future will become more and more difficult. Seedling quality in terms of morphology, physiology, and viability is a critical aspect for successful plantation establishment. Due to a large area in need of afforestation, and because of its diverse harsh sites, many studies have focused on nursery techniques of promoting seedling stress resistance, including inoculating ectomycorrhizal fungi, applying plant growth regulators, use of fall fertilization, induced water stresses, or a combined use of these methods. Most of relevant results of this research have been published in Chinese, and are unknown to researchers from other countries. Moreover, no comprehensive review of stress resistance research in forest tree seedlings in China has been completed. Therefore, this review intends to provide a concise synthesis of literature related to plant manipulation techniques that offer seedling stress resistance in Chinese nurseries, discuss potential shortcomings of these studies, and define priorities for future seedling stress resistance research. With this paper we hope to enhance communication about nursery and plantation seedling culture among researchers from China and other countries.

Full text

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New Forests
International Journal on the Biology,
Biotechnology, and Management of
Afforestation and Reforestation
ISSN 0169-4286
Volume 43
Combined 5-6
New Forests (2012) 43:639-649
DOI 10.1007/s11056-012-9341-9
Promoting seedling stress resistance
through nursery techniques in China
Y.Liu, S.L.Bai, Y.Zhu, G.L.Li &
P.Jiang

1 23
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Promoting seedling stress resistance through nursery
techniques in China
Y. Liu •S. L. Bai •Y. Zhu •G. L. Li •P. Jiang
Received: 5 October 2011 / Accepted: 2 May 2012 / Published online: 16 May 2012
Springer Science+Business Media B.V. 2012
Abstract Plantation forestry is one of the most important approaches to restoring forest
cover in China. Of the remaining sites suitable for afforestation in China, 52 % are con-
sidered harsh and only 13 % considered good, which indicates that successfully estab-
lishing a plantation in the future will become more and more difficult. Seedling quality in
terms of morphology, physiology, and viability is a critical aspect for successful plantation
establishment. Due to a large area in need of afforestation, and because of its diverse harsh
sites, many studies have focused on nursery techniques of promoting seedling stress
resistance, including inoculating ectomycorrhizal fungi, applying plant growth regulators,
use of fall fertilization, induced water stresses, or a combined use of these methods. Most
of relevant results of this research have been published in Chinese, and are unknown to
researchers from other countries. Moreover, no comprehensive review of stress resistance
research in forest tree seedlings in China has been completed. Therefore, this review
intends to provide a concise synthesis of literature related to plant manipulation techniques
that offer seedling stress resistance in Chinese nurseries, discuss potential shortcomings of
these studies, and define priorities for future seedling stress resistance research. With this
paper we hope to enhance communication about nursery and plantation seedling culture
among researchers from China and other countries.
Keywords Forest tree seedling Stress resistance Nursery technique Chinese forestry
Introduction
Plantation forestry is one of the most important approaches to restoring forest cover in
China. Significant advances have been achieved after more than 60 years of great effort.
Y. Liu Y. Zhu G. L. Li (&)P. Jiang
Key Laboratory for Silviculture and Conservation, Ministry of Education,
Beijing Forestry University, Beijing 100083, China
e-mail: glli226@163.com
S. L. Bai
College of Forestry, Inner Mongolia Agricultural University, Hohhot 010019, China
123
New Forests (2012) 43:639–649
DOI 10.1007/s11056-012-9341-9
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The total area of forest plantation is now 61.7 million ha, which is the largest in the world,
with a total standing volume of 2 billion m
3
(State Forestry Administration 2010). The
emphasis on plantations still continues, with more than 16.6 billion forest tree seedlings
produced, and over 4.7 million hectares of plantation established each year. With only
20 % forest cover, China still has a long way to meet its afforestation goals. This is a
challenge because more than half of the remaining sites in need of afforestation are
considered harsh, resulting in significant difficulty for successfully establishing plantations.
Seedling quality in terms of morphology, physiology, and viability is a critical com-
ponent of successful plantation establishment. Due to the large area requiring afforestation
and because of the diversity of harsh sites in China, many studies have focused on nursery
techniques for promoting seedling stress resistance. Most of the relevant study results have
been published in Chinese, and therefore are not readily available to researchers outside of
China. Moreover, there is no comprehensive review of Chinese research concerning stress
resistance in forest tree seedlings. Therefore, the objectives of this review are to: (1)
provide a concise synthesis of literature related to plant manipulation techniques that result
in increased seedling stress resistance in the nurseries of China; (2) discuss potential
shortcomings of these studies while defining priorities for future research; and (3) improve
communication about nursery and plantation seedling culture among researchers from
China and other countries.
Assessment indicators of seedling stress resistance
In order to promote seedling stress resistance through nursery techniques, the first problem
to solve is how to assess seedling stress resistance, a complicated genetic feature controlled
by morphology, anatomy, physiology, and biochemical characteristics (Yang et al. 2002).
Hence, one cannot fully evaluate plant stress resistance by just one or a few indicators.
Most researchers believe that an integrated method with multiple indicators is the best
approach to evaluate seedling stress resistance (Jia et al. 2007) (Table 1).
Chinese researchers have examined many indicators. For example, seedling transpira-
tion rate, water-absorbing ability, osmotic adjustment, antioxidant system, net photosyn-
thesis rate, water utilization efficiency, and biomass production were suitable indices in the
drought resistance assessment of Castanea mollissima Bl., Juglans regia L., Zanthoxylum
bungeanum Maxim, Diospyros kaki Thunb., Prunus armeniaca L., and Gleditsia sinensis
Table 1 Summary of methods and indicators for assessing seedling stress resistance in China
Methods Indicators
Multiple indicators Relative water content, superoxide dismutase (SOD) activity, and soluble
sugar
a
, nitrate reductase (NR) activity
b
Comprehensive evaluation by
function value
Seedling transpiration rate, water-absorbing ability, osmotic adjustment,
anti-oxidant system, net photosynthesis rate, water utilization efficiency,
and biomass production
c
Principal component analysis
(PCA)
Seedling height, root collar diameter, height/diameter ratio, tap root
length, lateral root length, lateral root diameter, total biomass, root
biomass, stem and branch biomass, leaf biomass, soluble sugar content,
total SOD activity, free amino acid content, chlorophyll a/b,
and electrolyte leakage
d
a
Xue et al. (2009b),
b
Xie and Shen (2000),
c
Jia et al. (2007),
d
Zhou et al. (2010)
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Lam. (Jia et al. 2007). In addition, relative water content, the activity of superoxide
dismutase (SOD), and soluble sugar were the best physiological indices for evaluating
drought resistance of Eucalyptus urophylla S. T. Blake and Liquidambar formosana Hance
seedlings (Xue et al. 2009a,b). Furthermore, nitrate reductase (NR) activities could be
used as an effective biochemical index for drought resistance for seedlings of Pinus
massoniana Lamb., Pinus taeda L., and Metasequoia glyptostrobides Hu et Cheng
(Xie and Shen 2000).
Because so many indicators can contribute to seedling stress resistance, formulating
conclusions from these indicators becomes a critical issue. Using correlation coefficient
data, Jia et al. (2007) found a comprehensive evaluation could be carried out to evaluate
seedling drought resistance by calculating a function value of subordination according to
seven indicators (Table 1). The results showed that relative seedling drought resistance
from high to low among species was: Z. bungeanum,D. kaki,G. sinensis,P. armeniaca,
C. mollissima, and J. regia.
Principal Component Analysis (PCA) has also been applied to evaluate seedling
drought resistance of Leucaena leucocephala (Lam.) de Wit (Zhou et al. 2010). After
seedlings were treated with different fertilization regimes (equal constant, linear, expo-
nential, and none) under two water conditions (normal irrigation, drought stress), 16
indicators (Table 1) were measured and analyzed by PCA. The conclusion was that the
relative seedling drought resistance from high to low among fertilization regimes was
exponential [equal constant [linear [none under normal irrigation, but under drought
stress the order was linear [equal constant [exponential [none.
However, because different indicators and methods are employed among researchers, a
comparison among present studies even with the same species is challenging, if not
impossible.
Promoting seedling drought resistance by nursery techniques
Mycorrhizal fungi
Mycorrhizae involve the intimate association of plant roots with specialized soil fungi
(Molina and Trappe 1984). Seedling drought resistance is believed to be enhanced by
inoculation with mycorrhizal fungi, which increases the surface area of the seedling root
system and thereby increases the potential of absorbing water and nutrients (Parke et al.
1983). When container seedlings of Pinus taulaeformis Carr. and Platycladus orientalis
(L.) Franco were inoculated with mycorrhizal fungi (Table 2) and then grown under arid
conditions, the median survival was 17–20 days longer than non-inoculated seedlings
(Lei et al. 1991;Wu1991; Wu and Liang 1991). Inoculating C. mollissima seedlings with
mycorrhizal fungi not only promoted growth but also increased the degree of leaf suc-
culence from 0.1 to 7.9 %, increased specific leaf area from 2.7 to 18.8 %, raised leaf
water-holding ability, decreased water saturation deficit from 3.5 to 29.6 %, and delayed
the time until leaves wilted under moisture stress conditions (Lu and Lei 2000).
The effects of ectomycorrihzal inoculation vary with the species of fungus and plant. A
study on Ostryopsis davidiana Decne. seedlings inoculated with five different ectomy-
corrhizal fungi (Table 2) demonstrated that fungal symbionts delayed the time to wilting
(24–44 days depending on fungus) and the time to mortality (36–60 days depending on
fungus) by influencing seedling water potential, SOD activity, growth, root to shoot
ratio, malondialdehyde (MDA), damage to cell membranes, and proline content
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(Yan et al. 2006). Because different mycorrihzal fungi promote different seedling stress
resistance mechanisms, inoculation with more than one mycorrihzal fungal species is a
possible approach to improving seedling stress resistance. A pot study of Populus tom-
entosa Carr. cuttings showed that cuttings inoculated with a mix of Glanus geosporum,
Glanus constrictum, and Scleroderma spp. had higher water and nutrient absorption
potential, larger N content in leaves, and greater drought tolerance than cuttings inoculated
with a single mycorrhizal fungus (Zhao et al. 2000).
Bai et al. (2006) found that survival of outplanted P. tabulaeformis seedlings, in the absence
of mycorrhizae, was poor on Daqing Mountain, Inner Mongolia. However, the survival was
more than 85 % and trees grew well if they were outplanted near naturally occurring
O. davidiana plants, even on extremely harsh sites. Further study showed that O. davidiana
facilitated ectomycorrhizae formation on P. tabulaeformis through hyphal filaments, and
therefore enhanced outplanting performance of P. tabulaeformis seedlings (Bai et al. 2009). It
is speculated that these species form a common mycorrhizal network and this association
serves to enhance performance of seedlings used for forest restoration on harsh sites.
Plant growth regulators
Plant growth regulators have been frequently used to enhance seedling stress resistance of
various tree species (Shi et al. 2006) (Table 2). Studies of Hippophae rhamnoides L., and
Amorgha fruticosa L. treated with 0.1–0.4 mg/L brassinosteroids (BR) and then subjected to
water stress conditions showed improved drought resistance; seedling water potential was
imcreased by 26–50 % and transpiration decreased by 23–40 % (Han et al. 2007; Li et al.
2004).
Table 2 Summary of nursery techniques for improving stress resistance in China
Techniques Methods
Mycorrhizal fungi
inoculation
Mycorrhizal fungal species:
Boletus edeuli, Xerocomus chrysenteron, Cortinarius sublanatus,Suillus luteus,
Gomphidius viscidus
a-d
,
Pisolithus tinctorius,Cenococcum geophilum,Suillus grevillei,
Suillus granulatus,Paxillus involutus
e
,
Glanus geosporum,Glanus constrictum,Scleroderma spp.
f
,
Leucocortinarius bulbiger,Rhizopogon luteolus, Suillus grevillei,
Tricholoma fulvum,Tricholoma terreum
g
Plant growth regulators Brassinosteroids (BR)
h,i
Salicylic acid (SA)
j,k
Paclobutrazol (PP333)
l
Abscisic acid (ABA)
m
5-aminolevulinic acid (ALA)
n
Ascorbic acid (VC)
o
Fertilization Fall fertilization
p,q
Foliar fertilizer
r
Controlled-release fertilizer (CRF)
s
Organic amendment ?inorganic fertilizer
t
Inducing water stress Periodically reducing irrigation quantities
q, u–y
a
Lei et al. (1991),
b
Wu (1991),
c
Wu and Liang (1991),
d
Lu and Lei (2000),
e
Yan et al. (2006),
f
Zhao
et al. (2000),
g
Bai et al. (2006),
h
Li et al. (2004),
i
Han et al. (2007),
j
Jiang and Chen (2004),
k
Li and Sun
(2010),
l
Gao et al. (2007),
m
Yu et al. (2009),
n
Li et al. (2010a,b),
o
Wang et al. (2007),
p
Liu et al. (2000),
q
Liu et al. (2002),
r
Cao et al. (2010),
s
Zhu et al. (2010),
t
Wei et al. (2012),
u
Xu et al. (2010),
v
Zhang et al.
(2008),
w
Xue et al. (2009a,b),
x
Li et al. (2010a,b),
y
Chen and Zhao (2011)
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Under water stress conditions, salicylic acid (SA) (3.5910
-5
mol/L, 7.0910
-5
mol/L,
1.1910
-4
mol/L, 1.4910
-4
mol/L) could decrease the level of MDA content by 30–48 %
and retard the decrease of chlorophyll and soluble protein content in seedlings of several
shrubs: Syringa oblata Lindl., Caragana microphylla Lam and Spiraea chamaedryfolia L.
(Jiang and Chen 2004). Li and Sun (2010) also found SA applied to P. tabulaeformis
seedlings at 5 mg/L could increase root length (11–33 %), root surface area (23–32 %),
and root number (18–40 %).
Abscisic acid (ABA) can induce plant stress resistance and allow the plant to adapt to
harsh (drought, cold, salt, etc.) sites (Montero et al. 1997). An experiment on potted 3-year-
old Fraxinus mandshurica Rupr. seedlings treated with different concentrations of ABA (0,
20, 35, and 50 mg/L) showed that the effect of ABA on seedlings varied with soil water
content (Yu et al. 2009). The inhibitory effects of exogenous ABA on the transpiration rate,
stomatal conductance, and photosynthetic rate was greatest when the soil water content
ranged from 47 to 33 %. As soil water content dropped to 30 and 21 %, so did the effects
of ABA; the effects disappeared when soil water content further dropped to 20 and 15 %
before resuming again when soil water content reached 10 %. This indicates that ABA can
enhance the drought resistance of F. mandshurica seedlings under some water conditions.
Widely used in agriculture, d-aminolevulinic acid (ALA) can control crop growth and
increase stress resistance. In a study with 2-year-old containerized seedlings of Pinus
sylvestris Linn. var. mongolica Litv., Amorpha fruticosa L., and Acer truncatum Bunge,
root morphology was changed by spraying leaves with ALA (Li et al. 2010b). A con-
centration of 400 mg/L ALA increased root length, area, and volume of P. sylvestris by
170, 800, and 740 %, respectively. Similarly, an application of 200 mg/L ALA to leaves of
A. fruticosa increased root length and area by 94 and 66 %, respectively. The effects were
not significant for A. truncatum. However, whether these changes in root morphology
improve seedling drought resistance needs further study.
Ascorbic acid (VC) is another plant growth regulator shown to improve drought tol-
erance. In mid summer, Wang et al. (2007) sprayed potted seedlings of S. oblate and
C. microphylla with various rates of VC. After 10 days of drought stress (non-irrigation),
the optimal VC rates for drought resistance were 11.50, and 8.50 mmol/L for S. oblate and
C. microphylla, respectively.
Fertilization
Optimal N level can generally improve the ability of seedlings to endure and grow during
drought in the field (Duryea 1984). Improved N status and seedling growth can be achieved
in Larix olgensis Henry with combinations of an organic amendment (chicken manure) and
inorganic fertilizer (Wei et al. 2012). For P. orientalis seedlings, fall fertilization (N, P, K)
increased N reserves, sugar concentrations, and planting survival the following spring by
13, 8, and 12 % respectively (Liu 1999; Liu et al. 2002). Foliar fertilizer that included
more than ten elements such as N, P, K, Ca, Mg, etc., applied Robinia pseudoacacia L., P.
armeniaca, and J. regia seedlings reduced transpiration rates, increased leaf water
potential, and enhanced drought resistance (Cao et al. 2010).
Controlled-release fertilizer (CRF), designed to release nutrients slowly over a longer
time, helps to reduce nutrient leaching and plant damage, and improve overall fertilizer use
efficiency (Donald 1991; Dumroese et al. 2005; Jacobs et al. 2005). A comparison between
CRF and conventional urea applied at 120 and 240 kg/ha to L. olgensis seedlings showed
that seedlings contained more N when given CRF, allocating it to stems and roots (Zhu
et al. 2010).
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Periodic water stress
Seedling drought resistance and outplanting survival may be increased if the seedling is
subjected to periodic water stress during its nursery culture (Pallardy and Rhoads 1993).
Liu et al. (2002) found that moderate water stress during the late growing season promoted
root growth, and subsequently lowered shoot to root ratio of P. orientalis seedlings.
Compared to seedlings that were provided normal irrigation, seedlings treated with peri-
odic water stress had a higher water use efficiency, greater root growth potential, and
higher outplanting survival. Similarly, reducing irrigation quantities by 30 % during L.
olgensis seedling cultivation did not significantly decrease growth, but enhanced root
length and stress resistance (Xu et al. 2010).
One prominent response of seedlings subjected to water stress is a change in seedling
allometry. Chen and Zhao (2011) studied the root characteristics and biomass allocation of
two-year-old seedlings of P. tabulaeformis,R. pseudocacia,P. orientalis and H.
rhamnoides exposed to three soil moisture levels (70, 50, and 35 % water holding capacity)
for three treatment durations (7, 14, and 21 days). They found that, as water stress
intensified and treatment time was prolonged, the root biomass and fine root index of P.
tabulaeformis increased significantly. Although the root biomass of R. pseudocacia
increased significantly, the fine root index was not affected. The root biomass and fine root
index of P. orientalis and H. rhamnoides increased with moderate water stress, but dropped
in severe drought. These results indicate a species-specific biomass allocation pattern in
response to water stress. A similar result, in terms of root biomass production, was found in
Acacia auriculiformis A. Cunn. ex Benth. seedlings exposed to a rising frequency and
gradient of water stress (Li et al. 2010b).
Physiological changes also occur in response to water stress treatments during seedling
culture. In a potted experiment with R. pseudoacacia seedlings exposed to five levels of
soil relative water content (SRW; 100 % (control), 88, 70, 52, and 40 %) for 30 days, the
contents of potentially damaging superoxide hydronium (O
2-
) and MDA in seedlings
under stress rose significantly compared with the nonstressed control treatment (Xue et al.
2009a,b). Concurrently, quantities of SOD and peroxidase (POD) increased, with the
highest amounts occurring when SRW was 52 %. When subsequently rewatered, SOD and
POD activity rapidly increased during the first 2 h, dramatically reducing seedling content
of O
2-
and MDA. Thus, exposure to water stress, compared to the control treatment,
strengthened the seedlings ability to protect leaf enzymes from potentially damaging free
radicals.
In Larrea tridentate seedling, the photosynthetic pattern was changed and water
utilization efficiency was raised when water stress was increased (Zhang et al. 2008).
Specifically, the diurnal curves of net photosynthetic rate and transpiration rate were
‘‘twin-peaked’’, showing a significant midday depression, when water was not limiting, but
a ‘‘single-peaked’’ diurnal curve under severe water stress.
Promoting seedling cold resistance by nursery techniques
Compared to drought resistance research, substantially fewer studies in China focus on
seedling cold resistance. We found, however, that some of the techniques used to improve
drought resistance have also been used to improve cold resistance. For example, proper
fertilization can enhance nutrient storage reserves and stress resistance (van den Driessche
1991). A study on P. tomentosa seedlings treated with different fertilization regimes
644 New Forests (2012) 43:639–649
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demonstrated that autumn fertilization after seedling height growth cessation, increased
seedling N and P levels and increased cold resistance by 40 % (Liu et al. 2000).
Paclobutrazol (PP333) sprayed on 20 cm tall P. massoniana seedlings at rates of 1,000,
1,500, and 2,000 mg/kg at 15 day intervals significantly improved fine root and stem
growth, decreased frost damage by 35 % (seedling damage grade after 4 days under -3to
-6C in middle December), and increased outplanting survival by 11 % (Gao et al. 2007).
Some plant growth regulators can be applied simultaneously. For example, spraying a 1:1
(v:v) mixture of PP333 and 6-BA at a concentration of 450 mg/l to Pyrus nanguo did not
affect seedling height, but increased root collar diameter, decreased relative conductivity
and MDA content, and increased soluble sugar content and proline, allowing seedlings to
achieve their strongest potential for cold resistance (Hu 2010).
Afforestation in northern China is challenged by a large geographical area with cold
temperatures that hamper seedling survival and growth. More in-depth studies on
increasing seedling cold resistance with nursery techniques are needed.
Interaction among techniques and subsequent seedling field performance
The techniques of mycorrhizal fungi inoculation, plant growth regulators, fertilization, and
water stress can be applied separately or simultaneously to improve seedling stress
resistance. When two nursery practices interact, however, the effect of one practice will
depend on the particular level of the other (Duryea 1984). Some examples of interaction
are:
•Under a normal irrigation condition, Leucaena leucephala seedlings were the most
drought resistant when fertilizer was applied exponentially, while under a water stress
condition, linear fertilization resulted in the highest seedling drought resistance (Zhou
et al. 2010).
•Compared with the treatment of no fertilization in combination with an inoculation of
Pisolithus tinctorius (Pt), the combination of steady-state nutrition and Pt inoculation
produced higher quality seedlings in terms of height, root collar diameter, number and
total length of lateral roots, and biomass (Jia et al. 2004).
•The effect of plant growth regulators on seedling drought resistance can be influenced
by the seedling’s water stress condition (Yu et al. 2009).
If a decision is made to employ a new technique, careful attention should be paid to
other nursery practices affected by this change (Duryea 1984).
The most important aspect of improving stress resistance with nursery techniques is
improving seedling performance after outplanting. Many studies in China have demon-
strated that nursery techniques, such as stock type (Song et al. 1990; Tian et al. 1990;
Zhang 2001; Li et al. 2011), seedling age (Tian et al. 1990; Li et al. 2012), growing density
(Tian et al. 1990; Wang 2010), root undercutting (Song et al. 1990), mycorrhizae (Lei et al.
1991), fall fertilization (Liu et al. 2000), plant growth regulators (Gao et al. 2007), packing
(Kou 1991), and storage (Liu 1995) have a substantial influence on seedling performance
after outplanting. Most of these studies, however, did not combine nursery techniques with
planting site conditions. Because nursery cultural practices vary by species, nursery
environment, and outplanting environment, the only way to fully understand seedling stress
resistance promoted by nursery techniques and its effectiveness is to consider the condi-
tions of the outplanting site along with the expected seedling performance under those
conditions.
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Conclusions and future directions
During the past several decades some advances have been made in plant manipulation
techniques that offer promising avenues for obtaining seedling stress resistance in the
nurseries of China. Noticeably concurrent with the increasing proportion of harsh planting
sites in China will be the challenge of successfully establishing a plantation and producing
suitable seedlings for these sites. Therefore more scientific studies and practical effort are
urgently needed to further increase seedling stress resistance through nursery techniques.
Extended drought, cold, saline, or alkaline soils, and poor nutrient availability are the
major obstacles encountered in forest plantations of China. While present studies mainly
focus on drought resistance, it is also important to study seedling resistance to other
environmental stresses, especially cold temperatures. Genetic differences among seedling
species might display different mechanisms for adaptation to a variety of harsh sites.
Understanding these mechanisms will help nursery people produce seedlings that have a
better chance to successfully establish on challenging sites.
Any single indicator cannot accurately reflect plant stress resistance; hence most
researchers believe that an integrated method with multiple indicators is a more appropriate
approach to evaluate the capacity of seedling stress resistance (Jia et al. 2007). The ideal
combination of indicators and methods to evaluate seedling stress resistance is still needed.
Besides the measures discussed above, other seedling characteristics and nursery
practices, such as seedling density, root undercutting, photoperiod, transplanting, stock
types, and others need to be studied to examine their relationship with seedling stress
resistance. In light of this, and according to the target plant concept (Rose et al. 1990;
Landis et al. 2010), Wuliyasi and Liu (2004) put forward a theory to raise seedlings
through a target plant protocol. The target can be determined according to site charac-
teristics, and the associated seedling morphology, physiology, and viability characteristics
best adapted to the site. To fulfill this objective, we believe that the following important
research facets should be considered:
•Mechanisms of seedling adaptation to different harsh sites, such as drought, cold, saline
or alkaline soils, and poor soil nutrient availability.
•Relationships among various technological measures and seedling stress resistance
under different target seedling scenarios. In addition to experiments on water stress,
fertilization, mycorrhizal fungi inoculation and plant growth regulator applications, the
effects of nursery cultural practices, such as seedling density, root undercutting,
photoperiod, and transplanting, on seedling stress resistance should also be studied.
•Stocktype should be more intensively studied because it reflects different combinations
of technological measures.
•Additional and longtime outplanting studies should be conducted to evaluate the
capacity of seedling stress resistance. The conditions of the outplanting site need to be
considered along with expected seedling performance under those conditions.
•Both nursery techniques and outplanting measures are important for successfully
establishing a plantation on a harsh site. Therefore nursery techniques and outplanting
techniques should be studied together for their important ties with seedling field
performance.
Acknowledgments This manuscript was funded by the 948 Plan (2012-4-66) and the Fundamental
Research Funds for the Central Universities (Contract No. JD2011-3 & BLJD200905). We especially thank
646 New Forests (2012) 43:639–649
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Mr. Richard R. Faltonson and Dr. Kasten Dumroese for improving the quality of English in this manuscript,
and the anonymous reviewers for their technical comments.
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