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Optimal Light Regime for the Rare Species Magnolia wufengensis in Northern China

珍稀树种红花玉兰在华北地区的最适光环境



全 文 :植物科学学报  2015ꎬ 33(3): 377~387
Plant Science Journal
    DOI:10􀆰 11913 / PSJ􀆰 2095-0837􀆰 2015􀆰 30377
珍稀树种红花玉兰在华北地区的最适光环境
杨 杨 1ꎬ 贾忠奎1ꎬ 陈发菊2ꎬ 桑子阳3ꎬ 马履一1∗
(1. 北京林业大学教育部森林培育与保护重点实验室ꎬ 北京 100083ꎻ 2. 三峡大学生物技术
研究中心ꎬ 湖北宜昌 443002ꎻ 3. 五峰土家族自治县林业局ꎬ 湖北五峰 443400)
摘  要: 珍稀树种红花玉兰对其华南原产地的自然环境有良好的适应性ꎬ 但在华北地区却生长不良ꎮ 通过对红花
玉兰在华北地区一个生长季内对三种光照水平(100%、 70%、 40%全光照)的光合和生长响应分析ꎬ 结果表明:
在 70%全光照条件下ꎬ 红花玉兰幼苗的净光合速率、 光饱和点、 株高、 基径、 根生物量和茎生物量均达到最高
水平ꎮ 随着光照强度的减弱ꎬ 暗呼吸速率、 光补偿点、 比叶重量、 叶片厚度和密度显著降低ꎬ 表观量子效率、
最大荧光 Fm、 可变荧光 Fv、 Fm/ Fo(Fo为初始荧光)、 Fv / Fo、 Fv / Fm、 叶绿素含量、 叶面积和叶柄角度均显
著增大ꎮ 说明 70%全光照最适于一年生红花玉兰幼苗在华北地区的生长ꎬ 全光照和 40%全光照条件下幼苗则因
光量的过剩和不足而生长不良ꎮ 因此建议将红花玉兰栽植在林缘或林窗地带ꎬ 可为这一珍稀濒危树种在华北地
区的引种提供有利的适生光照环境ꎮ
关键词: 红花玉兰ꎻ 光适应ꎻ 光合作用ꎻ 叶绿素荧光ꎻ 生长
中图分类号: Q945􀆰11ꎻ S685􀆰15          文献标识码: A          文章编号: 2095 ̄0837(2015)03 ̄0377 ̄11
      收稿日期: 2014 ̄11 ̄17ꎬ 退修日期: 2015 ̄01 ̄09ꎮ
  基金项目: 2014年林业科技成果国家级推广项目“红花玉兰苗木繁育技术示范推广与产业化”([2014]27号)ꎻ 北京科委“首都平原
百万亩造林科技支撑工程”项目(Z121100008512002)ꎻ 985优势学科创新平台开放课题“红花玉兰苗木繁育关键技术研究与推广”
(000 ̄9801005)ꎮ
  作者简介: 杨杨(1984-)ꎬ 男ꎬ 博士ꎬ 主要从事红花玉兰引种栽培生理生态学研究(E ̄mail: jiufengqujingren@163􀆰 com)ꎮ
  ∗通讯作者(Author for correspondence. E ̄mail: maluyi@bjfu􀆰 edu􀆰 cn)ꎮ
Optimal Light Regime for the Rare Species Magnolia
wufengensis in Northern China
YANG Yang1ꎬ JIA Zhong ̄Kui1ꎬ CHEN Fa ̄Ju2ꎬ SANG Zi ̄Yang3ꎬ MA Lu. .  ̄Yi1∗
(1. Ministry of Education Key Laboratory for Silviculture and Conservationꎬ Beijing Forestry Universityꎬ Beijing 100083ꎻ
2. Biotechnology Research Centerꎬ Three Gorges Universityꎬ Yichangꎬ Hubei 443002ꎬ Chinaꎻ
3. Forestry Bureau of Wufeng Countyꎬ Wufengꎬ Hubei 443400ꎬ China)
Abstract: The rare species Magnolia wufengensisꎬ which is adapted to the natural conditions
of its native habitat in southern Chinaꎬ has shown poor growth in northern regions. We
analyzed the photosynthetic and growth responses of M. wufengensis grown in northern China
under three light levels (100%ꎬ 70%ꎬ and 40% sunlight) during one growing season. Under
70% sunlightꎬ plants had a maximum net photosynthetic rate (Pmax )ꎬ light saturation point
(LSP)ꎬ seedling heightꎬ basal diameterꎬ root biomass and stem biomass. With decreasing
light levelꎬ the dark respiration rate (Rd )ꎬ light compensation point ( LCP)ꎬ specific leaf
weightꎬ leaf thickness and leaf density significantly decreasedꎬ and apparent quantum yield
(AQY)ꎬ maximum fluorescence (Fm)ꎬ variable fluorescence (Fv)ꎬ Fm/ initial fluorescence
(Fo)ꎬ Fv / Foꎬ Fv / Fmꎬ chlorophyll contentꎬ leaf area and petiole angle significantly increased.
We concluded that 70% sunlight was the optimum light level for 1 ̄year ̄old M. wufengensis
seedlings grown in northern China. Poor growth responses were observed under full and 40%
sunlightꎬ resulting from excessive and insufficient light energyꎬ respectively. For the successful
introduction to northern Chinaꎬ microsites at forest edges or gaps should be favored to provide
an optimal light environment for M. wufengensis.
Key words: Magnolia wufengensisꎻ Light adaptationꎻ Photosynthesisꎻ Chlorophyll fluores ̄
cenceꎻ Growth
    Magnolia wufengensisꎬ a new Magnolia spe ̄
ciesꎬ was discovered in Wufeng in Hubei Pro ̄
vinceꎬ southern China[1ꎬ 2] . Increasingly popular
for urban greeningꎬ M. wufengensis has consi ̄
derable ornamental and economic value owing to
its colorful flower (pureꎬ darkꎬ or pale red) and
varied flower petal numbers (9-25ꎬ 32ꎬ or 46) [3] .
Due to biological characteristics and anthropo ̄
genic disturbancesꎬ its distribution is mainly limi ̄
ted to mountainous areas at 1400-2000 m eleva ̄
tion in western Wufengꎬ and its current popula ̄
tion of less than 2000 individual plants continues
to decline[3] . Thusꎬ an urgent need exists to pre ̄
serve and propagate this rare species.
In recent yearsꎬ efforts have been made in
many parts of China to expand the geographic
distribution of M. wufengensis. During our intro ̄
duction and cultivation activitiesꎬ we found that
leaf color and morphology of M. wufengensis
showed considerable differences between the
seedlings grown in southern China and those
grown in northern China. Furthermoreꎬ in contrast
to the optimum conditions in its native habitat of
southern Chinaꎬ poor growth responses were
widespread in M. wufengensis seedlings trans ̄
planted to northern regions. The considerable
changes in leaf color and morphology appear to
be caused by the response of photosynthetic pig ̄
ments and processes to various ecological fac ̄
tors. These changes can ultimately affect seed ̄
ling growth and distribution.
Among the key ecological factorsꎬ light plays
an important role in the growth and distribution of
plant species[4ꎬ 5] . Insufficient light energy can
limit photosynthesisꎬ leading to reduced carbon
accumulation and plant growthꎻ converselyꎬ high
light levels can damage photosynthetic mecha ̄
nisms[5] . To cope with these stressesꎬ plants
have developed various strategiesꎬ such as leaf
plasticity for high / low light acclimationꎬ light
avoidanceꎬ and photo ̄protective means to dissi ̄
pate excess energy[6] . Variations in leaf morpho ̄
logyꎬ anatomyꎬ and physiology have been well
documented for species adapted to sunny or
shaded environments[4ꎬ 7ꎬ 8] . Investigations on the
photosynthetic and morphological responses of
plant species can provide information on a
species􀆳 tolerance and growth under different
light environmentsꎬ and this information can be
widely applied in agricultureꎬ ecologyꎬ forestryꎬ
and horticulture[4ꎬ 8-15] . This approach can also
be useful in assessing the optimal habitat condi ̄
tions for the conservation of rare species found in
only a few populations or under widely varying
conditions[16] .
Sufficient information about the critical life
history characteristics and habitat requirements is
the foundation of successful management of rare
and endangered species[17ꎬ 18] . Unfortunatelyꎬ
limited information is available on the biological
and ecological requirements of M. wufengensis.
Thusꎬ the purpose of this study was to determine
the optimal light regime for M. wufengensis grown
in northern China by comparing the photosynthe ̄
tic and growth responses under full sunlight and
alternative shade treatments. The following ques ̄
tions were addressed: How does M. wufengensis
adjust its leaves photosynthetically and morpho ̄
logically to different light levelsꎻ and does the
growth and biomass of M. wufengensis differ un ̄
der different light environments?
873 植 物 科 学 学 报 第 33卷 
1  Materials and Methods
1􀆰 1  Plant materialsꎬ study site and meteorologi ̄
cal conditions
M. wufengensis seedlings (1 ̄year ̄old)ꎬ ob ̄
tained from the Institute of Rare Plants in Wufeng
(29°56′Nꎬ 110°15′E)ꎬ were transplanted to our
study siteꎬ the Puzhaoyuan Nursery of Jiufeng
Experiment Stationꎬ Beijing Forestry Universityꎬ
Beijing (39°48′Nꎬ 116°28′E) . The site has a con ̄
tinental monsoon climateꎬ with strong spring
windsꎬ warmꎬ humid summersꎬ and dryꎬ cold
winters. The annual mean air temperature is 8􀆰5℃-
9􀆰5℃ꎬ with a range of -19􀆰6℃ to 39􀆰7℃. Mean
annual precipitation is 600 mmꎬ mean annual
sunlight is 2769 hoursꎬ and the frost ̄free period
is 180 days. The meteorological conditions in
Wufeng and Beijing from 1971 to 2000 were ob ̄
tained from China􀆳s Meteorological Administration
( Fig􀆰1) . The coefficient variation (CV) of the
meteorological data between Wufeng and Beijing
was determined by the formulaꎬ CV = standard
deviation / average value.
1􀆰 2  Experimental treatments
M. wufengensis seedlings were randomly
planted in three plots in late March 2013. The
planting space was 40 cm × 50 cm. Each plot
had an area of 15 m × 3 m and contained forest
topsoil to a depth of 40 cm. Each plot indicated a
treatment. Plants were subjected to three light
treatments during the main growing season be ̄
ginning on April 1 and ending on October 31ꎬ
2013. Light treatments consisted of high light
(100% sunlightꎬ LT100 )ꎬ moderate light ( 70%
sunlightꎬ LT70 )ꎬ and low light ( 40% sunlightꎬ
LT40 ) . Shading was achieved by suspending
several layers of black nylon netting above and
surrounding each plot. All seedlings were kept
well ̄irrigated and protected from bacterial patho ̄
gens and weed competition.
1􀆰 3  Photosynthetic measurements
Photosynthetic light response curves were de ̄
termined by measuring the photosynthetic rates at
14 levels of the photosynthetic photon flux density
(PPFD: 0ꎬ 25ꎬ 50ꎬ 75ꎬ 100ꎬ 150ꎬ 200ꎬ 400ꎬ
600ꎬ 800ꎬ 1000ꎬ 1200ꎬ 1600ꎬ 2000 μmol􀅰m-2􀅰s-1)
Su
ns
hi
ne
ra
te
(%
)
Month
Su
ns
hi
ne
d
ur
at
io
n
(d
)
Month
Ai
r t
em
pe
ra
tu
re
(
)

Month
R
el
at
iv
e
hu
m
id
ity
(%
)
Month
A B
C D
0
10
20
30
40
50
60
Apr May Jun Jul Aug Sep Oct
0
50
100
150
200
250
300
Apr May Jun Jul Aug Sep Oct
0
5
10
15
20
25
30
Apr May Jun Jul Aug Sep Oct
Wufeng
Wufeng
Beijing
Beijing
0
10
20
30
40
50
60
70
80
90
Apr May Jun Jul Aug Sep Oct
Wufeng
Wufeng
Beijing
Beijing
Fig􀆰 1  Monthly average values of meteorological data in Wufeng and Beijing in the growing season
973  第 3期                    杨 杨等: 珍稀树种红花玉兰在华北地区的最适光环境(英文)
under an ambient CO2 concentration of 400 μmol􀅰
mol-1 and a temperature of 25℃ in early May
(spring)ꎬ mid ̄July (summer)ꎬ and late Septem ̄
ber (autumn)ꎬ using an LI ̄6400 Portable Photo ̄
synthesis System (Li ̄Corꎬ USA) . The photosyn ̄
thetic parameters were estimated by fitting the
photosynthetic light response curve[19] including
the maximum net photosynthetic rate (Pmaxꎬ μmol
CO2􀅰m
-2􀅰s-1)ꎬ dark respiration rate (Rdꎬ μmol
O2􀅰m
-2􀅰s-1)ꎬ apparent quantum yield ( AQYꎬ
μmol O2􀅰m
-2􀅰s-1)ꎬ light compensation point (LCPꎬ
μmol􀅰m-2􀅰s-1)ꎬ and light saturation point (LSPꎬ
μmol􀅰m-2􀅰s-1) . For each treatmentꎬ one healthy
upper ̄crown leaf facing the sun was selected
from six representative seedlings and the above
parameters were measured.
1􀆰 4  Chlorophyll fluorescence
In the same season and on the same leaves
used to measure photosynthetic parametersꎬ chlo ̄
rophyll fluorescence parameters were measured
using a Plant Efficiency Analyzer (PEAꎻ Hansa ̄
tech Instruments Ltd.ꎬ King􀆳s Lynnꎬ Norfolkꎬ UK)ꎬ
including the initial fluorescence (Fo)ꎬ maximum
fluorescence ( Fm )ꎬ and variable fluorescence
(Fv). Fo was measured after 20 min of acclima ̄
tion to the dark. Fm was recorded in a 0􀆰8 s pulse
of saturating light (2000 μmol􀅰m-2􀅰s-1)
1􀆰 5  Chlorophyll content and specific leaf weight
Healthy upper ̄crown leaves facing the sun
were picked from plants in each light environment
during the same season when the photosynthetic
parameters were measured. The surface areas of
some leaves were immediately measured using
an LI ̄3000C Portable Area Meter (Li ̄Corꎬ USA)ꎬ
after which the leaves were killed out at 105℃ for
20 minꎬ and then dried at 80℃ to constant weight
for determination of the specific leaf weight. In
other leavesꎬ the chlorophyll contents were deter ̄
mined in 80% acetone extractꎬ according to
Li[20] .
1􀆰 6  Leaf morphology
In Septemberꎬ the leaf morphological para ̄
meters of plants (40 seedlings in each treatment)
were determined. The leaf density was calculated
as leaf number / seedling lengthꎬ and one healthy
upper ̄crown leaf facing the sun was selected
from each seedling for the remaining leaf mor ̄
phological measurements: leaf area was mea ̄
sured using an LI ̄3000C Portable Area Meter (Li ̄
Corꎬ USA)ꎻ leaf thickness was measured with a
micrometer and petiole angle was measured with
a protractor at 12∶00 on a sunny day.
1􀆰 7  Growth and biomass
In Novemberꎬ after entering dormancyꎬ
seedling height and basal diameter were measu ̄
red for each seedling. Five seedlings per treat ̄
ment were harvested and their rootꎬ stemꎬ and
total biomass were measured. The root biomass
ratio was calculated as root biomass / total bio ̄
massꎬ and stem biomass ratio was calculated as
stem biomass / total biomass.
1􀆰 8  Statistical analysis
All data were analyzed using SPSS Statistics
18􀆰0. Differences were considered significant at
P < 0􀆰05. All tables and figures were produced
using Microsoft Word 2007 and Microsoft Excel
2007ꎬ respectively.
2  Results
2􀆰 1  Leaf photosynthetic parameters across three
seasons
In each experimental seasonꎬ all photosyn ̄
thetic parameters showed significant differences
among light treatments (Table 1) . Both Pmax and
LSP followed the order LT70 > LT100 > LT40 . With
decreasing light intensityꎬ both Rd and LCP de ̄
creasedꎬ and AQY increased. Compared to high
light during the growing seasonꎬ Pmax increased
by 14􀆰38% - 44􀆰89% under moderate lightꎬ but
decreased by 27􀆰45% - 43􀆰26% under low light.
083 植 物 科 学 学 报 第 33卷 
Additionallyꎬ moderate light and low light treatments
increased AQY by 15􀆰56% - 40% and 35􀆰56% -
81􀆰82%ꎬ respectively.
2􀆰 2  Leaf fluorescence parameters across three
seasons
Leaf fluorescence parameters varied signifi ̄
cantly among light environments ( Fig􀆰2: A and
B) . Although Fo showed no significant difference
among light treatmentsꎬ Fmꎬ Fvꎬ Fm/ Foꎬ and
Fv / Fo all increased with decreasing light intensity
across seasons. No significant difference in Fv / Fm
was detected between the two shade treatmentsꎬ
Table 1  Photosynthetic parameters of Magnolia wufengensis seedlings under different light treatments
Parameter Treatment Spring Summer Autumn
Pmax
(μmol CO2􀅰m-2􀅰s-1)
Rd
(μmol CO2􀅰m-2􀅰s-1)
AQY
(μmol O2􀅰m-2􀅰s-1)
LCP
(μmol􀅰m-2􀅰s-1)
LSP
(μmol􀅰m-2􀅰s-1)
LT100 12.02 ± 3.73 b 13.10 ± 2.69 b 16.76 ± 3.97 b
LT70 15.77 ± 3.03 c 18.98 ± 2.56 c 19.17 ± 3.63 c
LT40 8.72 ± 2.81 a 9.24 ± 1.40 a 9.51 ± 2.26 a
LT100 0.59 ± 0.15 c 0.68 ± 0.16 c 0.52 ± 0.09 c
LT70 0.46 ± 0.14 b 0.51 ± 0.14 b 0.40 ± 0.08 b
LT40 0.31 ± 0.18 a 0.35 ± 0.15 a 0.33 ± 0.08 a
LT100 0.033 ± 0.011 a 0.035 ± 0.007 a 0.045 ± 0.005 a
LT70 0.041 ± 0.008 b 0.049 ± 0.003 b 0.052 ± 0.007 b
LT40 0.060 ± 0.004 c 0.061 ± 0.004 c 0.061 ± 0.002 c
LT100 43.80 ± 8.98 c 51.83 ± 10.84 c 33.72 ± 7.57 c
LT70 32.63 ± 5.85 b 43.79 ± 5.93 b 22.31 ± 5.42 b
LT40 20.58 ± 4.84 a 21.00 ± 2.70 a 9.66 ± 1.93 a
LT100 1346.66 ± 80.03 b 1401.51 ± 76.16 b 1669.38 ± 49.57 b
LT70 1613.12 ± 50.13 c 1833.39 ± 43.03 c 1898.76 ± 35.34 c
LT40 862.10 ± 43.04 a 878.24 ± 47.50 a 870.10 ± 27.06 a
Note: Different lowercase letters indicate significant differences (P < 0􀆰 05) among treatments. Pmax: Maximum net photosynthetic
rateꎻ Rd: Dark respiration rateꎻ AQY: Apparent quantum yieldꎻ LCP: Light compensation pointꎻ LSP: Light saturation point.
Fo1 Fo2 Fo3 Fm1 Fm2 Fm3 Fv1 Fv2 Fv3
0
500
1000
1500
2000
LT100 LT70 LT40
F Fm1 o1/ F Fm2 o2/ F Fm3 o3/ F Fv1 o1/ F Fv2 o2/ F Fv3 o3/ F Fv1 m1/ F Fv2 m2/ F Fv3 m3/
0
2
4
6
LT100 LT70 LT40
A
B
a a a
a a a
a a a
a
a
a
a a
a
a a
a
a a
a
a a a
b
b b
b
b b
b
b b
b
b b
b b b
b b b
c
c c
c
c c
c
c c
c c c
F
F
F
o,
m
a
nd
v
F
F
F
F
F
F
m
/
o,
v/
o
an
d
v/
m
Different lowercase letters indicate significant differences (P < 0􀆰 05) among treatments. Same below. Fo1ꎬ Fo2 and Fo3 are
initial fluorescence in springꎬ summer and autumnꎬ respectively. Fm1ꎬ Fm2 and Fm3 are maximal fluorescence in springꎬ
summer and autumnꎬ respectively. Fv1ꎬ Fv2 and Fv3 are variable fluorescence in springꎬ summer and autumnꎬ respectively.
Fig􀆰 2  Foꎬ Fm and Fvꎬ and Fm/ Foꎬ Fv / Fo and Fv / Fm of Magnolia wufengensis
seedlings under different light treatments
183  第 3期                    杨 杨等: 珍稀树种红花玉兰在华北地区的最适光环境(英文)
but both values were greater than those under full
sunlight. Compared to high light during the gro ̄
wing seasonꎬ Fv / Fm increased by 11􀆰11%-20%
and 11􀆰11%-25% under moderate light and low
lightꎬ respectively.
2􀆰 3  Chlorophyll content and specific leaf weight
in three seasons
Chlorophyll content increased and specific
leaf weight decreased with decreasing light inten ̄
sity in each experimental season (Fig􀆰3: A and B).
Compared to high light during the growing sea ̄
sonꎬ chlorophyll content increased by 21􀆰95% -
42􀆰09% and 57􀆰88% - 97􀆰77% under moderate
and low lightꎬ respectivelyꎬ and specific leaf weight
decreased by 8􀆰85%-20􀆰84% and 22􀆰81%-40􀆰84%
under moderate and low lightꎬ respectively.
2􀆰 4  Leaf morphological parameters
Leaf morphological parameters differed sig ̄
nificantly among treatments ( Fig􀆰 4 ) . With de ̄
creasing light levelꎬ leaf area and petiole angle
increasedꎬ but leaf thickness and leaf density de ̄
creased. Compared to full sunlightꎬ the moderate
shade treatment increased leaf area and petiole
angle by 29􀆰66% and 24􀆰9%ꎬ respectivelyꎬ and
decreased leaf thickness and leaf density by
11􀆰36% and 10%ꎬ respectivelyꎻ the heavy shade
treatment increased leaf area and petiole angle
by 82􀆰78% and 70􀆰7%ꎬ respectivelyꎬ and decrea ̄
sed leaf thickness and leaf density by 36􀆰36%
and 40%ꎬ respectively.
0
1
2
3
4
5
6
7
8
9
10
Spring Summer Autumn
LT100 LT70 LT40
0
10
20
30
40
50
60
70
80
90
100
Spring Summer Autumn
LT100 LT70 LT40
C
hl
or
op
hy
ll
co
nt
en
t (
m

g
)
-1
Sp
ec
ifi
c
le
af
w
ei
gh
t (

m
)
-2A B
a a
a
a
a
a
b b
b b
b
bc c c
c
c
c
Fig􀆰 3  Chlorophyll content and specific leaf weight of Magnolia wufengensis
seedlings under different light treatments
0
20
40
60
80
100
120
140
LT100 LT70 LT40
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
LT100 LT70 LT40
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
LT100 LT70 LT40
0
10
20
30
40
50
60
LT100 LT70 LT40
A B
C D
Le
af
a
re
a
(c
m
)2
Treatment
Le
af
th
ic
kn
es
s
(m
m
)
Treatment
Le
af
d
en
si
ty
(N
·c
m
)
-1
Treatment
Pe
tio
le
a
ng
le

)
Treatment
a
a
a
a
b
b
b
b
c
c
c
c
Fig􀆰 4  Leaf morphology of Magnolia wufengensis seedlings under different light treatments
283 植 物 科 学 学 报 第 33卷 
2􀆰 5  Growth and biomass parameters
All growth and biomass parameters reached
their maximum under moderate light condition
(Table 2). Compared to high lightꎬ seedling heightꎬ
basal diameterꎬ total biomassꎬ root biomass and
stem biomass increased by 24􀆰88%ꎬ 20􀆰3%ꎬ
26􀆰 34%ꎬ 12􀆰05% and 43􀆰5%ꎬ respectivelyꎬ under
moderate light. Under low lightꎬ in addition to an
increase in seedling height and stem biomass
ratio of 7􀆰38% and 41􀆰86%ꎬ respectivelyꎬ basal
diameterꎬ total biomassꎬ root biomassꎬ stem bio ̄
mass and root biomass ratio decreased by 33􀆰71%ꎬ
56􀆰19%ꎬ 67􀆰36%ꎬ 35􀆰23%ꎬ and 31􀆰 58%ꎬ respec ̄
tively. Neither root biomass ratio nor stem biomass
ratio showed significant differences between high
and moderate light conditions.
3  Discussion
The maximal value of Pmax was observed in
M. wufengensis grown under moderate light con ̄
ditions across the three seasons. Generallyꎬ light ̄
demanding plants exhibit significant capability to
modulate photosynthetic capacity to cope with
decreased light availability[21ꎬ 22] . This was well
exhibited in M. wufengensisꎬ which increased its
Pmax from low to moderate light. Howeverꎬ a sig ̄
nificant decrease in Pmax occurred from moderate
to high light. A response pattern of increasing
maximum photosynthetic rate with increasing light
up to intermediate light levelsꎬ followed by a de ̄
cline in Pmax at high light levelsꎬ has also been re ̄
ported for some shade ̄tolerant species[23-25] . A
lower Pmax was measured under low lightꎬ with a
significant decrease in Rd and LCPꎬ suggesting
that M. wufengensis can maintain a positive car ̄
bon balance in heavy shade[26] . The higher AQY
in lower light indicated that shaded leaves had
higher light ̄use efficiencyꎬ which is important for
seedling establishment and growth[27] . The LCP
of M. wufengensis seedlings under different light
levels during the growing season varied from
9􀆰66 to 51􀆰83 μmol􀅰m-2􀅰s-1ꎬ which lies within the
typical LCP values for sciophytes (LCP < 20 μmol􀅰
m-2􀅰s-1) and heliophytes (LCP > 50 μmol􀅰m-2􀅰
s-1) [28]ꎬ demonstrating adaptability in M. wufen ̄
gensis to a wide range of light levels.
In our studyꎬ the shade treatments appeared
to reduce the negative impacts of excessive sun ̄
light on the photosynthetic system. For exampleꎬ
maximum quantum efficiency (Fv / Fm) reached
its expected optimum value (0􀆰75-0􀆰85) [29] un ̄
der both shade environments. In contrastꎬ these
values always fell between 0􀆰64 and 0􀆰72 for the
seedlings in high lightꎬ indicating that the photo ̄
synthetic systems of seedlings under full sunlight
were unable to recover during the nighttime. Both
AQY and Fv / Fm values declined sharply under
high lightꎬ indicating that M. wufengensis seedlings
suffered photoinhibition under full sunlight[30-32] .
The variation in chloroplast composition in re ̄
sponse to varied light levels could lead to suc ̄
cessful acclimation of tree growth to different light
conditions[33] . Chlorophyll content would decline
when the trees were exposed to excess light due
Table 2  Growth and biomass parameters of Magnolia wufengensis seedlings under different light treatments
Parameter LT100 LT70 LT40
Seedling height (mm) 674.73 ± 36.98 a 842.60 ± 46.02 c 724.53 ± 33.43 b
Basal diameter (mm) 15.22 ± 2.54 b 18.31 ± 2.47 c 10.09 ± 1.98 a
Total biomass (g) 236.11 ± 6.50 b 298.29 ± 6.49 c 103.44 ± 4.48 a
Root biomass (g) 139.25 ± 3.46 b 156.03 ± 2.11 c 43.45 ± 3.37 a
Stem biomass (g) 94.18 ± 3.13 b 135.15 ± 2.50 c 61.00 ± 0.80 a
Root biomass ratio 0.57 ± 0.01 b 0.54 ± 0.01 b 0.39 ± 0.01 a
Stem biomass ratio 0.43 ± 0.01 b 0.46 ± 0.00 b 0.61 ± 0.01 a
383  第 3期                    杨 杨等: 珍稀树种红花玉兰在华北地区的最适光环境(英文)
to a breakdown of the structural integrity of the
chloroplasts[34] . The leaf chlorophyll content of M.
wufengensis seedlings increased with decreasing
light levelsꎬ which was perhaps because the
seedlings enhanced their light harvesting capaci ̄
ty under low light conditions by increasing chloro ̄
phyll content. Close positive correlations have
been observed between specific leaf weight and
light level[35] . Through decreased specific leaf
weightꎬ plants increase leaf area and enhance their
light harvesting capacity under low light condi ̄
tions[36]ꎬ which could be beneficial for increasing
carbon accumulation[37] . The specific leaf weight of
M. wufengensis seedlings declined with decreasing
light levelꎬ which could prevent photoinhibition un ̄
der higher irradiance and enhance the ability to
capture light under lower irradiance[38] .
The responses of the leaf morphological
traits to environmental changes represent a sur ̄
vival strategy of plants in varied environments[39] .
In generalꎬ leaves exposed to high light may suf ̄
fer from severe heatꎬ water and photoinhibition
stress[40] . Decreased leaf size can reduce the
boundary layer between the leaf and the atmos ̄
phereꎬ allowing high heat loss through convec ̄
tion and a low transpiration rateꎬ which are ne ̄
cessary to cool the leaves[41ꎬ 42] . On the other
handꎬ increased leaf size in response to low light
demonstrates the shade tolerance of plant spe ̄
cies[43] . In our studyꎬ leaf area increased with
decreasing light levelꎬ demonstrating that M.
wufengensis can modulate leaf area for self ̄pro ̄
tection under high light conditions and for light
capture under low light conditions. Similarlyꎬ the
response of leaf thickness to light level may also
reflect a high adaptability of M. wufengensis to ir ̄
radiance[44] . Some plant species can reduce leaf
injury resulting from exposure to strong light by
adjusting the petiole angle[45]ꎬ or enhancing the
degree of overlap of the leavesꎬ resulting in an
increase in shade[46] . The decreased petiole an ̄
gle and increased leaf density of M. wufengensis
seedlings with increasing light level demonstrated
their adaptation to strong light.
Both optimal seedling height and stem dia ̄
meter were observed in moderate lightꎬ which is
consistent with the conclusions from other studies
of enhanced seedling growth with appropriate
shading[47] . Under low lightꎬ M. wufengensis
seedlings showed an increase in seedling height
and decrease in stem diameterꎬ suggesting that
the seedlings tended to maximize their height to ̄
ward the lightꎬ at the expense of incrementing
stem diameter[48] . An appropriate shade level
promotes biomass accumulationꎬ but excessive
shade is harmful[49ꎬ 50] . Our results correspond to
this viewꎬ as 70% sunlight significantly promoted
both root and stem biomass accumulation. Plants
in light ̄limited environments often increase alloca ̄
tion to aboveground organs at the expense of be ̄
lowground organs[51-53]ꎬ in agreement with our
observation for M. wufengensis seedlings in 40%
sunlight. Howeverꎬ the differences under high
light conditions in biomass partitioning between
aboveground and belowground plant parts were
not observed in moderate lightꎬ which has also
been confirmed in other studies[54ꎬ 55] . These in ̄
consistencies could reflect species ̄specific re ̄
sponses in biomass partitioning to light condi ̄
tions. The degree of partitioning has been shown
to differ among species and may change as a
plant grows[52ꎬ 53ꎬ 56ꎬ 57] . Thusꎬ moderate shade
(70% sunlight) promoted growth and biomass in
M. wufengensis seedlingsꎬ but heavy shade
( 40% sunlight ) showed adverse effectsꎬ in
agreement with the negative effects of excessive
shade (25% and 10% sunlight) observed in M.
wufengensis seedlings previously[58] .
A relatively high degree of similarity in envi ̄
ronmental conditions between the original and in ̄
483 植 物 科 学 学 报 第 33卷 
troduced area is beneficial to the growth and sur ̄
vival of plant species[59ꎬ 60] . In the main growing
months of M. wufengensis seedlingsꎬ the CV ranges
of sunshine percentageꎬ sunshine durationꎬ air
temperature and relative humidity were 10􀆰81% -
55􀆰22%ꎬ 13􀆰18% - 55􀆰76%ꎬ 2􀆰65% - 11􀆰26%ꎬ
and 0􀆰91% - 33%ꎬ respectively ( Fig􀆰 1) . Thusꎬ
the 70% sunlight treatment in Beijing provided a
relatively ideal environment with similar ecological
factors to Wufeng (seedling origin)ꎬ which resul ̄
ted in better growth conditions for the seedlings
transplanted to this northern China environment.
Howeverꎬ we currently lack the scientific data to
support this hypothesis. Further research should
be performed on comparing the growth and
physiological characteristics of M. wufengensis
seedlings grown in southern and northern China.
In conclusionꎬ 70% sunlight was the opti ̄
mum light level for 1 ̄year ̄old M. wufengensis
seedlings grown in northern China. The poor
growth conditions of M. wufengensis seedlings
under full and 40% sunlight resulted from exces ̄
sive and insufficient light energyꎬ respectively.
For successful introduction to northern Chinaꎬ mi ̄
crosites at forest edges or gaps should be fa ̄
vored to provide an optimal light environment for
this endangered species.
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783  第 3期                    杨 杨等: 珍稀树种红花玉兰在华北地区的最适光环境(英文)