全 文 ：Journal of Forestry Research (2010) 21(4): 465−468
DOI 10.1007/s11676-010-0099-7





Persistent and advanced reddening of sweetgum leaves after major
veins severing

WANG Fei




Received: 2009-12-08; Accepted: 2010-01-26
© Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2010

Abstract: The effects of major veins severing on morphological and
physiological features of sweetgum (Liquidambar styraciflua L.) leaves
were investigated by observing leaf color change and measuring leaf
temperature, green/luminance (G/L) value of half-lobes, leaf stomata
conductance, and water content in Yamaguchi University, Japan. The
palmately veined leaves of sweetgum (Liquidambar styraciflua L.) were
found more sensitive to the major vein severing than that of other species.
Major veins severing resulted in serious water stresses, as indicated by
the persistent reddening and/or advanced reddening of local leaf, lower
leaf stomatal conductance, and higher leaf temperature, etc. Severed leaf
can be clearly divided into non-severed area, transitional area, and
stressed area, which the three areas have different colours and tempera-
ture. The major vein barrier can also be seen clearly. The persistent red-
dening and advanced reddening seem consistent with the phenomenon of
red crown top of some sweetgum trees and may have similar mechanism.
Keywords: advanced reddening; G/L value; leaf vein severing; persistent
reddening; red top crown; stomatal conductance; sweetgum; water stress


Introduction

Morphologies of plants or trees are usually the equilibrium be-
tween genetic property and environmental effects. The catastro-
phically environmental extremes occasionally happen in field, it
can generate direct damage to plants (Baig and Tranquillini 1980;
Chiba 1994; Yamamoto et al. 1996), also induce plant protective
responses (Alexieva et al. 2001; Liu et al. 2007). Some tree spe-
cies or individuals at special stages or status are especially sensi-
tive to environmental extremes such as excessive irradiation.
Excessive irradiation energy is a relative concept (Fitter and Hay

The online version is available at http://www.springerlink.com
WANG Fei ( )
Shandong Forestry Research Academy, 250014, Jinan, China
E-mail: wf-126@126.com
Responsible editor: Hu Yanbo

2002). For stressed plants or trees, even the scatter light might be
occasionally excessive to them. Plants or trees usually protect
against excessive photo energy acceptation through heat trans-
formation (Donald 2001; Fitter and Hay 2002) and anthocyanin
accumulation in leaves (Chalker-Scott 1999). Leaf transpiration
is an important procedure of excessive heat energy dissipation
(Clements 1934; Gates 1968; Fitter and Hay 2002). Stomatal
status plays an important role in leaf transpiration. Anthocynin
content in a leaf is a negative regulation factor of leaf stomatal
conductance (Farooq et al. 2009), thus anthocyanin accumulation
might induce protective response to the excessive light or heat
energy.
Many plant species with leaf major vein severing were re-
ported to survive without apparent symptom (Wylie 1927; 1930).
Conversely it is also reported that the major vein severing can
induce leaf death or dysfunction of water transportation in leaf
lamina for some tree species (Sack et al. 2003). Expanding
leaves on new shoots of many tree species appeared red or
non-green colors, which are often called “delayed greening”
(Lambers et al. 1998; Numata et al. 2004). The expanding or
fully expanded sweetgum (Liquidambar styraciflua L.) leaves
with the characteristic of delayed greening often appeared per-
sistent red or purplish red color at stressed part after severing the
major veins. It is named as the “persistent reddening” in this
paper. In contrast, the chlorophyll mature leaves early becoming
red or purplish red at stressed part after severing the major veins
is called “advanced reddening” in the study. The appearance of
red top crown, persistent reddening and advanced reddening of
sweetgum leaves seems to be an instance of transpiration cooling
failure. In some extent, an increase in leaf anthocyanin content is
considered as the results of inter-relation of many environmental
factors such as photoperiod and drought stress (Alexieva et al.
2001; Yang et al. 2005; Farooq et al. 2009). According to the
measurement of leaf stomatal conductance, thermo image tem-
perature, water content measurement and RGB image analysis,
the present study inferred that the sweetgum leaves with major
veins severed may be one of the examples special sensitive to the
excessive irradiation energy and water stress.

ORIGINAL PAPER
Journal of Forestry Research (2010) 21(4): 465−468

466

Materials and methods

The study was conducted in Yamaguchi University, Japan. The
observed sweetgum trees were several new sprouting plants from
stem cutting stocks, one old stem sprouting plant, and some
street trees in Yamaguchi City, Japan. During the study, leaf
laminas of sweetgum usually were divided into 10 half-lobes in
responding to their special palmate venation and in the order
against hour hand. If there are seven lobes on the leaf, the small-
est two lobes at leaf base are incorporated into half-lobe 1 or 10.
Analysis of RGB images, thermo images and water content of
leaf laminas were conducted by using these half-lobes as basic
unit.
Leaf temperature was determined by using thermography
(Jones 1999; Jones et al. 2002; Jones and Leinonen 2003; Prytz
et al. 2003). In this study, a NEC TH7100 thermal infrared (8−14
µm) camera, with the temperature measuring range from –20°C
to 100°C and minimum sensible temperature 0.06°C, was
hand-held about 50 cm above the objective leaves and then fo-
cused to clear. Thermo image temperature was measured by
using the active heat method in field under direct sunshine heat-
ing from 8:00 to 10:00 a.m. Smoothly expanded leaves were
selected to take the thermo images.
Water content of the leaf half-lobes, directly cut from attached
leaves and taken back to lab with plastic bags, was measured by
rapid weighing method in room temperature with an electronic
balance (Shimadzu Auw220, 1/10000 g) on Sep. 21, 2009. The
water content of non-severed area (N), transitional area (T) and
stressed area (S) was the average value of half-lobes in these
areas.
The Green/Luminance (G/L) value of half-lobes is a propor-
tion between green and luminance value from RGB images. It
was obtained with image analysis method (Wang et al. 2008,
2009a, 2009b) to describe the persistent reddening and advanced
reddening of leaves. Images were scanned with a scanner (Canon
D125u2) or taken with a CCD camera (Canon IXY 6.0). The
photo making (PM) and vein severing (VS) date were noted at
figure caption, respectively.
Leaf stomata conductance from different areas on the same
leaf was measured with a SC-1 leaf porometer in clear field en-
vironment from 9:00 to 11:00 a.m. on Sep. 10, 2009. During the
measurement, the sensor clip was fixed on non-severed, transi-
tional, and stressed half-lobes of attached leaves and automati-
cally measured.


Results and discussion

By observations, juvenile leaves from sweetgum showed varied
coloration and were green or light green during leaf expansion in
early April in Yamaguchi. However, some of sweetgum trees in
growing season presented delayed greening leaves on top of the
crown or twigs, especially the trees growing at constricted sites
and/or during the extreme hot/dry period (Fig. 1a). As the leaves
grew, the delayed greening leaves became green gradually and
usually maintained two apical red leaves on shoots as reported by
Hughes et al. (2007). The persistent reddening of expanding
leaves locally appeared on leaves by carefully designed experi-
ment in this study. Sweetgum leaves usually possess five or
seven lobes on a leaf lamina with one main vein on each lobe
(Fig. 1a). Their major-veins and sub-major-veins terminate at the
end of leaf edge. There is no anastomose among major veins or
sub-major veins, and only local minor veins anastomose at the
joint part between two lobes (Fig. 1b). If the major vein in one
lobe is severed, the leaf lamina of the lobe would have to obtain
water only from the nearest non-severed lobes via the minor vein
joints. If more than one adjacent major vein is severed, there is
always a part far from theses minor vein joints. Therefore, it is
easy to induce the local leaf lamina far from these joints into
water imbalance by major vein basally severing, for instance, the
II, III and IV major veins severing (Fig. 1a, 1b), especially for
the rapid expanding younger leaves. As the stress continues,
persistent reddening occurred (Fig. 1b-S, 1c-S) at the local area.
Severed leaf can be clearly divided into non-severed area (Fig.
1b-N, 1c-N), transitional area (Fig. 1b-T, 1c-T), and stressed area
(Fig. 1b-S, 1c-S).
Fig. 1 A persistent
reddening juvenile
sweetgum leaf with
five major veins
signed with I, II, III,
IV and V, respec-
tively. (a, photo
making (PM) and
vein severing (VS)
on Jun. 1). The leaf is
severed at the base of
II, III and IV major
veins with mark
“ ”and divided into ━
10 half-lobes in the
order against hour
hand. The same leaf (b, PM on Aug. 1) with the persistent reddening area
at stressed part (S, half-lobes of 4,5,6 and 7), with greened area at
non-severed part (N, half lobs of 1,2,9 and 10) and the transitional area
between them (T, half-lobes of 3 and 8); another persistent reddening
stem-developed juvenile leaf (c, VS on Jun. 1 and PM on Aug. 1) and its
thermograph (d, PM on Aug. 18). The persistent reddening test had been
duplicated more than six leaves and these two are typical examples.

The non-severed area usually turned to green color as the leaf
grew, while the stressed area maintained red color or purplish red
color. The transitional area showed the intermediate coloration
and more greening near the minor vein joint (Fig. 1b). The per-
sistent reddening even persisted in all of the growing season. It
was observed that the major veins of II and IV became the de-
marcation line between persistent reddening area and greened
area (Fig. 1b, 1c) for the leaves of II, III and IV major veins sev-
ered. This means they are the main barriers to interrupt water
transporting into the half-lobes next to the severed veins. There-
fore, they are important lines dividing the stressed area, transi-
Journal of Forestry Research (2010) 21(4): 465−468

467
tional area and non-severed area. By thermograph taking, a high
temperature area was observed at the farthest part from
non-severed-area (Fig. 1d). From the thermo-image, the major
vein barrier and the difference among non-severed area, transi-
tional area and stressed area were also seen clearly. However,
this difference was not observed on the normal leaves. It implies
significant difference of leaf temperature before and after leaf
severing.
Using the same major vein severing method, partially ad-
vanced reddening on chlorophyll mature leaves have also been
induced (Fig. 2). It is clear that the advanced reddening from
severed leaf (Fig. 2b) appeared significantly different color from
its normal status before severing (Fig. 2a). While it was similar
to that of severed leaves in persistent reddening process (Fig. 1b,
1c), which showed red color in the stressed area. The major vein
barrier from vein II and IV also appeared on the leaves of II, III
and IV major vein severed in the advanced reddening process. In
the situation of major veins III and IV severed, the major vein
barriers also could be seen and showed slight leaf advanced red-
dening (Fig. 2c-S) at stressed area. In fact, the difference of leaf
stomata conductance (Fig. 2c-L) and G/L value (Fig. 2c-G) from
RGB images have been measured among the non-severed area
(Fig. 2c-N), transitional area (Fig. 2c-T) and stressed area (Fig.
2c-S). The leaf similarly showed the high temperature area (Fig.
2d-S), transitional temperature area (Fig. 2d-T) and
low-temperature area (Fig. 2d-N) as well as the major vein bar-
rier from veins III and IV 18 min after III and IV major veins
severed. It is clear that the high temperature and low leaf stomata
conductance (Fig. 2c-L) occurred in stressed area, which was
caused by the termination of direct water supply (Fig. 2b-w).
This tendency not only appeared on sunlit leaves but also oc-
curred on shaded leaves (Fig. 2e, 2f). It also showed partially
advanced reddening in stressed area on RGB image (Fig. 2e) and
high temperature area in thermo-image (Fig. 2f), although the
relative area was smaller than that appeared on the leaves shown
in Fig. 2b and it took a longer period for the symptom occurrence.
Both the persistent reddening and advanced reddening of the
major veins severed leaves were tree specific or age specific. Fig.
2g presented an entirely reddening leaf on the main stem of a
sensitive tree to abiotic or biotic stimulation, whose leaves are
usually small, thin and light colored. The phenomenon of major
vein barrier could still be seen on this leaf. On the other hand, a
recently pruned tree with large, thick and deep green colored
leaves maintained greening (Fig. 2h). By measurement, the dif-
ference of water content among the non-severed, transitional and
stressed area was very small even no statistically meaningful
difference. It matched with the phenomenon that leaves on
pruned trees often turn yellow but not red or purplish red in the
late autumn.
Therefore, acute reduction of water supply after major-vein
severed, especially for multi-vein-severing, caused the leaf sto-
mata close as indicated by the immediate reduction of leaf sto-
mata conductance. The relative high temperature on stressed area
of leaf lamina should be the direct result of transpiration cooling
failure caused by stomata closure and the water content reduction.
The evident temperature limit from major vein indicates that
inversely transport water into the area far from water source is
difficult. This kind of barrier properly matches the limit line
between persistent reddening area and greened area of severed
sweetgum leaves. It indirectly suggests that there is a potential to
pre-detect the water stress, persist-reddening and pre-reddening
status of these sweetgum leaves by using thermography as pre-
vious researches (Chaerle and Van Der Straeten 2000; Grant et al.
2006). The persistent reddening and advanced reddening of
sweetgum leaves occurred in the process of persistent water,
light and heat energy imbalance after leaf severing. The photo-
protection mechanism in the sweetgum leaves triggers the an-
thocyanin production and causes the leaf persistent reddening
and advanced reddening.

Fig. 2 A normal chloro-
phyll mature leaf (a, PM
and VS on Aug. 9) and the
stressed area advanced
reddening for the same leaf
after II, III and IV major
veins severed (b, PM on
Sep. 21) with the severed
position marked with “━”
and water content (w) at
non-severed area (N), tran-
sitional area (T) and
stressed area (S); A slightly
advanced reddening leaf at
the stressed area (c-S) after
III and IV major veins
severed (c, VS on Jul. 6
and PM on Sep.6), in which
the number next to “L” is
the leaf stomata conduc-
tance value and next to “G”
is the ratio between green
and luminance values from
RGB image; The thermo-
graph (d, VS on Aug.11and PM 18 minute after VS) of a III and IV ma-
jor veins severed leaf with different image temperature (t); The thermo-
graph (f, PM on Aug.18) and the RGB image (e, VS on Jun.1 and PM on
Aug.18) of a shade leaf; an entire red leaf (g, VS on Aug. 9 and PM on
Sep.21) with advanced reddening area and an entire green leaf (h, VS on
Jul. 5 and PM on Sep. 4) without advanced reddening area. Leaves in e, f,
g and h are II, III and IV major veins severed. The advanced reddening
test had been duplicated more than twenty times and here are some typi-
cal examples.

Significantly changed characteristics of climate appeared in
Yamaguchi, Japan from 2006 to 2008 accompanying with some
extreme weather events, such as extreme strong wind mingled
with less rainfall during hit by typhoon number 13 in 2006
(T0613) and persistent high temperature and drought in 2007
(Wang et al. 2009b). Prolonged vegetative growth of sweetgum
trees benefited from the abundant precipitation during the grow-
ing season in 2006 and almost showed no red top crown (Fig. 3a),
Journal of Forestry Research (2010) 21(4): 465−468

468
although the T0613, characterized by strong wind and less rain
accompanying with more than one month of no rain period,
made the crown of sweetgum trees asymmetrically leaf scorching
from windward to leeward. During 2007 and 2008, the persistent
extreme weather of high temperature and less rainfall, especially
during the growing season (Fig. 3b), induced the sweetgum trees
into asymmetrically advanced discoloration from top to base of
their crowns (Fig. 3a) in fall. By integration, the red top crown
phenomenon was consistent with the precipitation during the
growing season (Fig. 3b). It also indicates that the heavy rainfall
in 2006 provided sufficient water supply to soil system, met the
normal transpiration cooler requirement of the trees and reduced
the impact from summer heat weave. The persistent reddening
and advanced reddening seem consistent with the phenomenon
of red crown top of some sweetgum trees and may have similar
mechanism.



Fig. 3 The observation results of red crown top of sweetgum trees in
mid-October in 2006, 2007 and 2008 (a), in which single sweet gum
trees along the high way or street in Yamaguchi were visually scaled
into classes of entire crown green (Green), reddening crown <1/2
(<1/2 Red) and reddening crown >1/2 (>1/2 Red); the proportion
between green crowns and reddening crowns (b, histogram), and the
precipitation from April to September (b, ○─○). The precipitation data
was obtained from Automated Meteorological Data Acquisition System
of Japan.

Acknowledgements
The gratitude will be expressed to the Environmental Ecological
lab. of Agricultural Faulty in Yamaguchi University, Japan for
providing the experimental instruments.


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