全 文 ：井冈山大学学报(自然科学版)

96
文章编号：1674-8085(2012)03-0096-06

EFFECTS OF HAND POLLINATION ON FRUIT AND
SEED SET IN THE ENDANGERED PLANT
DISANTHUS CERCIDIFOLIUS VAR. LONGIPES

* XIAO Yi-an1, 2, LI Xiao-hong1, 2, ZENG Jian-jun1, 2, HU Wen-hai1, 2, HU Xue-hua1, 2, ZHOU Bing1, 2
(1. School of Life Sciences, Jinggangshan University, Ji’an, Jiangxi 343009, China;
2. The Key Laboratory for Biodiversity Science and Ecological Engineering of Jiangxi Province, Ji’an, Jiangxi 343009, China)

Abstract：Pollen and resource availability are main factors that affect the reproductive success of flowering plants. Hand
pollination experiment was conducted to investigate the patterns of female reproduction in the endangered plant
Disanthus cercidifolius Maxim. var. longipes H.T.Chang (Hamamelidaceae). The results showed across-pollination
induced significant differences between early-blooming flowers and late-blooming flowers so far as fruit-set and seed-set
per plant concerned, and significantly increased the seed weight per plant and per fruit respectively. But self-pollination
significantly decreased the fruit-set and seed-set. A trade-off between the number of seeds and weight per seed exists
under hand-pollination but not under nature pollination.
Keywords: pollen specificity; fruit set; seed set; trade-off; Disanthus cercidifolius Maxim. var. longipes H.T.Chang
CLC number:O945.6+5 Document code:A DOI:10.3969/j.issn.1674-8085.2012.03.022


人工授粉对濒危植物长柄双花木结果率和结籽率的影响
*
肖宜安 1, 2，李晓红 1, 2，曾建军 1, 2，胡文海 1, 2，胡雪华 1, 2，周 兵 1, 2
(1.井冈山大学生命科学学院，江西，吉安 343009; 2. 江西省生物多样性与生态工程重点实验室，江西，吉安 343009)
摘 要：花粉和资源有效性是影响有花植物生殖成功的关键因素。本研究探讨了人工授粉对濒危植物长柄
双花木雌性生殖模式，尤其是对其结果率、结籽率以及果实和种子重量的影响。研究结果表明：异花授粉
提高了长柄双花木的结果率和结籽率，且前期花的结果率、结籽率均显著高于后期花的；而自花授粉不但
显著降低了其结果率和结籽率，同时在前期和后期花的结果率、结籽率之间均无显著差异。异花授粉显著
提高了单株植物种子重量及单果种子重量，而自花授粉则显著降低了它们的重量。异花授粉后前期花的果
实重量及单果种子重量均显著高于后期花的。同时，异花人工授粉后种子数量和单粒种子重量之间存在权
第 33卷第 3期 Vol.33 No.3 井冈山大学学报(自然科学版)
2012年 5 月 May. 2012 Journal of Jinggangshan University (Natural Science) 96


Received date：2011-03-18; modified date:2011-04-11
Foundation item：Natural Science Foundation of China (30560025);Program for New Century Excellent Talents in University in China (No.NCET-07-0385)
Biographies: XIAO Yi-an (1968-)，Male，Yongfeng, Jiangxi, PhD, Professor, Master Instructor,Research interesting is plant ecology and conservation biology
(Email: iyanxiao@yahoo.com.cn)
LI Xiao-hong (1970-)，Female，Jishui, Jiangxi, Bachelor, Senior Experimentalist,Research interesting is plant ecology and plant physiology
(Email: lxhxya@yahoo.com.cn)
ZENG Jian-jun (1974-)，Female，Wanan, Jiangxi,PhD, Associate Professor, Research interesting is plant ecology and plant physiology
(Email: jianjunzeng@139.com)
HU Wen-hai (1973-)，Male，Jian, Jiangxi,PhD, Professor, Master Instructor, Research interesting is plant ecology and plant physiology
(Email: huwenhaicy@yahoo.com.cn)
HU Xue-hua (1977-)，Female，Xiajiang, Jiangxi, Master, Experimentalist,Research interesting is plant ecology(Email: huxuehua1210@126.com)
ZHOU Bing (1977-)，Male，Huangmei, Hubei,PhD, Associate Professor,Research interesting is plant ecology and conservation biology
(Email: zhoubing113@126.com.)
井冈山大学学报(自然科学版) 97
衡，而自然授粉条件下则不存在这种权衡。
关键词：花粉特异性；结果率；结籽率；权衡；长柄双花木

Plants show great diversity in their patterns of
sexual expression [1], and over the past decades many
effort has been devoted to understanding of this
diversity [1-2]. On the other hand, often only a small
proportion of flowers become mature fruits, and in
which only an average of one to five flowers can
produce seeds. For instance, 50~85% of ovules in
mature fruits can produce seeds, such as plants of
Geranium sylvaticum and G. sylvaticum [3-4]. The
proportion of flowers that produce fruits, namely fruit
level, is highly relevant to a plant’s reproductive
success [5]. “Excess” flowers seem to have little
contribution to fruit and seed-set [6-7]. This
phenomenum appears usually because of initial
overproduction of flowers and later reduction of the
fruit yield due to limited resource capacity for fruit
maturation [6]. Many ecological studies suggested that,
in flowering plants, low seed-set can result from
limitation of resource availability [8-10], low pollen
source [11-12], pollen and/or pollinator limitation [13-16],
low flower or seed predation [17], adverse climatic
conditions, and/or genetic factors [18-19]. During last
two decades, a surge of studies has been devoted to
assessing the relative importance of those factors.
However, most of the previous discussions of pollen
and resource limitations have focused mainly on fruit
set, and little attention has been paid to seed set, seed
biomass per plant [15, 20].
The small tree Disanthus cercidifolius Maxim.
var. longipes H.T.Chang (Hamamelidaceae), like
many other plant species [5], produce many flowers,
but only few flowers can produce fruits. It is
hypothesized here that pollen and resource affect the
ratio of flower to fruit, and a trade-off between the
number of seeds and weight per seed exists. We tested
this hypothesis in a hand pollination experiments.
1 Materials and Methods
1.1 Study area
This study was done on the south-facing slope of
Caijiatian (26°46′N, 113°53′E) at 810 m
elevation in Jinggangshan of Jiangxi province of
China, which is in the middle of Luoxiao Mountains
region where vegetation is the natural secondary forest
or shrub after the subtropical evergreen broad-leaved
forest was destroyed [21]. The plots were dominated by
Disanthus cercidifolius Maxim. var. longipes
H.T.Chang (Hamamelidaceae), Indocamus latifolius,
Hydrangea davidii, etc. And D. cercidifolius lies in the
canopy layer.
The soil in this area is mainly made of red brown
soil. Its average annual temperature is 15.1℃, the
average temperature is 3.9℃ in January, the mean
temperature of July is 23.7℃ , the most extreme
low-temperature is -13.4℃, and the most extreme
high temperature is 35.2℃. The annual precipitation is
1, 872 mm, the frost-free period is 247 to 263 days. It
is cool, rainy, and is of heavy clouds and high
humidity.
1.2 Study species
Disanthus cercidifolius Maxim. var. longipes
H.T.Chang (Hamamelidaceae) (hereafter, it is referred
to as its genus name, Disanthus), a plant species that
only occurs in a few counties in Hunan, Jiangxi and
Zhejiang Provinces of China and with relatively small
numbers of plants. Therefore it has been ranked as a
2nd Class endangered species for conservation in
China [22-23]. Disanthus is a small tree (up to 3m in
height), has two inflorescences growing in opposite
directions in the axil at the same node. Each
inflorescence has two opposite bisexual flowers
without pedicels. The flower is of 1.0cm to 2.0cm in
diameter and sub rotund capsule of about 1.5cm in
diameter and lasts 6 to 7 days [24]. The average total
ouvals are 12 per flower. In this area, the flowering
period extends from September to November, and the
flowering span of the individuals is about 49~55 days.
The mature fruits appear in the July and August in the
next year.
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1.3 Hand-pollination experiment
We employed hand pollination experiments in
addition to assessing whether the amounts and source
of pollen reaching stigmas constrain fruit and seed set.
In September, both in 2002 and 2003, we
randomly selected 90 flowering plants of Disanthus
with similar initiative situation in the wild population
in the study area. About 520 inflorescences (1040
flowers) on 30 reproductive branches were marked on
each plant, respectively. 30 plants were hand
pollinated early-blooming flowers on 16~18
September, and half of these plants were pollinated
with cross-pollen, and the others were pollinated with
self-pollen. 30 plants were hand pollinated
late-blooming flowers on 6~8 October, and half of
these plants were pollinated with cross-pollen, and the
others were pollinated with self-pollen. The other 30
plants were natural pollination as control. In this study,
the first 50% of flowers to open on a plant were
identified as the “early blooming flowers”, and the
late 50% as “late blooming flowers”.
We collected all of mature fruits on each marked
branch and counted the number of seeds in each fruit.
The dry weight of each fruit and seed was weighted
respectively. And the parameters in each treatment as
follows were calculated: fruit set, seed set, seed dry
weight per plant, number of fruit per plant (only the
marked branches), number of seed per plant and per
fruit. The data were analyzed using one-way ANOVA
followed by Tukey’s HSD tests to investigate the
differences among the pollen pollination treatments.
1.4 Data analysis
The data were analyzed using two one-way
ANOVA followed by Tukey’s HSD tests to investigate
the differences among the flower removal treatments.
2 Results
2.1 Effects of pollen source on fruit-set and
seed-set
In the year 2002, cross-pollination increased
fruit-set (Fig.1) and seed-set per plant not only in
early-blooming flowers (hand pollinated flowers were
(40.75±3.269)% and (37.08±1.313)% respectively,
controls were(5.73±0.528)%and (13.6±0.605)%, but
also in late-blooming flowers(hand pollinated flowers
are(15.44±3.119)%and(20.5±0.798) %respectively,
controls were (2.58±0.531)% and(6.70±0.425)%. In
the 2nd year, the average fruit-set from cross-
pollination was 53.44%, which was found to be
significantly higher than that of control. There were
significant differences between early-blooming
flowers and late-blooming flowers so far as fruit-set
and seed-set per plant concerned. But the
self-pollination significantly decreased the fruit-set
and seed-set (see Fig.1), and there was no significant
difference between early-blooming flowers and
late-blooming flowers.

Fig.1 Effects of pollen source on fruit-set and seed-set per
plant in 2002 and 2003. (A, B) Fruit set per plant. Data shows
means ± SE for all plants in each treatment. (C, D) Seed set per
fruit, data show means ± SE for all fruits in each treatment.
Symbols above each subfigure show significance levels of the
F test among levels of each factor in an ANOVA. N.S. = not
significant. * P < 0.05, ** P < 0.01.
2.2 Effects of pollen source on weight of mature
seeds
Cross-pollination also significantly increased the
seed weight per plant and per fruit respectively (Fig.2).
There were significant differences between
early-blooming and late-blooming flowers in seed
weight per plant and seed weight per fruit.
Self-pollination significantly decreased the seed
weight per plant and per fruit. However, there was no
significant difference between early-blooming and
late-blooming flowers.
井冈山大学学报(自然科学版) 99

Fig.2 Effects of pollen source on weight of mature seeds per
plant and per fruit in 2002 and 2003. (A, B) Weight of mature
seeds per plant, data show means ± SE for all plants in each
treatment. (C, D) Weight of mature seeds per fruit, data show
means ± SE for all fruits in each treatment. Symbols above
each subfigure show significance levels of the F test among
levels of each factor in an ANOVA. N.S. = not significant.
* P < 0.05, ** P < 0.01.
3 Discussion
Willson and Rathcke [25] argued that the excess
hermaphroditic flower production usually attributed to
selection, acting through male function [27](Burd,
1998). Most of the previous researches on pollen and
resource limitations have focused mainly on fruit set;
little attention was paid to seed set, biomass of seed
per plant. It was interpreted as that the levels of
pollination were not affected by the number of flowers
produced within the same season, although elevated
seed production can cost a plant or population in terms
of flower production in future years. However this
argument depends on the types of inflorescence [15, 20].
3.1 Pollen specificity and resource limitation
Data collected from present investigation showed
a considerable significant effect of pollen specificity
on overall fruit set and seed set. It was also observed
in the present study that the source of pollen
significantly affected the fruit-set[26].The selfing
lowered fruit-set but crossing did not. This indicates
the existence of strong self-incompatibility mechanisms
in Disanthus. Many studies also have showed the
existence of strong self-incompatibility [27-29],and if
there is a complicated self-i may even become a
stronger constraint for fruit production [30]
compatibility system, self-pollination would have lead
to pollen specificity [27, 31], and pollen specificity. The
fruit and seed-set of Disanthus observed in the current
study was very low [26], which suggesting that the
self-incompatibility mechanism is functional, but of
course not absolute. In Disanthus, after flowering, the
selfed-pollen may cover the stigmas, so the
cross-pollen cannot disperse on it. So most proportion
of stigma would not have received enough crossed
pollen to have fruit-set and seed-set.
In the 2nd years where it was observed that
Disanthus plants were frequently visited by few
insects, and in fact the efficiency of wind pollination
was very low. Pollen quantity may be a limiting factor
if pollinators are scarce or inefficient [32-34]. The results
of hand-pollination indicate the evidence of pollen
specificity and; pollen reaches stigmas, germinates,
and pollen tube growth occurs. It was found to be the
source and not the quantity of pollen grains that limits
the fruit-set and seed-set in our study in the 2nd years.
Some studies showed that the pollen limitation is
irrelevant to overall reproductive allocation and sex
allocation in density-dependent populations.
Increasing the extent of pollen limitation will lead to
more resource allocated to ovule production,
amplifying the effect of pollen limitation[35].According
to Haig and Westoby’s [36] model, a chronic pollen
limitation situation should favor traits that either
increase pollen receipt or decrease the dependence on
pollinators for pollen receipt. However, some data also
showed that pollen limitation may not be spatially
constant, even within the same population [37]. In the
present study, hand-pollination increased the fruit-set
in Disanthus, and the validity of pollen would strictly
limit the fruit-set. That indicated the excess flowers
would act as male organs and pollen donors [7, 38].
3.2 Trade-offs between weight per seed and
number of seed per fruit
There did not exist trade-off between the weight
per seed and number of seed per fruit with nature
pollination (Fig.3A), but after hand-pollination with
across pollen, the trade-offs between them existed
(Fig.3B). After hand-pollinating, the fruit-set and
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seed-set were significantly increasing (Fig.1A, B). But
the resources which the plant can provide to the fruits
or seeds in it are limited, so that, with the seeds
increasing, the trade-off would exist between the
weight per seed and the number of seed per fruit.
However, the resource which the plant provide were
enough to the seeds need under nature pollination, so
that the weight per seed may correspondingly
stabilization, and there was no correlation between the
weight per seed and number of seed per fruit.

Fig.3 Effects of pollen source on the trade-off between
number of per fruit and weight per seed. A and B, are natural
pollination and hand-pollination with across pollen,
respectively.
Acknowledgements: We express our appreciation
to the National Natural Science Foundation of China
(No 30560025, 31060069) and the Program for New
Century Excellent Talents in University of China (No
NCET-07-0385).
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