研究准噶尔无叶豆(Eremosparton songoricum) 6个居群间果实和种子特性及种子萌发差异, 以揭示异质生境下准噶尔无叶豆果实和种子的生态适应机制。结果显示: 居群间准噶尔无叶豆的植株距离(F = 2.34, p = 0.03)和植株冠幅(F = 8.49, p < 0.01)存在显著差异, 沙漠北缘E、F居群和沙漠腹地C居群(受人类干扰剧烈)的植株距离和植株冠幅高于沙漠腹地A、B、D居群; 居群间准噶尔无叶豆果实和种子的长度、宽度、厚度、重量存在显著差异, 居群E、F和C的大部分参数显著高于其他沙漠腹地居群; 居群间果实多子性(F = 6.96, p < 0.01)也存在显著差异, 居群C的果实多子性最高((32.50 ± 4.79)%); 萌发结果表明, 居群间新鲜的成熟种子萌发不存在显著差异, 且萌发率都低于15%; 所有居群的大部分种子都存在物理性休眠现象, 人为划破种皮能显著提高种子萌发率, 但在低温(15/5 ℃)条件下, 所有居群的种子萌发率都较低, 说明低温抑制了种子萌发; 经人为划破种皮解除物理休眠后, 种子的休眠没有完全释放, 居群C、E和F (大种子居群)的种子萌发率显著高于居群A、B和D (小种子居群) (F = 30.77, p < 0.01), 说明准噶尔无叶豆种子不仅存在物理性休眠现象, 也可能存在生理休眠现象。不同程度的种子复合休眠可能是准噶尔无叶豆不同居群适应古尔班通古特沙漠的重要生存策略。
Aims Eremosparton songoricum is a rare and endangered endemic species in Central Asia. In China, it occurs in severely wind-eroded mobile and semi-mobile sand dunes of the Gurbantünggüt Desert. It has low fruit set, low seed set and rare seedling establishment. Our objectives were to determine the characteristics of populations, i.e., the variation of fruit or seed traits and seed germination among populations, to explain mechanisms of ecological adaptations of E. songoricum in different heterogeneous environments. Methods We determined the density and distance of plants and differences of shape, mass and proportion of multi-seed in six populations. Temperatures simulating those in the natural habitat of E. songoricum were used to determine the type of seed dormancy. Important findings The distance (F = 2.34, p = 0.03) and crown size (F = 8.49, p < 0.01) of plants were significantly different among populations and were highest in site C that was severely disturbed by humans. The distance and crown size located in the northeastern Gurbantünggüt Desert with abundant soil moisture (E and F) were higher than populations located in the hinterland of desert (A, B, D) except population C. The characteristics of fruit and seed (length, width, thickness and mass of fruits and seeds) in the populations were significantly different but seed length and width were not. The majority of traits values were higher in populations E, F and C. The proportion of multi-seed per fruit was significantly different (F = 6.96, p < 0.01) and was highest in population C (32.50% ± 4.79%). Freshly matured E. songoricum seeds were dormant since germination percentages were <15% in all the tested temperature regimes in the populations. Scarified seeds germinated to a significantly higher percentage than non-scarified ones in all temperature regimes, indicating freshly matured E. songoricum seeds were physically dormant. A significantly lower germination percentage was recorded at 15/5 °C than at the higher-temperature regimes, indicating that low temperature inhibited seed germination. Large-seeded populations (C, E and F) had higher germination percentages (<70%) than small-seeded populations (A, B and D; <50%) after scarified treatments (F = 30.77, p < 0.01), indicating that seeds from all populations had physical and physiology dormancy (PY + PD). The varying degree of PY + PD of E. songoricum seeds in different populations may be an important survival strategy for E. songoricum in the heterogeneous environments in the Gurbantünggüt Desert.
全 文 :植物生态学报 2012, 36 (8): 802–811 doi: 10.3724/SP.J.1258.2012.00802
Chinese Journal of Plant Ecology http://www.plant-ecology.com
——————————————————
收稿日期Received: 2011-12-09 接受日期Accepted: 2012-04-24
* 通讯作者Author for correspondence (E-mail: zhangdy@ms.xjb.ac.cn)
不同居群准噶尔无叶豆果实和种子特性及种子萌
发差异
刘会良1,2 张永宽1,2 张道远1* 尹林克1 张元明1
1中国科学院干旱区生物地理与生物资源重点实验室, 中国科学院新疆生态与地理研究所, 乌鲁木齐 830011; 2中国科学院研究生院, 北京 100049
摘 要 研究准噶尔无叶豆(Eremosparton songoricum) 6个居群间果实和种子特性及种子萌发差异, 以揭示异质生境下准噶
尔无叶豆果实和种子的生态适应机制。结果显示: 居群间准噶尔无叶豆的植株距离(F = 2.34, p = 0.03)和植株冠幅(F = 8.49,
p < 0.01)存在显著差异, 沙漠北缘E、F居群和沙漠腹地C居群(受人类干扰剧烈)的植株距离和植株冠幅高于沙漠腹地A、B、D
居群; 居群间准噶尔无叶豆果实和种子的长度、宽度、厚度、重量存在显著差异, 居群E、F和C的大部分参数显著高于其他
沙漠腹地居群; 居群间果实多子性(F = 6.96, p < 0.01)也存在显著差异, 居群C的果实多子性最高((32.50 ± 4.79)%); 萌发结果
表明, 居群间新鲜的成熟种子萌发不存在显著差异, 且萌发率都低于15%; 所有居群的大部分种子都存在物理性休眠现象,
人为划破种皮能显著提高种子萌发率, 但在低温(15/5 ℃)条件下, 所有居群的种子萌发率都较低, 说明低温抑制了种子萌发;
经人为划破种皮解除物理休眠后, 种子的休眠没有完全释放, 居群C、E和F (大种子居群)的种子萌发率显著高于居群A、B和
D (小种子居群) (F = 30.77, p < 0.01), 说明准噶尔无叶豆种子不仅存在物理性休眠现象, 也可能存在生理休眠现象。不同程度
的种子复合休眠可能是准噶尔无叶豆不同居群适应古尔班通古特沙漠的重要生存策略。
关键词 适应策略, 生态型, 果实种子大小, 物理生理性复合休眠, 种子萌发
Variation in fruit and seed traits and seed germination among different populations of Ere-
mosparton songoricum
LIU Hui-Liang1,2, ZHANG Yong-Kuan1,2, ZHANG Dao-Yuan1*, YIN Lin-Ke1, and ZHANG Yuan-Ming1
1Key Laboratory of Biogeography and Bioresource in Arid Land, Chinese Academy of Sciences, Xinjiang Institute of Ecology and Geography, Chinese Acad-
emy of Sciences, Ürümqi 830011, China; and 2Graduate University of Chinese Academy of Sciences, Beijing 100049, China
Abstract
Aims Eremosparton songoricum is a rare and endangered endemic species in Central Asia. In China, it occurs in
severely wind-eroded mobile and semi-mobile sand dunes of the Gurbantünggüt Desert. It has low fruit set, low
seed set and rare seedling establishment. Our objectives were to determine the characteristics of populations, i.e.,
the variation of fruit or seed traits and seed germination among populations, to explain mechanisms of ecological
adaptations of E. songoricum in different heterogeneous environments.
Methods We determined the density and distance of plants and differences of shape, mass and proportion of
multi-seed in six populations. Temperatures simulating those in the natural habitat of E. songoricum were used to
determine the type of seed dormancy.
Important findings The distance (F = 2.34, p = 0.03) and crown size (F = 8.49, p < 0.01) of plants were signifi-
cantly different among populations and were highest in site C that was severely disturbed by humans. The distance
and crown size located in the northeastern Gurbantünggüt Desert with abundant soil moisture (E and F) were
higher than populations located in the hinterland of desert (A, B, D) except population C. The characteristics of
fruit and seed (length, width, thickness and mass of fruits and seeds) in the populations were significantly different
but seed length and width were not. The majority of traits values were higher in populations E, F and C. The pro-
portion of multi-seed per fruit was significantly different (F = 6.96, p < 0.01) and was highest in population C
(32.50% ± 4.79%). Freshly matured E. songoricum seeds were dormant since germination percentages were <15%
in all the tested temperature regimes in the populations. Scarified seeds germinated to a significantly higher per-
centage than non-scarified ones in all temperature regimes, indicating freshly matured E. songoricum seeds were
physically dormant. A significantly lower germination percentage was recorded at 15/5 °C than at the
刘会良等: 不同居群准噶尔无叶豆果实和种子特性及种子萌发差异 803
doi: 10.3724/SP.J.1258.2012.00802
higher-temperature regimes, indicating that low temperature inhibited seed germination. Large-seeded populations
(C, E and F) had higher germination percentages (<70%) than small-seeded populations (A, B and D; <50%) after
scarified treatments (F = 30.77, p < 0.01), indicating that seeds from all populations had physical and physiology
dormancy (PY + PD). The varying degree of PY + PD of E. songoricum seeds in different populations may be an
important survival strategy for E. songoricum in the heterogeneous environments in the Gurbantünggüt Desert.
Key words adaption strategy, ecotype, fruit and seed mass, physical + physiological dormancy (PY + PD), seed
germination
种子是种子植物生活史的重要阶段, 也是植物
成功定居和更新的保障, 能保证植物在时空上逃避
不利环境(Bu et al., 2007)。种子大小影响植物后代
的适合度, 决定了幼苗建成和幼苗活力(Chhina &
Phul, 1982; Roach & Wulff, 1987; Westoby et al.,
1992; Milberg & Lamont, 1997; Kidson & Westoby,
2000)。物种间种子大小有别, 而同种植物居群及个
体间种子也存在大小之分(Capinera, 1979; Cavers &
Steel, 1984; Stanton, 1984a; van Noordwijk & Jong,
1986; Wulff, 1986; Michaels et al., 1989)。居群间种
子差异是由纬度、气候、环境异质性、母株作用、
植株大小、植株密度、可利用资源等因素造成的
(Janzen, 1977; Gross, 1984; Stanton, 1984b; Roach &
Wulff, 1987; Nakamura, 1988; Argren, 1989; Mazer,
1989a, 1989b; Herrera, 1990; Matthies, 1990; Winn &
Gross, 1993; Susko & Lesley, 2000; Murray et al.,
2004), 它影响幼苗存活 (Andersson & Milberg,
1998; Meyer et al., 1995)、种群更新和植被动态
(Harper, 1977)。
由于环境的异质性, 同一物种产生了生态型分
异, 导致种子萌发特性差异显著, 而在居群间主要
反映在种子休眠程度的不同 (Baskin & Baskin,
1998)。为了适应其所在生境, 每种生态型种子都有
其独特的种子萌发和休眠释放策略, 同样环境条件
对某一生态型的种子萌发有利而可能对其他生态
型不利(Hacker et al., 1984; Meyer et al., 1995)。居群
间种子萌发特性受纬度、海拔、土壤湿度、土壤营
养、温度、植物种类和密度、种群的受破坏程度等
异质性环境的影响(Baskin & Baskin, 1998), 但大多
数学者认为温度、降水和光照等差异是影响居群间
种子萌发差异的主要因素(Fenner, 1992)。因此, 研
究异质生境对不同居群间果实和种子表型特征以
及种子萌发行为的影响, 有助于理解植物有性繁殖
过程对环境的适应机理。
准噶尔无叶豆(Eremosparton songoricum)系豆
科无叶豆属超旱生小半灌木、中亚荒漠特有种和稀
有种(尹林克等, 2006), 是典型的兼性克隆植物。该
种分布区和生态幅狭窄, 在中国仅片断化分布于新
疆古尔班通古特沙漠局部区域(刘瑛心, 1987; 张立
运和海鹰, 2002)。准噶尔无叶豆居群近几十年来受
到人类活动的强烈干扰(主要是沙漠油田开发、农垦
开荒、筑路修渠等行为), 居群间日益隔绝且发生显
著遗传分化(陆雪莹等, 2007); 另一方面, 植株成熟
种子普遍存在物理休眠, 自然居群种子萌发及幼苗
建成困难(Liu et al., 2011), 使得种群数量减少, 面
积逐渐缩小, 在自然生境中主要靠无性克隆方式
(无性繁殖体)实现种群自我维持和扩散。然而, 不同
居群准噶尔无叶豆的有性繁殖体在长期适应异质
生境的过程中, 表型特征是否会发生变化?导致这
种变化的驱动因子是什么?种子的萌发行为是否
在异质生境中产生了分异?前人在准噶尔无叶豆
生活史策略(张道远等, 2008)、开花物候与生殖成功
(马文宝等, 2008)、繁育系统与传粉生态(Shi et al.,
2010a)、结实限制(Shi et al., 2010b)、遗传变异(陆雪
莹等, 2007; 刘燕等, 2010)、克隆种群动态(王建成
等, 2009)、种子萌发(马文宝等, 2007)和种群更新
(Liu et al., 2011)等领域和方向开展了较多的研究,
但对上述科学问题, 国内外尚无相关研究报道。因
此, 本文通过比较和研究不同居群果实和种子特征
以及种子萌发行为差异, 探讨影响果实和种子特征
及种子萌发行为的关键环境因素, 阐明异质生境下
准噶尔无叶豆果实和种子的生态适应机制, 为该物
种的保护提供理论依据。
1 材料和方法
1.1 研究区概况及取样地点
研究区古尔班通古特沙漠位于新疆准噶尔盆
地中央低洼地, 面积4.88万km2, 是我国第二大沙漠
804 植物生态学报 Chinese Journal of Plant Ecology 2012, 36 (8): 802–811
www.plant-ecology.com
(张立运和海鹰, 2002)。该区年平均气温为6–10 ℃, 7
月平均气温为24–27 ℃, 极端最高气温高达40 ℃以
上, ≥10 ℃的活动年积温可达3 000–3 500 ℃; 空
气相对湿度平均为50%–60%; 冬春有雨雪, 年降水
量普遍不超过150 mm。分别选择沙漠北缘和沙漠腹
地为两个异质生境。沙漠北缘因乌伦古河流经, 水
分条件较好(王建成等, 2009), 而沙漠腹地年降水量
70–l00 mm, 蒸发量大于2 000 mm, 气候干燥。因此,
沙漠北缘样地中分布的准噶尔无叶豆的开花与结
实物候期均晚于沙漠腹地样地约15天。
2009年9月, 在古尔班通古特沙漠腹地样地选
择了A、B、C、D 4个自然居群, 其中C居群离彩南
石油作业区较近, 受人为干扰较重; 在沙漠北缘富
蕴县杜热乡样地中选择了E、F两个自然居群。居群
间距离大于5 km (图1)。
1.2 研究方法
1.2.1 准噶尔无叶豆植株距离及植株冠幅的测定
选择的6个居群, 从沙丘底部至顶部各做3个50
m样带, 每个样带设置为5 m × 5 m的连续样方10
个。各样方内随机选择20株植株, 测量植株间距离
(cm)及植株冠幅(m2), 评估居群植株密度及结构。植
株冠幅根据以下公式进行计算: 植株冠幅(crown
size) = π × 0.25 (长×宽)。
1.2.2 不同居群间繁殖体的形态及重量特征测定
在果实成熟期, 分不同居群随机取30株植株的
果实带回实验室, 风干后充分混匀, 使用1/10 000
天平称量其百粒重; 小心剥去果皮, 取出种子, 称
量其百粒重, 5个重复, 计算果实种子单粒重(mg)。
然后, 随机取10粒果实或种子, 使用游标卡尺测量
其长度、宽度、厚度(mm), 并记录(Thompson et al.,
1993)。
在发育过程中, 准噶尔无叶豆果实中多个胚珠
败育, 最后只形成1–3粒种子, 为了检验果实中种
子数量, 分不同居群随机选取20粒果实, 小心剥离
果皮, 观察果实中种子个数, 若果实中种子个数多
于1粒, 定义其有多子性, 反之则为无多子性(Shi et
al., 2010a)。
1.2.3 不同居群间种子的萌发行为
为了明确居群间种子萌发行为的差异, 种子分
为划破种皮和对照两种处理, 进行萌发实验。萌发
实验采用直径为9 cm的培养皿, 以石英砂为培养
基, 每个处理播种25粒种子于沙土表面, 重复4次。
然后随机放到光照培养箱里, 培养箱设置为35/20、
30/15、25/10和15/5 ℃, 12/12 h昼夜交替光照条件;
图1 6个居群的准噶尔无叶豆在古尔班通古特沙漠的位置。
Fig. 1 Location of six populations of Eremosparton songoricum in Gurbantünggüt Desert.
刘会良等: 不同居群准噶尔无叶豆果实和种子特性及种子萌发差异 805
doi: 10.3724/SP.J.1258.2012.00802
4个温度接近生长地月平均温度的最大和最小值,
例如, 35/20 ℃ (7月), 30/15 ℃ (6月和8月), 25/10 ℃
(5月和9月)和15/5 ℃ (4月和10月)。每隔两天统计种
子萌发个数, 并移除, 持续30天。实验开始于2009
年10月。
1.3 数据分析
数据分析使用SPSS 15.0软件(SPSS, Chicago,
USA), 作图使用Origin 8.0软件。居群间的植株冠
幅、植株距离、果实和种子长度、宽度、厚度、果
实多子性及不同温度下的种子萌发都在95%显著水
平上使用单因素方差分析, 用Tukey多重比较上述
指标变量差异; 通过线性相关分析, 检验各个变量
(植株冠幅、植株距离、果实和种子长度、宽度、厚
度、果实多子性及种子萌发和经纬度)之间的联系。
2 结果
2.1 居群间准噶尔无叶豆植株差异
研究结果显示: 居群间准噶尔无叶豆的植株距
离(F = 2.34, p = 0.03)和植株冠幅(F = 8.49, p < 0.01)
存在显著差异。居群C的植株冠幅最大((0.36 ± 0.04)
m2), 居群B最小((0.10 ± 0.02) m2); 居群C的植株距
离最大((65.06 ± 5.43) cm), 居群D最小((44.85 ±
2.67) cm)。在植株冠幅方面, 居群C和E显著高于居
群A、B、D、F, 而居群C和E之间无显著差异; 居群
F显著高于居群B, 与居群A和D无显著差异; 居群
A、B、D之间不存在显著差异。在植株距离方面, 居
群C和E显著高于居群B和D居群, 而居群C和E之间
无显著差异。沙漠北缘E和F居群和沙漠腹地C居群
的植株距离和植株密度都高于其他沙漠腹地居群
(A、B、D居群) (表1)。通过线性相关分析, 显示经
纬度和植株距离及植株冠幅无相关关系(p > 0.05)。
2.2 居群间准噶尔无叶豆果实和种子特性的差异
研究结果显示: 居群间果实长度(F = 3.14, p =
0.03)、果实宽度(F = 8.05, p < 0.01)、果实厚度(F =
3.71, p = 0.01)、果实重量(F = 4.75, p < 0.01)、种子
厚度(F = 4.01, p < 0.01)、种子重量(F = 2.76, p =
0.04)和果实多子性(F = 6.96, p < 0.01)等都存在显
著差异, 但种子长度(F = 1.49, p = 0.23)和种子宽度
(F = 1.98, p = 0.12)等不存在显著差异。居群C的果
实长度最长, 为(11.56 ± 0.92) mm, 居群B最短, 为
(9.55 ± 0.65) mm; 居群E的果实宽度最大, 为(7.54
± 0.40) mm, 居群B最小, 为(5.49 ± 0.18) mm; 居群
E的果实厚度最大, 为(5.78 ± 0.33) mm, 居群B最
小, 为(4.15 ± 0.10) mm; 居群C的种子长度最长,
为(4.72 ± 0.16) mm, 居群A最短, 为(4.23 ± 0.09)
mm; 居群C的种子宽度最大, 为(3.56 ± 0.16) mm,
居群A最小, 为(3.08 ± 0.12) mm; 居群F的种子厚度
最大, 为(1.69 ± 0.05) mm, 居群B最小, 为(1.32 ±
0.08) mm (图2)。居群C的果实重量最重, 为(4.76 ±
0.55) mg, 居群A最轻, 为(2.36 ± 0.28) mg (图3)。居
群C的果实多子性最高, 为(32.50 ± 4.79)%, 居群A
和B最小, 为(5.00 ± 2.89)% (图4)。多项指标的差异
说明居群间果实和种子特性差异显著, 由于沙漠腹
地的C居群和沙漠北缘的E、F居群的多项指标都高
于沙漠腹地的A、B和D居群, 因此, 将居群C、E、
F视为大种子居群, A、B、D视为小种子居群。通过
线性相关分析, 显示经纬度与果实特性和种子无相
关关系(p > 0.05)。
2.3 居群间种子的萌发特性
研究结果显示: 4个温度梯度下, 居群间未处理
的、新鲜成熟种子的萌发率不存在显著差异, 且萌
发率都小于15%, 说明所有居群新鲜种子的种皮不
渗透率相差无几, 都维持在85%以上; 而划破种皮
的种子萌发率显著高于未处理的: 35/20 ℃ (F =
112.13, p < 0.01)、30/15 ℃ (F = 171.80, p < 0.01)、
25/10 ℃ (F = 144.11, p < 0.01)、15/5 ℃ (F = 29.51, p
< 0.01), 表明划破处理能够促进种子萌发且减轻种
子的物理性休眠; 但15/5 ℃的种子萌发率低于在其
表1 6个居群的准噶尔无叶豆植株间距离和植株冠幅的特性比较(平均值±标准误差)
Table 1 Comparison of characteristics of distance and crown size of Eremosparton songoricum in six populations (mean ± SE)
居群 Population A B C D E F
植株间距离 Distance of plant (cm) 51.63 ± 3.16ab 46.48 ± 1.76bc 65.06 ± 5.43a 44.85 ± 2.67bc 62.06 ± 4.33a 59.82 ± 2.01ab
植株冠幅 Crown of plant (m2) 0.13 ± 0.03bc 0.10 ± 0.02c 0.36 ± 0.04a 0.14 ± 0.02bc 0.33 ± 0.04a 0.21 ± 0.02b
在同一行中, 相同小写字母表示差异不显著(p > 0.05)。
The same lower-case letters within a row indicate no significant difference (p > 0.05).
806 植物生态学报 Chinese Journal of Plant Ecology 2012, 36 (8): 802–811
www.plant-ecology.com
图2 准噶尔无叶豆6个居群间果实和种子长度(A)、宽度
(B)、厚度(C)比较(平均值±标准误差)。相同的大、小写字母
分别表示6个居群间果实和种子的差异不显著(p > 0.05)。
Fig. 2 Comparison of length (A), width (B) and thickness (C)
of fruit and seed of Eremosparton songoricum in six popula-
tions (mean ± SE). The same upper-case and lower-case letters
indicate no significant differences between fruits and seeds in
six populations, respectively (p > 0.05).
他温度梯度的, 暗示准噶尔无叶豆种子萌发对低温
较敏感; 同时, 除35/20 ℃外(F = 1.79, p = 0.19), 在
另外3个温度下, 居群间的种子萌发存在显著差异
(30/15 ℃ (F = 3.71, p = 0.03)、25/10 ℃ (F = 13.93, p
< 0.01)、15/5 ℃ (F = 12.97, p < 0.01)), 且沙漠腹地
的C居群和沙漠北缘的E、F居群(大种子)的种子萌
发率(<70%)显著高于沙漠腹地的A、B、D居群(小
图3 准噶尔无叶豆6个居群间果实和种子重量的比较(平均
值±标准误差)。相同的大、小写字母分别表示6个居群间果
实和种子差异不显著(p > 0.05)。
Fig. 3 Comparison of fruit and seed mass of Eremosparton
songoricum in six populations (mean ± SE). The same up-
per-case and lower-case letters indicate no significant differ-
ences between fruits and seeds in six populations, respectively
(p > 0.05).
图4 准噶尔无叶豆6个居群间果实多子性比较(平均值±标
准误差)。相同的小写字母表示6个居群间差异不显著(p >
0.05)。
Fig. 4 Comparison of proportion of multi-seed in fruit of
Eremosparton songoricum in six populations (mean ± SE). The
same lower-case letters indicate no significant differences in six
populations (p > 0.05).
种子) (<50%) (F = 30.77, p < 0.01) (图5)。通过线性
相关分析, 显示经纬度与种子萌发无相关关系(p >
0.05)。
刘会良等: 不同居群准噶尔无叶豆果实和种子特性及种子萌发差异 807
doi: 10.3724/SP.J.1258.2012.00802
图5 15/5 ℃ (A), 25/10 ℃ (B), 30/15 ℃ (C)和35/20 ℃ (D) (光/暗, 12 h:12 h)培养30天后, 6个居群准噶尔无叶豆种子的累积萌
发率(平均值±标准误差)。在相同的培养温度下, 相同字母表示同一处理下居群间差异不显著(p > 0.05)。
Fig. 5 Cumulative germination of Eremosparton songoricum seed from six populations after incubated 30 days at 15/5 °C (A),
25/10 °C (B), 30/15 °C (C) and 35/20 °C (D) (light/dark, 12:12 h) (mean ± SE). The same letters on the same treatment indicate no
significant differences in six populations at the same temperature regime (p > 0.05).
3 讨论
3.1 果实和种子特性与环境的关系
居群间的环境异质性造成物种果实和种子特
性差异(Roach & Wulff, 1987; Stanton, 1984a; Wulff,
1986)。种子重量是衡量物种适应能力的重要指标,
但是对不同植物的研究具有不同结论。Baker (1972)
对Californian地区的Juglans、Aesculus和Quercus属
植物研究后认为在极度干旱危险的环境条件下, 植
物趋向于产生大种子, 但Mazer (1989a)对Indiana
Dune地区的Raphanus raphanistrum研究后发现干旱
不影响种子重量。准噶尔无叶豆分布在沙漠腹地,
该地以流动-半流动风沙土壤占主导, N、P、K营养
元素比较贫瘠(张道远等, 2008)。我们的研究表明,
沙漠北缘E和F居群及沙漠腹地C居群的果实和种子
特性都较沙漠腹地居群(A、B、D)大, 可能是E和F
居群水分充足和植株密度较低, 植株分配的资源和
水分较多, 造成沙漠北缘居群的果实和种子特性比
沙漠腹地居群大; 而C居群人为干扰严重, 植株密
度最低, 单株植物分配的资源较多, 用于生殖生长
的资源较充分。随着干扰强度的增加, 种子重量一
般有升高的趋势(Salisbury, 1974), 同时大种子能储
存较多能量物质, 能有效适应恶劣的干扰环境, 并
能顺利完成其种子萌发和幼苗更新(Murray et al.,
2003), 这也印证了资源可能是限制准噶尔无叶豆
结实和结籽的外在因素(Shi et al., 2010b)。
808 植物生态学报 Chinese Journal of Plant Ecology 2012, 36 (8): 802–811
www.plant-ecology.com
在胚珠形成种子的过程中, 由于资源的限制作
用 , 导致随机受精的胚珠发生败育 (Stephenson,
1981)。这种通过选择性败育来提高后代适合度的现
象, 可能是某些生活在资源贫乏、干旱少雨条件下
的植物在长期进化过程中形成的一种生殖保障(王
迎春等, 2001)。准噶尔无叶豆果实发育初期, 荚果
内多具有2–3枚受精胚珠, 荚果发育成熟后仅有1枚
胚珠发育成种子(Shi et al., 2010b)。相对于生成2–3
粒种子, 荚果内仅形成一粒种子的优势在于明显降
低了以果实作为扩散单位的重量, 这样将利于扩大
种子传播距离。另外, 当果实进入种子库后, 果皮
腐烂, 种子主要分布在0–6 cm的浅层沙土中(Liu et
al., 2011), 由于准噶尔无叶豆生长在流动沙丘上,
浅层沙土中的种子被沙粒打磨的几率就大, 种皮硬
实性的破除就更容易, 从而有利于种子萌发, 这对
种群占领新生境具有一定的生态意义。
3.2 种子萌发特性与环境的关系
在长期的自然选择压力下, 生境异质性决定了
居群间种子萌发行为的差异, 居群间的水分异质性
影响了种子萌发率(Meyer et al., 1995)。Temel等
(2011)研究不同居群的Pinus nigra subsp. pallasiana
的萌发, 发现水分条件差的内陆居群种子萌发速率
慢于沿海居群, 但内陆居群的种子萌发率高; 而
Hacker和Ratcliff (1989)发现水分条件好的Cenchrus
ciliari居群的种子萌发率显著高于水分条件差的居
群。对于种子存在物理性休眠的物种而言, 居群间
的水分差异也会影响种子休眠, 例如, 水分胁迫下
Gossypium sp.种子休眠能够减轻(Baskin & Baskin,
1998), 也能够缩短Erodium brachycarpum的种子休
眠时间(Stamp, 1990), 然而水分胁迫增加了Cassia
sophera (Baskin & Baskin, 1998)和Sebania bispinosa
(Sharma et al., 1978)的种子物理休眠率。可见, 居群
间种子萌发特性与自然生境中的水分条件有关, 水
分胁迫能够促进或者抑制种子的萌发(Baskin &
Baskin, 1998)。我们的研究表明, 沙漠北缘、水分条
件好的E、F居群和沙漠腹地、水分条件差的A、B、
C、D居群的新鲜种子均存在物理性休眠现象, 但是
萌发率在居群间不存在显著不同, 由此可见, 依据
物种的不同, 自然生境中的水分条件对种子萌发的
影响也相同。
温度差异能够影响居群内种子萌发特征。
Peacock和McMillan (1965)采集了多个居群Prosopis
glandulosa的种子, 发现种子具有硬实性, 在所有
温度条件下划破种皮后种子萌发率几乎达到100%,
说明温度对居群内种子萌发无显著影响。而
Espigares 和 Peco (1993) 发现低温 25/10 ℃抑制
Trifolium striatum、T. gemellum和T. suffocatum种子
的萌发。我们的结果与Espigares和Peco (1993)的结
果相似, 即在不同温度下, 居群内划破种皮种子的
萌发率存在显著差异, 均表现出15/5 ℃的低温条件
抑制了种子萌发。准噶尔无叶豆这种低温抑制种子
萌发的特性, 对该种的种群维持具有重要意义。当
准噶尔无叶豆种子在秋季扩散后, 秋末初冬的低温
使种子萌发受到抑制, 种子能很好地保存于沙土
中, 冬天的沙埋可有效地软化种皮而破除种子硬
实, 并且冷层积也有利于种子打破生理性休眠, 随
着次年春天温度的升高, 种子得以顺利地在晚春和
初夏萌发和幼苗建植。
3.3 种子休眠与环境的关系
种子的物理性休眠能保证种子存活很长时间
(Egley, 1979; Rolston, 1978), 尤其是在极端环境下,
更容易形成持久种子库(Tran & Cavanagh, 1984)。准
噶尔无叶豆种子存在物理性休眠, 能够在胁迫的环
境下保存种子, 分摊了种子一次性集中萌发的风
险, 保证在环境条件适宜的年份完成种群的更新,
对适应干旱区的生长环境具有重要的生态学意义
(Venable, 1989)。通过人为划破种皮, 准噶尔无叶豆
种子的萌发率显著提高, C、E、F居群(大种子)种子
萌发率近70%, 而A、B、D居群(小种子)种子萌发率
低于50%。Leishman和Westoby (1994a , 1994b)发现
在干旱条件下大种子比小种子具有更高的萌发率,
幼苗生存时间与种子重量有正相关关系。而居群内
大种子的种子萌发和幼苗建植比小种子有更大的
优势 , 尤其是在资源受限制的条件下 (Jurado &
Westoby, 1992)。这表明居群间种子萌发的差异可能
是由种子大小决定的, 也就是说环境异质性导致了
物种生态型分异, 种子大小产生差异, 形成了不同
的萌发生态学特性(Quinn, 1977)。然而人为地划破
种皮的处理只能部分打破种子的物理性休眠, 不能
萌发的种子是否是死种子?作者前期的研究显示
种子储存7个月后, 98%的种子仍然具有活力(Liu et
al., 2011), 说明不是死种子影响了种子萌发率。我
们认为准噶尔无叶豆种子可能存在种子复合型休
眠类型(PY + PD), 虽然划破种皮打破了种子物理
刘会良等: 不同居群准噶尔无叶豆果实和种子特性及种子萌发差异 809
doi: 10.3724/SP.J.1258.2012.00802
性休眠, 但生理性休眠还没破除, 而种子生理性休
眠的释放可能要经过更长的时间, 而且沙漠腹地的
小种子居群的种子生理性休眠的比率较大, 这可能
是准噶尔无叶豆种子在长期自然选择下适应干旱
环境的一种策略。
综上所述, 环境选择压力是多种环境因子综合
作用的结果, 导致物种生态型分化, 为了适应异质
性环境条件, 不同居群的准噶尔无叶豆形成了不同
的策略: 准噶尔无叶豆在水分和营养好的生境下生
产大种子(C、E、F居群); 居群间准噶尔无叶豆的种
子由于存在物理性休眠而使萌发不存在显著差异,
划破种皮能提高种子物理性休眠释放率, 且低温抑
制种子萌发的保护机制; 准噶尔无叶豆种子还存在
生理休眠, 且小种子(A、B、D居群)的生理性休眠
程度比大种子高。可见, 不同程度的种子复合休眠
是准噶尔无叶豆不同居群适应古尔班通古特沙漠
的重要生存策略之一, 从而能够保证准噶尔无叶豆
种群在胁迫的异质性生境中的更新和存活。
致谢 国家国际科技合作计划(2010DFA92720-06)
和国家自然科学基金(31100399和31070472)资助。
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