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Variability and association of leaf traits between current-year and former-year leaves in evergreen trees in Tiantong, Zhejiang, China

浙江天童常绿植物当年生与往年生叶片性状的变异与关联


植物叶片性状随叶龄的变化是植物生活史策略的体现, 反映了植物叶片的物质投资和分配方式。该研究通过在个体和物种2个水平, 比较浙江天童1 hm2样地内常绿阔叶树种的平均叶面积(MLA)、比叶面积(SLA)和叶片干物质含量(LDMC)在当年生和往年生叶片间的差异和关联, 探究叶片物质分配策略在异龄叶间的变化, 并分析叶龄对植物叶片性状, 特别是叶片面积建成消耗的影响。结果显示: 1)在个体和物种水平上, MLA变异系数最大(个体: 79.5%; 物种: 66.5%), SLA次之(个体: 28.1%; 物种: 24.7%), LDMC较低(个体: 17.0%, 物种: 14.1%); 当年生叶片MLALDMCSLA的变异系数均高于往年生叶片; 2)往年生叶MLA显著大于当年生叶(t = -38.53, p < 0.001), 往年生叶SLA显著小于当年生叶(t = 45.30, p < 0.001), 往年生叶LDMC显著大于当年生叶(t = -9.71, p < 0.001); 3)在个体水平, 当年生叶片MLASLALDMC值分别解释了往年生叶片MLASLALDMC变异的86%、48%和41%; 在物种水平, 当年生叶片MLASLALDMC值分别解释了往年生叶片MLASLALDMC变异的97%、83%和85%; 4) SLA在异龄叶间的变化表明, 与往年生叶片相比, 投资相同干物质, 当年生叶片可形成较大的叶面积, 其叶片面积建成消耗较小。研究认为, 植物叶性状在异龄叶间具有较大的变异性和关联性, 叶面积形成过程中生物量建成与消耗的协调可能影响植物叶片的发育。

Aims Variation in leaf traits with changing leaf age denotes plant life history strategy and reflects biomass allocation pattern in plant leaves. Our objective was to explore variability and correlation of leaf traits between current-year and former-year leaves for evergreen broad-leaved trees, in order to reveal effects of leaf age on the pattern of construction and cost during development of leaf area.
Methods Our one hectare study site is located in Tiantong National Forest Park (29°52′ N, 121°39′ E), Zhejiang Province. Three key functional traits (mean leaf area (MLA), specific leaf area (SLA) and leaf dry matter content (LDMC)) in each of current-year leaves and former-year leaves were measured for 2 277 evergreen trees belonging to 41 species. Variability and correlations for each of three leaf traits were compared between current-year and former-year leaves at both individual and species levels.
Important findings At both individual and species levels, variability coefficients (i.e., CV) were highest in MLA (individual: 79.5%; species: 66.5%), intermediate in SLA (individual: 28.1%; species: 24.7%) and lowest in LDMC (individual: 17.0%; species: 14.1%). Variability coefficients among the three leaf traits were greater in current-year leaves than in former-year leaves. Former-year leaves had significantly greater MLA (t = -38.53, p < 0.001) and LDMC (t = -9.71, p < 0.001), but lower SLA (t = 45.30, p < 0.001) than current-year leaves. At the individual level, the values for MLA, SLA and LDMC in current-year leaves explained 86%, 48% and 41% of the total variation for MLA, SLA and LDMC in former-year leaves. More significantly, at the species level 97%, 83% and 85% of the total variation in each of MLA, SLA and LDMC for former-year leaves resulted from variability of MLA, SLA and LDMC from current-year leaves. Variation in SLA between differently aged leaves demonstrated that, at a given unit investment of biomass, a relatively larger leaf area can be structured by current-year leaves than by former-year leaves, thus having a low cost in constructing leaf area for current-year leaves. In conclusion, plant leaf traits vary and connect significantly with change of leaf age. Trade-offs between biomass construction and cost in leaf area production might affect plant leaf development.


全 文 :植物生态学报 2013, 37 (10): 912–921 doi: 10.3724/SP.J.1258.2013.00094
Chinese Journal of Plant Ecology http://www.plant-ecology.com
——————————————————
收稿日期Received: 2013-04-15 接受日期Accepted: 2013-08-08
* 通讯作者Author for correspondence (E-mail: eryan@des.ecnu.edu.cn)
浙江天童常绿植物当年生与往年生叶片性状的变
异与关联
黄海侠1,2 杨晓东1,2 孙宝伟1,2 张志浩1,2 阎恩荣1,2*
1华东师范大学环境科学系, 上海 200062; 2浙江天童森林生态系统国家野外科学观测研究站, 浙江宁波 315114
摘 要 植物叶片性状随叶龄的变化是植物生活史策略的体现, 反映了植物叶片的物质投资和分配方式。该研究通过在个体
和物种2个水平, 比较浙江天童1 hm2样地内常绿阔叶树种的平均叶面积(MLA)、比叶面积(SLA)和叶片干物质含量(LDMC)在
当年生和往年生叶片间的差异和关联, 探究叶片物质分配策略在异龄叶间的变化, 并分析叶龄对植物叶片性状, 特别是叶片
面积建成消耗的影响。结果显示: 1)在个体和物种水平上, MLA变异系数最大(个体: 79.5%; 物种: 66.5%), SLA次之(个体:
28.1%; 物种: 24.7%), LDMC较低(个体: 17.0%, 物种: 14.1%); 当年生叶片MLA、LDMC和SLA的变异系数均高于往年生叶片;
2)往年生叶MLA显著大于当年生叶(t = –38.53, p < 0.001), 往年生叶SLA显著小于当年生叶(t = 45.30, p < 0.001), 往年生叶
LDMC显著大于当年生叶(t = –9.71, p < 0.001); 3)在个体水平, 当年生叶片MLA、SLA和LDMC值分别解释了往年生叶片MLA、
SLA和LDMC变异的86%、48%和41%; 在物种水平, 当年生叶片MLA、SLA和LDMC值分别解释了往年生叶片MLA、SLA和
LDMC变异的97%、83%和85%; 4) SLA在异龄叶间的变化表明, 与往年生叶片相比, 投资相同干物质, 当年生叶片可形成较大
的叶面积, 其叶片面积建成消耗较小。研究认为, 植物叶性状在异龄叶间具有较大的变异性和关联性, 叶面积形成过程中生
物量建成与消耗的协调可能影响植物叶片的发育。
关键词 叶龄, 叶建成消耗, 干物质含量, 平均叶面积, 资源分配策略, 比叶面积
Variability and association of leaf traits between current-year and former-year leaves in ev-
ergreen trees in Tiantong, Zhejiang, China
HUANG Hai-Xia1,2, YANG Xiao-Dong1,2, SUN Bao-Wei1,2, ZHANG Zhi-Hao1,2, and YAN En-Rong1,2*
1Department of Environment Science, East China Normal University, Shanghai 200062, China; and 2Tiantong National Forest Ecosystem Observation and
Research Station, Ningbo, Zhejiang 315114, China
Abstract
Aims Variation in leaf traits with changing leaf age denotes plant life history strategy and reflects biomass allo-
cation pattern in plant leaves. Our objective was to explore variability and correlation of leaf traits between
current-year and former-year leaves for evergreen broad-leaved trees, in order to reveal effects of leaf age on the
pattern of construction and cost during development of leaf area.
Methods Our one hectare study site is located in Tiantong National Forest Park (29°52′ N, 121°39′ E), Zhejiang
Province. Three key functional traits (mean leaf area (MLA), specific leaf area (SLA) and leaf dry matter content
(LDMC)) in each of current-year leaves and former-year leaves were measured for 2 277 evergreen trees belong-
ing to 41 species. Variability and correlations for each of three leaf traits were compared between current-year and
former-year leaves at both individual and species levels.
Important findings At both individual and species levels, variability coefficients (i.e., CV) were highest in MLA
(individual: 79.5%; species: 66.5%), intermediate in SLA (individual: 28.1%; species: 24.7%) and lowest in
LDMC (individual: 17.0%; species: 14.1%). Variability coefficients among the three leaf traits were greater in
current-year leaves than in former-year leaves. Former-year leaves had significantly greater MLA (t = –38.53, p <
0.001) and LDMC (t = –9.71, p < 0.001), but lower SLA (t = 45.30, p < 0.001) than current-year leaves. At the in-
dividual level, the values for MLA, SLA and LDMC in current-year leaves explained 86%, 48% and 41% of the
total variation for MLA, SLA and LDMC in former-year leaves. More significantly, at the species level 97%, 83%
and 85% of the total variation in each of MLA, SLA and LDMC for former-year leaves resulted from variability of
MLA, SLA and LDMC from current-year leaves. Variation in SLA between differently aged leaves demonstrated
黄海侠等: 浙江天童常绿植物当年生与往年生叶片性状的变异与关联 913

doi: 10.3724/SP.J.1258.2013.00094
that, at a given unit investment of biomass, a relatively larger leaf area can be structured by current-year leaves
than by former-year leaves, thus having a low cost in constructing leaf area for current-year leaves. In conclusion,
plant leaf traits vary and connect significantly with change of leaf age. Trade-offs between biomass construction
and cost in leaf area production might affect plant leaf development.
Key words leaf age, leaf construction cost, leaf dry mass content, mean leaf area, resource allocation strategy,
specific leaf area

叶片是植物与周围环境进行能量和物质交换
的主要器官, 其生长发育和性状特征直接影响着植
物的基本行为和功能。常绿树种在储存养分、适应
贫瘠生境上有很大优势, 主要原因是其长的叶片寿
命可有效地减少营养损失 (Monk, 1966; Aerts,
1995)。而这些具有较长生活史的常绿植物叶片, 由
于其形成的年份、经历的环境条件及所处的发育阶
段的差异, 使其资源分配模式和性状特征随叶龄变
化产生差别(Doust, 1980; Reich et al., 1991)。
以往的研究认为, 生长初期的叶片对环境变化
敏感, 轻微的环境扰动就能诱导叶片性状发生改
变 , 表现出较强的可塑性(Sims & Pearcy, 1992;
Wyka et al., 2000; Frak et al., 2001), 因此, 当年生
叶片性状的变异较大。随着叶片老化, 叶内主要养
分元素(如氮和磷)含量以及光合速率降低(Field &
Mooney, 1983; Bleecker, 1998; Ono et al., 2001), 叶
片结构充分形成而固化, 再当环境发生扰动时, 较
生长前期的叶片响应迟缓(Oguchi et al., 2003)。因而
可以推测, 常绿树种当年展成的叶片(本研究中称
当年生叶片)和生长时间大于1年的叶片(往年生叶
片)性状大小的变异程度存在差异。
叶片随叶龄变化的物质投资和分配格局是植
物适应环境的重要途径之一 (Silvertown et al.,
1997)。在叶片生长早期, 为最大程度地获取光资源,
叶片需投资较多的生物量以优化同化器官, 如扩展
平均叶面积(mean leaf area, MLA) (Tilman, 1988;
Sultan, 2000), 从而可增大光截获和碳收益方面的
竞争优势, 以补偿其自身建成的消耗(Williams et
al., 1987; Wright et al., 2004)。因而, 相对于生长后
期的叶片, 生长早期的叶片在单位生物量投入下其
面积的增大程度较大。再如, 比叶面积(specific leaf
area, SLA, 面积与干重的比例)在叶片生长早期较
大, 反映了生长早期叶片具有较强的光资源获取能
力(Field & Mooney, 1983; Kitajima et al., 1997)。相
反, 叶片干物质含量(leaf dry matter content, LDMC,
鲜重与干重的比率)在生长前期则较小, 反映了发
育初期叶片一般含水率较高, 代谢活动活跃(Sims
& Pearcy, 1992)。
在生长中后期, 随着叶片比表面积增大, 一般
会经历更多复杂多变的环境胁迫, 因此需要在抗机
械胁迫和结构建造方面投资更多的生物量, 从而维
持叶片的停留和存活时间(Witkowski & Lamont,
1991; Wilson et al., 1999; Gratani & Bombelli, 2000;
Westoby et al., 2002)。加之, 随着Ca2+和一些次生代
谢物在老叶中沉积, 叶片组织密度会增大, 因而,
SLA和 LDMC会发生变化 (Reich et al., 1998;
Pérez-Harguindeguy et al., 2013)。具体而言, 由于老
叶组织密度和厚度的增大可直接导致叶片光合能
力的衰退(Field & Mooney, 1983; He et al., 2009),
叶片通过继续增大光合面积MLA的边际收益已甚
小, 因而, MLA在叶片生长后期的增大空间有限,
其大小的变动不大。相反, MLA在叶片生长前期的
变幅应该更大。与MLA相比, SLA和LDMC因叶片生
长后期叶片组织密度和厚度的增大, 相对于生长前
期则会发生较大程度的变动。因而, 我们推断当年
生叶片MLA基底值对往年生叶片的MLA影响较大,
而当年生叶片的SLA和LDMC对往年生叶片SLA和
LDMC的影响相对较小, 其变化主要受叶片生长后
期代谢物质的积累和环境胁迫的影响。
不同年龄叶片资源分配模式的差别, 以及由其
导致的性状特征变化可体现异龄叶间不同的物质
建成消耗策略(Griffin, 1994)。叶片建成消耗是指构
建单位面积叶片所需要的葡萄糖当量, 是植物碳收
获过程中必要的成本投资(Williams et al., 1987;
Griffin, 1994)。相对于当年生叶片, 往年生叶片为忍
受多年环境变化, 在机械和防御构造上的额外投资
较多(Chabot & David, 1982), 故可以推断, 往年生
叶片的建成消耗大于当年生叶片。由于SLA代表投
资单位生物量所构建的叶片面积, 与叶片建成消耗
负相关(Feng et al., 2008), 故可通过比较SLA在当年
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生和往年生叶片之间的大小来判断异龄叶建成消
耗的差异。
基于以上推断, 本文提出如下科学假说: 1)当
年生和往年生叶片的MLA、SLA和LDMC存在差异;
2)当年生叶片MLA对往年生叶片MLA的解释度更
高, 当年生叶片SLA和LDMC对往年生叶片SLA和
LDMC的解释度相对稍低; 3)当年生叶片MLA、SLA
和LDMC大小的变异程度大于往年生叶片; 4)往年
生叶片的单位面积建成消耗大于当年生叶片。为了
验证以上科学假说, 本研究以浙江天童的常绿树种
为研究对象, 通过测量1 hm2样地内胸径(DBH) > 1
cm所有常绿木本植物的MLA、SLA和LDMC, 在个体
和物种水平上, 分别比较当年生和往年生叶片3个
性状的变异和关联性, 以及不同叶龄单位面积叶片
建成消耗的差异。
1 材料和方法
1.1 研究地概况和样地描述
研究地位于浙江省宁波市天童国家森林公园,
地处29°52′ N, 121°39′ E, 其自然条件参见宋永昌和
王祥荣(1995)的文献。本研究选择天童酸枣沟区域
的1 hm2常绿落叶阔叶混交林为研究样地, 该样地
中木本植物总计有14科76个物种。根据王希华等
(2000)的研究结果, 少量常绿树种叶寿命小于1年
(本研究样地中包含苦槠(Castanopsis sclerophylla)、
云山青冈(Cyclobalanopsis sessilifolia)), 本研究以
其中叶寿命大于1年的常绿树种为研究对象, 共41
种, 分属于14科, 包含2 277个个体(表1)。样地中薄
叶润楠 (Machilus leptophylla)和港柯 (Lithocarpus
henryi)为乔木层优势种, 黄丹木姜子(Litsea elon-
gata)、毛柄连蕊茶 (Camellia fraterna)和细枝柃
(Eurya loquaiana)为灌木层优势种。
1.2 取样和测量
野外工作于2010年7至8月间进行。在样地内,
对于DBH在1 cm以上的所有常绿木本植物个体, 逐
株进行样品采集。采集时, 用高枝剪从每个个体的
不同方向上采集3个生长良好的枝条, 小灌木采集1
个枝条(防止过度破坏)。根据枝条上芽鳞痕形成的
节环, 辨别不同年龄枝段, 并在其上采集叶片(王希
华等, 2000), 当年生枝段上已完全展开的叶片定义
为当年生叶片(不采集少量未完全展开和不完整叶
片), 当年生枝段以外的其他较老枝条上的叶片统
称为往年生叶片(不采集发黄衰老和不完整叶片)。
每株植物分别采集两类型叶片各40–100片, 并分开
保存在自封袋中, 记录编号带回实验室。
于12 h内从当年生叶片和往年生叶片的样品中
各随机挑选20片称其湿重 , 后用叶面积仪 (LI-
3100C, LI-COR, Lincoln, USA)测量叶面积。待完成
后, 将叶片编号装入信封, 置于75 ℃干燥箱中烘干
至恒重, 称量样品干重。通过公式(1–3)计算出样地
内每株常绿植物的MLA、SLA和LDMC。
MLA (cm2) =总叶面积/总叶片数 (1)
SLA (m2·kg–1) =叶面积/叶干重 (2)
LDMC (mg·g–1) =叶干重/叶湿重 (3)
1.3 数据分析
由于在自然植物群落中存在优势种和稀有种,
因而从个体水平或是从物种水平来分析群落中异
龄叶的性状特性各有利弊: 若仅以植物个体为研究
对象来分析, 势必掩盖了稀有种不同叶龄之间的差
异, 弱化了稀有种的作用; 反过来, 若仅用物种来
进行分析 , 则放大了稀有种在群落中的重要性
(Reich & Oleksyn, 2004)。因此, 为确保结论的准确
性, 依据Reich和Oleksyn (2004)、Liao等(2012)和闫
帮国等(2012)的建议, 本文同时基于个体和物种对
常绿树种当年生和往年生叶片性状的变异和关联
作了探索。分析物种水平时, 将同一物种的所有个
体数据平均后再进行计算。
首先, 以1 hm2样地内所调查的每木个体为数
据集, 定义为个体研究水平。后将同一物种的所有
个体合并, 计算平均值, 将平均值定义为该物种的
LMA、SLA和LDMC值。依次以样地内所有常绿木
本植物的个体和物种为研究对象, 对其当年生叶
片、往年生叶片的3个性状(MLA、SLA和LDMC)进
行基本统计学分析, 以掌握不同年龄叶片的性状变
化特征。
其次, 为了解叶片性状的变异情况, 当年生叶
片性状的变异性表示为当年生叶片所构成的样本
的性状变异系数(变异系数=标准偏差/平均值), 类
似地, 往年生叶片的变异系数则以往年生叶片为样
本量计算。然后, 采用配对数据t检验判断叶片性状
在当年生和往年生叶片之间的差异。
最后, 为验证叶龄间物质投资策略的转变是否
会对异龄叶性状的关联性产生影响, 采用线性回归
方程依次在个体水平和物种水平上分别拟合3个性
黄海侠等: 浙江天童常绿植物当年生与往年生叶片性状的变异与关联 915

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黄海侠等: 浙江天童常绿植物当年生与往年生叶片性状的变异与关联 917

doi: 10.3724/SP.J.1258.2013.00094
状指标在往年生和当年生叶片之间的关系, 在此基
础上分别比较3个性状在叶龄间的关联性(决定系数
R2)的大小。所有数据分析采用R 2.14.2中vegan
package (R Development Core Team, 2009)进行。
2 结果
2.1 叶性状随叶龄的变异
对1 hm2样地内所有常绿植物个体的叶片的3个
性状(MLA、SLA和LDMC)分析后发现, 在个体水平
上, MLA变异系数最大(79.5%), 约为SLA (28.1%)和
LDMC (17.0%)的2.8倍和4.7倍(表2)。当把叶片分为
当年生和往年生2种类型时, MLA、SLA和LDMC在
当年生叶片的变异程度分别为79.2%、27.5%和
17.7%, 均高于往年生叶片的变异 (MLA, 76.4%;
SLA, 22.9%; LDMC, 15.9%)。3个性状在当年生与往
年生叶片之间均有显著差异, 其中, 往年生叶片
MLA显著大于当年生叶片(t = –38.5, p < 0.001), 往
年生叶片SLA显著小于当年生叶片(t = 45.3, p <
0.001), 往年生叶片LDMC显著大于当年生叶片(t =
–9.7, p < 0.001)。
在物种水平, MLA、SLA和LDMC在当年生叶片
和往年生叶片间的大小和变异系数的变化规律与
个体水平的结果基本一致(表2)。
2.2 异龄叶性状的关联
在个体水平, MLA、SLA和LDMC分别在当年生
与往年生叶片之间均具有显著线性关系(p < 0.001),
但3个性状的相关程度(R2)不同。当年生叶片MLA解
释了往年生叶片MLA变异的86% (图1A), 当年生叶
片SLA对往年生叶片SLA的解释率为48% (图1B),
当年生叶片LDMC对往年生叶片LDMC的解释率为
41% (图1C)。
在物种水平, MLA、SLA和LDMC分别在当年生
与往年生叶片之间也具有显著线性关系 ( p <
0.001)。同样地, MLA在当年生与往年生叶片间的关
联性强于SLA和LDMC (R2分别为0.97、0.83和0.85)
(图1D、1E、1F)。比较显著的结果是: 物种水平上3
个性状在2个叶龄间的相关性均大于个体水平, 这
主要是因为分析物种水平时, 是将同一物种的所有


图1 浙江天童1 hm2样地常绿植物在个体(A、B、C)和物种水平(D、E、F)上当年生与往年生叶片性状的回归关系。LDMC, 叶
片干物质含量; MLA, 平均叶面积; SLA, 比叶面积。
Fig. 1 Regression relationships of leaf traits between current-year and former-year leaves at both individuals (A, B, C) and species
levels (D, E, F) among evergreen trees in 1 hm2 plot in Tiantong, Zhejiang. LDMC, leaf dry matter content; MLA, mean leaf area;
SLA, specific leaf area.
918 植物生态学报 Chinese Journal of Plant Ecology 2013, 37 (10): 912–921

www.plant-ecology.com
个体的数据平均后再进行分析, 消除了个体水平上
某些物种的离散值, 使各物种的性状值分布更聚
集, 从而提高了在不同叶龄间的关联性。
3 讨论
3.1 异龄叶片性状的变异
由于常绿植物叶片的生活周期长、生活史策略
复杂, 异龄叶间的性状变异程度存在差别。以往的
研究表明, 为适应多变的气候与其他环境条件, 叶
面积在全球范围内变化极大 , 可达到6个数量级
(Milla & Reich, 2007)。本研究的1 hm2样地内MLA
的变化达到3个数量级(个体水平1.6–138.9 cm2, 物
种水平5.5–80.8 cm2), 变异程度在个体和物种水平
分别达到79.5%和66.5%, 表现出较大的环境可塑
性。究其原因, 多数学者认为叶面积的变异是由植
物其他性状的协同变异引起, 如植物高度(Ackerly
& Donoghue, 1998; Cornelissen, 1999)、干材密度
(Pickup et al., 2005)、支撑枝条的大小(Westoby &
Wright, 2003)和单位体积枝上叶稠密度的大小(Yan
et al., 2012), 甚至与单位枝条上果实或种子的大小
也有关 (Ackerly & Donoghue, 1998; Cornelissen,
1999; Westoby & Wright, 2003)等。在本研究中, 个
体水平上当年生和往年生叶片MLA的变幅分别为
1.6–114.2和3.4–138.9 cm2, 物种水平分别为5.5–
60.1和6.1–80.8 cm2 (表2), 均表现出往年生叶片
MLA显著大于当年生叶片(p < 0.001), 由此可见,
叶龄也是影响MLA变异的主要原因之一。
叶龄也影响LDMC和SLA的变异格局。本研究
表明: 无论个体还是物种水平, 相比于当年生叶片,
往年生叶片的LDMC显著增大(p < 0.001), SLA显著
减小(p < 0.001) (表2)。这可能是因为随叶龄增加,
叶片老化, 养分从即将衰老的叶片转移到正在发育
的组织中(Wright & Westoby, 2003), 而Ca2+和一些
次生代谢物则在老叶中沉积, 加之防虫食、防过度
失水的保卫构造组织的增多, 引起老叶LDMC增大,
SLA减小(Witkowski & Lamont, 1991; Reich et al.,
1998; Wilson et al., 1999; Kayama et al., 2002)。SLA
和LDMC是表征植物生活史策略的综合性状, 正如
Poorter和Garnier (1999)所认为的那样, LDMC和SLA
的相反的变化格局反映了植物在快速扩展光获取
能力(高SLA, 低LDMC)和高效储存物质(低SLA, 高
LDMC)这两种生物量投资策略之间的权衡。结合本
文的结果, 当年生叶片SLA较高, LDMC较低, 而往
年生叶片正好相反(表2), 表明随叶龄增加, 叶片生
活史策略发生转变, 即: 当年生叶片偏向于快速利
用积累的生物量以扩大光捕获面积, 而往年生叶片
更注重结构的投资。
不同叶龄性状的差别也可通过性状变异系数
来体现, 其大小反映了叶片不同发育阶段的形态可
塑性(胡启鹏等, 2008)。变异系数大说明性状值较分
散, 性状的可塑性较强。相反, 较小的变异系数则
联系着较小的性状可塑性, 表明性状值更为聚拢和
稳定。本研究中, 往年生叶片MLA、LDMC和SLA的
变异系数均小于当年生叶片, 即当年生叶片的性状
值较为发散, 而往年生叶片的性状值更为聚拢和稳
定。这说明: 1)当年生叶片处于叶片发育前期, 对环
境变化更为敏感, 轻微的环境改变就会促使其性状
发育方向改变, 即响应环境过滤的能力更强, 从而
表现出较大的可塑性(Sims & Pearcy, 1992; Wyka et
al., 2000; Frak et al., 2001)。相比之下, 发育更为成
熟的往年生叶片对环境变化不敏感 , 反应迟缓
(Oguchi et al., 2003), 故可塑性较低; 2)植物为获取
光资源优势, 初生新叶通常取代了大多数老叶的空
间位置而占据树冠最外层, 而老叶则被“推进”到树
冠内层(Niinemets et al., 2006), 老叶所能获得的光
资源变少, 加上其自身养分元素(N、P)迁移, 光合
能力减弱等原因(Field & Mooney, 1983; Bleecker,
1998; Ono et al., 2001), 导致其生长发育受到抑制,
可塑性降低。
3.2 异龄叶性状的关联性
叶片在不同生长阶段的资源分配方式在很大
程度上反映了植物的生活史特征(Weiner, 2004), 该
特征可通过叶片性状(MLA、SLA和LDMC)在当年生
和往年生叶片间的关联性体现。从个体水平到物种
水平, MLA在当年生和往年生叶片间的关联性均大
于SLA和LDMC (图1), 表明当年生叶片MLA的变异
对往年生叶片MLA变异的解释度更高, 当年生叶片
的SLA和LDMC虽然也可部分解释往年生叶片SLA
和LDMC的变异, 但解释度稍低。MLA是植物获取
光资源最直接的策略, 其在异龄叶间较高的相关性
反映了以下两个方面的事实: 1)新生叶片为补偿叶
片自身的建成消耗, 在生长当年就将叶片面积展开
至最大, 以获取最大的光资源和碳生产(Williams et
al., 1987; Tilman, 1988; Sultan, 2000), 因此MLA在
黄海侠等: 浙江天童常绿植物当年生与往年生叶片性状的变异与关联 919

doi: 10.3724/SP.J.1258.2013.00094
生长早期的增大程度较大, 而在生长后期, 叶片光
合能力衰退(Field & Mooney, 1983; Kitajima et al.,
1997; Bleecker, 1998; Ono et al., 2001), 这种情况下,
再通过增大MLA从而提升光合物质的收益已不显
著, 因此, 老叶的MLA大小主要还是由当年生叶片
的MLA所决定; 2)在生长当年将叶片尽可能地展开
至最大, 可减少翌年环境变化带来的生长风险。
此外, 在生长早期, SLA具有较大值, LDMC值
较小, 说明此时叶片具有更优的光资源获取能力
(Field & Mooney, 1983; Kitajima et al., 1997)和较为
活跃的代谢水平(Sims & Pearcy, 1992)。然而, 随着
叶龄增加, 次生代谢物质积累, 叶片光合能力衰退
(Field & Mooney, 1983), 外界环境因子胁迫作用加
强, 植物主要采取加强结构的建构来延长叶片停留
时间 (Gratani & Bombelli, 2000; Westoby et al.,
2002)。因此, 往年生叶片投资较多营养在组织密度
和叶片厚度上, 以抵御环境胁迫和病虫害的侵蚀
(Reich et al., 1998), 从而引起叶片SLA和LDMC在
生长后期发生较大的变化。由此可以看出, 往年生
叶片SLA和LDMC的改变主要取决于生长后期生长
策略的转变, 当年生叶片SLA和LDMC基底值大小
对其贡献相对较小。
3.3 叶龄对叶面积建成消耗的影响
由于叶片不同生长阶段物质分配策略的不同,
因而表现出异龄叶间性状特征的差异, 这也可以在
当年生和往年生叶片的建成消耗上得到体现
(Griffin, 1994)。本研究中, 当年生叶片SLA显著大于
往年生叶片(p < 0.001), 这说明与往年生叶片相比,
投资相同的生物量, 当年生叶片可构建较大的叶面
积, 其单位面积叶片的建成消耗较小, 这与对针叶
树种叶片建成消耗的研究结果一致(Feng et al.,
2008 )。因为当年生叶片在较短时间内需将叶片展
开, 以获得最大的光资源竞争优势(Tilman, 1988;
Sultan, 2000), 因此, 必须以牺牲厚度和质量为代
价 , 从而叶片较薄 , 干物质密度较小 (Field &
Mooney, 1983), 故建成消耗较小。对于往年生叶片,
其物质投资主要用于增加保卫构造(防虫食、防止过
度失水等 )或者增加叶片细胞密度 (Reich et al.,
1998; Westoby et al., 2002), 因而单位叶面积具有更
高的生物量, 叶片建成成本相应增大。
总之, 由于异龄叶发育阶段的迥异, 其物质投
资策略不同, 从而导致叶片性状特征的差异, 体现
了叶面积建成与消耗权衡的转化。这既是植物长期
适应环境的结果, 也是提高其生存适合度的途径。
基金项目 国家自然科学基金(31070383和31270-
475)。
致谢 感谢郭明、仲强和康蒙在野外协助收集数
据。
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特邀编委: 王国宏 责任编辑: 李 敏