生物多样性 ›› 2019, Vol. 27 ›› Issue (12): 1279-1290.doi: 10.17520/biods.2019267

• 研究报告:植物多样性 • 上一篇    下一篇

鼎湖山南亚热带常绿阔叶林叶功能性状沿群落垂直层次的种内变异

张入匀1, 2, 3, 李艳朋1, 2, 3, 倪云龙1, 2, 3, 桂旭君1, 2, 3, 练琚愉1, 2, 叶万辉1, 2, *()   

  1. 1 中国科学院华南植物园退化生态系统植被恢复与管理重点实验室, 广州 510650
    2 中国科学院华南植物园广东省应用植物学重点实验室, 广州 510650
    3 中国科学院大学, 北京 100049
  • 收稿日期:2019-08-28 接受日期:2019-12-02 出版日期:2019-12-20
  • 通讯作者: 叶万辉 E-mail:why@scbg.ac.cn
  • 基金项目:
    中国科学院战略性先导科技专项(XDB31030000);国家重点研发计划(2017YFC0505802);中国森林生物多样性监测网络建设项目;广东省国家级自然保护区植物多样性监测服务项目(1210-1741YDZB0401-1)

Intraspecific variation of leaf functional traits along the vertical layer in a subtropical evergreen broad-leaved forest of Dinghushan

Ruyun Zhang1, 2, 3, Yanpeng Li1, 2, 3, Yunlong Ni1, 2, 3, Xujun Gui1, 2, 3, Juyu Lian1, 2, Wanhui Ye1, 2, *()   

  1. 1 Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden,Chinese Academy of Sciences, Guangzhou 510650
    2 Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650
    3 University of Chinese Academy of Sciences, Beijing 100049
  • Received:2019-08-28 Accepted:2019-12-02 Online:2019-12-20
  • Contact: Ye Wanhui E-mail:why@scbg.ac.cn

探究功能性状沿着环境梯度如何变化一直以来是基于性状的群落生态学的核心问题之一。尽管功能性状存在种内和种间变异, 但种内变异沿环境梯度如何变化仍有待探究。本文以鼎湖山南亚热带常绿阔叶林1.44 ha塔吊样地内16个树种的2,820个个体为研究对象, 探究4种叶功能性状(比叶面积、叶干物质含量、叶厚度和叶面积)沿群落垂直层次的种内变异。首先, 利用随机效应线性模型量化塔吊样地内的种内变异和种间变异; 其次, 利用Kmeans函数将森林的垂直层次划分为灌木层、亚冠层和林冠层, 并通过构建回归模型探究叶功能性状在群落垂直层次中的种内变异格局。最后, 应用混合线性模型和单因素方差分析的方法探究叶功能性状沿垂直层次的种内变异是否具有物种依赖性。结果表明: 在局域群落中, 并非所有叶功能性状的种内变异都低于种间变异; 叶功能性状在不同垂直层次的种内变异格局存在显著差异, 且种内变异与垂直范围呈正相关; 叶功能性状的种内变异具有较强的物种依赖性, 因此树种差异相对于小环境解释了更多的性状变异; 此外, 不同叶功能性状的种内变异沿垂直层次的变化趋势并不一致。本研究发现种内变异对于物种共存具有重要作用。

关键词: 种内变异, 垂直层次, 小环境, 叶功能性状, 物种共存

Exploring how functional traits vary along environmental gradients has always been one of the core issues of trait-based community ecology. While functional traits vary both among species and within species, little is known about how intraspecific variation changes along environmental gradients. We explored how intraspecific trait variations of four leaf functional traits (specific leaf area, leaf dry matter content, leaf thickness, leaf area) varied along vertical layer within community using data for 2,820 individuals belonging to 16 species in a 1.44-ha plot in the south subtropical evergreen broad-leaved forest in Dinghushan. First, we quantified the relative importance of intra- and interspecific trait variation within the canopy crane plot using linear random effect model. Trees were classified into three categories: shrub, subcanopy, canopy using the Kmeans method and investigated the patterns of intraspecific trait variation in different vertical layer using regression models. Finally, we explored whether intraspecific trait variation in different vertical layers depended on species differences using linear mixed effect models and a one-way analysis of variance. Results suggest that general intraspecific trait variation was lower than interspecific variation in the local community. Moreover, the pattern of intraspecific trait variation differed significantly among different vertical layer, and intraspecific trait variation was positively correlated with the vertical range. Intraspecific variation of leaf functional traits strongly depended on species differences, so species differences were relatively more important than microenvironment in explaining trait variation. In addition, intraspecific variation of different leaf functional traits showed different trends along vertical layer. Our study found the important role of intraspecific trait variation in species coexistence.

Key words: intraspecific variation, vertical layer, microenvironments, leaf functional traits, species coexistence

图1

叶功能性状变异来源, 基于物种间和物种内两个水平的方差分解。"

图2

叶功能性状在群落不同垂直层的种内变异格局。(A)叶功能性状的变异系数平均值在各个垂直层次的差异, 不同字母表示差异显著(P < 0.05)。(B)叶功能性状的变异系数平均值与垂直范围的关系。"

表1

比较叶功能性状-小环境模型(AIC)和边际决定系数(R2m), 条件决定系数(R2c)。"

叶功能性状 Leaf functional traits 固定效应 Fixed effect R2m R2c AIC
比叶面积 Specific leaf area 垂直层次 Vertical layer 0.82 0.82 -402.55
干物质含量 Leaf dry matter content 垂直层次 Vertical layer 0.77 0.77 2,314.78
叶厚度 Leaf thickness 垂直层次 Vertical layer 0.85 0.85 -1,433.96
叶面积 Leaf area 垂直层次 Vertical layer 0.88 0.88 1,547.18

图3

模型中各个叶功能性状由固定效应解释的方差占总体方差的比例"

图4

16个树种比叶面积种内变异与垂直层次的关系(平均值 ± 标准差), 括号中是物种多度信息。不同字母表示同一物种的比叶面积在不同垂直层次存在显著差异(P < 0.05)。"

图5

16个树种叶厚度种内变异与垂直层次的关系(平均值 ± 标准差)。不同字母表示同一物种的叶厚度在不同垂直层次存在显著差异(P < 0.05)。"

图6

16个树种叶干物质含量种内变异与垂直层次的关系(平均值 ± 标准差)。不同字母表示同一物种的叶干物质含量在不同垂直层次存在显著差异(P < 0.05)。"

图7

16个树种叶面积种内变异与垂直层次的关系(平均值 ± 标准差)。不同字母表示同一物种的叶面积在不同垂直层次存在显著差异(P < 0.05)。"

[1] Agusti S, Enriquez S, Frostchristensen H, Sandjensen K, Duarte CM ( 1994) Light-harvesting among photosynthetic or ganisms. Functional Ecology, 8, 273-279.
[2] Anhuf D, Rollenbeck R ( 2001) Canopy structure of the Rio Surumoni rain forest (Venezuela) and its influence on microclimate. Ecotropica, 7, 21-32.
[3] Auger S, Shipley B ( 2013) Inter-specific and intra-specific trait variation along short environmental gradients in an old-growth temperate forest. Journal of Vegetation Science, 24, 419-428.
[4] Burton JI, Perakis SS, McKenzie SC, Lawrence CE, Puettmann KJ ( 2017) Intraspecific variability and reaction norms of forest understorey plant species traits. Functional Ecology, 31, 1881-1893.
[5] Cach-Perez MJ, Andrade JL, Cetzal-Ix W, Reyes-Garcia C ( 2016) Environmental influence on the inter- and intraspecific variation in the density and morphology of stomata and trichomes of epiphytic bromeliads of the Yucatan Peninsula. Botanical Journal of the Linnean Society, 181, 441-458.
[6] Condit R ( 1998) Tropical Forest Census Plots: Methods and Results from Barro Colorado Island, Panama and A Comparison with Other Plots. Springer, Berlin.
[7] Cornelissen JHC, Lavorel S, Garnier E, Díaz S, Buchmann N, Gurvich DE, Reich PB, ter Steege H, Morgan HD, van der Heijden MGA, Pausas JG, Poorter H ( 2003) A handbook of protocols for standardised and easy measurement of plant functional traits worldwide. Australian Journal of Botany, 51, 335-380.
[8] Coyle JR ( 2017) Intraspecific variation in epiphyte functional traits reveals limited effects of microclimate on community assembly in temperate deciduous oak canopies. Oikos, 126, 111-120.
[9] Douglas B, Martin M, Ben B, Steve W ( 2015) Fitting linear mixed-effects models using lme4. Journal of Statistical Software, 67, 1-48.
[10] Gui XJ, Lian JY, Zhang RY, Li YP, Shen H, Ni YL, Ye WH ( 2019) Vertical structure and its biodiversity in a subtropical evergreen broadleaved forest at Dinghushan in Guangdong Province, China. Biodiversity Science, 27, 619-629. (in Chinese with English abstract)
[ 桂旭君, 练琚愉, 张入匀, 李艳朋, 沈浩, 倪云龙, 叶万辉 ( 2019) 鼎湖山南亚热带常绿阔叶林群落垂直结构及其物种多样性特征. 生物多样性, 27, 619-629.]
[11] He D, Chen YF, Zhao KN, Cornelissen JHC, Chu CJ ( 2018) Intra- and interspecific trait variations reveal functional relationships between specific leaf area and soil niche within a subtropical forest. Annals of Botany, 121, 1173-1182.
[12] He D, Yan ER ( 2018) Size-dependent variations in individual traits and trait scaling relationships within a shade-tolerant evergreen trees pecies. American Journal of Botany, 105, 1165-1174.
[13] Heilmeier H ( 2019) Functional traits explaining plant responses to past and future climate changes. Flora, 254, 1-11.
[14] Hietz P, Wanek W ( 2003) Size-dependent variation of carbon and nitrogen isotope abundances in epiphytic bromeliads. Plant Biology, 5, 137-142.
[15] Hopkin M ( 2005) Biodiversity and climate form focus of forest canopy plan. Nature, 436, 452.
[16] Ichie T, Inoue Y, Takahashi N, Kamiya K, Kenzo T ( 2016) Ecological distribution of leaf stomata and trichomes among tree species in a Malaysian lowland tropical rain forest. Journal of Plant Research, 129, 625-635.
[17] Jin MY, Jiang F, Jin GZ, Liu ZL ( 2018) Variations of specific leaf area in different growth periods and canopy positions of Betula platyphylla at different ages. Scientia Silvae Sinicae, 54(9), 18-26. (in Chinese with English abstrac)
[ 金明月, 姜峰, 金光泽, 刘志理 ( 2018) 不同年龄白桦比叶面积的生长阶段变异及冠层差异. 林业科学, 54(9), 18-26.]
[18] Jung V, Violle C, Mondy C, Hoffmann L, Muller S ( 2010) Intraspecific variability and trait-based community assembly. Journal of Ecology, 98, 1134-1140.
[19] Kenzo T, Inoue Y, Yoshimura M, Yamashita M, Tanaka-Oda A, Ichie T ( 2015) Height-related changes in leaf photosynthetic traits in diverse Bornean tropical rain forest trees. Oecologia, 177, 191-202.
[20] Kraft NJB, Valencia R, Ackerly DD ( 2008) Functional traits and niche-based tree community assembly in an Amazonian forest. Science, 322, 580-582.
[21] Kuznetsova A, Brockhoff PB, Christensen RHB ( 2017) lmerTest package: Tests in linear mixed effects models. Journal of Statistical Software , 82, 1-26.
[22] Leal DB, Thomas SC ( 2003) Vertical gradients and tree-to-tree variation in shoot morphology and foliar nitrogen in an old-growth Pinus strobus stand. Canadian Journal of Forest Research, 33, 1304-1314.
[23] Long WX, Zang RG, Schamp BS, Ding Y ( 2011) Within- and among-species variation in specific leaf area drive community assembly in a tropical cloud forest. Oecologia, 167, 1103-1113.
[24] Ma KP ( 2015) Biodiversity monitoring in China: From CForBio to Sino BON. Biodiversity Science, 23, 1-2. (in Chinese)
[ 马克平 ( 2015) 中国生物多样性监测网络建设: 从CForBio到Sino BON. 生物多样性, 23, 1-2.]
[25] Markesteijn L, Poorter L, Bongers F ( 2007) Light-dependent leaf trait variation in 43 tropical dry forest tree species. American Journal of Botany, 94, 515-525.
[26] McGill BJ, Enquist BJ, Weiher E, Westoby M ( 2006) Rebuilding community ecology from functional traits. Trends in Ecology & Evolution, 21, 178-185.
[27] McMurtrie RE, Dewar RC ( 2011) Leaf-trait variation explained by the hypothesis that plants maximize their canopy carbon export over the lifespan of leaves. Tree Physiology, 31, 1007-1023.
[28] Messier J, McGill BJ, Lechowicz MJ ( 2010) How do traits vary across ecological scales? A case for trait-based ecology. Ecology Letters, 13, 838-848.
[29] Moran EV, Hartig F, Bell DM ( 2016) Intraspecific trait variation across scales: Implications for understanding global change responses. Global Change Biology, 22, 137-150.
[30] Nakagawa S, Schielzeth H ( 2013) A general and simple method for obtaining R 2 from generalized linear mixed-effects models . Methods in Ecology and Evolution, 4, 133-142.
[31] Nakamura A, Kitching RL, Cao M, Creedy TJ, Fayle TM, Freiberg M, Hewitt CN, Itioka T, Koh LP, Ma K, Malhi Y, Mitchell A, Novotny V, Ozanne CMP, Song L, Wang H, Ashton LA ( 2017) Forests and their canopies: Achievements and horizons in canopy science. Trends in Ecology & Evolution, 32, 438-451.
[32] Oliveira BF, Scheffers BR ( 2019) Vertical layer influences global patterns of biodiversity. Ecography, 42, 249-258.
[33] Pérez-Harguindeguy N, Díaz S, Garnier E, Lavorel S, Poorter H, Jaureguiberry P, Bret-Harte MS, Cornwell WK, Craine JM, Gurvich DE, Urcelay C, Veneklaas EJ, Reich PB, Poorter L, Wright IJ, Ray P, Enrico L, Pausas JG, de Vos AC, Buchmann N, Funes G, Quétier F, Hodgson JG., Thompson K, Morgan HD, ter Steege H, van der Heijden MGA, Sack L, Blonder B, Poschlod P, Vaieretti MV, Conti G, Staver AC, Aquino S, Cornelissen JHC ( 2013) New handbook for standardised measurement of plant functional traits worldwide. Australian Journal of Botany, 61, 167-234.
[34] Perez-Ramos IM, Urbieta IR, Zavala MA, Maranon T ( 2012) Ontogenetic conflicts and rank reversals in two Mediterranean oak species: Implications for coexistence. Journal of Ecology, 100, 467-477.
[35] Petter G, Wagner K, Wanek W, Delgado EJS, Zotz G, Cabral JS, Kreft H ( 2016) Functional leaf traits of vascular epiphytes: Vertical trends within the forest, intra- and interspecific trait variability, and taxonomic signals. Functional Ecology, 30, 188-198.
[36] Pickup M, Westoby M, Basden A ( 2005) Dry mass costs of deploying leaf area in relation to leaf size. Functional Ecology, 19, 88-97.
[37] Poorter L, Kwant R, Hernandez R, Medina E, Werger MJA ( 2000) Leaf optical properties in Venezuelan cloud forest trees. Tree Physiology, 20, 519-526.
[38] Reich PB ( 2014) The world-wide ‘fast-slow’ plant economics spectrum: A traits manifesto. Journal of Ecology, 102, 275-301.
[39] Rosbakh S, Romermann C, Poschlod P ( 2015) Specific leaf area correlates with temperature: New evidence of trait variation at the population, species and community levels. Alpine Botany, 125, 79-86.
[40] Rosindell J, Harmon LJ, Etienne RS ( 2015) Unifying ecology and macroevolution with individual-based theory. Ecology Letters, 18, 472-482.
[41] Rozendaal DMA, Hurtado VH, Poorter L ( 2006) Plasticity in leaf traits of 38 tropical tree species in response to light; relationships with light demand and adult stature. Functional Ecology, 20, 207-216.
[42] Salgado-Luarte C, Gianoli E ( 2011) Herbivory may modify functional responses to shade in seedlings of a light-demanding tree species. Functional Ecology, 25, 492-499.
[43] Scheepens JF, Frei ES, Stocklin J ( 2010) Genotypic and environmental variation in specific leaf area in a widespread alpine plant after transplantation to different altitudes. Oecologia, 164, 141-150.
[44] Scheffers BR, Evans TA, Williams SE, Edwards DP ( 2014) Microhabitats in the tropics buffer temperature in a globally coherent manner. Biology Letters, 10, 12-15.
[45] Shen H, Cai JN, Li MJ, Chen Q, Ye WH, Wang ZF, Lian JY, Song L ( 2017) On Chinese forest canopy biodiversity monitoring. Biodiversity Science, 25, 229-236. (in Chinese with English abstract)
[ 沈浩, 蔡佳宁, 李萌姣, 陈青, 叶万辉, 王峥峰, 练琚愉, 宋亮 ( 2017) 中国森林冠层生物多样性监测. 生物多样性, 25, 229-236.]
[46] Shipley B, de Bello F, Cornelissen JHC, Laliberte E, Laughlin DC, Reich PB ( 2016) Reinforcing loose foundation stones in trait-based plant ecology. Oecologia, 180, 923-931.
[47] Siefert A, Violle C, Chalmandrier L, Albert CH, Taudiere A., Fajardo A, Aarssen LW, Baraloto C, Carlucci MB, Cianciaruso MV, de Dantas V, de Bello F, Duarte LDS, Fonseca CR, Freschet GT, Gaucherand S, Gross N, Hikosaka K, Jackson B, Jung V, Kamiyama C, Katabuchi M, Kembel SW, Kichenin E, Kraft NJB, Lagerström A, Le Bagousse-Pinguet Y, Li YZ, Mason N, Messier J, Nakashizuka T, Overton JM, Peltzer DA, Pérez-Ramos IM, Pillar VD, Prentice HC, Richardson S, Sasaki T, Schamp BS, Schöb C, Shipley B, Sundqvist M, Sykes MT, Vandewalle M, Wardle DA ( 2015) A global meta-analysis of the relative extent of intraspecific trait variation in plant communities. Ecology Letters, 18, 1406-1419.
[48] Silvertown J ( 2004) Plant coexistence and the niche. Trends in Ecology & Evolution, 19, 605-611.
[49] Tang QQ, Huang YT, Ding Y, Zang RG ( 2016) Interspecific and intraspecific variation in functional traits of subtropical evergreen and deciduous broad-leaved mixed forests. Biodiversity Science, 24, 262-270. (in Chinese with English abstract)
[ 唐青青, 黄永涛, 丁易, 臧润国 ( 2016) 亚热带常绿落叶阔叶混交林植物功能性状的种间和种内变异. 生物多样性, 24, 262-270.]
[50] Travis JMJ, Delgado M, Bocedi G, Baguette M, Barton K, Bonte D, Boulangeat I, Hodgson JA, Kubisch A, Penteriani V, Saastamoinen M, Stevens VM, Bullock JM ( 2013) Dispersal and species’ responses to climate change. Oikos, 122, 1532-1540.
[51] Valen LV ( 1965) Morphological variation and width of ecological niche. The American Naturalist, 99, 377-390.
[52] Violle C, Enquist BJ, McGill BJ, Jiang L, Albert CH, Hulshof C, Jung V, Messier J ( 2012) The return of the variance: Intraspecific variability in community ecology. Trends in Ecology & Evolution, 27, 244-252.
[53] Violle C, Navas ML, Vile D, Kazakou E, Fortunel C, Hummel I, Garnier E ( 2007) Let the concept of trait be functional! Oikos, 116, 882-892.
[54] Weerasinghe LK, Creek D, Crous KY, Xiang S, Liddell MJ, Turnbull MH, Atkin OK ( 2014) Canopy position affects the relationships between leaf respiration and associated traits in a tropical rainforest in Far North Queensland. Tree Physiology, 34, 564-584.
[55] Wickham H ( 2016) ggplot2: Elegant Graphics for Data Analysis. Springer-Verlag, New York.
[56] Wilson PJ, Thompson K, Hodgson JG ( 1999) Specific leaf area and leaf dry matter content as alternative predictors of plant strategies. New Phytologist, 143, 155-162.
[57] Wright IJ, Reich PB, Westoby M, Ackerly DD, Baruch Z, Bongers F, Cavender-Bares J, Chapin T, Cornelissen JHC, Diemer M, Flexas J, Garnier E, Groom PK, Gulias J, Hikosaka K, Lamont BB, Lee T, Lee W, Lusk C, Midgley JJ, Navas ML, Niinemets U, Oleksyn J, Osada N, Poorter H, Poot P, Prior L, Pyankov VI, Roumet C, Thomas SC, Tjoelker MG, Veneklaas EJ, Villar R ( 2004) The worldwide leaf economics spectrum. Nature, 428, 821-827.
[58] Yang J, Cao M, Swenson NG ( 2018) Why functional traits do not predict tree demographic rates. Trends in Ecology & Evolution, 33, 326-336.
[59] Ye WH, Cao HL, Huang ZL, Lian JY, Wang ZG, Li L, Wei SG, Wang ZM ( 2008) Community structure of a 20 hm 2 lower subtropical evergreen broadleaved forest plot in Dinghushan, China . Journal of Plant Ecology (Chinese Version), 32, 274-286. (in Chinese with English abstract)
[ 叶万辉, 曹洪麟, 黄忠良, 练琚愉, 王志高, 李林, 魏识广, 王章明 ( 2008) 鼎湖山南亚热带常绿阔叶林20公顷样地群落特征研究. 植物生态学报, 32, 274-286.]
[60] Zotz G ( 2000) Size-related intraspecific variability in physiological traits of vascular epiphytes and its importance for plant physiological ecology. Perspectives in Plant Ecology, Evolution and systematics, 3, 19-28.
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[12] 张全国, 张大勇. (2003) 生物多样性与生态系统功能:最新的进展与动向. 生物多样性, 11(5): 351-363.
[13] 侯继华, 马克平. (2002) 植物群落物种共存机制的研究进展. 植物生态学报, 26(增刊): 1-8.
[14] 张晓爱, 赵亮, 康玲. (2001) 生态群落物种共存的进化机制. 生物多样性, 09(1): 8-17.
[15] 李博 陈家宽 A. R. 沃金森. (1998) 植物竞争研究进展. 植物学报, 15(04): 18-29.
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