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植物C、N、P元素的生态化学计量是衡量陆地生态系统动态特征的关键指标[1-4],尤其是在植物生长的元素限制性特征以及资源利用效率等领域,C、N、P化学计量比的研究已经成为至关重要的方法途径[5-6]。全球气候变化背景下,陆地生态系统的响应更具复杂性[7-8],其中热带森林对气候变化的响应尤为敏感[9]。不同森林类型群落结构与功能随外界环境发生的变化,会引起植物体内化学元素含量分配格局、受限制状况、吸收和利用养分效率的改变[10-12],进而对生态系统的养分供求和循环模式产生影响[13]。深入研究森林群落植物体内的元素化学计量特征,对于揭示不同环境梯度下的群落类型对气候变化的响应及生态适应策略,具有重要科学意义[8]。
植物不同器官之间养分含量的差异,与生态系统养分动态平衡和分配格局存在内在关联[14-15]。已有研究表明,植物各器官内养分元素含量及其计量比与其自身光合作用、支持和储存功能等特性紧密相关[16],尤其植物茎干组织作为植物体内各种营养元素传输和储存的重要器官[14],在连接叶片与根系和提供养分储存空间等方面具有至关重要的作用[17]。当前,国内外有关生态化学计量的研究多集中于植物叶片以及土壤等方面,诸如针对荒漠[18]、草地[19]、森林[11]、湿地[6]等。近几年来,张雨鉴等[16]和吴一博等[20]的研究,广泛涉及到乔木和灌木各器官间养分元素的分配特征,但对树干这一特定器官开展的相关研究还非常缺乏。
滇南热带森林生态系统,即在中国植被区划的热带季雨林、雨林区域(V区)和亚热带常绿阔叶林区域(IV区),是中国西南部阔叶林植被类型南北向空间分布格局、沿纬度和海拔梯度变化的典型代表[21]。在这一植被区域中,胡朝臣等[22]和卢同平等[23]对热带雨林植物和土壤进行生态化学计量特征分析,而滇南区域季节雨林、山地雨林、中山湿性常绿阔叶林等主要优势种生态化学计量沿海拔变化的生态适应研究仍处于空白阶段。幼树是对环境变化响应最为敏感的类群之一[8,24],群落中幼树的生态化学计量格局,对于揭示系统物质循环及其对气候气候变化的响应机制等均具有更为重要的意义[25],而当前面向滇南热带森林幼树的生态化学计量特征的研究,仅见少量报道[26-27],相关科学问题仍缺乏系统深入的了解。本研究面向上述3种森林类型,选取群落主要优势种幼树,对树干全C、全N、全P化学计量特征开展研究,探讨其随物种差异、森林类型、海拔梯度以及气候环境等变化下的特征规律,为深入揭示生态系统的养分供需状况、物种对环境变化的适应机制等提供科学依据。
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本试验于2009年8月(雨季)期间,在西双版纳勐仑、勐宋生态站和哀牢山国家级自然保护区核心区的徐家坝内,分别选取中心海拔为600 m、1 600 m和2 500 m的各森林群落类型,按照《生物多样性观测技术指导-陆生维管植物》(HJ 710.1—2014)中的标准[28],选取坡度、方向等立地条件基本一致的典型地段,分别建立热带季节雨林、热带山地雨林以及中山湿性常绿阔叶林样地各3块,每块样地面积为100 m × 100 m,重复3次。各个样地具体情况见表1。
表 1 滇南地区各森林类型研究样地概况
Table 1. Geophysical characteristics of the investigating plots in each forest type in southern Yunnan
植被类型
Vegetation type样地
Plot No.林龄
Age/a海拔
Elevation/
m植被盖度
Vegetation
coverage/%坡度
Slop
gradient/
(°)坡向
Slope
aspect株数
Number of
samples平均胸径
Average
DBH/
cm土壤类型
Soil
category热带季节雨林 1 6 589 75.33 22 西北 NW 21 1.5 砖红壤 2 6 644 82.65 18 西北 NW 21 1.5 砖红壤 3 5 621 85.14 26 西北 NW 21 1.5 砖红壤 热带山地雨林 1 7 1 657 77.32 25 西北 NW 21 1.5 红壤 2 5 1 782 72.56 30 西北 NW 21 1.5 红壤 3 6 1 715 65.73 20 西北 NW 21 1.5 赤红壤 中山湿性常绿阔叶林 1 7 2 593 80.24 16 东北 NE 21 1.5 黄棕壤 2 6 2 522 73.61 20 东北 NE 21 1.5 黄棕壤 3 7 2 548 78.19 18 东北 NE 21 1.5 黄棕壤 热带季节雨林 6±0.47 A 618±22.55 A 81±4.16 A 22±3.27 A 热带山地雨林 6±0.82 A 1 718±51.08 B 72±4.76 B 25±4.08 A 中山湿性常绿阔叶林 7±0.47 A 2 554±29.33 C 77±2.77 AB 18±1.63 A 注:不同大写字母表示不同植被类型间差异显著(P<0.05),不同小写字母表示不同层次间差异显著(P<0.05),下同。
Notes: Different capital letters indicate that there are significant differences among different forest types, different small letters indicate that there are significant differences among different tree community; the same below. DBH: Diameter at breast height.在各样地中,选取7种不同层次(上层、下层)的主要优势种幼树,每种幼树选择胸径约1.5 cm的3~5棵植株,用生长锥在其胸径处(离地面约1.3 m)钻取树心,每棵树钻取2~3次。将采集的样品带回实验室,放入75 ℃恒温箱中烘干至恒质量,随后进行全C、全N、全P元素含量测量。样品全C含量采用vario MACRO cube碳氮分析仪测定,全N含量采用半微量凯氏定氮法(LY/T 1269—1999)测定[12,24],全P含量采用H2SO4-H2O2消煮后,采用ICP-AES方法进行测定[16]。
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采用Excel 2013软件对原始数据进行整理、计算平均值以及作图。以SPSS 22.0、OriginLab及Canoco 5软件分别对原始数据进行单因素方差分析(one-way ANOVA)、差异性显著分析(T检验和Duncan检验)、相关性分析(Pearson检验)和冗余分析(Redundancy Analysis,RDA)。
滇南3种不同类型热带森林优势种幼树树干生态化学计量特征
Sapling Stem Stoichiometry of Dominant Species in Three Types of Tropical Forests in Southern Yunnan
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摘要:
目的 探讨滇南地区热带、亚热带森林物种养分元素分配模式、受限制状况、吸收利用资源能力等特征,以期揭示外界环境变化下物种的适应性机制。 方法 以滇南区域热带季节雨林、热带山地雨林和中山湿性常绿阔叶林3种热带森林主要优势种为研究对象,分析不同类型森林不同层次优势种幼树树干C、N、P化学计量特征变化。 结果 1)3种森林优势种幼树树干全C含量随海拔梯度的增加总体呈增加趋势,全N含量和全P含量随海拔梯度的增加呈降低趋势;2)中山湿性常绿阔叶林的C:N、C:P相对较高,热带季节雨林和热带山地雨林N:P均小于14,中山湿性常绿阔叶林大于16;3)森林上层优势种幼树树干全C、全N含量均低于下层树种,全P含量则高于下层树种,上层优势种N:P均小于14,下层优势种大于16,说明上层优势种生长主要受到N元素的限制,且吸收和利用养分能力高于下层优势种;4)冗余分析表明:海拔和层次对优势种幼树树干养分含量及化学计量比的影响较大。 结论 滇南地区3种森林中,中山湿性常绿阔叶林拥有相对较高的氮、磷利用效率,本区生态系统主要受到N、P元素的共同限制作用。不同生长环境条件下植物体内养分元素生态化学计量特征的差异性,可以进一步揭示物种适应各种生态环境的应对机制。 Abstract:Objective The aim this study was to explore the distribution patterns and limitation of nutrient elements in subtropical forest species in southern Yunnan, for revealing the adaptive mechanism of tree species under a changing environment. Method The dominant species in three types of tropical forests, i.e., tropical seasonal rain forests, tropical montane rain forests and montane moist evergreen broad-leaved forests, were sampled in southern Yunnan to analyze C, N, P and their stoichiometric ratios in sapling stems. Result 1) The total C of sapling stems of dominant species in the three types of tropical forests generally increased, but total N and P decreased with increasing elevation. 2) The ratios of stem C:N and C:P in montane moist evergreen broad-leaved forests were relatively high compared to other two types of forests. The ratio of stem N:P both in tropical seasonal rain forests and tropical montane rain forests were less than 14, while this value in montane moist evergreen broad-leaved forests was higher than 16. 3) The stem C and N of dominant species in upper canopy were smaller than lower canopy. However, total P contents in upper canopy was higher than those in lower canopy. The value of N:P in upper canopy was less than 14, whereas it was higher than 16 in lower canopy. These results suggested that the growth of dominant species in upper canopy was mainly limited by N. 4) The results of Redundancy analysis revealed that elevation and community had a great effect on C, N and P contents and their stoichiometric ratios in sapling stems of dominant species. Conclusion Montane moist evergreen broad-leaved forest has a relatively high nutrient efficiency, and the forest ecosystems in southern Yunnan are mainly limited by N and P contents. The difference of ecological stoichiometric characteristics in trees under different environments can reveal the coping mechanisms of species adaptating to changing environments. -
Key words:
- tropical forest
- / stoichiometry
- / elevation gradient
- / tree community
- / tree stems
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表 1 滇南地区各森林类型研究样地概况
Table 1. Geophysical characteristics of the investigating plots in each forest type in southern Yunnan
植被类型
Vegetation type样地
Plot No.林龄
Age/a海拔
Elevation/
m植被盖度
Vegetation
coverage/%坡度
Slop
gradient/
(°)坡向
Slope
aspect株数
Number of
samples平均胸径
Average
DBH/
cm土壤类型
Soil
category热带季节雨林 1 6 589 75.33 22 西北 NW 21 1.5 砖红壤 2 6 644 82.65 18 西北 NW 21 1.5 砖红壤 3 5 621 85.14 26 西北 NW 21 1.5 砖红壤 热带山地雨林 1 7 1 657 77.32 25 西北 NW 21 1.5 红壤 2 5 1 782 72.56 30 西北 NW 21 1.5 红壤 3 6 1 715 65.73 20 西北 NW 21 1.5 赤红壤 中山湿性常绿阔叶林 1 7 2 593 80.24 16 东北 NE 21 1.5 黄棕壤 2 6 2 522 73.61 20 东北 NE 21 1.5 黄棕壤 3 7 2 548 78.19 18 东北 NE 21 1.5 黄棕壤 热带季节雨林 6±0.47 A 618±22.55 A 81±4.16 A 22±3.27 A 热带山地雨林 6±0.82 A 1 718±51.08 B 72±4.76 B 25±4.08 A 中山湿性常绿阔叶林 7±0.47 A 2 554±29.33 C 77±2.77 AB 18±1.63 A 注:不同大写字母表示不同植被类型间差异显著(P<0.05),不同小写字母表示不同层次间差异显著(P<0.05),下同。
Notes: Different capital letters indicate that there are significant differences among different forest types, different small letters indicate that there are significant differences among different tree community; the same below. DBH: Diameter at breast height. -
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