非洲和澳大利亚稀树草原树种幼苗的温室比较研究
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摘要
稀树草原是全球生态系统的重要组成部分,世界主要稀树草原生态系统具有不同的地貌特征和独立的演化历史。水分、养分、火烧和和放牧是稀树草原生态系统结构和功能特征的最重要影响因素,树种幼苗的补充和更新是影响稀树草原长期动态平衡的关键阶段。然而,前人的研究尚未阐明资源和干扰对树种幼苗生长的影响及相对重要性、树种适应模式的共性和特性、以及适应模式与树种起源的关系。
本研究选取热带亚热带地区非洲和澳大利亚的稀树干草原和稀树湿草原的代表性树种,进行树种幼苗的温室实验,观察水分、养分梯度和树草竞争对树种幼苗生长的影响,探讨主要的植物功能性状对树种起源和不同处理条件的响应,研究功能性状间的相关性,以发现树种的适应模式,并分析不同的适应模式是否能够反映不同大洲的地貌特征及稀树草原独立的演化进程。
研究发现:(1)植物通过调整自身的生长模式和资源分配格局来适应环境,树种在长期进化过程中发展出的不同适应模式反映了其生长地的气候和干扰特征。(2)植物体需要平衡相对生长速率与自我防卫和养分保有能力间的关系。二者的平衡态势随植物体生长发育的不同阶段而不同,并受环境条件的影响。(3)稀树草原树种的生长受水分、养分的促进和树草竞争的抑制。氮供应的增加促进了地上部的生长尤其是增加了茎部的生物量分配,提高了叶片的光合能力。土壤含水量主要影响根系的形态结构、生长模式和植物体内水分含量。树种幼苗与草在地下为获取更多的水分和养分的竞争和在地上为获取更多光能的竞争同样激烈。(4)植物对环境的适应具有趋同进化的特点;植物功能性状间相互关联,性状的组合决定着植物群落与生态系统功能之间的相互作用。这些研究结果提示,不同大陆的稀树草原树种对环境的适应性生长策略具有一致性,但受到自身独立演化进程的影响,种系发生可能对树种的响应模式有重要影响。
Savanna is an important ecosystem throughout the world, characterized by the co-occurrence of trees and grasses. Savanna vegetation has variable physiognomy and floristic composition, the result of independent evolution on different continents from a host of plant genera in response to local environmental conditions. Water, nutrient, fire and herbivory are key environmental determinants. Tree seedling recruitment and establishment is the critical stage to long-term balance and dynamics in savanna.
However, the questions of whether and how species have adapted to differences in environmental variables expressed at continental scales and whether these adaptations have affected their abilities to grow in competition with grasses remain elusive. In order to access this, I conducted a greenhouse pot trial experiment to test the effect of resource availability and competition with grass on the growth of tree seedlings of species that are dominant in semi-arid and humid savannas in Africa and Australia. Various plant functional traits in relation to treatments, continents and savanna types have been evaluated using General Linear Model; correlations between these traits are further calculated by Spearman’s correlation.
Main findings are: (1) Biomass allocation pattern is a major factor in the response of plants to limited resource supply and disturbance; (2) The trade-off between relative growth rate and nutrient acquisition and conservation is affected by plant developmental stage and environmental stress; (3) Seedling growth is positively correlated with water and nutrient availability and inhibited by tree-grass competition. Growing pattern reflects local environmental conditions and is modified by independent flora evolution across continents; (4) Species’seedlings show convergent traits for environmental conditions. The association of plant functional traits and trait-environment linkage affect and reflect the ecological interaction between plant community and their ecosystem.
本研究选取热带亚热带地区非洲和澳大利亚的稀树干草原和稀树湿草原的代表性树种,进行树种幼苗的温室实验,观察水分、养分梯度和树草竞争对树种幼苗生长的影响,探讨主要的植物功能性状对树种起源和不同处理条件的响应,研究功能性状间的相关性,以发现树种的适应模式,并分析不同的适应模式是否能够反映不同大洲的地貌特征及稀树草原独立的演化进程。
研究发现:(1)植物通过调整自身的生长模式和资源分配格局来适应环境,树种在长期进化过程中发展出的不同适应模式反映了其生长地的气候和干扰特征。(2)植物体需要平衡相对生长速率与自我防卫和养分保有能力间的关系。二者的平衡态势随植物体生长发育的不同阶段而不同,并受环境条件的影响。(3)稀树草原树种的生长受水分、养分的促进和树草竞争的抑制。氮供应的增加促进了地上部的生长尤其是增加了茎部的生物量分配,提高了叶片的光合能力。土壤含水量主要影响根系的形态结构、生长模式和植物体内水分含量。树种幼苗与草在地下为获取更多的水分和养分的竞争和在地上为获取更多光能的竞争同样激烈。(4)植物对环境的适应具有趋同进化的特点;植物功能性状间相互关联,性状的组合决定着植物群落与生态系统功能之间的相互作用。这些研究结果提示,不同大陆的稀树草原树种对环境的适应性生长策略具有一致性,但受到自身独立演化进程的影响,种系发生可能对树种的响应模式有重要影响。
Savanna is an important ecosystem throughout the world, characterized by the co-occurrence of trees and grasses. Savanna vegetation has variable physiognomy and floristic composition, the result of independent evolution on different continents from a host of plant genera in response to local environmental conditions. Water, nutrient, fire and herbivory are key environmental determinants. Tree seedling recruitment and establishment is the critical stage to long-term balance and dynamics in savanna.
However, the questions of whether and how species have adapted to differences in environmental variables expressed at continental scales and whether these adaptations have affected their abilities to grow in competition with grasses remain elusive. In order to access this, I conducted a greenhouse pot trial experiment to test the effect of resource availability and competition with grass on the growth of tree seedlings of species that are dominant in semi-arid and humid savannas in Africa and Australia. Various plant functional traits in relation to treatments, continents and savanna types have been evaluated using General Linear Model; correlations between these traits are further calculated by Spearman’s correlation.
Main findings are: (1) Biomass allocation pattern is a major factor in the response of plants to limited resource supply and disturbance; (2) The trade-off between relative growth rate and nutrient acquisition and conservation is affected by plant developmental stage and environmental stress; (3) Seedling growth is positively correlated with water and nutrient availability and inhibited by tree-grass competition. Growing pattern reflects local environmental conditions and is modified by independent flora evolution across continents; (4) Species’seedlings show convergent traits for environmental conditions. The association of plant functional traits and trait-environment linkage affect and reflect the ecological interaction between plant community and their ecosystem.
引文
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