被子植物树种吸收根功能属性变异：热带和温带的对比研究

Functional trait variation in absorptive roots is closely linked with plant life histroy strategies and constitutes an important driver for ecosystem structure and functions.Mycorrhizal colonization is a key factor in driving root trait variation and may underlie mixed relationships between leaf and root traits. Actually, both the type and intensity of mycorrhizal colonization are affected by environmental water availability, temperature and nutrient level. Thus, it is important for studying root functional trait variation among ecosystems differing in mycorrhizae and these environment factors. However, patterns and mechanisms for absorptive root functional trait variation within and among ecosystems have been poorly understood because of little advance in root theory, as well as the tedious and laborious work in root sampling and processing. Moreover, plant phylogeny, often influential for plant functional trait variation, has little been evaluated for its role in driving root trait variation.In this project, variation of absorptive root traits will be studied in temperate and tropic forest ecosystems with contrasting mean annual precipitation and temperature and mycorrhizal colonization. Angiosperm tree species differing in plant phylogeny and mycorrhizal type are to be selected for root and leaf sampling. By examining a range of absorptive root functional traits, we aim to reveal their variation patterns within and among ecosystems. Meanwhile, we will assess contribution of environmental factors, mycorrhizal colonization and plant phylogeny to variation of absorptive root functional traits. The results and conclusions of this study will contribute to our understanding of patterns and mechanisms of absorptive root functional trait variation. The integration of mycorrhizal colonization in root trait variation could also help to classify confusing relationships between root and leaf functional traits in previous work.This also represents an important step further in studying plant adaption to environmental conditions and species coexistence in a community.

吸收根功能属性的变异与植物生活史策略、生态系统结构与功能密切相关。真菌侵染是驱动根属性变异以及根和叶属性差异的驱动因素，而真菌类型和程度主要决定于水、热和养分等环境因子。因此，在菌根类型和环境因子差异显著的生态系统之间进行吸收根功能属性的比较研究更能揭示其变异格局和机制。由于理论滞后和取样困难，目前对系统内和系统间吸收根属性变异格局和机制的认识十分有限。此外，物种间系统发育关系也是塑造植物功能属性的重要因素，但在根的研究中极少涉及。本项目拟以温带和热带森林生态系统为研究对象，选取不同系统发育背景和菌根类型的被子植物树种进行根、叶取样，通过比较两个系统内和系统间吸收根功能属性，并结合物种系统发育信息和环境因子，探讨吸收根属性变异格局及其与系统发育、真菌侵染以及环境因子之间的关系。研究结果将揭示吸收根功能属性变异格局和机制，深化对根-叶关系的理解，拓展对物种的环境适应和共存机制的认识。

吸收根是指根枝末端具有初生结构、执行水分和养分吸收功能的根级。吸收根的性状特征是反映植物进化以及响应环境变化的重要方面。本项目主要考察吸收根性状的种间变异格局，并探讨菌根类型和物种系统发育背景等因素的影响。结果表明：（1）吸收根直径有两个明显不同的进化格局：a)进化早期的树种吸收根直径较粗，进化晚期的直径较细；b)另有一些进化早期的物种的吸收根直径较细，而进化晚期物种吸收根直径较粗。这一发现提示，前人发现的吸收根进化规律，即这里的格局a)，仅限于一部分树种。（2）将吸收根分为粗和细两类时，我们发现粗吸收根并没有表现出指示经济学谱的conservation-acquisition tradeoff关系，而细吸收根具有这种经济学谱关系。这个结果为吸收根中经济学谱的争议提供了新的观点，并启发未来研究。（3）我们提出植物根序和根功能的关系有至少两种对应关系，而非目前认为的仅有一种对应模式。（4）我们还提出一种新的分离吸收根的方法：揉根法。该方法简单易行，具有一定的应用价值。通过本项目的研究，我们提出关于吸收根的一些新观点和方法，这些结果将丰富我们对根系结构和功能关系的理解，深化我们从器官性状到物种进化、分布和适应性，以及物种组成与生态系统功能关系等方面的理解。