热带雨林土壤种子库小生境特征变化规律及其与种子存活的关系研究

Survival of seeds in the soil seed bank is important for the forest dynamics and natural regeneration, the habital factors that affected the seed survival at forest ecosystem level remain poorly understood. It was hypothesized that seeds of the soil seed bank may prevent lethal infection from external conditions and survived via two hypothetic mechanisms of "endogenous chemical defences of seeds" and "exotic chemical defences of beneficial seed-microbial associations", nevertheless further researchs are needed for these theories being verified. Especially，more researchs are needed concerning the habital condition affecting seed survival under artificial controlled conditions. There are two community types of germination of:(1) Germination inhibited without the external condition influence over a quiescence period; (2)Germination under favorable environmental conditions allowed to successfully exit a dormant state. Dormancy generates a seed bank. It is proposed that the individual seed variety and survival time are closely linked to the ecological conditions of a plant's habitat. In this project, we will investigate the mechanism of seed survival in soil seed bank by the habitat traits of soil seed banks and its relationship with seed survival. The dormancy seeds (Dillenia turbinata and Elaeocaepus dubius) without physical barriers and quiescence seeds (Syzygium cumini and Archidendron clypearia) were selected to verify these theories. The variation in soil habitat traits for the seed banks which comprises physical, chemical and microbial characters were explored. Meanwhile, primary ecological factors affecting seed survival in the soil were determined according to the experimental data analysis. Verification experiments will be carried out under those controlled fators. The variation rule of habitat traits of soil seed banks and its relationship with seed survival concerning the above mentioned plants will be studied and examples of the diverse plant seeds survival mechanism would be disclosed finally.

种子库是森林生态研究的重要内容，有助于认识森林种群动态与自然更新过程。热带雨林土壤高温高湿，土壤中的种子容易发霉死亡。但有一些种子却能存活下来，形成种子库，它们存活的机制是什么？目前处在学说阶段，最被接受的学说有"种子内源化学防御说"和"种子外源有益微生物化学防御学说"，但需要有效的案例验证。种子在土壤中，无论是休眠状态，还是待萌发的静止状态，它们的存活机制与种子库土壤理化性质及微生物活动情况有着必然的联系。本项目在完成林窗促进土壤种子库萌芽的机制研究基础上，拟通过以休眠种子（大花五桠果、高枝杜英）和静止待萌发种子（乌墨、猴耳环）为目标种子，在热带雨林土壤中和实验室无菌条件下开展这些种子的存活对比实验，探索这两类种子在土壤中存活状况与土壤理、化及微生物特征的关系，进而筛选影响的主导因子，进行人工控制实验，分析这两类种子在土壤中存活与它们变化的定理关系，达到揭示种子在土壤中存活机制的目的。

土壤种子库是热带雨林生态系统的重要组成部分，对森林植被的多样性保护，植被的更新和恢复、演替和扩散过程等起着至关重要的作用。热带雨林土壤高温高湿，土壤中的种子容易发霉死亡。但有一些种子却能存活下来，形成种子库，它们存活的机制是什么？至今仍未阐明。目前普遍接受的理论是种子休眠-防御综合理论，但仍缺少有效的案例验证。本项目以海南霸王岭热带雨林入侵林缘和林窗草本植物鬼针草（Bidens pilosa），演替早、中期树种楹树（Albizzia chinensis）和演替中后期树种山杜英（Elaeocaepus sylvestris）作为研究对象，从种子物理形态特征、化学组成和微生物组成及与土壤微生物的相互作用等多方面开展比较研究，综合探讨三种种子在热带雨林土壤种子库中存活的特性，研究结果充分表明，土壤种子库中种子存活与微生物的相互作用密切相关，由于土壤中病原真菌较多，种子能否存活到萌发取决于种子物理、化学及有益微生物防御等综合作用。本项目初步探明了两个类型的3种种子在土壤种子库中的存活特性：（1）静止待萌发种子，鬼针草种子为非休眠种子，可通过种子快速萌发逃脱病原菌的侵袭，也可依赖种子或种子际土壤有益微生物的防御，以“静止状态”在土壤种子库中存活下来。（2）休眠种子，楹树种子为物理休眠种子，主要依靠种皮的物理和化学防御抵御病原菌的侵袭，种子或种子际土壤有益微生物也参与种子的防御；山杜英种子为综合休眠的种子，主要依靠种皮的物理防御抵御病原菌的侵袭，种子或种子际土壤有益微生物也参与种子的防御。部分研究成果已经发表，共发表学术论文15篇，其中SCI收录2篇，其他均为国内核心刊物。本项目的研究成果达到了预期目标。