广西亚热带森林在海拔梯度上群落增补限制和萌发可塑性研究

Recruitment limitation, defined as combined factors that limit seed production, seed dispersal, seedling emergence, and sapling and adult tree establishment, can favor rare species when microsites remain unoccupied by more abundant species. Germination plasticity could favor the establishment of faster growing species via seasonal priority effects resulting in their dominance in comparison to slower growing late successional species. However, in addressing how these two processes determine forest community assembly, most studies ignore life history stages beyond seeds and seedlings, transitional climatic zones where seasonality that govern biological rhythms is a major factor and elevational effects that determine plant range limits. This study is proposed to assess recruitment limitation and germination plasticity across elevational gradients in the Cen Wang Lao Shan, Da Ming Shan, Shi Wan Da Shan, and Da Yao Shan forests in Guangxi Zhuang Autonomous Region in southern China. We will censes recruitment limitation every two months for three years, using seed traps, seedling and sapling census plots and forest dynamic plots placed across elevational gradients. We will complement this data with an experimental study placed parallel to the forest dynamic plots in the same elevations by subjecting seedlings to three watering treatments that simulate climate change driven early season rainfall shifts. We will assess whether priority effects resulting from germination plasticity could change the trajectory of regeneration and thereby affect future community composition. This study data will increase our knowledge of regeneration ecology in this part of Asia, and will be globally important for understanding the ecology of these species rich transitional climatic zones. Further, this will be the most systematic assessment of recruitment limitation ever conducted over an elevational gradient and across life history stages, while considering the effect of germination plasticity in driving community composition due to global climate change driven precipitation shifts.

增补限制即从种子成熟、传播到幼苗萌发及幼树和成年树的建成均受外界环境的各种限制；其导致优势种无法占据所有微生境而有利于稀有种。速生树种萌发可塑性即抢先萌发特性；确立了其相对于演替后期树种的优势。以往研究发现两因素均显著影响森林群落组成，但较少关注海拔梯度、气候变化（降雨）和幼苗建成之后的生活史阶段的影响。为了探讨上述3个因素的影响，我们选择了广西境内的岑王老山、大明山、十万大山和大瑶山不同海拔的森林动态监测样地，在各样地内设置种子筐、幼苗和幼树监测样方，此外在附近设置三个水分梯度处理模拟降雨变化对幼苗更新的影响。在三年实验期内，通过种子雨及每两月一次的幼苗及幼树的调查，来评估由萌发可塑性效应能否改变更新进程。本研究是在一个沿海拔梯度的森林中、跨生活史不同阶段来验证更新限制假说最系统的研究，并且考虑降雨量变化的影响。研究结果将极大增进我们关于森林更新过程和物种共存机制的认识。

森林系统的自然再生对维持森林的物理和生物结构提供了一个关键的机制，对保护森林物种多样性和提供生态系统服务具有重要的价值。然而，人们对这一森林自然更新过程及其在群落构建和动态中所起的关键作用仍缺乏了解。本项目选择位于中国广西亚热带森林带上的岑王老山、花坪、木论及大瑶山的山地或喀斯特常绿落叶阔叶混交林作为研究对象，重点研究种子的产出（即种子雨）、土壤种子库和种子萌发形成的幼苗库这三个相互联系的自然更新过程，分析生物和非生物因素对种群成功更新的影响。研究结果揭示了生物和非生物生态因子如何相互作用并影响植物更新关键瓶颈的幼苗期。除了幼苗本身的特征，发现了非生物环境因素对林地上的发生过程也起着重要作用，不仅直接影响幼苗高度的生长和存活率的衡量，而且还间接影响幼苗群落与其消费者之间生物的相互作用。具体而言，这项研究清楚的证明了土壤锰和硫元素与幼苗成功再生之间的关系，以及光和氮对生物相互作用的间接影响。由于亚热带山地森林生态系统是一个尚未被充分研究的具有高生物多样性的地区，同时也是受威胁的地区，研究结果有助于增加对最终塑造森林生态系统的早期植物个体发生阶段的生态过程的了解，为进一步探究亚热带森林更新动态提供理论依据，并为制定造林、保育和自然资源教育的政策提供科学依据。