基于种子大小及其频率依赖的六盘山区辽东栎种子扩散和幼苗增补策略

Seed dispersal and seedling recruitment mediated through behavioral preferences of predation/dispersal by rodents are two key steps in the regeneration of plant population. It is well acknowledged that the seed size of Quercus wutaishanica has important effects on the strategy of behavioral decision of predation or hoarding/dispersal by rodents and seed fate after dispersal. However, it remains unclear how seed size impact seedling recruitment of Q. wutaishanica in heterogeneous forest environment and whether the frequency-dependent selection of predation and scatter-hoarding/dispersal on Q. wutaishanica seeds of different size. Based on available data, we hypothesized that the selection of predation and dispersal behaviour by scatter-hoarding rodents could be frequency-dependent and play an important role in the seed dispersal, seedling recruitment and the whole natural regeneration of Q. wutaishanica forest. In this project, we aim to test this hypothesis by clarifying the composition of seed rain and seed bank of secondary Q. wutaishanica forest and by employing various analysing methods on natural regeneration of forest species including tracking of seed fate. We will examine the satiation effect of Q. wutaishanica seeds of different size and frequency on predation/dispersal animals and the preferences of seed germination and seedling establishment. We will explore the influences of seed size- and frequency-dependent selection on the strategy of seed dispersal and seedling recruitment of Q. wutaishanica and the coevolution relationship between seed characteristic and dispersal animals. The results will deepen our understanding of the seed size- and frequency-dependent selection of seed-dispersal animals on seeds of different size and will has important significance to establishing theoretical framework of the seed dispersal and seedling recruitment limitation and the technology system of cultivation.

啮齿动物介导的种子扩散和幼苗增补是植物种群天然更新的2个关键环节。辽东栎种子大小对啮齿动物的取食和扩散行为决策及种子的命运具有重要影响；然而，在异质性森林生境中，种子大小如何影响幼苗增补以及动物对种子的取食和扩散选择是否具有频率依赖性还没有得到验证。根据已有研究提出假设：啮齿动物对不同大小的辽东栎种子的取食和扩散行为可能表现为频率依赖性选择，并对种子扩撒、幼苗增补和整个天然更新具有重要影响。本项目拟在明确辽东栎种子雨和种子库成分组成的基础上，采用种子命运跟踪等多种天然更新策略分析手段，研究不同大小和相对频率的种子对捕食动物的饱和效应及种子萌发和幼苗建立的生境选择，揭示种子大小和频率对辽东栎种子扩散和幼苗增补策略的影响及扩散动物与种子间的协同进化关系。研究结果有助于深刻理解扩散动物对不同大小种子及其频率依赖性选择，对构建辽东栎种子扩散和幼苗增补限制的理论框架和森林培育技术体系具有重要意义。

啮齿动物介导的种子扩散和幼苗增补是森林树种天然更新的2个重要生态学过程。本项目以宁夏六盘山区落叶阔叶林优势树种辽东栎为研究对象，结合野外观测和控制试验，研究了基于种子大小及其频率依赖的辽东栎种子扩散和幼苗增补策略。结果发现：辽东栎大种子含水量和萌发率在脱水过程中始终显著高于小种子，且在脱水后期萌发参数在不同大小种子间均差异显著；辽东栎种子不能耐受低温贮藏，冷藏90d或冻藏48h后种子全部丧失活力。全部大:小种子频率处理的大种子就地取食率、扩散后取食率、贮藏率和扩散距离均显著大于小种子；啮齿动物对辽东栎种子的取食和扩散行为表现为对种子大小及其频率的依赖性。大种子比小种子更有可能被啮齿动物扩散后贮藏；随着埋藏点密度增大，啮齿动物减少就地取食种子数量，增加搬运后取食和分散贮藏种子数量，并增大种子搬运后的取食和贮藏距离。啮齿动物在结实大年和小年均表现出对大种子的扩散偏好，且大种子被扩散的距离更远；啮齿动物在不同结实年份均偏好于就地取食中等单宁含量种子，而扩散高单宁含量种子。种子萌发状态对啮齿动物就地取食率、搬运后取食率和贮藏率均无显著影响。大种子萌发参数在所有播种深度均高于小种子，去皮可促进大种子萌发，但抑制小种子萌发；不同大小种子所有萌发参数均在0 cm播种深度最大，在10 cm播种深度最小。幼苗株高(SN)、叶片数(LN)、单株叶面积(LAPP)、总干质量(TDM)和根冠比(RSR)均随播种深度增大呈减小趋势。幼苗生长参数随子叶去除强度增大呈减小趋势，小种子幼苗对子叶损失反应更为敏感。幼苗生长和生理能够对光强变化做出快速响应，并表现出较大形态和生理可塑性；大种子幼苗可依赖其生长和生理特性方面的优势而比小种子幼苗具有更强的干旱耐受性。啮齿动物对辽东栎幼苗子叶的取食行为选择也表现出种子大小及其频率的依赖性，大种子幼苗生长参数均显著大于小种子幼苗，林窗生境比林下更有利于辽东栎幼苗生长与存活。这些研究结果有助于深入理解种子扩散动物对不同大小种子取食和扩散的频率依赖性选择及其对种子扩散和幼苗增补的贡献，并可为六盘山区的辽东栎种群天然更新和退化森林生态系统管理提供科学依据。