氮添加对海防林林隙天然更新幼苗建植的影响及其机制

海防林对于维护沿海区域生态安全意义重大，但风暴侵袭和自然衰退使得海防林受损和退化严重，当前亟需对这些林分进行修复和更新。而利用林隙的天然更新，辅以人工促进更新是当前近自然森林经营中林分修复的重要方法。前期研究发现海防林林隙中天然更新幼苗建植失败的首要原因是氮限制，但目前还不清楚其过程和机理以及与林隙大小的关系。因此，本项目在浙江省海防林中选择大小不同的林隙，通过添加不同浓度和形态的外源性氮，研究氮添加对林隙内天然更新幼苗建植的影响过程和机制。重点分析不同大小林隙中天然更新幼苗的分布格局，比较幼苗生长和表型可塑性对氮添加的适应特征；揭示幼苗养分格局和生物量分配对氮异质性的响应特征；探讨幼苗光合和抗性特征对氮变化的生理响应机制，以期阐明海防林林隙中天然更新幼苗对氮添加的响应过程和机制。研究结果能为受损和退化海防林的林隙天然更新和生态恢复提供科学依据。

Coastal forests are of great importance to maintain the ecological security of coastal areas, but they are facing serious degeneration caused by storm damages and internal aging and death, it is therefore essential to recover and regenerate these forests. Utilizing the natural regeneration capacity of forest gaps, supplemented by assisted regeneration has presently become an important method of close-to-natural forest management considering the restoration of damaged stands. Previous studies have proved that nitrogen (N) limitation is the most important factor for the failure of naturally regenerated seedling establishment within gaps of coastal forests, but the process and mechanisms and their relationship with gap size are still unclear. This project selects gaps of different sizes in the coastal forests of Zhejiang Province, and studies the effects and mechanism of N addition on the establishment of naturally regenerated seedlings in gaps by adding different concentrations and forms of exogenous N. Specifically, the study aims to 1) analyze the distribution patterns of naturally regenerated seedlings in gaps with different sizes and compare the adaptation characteristics of seedling growth and phenotypic plasticity to N addition; 2) reveal the response characteristics of seedling nutrient pattern and biomass allocation to N heterogeneity; 3) explore the physiological response mechanism of seedling photosynthesis and resistance characteristics to N changes, so as to clarify the response process and mechanism of naturally regenerated seedlings to N addition in the gaps of coastal forests. The results of the study are expected to provide a scientific basis for the natural regeneration in the gaps of coastal forests and the artificial promotion of ecological restoration.