西沙珊瑚岛屿生态环境演化过程中的氮循环研究

南海西沙群岛对于全球气候变化和人类活动响应非常灵敏。我们已经对西沙珊瑚岛屿过去1000年海鸟古生态演化过程及其主要控制因素开展了大量研究，但对于岛屿生态系统的氮循化过程和机理认识还非常有限。本项目拟选取发育程度不同的一系列西沙岛屿为研究对象，在生态地质学的基本原理和框架下，利用不同形态氮含量和同位素组成作为主要指标，分析处于不同生态系统发育阶段的珊瑚岛土壤和植物的氮源以及植物用氮策略，从空间对比和时间演替两个角度揭示西沙岛屿生态系统演变过程中氮循环规律和变化机制，查明历史时期海鸟数量变化以及人类活动对岛屿氮循环的影响，并评估在近现代海鸟数量快速下降以及人类活动加剧的背景下，西沙岛屿生态系统氮循化过程可能发生的变化。研究结果将丰富我们对热带珊瑚岛屿物质能量循环体系的认识，并为准确评估热带岛屿生态演化与气候变化和人类活动的关系，以及预测西沙岛屿生态系统演变趋势提供科学依据。

The Xisha Islands ecosystem in the South China Sea responds sensitively to global climate change and human activities. Although we reconstructed the ecological evolution process of seabirds at Xisha Coral Islands in the past 1000 years and identified its key controlling factors, the processes and mechanisms of nitrogen cycle in island ecosystem were still poorly understood. In this study, under the basic principles and framework of eco-geology, we will select and study typical islands at different development stages, and mainly use proxies of concentrations and isotope ratios of different nitrogen species in attempt to: (1) comparatively identify the nitrogen source of plants and soils as well as nitrogen utilization strategies of plants in ocean islands at different stage of ecosystem development; (2) reveal the nitrogen cycle rule and change mechanism in the evolution of Xisha Islands ecosystem through the perspective of spatial comparison and temporal succession; (3) delineate the impact of historical change of seabird population and human activities on nitrogen cycle in islands; and (4) assess the possible changes of nitrogen cycle in Xisha Island ecosystem given the rapidly declined seabird population and increased human activities in modern times. Findings from this study will improve the understanding of the cycle of material and energy in tropical coral islands, and also support the assessment of the relationship between eco-evolution of tropical islands, and climate change and human activities. In addition, this study will also shed light on predicting the evolution trend of Xisha Islands ecosystem.