青藏高原东北部典型建群树种碳氮利用与环境适应的相互作用机制

The Qinghai-Tibet Plateau is the sensitive areas and vulnerable areas, and its forest vegetation areas has emerged in decline during the global climate change. The carbon and nitrogen cycles and their functional coupling in forest ecosystems are the popular topic of research in the field of ecology, and also provide an important reference to evaluate the regional ecological health. Sabina przewalskii and Picea crassifolia are main species in ecological fragile area in the northeastern Qinghai-Tibet Plateau. Based on the technique of stable nitrogen isotope tracer and using the combining methods of fixed-point field observation and controlling experiments,the relationship between carbon and nitrogen utilization and the law of their spatio-temporal variation are analyzed in Sabina przewalskii and Picea crassifolia. We want to reveal effects of environment and climate factors on carbon and nitrogen utilization in both evergreen trees, discuss the interactive mechanisms of carbon and nitrogen utilization and feedback regulation to environment, clarify the coupling of carbon and nitrogen metabolism responded to environment and their adaptive mechanisms in the two evergreen species, and also serve for the maintenance of ecological balance and the ecological construction in ecologically fragile areas in the Qinghai-Tibet Plateau.

青藏高原是全球气候变化的敏感区和脆弱区，全球气候变化背景下其森林植被已出现了区域性锐减。森林生态系统碳、氮循环及其功能耦合是目前生态学领域研究的热点，也是区域生态健康评价的重要参照。本项目以青藏高原东北部生态极其脆弱区建群的主要森林树种祁连圆柏和青海云杉为材料，利用稳定氮同位素示踪技术，采用野外定点观测和人工控制试验相结合的方法，通过分析两种常绿植物碳、氮利用之间的关系和时空变异规律，揭示环境气候因子对这两种植物碳、氮利用的影响，探讨它们碳、氮利用的相互作用机制和对环境的反馈调节，旨在阐明两种常绿树种响应环境气候变化碳、氮代谢的耦合及其适应机制，为维持青藏高原生态脆弱区的生态平衡和生态建设服务。

青藏高原是全球气候变化的敏感区和脆弱区，全球气候变化背景下其森林植被已出现了区域性锐减。选择青藏高原东北部祁连圆柏和青海云杉主要分布区祁连山和柴达木盆地采集样品，收集样地附近的气象资料；测定和调查了两种树种叶片中稳定碳和氮同位素的组成、碳和氮含量、非结构性碳水化合物和矿质元素含量，测定了碳和氮含量及其稳定同位素的季节变化，研究了碳、氮积累与环境气候因子空间和季节变化规律及其种间和种内的差异，15N示踪试验分析了青海云杉碳分配、氮积累及其稳定氮同位素变化规律。结果显示，海拔、温度和降雨及其年内变化对稳定碳同位素值有明显的影响，而对稳定氮同位素的影响较弱，揭示稳定碳同位素而不是稳定氮同位素对气候和环境因子有明显的指示作用，但没有发现碳氮利用之间的相互促进或抑制作用。碳氮积累的季节变化进一步证实碳及其同位素组成更依赖于气候因子的变化，C/N比值可有效地反应碳氮代谢的季节变化特征；叶非结构性碳水化合物与树龄和胸径均呈弱的正相关关系。矿质元素与气候因子的相关性分析显示，非必需元素硅而不是必需元素钾、钙和镁等对环境的依赖高，推测硅积累对高山环境的适应具有积极的作用；15N示踪发现增施氮提高叶中氮量，却降低了氮利用率；一定量的氮施加增加了结构性碳的比例，却降低了非结构性碳的含量，这些碳的分配将会影响到植物的生长，进而解析土壤供氮差异对碳、氮积累的影响。这些研究将为建设和维护青藏高原森林生态系统的平衡服务。