温度和光周期对华北落叶松秋季物候与养分再吸收的影响机制

Plant phenology is one of the most sensitive biological indicators of ecosystem to global climate change, and has become a hot topic in the global change ecology. Climate warming may delay the autumn leaf phenology, which, in turn, on the one hand, leads plants to short photoperiod conditions, and on the other hand, affects nutrient resorption (one of the most important nutrient conservation mechanisms) of plants. Larch (Larix spp.) is the dominant timber species in north China. To date, however, the underlying mechanisms for phenological changes of autumn leaf senescence remain poorly understood. Our field experiment will be conducted at the Saihanba ecological station of Peking University, which is situated in Saihanba National Forest Park (has the largest area of plantations in China), Hebei Province, north China. Seasonal asymmetric warming (by OTC) and autumn photoperiod regulation (by artificial) were applied to the Larix principis-rupprechtii plantation to observe the timing of spring and autumn phenological events. The specific objectives of this project are as follows: 1) to explore the legacy effect of spring phenology on autumn phenology; 2) to reveal the underlying mechanisms of temperature and photoperiod on autumn phenology; 3) to explicit the responses of autumn phenology to environmental drivers and the associated effects on carbon assimilation, nitrogen resorption and productivity. The results obtained in this project will enhance our understanding of leaf phenology response to the ongoing climate change, and provide parameters for phenology model, which potentially improve the prediction accuracy of phenology and its impacts on ecosystem carbon and nitrogen cycles.

植物物候是全球变化最敏感的生态系统变化指标之一，目前物候学研究已成为全球变化生态学中的热点。气候变暖可能延迟植物秋季物候，从而使植物经历较短光周期的同时影响其养分再吸收（重要的养分保存机制之一）。落叶松人工林是我国北方最主要的人工用材林树种，然而目前关于驱动落叶松秋季物候的机制尚不明确。本项目拟利用位于我国最大的人工林种植基地——河北省塞罕坝机械林场的“北京大学塞罕坝生态站”为试验基地，对华北落叶松进行季节不对称增温（OTC法）和秋季人为光周期控制实验，观测其春、秋两季物候发生时间，从而明确春季物候对秋季物候影响的滞后效应；阐明温度、光周期对落叶松秋季物候的影响；揭示秋季物候对气候变化的响应及对碳同化、氮再吸收和生产力的影响。本研究结果不仅有利于提高物候对气候变化响应的机理性认识，更可为植物物候模型提供参数，提高未来气候变化下物候预测精度，为准确评估气候变化对生态系统碳、氮循环提供理论依据

植物物候是全球变化最敏感的生态系统变化指标之一，目前物候学研究已成为全球变化生态学中的热点。气候变暖可能延迟植物秋季物候，从而使植物经历较短光周期的同时影响其养分再吸收（重要的养分保存机制之一）。落叶松人工林是我国北方最主要的人工用材林树种，然而目前关于驱动落叶松秋季物候的机制尚不明确。本项目选择位于我国最大的人工林种植基地——河北省塞罕坝机械林场的“北京大学塞罕坝人工林生态系统国家野外科学观测研究站”为试验基地，对华北落叶松幼苗进行季节不对称增温（OTC法）和秋季人为光周期控制实验，观测其春、秋两季物候发生时间。结果发现：（1）春季增温显著提前萌芽和展叶的物候期（分别提前7天和2天），全年增温使得萌芽提前4天，但对展叶无显著影响。夏季和冬季增温对春季物候的发生期和持续时间无显著影响。值得注意的是，秋季增温处理使得第二年的春季展叶显著延迟2天，即存在遗留效应（秋季物候每延迟1天将使得第二年春季展叶延迟0.3天）。春季增温处理下萌芽和展叶的温度敏感性（分别为9.56和2.66天/摄氏度）显著高于全年增温处理（分别为6.43和0.66天/摄氏度）。此外，我们还发现，春季增温和全年增温处理下，萌芽与展叶二者的持续时间间存在权衡关系。（2）湿润年份，秋季增温和全年增温分别使得秋季物候显著延迟6和7天，对应的温度敏感性分别为6.73和8.26天/摄氏度；干旱年份，增温处理对秋季物候无显著影响。秋季物候延迟伴随着生物量累积的显著增加。无论是湿润年份还是干旱年份，夏季增温均显著提高幼苗的死亡率。这些研究结果表明，水文状况显著地调节着秋季物候和生长对季节增温的响应。而物候对光周期缩短不敏感，且物候变化对幼苗氮回收效率无显著影响。在本项目资助下，以第一标注发表SCI论文5篇，分别发表在Global Change Biology、Forest Ecology and Management、Biology and Fertility of Soils、Agricultural and Forest Meteorology、Science of the Total Environment等林学和生态与环境领域TOP期刊。超额完成项目既定研究目标。为开展接下来研究工作奠定扎实基础。

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