中国温带植被秋季物候对春季物候的影响研究

Spring phenology of temperate forests, which indicates the onset of growing season, determines carbon, water and energy cycles in terrestrial ecosystem. However, current understanding of the drivers of spring phenology is limited, and the most commonly accepted mechanism is that climate factors including temperature, precipitation and solar radiation primarily control the onset of spring phenology for each plant functional type, which leading to a large uncertainty in predictions of the timing of spring phenology under future climate conditions. In this project, deciduous forest, mixed forest, brush and grassland in temperate China are selected as study objects for investigating the underlying mechanisms of spring phenology based on datasets of remote monitoring and in-situ observations. Firstly the autumn phenology effects on spring phenology will be explored except for climate factors. Furthermore, based on the observed relationship a new spring phenology model considering autumn phenology will be developed. Finally, combining with the current spring phenology models, the most proper model will be evaluated for deciduous forest, mixed forest, bushes and grassland in temperate China, respectively. The realization of this project will shed light on the underlying drivers of spring phenology in temperate vegetation and improvement of spring phenology models. Furthermore, it will also bring clear light to the dynamics of ecosystems productivity, and then provide a firm theoretical basis for figuring out the carbon sequestration of our country in the future. Therefore, this project has important impacts to the ecosystem carbon cycle filed of our country.

春季物候是植物生长季开始的标志，是陆地生态系统的碳、水以及能量循环的决定因素之一。然而，目前对于春季物候的驱动因子的认识很有限，普遍认为气候因素是控制不同植被类型春季物候发生的基本要素，导致未来气候情景下的春季物候预测仍然存在很大不确定性。本项目以中国温带地区具有明显季节变化的主要植被类型（落叶林、针阔混交林、灌丛以及草地）为研究对象，利用遥感监测和地面观测网数据展开春季物候的潜在影响机制研究。首先探究除气候因素外，秋季物候对春季物候的影响；基于此影响进一步构建包括秋季物候的春季物候模型；最后结合目前存在的物候模型，针对每种植被类型评估出最适合的物候模型。本项目的实现，有助于揭示春季物候的潜在驱动机制，提高春季物候模型的准确性，进而明确生态系统生产力在未来的动态变化，为摸清我国未来碳家底提供扎实的理论依据，因此对我国生态系统碳循环研究具有十分重要的意义。

近几十年来，气候变暖已经导致中国北方温带植被春季物候显著提前。但是迄今为止，春季物候和气候因子之间的统计关系还不能充分解释春季物候的时间变化，这给春季物候变化预测以及未来全球陆地生态系统碳循环的预测带来了挑战。因此，本研究将进一步探索可能影响植被春季物候的驱动因素上。利用1982-2014年中国北方地区(30°N以北)的植被总初级生产力(GPP)数据和同区域1983-2015年的植被春季返青期(SOS)的数据，分析了1982-2015年植被生产力与其春季返青期之间的关系。结果表明，67%的地区显示年际SOS和GPP存在负相关关系，其中29%的地区显著负相关，表明该地区过去植被总初级生产力的增加会促进次年春季物候的提前，主要集中在华中地区、东北北部、渤海湾附近、和新疆北部地区。在植被类型水平上，低矮的草类和灌木的春季物候相对于高大的森林生物群落更容易受到GPP的影响，并且草类、灌木和森林生物群落的GPP对次年春季物候的贡献分别相当于季前平均温度的1/2和1/3，这说明相对于温度，过去植被生产力对春季物候的重要性也是不可忽略的。我们猜测植被生产力增加可能会通过改变自身结构、碳分配速率和碳分配优先原则而增加抗性和提前展叶，并且树木高度也可能会影响碳输送速率和浓度，进而影响植被春季展叶的发生。