基于碳饥饿-水力失衡的城市化进程中乡土树种干旱脆弱性研究

The global climate change and urbanization is profoundly changing the biology geochemical cycle of forest ecosystem around the city. Recently, the forest ecological system is found to be degraded during urbanization, which is conversed to the theoretically promoted productivity by the fertilization effect. The seasonal drought induced by changed pattern of precipitation is considered to be responsible for this negative effect. Due to the limitations of traditional methods, it is still not well illustrated for the changed plant functional traits by fertilization effect, and induced plant hydraulic failure and reduction in carbon assimilation by rising seasonal drought during urbanization. Those endangered native plants are calling for more attentions. The application of plant carbon starvation - hydraulic failure model provide a thought provoking way to reveal the threats on plant fitness introduced by the urbanization. Our study focused on the establishment of plant carbon starvation - hydraulic failure model combing with the plant functional traits measurements under urbanization gradients, with an aim to quantify the effect of urbanization process on plant survival strategy during drought stress, in order to provide theoretical basis for the ecological red lines during urbanization.

城市化深刻改变城市及周边地区森林生态系统的生物地球化学循环。与理论上施肥效应会促进植物的生产力相悖，近年相关研究结果表明，城市化虽然增加了额外可利用资源向森林生态系统的输入，但森林却出现严重的退化，其中降雨格局变化带来的季节性干旱被认为是导致这种负效应的重要原因。由于受传统研究方法的局限，已有的研究依然未能很好地揭示施肥效应引起的植物功能性状改变、不断加剧的季节干旱导致植物水力失衡和降低植物光合碳同化等过程的内在机制，人们对城市化进程中对乡土植物带来的胁迫认识不足。植物碳饥饿—水力失衡耦合模型的出现为揭示城市化对乡土植物的危害机理提供了新的研究方法。本项目将通过控制实验建立植物碳饥饿—水力失衡模型，结合自然状态下不同城市化梯度下植物功能性状变化的长期监测，分析城市化过程对植物水分胁迫下的生存策略的影响，评价乡土树种的生存风险，为我国生态红线制度的设定和有效实施提供理论依据。

城市化深刻改变城市及周边地区森林生态系统的生物地球化学循环。与理论上施肥效应会促进植物的生产力相悖，相关研究结果表明，城市化虽然增加了额外可利用资源向森林生态系统的输入，但森林却出现严重的退化，其中降雨格局变化带来的季节性干旱被认为是导致这种负效应的重要原因。针对这一问题，我们首先以杭州市为中心，沿着钱塘江流域，通过在不同城市化梯度下开展植物功能性状测定，对季节干旱和城市化双重影响下植物功能性状的响应方式进行研究。紧接着通过控制实验，验证亚热带地区常绿和落叶阔叶树种在氮添加的处理下，植物功能性状的变化。最后分析了降水格局变化对植物水分利用特征的影响。结果表明，在城市化梯度上，无论是常绿树种还是落叶树种，越靠近城区，植物生存策略越倾向于粗放型生存方式，这印证了加剧的植物水力安全风险。而相对于常绿树种，氮添加对落叶树种的促进作用更强。而隔除降水实验表明，适度的干旱反而导致植物水分利用能力的显著提高。这些结果意味着氮沉降和季节干旱的影响会导致植物水力风险的增加，对城市周边森林的保育工作具有十分重要的指导意义。