上海城乡梯度森林土壤碳固持机制研究

With the fast urbanization in China, urban forests converted from farmland are playing major roles in ecosystem services; meanwhile, these services are affected by urban environment such as heat island effect, nitrogen deposition and pollution. Nevertheless, soil carbon dynamics and its possible environmental factors from old forests in urban area to new forests in the suburbs have been seldom studied, which limits our evaluation of the ecological functions of city forests. . Two typical forests along the urban-rural gradient in Shanghai, Cinnamomum Camphora plantations and broadleaf mixed plantations, will be selected as our research sites. In these sites, using 13C and 15N double-labeling technique, the influences of environment on litter decomposition, soil respiration, microbial communities, and dynamics of soil organic matter will be investigated; translocation and transformation of litter C and N within different soil aggregate fractions will be traced. . Our goal is to better understand the relationships between microbial community composition and activity and soil organic carbon stabilization and to systematically explore how soil microbes and soil aggregates have synergically affected soil organic carbon and how these effects have been influenced by environmental change along the urban-rural forest gradient. A better understanding of urbanization impacts on soil organic carbon has great implications for evaluating the structure and function of urban forest ecosystems, and will assist us in developing urban forest management formulation and strategies.

在我国快速的城市发展过程中，大量的农田转化成城市森林和绿地，发挥着重要的生态系统服务功能，同时，这些森林的功能也受到城市环境（例如，热岛效应、氮沉降、污染等）的影响。在城乡梯度上，城区老龄森林绿地到郊区新造林分的土壤碳动态及其与城郊环境因子之间关系的研究较少，限制了我们对城市森林生态功能的科学评价。在本项目中，选择上海城乡梯度上最主要的两种森林类型（香樟纯林和阔叶混交林），结合13C和15N稳定同位素双标记试验，探讨城乡梯度上环境的改变对同位素标记凋落物的分解过程、土壤呼吸、土壤动物和微生物种群、土壤有机质动态等的影响；解析同位素标记凋落物C、N在土壤团聚体水平上的迁移与转化；深入了解团聚体有机碳固定与微生物活性的本质；揭示城乡梯度森林土壤有机质-微生物-团聚体的协同作用与稳定机制。研究结果可加深理解我国冲积平原地区城市森林生态系统的结构和功能，对制定城市森林经营管理措施具有重要指导意义。

在我国快速的城市发展过程中，大量的农田转化成城市森林和绿地，发挥着重要的生态系统服务功能，同时，这些森林的功能也受到城市环境的影响。在城乡梯度上，对城区老龄森林绿地到郊区新造林分的土壤碳积累特征及其与城郊环境因子之间关系的研究，将有助于我们更好地评价城市森林的生态功能和理解城市森林的固碳机制。本研究选择了城乡梯度上三种典型的森林类型（香樟纯林、水杉纯林、阔叶混交林）为研究对象，研究了环境的改变对城市森林凋落物分解过程、土壤呼吸、土壤有机质的形成与转化、土壤微生物群落结构和功能等的影响，系统探讨了上海城市森林土壤碳积累特征和影响因素。主要结果如下：（1）探讨了城乡梯度森林土壤有机碳积累特征及其影响因素，提出城乡梯度上林龄和氮沉降对土壤有机碳的积累具有非常重要的影响；在城乡梯度上土壤有机质化学组成与有机质含量及微生物关系紧密，特别是木质素相对含量与有机碳含量有强烈的正相关关系。（2）揭示长期的自然高氮沉降驱动城乡梯度上微生物群落组成，氮的有效性可能会导致微生物群落发生显著变化。（3）强调树种组成和林龄对土壤有机质和土壤微生物群落组成的影响，提出成熟的阔叶混交林具有更高的固碳效果。研究结果可加深对城市森林碳积累机制的理解，并为上海行业管理部门在推进生态补偿机制、加强森林培育和经营等方面提供技术支撑；为政府部门建设生态宜居型城市提供决策依据。