Long term studies of effects of climate manipulations on subarctic ecosystems

Since June 2000, we have been conducting a field manipulation experiment simulating climate scenarios in a subarctic Sphagnum-dominated blanket bog near Abisko, N Sweden. This experiment is unique in that it mimics six different combinations of (current and predicted) spring, summer and winter climate, each replicated five times. Passive spring and summer warming is achieved through transparent tent-like open-top chambers (OTC, 2.5 m diameter). In winter the same OTCs are effectively used to capture and retain snow, which in this wind-exposed site is often blown away from ambient plots but into the OTCs. The statistical design is factorial, i.e. there are 30 OTCs. i.e. 15 + 15 OTCs for ambient and warmed summer treatment and, within each summer treatment 5 for ambient spring and winter conditions, 5 with ambient spring but OTC in winter, and 5 with OTC both in spring. The replicates are organized in blocks each containing all 6 treatments.

Here we are measuring or have measured a range of features of the microclimate, soil (peat) properties, vegetation composition, diversity, structure and growth, carbon and nutrient exchange parameters, aspects of species responses (plants, microbes, soil invertebrates).

The experiment, which is planned to run until at least 2020, is embedded in international scientific networks for global change investigations, for instance the International Tundra Experiment (ITEX).

Datasets have been or are being assembled for:
- microclimate in the different treatments, including continuous recording of soil temperatures (ongoing) and (2000-2005) air temperatures; weekly snow depth; soil moisture and air humidity (in specific years); permafrost depth (active layer depth);
- soil (peat) properties at different depths;
- vegetation structure and composition down to species level, both vascular plants and cryptogams (2-yearly, through point-frame recording with associated biomass calibrations);
- plant species and functional diversity
- Sphagnum growth (in several specific years)
- annual shoot increments of target vascular species (in specific years)
- vegetative and reproductive phenology
- nutrient recycling, e.g. through resorption processes
- litter decomposition rates at the ecosystem and species level (environmental and species effects on decomposition; specific years)
- ecosystem level carbon exchange including soil respiration and photosynthesis; 13C signatures as indicators of respiration responses to warming for different peat horizons
- microbial community composition with special focus on their contributions on different nitrogen-transforming functions
- community composition of invertebrate soil fauna (Collembola, mites) and Thecamoebic protozoans (both being prepared).

自2000年6月起，我们在瑞典北部阿比斯科附近一处以泥炭藓（Sphagnum）为优势种的亚寒带毯状沼泽中，开展了模拟当前及预测气候情景的野外控制实验。本实验的独特之处在于，其覆盖春、夏、冬三季的6种气候组合方案（包含当前与预估气候条件），每种方案均设置5次生物学重复。春季与夏季的被动增温通过透明帐篷状开顶箱（open-top chamber, OTC，直径2.5米）实现；冬季时，同款OTC可有效捕获并留存积雪——在该多风样地中，自然对照样方的积雪常被风吹散，而OTC内部则会积聚更多积雪。本实验采用析因实验设计，共设置30台OTC：其中夏季自然对照与增温处理各设15台，在每个夏季处理组内，又进一步划分为3个亚组：5台维持春季与冬季自然气候条件、5台维持春季自然气候但冬季加装OTC、5台春冬两季均加装OTC。重复样方以区组为单位排布，每个区组包含全部6种处理组合。

本实验已测定或正在测定一系列观测指标，涵盖微气候特征、土壤（泥炭）理化性质、植被组成、多样性、结构与生长动态、碳氮养分交换参数，以及植物、微生物与土壤无脊椎动物的物种响应特征。

本实验计划至少持续至2020年，并嵌入了全球变化研究的国际科学合作网络，例如国际苔原实验计划（International Tundra Experiment, ITEX）。

目前已组装或正在组装的数据集涵盖以下类别：
- 不同处理下的微气候数据：包括持续监测的土壤温度（当前仍在进行）、2000-2005年的空气温度监测数据、每周积雪深度测定结果、特定年份测定的土壤湿度与空气湿度，以及永久冻土活动层厚度；
- 不同深度土层的土壤（泥炭）理化性质数据；
- 物种级别的植被结构与组成数据，涵盖维管植物与隐花植物（cryptogams），采用定点框架记录法结合生物量校准，每2年开展一次调查；
- 植物物种多样性与功能多样性数据；
- 特定年份测定的泥炭藓生长状况；
- 特定年份测定的目标维管植物当年枝条生长增量；
- 植物营养生长与生殖生长的物候期；
- 养分循环过程，例如通过养分重吸收实现的养分回收；
- 生态系统与物种水平的枯落物分解速率（包括环境与物种自身对分解过程的影响，测定于特定年份）；
- 生态系统尺度的碳交换数据，包括土壤呼吸与光合作用，以及用于表征不同泥炭层呼吸对增温响应的13C同位素指纹特征；
- 微生物群落组成数据，重点关注其在各类氮转化功能过程中的贡献；
- 土壤无脊椎动物群落组成数据，包括弹尾虫（Collembola）、螨类，以及有壳变形虫原生动物（Thecamoebic protozoans），相关数据集正在筹备中。