Year-round soil pore space carbon dioxide and temperature at Toolik Field Station, Alaska, 2017-2018

This data set reports the concentration of carbon dioxide and soil temperature in a permafrost soil under moist acidic tussock tundra near Toolik Field Station. This data was collected in support of a project that aims to understand the sources of carbon dioxide emitted from Arctic tundra year-round. Carbon dioxide is a greenhouse gas produced in soils by the respiration of roots and of microorganisms decomposing soil organic matter, and both processes are sensitive to changes in temperature and water content. Increases in carbon dioxide emissions can be related to increased plant productivity (photosynthesis and storage of carbon in plants and soils) or increased microbial activity (loss of carbon previously stored in soils). However, measuring the radiocarbon content (age) of carbon dioxide emissions can be used to understand how Arctic ecosystems are responding to climate change, because roots and microorganisms respire carbon with distinct isotopic signatures. In this project, our team built and deployed new technology to characterize the sources of carbon emissions from Arctic tundra year-round, with a special focus on winter emissions. Specifically, we developed a sampling system that continuously collects carbon dioxide over a period of 1-4 weeks. The system is passive (no power requirements, ambient pressure and temperature), rugged (suitable for well-aerated, waterlogged, and frozen soils), light-weight (<0.5 kg/sample), and isotopically-clean (i.e. the recovered carbon dioxide is suitable for radiocarbon analysis and the sampler itself does not emit carbon). The samples are shipped to the W. M. Keck Carbon Cycle Accelerator Mass Spectrometer facility at the University of California, Irvine, where they are analyzed for their radiocarbon content. Their isotopic information allows us to elucidate which soil carbon pools are being consumed by microorganism during the winter, and to quantify what proportion of the carbon originates from microorganisms decomposing organic matter (as opposed to from the roots of plants that are fixing carbon from the atmosphere) during the summer.

本数据集记录了图利克野外站（Toolik Field Station）附近湿润酸性草丛苔原下多年冻土土壤中的二氧化碳浓度与土壤温度。本数据集的采集服务于一项旨在厘清北极苔原全年二氧化碳排放来源的研究项目。

二氧化碳是一种温室气体，由土壤中植物根系的呼吸作用，以及分解土壤有机质的微生物的呼吸作用共同产生。这两类代谢过程均对温度与土壤水分含量的变化极为敏感。二氧化碳排放量的升高，既可能源于植物生产力提升（即光合固碳及碳在植物与土壤中的储存量增加），也可能源于微生物活动增强（即土壤中既往储存的碳流失加剧）。不过，通过测定二氧化碳排放物的放射性碳（radiocarbon）含量（即其驻留年代），可解析北极生态系统对气候变化的响应机制——这是因为植物根系与微生物呼吸释放的碳具有截然不同的同位素特征。

本项目中，研究团队搭建并部署了全新技术手段，以表征北极苔原全年的碳排放来源，其中重点关注冬季碳排放。具体而言，团队研发了一套可连续1至4周采集二氧化碳样本的采样系统。该系统具备四大特性：一是无源运行，无需外部供电，可适配环境压力与温度；二是坚固耐用，可用于通气良好、积水或封冻的土壤环境；三是轻量化设计，单套采样装置重量小于0.5千克；四是无同位素污染，即采集回收的二氧化碳可直接用于放射性碳分析，且采样装置本身不会释放碳。

所有采集的样本将被寄送至加利福尼亚大学欧文分校（University of California, Irvine）的W.M.凯克碳循环加速器质谱实验室（W. M. Keck Carbon Cycle Accelerator Mass Spectrometer Facility），在此完成放射性碳含量的检测分析。通过这些同位素信息，研究团队可阐明冬季时哪些土壤碳库正在被微生物消耗，并量化夏季碳排放中，源自分解有机质的微生物释放的碳占比（区别于从大气中固碳的植物根系释放的碳）。