Effects of lengthening growing season and increasing temperature on soil carbon fluxes and stocks in Arctic tundra

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。全球变暖使北极生态系统的生长期延长，温度升高。生长季节延长的特点是融雪早，霜冻晚。光合作用和呼吸作用可能对这些变化作出不同的反应，从而导致北极的季节模式、年度碳收支、全系统碳储量和营养供应的变化。考虑到北极系统中大量的碳储量和碳对温度的高度敏感性，季节性的变化将影响全球碳循环和气候系统。该项目的目标是研究微生物呼吸、根呼吸和光合作用是否以及如何对春季早雪融化和秋季晚土壤冻结做出不同的反应，这些过程是否以及如何对生长季节温度升高做出不同的反应，年度碳预算如何变化，以及这对未来北极苔原生态系统和全球碳循环的影响。研究地点将在阿拉斯加北坡图里克野外站的苔原生态系统中。开顶室将用于控制温度和生长季节。采用迷你沟法对土壤呼吸进行分区，分离根呼吸和微生物呼吸对不同生长季节和土壤温度的不同响应。2个处理（增温+挖沟）相结合，建立9个增温、9个增温+挖沟、9个挖沟和9个对照区。在冻土带生态系统中，利用地下CO2剖面系统对微生物和根呼吸进行连续、自动的测量，是一种比室内测量法更好的方法。这个连续的系统可以检查光合作用和呼吸作用的不匹配，以响应温度的变化和融雪和再冻结的时间，同时对苔原上的土壤和地上植物造成微不足道的干扰。还将进行相应的土壤温度、含水量、冠层气压、空气温度和水蒸气压力的测量。一种内置光源的便携式光合作用测量系统将用于测量叶片光合作用及其对光的响应。光合作用和叶呼吸的周期性测量将通过光合作用模型外推。分析光合作用、叶呼吸、根呼吸和微生物呼吸的连续时间序列数据及其与温度的相关性，探讨其对季节变化的响应。将计算净生态系统产量，以检查年度碳预算的变化，其与氮有效性的耦合，以及对北极和全球系统碳储量的影响。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Abstract Global warming is lengthening the growing season and increasing temperature in the arctic ecosystem. The lengthened growing season is featured by earlier snow melt and later fall freeze-up. Photosynthesis and respiration may respond differently to these changes, resulting in changes in the seasonal pattern, the annual carbon budget, whole-system carbon stocks, and the nutrient supply in the Arctic. Given the large amount of carbon stored in the arctic system and high sensitivity of carbon to temperature, the changing seasonality will influence the global carbon cycle and the climate system.The objectives of this project are to examine if and how microbial respiration, root respiration, and photosynthesis respond differently to earlier snow melt in spring and later soil freeze-up in fall, if and how these processes respond differently to enhanced temperature in the growing season, how the annual carbon budget changes, and what the implication is for the future arctic tundra ecosystem and the global carbon cycle.The study site will be in a tussock tundra ecosystem at the Toolik Field Station on the North Slope of Alaska. Open-top chambers will be used to manipulate temperature and the growing season. A mini-trenching approach will be used to partition soil respiration and separate the different response between root respiration and microbial respiration to the manipulated growing season and soil temperature. Combining two treatments (warming and trenching), 9 warming, 9 warming + trenching, 9 trenching, and 9 control plots will be established.Microbial and root respiration will be continuously, automatically measured with a belowground CO2 profile system, which is a better approach than the chamber measurement method in the tundra ecosystem. This continuous system allows examination of the mismatch of photosynthesis and respiration in response to the change in temperature and the timing of snowmelt and refreezing, while causing negligible disturbance to soils and aboveground plants in the tundra. Corresponding measurement of soil temperature, water content, canopy air pressure, air temperature and water vapor pressure will also be conducted. A portable photosynthesis measurement system with imbedded light sources will be used to measure leaf photosynthesis and its response to light. Periodic measurement of photosynthesis and leaf respiration will be extrapolated with a photosynthesis model. Continuous time-series data of photosynthesis, leaf respiration, root respiration, and microbial respiration with its correlation with temperature will be analyzed to examine the response to changing seasonality. Net ecosystem production will be calculated to examine changes in the annual carbon budget, its coupling with nitrogen availability, and implication for the carbon stock in the arctic and global system.