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。生长季节延长的特点是较早的积雪融化和较晚的秋季结冰。光合作用和呼吸作用可能会对这些变化做出不同的反应，从而导致北极地区的季节模式、年度碳收支、全系统碳储量和养分供应的变化。考虑到北极系统中储存的大量碳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、根系呼吸和光合作用是否以及如何对春季较早的积雪融化和秋季较晚的土壤冻结做出不同的反应，这些过程是否和如何对生长季升温的温度做出不同的反应，年度碳收支如何变化，以及对未来的北极冻土带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的图利克野外站的一个草袜苔原生态系统中。开顶室将被用来控制温度和生长季节。将使用小型沟槽方法来划分土壤呼吸，并分离根呼吸和微生物呼吸对生长季节和土壤温度的不同响应。结合两种处理(升温和开沟)，将建立9个升温、9个升温+挖沟、9个挖沟和9个对照小区，利用地下CO2剖面系统连续、自动地测量微生物和根系的呼吸，这是一种比冻土带生态系统中的小室测量方法更好的方法。这个连续的系统允许检查光合作用和呼吸作用的不匹配，以响应温度的变化和积雪融化和重新冻结的时间，而对冻土带的土壤和地上植物造成的干扰可以忽略不计。还将进行相应的土壤温度、水分、冠层气压、气温和水汽压的测量。便携式光合作用测量系统将用于测量叶片的光合作用及其对光的响应。光合作用和叶片呼吸的定期测量将用光合作用模型进行外推。光合作用、叶片呼吸、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将被分析，以考察其对季节性变化的响应。将计算生态系统净生产量，以检查年度碳收支的变化，其与氮素供应的耦合，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.