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科学问题/Scientific Question

工业革命以来,人类活动持续地改变大气组成(升高温室气体含量包括二氧化碳、甲烷及氧化亚氮等以及活性氮沉降)和气候系统(气候变暖及改变降雨格局)。多个驱动因子间可能存在的交互作用为气候变化-陆地碳反馈的预测提出较大的挑战。操作一个或者两个全球变化驱动因子的实验提高了我们对于全球变化如何影响陆地生物圈的理解,但是这些实验不能揭示多个全球变化驱动因子共同发生时的陆地生态系统动态以及潜在的响应机理。然而,限制于技术、经费、人员及其他因素,使用控制实验手段的全球变化研究较少的探讨陆地生态系统对上述多个驱动因子共同发生时的响应。

Anthropogenic activities since Industrial Revolution have caused concurrent changes in atmospheric composition (rising greenhouse gases, i.e., carbon dioxide, methane, and nitrous oxide, reactive nitrogen) and climate (climate warming and changing precipitation regimes). Possible interactions among these driving factors pose great challenges for the projections of climate change-terrestrial C feedbacks. Manipulative Experiments with one or two driving factors have improved our understanding of the global change impacts on the terrestrial biosphere, but may not be able to reveal the terrestrial ecosystem dynamics and their underlying mechanisms under global change scenarios with multiple driving factors. Nevertheless, due to technical, financial, and other limitations, global change research has seldom examined the responses of terrestrial ecosystems to the commitment changes in the above driving factors using manipulative Experiments.

 

 

 

实验设计/Experimental Design

全球变化实验室的全球变化影响实验建立于20115月。该实验操作四个全球变化因子,每个因子设置两个水平,分别是大气CO2含量-(自然大气CO2含量和提高大气CO2含量200 ppm)、降雨量-(自然降雨和增加30%降雨)、大气氮沉降-(自然沉降和10 g N m-2 yr-1添加)及温度-(不增温和夜间(18:00-06:00, 当地时间)增温)。使用全因子实验设计操作提高CO2含量、增加降雨及夜间增温处理,共8个处理组合,每个组合3个重复。244 × 4米样地被建立并被排列成64列,任何两个相邻的样地间设置4米的缓冲区。此外,裂区实验设计被用来操作两水平的大气氮沉降,将24个样地都均分成两个子样地,一个子样地不添加氮,而另一个样地添加氮。因此,该实验共包括16个处理组合:1) 对照, 2) 提高CO2 3) 增雨, 4) 氮添加, 5) 夜间增温, 6) 提高CO2 + 增加降雨, 7) 提高CO2 + 氮添加, 8) 提高CO2 + 夜间增温, 9) 增雨 + 氮添加, 10) 增雨 + 夜间增温, 11) 氮添加 + 夜间增温, 12) 提高CO2 + 增加降雨 + 氮添加, 13) 提高CO2 + 增加降雨 + 夜间增温, 14) 提高CO2 + 氮添加 + 夜间增温, 15) 增加降雨 + 氮添加 + 夜间增温,16) 提高CO2 + 增加降雨 + 氮添加 + 夜间增温。

为了控制大气CO2含量,在每一个样地使用铁架和玻璃建设了八边形的开顶箱(任意两个平行边距离4米,2米高,覆盖13.2平方米的地面面积)。此外,为了评估开顶箱对空气和土壤微气候的影响,3个额外的没有玻璃的开顶箱被建立。每年的六月到九月,在每一个提高CO2样地,为了获得200 ppm CO2含量的提高,纯净的CO2被通入开顶箱。我们使用LI-820 CO2 检测系统 (LiCor, Lincoln, NE, USA) 和一个自动控制系统 (Luzhai Co., Beijing, China) 来操作CO2浓度。在每年的六月到九月,每次自然降雨的同时,使用自动喷灌系统添加30%的降雨。这种操作方式避免了改变降雨频度。此外,我们使用硝酸铵模拟增加氮沉降,分别在6月中旬(5 g N m-2)和7月中旬(5 g N m-2)分两次添加10 g N m-2。所有的27个样地被分成两个子样地,一个添加氮另一个不添加。我们使用悬挂于地面以上2.75米高的1.65米长 × 0.15米宽的MSR-2420型红外辐射器 (Kalglo Electronics Inc., Bethlehem, PA, USA)对所有夜间增温样地进行增温处理。设置输出功率为1800 W136 W m-2).

Global Change Ecology laboratory’s Global Change Impacts experiment has been established since May 2011 to manipulate four global change factors and each at two levels: atmospheric CO2 concentrations [CO2] [ambient (aCO2) and elevated [CO2] by 200 ppm (eCO2)], precipitation [ambient (aP) and 30% above the ambient precipitation (iP)], nitrogen (N) deposition [ambient (aN) and ambient plus 10 g N m-2 yr-1 (eN)], and temperature [unwarming (UW) and nighttime (18:00-06:00, local time) warming (W)]. A full factorial design was used for eCO2, iP, and W with eight treatment combinations and three replications for each treatment. Twenty-four 4-m × 4-m plots were set up and arranged into six rows and four columns, with a 4 m buffer zone between any two adjacent plots. In addition, a split-plot design, that each of the 24 plots was divided into two sub-plots, one with N addition and the other one without N addition, was used to manipulate the two-level N deposition. Therefore, the GCE Global Change Impacts experiment included 16 treatment combinations in total, including 1) control, 2) eCO2, 3) iP, 4) eN, 5) W, 6) eCO2 plus iP (eCO2iP), 7) eCO2 plus eN (eCO2eN), 8) eCO2 plus W (eCO2W), 9) iP plus eN (iPeN), 10) iP plus W (iPW), 11) eN plus W (eNW), 12) eCO2, iP, plus eN (eCO2iPeN), 13) eCO2, iP, plus W (eCO2iPW), 14) eCO2, eN, plus W (eCO2eNW), 15) iP, eN, plus W (iPeNW), and 16) eCO2, iP, eN, plus W (eCO2iPeNW).

Twenty-four octagon open-top chambers (OTCs; 4 m distance between any two parallel sides, 2 m height, and enclosing 13.2 m2 ground areas) were constructed in the 24 4-m × 4-m plots, using steel frames and optical glasses to manipulate [CO2]. In addition, three additional OTCs only with steel frames were built as ambient OTCs to estimate the effect of OTC on air and soil microclimate. In each eCO2 plot, pure CO2 was introduced into the OTC to achieve a diurnal CO2 enrichment of 200 ppm over ambient air from June-September of each year, controlled by LI-820 CO2 test system (LiCor, Lincoln, NE, USA) and an automatic control system (Luzhai Co., Beijing, China). Increased precipitation was applied with an automatic sprinkler system during each natural rain event to avoid changing rainfall frequency from June-September of each year. Nitrogen deposition was mimicked by applying NH4NO3 in the mid-June (5 g N m-2 yr-1) and mid-July (5 g N m-2 yr-1) of each year. All the 27 OTCs were divided into two sub-plots, one sub-plot with N addition and the other one without N addition. All the nighttime-warmed plots were heated continuously by 136 W m-2 of infrared radiation from mid-March to mid-November in each year, using 1.65-m (length) × 0.15-m (width) MSR-2420 infrared radiators (Kalglo Electronics Inc., Bethlehem, PA, USA) suspended 2.75 m above the ground.

 

 

 

 

基金支持

中国国家自然科学基金 (41030104/D0308)

 

实验人员

宋健,马改改,钟明星,刘银占

 

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