CO2 exchange in three Canadian High Arctic ecosystems: response to long‐term experimental warming
CO2 exchange in three Canadian High Arctic ecosystems: response to long‐term experimental warming
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DOI：
10.1111/j.1365-2486.2004.00857.x
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发表时间：
2004-12
影响因子：
11.6
通讯作者：
J. Welker;J. Fahnestock;G. Henry;Kevin W. O'Dea;R. Chimner
中科院分区：
文献类型：
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作者：
J. Welker;J. Fahnestock;G. Henry;Kevin W. O'Dea;R. Chimner
在环境条件和长期（9年）变暖（约2°C）条件下，对三个高北极苔原生态系统进行了为期两年的二氧化碳交换、土壤碳和氮、叶片矿物质营养以及叶片碳同位素判别（LCID - Δ）的测量。这些生态系统位于努纳武特地区埃尔斯米尔岛的亚历山德拉峡湾（北纬79°），跨越一个土壤水分梯度：干燥、中生和湿润苔原。使用红外气体分析仪测量生长季的二氧化碳通量（即净生态系统交换（NEE）、总生态系统光合作用（GEP）和生态系统呼吸（Re）），并通过化学吸收估算冬季的碳损失。所有三个苔原生态系统在冬季都向大气中释放二氧化碳，每季节每平方米7到12克二氧化碳 - 碳不等，湿润苔原最高。由于变暖以及GEP的增加，中生苔原从二氧化碳源转变为二氧化碳汇的生长季期间延长了2周。夏季变暖对干燥苔原GEP的刺激大于对Re的刺激，因此，与环境温度相比，变暖条件下的NEE始终更大。在中生苔原中，变暖刺激了GEP，对Re无影响，使NEE增加了约10%，特别是在夏季前半段。在约70天的生长季（6月中旬 - 8月中旬），在环境温度条件下，干燥和湿润苔原生态系统是二氧化碳 - 碳的净汇（分别为每季节每平方米30克和67克碳），中生生态系统是大气的净碳源（每季节每平方米58克碳），部分原因是中生苔原发生了异常的冰川融水泛滥。生长季的实验性变暖使干燥苔原的净碳吸收增加了约12%，但使湿润苔原的净碳吸收减少了约20%，主要是因为Re的速率增加而非GEP的速率降低。中生苔原对长期变暖的响应是GEP增加了约30%，Re几乎没有变化，使这种苔原类型变为一个轻微的碳源（每季节每平方米17克碳）。变暖导致干燥苔原的仙女木（Dryas integrafolia）植物的LCID升高，中生和湿润苔原的北极柳（Salix arctic）植物的LCID降低。我们的研究结果表明：（1）处于相似中气候的高北极生态系统与大气的净二氧化碳交换速率不同；（2）长期变暖可以通过刺激GEP增加高北极苔原的净二氧化碳交换，但在夏季也可以通过对Re的刺激程度大于对GEP的刺激程度而减少某些苔原类型的净二氧化碳交换；（3）经过9年的实验性变暖，部分由于落叶灌木覆盖度、生物量和落叶输入的增加，可以检测到土壤碳和氮的增加；（4）干燥苔原因长期变暖而导致的GEP增加反映在仙女木的LCID上；（5）干燥、中生和湿润苔原对相似变暖幅度的不同碳交换响应似乎部分取决于水文（土壤水分）条件。年净生态系统二氧化碳 - 碳交换速率从每平方米每年损失64克碳到每平方米每年获得55克碳不等。这些正的NEE数值接近基于破坏性收获对亚历山德拉峡湾以及其他高北极地区这些苔原类型的净初级生产力（NPP）的估计值。
Carbon dioxide exchange, soil C and N, leaf mineral nutrition and leaf carbon isotope discrimination (LCID‐Δ) were measured in three High Arctic tundra ecosystems over 2 years under ambient and long‐term (9 years) warmed (∼2°C) conditions. These ecosystems are located at Alexandra Fiord (79°N) on Ellesmere Island, Nunavut, and span a soil water gradient; dry, mesic, and wet tundra. Growing season CO2 fluxes (i.e., net ecosystem exchange (NEE), gross ecosystem photosynthesis (GEP), and ecosystem respiration (Re)) were measured using an infrared gas analyzer and winter C losses were estimated by chemical absorption. All three tundra ecosystems lost CO2 to the atmosphere during the winter, ranging from 7 to 12 g CO2‐C m−2 season−1 being highest in the wet tundra. The period during the growing season when mesic tundra switch from being a CO2 source to a CO2 sink was increased by 2 weeks because of warming and increases in GEP. Warming during the summer stimulated dry tundra GEP more than Re and thus, NEE was consistently greater under warmed as opposed to ambient temperatures. In mesic tundra, warming stimulated GEP with no effect on Re increasing NEE by ∼10%, especially in the first half of the summer. During the ∼70 days growing season (mid‐June–mid‐August), the dry and wet tundra ecosystems were net CO2‐C sinks (30 and 67 g C m−2 season−1, respectively) and the mesic ecosystem was a net C source (58 g C m−2 season−1) to the atmosphere under ambient temperature conditions, due in part to unusual glacier melt water flooding that occurred in the mesic tundra. Experimental warming during the growing season increased net C uptake by ∼12% in dry tundra, but reduced net C uptake by ∼20% in wet tundra primarily because of greater rates of Re as opposed to lower rates of GEP. Mesic tundra responded to long‐term warming with ∼30% increase in GEP with almost no change in Re reducing this tundra type to a slight C source (17 g C m−2 season−1). Warming caused LCID of Dryas integrafolia plants to be higher in dry tundra and lower in Salix arctic plants in mesic and wet tundra. Our findings indicate that: (1) High Arctic ecosystems, which occur in similar mesoclimates, have different net CO2 exchange rates with the atmosphere; (2) long‐term warming can increase the net CO2 exchange of High Arctic tundra by stimulating GEP, but it can also reduce net CO2 exchange in some tundra types during the summer by stimulating Re to a greater degree than stimulating GEP; (3) after 9 years of experimental warming, increases in soil carbon and nitrogen are detectable, in part, because of increases in deciduous shrub cover, biomass, and leaf litter inputs; (4) dry tundra increases in GEP, in response to long‐term warming, is reflected in D. integrifolia LCID; and (5) the differential carbon exchange responses of dry, mesic, and wet tundra to similar warming magnitudes appear to depend, in part, on the hydrologic (soil water) conditions. Annual net ecosystem CO2‐C exchange rates ranged from losses of 64 g C m−2 yr−1 to gains of 55 g C m−2 yr−1. These magnitudes of positive NEE are close to the estimates of NPP for these tundra types in Alexandra Fiord and in other High Arctic locations based on destructive harvests.