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Nitrogen fixation by associative cyanobacteria in the Canadian Arctic.

机译:在加拿大北极地区,蓝藻伴有固氮作用。

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摘要

Atmospheric Nu2082-fixation by cyanobacteria is a key source of newly fixed N in nutrient-poor arctic ecosystems. To further determine the causes of N limitation and predict long-term responses to climate change the controls of biological Nu2082-fixation must be better understood. Using acetylene reduction assays we evaluated the spatial and temporal variation in Nu2082-fixation by associative cyanobacteria in various ecosystem types in both the low and high Canadian Arctic. The direct and indirect effects of soil moisture, plant community functional composition, and bryophyte and lichen abundance on rates of Nu2082-fixation were examined at sites varying in latitude and vegetation type. The linkages between N and C cycling processes in arctic systems were examined through paired measurements of Nu2082-fixation, inorganic soil N with surface greenhouse gas fluxes, including COu2082, Nu2082O and CHu2084. Total growing season Nu2082-fixation input across a low arctic landscape was estimated at 0.68 kg hau207b~yru207b~, which is slightly less than twice the estimated average N input 0.39 kg hau207b~yru207b~ via precipitation. Nu2082-fixation by bryophyte-cyanobacterial associations appear to be very important across the Canadian Arctic. Increasing soil moisture was strongly associated with an increasing presence of bryophytes and increasing bryophyte abundance was a major factor determining higher Nu2082-fixation rates at all sites. Shrubs had a negative effect on bryophyte abundance; competition from vascular plants, potentially through shading, may negatively influence Nu2082-fixation. Soil N status was linked to rates or Nu2082-fixation in both the high and low Arctic indicating that these Nu2082-fixing associations act as important point sources of soil N. Higher rates of nitrification may be associated with warmer and drier vegetation types; however, increasing NOu2083-N availability does not appear to increase rates of denitrification. Loss of N through denitrification was not a significant factor in the N cycle at the high arctic sites examined. We found many factors control both the spatial and temporal variability of Nu2082-fixation, including topography, microtopography, vegetation characteristics, microclimatic conditions, nifH abundance and availability of other nutrients, such as phosphorus. Moisture, however, appears to be a key factor not only in determining Nu2082-fixation but also by influencing related nutrient cycling processes.
机译:蓝细菌对大气中N u2082-的固定作用是北极营养缺乏的生态系统中新固定N的关键来源。为了进一步确定N限制的原因并预测对气候变化的长期响应,必须更好地理解生物N u2082固定的控制。使用乙炔还原测定法,我们评估了高低北极地区各种生态系统类型中相关蓝藻在N u2082-固着中的时空变化。在不同纬度和植被类型的地点,研究了土壤水分,植物群落功能组成以及苔藓植物和地衣的丰富度对N u2082-固着率的直接和间接影响。通过配对测量N u2082-固着,无机土壤N和表面温室气体通量(包括CO u2082,N u2082O和CH u2084),研究了北极系统中N和C循环过程之间的联系。整个低北极地区整个生长期的N u2082-固定输入估计为0.68 kg ha u207b〜yr u207b〜,略小于估计的平均N输入0.39 kg ha u207b〜yr u207b〜的两倍。沉淀。在整个加拿大北极地区,苔藓植物-蓝细菌缔合的N u2082-固定似乎非常重要。土壤湿度的增加与苔藓植物的存在密切相关,而苔藓植物的丰度增加是决定所有地点较高的N u2082-固着率的主要因素。灌木对苔藓植物的丰度有负面影响。维管植物的竞争(可能通过遮挡)可能会对N u2082-固定产生负面影响。土壤氮的状况与北极和高北极地区的氮素固定比率有关,这表明这些氮素固定关联是土壤氮素的重要来源。较高的硝化速率可能与植被变暖和干燥有关类型;但是,增加NO u2083-N的可用性似乎并不会增加反硝化率。在高北极地区,通过反硝化作用损失的氮不是氮循环的重要因素。我们发现许多因素都控制N u2082-固定的时空变异,包括地形,微地形,植被特征,微气候条件,nifH丰度和其他养分(如磷)的利用率。但是,水分似乎不仅是决定N u2082固定的关键因素,而且还通过影响相关的养分循环过程而成为关键因素。

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