Constraints to nitrogen fixation by cryptogamic crusts in a polar desert ecosystem, Devon Island, NWT, Canada
Constraints to nitrogen fixation by cryptogamic crusts in a polar desert ecosystem, Devon Island, NWT, Canada
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DOI：
10.2307/1552408
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发表时间：
2000-02-01
影响因子：
2
通讯作者：
Dickson, LG
中科院分区：
文献类型：
--
作者：
Dickson, LG
在北极大部分地区占据主导地位的极地沙漠生态系统，在开发过程中受到环境压力和限制。间歇性地散布在这些景观上的是与维管植物丰度增加相关的隐配型结壳发育区域。因为营养限制，特别是氮，在这些生态系统中是重要的。我希望研究这些隐形结壳在固定氮素供应中的作用以及对这种固定的限制。固氮率(通过乙炔还原测定)在隐花结皮发育良好的地点最高，在仅有裸露矿物土壤的地点最低，在结皮部分发育的地点居中。乙炔还原(即固氮)的最高速率出现在融雪后的几天内(6月下旬至7月初)，并随着季节的推移而下降，直到生长季接近尾声(8月1日至5日)，此时的速率约为季节早期速率的50%。季末降水事件使乙炔还原速率恢复到接近原始水平。在操作实验中，乙炔还原速率随着结皮含水率的下降而急剧下降，随着土壤表面温度升高到24摄氏度而增大。一个重要的发现是，在3摄氏度时，乙炔还原速率是12至13℃时的40%。因此，即使在生长季节的较冷时期，也有可能积累氮素。计算表明，这些隐形结壳固定的氮量足以支持这些正在发展的生态系统中苔藓和维管植物的氮素需求。
Polar desert ecosystems, which dominate the landscape throughout much of the High Arctic, are environmentally stressed and limited in their development. Scattered intermittently over these landscapes are areas of cryptogamic crust development that are associated with increased vascular plant abundance. Since nutrient limitation, especially nitrogen, is significant in these ecosystems. I wished to examine the role of these cryptogamic crusts in the supply of fixed nitrogen and the constraints to that fixation. Nitrogen fixation rates (as measured by acetylene reduction) were highest in sites with a well-developed cryptogamic crust, lowest in sites with only bare mineral soil, and intermediate in sites with a partially developed crust. Highest rates of acetylene reduction (i.e., nitrogen fixation) were seen within a few days of snowmelt (late June to early July) and declined as the season progressed, until near the end of the growing season (1-5 August) when rates were approximately 50% of early season rates. Late season precipitation events restored acetylene reduction rates to near original levels. In manipulative experiments, acetylene reduction rates dropped dramatically as crust moisture content declined and rates increased as soil surface temperature increased to 24 degrees C. A significant finding was that acetylene reduction at 3 degrees C was 40% of that round at 12 to 13 degrees C. Thus, there is a potential for nitrogen accumulation even during the colder periods of the growing season. As calculations show, the quantity of nitrogen fixed by these cryptogamic crusts was adequate to support the nitrogen needs of the mosses and vascular plants of these developing ecosystems.