Sinks for inorganic nitrogen deposition in forest ecosystems with low and high nitrogen deposition in China.
Sinks for inorganic nitrogen deposition in forest ecosystems with low and high nitrogen deposition in China.
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DOI：
10.1371/journal.pone.0089322
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发表时间：
2014
期刊：
影响因子：
3.7
通讯作者：
Zhou M
中科院分区：
文献类型：
--
作者：
Sheng W;Yu G;Fang H;Jiang C;Yan J;Zhou M
在两种不同N沉降水平下，在中国东部森林生态系统中添加（15NH4）2SO4和K15NO3形式的稳定同位素15N，研究不同形式N沉降的走向。在添加15N示踪剂之前，顶湖山（DHS）重N沉降下森林的自然15N丰度为- 3.4‰~ +10.9‰，大兴安岭（DXAL）轻N沉降下森林的自然15N丰度为- 3.92‰~ +7.25‰。施用示踪剂4个月后，主要生态系统区室的15N总回收率在55.3% ~ 90.5%之间。在（15NH4）2SO4示踪剂处理下，两种森林生态系统的15N总恢复量相似，而在K15NO3示踪剂处理下，DHS的亚热带森林生态系统的15N总恢复量显著低于DXAL的北方森林生态系统。林木生物量吸收的15N仅占森林生态系统添加15N的8.8% ~ 33.7%。在两种示踪剂处理下，DHS的亚热带森林生态系统比DXAL的北方森林生态系统从树木生物量中回收了更多的15N。两种森林生态系统中，K15NO3示踪剂处理对林木生物量吸收的15N量均大于（15NH4）2SO4处理。研究表明，尽管在氮沉降强度较大的条件下，森林生态系统中固定的氮较少，但在中国森林生态系统中，即使在氮沉降强度较大的地区或在春季冻融融化的生态系统中，也能保持较强的氮沉积。与铵沉降相比，沉积的硝态氮更容易从森林生态系统中释放出来。然而，硝酸盐沉积可能主要保留在植物氮库中，这可能导致这些生态系统中更多的碳固存。
We added the stable isotope 15N in the form of (15NH4)2SO4 and K15NO3 to forest ecosystems in eastern China under two different N deposition levels to study the fate of the different forms of deposited N. Prior to the addition of the 15N tracers, the natural 15N abundance ranging from −3.4‰ to +10.9‰ in the forest under heavy N deposition at Dinghushan (DHS), and from −3.92‰ to +7.25‰ in the forest under light N deposition at Daxinganling (DXAL). Four months after the tracer application, the total 15N recovery from the major ecosystem compartments ranged from 55.3% to 90.5%. The total 15N recoveries were similar under the (15NH4)2SO4 tracer treatment in both two forest ecosystems, whereas the total 15N recovery was significantly lower in the subtropical forest ecosystem at DHS than in the boreal forest ecosystem at DXAL under the K15NO3 tracer treatment. The 15N assimilated into the tree biomass represented only 8.8% to 33.7% of the 15N added to the forest ecosystems. In both of the tracer application treatments, more 15N was recovered from the tree biomass in the subtropical forest ecosystem at DHS than the boreal forest ecosystem at DXAL. The amount of 15N assimilated into tree biomass was greater under the K15NO3 tracer treatment than that of the (15NH4)2SO4 treatment in both forest ecosystems. This study suggests that, although less N was immobilized in the forest ecosystems under more intensive N deposition conditions, forest ecosystems in China strongly retain N deposition, even in areas under heavy N deposition intensity or in ecosystems undergoing spring freezing and thawing melts. Compared to ammonium deposition, deposited nitrate is released from the forest ecosystem more easily. However, nitrate deposition could be retained mostly in the plant N pool, which might lead to more C sequestration in these ecosystems.
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