Johannisson Christian, Högberg Peter
Section of Forest Soils, Department of Forest Ecology, Swedish University of Agricultural Sciences, S-901 83, Umeå, Sweden.
Oecologia. 1994 Apr;97(3):322-325. doi: 10.1007/BF00317321.
N abundances of soils and a grass species (Deschampsia flexuosa (L.) Trin.) were analysed in a forest fertilization experiment 10 years after the last fertilization. Nitrogen had been given as urea, at seven doses, ranging from 0 to 2400 kg N ha. Previously, we have shown that plants in systems experiencing large losses of N become enriched with N. This was explained by the fact that processes leading to loss of N, e.g. ammonia volatilization, nitrification followed by leaching or denitrification and denitrification itself, tend to fractionate against N. In this experiment, N abundance increased with dose of N applied in both grass and soil total-N, but more so in the grass. This was interpreted to be due to the grass sampling small but active pools of N subject to losses. In contrast, soil total-N largely consists of inactive N that does not immediately exchange with pools of N from which fractionating losses occur. Hence, soil total-N shows a large pretreatment N memory effect, and is, therefore, and integrator of the long-term N balance. When short-term changes (years, decades) in N balances are monitored using variations in N abundance, plants are more suitable indicators of such change than is soil total-N.
在最后一次施肥10年后的森林施肥试验中，分析了土壤和一种禾本科植物（柔枝莠竹（Deschampsia flexuosa (L.) Trin.））中的氮丰度。氮以尿素形式施入，施用量为7个水平，范围从0至2400 kg N/ha。此前，我们已经表明，在经历大量氮损失的系统中，植物会富集氮。这可以用导致氮损失的过程来解释，例如氨挥发、硝化作用后接着淋溶或反硝化作用以及反硝化作用本身，往往会对氮进行分馏。在本试验中，禾本科植物和土壤全氮中的氮丰度均随施氮量的增加而增加，但禾本科植物中增加得更多。这被解释为是由于禾本科植物采样的是少量但活跃的易发生损失的氮库。相比之下，土壤全氮主要由不活跃的氮组成，这些氮不会立即与发生分馏损失的氮库进行交换。因此，土壤全氮表现出较大的预处理氮记忆效应，因此是长期氮平衡的一个整合指标。当使用氮丰度变化监测氮平衡的短期变化（数年、数十年）时，植物比土壤全氮更适合作为此类变化的指标。
