Department of Forest and Ecosystem Science, University of Melbourne, Water Street, Creswick, VIC, 3363, Australia,
Oecologia. 2013 Nov;173(3):1063-74. doi: 10.1007/s00442-013-2665-0. Epub 2013 May 7.
This before-and-after-impact study uses the natural abundance N isotope ratio (δ(15)N) to investigate the effects of a wildfire on sub-alpine ecosystem properties and processes. We measured the (15)N signatures of soil, charred organic material, ash and foliage in three sub-alpine plant communities (grassland, heathland and woodland) in south-eastern Australia. Surface bulk soil was temporarily enriched in (15)N immediately after wildfire compared to charred organic material and ash in all plant communities. We associated the enrichment of bulk soil with fractionation of N during combustion and volatilization of N, a process that also explains the sequential enrichment of (15)N of unburnt leaves > ash > charred organic material in relation to duration and intensity of heating. The rapid decline in (15)N of bulk soil to pre-fire values indicates that depleted ash, containing considerable amounts of total N, was readily incorporated into the soil. Foliar δ(15)N also increased with values peaking 1 year post-fire. Foliar enrichment was foremost coupled with the release of enriched NH4(+) into the soil owing to isotopic discrimination during volatilization of soluble N and combustion of organic material. The mode of post-fire regeneration influenced foliar (15)N enrichment in two species indicating use of different sources of N following fire. The use of natural abundance of (15)N in soil, ash and foliage as a means of tracing transformation of N during wildfire has established the importance of combustion products as an important, albeit temporary source of inorganic N for plants regenerating after wildfire.
本项火前-火后研究采用自然丰度 N 同位素比值（δ(15)N）来探究野火对亚高山生态系统特性和过程的影响。我们在澳大利亚东南部三个亚高山植物群落（草地、石南灌丛和林地）中测量了土壤、烧焦的有机物质、灰分和叶片的（15)N 特征。与所有植物群落中的烧焦有机物质和灰分相比，野火后表面土壤的（15)N 暂时增加。我们将土壤的富集与燃烧过程中 N 的分馏和 N 的挥发联系起来，这一过程也解释了未燃烧的叶子 > 灰分 > 烧焦的有机物质的（15)N 依次增加与加热的持续时间和强度有关。土壤（15)N 迅速下降到火前水平，表明含有大量总 N 的贫灰很容易被掺入土壤中。叶片 δ(15)N 也随着值的增加而增加，峰值出现在火后 1 年。叶片的富集主要与挥发过程中可溶性 N 和有机物质燃烧过程中同位素分馏导致的富 NH4(+)释放到土壤中有关。火后再生的模式影响了两种物种的叶片（15)N 富集，表明火灾后植物利用了不同来源的 N。利用土壤、灰分和叶片中（15)N 的自然丰度作为追踪野火期间 N 转化的一种手段，确立了燃烧产物作为植物在野火后再生的重要（尽管是暂时的）无机 N 来源的重要性。
