燃烧过程植物体氮含量和氮同位素组成变化

The Effects of Burning on Plant's Nitrogen Content and Nitrogen Stable Isotopic Compositions

自然和人类活动引起的火事件可导致生态系统的碳、氮循环以及分布格局的改变,进一步影响区域碳、氮生物地球化学循环。利用稳定同位素方法可以帮助我们示踪火事件所伴生的碳、氮转化的生物地球化学过程。为了解植物体燃烧前后植物、植物灰烬和气态挥发部分氮之间以及不同植物类型(C_3和C_4,草本和木本)之间的氮素差异,通过室内模拟燃烧实验研究了植物和燃烧后残余部分的氮同位素组成和氮含量变化,研究表明:不同植物种类之间氮同位素组成的变化受植物种类和生长条件的影响,比较C_3和C_4植物不同光合类型之间的氮同位素组成表明,植物体燃烧前后氮同位素变化和植物的光合类型无关。燃烧导致植物90%以上的氮素损失。不同植物氮同位素值在-4.0‰～+5.2‰变化,燃烧导致植物灰烬的氮同位素值偏正0～1.6‰,其同位素分馏主要是由于燃烧过程中植物体中^(14)N较^(15)N优先以气态形式逃逸。因此在利用氮同位素进行的古环境研究、环境模拟过程中,必须考虑火烧对植物氮同位素值的影响。植物、植物灰烬和气态部分氮同位素之间具有较好的相关性,这种关系启示我们也许可以利用生态系统不同部分的氮同位素组成来研究植物—土壤—大气之间的氮素循环规律。

Fire affair can cause to changes of ecosystem＇s carbon or nitrogen cycles and its distribution,and further effect on the local area even global climate change. However, stable isotopic techniques can help us to understand correlations between vegetation and gaseous material caused by fire affair. For better understanding correlations among plant, ash and gaseous by plant burning,controlled experiment was done in order to know changes of nitrogen content and nitrogen stable isotopic composition of different part. The results show that： more than 65 % weight of plant and 90% nitrogen content losing by form of gaseous material during burning. Nitrogen isotopic composition of different plant is from -4.0‰ to 5.2‰. Ash nitrogen isotopic composition increased from 0 to 1.6‰, which may be caused by 14 N volatilized by means of gaseous material. The higher correlation was found among plant, plant ash and gaseous material, and the relationship implied us that nitrogen isotopic composition can be used to trace nitrogen cycle mechanism among plant, soil and atmosphere.