蒙古栎叶片及其土壤碳、氮同位素自然丰度对大气CO2浓度升高的响应

大气CO₂浓度升高对土壤氮素转化过程产生重要影响,研究其变化有助于更好地预测陆地生态系统的固碳潜力.氮同位素自然丰度作为生态系统氮素循环过程的综合指标能够有效地指示CO₂浓度升高对土壤氮素转化过程的影响.本研究采用开顶箱CO₂ 熏蒸法研究连续10年的大气CO₂ 浓度升高对我国东北地区蒙古栎及其土壤和微生物生物量碳、氮同位素自然丰度的影响.结果表明: 大气CO₂浓度升高改变了土壤氮循环过程,增加了土壤微生物和植物叶片δ¹⁵N;促进了富¹³C土壤有机碳分解,中和了贫¹³C植物光合碳输入的效果,导致土壤可溶性有机碳和微生物碳δ¹³C在CO₂升高条件下没有发生显著变化.这些结果表明,CO₂浓度升高很可能促进了土壤有机质矿化过程,并加剧了系统氮限制的状态.

Responses of the natural abundance of carbon and nitrogen isotopes of Quercus mongolica leaf and soil to elevated CO2

The rising atmospheric CO₂ concentration significantly changed soil nitrogen (N) cycling which is important for us to predict the carbon (C) sequestration potential of terrestrial ecosystems. The natural abundance of N isotope as an integrative indicator of ecosystem N cycling processes can effectively indicate the effect of elevated CO₂ on soil N cycling processes. Here, we used an open top chamber experiment to examine the effects of elevated CO₂for ten years on the natural abundance of Quercus mongolica, soil and microbial biomass C and N isotopes in northeastern China. Our results showed that elevated CO₂ significantly changed soil N cycling processes, resulting in the increase of microbial and leaf δ¹⁵N; stimulated the decomposition of ¹³C-enriched soil organic C, and offset the effect of more ¹³C-depleted plant photosynthetic C inputs, resulting in unchanged δ¹³C of soil dissolved organic C and microbes under elevated CO₂. These results indicated that elevated CO₂ likely increased the mineralization of soil organic matter, and the system is getting more N-limited.