Nitrogen cycling under elevated CO2: response of a key soil nutrient to global change

二氧化碳浓度升高下的氮循环：关键土壤养分对全球变化的响应

• 批准号: 2858636
• 金额: --
• 依托单位: University of Birmingham
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2858636
• 关键词: Nitrogen; cycling; under; elevated; CO2

Increasing atmospheric CO2 concentrations in the atmosphere due to human activities, is projected to enhance photosynthesis and carbon storage of forest ecosystem. However, it is unclear how nutrient limitation will constrain the projected CO2 fertilization effect. Therefore, it is essential to evaluate how nutrient limitation will affect the response of forests to rising CO2 concentration and how it will feedback on nutrient availabilities and more especially nitrogen (N) which can become limiting with time. The purpose of this research is to evaluate the response of N cycling processes to elevated CO2 fumigation in a N-limited northern deciduous temperate forest and a phosphorus (P)-limited Eucalyptus dominated forest. The research was conducted in two Free Air Carbon Dioxide Enrichment (FACE) facilities: BIFOR FACE located near Birmingham, UK and EucFACE in New South Wales, Australia. Furthermore, EucFACE (P-limited forest) received partial phosphorus fertilization to study its effect on N cycling.A 15N pool dilution method will be used to quantify gross protein depolymerization and gross mineralization and estimate the microbial nitrogen use efficiency. N2O emissions from nitrification and denitrification will be assessed using a 15N Gas Flux method and free-living N fixation in soils will be assessed by the 15N assimilation method. Additionally, the isotopic measurements will be compared by a metagenomic approach quantifying the expression of N cycling genes. We hypothesize that in a N limited forest, trees will allocate a greater proportion of carbon belowground to boost soil organic matter (SOM) decomposition for N supply to trees. This process will enhance N availability for trees but will also lead to nitrogen losses via leaching and denitrification. Conversely, in the phosphorus-limited forest, tree exudates will fail to effectively unlock phosphorus (P) availability, hindering the enhancement of photosynthesis and the feedback on N cycling in the soil. However, fertilizing these forests with phosphorus will shift the ecosystem from being P-limited to N-limited, triggering an enhancement of N supply processes. In addition, EucFACE (P-limited forest) will be partially fertilized with phosphorus in order to explore how a sudden P limitation alleviation will affect N cycling. Results from this research aim at improving our understanding of forest response to future climate by unveiling the role of nutrient limitation in future C uptake.

由于人类活动导致大气中CO2浓度的增加，预计会增强森林生态系统的光合作用和碳储量。然而，目前尚不清楚养分限制将如何限制预计的二氧化碳施肥效应。因此，必须评估养分限制将如何影响森林对二氧化碳浓度上升的反应，以及它将如何反馈养分有效性，尤其是氮(N)，后者可能随着时间的推移而变得有限。本研究的目的是评价氮素限制的北方落叶温带森林和磷(P)限制的桉树主导森林中氮素循环过程对CO2熏蒸的响应。该研究在两个自由空气二氧化碳富集（FACE）设施中进行：位于英国伯明翰附近的BIFOR FACE和位于澳大利亚新南威尔士州的EucFACE。此外，对限磷林进行部分磷施肥，研究其对氮素循环的影响。采用15N池稀释法定量测定总蛋白解聚和总矿化，估算微生物氮利用效率。硝化和反硝化过程中的N2O排放将采用15N气体通量法进行评估，土壤中的游离氮固定将采用15N同化法进行评估。此外，同位素测量将通过量化N循环基因表达的宏基因组方法进行比较。我们假设，在氮素有限的森林中，树木将分配更大比例的碳到地下，以促进土壤有机质（SOM）分解，为树木提供氮素。这一过程将提高树木的氮利用率，但也会通过淋滤和反硝化导致氮损失。相反，在限磷森林中，树木渗出液将不能有效地释放磷(P)有效性，阻碍了光合作用的增强和土壤中N循环的反馈。然而，向这些森林施磷将使生态系统从磷限制转变为氮限制，引发氮供应过程的增强。此外，EucFACE（限磷森林）将部分施磷，以探索磷限制的突然缓解将如何影响N循环。这项研究的结果旨在通过揭示营养限制在未来碳吸收中的作用，提高我们对森林对未来气候响应的理解。