N trace gas emissions from tropical savanna ecosystems and responses to global changes

热带稀树草原生物群落约占全球陆地面积的11.5%。这些生态系统的稀树草原土壤被认为对全球大气中一氧化二氮（N2O）和其他重要的大气微量气体（NO, CH4, CO2）的浓度有很大贡献。稀树草原的特点是干湿季节的季节性很强，再湿润事件大多伴随着N和C微量气体的显著脉冲排放。频繁的火灾事件会通过凋落物、储存、损失以及土壤中养分的可用性对氮和碳输入产生影响，从而导致土壤-大气交换的进一步变化。与稀树草原系统对全球大气N微量气体预算的重要性相反，土壤-大气微量气体交换的原位测量相对较少，并且对汇/源强度的估计仍然高度不确定。我们将使用最先进的实验和建模方法来提高对当前环境条件下稀树草原N和C转化过程的理解，并预测未来的土地利用和气候。详细的高时间分辨率现场测量（覆盖至少一整年）将在澳大利亚稀树草原上进行N和C微量气体交换和潜在的环境过程控制，并将与澳大利亚合作机构正在进行的项目的补充数据相结合。澳大利亚的热带稀树草原覆盖了大约20%的大陆面积，并沿著陡峭的降雨量和温度梯度发生，因此，覆盖了广泛的气候和环境条件，这对世界上其他热带稀树草原地区具有代表性。因此，该项目将产生的数据和模型不仅适用于澳大利亚，也适用于其他大陆的稀树草原系统。我们与澳大利亚研究人员的密切合作将提高拟议项目以及澳大利亚合作伙伴项目（澳大利亚研究理事会联系项目LP0774812 -干扰和土地利用变化对热带草原生态系统温室气体总量平衡和养分循环的综合评估）的研究成果的质量。这两个项目的数据将用于开发和完善ForestDNDC-tropica / MOBILE生物地球化学模型。模型开发将基于先进的贝叶斯校准技术，并将首次提供模型参数和模型输出的详细不确定性评估。此外，通过在我们的模型框架中实施一个已建立的火灾模块，我们将能够模拟火灾管理、土地利用和气候变化对热带稀树草原生态系统养分周转的综合影响。改进后的模型将用于研究北澳大利亚热带稀树草原生态系统的营养循环和N和C微量气体的土壤-大气交换，特别是包括火灾的影响。此外，ForestDNDC-tropica / MOBILE模型将与一个GIS数据库相结合，用于计算澳大利亚热带稀树草原系统的N微量气体交换清单。将对该地区预计的气候影响（如干旱和火灾强度和频率的变化）和土地利用变化情景进行具体的模式模拟，以评估其对生态系统N养分循环和相关微量气体交换的影响。

The tropical savanna biome covers approximately 11.5% of the global land surface. Savanna soils of these ecosystems are thought to contribute substantially to the global atmospheric concentration of nitrous oxide (N2O) and other important atmospheric trace gases (NO, CH4, CO2). Savannas are characterised by a strong seasonality of dry and wet seasons, with rewetting events mostly accompanied by significant pulse emissions of N and C trace gases. Frequent fire events induce further variability in the soil-atmosphere exchange due to effects on N and C inputs via litter fall, storage, loss and, thus, availability of nutrients in the soil. In contrast to the importance of savanna systems for the global atmospheric N trace gas budgets only relatively few in-situ measurements of the soil-atmosphere trace gas exchange have been performed and estimates about the sink/ source strength are still highly uncertain. We will use state-of-the-art experimental and modelling approaches to improve the understanding of N and C transformation processes in savannas under current environmental conditions and predicted future land-uses and climate. Detailed high time resolution field measurements (covering at least an entire year) on N and C trace gas exchange and underlying environmental process controls will be conducted in Australian savannas and will be combined with supplementary data from ongoing projects of Australian partner institutions. Australian savannas cover approximately 20% of the continent and occur along a steep rainfall and temperature gradient, thus, covering a wide range of climatic and environmental conditions, which are representative for other savanna regions worldwide. Therefore, this project will generate data and models which are applicable not only for Australian but also for savanna systems of other continents. Our close collaboration with Australian researchers will enhance the quality of research outcomes from the proposed project as well as the Australian partner project (Australian Research Council Linkage project LP0774812 - Integrated assessment of disturbance and land-use change on total greenhouse gas balance and nutrient cycling in savanna ecosystems ). Data from both projects will be used to develop and refine the biogeochemical model ForestDNDC-tropica / MOBILE. Model development will be based on advanced Bayesian calibration techniques and will, for the first time, provide a detailed uncertainty assessment of model parameters and model outputs. Furthermore, by implementing an established fire module in our model framework we will be able to simulate the combined effects of fire management, land-use and climate change on nutrient turnover in tropical savanna ecosystems. The improved model will be used to investigate nutrient cycling and the soilatmosphere exchange of N and C trace gases for a range of tropical savanna ecosystems of Northern Australia, specifically including the effect of fire. Further, the ForestDNDC-tropica / MOBILE model will be coupled to a GIS database for calculating inventories of N trace gas exchange for the savanna systems of tropical Australia. Specific model simulations will be conducted covering projected climatic effects (e.g., changes in drought and fire intensity and frequency) and land-use change scenarios for this region in order to assess their impact on ecosystem N nutrient cycling and associated trace gas exchange.