The effect of elevated atmospheric CO2 concentration on gross nitrogen dynamics, plant N-uptake and microbial community dynamics in a permanent grassland

要预测生态系统对大气CO2浓度升高的反应，必须了解植物碳输入、微生物群落组成和活性以及相关营养动态之间的相互作用。对永久草原的吉森自由空气二氧化碳浓缩(Giessen Face)研究进行的长期观察(&gt；13年)显示，除了生物量的增加，生态系统呼吸和一氧化二氮(N2O)的产生也出现了意想不到的强正反馈效应。本研究的总体目标是了解生态二氧化碳和碳输入对永久草地微生物群落组成和活性的长期影响，以及相关的氮素动态、N2O产生和植物氮素吸收。将在现场进行13CO2脉冲标记与15NH4+和15NO3-的15N示踪相结合。将量化土壤有机质的不同部分(顽固的、不稳定的SOM)和土壤中不同的矿质N库(NH4+、N03-、NO2-)、总N转化率、与池大小有关的N2O和N 2排放以及与N物种有关的植物N吸收速率和CO2呼吸的来源。微生物分析将包括探索参与NH4+、N3-、N2O和N2周转的微生物群落组成的变化，即氨氧化、反硝化和参与异化硝酸盐还原为氨(DNRA)的微生物群落。稳定同位素探测(SIP)和基于mRNA的分析将被用来比较评估Eco2对这些群落的结构和丰度的长期影响，而这些基因的转录本将被用来定位那些积极促进N转化的群落的部分。

To predict ecosystem reactions to elevated atmospheric CO2 (eCO2) it is essential to understandthe interactions between plant carbon input, microbial community composition and activity and associated nutrient dynamics. Long-term observations (> 13 years) within the Giessen Free Air Carbon dioxide Enrichment (Giessen FACE) study on permanent grassland showed next to an enhanced biomass production an unexpected strong positive feedback effect on ecosystem respiration and nitrous oxide (N2O) production. The overall goal of this study is to understand the long-term effects of eCO2 and carbon input on microbial community composition and activity as well as the associated nitrogen dynamics, N2O production and plant N uptake in the Giessen FACE study on permanent grassland. A combination of 13CO2 pulse labelling with 15N tracing of 15NH4+ and 15NO3- will be carried out in situ. Different fractions of soil organic matter (recalcitrant, labile SOM) and the various mineral N pools in the soil (NH4+, NO3-, NO2-), gross N transformation rates, pool size dependent N2O and N2 emissions as well as N species dependent plant N uptake rates and the origin of the CO2 respiration will be quantified. Microbial analyses will include exploring changes in the composition of microbial communities involved in the turnover of NH4+, NO3-, N2O and N2, i.e. ammonia oxidizing, denitrifying, and microbial communities involved in dissimilatory nitrate reduction to ammonia (DNRA). Stable Isotope Probing (SIP) and mRNA based analyses will be employed to comparably evaluate the long-term effects of eCO2 on the structure and abundance of these communities, while transcripts of these genes will be used to target the fractions of the communities which actively contribute to N transformations.