Linking the composition of dissolved organic matter and nutrient cycling in streams of temperate forested catchments

溶解有机质（DOM）是陆地和水生生态系统碳（C）和营养盐循环的重要组成部分。变化的环境条件，如减少酸性和氮沉降和改变水制度，更频繁和更强烈的风暴和干旱事件，强烈影响DOM的动态与未知的影响DOM的重要生态功能，作为其在C和养分循环中的作用。溶解有机碳（DOC）、氮（DON）和磷（DOP）的化学计量在调节生态系统功能中起着至关重要的作用。土壤决定了有机物进入河流的输入量，根据水文条件，表层有机层或底土矿物层将控制河流DOM的数量和组成。然而，DOM组成的变化，因为它的来源的变化还没有联系到DOM的营养循环的作用。因此，所要求的项目的总体目标是阐明控制溪流中DOM的数量、组成和功能的陆地和水生生态系统界面的复杂相互作用。我们的总体假设是，DOM的组成决定了其对森林溪流养分循环的贡献，即作为微生物的C，N或P来源。选定的森林集水区与不同的基岩和土壤提供了一个合适的梯度，在潜在的养分限制，研究DOM组合物对其功能的影响。在不同水文条件下，将沿着土壤-水连续体（即连接土壤有机质和DOM的组成）分析选定集水区的DOM组成。DOM组成的差异将用于根据水流条件确定流域中最重要的DOM来源。这些研究DOM组成将被链接到营养脉冲添加实验中的流确定DOM是否主要作为微生物的C，N或P源。这种对实地观察和实验的强烈关注将伴随着实验室中的培养实验，以进一步阐明土壤有机质和DOM的组成之间的联系，以及沿着陆生水生连续体的养分循环的后果。将结合不同复杂性的方法来确定土壤和水中有机物质的组成（荧光激发-发射矩阵、傅里叶变换红外光谱法、热解气相色谱质谱法、31 P核磁共振光谱法）。只有将捷克和德国合作伙伴的独特专业知识与捷克合作伙伴的长期监测集水区以及德国合作伙伴的现代实验室设备相结合，才能确保项目的成功，即阐明DOM成分在持续环境变化压力下对其生态功能的作用。

Dissolved organic matter (DOM) is an important component of the carbon (C) and nutrient cycles in terrestrial and aquatic systems. Changing environmental conditions, such as decreasing acidic and nitrogen deposition and changing water regimes with more frequent and intense storm and drought events, strongly influence the dynamics of DOM with unknown effects on important ecological functions of DOM as its role in C and nutrient cycling. The stoichiometry of dissolved organic carbon (DOC), nitrogen (DON) and phosphorous (DOP) plays a crucial role in regulating ecosystem functioning. Soils determine the input of organic matter into the streams and depending on hydrological conditions surface organic horizons or subsoil mineral horizons will control amount and composition of stream DOM. However, changes in DOM composition because of changes on its source have not been linked to the role of DOM for nutrient cycling. Thus, the overall objective of the requested project is to shed light upon the complex interactions at the interface of terrestrial and aquatic ecosystems controlling amount, composition and functionality of DOM in streams. Our overarching hypothesis is that the composition of DOM determines its contribution to nutrient cycling in forested streams, i.e. serving as a C, N or P source for microorganisms. The selected forested catchments with differing bedrock and soil offer a suitable gradient in potential nutrient limitations to study the envisaged effects of DOM composition on its function. DOM composition will be analyzed along the soil-water-continuum (i.e. linking the composition of soil organic matter and DOM) in the selected catchments at different hydrological conditions. Differences in DOM composition will be used to determine the most important DOM sources in the catchment depending on the flow conditions. These studies on DOM composition will be linked to nutrient pulse addition experiments in the streams determining whether DOM serves mainly as a C, N or P source for microorganisms. This strong focus on field observations and experiments will be accompanied by incubation experiments in the laboratory to further elucidate the linkages between the composition of soil organic matter and DOM and the consequences for nutrient cycling along the terrestrial aquatic continuum. Methods of different complexity will be combined to determine the composition of organic matter in soils and water (Fluorescence Excitation-Emission Matrices, Fourier-Transform Infrared Spectrometry, Pyrolysis Gas Chromatography Mass Spectrometry, 31P-Nuclear Magnetic Resonance Spectroscopy). Only the combination of the unique expertise of the Czech and German partners with the well characterized long-term monitoring catchments of the Czech partner and the modern lab equipment of the German partner will ensure the success of the project, i.e. elucidating the role of DOM composition for its ecological function under the pressure of ongoing environmental changes.