SpatEn - Spatial and temporal substrate supply controls energy channelling in the soil system

天然土壤在分子多样性、空间异质性和有机质(OM)来源的时间变异性方面的功能复杂性可能是影响土壤作为开放热力学系统的能量排放和碳(C)消耗的关键因素。到目前为止，对土壤中碳循环的研究大多集中在碳通过生物和非生物土壤组分的质量流动上，而忽视了碳作为能源和微生物能量需求的重要性。此外，现有的关于微生物C在分解代谢和合成代谢之间的分配的研究通常没有考虑到底物可用性的空间异质性和时间波动的影响。本提案审查了(1)分子底物多样性、(2)空间非均质底物添加、(3)底物供应的时间变化作为单独影响因素和组合对通过微生物群落的代谢通量的影响。我们将测定微生物碳和底物利用效率(CUE，Sue)、热量呼吸比和酶动力学，作为分解代谢和合成代谢途径效率的衡量标准，以及微生物群落投资于胞外酶的相关指标。化合物特有的13C PLFA分析和高通量下一代测序将使结果能够与特定的微生物组相联系。实验设计包括在受控条件下进行的四个工作包(WPS)。WP1和WP2的培养研究将模拟基质多样性和空间异质性增加的梯度(I)，无论是在土壤斑块严格空间分离的条件下(II)，还是在菌丝C运输的调制影响下。WP3模拟了来自热点的不规则底物供应和不同的底物释放速率，而WP4则专注于不同空间和时间底物可用性的综合影响。该项目的结果将揭示一个基本的理解，即供应基质的不同程度的分子多样性、空间异质性和时间变异性如何通过土壤微生物群落的合成代谢和分解代谢影响有机碳通道。我们的结果还将为将基于底物异质性的微生物生长热力学预测纳入C循环模型提供数据基础。

Natural soils’ functional complexity with regard to molecular diversity, spatial heterogeneity and temporal variability of organic matter (OM) sources is likely a crucial factor affecting energy discharge and carbon (C) consumption in soils as open thermodynamic systems. The majority of research on C cycling in soil was focused on C mass flow through living and non-living soil components so far, neglecting the importance of C as energy source and microbial energy demand. Furthermore, existing research on microbial C partitioning between catabolism and anabolism usually does not account for the effect of spatially heterogeneous and temporally fluctuating substrate availability. The present proposal examines the effects of (i) molecular substrate diversity, (ii) spatial heterogeneous substrate addition, (iii) and temporal variations in substrate supply, both, as individual impact factors and in combination, on metabolic fluxes through the microbial community. We will determine microbial carbon and substrate use efficiency (CUE, SUE), calorespirometric ratio, and enzyme kinetics as measures for the efficiency of catabolic and anabolic pathways and relative proxy for the investment of the microbial community into extracellular enzymes. Compound specific 13C PLFA analysis and high-throughput next generation sequencing will enable to link the results to specific microbial groups. The experimental design consists of four working packages (WPs) conducted under controlled conditions. The incubation studies of WP1 and WP2 will mimic gradients of increasing substrate diversity and spatial heterogeneity (i) either under conditions of strict spatial disconnection of soil patches (ii) or under the modulating impact of hyphal C transport. WP3 simulates irregular substrate supply and different rates of substrate release from hot spots and WP4 focusses on the combined effects of varying spatial and temporal substrate availabilities. The results of the proposed project will reveal a fundamental understanding, how different degrees of molecular diversity, spatial heterogeneity and temporal variability of a supplied substrate affect OC channeling through anabolism and catabolism of the soil microbial community. Our results will furthermore provide the data basis to include substrate heterogeneity based thermodynamic predictions of microbial growth into C cycling models.