Sorption thermodymamics and aggregation as controls of substrate use and mineralization

有机分子对矿物的吸附强度和保护有机底物的团聚体的稳定性是土壤系统微生物群落“形成能量和物质利用通道”的边界条件之一(SPP 2223的总体假设C)。虽然土壤中有机质对微生物利用和矿化的稳定性与吸附有关，但它与吸附过程热力学的关系到目前为止还没有量化。此外，土壤团聚体和土壤微生物多样性对这种关系的影响尚不清楚。为了分析形成能量和物质利用通道的边界条件，我们将检验以下假设：(I)吸附和解吸能随着吸附物的极性和氧化程度的增加以及吸附剂表面羟基的增加而增加，(H Ii)微生物基质的利用随着deltaG的减小而减少，热力学吸附滞后和解吸激活能随吸附基质使用的热力学阈值而增加，(H Iii)微生物利用吸附床基质的热力学阈值随着土壤微生物群落功能多样性的增加而增加，(H IV)聚集体内基质的高物理保护削弱了吸附热力学对微生物基质利用的重要性。我们将在四个相应的工作包中测试这些假设。在WP1中，我们将通过不同温度下的吸附-脱附实验、Arrhenius图和微量热，测定6种模型基质和3种模型矿物的吸附反应吉布斯自由能ΔG、吸附热焓(ΔH)和吸附熵(Δtas)、脱附反应活化能Ea和吸附滞后造成的摩尔自由能损失(Tii)。WP2将使用SPP土壤样本的微型培养实验来确定14C标记的模型底物的使用和矿化作用，这些底物被吸附到4个SPP土壤中的模型矿物中。在WP3中，将通过第二次培养试验来研究功能多样性在矿化中的作用，该试验与添加了提取微生物的SPP土壤进行培养，以利用生态板进行酶分析来操纵微生物多样性或养分。最后，在WP 4中，将测量被吸附到分散和聚集的土壤系统中的选定的13C标记的模型物质的矿化程度，这些土壤系统具有形态和物理特征。结合预期结果，我们的项目将提供将吸附过程和聚集整合到土壤生态系统功能和发展的热力学概念中的基本见解。

Sorption strength of organic molecules to minerals and the stability of aggregates protecting organic substrates are among the boundary conditions that “shape the channel for energy and matter use” by the microbial community of soil systems (overall Hypothesis C of SPP 2223). Although the stabilization of organic matter against microbial use and mineralization in soil has been linked to sorption, its relationship to the thermodynamics of sorption processes has not been quantified so far. Furthermore, the impact of soil aggregation and soil microbial diversity on this relationship is unknown. To analyze the boundary conditions shaping the channel for energy and matter use, we will test the following hypotheses: (H I) sorption and desorption energies increase with increasing polarity and degree of oxidation of the sorbate and increasing number of surface hydroxyl groups of the sorbent, (H II) microbial substrate use decreases with decreasing deltaG, increasing thermodynamic sorption hysteresis and activation energy of desorption with thermodynamic thresholds for the use of sorbed substrates, (H III) thermodynamic thresholds for microbial use of sorbed substrates increases with increasing functional diversity of the soil microbial community and (H IV) high physical protection of substrates within aggregates undermines the importance of sorption thermodynamics for microbial substrate use. We will test these hypotheses in four corresponding workpackages. In WP1 we will be determine Gibbs free energies deltaG of sorption reactions, sorption enthalpies (deltaH) and entropies (deltaS), activation energies Ea of desorption reactions and losses of molar free energy due to sorption hysteresis (Tii) for 6 model substrates and three model minerals via sorption-desorption experiments at different temperatures, Arrhenius plots and microcalorimety. WP2 will use miniaturized incubation experiments with SPP soil samples to determine use and mineralization of 14C labelled model substrates adsorbed to model mineral mixed into 4 SPP soils. The role of functional diversity in mineralization will be studied in WP3 by a second incubation experiment with SPP soils spiked with extracted microbes to manipulate microbial diversity or nutrients based on enzymatic analyses using ecoplates. Finally, in WP 4, the mineralization of selected 13C-labelled model substances adsorbed to dispersed and aggregated soil systems that were characterized morphologically and physically will be measured. Combining the expected results, our project will deliver essential insights for the integration of sorption processes and aggregation into thermodynamic concepts of soil ecosystem functioning and development.