Spatial heterogeneity is a pervasive feature of soils, affecting the distribution of carbon sources as well as their microbial consumers. Heterogeneous addition of substrates typically results in delayed microbial growth compared to homogeneous addition, and this effect has frequently been attributed to spatial separation of microorganisms from their food. We investigated the importance of two other potential causes of this effect, the availability of nutrients and oxygen, by measuring heat and CO release along with O consumption from soil samples after homogeneous or heterogeneous addition of glucose as well as with or without further addition of a nutrient solution. We then employed a microbial-explicit model to quantitatively interpret our observations. The results revealed that delayed growth after spatially heterogeneous substrate addition was primarily caused by nutrient limitation. While sufficient co-location of all entities - substrate, microorganisms, and nutrients - is required for optimal growth, spatial separation of glucose and microorganisms only played a minor role in our experiment. Model simulations captured the dynamics based on aerobic growth and maintenance, utilizing a simple formulation of nutrient limitation coupled with dynamic transition of microbes between activity and dormancy. The model predicted an overall lower microbial activity over the course of the incubation in treatments with heterogeneous substrate addition. Despite reduced rates, neither the experimental carbon and energy balances nor modeling showed an effect of heterogeneity on the growth efficiency after 50 h of incubation. In all treatments, energy use efficiency exceeded carbon use efficiency by 9–21%. We found no evidence of anaerobiosis. The application of a bioenergetic framework facilitated the interpretation of complex experimental data and quantitatively captured the mechanisms underlying the effects of spatial heterogeneity.

中文翻译：

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碳和热通量的联合实验量化和建模揭示了空间基质的异质性限制了微生物的生长


空间异质性是土壤的普遍特征，影响碳源及其微生物消费者的分布。与均匀添加相比，底物的不均匀添加通常会导致微生物生长延迟，并且这种效应通常归因于微生物与其食物的空间分离。我们通过测量均匀或不均匀添加葡萄糖以及进一步添加或不添加葡萄糖后土壤样品的热量和二氧化碳释放量以及氧气消耗量，研究了造成这种影响的另外两个潜在原因（养分和氧气的可用性）的重要性。营养液。然后，我们采用微生物显式模型来定量解释我们的观察结果。结果表明，添加空间异质基质后生长延迟主要是由营养限制引起的。虽然所有实体（底物、微生物和营养物）充分共置是最佳生长所必需的，但葡萄糖和微生物的空间分离在我们的实验中只发挥了次要作用。模型模拟利用营养限制的简单公式以及微生物在活动和休眠之间的动态转换，捕获了基于有氧生长和维持的动态。该模型预测，在添加异质底物的处理过程中，微生物活性总体较低。尽管速率降低，但实验碳和能量平衡以及建模均未显示异质性对培养 50 小时后生长效率的影响。在所有处理中，能源利用效率超过碳利用效率 9-21%。我们没有发现厌氧的证据。 生物能量框架的应用促进了复杂实验数据的解释，并定量捕获了空间异质性影响的机制。