School of Life and Environmental Sciences, University of Sydney, Sydney, NSW, Australia.
Plant, Soil and Environment Systems, School of Environmental and Rural Science, University of New England, Armidale, NSW, Australia.
Sci Rep. 2016 Sep 12;6:33012. doi: 10.1038/srep33012.
Aggregates play a key role in protecting soil organic carbon (SOC) from microbial decomposition. The objectives of this study were to investigate the influence of pore geometry on the organic carbon decomposition rate and bacterial diversity in both macro- (250-2000 μm) and micro-aggregates (53-250 μm) using field samples. Four sites of contrasting land use on Alfisols (i.e. native pasture, crop/pasture rotation, woodland) were investigated. 3D Pore geometry of the micro-aggregates and macro-aggregates were examined by X-ray computed tomography (μCT). The occluded particulate organic carbon (oPOC) of aggregates was measured by size and density fractionation methods. Micro-aggregates had 54% less μCT observed porosity but 64% more oPOC compared with macro-aggregates. In addition, the pore connectivity in micro-aggregates was lower than macro-aggregates. Despite both lower μCT observed porosity and pore connectivity in micro-aggregates, the organic carbon decomposition rate constant (Ksoc) was similar in both aggregate size ranges. Structural equation modelling showed a strong positive relationship of the concentration of oPOC with bacterial diversity in aggregates. We use these findings to propose a conceptual model that illustrates the dynamic links between substrate, bacterial diversity, and pore geometry that suggests a structural explanation for differences in bacterial diversity across aggregate sizes.
团聚体在保护土壤有机碳（SOC）免受微生物分解方面起着关键作用。本研究的目的是使用野外样本调查孔几何形状对大团聚体（250-2000 μm）和微团聚体（53-250 μm）中有机碳分解率和细菌多样性的影响。研究了 Alfisols 上四种不同土地利用方式的四个地点（即原生牧场、作物/牧场轮作、林地）。通过 X 射线计算机断层扫描（μCT）检查了微团聚体和大团聚体的 3D 孔隙几何形状。通过大小和密度分级方法测量了团聚体中被封闭的颗粒有机碳（oPOC）。与大团聚体相比，微团聚体的 μCT 观察到的孔隙率低 54%，但 oPOC 多 64%。此外，微团聚体的孔隙连通性低于大团聚体。尽管微团聚体的 μCT 观察到的孔隙率和孔隙连通性均较低，但两种团聚体大小范围内的有机碳分解速率常数（Ksoc）相似。结构方程模型显示，团聚体中 oPOC 的浓度与细菌多样性之间存在很强的正相关关系。我们利用这些发现提出了一个概念模型，说明了基质、细菌多样性和孔隙几何形状之间的动态联系，为细菌多样性在团聚体大小上的差异提供了结构解释。
