Land use changes (LUC) for the expansion of bioenergy cropping have caused consistent reductions in soil organic carbon (SOC) stocks in tropical soils. This study addresses the mechanisms underlying such SOC losses by assessing LUC effects on, and relationships between, soil engineering invertebrate fauna, soil structural stability, and C allocation and sequestration within soil aggregates. We sampled three sites with sets of land use types varying in the level of anthropogenic stress in sandy loam, sand clay loam, and clay soils along a 1000-km-long transect in central Brazil, where bioenergy cropping expands across pasturelands. We quantified the effects of LUC on soil engineer fauna (i.e., termites, earthworms, coleopterans, and ants), soil structural stability, and C allocation and fitted structural equation models (SEM) to elucidate mechanistic links between the measured variables. We found that reductions in SOC stocks following LUC were concomitant with reductions in the abundance of soil engineers (log abundance of soil engineers, −1.17 ± 0.54; P = 0.0322), destabilization of soil structure (normalized stability index, −0.16 ± 0.04; P < 0.0001), and soil depth-dependent decreases in the amounts and increases in the humification degree of aggregate-occluded SOC. Our SEMsupported the predicted relationships among these responses, and indicated that soil engineering by invertebrates indirectly mediated changes in SOC stocks across land uses by controlling the physical protection of low-humified, aggregate-occluded SOC, a C fraction that accounted for over 90% of the change in total SOC stocks following LUC. When analysing the influence of the different invertebrate groups separately, we found stronger support for the role of termites in this process compared to that of earthworms, coleopterans, and ants. Hence, negative LUC effects on populations of soil engineers weaken soil functioning and its C storage. These results highlight the need for land-use strategies that maintain soil fauna in order to sustain key ecosystem processes like soil structural formation and soil C stabilization.

扩大生物能源作物种植的土地利用变化（LUC）导致热带土壤中土壤有机碳（SOC）储量持续减少。这项研究通过评估LUC对土壤工程无脊椎动物动物区系，土壤结构稳定性以及土壤团聚体中C的分配和封存的影响以及它们之间的关系，解决了造成此类SOC损失的机制。我们在巴西中部沿1000公里长的样带采样了三个地点，这些地点的土地利用类型因人为胁迫的水平在沙壤土，沙质壤土和黏土中有所不同，那里的生物能源种植遍及牧场。我们量化了LUC对土壤工程动物区系（即白蚁，earth，鞘翅目和蚂蚁），土壤结构稳定性，和C分配以及拟合的结构方程模型（SEM），以阐明测量变量之间的机械联系。我们发现，LUC后SOC的减少与土壤工程师数量的减少（土壤工程师的对数丰度，-1.17±0.54； P = 0.0322），土壤结构的失稳（标准化稳定性指数，-0.16±0.04；以及P <0.0001），并且土壤深度依赖性减少了聚集体SOC的含量并增加了腐殖化程度。我们的SEM支持了这些响应之间的预测关系，并指出，无脊椎动物通过控制低腐化，聚集体SOC的物理保护来间接介导不同土地利用SOC存量变化的土壤工程，LUC。当分别分析不同无脊椎动物群体的影响时，我们发现与compared，鞘翅目和蚂蚁相比，白蚁在此过程中的作用得到了更强的支持。因此，LUC对土壤工程师种群的负面影响削弱了土壤功能及其碳储量。这些结果凸显了维持土地动物群以维持关键生态系统过程（如土壤结构形成和土壤碳稳定）的土地利用策略的必要性。