Shifts in soil microbial biological and functional diversity under long-term carbon depletion

Soil organisms are crucial to the support and maintenance of ecosystems through the provision of ecosystem services. Nutrient cycling and decomposition are important processes by which soil organisms support aboveground plant communities. Anthropogenic disturbances can disrupt these processes. However, some organisms respond positively to disturbance and could mitigate the effects of disturbance. We assessed soil community composition and functional processes during a long-term carbon deprivation field experiment. Two sets of paired samples were deprived of carbon inputs for 10 years and 1 year, respectively. Soil DNA was extracted for metabarcoding and Geochip microarray analyses. Richness of bacteria, fungi, protists, and viruses fell under carbon depravation after 10 years, but not after 1 year. Log-fold change in gene expression of carbon cycling genes generally fell as well, though it increased for some genes involved in decomposing recalcitrant carbon. Similarly, log-fold change of several methanogenesis genes increased under carbon starvation. Several taxa were identified as indicators of both normal and deprived soils. Our results highlight the dynamic nature of soil communities. Bioindicators of carbon depravation may utilise alternative gene pathways to take advantage of opened niche space. The impact of carbon depletion requires long timescales and may be prevented with timely interventions.

土壤生物通过提供生态系统服务，对生态系统的支撑与维持至关重要。养分循环与分解是土壤生物支撑地上植物群落的关键过程。人为扰动会破坏上述过程，但部分生物对扰动可产生正向响应，并能缓解扰动带来的影响。本研究在一项长期碳剥夺野外实验中，对土壤群落组成与功能过程展开了评估：两组配对样本分别被剥夺碳输入长达10年与1年。研究人员提取土壤DNA，用于宏条形码（metabarcoding）与Geochip微阵列分析。结果显示，10年碳剥夺处理后，细菌、真菌、原生生物与病毒的丰富度均出现下降，但1年处理组未出现该变化。碳循环基因的基因表达对数倍变化量整体呈下降趋势，但部分参与难降解碳分解的基因表达量却有所上升；类似地，在碳饥饿条件下，多个产甲烷基因的对数倍变化量也出现升高。本研究还鉴定出多个可作为正常土壤与碳剥夺土壤指示类群的分类类群。研究结果凸显了土壤群落的动态特性：碳剥夺的生物指示物或许可利用替代基因通路，以抢占开放的生态位空间。碳剥夺的影响需要较长时间尺度才能显现，且可通过及时干预加以规避。