Soil Organic Carbon Attenuates the Influence of Plants on Root-Associated Bacterial Community.

Plant-derived carbon (PDC) released by roots has a strong effect on root-associated bacterial community, which is critical for plant fitness in natural environments. However, the freshly exuded PDC can be diluted by the ancient soil-derived carbon (SDC) at a short distance from root apices. Thus, the rhizosphere C pools are normally dominated by SDC rather than PDC. Yet, how PDC and SDC interact to regulate root-associated bacterial community is largely unknown. In this study, a grass species and a legume species were planted in two contrasting matrixes, quartz sand and soil, to assess the role of PDC and SDC in regulating root-associated bacterial community, and to explore whether SDC affects the influence of PDC on bacterial community in soil. Our results indicated that the legume plant showed significantly positive priming effect on soil organic matter decomposition but the grass plant did not. PDC significantly shaped bacterial community in sand culture as indicated by PCR-DGGE and high-throughput sequencing of bacterial 16S rRNA gene. Intriguingly, we found that dissimilarity of bacterial communities associated with two plant species and the percentage of specific OTUs in quartz sand were significantly higher than those in soil. Moreover, several biomarkers enriched by plants in quartz sand turned to be general taxa in soil, which indicated that SDC attenuated the regulation of bacterial community by PDC. Taken together, these results suggest that SDC interacted with PDC and the root-associated microbial community, thus acted as soil buffering component of biological process contributing to soil resilience. The importance of PDC in structuring rhizosphere bacterial community needs to be reconsidered in the context of wider contribution of other C pool, such as SDC.

根系释放的植物源碳（PDC）对根际相关细菌群落有强烈影响，这对自然环境中植物的适应性至关重要。然而，在距根尖较短距离处，新分泌的植物源碳会被古老的土壤源碳（SDC）稀释。因此，根际碳库通常以土壤源碳而非植物源碳为主。然而，植物源碳和土壤源碳如何相互作用来调节根际相关细菌群落，在很大程度上尚不清楚。在本研究中，将一种禾本科植物和一种豆科植物种植在两种对比基质（石英砂和土壤）中，以评估植物源碳和土壤源碳在调节根际相关细菌群落中的作用，并探究土壤源碳是否会影响植物源碳对土壤中细菌群落的影响。我们的结果表明，豆科植物对土壤有机质分解有显著的正激发效应，而禾本科植物则没有。通过细菌16S rRNA基因的PCR - DGGE和高通量测序表明，在砂培条件下植物源碳显著塑造了细菌群落。有趣的是，我们发现与两种植物相关的细菌群落差异以及石英砂中特定操作分类单元（OTU）的百分比显著高于土壤中的情况。此外，在石英砂中被植物富集的几种生物标记物在土壤中变成了常见类群，这表明土壤源碳减弱了植物源碳对细菌群落的调节作用。综上所述，这些结果表明土壤源碳与植物源碳以及根际相关微生物群落相互作用，从而作为生物过程的土壤缓冲成分，有助于土壤的恢复力。在考虑其他碳库（如土壤源碳）更广泛贡献的背景下，需要重新审视植物源碳在构建根际细菌群落结构中的重要性。