State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai, China.
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai, China.
Sci Total Environ. 2022 Jul 15;830:154695. doi: 10.1016/j.scitotenv.2022.154695. Epub 2022 Mar 23.
The rhizosphere of coastal wetland plants is the active interface of iron (Fe) redox transformation. However, coupling mechanism between organic acids (OAs) exuded by plant roots and Fe speciation transformation participated by Fe redox cycling bacteria in the rhizosphere is still unclear. Effects of four common OAs (citric acid, malic acid, tartaric acid, and oxalic acid) on root exudation, rhizosphere bacterial community structure, root Fe plaque, and Fe redox cycling bacterial communities of Kandelia obovata were investigated in this study. Long-term flooding (10 h) was conducive to K. obovata seedlings exuding additional dissolved organic carbon (DOC) and nitrogen and phosphorus organic matter (NH-N, NO-N, and dissolved inorganic phosphorus [DIP]) under each OA level. DOC, NH-N, NO-N, and DIP in root exudates increased significantly with the increase of exogenous OA level. Notably, long flooding time corresponds to an evidently increasing trend. Exogenous OAs also significantly increased contents of formic and oxalic acids in root exudates. Exogenous OAs and flooding enhanced the rhizosphere effect of K. obovata and significantly enhanced bacterial diversity of the rhizosphere and relative abundance of dominant bacteria in rhizoplane. Bacterial diversity in the rhizosphere of K. obovata seedlings was significantly higher than that in the rhizoplane under the same level of OAs and flooding. Fe plaque content of K. obovata root decreased significantly and the relative abundance of typical Fe-oxidizing bacteria, such as Gallionella, unclassified_f__Gallionellaceae, and Sideroxydans, decreased significantly in the rhizosphere but increased significantly in the rhizoplane with the increase of the treatment level of exogenous OAs. This finding is likely due to the Fe reduction caused by acidification of rhizosphere environment after exogenous OA treatment rather than the result of chemotactic colonization of Fe redox cycling bacteria in the rhizoplane.
滨海湿地植物根际是铁（Fe）氧化还原转化的活跃界面。然而，植物根系分泌的有机酸（OAs）与参与根际Fe 氧化还原循环细菌的 Fe 形态转化之间的耦合机制仍不清楚。本研究调查了四种常见的 OAs（柠檬酸、苹果酸、酒石酸和草酸）对秋茄幼苗根分泌、根际细菌群落结构、根铁斑和 Fe 氧化还原循环细菌的影响。长期淹水（10 h）有利于秋茄幼苗在每个 OA 水平下分泌额外的溶解有机碳（DOC）和氮磷有机物质（NH-N、NO-N 和溶解无机磷[DIP]）。DOC、NH-N、NO-N 和 DIP 在根分泌物中的含量随外源性 OA 水平的增加而显著增加，特别是随着淹水时间的延长，呈明显增加趋势。外源性 OAs 还显著增加了根分泌物中甲酸和草酸的含量。外源性 OAs 和淹水增强了秋茄的根际效应，显著增强了根际细菌多样性和根际表面优势细菌的相对丰度。在相同 OAs 和淹水水平下，秋茄幼苗根际的细菌多样性明显高于根际表面。秋茄根铁斑含量显著降低，根际典型 Fe 氧化细菌如节杆菌属、未分类_f__节杆菌科和铁氧化亚铁还原菌的相对丰度显著降低，但在外源 OAs 处理水平增加时，根际表面的相对丰度显著增加。这一发现可能是由于外源 OA 处理后根际环境酸化导致 Fe 还原，而不是根际 Fe 氧化还原循环细菌化学趋化定植的结果。
