College of Environmental and Resource Sciences, Key Laboratory of Environment Remediation and Ecosystem Health of the Ministry of Education, Zhejiang University, Hangzhou 310029, China.
Ann Bot. 2010 May;105(5):835-41. doi: 10.1093/aob/mcq071. Epub 2010 Mar 31.
Soil microbes have been demonstrated to play an important role in favouring plant iron (Fe) uptake under Fe-limiting conditions. However, the mechanisms involved are still unclear. This present study reported the effects of plant Fe status on the composition of siderophore-secreting microbes in the rhizosphere, and their potential function in improving plant Fe nutrition.
An Fe-efficient plant, red clover (Trifolium pratense 'Kenland') was cultured in a calcareous soil to obtain rhizosphere soils with (Fe-sufficient) or without (Fe-stressed) foliar FeEDTA spraying. The siderophore-producing ability of rhizospheric microbes was measured. The bioavailability of the siderophore-solubilized Fe from iron oxides/hydroxides was tested in hydroponic culture.
In rhizosphere soil, the number of microbes that secreted siderophores quickly was more in the Fe-stressed treatment than in the Fe-sufficient one, while the number of microbes that did not secret siderophores was the opposite. A significantly higher concentration of phenolics was detected in the rhizosphere soil of Fe-stressed plants. Moreover, after the soil was incubated with phenolic root exudates, the composition of the siderophore-secreting microbial community was similar with that of the rhizosphere of Fe-stressed plant. Additionally, the siderophores produced by a rhizospheric microbe isolated from the Fe-stressed treatment can well solubilize iron oxides/hydroxides, and the utilization of the siderophore-solubilized Fe by plant was even more efficient than EDTA-Fe.
Iron-deficiency stress of red clover would alter the composition of siderophore-secreting microbes in the rhizosphere, which is probably due to the phenolics secretion of the root, and may in turn help to improve the solubility of Fe in soils and plant Fe nutrition via elevated microbial siderophore secretion.
土壤微生物在缺铁条件下促进植物铁（Fe）吸收方面发挥着重要作用。然而，其中涉及的机制尚不清楚。本研究报道了植物铁状况对根际分泌铁载体微生物组成的影响，以及它们在改善植物铁营养方面的潜在功能。
在石灰性土壤中培养高效植物红三叶草（Trifolium pratense 'Kenland'），以获得叶面喷施 Fe-EDTA（铁螯合物）的根际土壤（Fe 充足）或未喷施 Fe-EDTA 的根际土壤（Fe 胁迫）。测量根际微生物的产铁载体能力。在水培培养中测试铁载体溶解的氧化铁/氢氧化物中的铁的生物有效性。
在根际土壤中，分泌铁载体的微生物数量在 Fe 胁迫处理中比在 Fe 充足处理中更快，而不分泌铁载体的微生物数量则相反。在 Fe 胁迫植物的根际土壤中检测到酚类物质的浓度明显更高。此外，在土壤用酚类根分泌物孵育后，分泌铁载体的微生物群落组成与 Fe 胁迫植物的根际相似。此外，从 Fe 胁迫处理中分离出的一种根际微生物产生的铁载体可以很好地溶解氧化铁/氢氧化物，并且植物对铁载体溶解的铁的利用效率甚至高于 EDTA-Fe。
红三叶草缺铁胁迫会改变根际分泌铁载体微生物的组成，这可能是由于根分泌的酚类物质引起的，而这反过来又可能通过提高微生物铁载体的分泌来帮助提高土壤中 Fe 的溶解度和植物铁营养。
