Plant Fe status affects the composition of siderophore-secreting microbes in the rhizosphere.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Jin
Chong Wei
CW
College of Environmental and Resource Sciences, Key Laboratory of Environment Remediation and Ecosystem Health of the Ministry of Education, Zhejiang University, Hangzhou 310029, China.
Li
Gui Xin
GX
Yu
Xue Hui
XH
Zheng
Shao Jian
SJ
Zheng
Shao Jiang
SJ
D007501:Iron / Q000378:metabolism* / Q000502:physiology; D018517:Plant Roots / Q000378:metabolism* / Q000382:microbiology*; D017262:Siderophores / Q000378:metabolism*; D029921:Trifolium / Q000378:metabolism* / Q000382:microbiology*
D017262:Siderophores; D007501:Iron