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TECHNICAL REPORTS

Plant and Environment Interactions

Responses to Iron Limitation in Hordeum vulgare L. as Affected by the Atmospheric CO₂ Concentration

^a Inst. of Soil Science, Univ. of Hohenheim, 70599 Stuttgart, Germany
^b Inst. of Plant Nutrition, Univ. of Hohenheim, 70593 Stuttgart, Germany
^c Creative Research Initiative ‘Sousei’ (CRIS), Hokkaido Univ., N21W10, Kita-ku, Sapporo 001-0021, Japan
^d Inst. of Plant Cultivation and Plant Nutrition, Humboldt Univ., Berlin, Germany

^* Corresponding author (gd.neumann{at}t-online.de).

Received for publication April 6, 2006. Elevated atmospheric CO₂ treatments stimulated biomass production in Fe-sufficient and Fe-deficient barley plants, both in hydroponics and in soil culture. Root/shoot biomass ratio was increased in severely Fe-deficient plants grown in hydroponics but not under moderate Fe limitation in soil culture. Significantly increased biomass production in high CO₂ treatments, even under severe Fe deficiency in hydroponic culture, indicates an improved internal Fe utilization. Iron deficiency-induced secretion of PS in 0.5 to 2.5 cm sub-apical root zones was increased by 74% in response to elevated CO₂ treatments of barley plants in hydroponics but no PS were detectable in root exudates collected from soil-grown plants. This may be attributed to suppression of PS release by internal Fe concentrations above the critical level for Fe deficiency, determined at final harvest for soil-grown barley plants, even without additional Fe supply. However, extremely low concentrations of easily plant-available Fe in the investigated soil and low Fe seed reserves suggest a contribution of PS-mediated Fe mobilization from sparingly soluble Fe sources to Fe acquisition of the soil-grown barley plants during the preceding culture period. Higher Fe contents in shoots (+52%) of plants grown in soil culture without Fe supply under elevated atmospheric CO₂ concentrations may indicate an increased efficiency for Fe acquisition. No significant influence on diversity and function of rhizosphere-bacterial communities was detectable in the outer rhizosphere soil (0–3 mm distance from the root surface) by DGGE of 16S rRNA gene fragments and analysis of marker enzyme activities for C-, N-, and P-cycles.

Abbreviations: PS, phytosiderophores • MAs, mugineic acids • DAS, days after sowing • DGGE, denaturing gradient gel electrophoresis