In this experiment we (i) tested the hypothesis that, besides decreasing leaf C fixation, lime induced iron (Fe) deficiency increases root C fixation via PEP carboxylase and (ii) assessed the Fe-induced modifications in the elemental composition of plant tissues. Sugar beet plants were grown in nutrient solutions with Fe (45 μM Fe-EDTA; +Fe control) or in a similar nutrient solution without Fe (-Fe) and in presence of CaCO3 (1.0 gL -1), either labelled with 13C (20 at. %) or unlabelled. After 7 and 17 days from treatment imposition, plants were harvested and single organs analysed for total O, C, H, macro and micronutrients. 13C abundance was also assessed in control, unlabelled and labelled -Fe plants. Iron deficiency caused significant growth reductions; chlorophyll and net photosynthesis decreased markedly in Fe-deficient plants when compared to the controls, whereas leaf transpiration rates and stomatal conductance were not affected by Fe deficiency. Iron deficient plants had leaf biomass with lower C (2 to 4%) and higher O (3 to 5%) concentrations than +Fe plants. The δ13C was higher (less negative) in +Fe than in -Fe unlabelled plants. Iron deficient plants grown in the nutrient solution enriched with labelled CaCO3 absorbed a relatively small amount of labelled C, which was mainly recovered in the fine roots and accounted for less than 2% of total C gain in the 10 d treatment period. Evidences suggest that iron deficient sugar beets grown in the presence of CaCO3 do not markedly shift their C fixation from leaf RuBP to root PEPC. © Springer 2005.

The study was supported by grants MURST ex 40% (Roma, grant Cofin 2000) to M.T., Spanish MCYT grant BOS2001-2343 and AGL2002-1999 and MURST-MCYT ‘Azioni Integrate/Acción Integrada’ (HI2002-0178) to J.A. and M.T.; Y.G. was the recipient of a postdoctoral contract from the Consejo Superior de Investigaciones Científicas.

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