Abstract
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 CaCO 3 (1.0 gL −1), either labelled with 13 C (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. 13 C 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 δ 13 C was higher (less negative) in +Fe than in −Fe unlabelled plants. Iron deficient plants grown in the nutrient solution enriched with labelled CaCO 3 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 CaCO 3 do not markedly shift their C fixation from leaf RuBP to root PEPC.