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Summary• The effects of zinc (Zn) toxicity on photosynthesis and respiration were investigated in sugar beet (Beta vulgaris) plants grown hydroponically with 1.2, 100 and 300 lM Zn.• A photosynthesis limitation analysis was used to assess the stomatal, mesophyll, photochemical and biochemical contributions to the reduced photosynthesis observed under Zn toxicity.• The main limitation to photosynthesis was attributable to stomata, with stomatal conductances decreasing by 76% under Zn excess and stomata being unable to respond to physiological and chemical stimuli. The effects of excess Zn on photochemistry were minor. Scanning electron microscopy showed morphological changes in stomata and mesophyll tissue. Stomatal size and density were smaller, and stomatal slits were sealed in plants grown under high Zn. Moreover, the mesophyll conductance to CO 2 decreased by 48% under Zn excess, despite a marked increase in carbonic anhydrase activity. Respiration, including that through both cytochrome and alternative pathways, was doubled by high Zn.• It can be concluded that, in sugar beet plants grown in the presence of excess Zn, photosynthesis is impaired due to a depletion of CO 2 at the Rubisco carboxylation site, as a consequence of major decreases in stomatal and mesophyll conductances to CO 2 .Abbreviations: A N , net photosynthesis; AOX, alternative oxidase; APX, ascorbate peroxidase; BL, DL, MCL, NSL and SL, biochemical conductance, diffusional conductance, mesophyll conductance, and nonstomatal and stomatal limitations, respectively; C a , C C and C i, atmospheric, chloroplastic and substomatal CO 2 concentrations, respectively; CA, carbonic anhydrase; Chl, chlorophyll; ETR, electron transport rate; F PSII, actual photosystem II efficiency; FAAS, flame atomic absorption spectroscopy; F o , minimal Chl fluorescence in the dark; F v ⁄ F m , maximum potential photosystem II efficiency; g m and g s , CO 2 mesophyll and stomatal conductances, respectively; J max , in vivo maximum rate of electron transport driving regeneration of RuBP; Mn-SOD, manganese-superoxide dismutase; PPFD, photosynthetic photon flux density; PSII and PSI, photosystems II and I, respectively; V c,max , in vivo maximum rate of Rubisco carboxylation; WC, water content.

Cadmium and arsenic are two of the most important and toxic pollutants ubiquitous in the environment. The occurrence of numerous polluted areas as the affected by the accident of Aznalcóllar pyrite mine has promoted the employment of the phytoremediation as a feasible technology able to control and reduce the risk of this contamination at low cost. White lupin plant is proposed as a candidate for phytoremediation. This work aims to study if it is possible to use white lupin in phytoremediation of soils affected by acid pyrite sludge, with simultaneous As and Cd pollution. Pot and field experiments with sludge-affected soil were carried out. The pot trial showed that the NTA treatment increased Cd and As concentrations in lixiviates, exceeding the maximum permissible levels, so that its use in field experiments was avoided. In the field experiment, phytoextraction of Cd and As by lupin plants was very low, suggesting that it was not recommended for phytoextraction. However, lupin culture in the field produced several benefits as: increase of acid soil pH probably by citrate excretion, decrease in soluble As and Cd fractions in soil, high concentration of As and Cd in roots with accumulation of heavy metals in root nodules. All these results support the use of Lupinus albus for phytostabilization and revegetation of the spill polluted soils.