A solution culture experiment was conducted to investigate the effect of silicate on the yield and arsenate uptake by rice. Rice seedlings (Oryza sativa L. cv. Weiyou 77) were cultured in modified Hoagland nutrient solution containing three arsenate levels (0, 0.5 and 1.0 mg L )1 As) and four silicate levels (0, 14, 28 and 56 mg L )1 Si). Addition of Si significantly increased shoot dry weight (P ¼ 0.001) but had little effect on root dry weight (P ¼ 0.43). Addition of As had no significant effect on shoot dry weight (P ¼ 0.43) but significantly increased root dry weight (P ¼ 0.01). Silicon concentrations in shoots and roots increased proportionally to increasing amounts of externally supplied Si (P < 0.001). The presence of As in the nutrient solution had little effect on shoot Si concentration (P ¼ 0.16) but significantly decreased root Si concentration (P ¼ 0.005). Increasing external Si concentration significantly decreased shoot and root As concentrations and total As uptake by rice seedlings (P < 0.001). In addition, Si significantly decreased shoot P concentration and shoot P uptake (P < 0.001). The data clearly demonstrate a beneficial effect of Si on the growth of rice seedlings. Addition of Si to the growth medium also inhibited the uptake of arsenate and phosphate by the rice seedlings.Abbreviation: ICP-OES -inductively coupled plasma-optical emission spectrometer

Snap bean genotypes (Phaseolus vulgaris L.) with different ozone (O 3 ) sensitivities (line S156: O 3 -sensitive; line R123: O 3 -tolerant) were grown for 70 days with or without inoculation of arbuscular mycorrhizal (AM) fungi under ambient (C AMB = 20 nanolitres (nl)/l and elevated (C MID = '50 nl/l and C HIG = 80 nl/l) O 3 . Sequential determinations (leaf injury, pigment concentration, chlorophyll fluorescence, photosynthesis, etc) were carried out during plant growth to evaluate mycorrhizal influence on the photosynthetic function of the two genotypes under elevated O 3 . Inoculation with AM fungi alleviated leaf injury in both genotypes and delayed time of injury manifestation (TIM) in the R123 line at the blooming stage (growth stage (GS): 61-65 (Zadoks scale, Zadoks et al. 1974), 30-35 days after the onset of O 3 fumigation), but mycorrhizal effect was slight at the initial growth stage (GS 11-13, 0-5 days after onset of O 3 fumigation). Relative to the non-mycorrhizal plant, AM fungi inoculation increased the concentrations of chlorophyll (Chl) a, Chl b and carotenoids in S156 plants, regardless of O 3 levels, while in R123 plants a similar effect was observed only in the C AMB treatment. At the blooming (GS 61-65) and the pod filling (GS 71-77, 45-50 days after starting O 3 fumigation) stages, photosynthetic rate, stomatal conductance and transpiration rate for the two genotypes decreased with elevated O 3 in all treatments, although the effect was reduced in C AMB and C MID treatments in AM-inoculated plants; however, the mycorrhizal effect was slight in the C HIG treatment. Intercellular carbon dioxide concentration increased with elevated O 3 regardless of AM fungi inoculation, but it was lower in the mycorrhizal plants than in the non-mycorrhizal plants, in most cases. Furthermore, AM fungi inoculation significantly increased the maximum quantum yield of photosystem II (PS II) photochemistry (Fv/Fm) and electron transport rate in both genotypes in the C HIG treatment. The present study indicated that in some cases, AM fungi inoculation can enhance plant tolerance to elevated O 3 through improving plant photosynthetic function, but the effect was reduced by serious O 3 stress.