Ecophysiological responses of winter wheat seedling to aerosol wet deposition of Xi'an area, China

Aerosol leads to 30% reduction in solar radiation reaching the earth’s surface, and a similar reduction in crops yield for both wheat and rice. To determine the effect of aerosol wet deposition on crops, aerosol samples were collected in September, 2006 at Xi’an urban suburb （34 44 N, 109 49 E）, and wheat seedlings were treated with aerosol of different concentrations in laboratory conditions. Changes in physiological and biochemical parameters of wheat seedlings were measured. In comparison with the control, the activities of superoxide dismudase （SOD） and catalase （CAT） and the concentration malondialdehyde （MDA） and oxidized glutathione （GSSG） of wheat seedlings increased progressively with increasing concentrations of added aerosol, while the opposite trend was seen for the activities of nitric oxide synthase （NOS）, the concentrations of glutathione （GSH） and nitric oxide （NO）, and the ratio of GSH/GSSG. When the seedlings were treated with the aerosol of 1 and 2 mg/L, the coleoptile elongation, shoot elongation and biomass accumulation were increased, the effect at treatment of 2 mg/L was most significant. However, aerosol treatments with rates of 3 and 4 mg/L resulted in a decrease in coleoptile elongation, shoot elongation and biomass accumulation in seedlings, and significant effect was for the treatment of 4 mg/L. Hence, lower concentrations of aerosol wet deposition were in favor of crops growth, but its higher concentrations could result in deleterious effects for crops and decreased crops growth.

Chemical composition and Zn bioavailability of the soil solution extracted from Zn amended variable charge soils

A study on variable charge soils （volcanic Italian and podzolic Scottish soils） was performed to investigate the influence of soil properties on the chemical composition of soil solution. Zinc speciation, bioavallability and toxicity in the soil solution were examined. The soils were spiked with increasing amounts of Zn （0, 100, 200, 400 and 1000 mg/kg） and the soil solutions were extracted using rhizon soil moisture samplers. The pH, total organic carbon （TOC）, base cations, anions, total Zn and free Zn^2＋ in soil solution were analysed. A rapid bioassay with the luminescent bacterium Escherichia coli HB 101 pUCD607 was performed to assess Zn toxicity. The influence of soil type and Zn treatments on the chemical composition of soil solution and on Zn toxicity was considered and discussed. Different trends of total and free Zn concentrations, base cations desorption and luminescence of E. coli HB 101 pUCD607 were observed. The soil solution extracted from the volcanic soils had very low total and free Zn concentrations and showed specific Zn^2＋/Ca^2＋ exchange. The soil solution from the podzolic soil had much higher total and free Zn concentrations and showed no evidence of specific Zn^2＋/Ca^2＋ exchange. In comparison with the subalkaline volcanic soils, the acidic podzol showed enhanced levels of toxic free Zn^2＋ and consequently stronger effects on E. coli viability.