Yanqun Zu

Cadmium and lead accumulation and low-molecular-weight organic acids secreted by roots in an intercropping of a cadmium accumulator Sonchus asper L. with Vicia faba L.

Sonchus asper L. and Vicia faba L. are a local cadmium (Cd) accumulator and a main winter crop, respectively, found in the Huize lead–zinc mining area in Yunnan Province, Southwest China. The biomass and low-molecular-weight organic acids (LMWOAs) secreted by the roots of these plants, Cd and lead (Pb) contents and their accumulation in a S. asper monoculture, V. faba monoculture and S. asper/V. faba intercrop were investigated in a field experiment at 35, 80 and 180 d after planting. The results showed that (1) intercropping had no notable influences on plant biomass and grain yields of V. faba but led to a significant increase in the amount of stem and leaf biomass of S. asper at 180 d after planting. (2) The major LMWOAs secreted by the roots of both V. faba and S. asper were oxalic acid, tartaric acid and citric acid. Intercropping resulted in an increase and decrease in the LMWOA contents secreted by V. faba and S. asper roots, respectively. (3) Along with plant growth, the available Cd content decreased and the available Pb contents did not exhibit obvious changes in the soil samples of a V. faba monoculture. The amount of available Cd and Pb both increased in the soil of the S. asper monoculture, but decreased in that of the S. asper/V. faba intercrop. (4) Intercropping resulted in a decrease in the contents and accumulation of Cd and Pb in V. faba plants, but an increase in both the contents and accumulation of Cd and Pb in S. asper plants. Moreover, intercropping enhanced the enrichment and translation coefficients of Cd for S. asper. The remediation efficiency was the highest at 180 d after planting. (5) There were significant negative correlations between the contents of citric acid, malic acid (secreted by V. faba roots), oxalic acid and tartaric acid (secreted by S. asper roots) and the available Cd content in the soil samples. In addition, there was a significant positive correlation between the available Cd content in the soil and the Cd contents in the roots and grains of V. faba. Intercropping reduced the Cd contents in the plants and grains of V. faba and was closely related to the decrease in the available Cd content in the soil samples, which was mediated by plant roots that secreted LMWOAs.

Mobility and distribution of lead, cadmium, copper and zinc in soil profiles in the peri-urban market garden of Kunming, Yunnan Province, China

Five profiles located in the peri-urban market garden of Yunnan Province, China were investigated for the distribution and sequential extraction fractions (SEF) of Pb, Cd, Cu and Zn, and mobility in relation to soil properties. SEF heavy metals included acetic acid extractable (A-fraction), hydroxylamine hydrochloride extractable (B-fraction) and hydrogen peroxide and ammonium acetate extractable fractions (C + D-fraction). The results showed that: (1) Total Pb and Zn contents decreased with soil depth. The accumulation of different fractions of Pb and Zn was due to accumulation of organic carbon and Fe–Mn oxides. (2) Total Cd content increased with soil depth with the ratio of A to C horizons (RAC) < 1.0. Cd was relatively mobile within the A horizon. C + D-Cd contents were consistent with organic carbon accumulation. (3) Total Cu content in profiles 2 and 3 decreased with depth, while in other profiles it increased. A-Cu contents in the B horizon in profiles 1, 2 and 3 were higher than in the A and C horizons, and decreased with depth in profiles 4 and 5 in the transition unit. B-Cu content increased with depth, whereas C + D-Cu contents decreased. The mobility and redistribution of heavy metals in soil profiles were influenced by clay content, organic carbon and Fe–Mn oxides.

Factors affecting trace element content in periurban market garden subsoil in Yunnan Province, China

Field investigations were conducted to measure subsoil trace element content and factors influencing content in an intensive periurban market garden in Chenggong County, Yunnan Province, South-West China. The area was divided into three different geomorphological units: specifically, mountain (M), transition (T) and lacustrine (L). Mean trace element content in subsoil were determined for Pb (58.2 mg/kg), Cd (0.89 mg/kg), Cu (129.2 mg/kg), and Zn (97.0 mg/kg). Strong significant relationships between trace element content in topsoil and subsoil were observed. Both Pb and Zn were accumulated in topsoil (RTS (ratio of mean trace element in topsoil to subsoil) of Pb and Zn > or =1.0) and Cd and Cu in subsoil (RTS of Cd and Cu < or = 1.0). Subsoil trace element content was related to relief, stoniness, soil color, clay content, and cation exchange capacity. Except for 7.5 YR (yellow-red) color, trace element content increased with color intensity from brown to reddish brown. Significant positive relationships were observed between Fe content and that of Pb and Cu. Trace element content in mountain unit subsoil was higher than in transition and lacustrine units (M > T > L), except for Cu (T > M > L). Mean trace element content in calcareous subsoil was higher than in sandstone and shale. Mean trace element content in clay texture subsoil was higher than in sandy and sandy loam subsoil, and higher Cu and Zn content in subsoil with few mottles. It is possible to model Pb, Cd, Cu, and Zn distribution in subsoil physico-chemical characteristics to help improve agricultural practice.

Effects of a dark septate endophyte (DSE) on growth, cadmium content, and physiology in maize under cadmium stress

Dark septate endophytes (DSE) are widely distributed in plant roots grown in stressful habitats, especially in heavy metal-polluted soils. But little is known about the physiological interactions between DSE and plants under heavy metal stress. In the present study, the growth, Cd content, and physiological response of Zea mays L. to a root-colonized DSE, Exophiala pisciphila, were analyzed under Cd stress (0, 5, 10, 20, and 40xa0mg/kg) in a sand culture experiment. Under high Cd (10, 20, and 40xa0mg/kg) stress, the DSE colonization in roots increased the maize growth, kept more Cd in roots, and decreased Cd content in shoots. The DSE colonization improved the photosynthesis and induced notable changes on phytohormones but had no significant effect on the antioxidant capability in the maize leaves. Moreover, there were significant positive correlations between the gibberellic acid (GA) content and transpiration rate, zeatin riboside (ZR) content, and photosynthetic rate in maize leaves. These results indicated that the DSE’s ability to promote plant growth was related to a decrease on Cd content and the regulation on phytohormone balance and photosynthetic activities in maize leaves.

Availability of Trace Elements for Chinese Cabbage Amended with Lime in a Periurban Market Garden in Yunnan Province, China

Pot experiments were conducted in the laboratory with lime applications to decrease trace elements in Chinese cabbage produced on soils contaminated by trace elements in the intensive periurban area in Chenggong County, Yunnan Province, China. Soil was an acidic loam developed from lacustrine-alluvial deposits. Results showed the following: (1) soil pH increased from 5.3 to 6.5, and acetic-acid-extractable trace-element contents and ratio of acetic-acid-extractable trace-element contents in treatments relative to those in the control (RRCT) decreased with increased rate of lime application. (2) Chinese cabbage more easily absorbed acetic-acid-extractable trace elements. Enrichment coefficients related to trace-element availability (AEC) of lead (Pb; mean: 3.3) and zinc (Zn; mean: 5.8) were stable, and the AEC of cadmium (Cd) was 1.8–2.0 with increased lime application rate. (3) Trace-element contents in Chinese cabbage decreased, and biomass of Chinese cabbage increased, with lime application rate. Trace-element contents in soil solution and acetic-acid-extractable trace-element contents can predict trace-element contents in Chinese cabbage, especially for soil solution. Lime quality and trace-element accumulation in Chinese cabbage should be taken into account when amendment is added to in situ soil contaminated with trace elements.

Subcellular distribution and chemical form of Pb in hyperaccumulator Arenaria orbiculata and response of root exudates to Pb addition

Solution culture was conducted in order to understand accumulation characteristics and chemical forms of Pb in Arenaria orbiculata (A. orbiculata) and the response of root exudates to Pb addition. The results showed that: 1) Pb contents in the shoot and root of A. orbiculata increased with increasing in Pb concentrations in solution. 2) The contents of Pb chemical forms under Pb addition followed as: HAc extractable fraction (FHAC)> HCl extractable fraction (FHCl)> NaCl extractable fraction (FNaCl)> ethanol-extractable fraction (FE)>water extractable fraction (FW). 3) Increased Pb level in the medium caused increases in Pb contents in the four subcellular fractions of shoots and roots, with most accumulation in FIV (Fraction IV, soluble fraction) in shoots and FI (Fraction I, cell wall fraction) in roots. 4) Contents of soluble sugar and free amino acid of root exudates increased with increasing Pb concentration in solution. Significantly positive correlations between Pb and contents of soluble sugar and free amino acid were observed. 5) With Pb concentrations in solution, low molecular weight organic acids (LMWOAs) contents followed the tendency: tartaric acid>acetic acid>malic acid>citric acid. Significantly positive correlation was observed between Pb and citric acid contents. The results indicate that soluble sugars, free amino acid and citric acid in root exudates of A.orbiculata facilitate the absorption and accumulation of Pb, which exist in NaCl-, HCl- and HAc- extractable Pb forms, FI and FIV fractions, resulting in tolerance of A.orbiculata to Pb.

Soil affects on the cadmium and zinc contents of Chinese cabbage in Yunnan Province, China

Chinese cabbage and surface soil samples (0–20 cm) from a periurban market garden in Yunnan Province (P.R. China) were collected to determine variations of cadmium (Cd) and zinc (Zn) contents in Chinese cabbage and the influence of soil factors. Mean Cd content was 0.49 mg kg−1 dry materials (DM) in Chinese cabbage, ranging between 0.23 and 1.34 mg kg−1 DM (n = 21 samples). Mean Zn content was 51.2 mg kg−1 DM, ranging from 34.9 to 157.5 mg kg−1 DM (n = 21 samples). The soil factors best predicting Chinese cabbage Cd and Zn contents were total and available Cd and Zn contents and cation exchange capacity (CEC). Soil samples and corresponding Chinese cabbage samples were divided into two groups: soils with low pH (<6.5, n = 10) and soils with high pH (>6.5, n = 11). Positive correlation between CEC with pH > 6.5 and Cd and Zn contents in Chinese cabbage were observed. Available trace element contents and CEC explained 77% and 69% of variation of Cd and Zn contents in Chinese cabbage, respectively. AEC (enrichment coefficient related to trace element availability) and BCF (bioaccumulation factors) could be used to understand Cd and Zn accumulation in Chinese cabbage.

Resistance-related physiological response of rice leaves to the compound stress of enhanced UV-B radiation and Magnaporthe oryzae

ABSTRACT An enhanced UV-B radiation (5.0u2005kJu2005m−2) was supplied before, during, and after Magnaporthe oryzae infection. The effects of single and compound stress of the UV-B radiation and M. oryzae on the resistance physiology and gene expression of rice leaves were examined. Results revealed that UV-B radiation given before M. oryzae infection (UV-Bu2009→u2009M.) significantly increased the pathogenesis-related proteins (PRs) activities of phenylalanine ammonialyase (PAL), lipoxygenase (LOX), chitinase (CHT), and β-1,3-glucanase, the resistance-related substances (flavonoids and total phenols) content, and resistance-related genes (OsPAL and OsCHT) expression, thereby improving the disease resistance of rice leaves. Simultaneous exposure to UV-B radiation and M. oryzae (UV-B/M.) significantly increased the OsLOX2 expression and the PRs activities. Exposure to UV-B radiation after M. oryzae infection (M.u2009→u2009UV-B) decreased the flavonoid content, did not improve the PRs activity, and increased OsLOX2 expression. Compound treatments of UV-Bu2009→u2009M., UV-B/M., and M.u2009→u2009UV-B reduced the disease index by 62.3%, 40.2%, and 26.6%, respectively, indicating UV-B radiation inhibited the occurrence of M. oryzae disease, but its inhibitory effect weakened when it was provided after M. oryzae infection. Hence, rice responded to the compound stress of UV-B radiation and M. oryzae through a resistance-related physiological mechanism associated with the sequence of stress occurrence.

Distribution characteristics of cadmium and lead in particle size fractions of farmland soils in a lead–zinc mine area in Southwest China

BackgroundCd and Pb were the main pollution elements in Pb–Zn mining areas. Several studies have focused on heavy metal pollution and risk assessment in the Huize Pb–Zn mining area. In the present study, the soil aggregate composition, chemical properties, contents and chemical fractions of Cd and Pb were analysed in soils at depths of 0–60xa0cm in the Huize Pb–Zn mining area. Agricultural soils were sampled at depths of 0–20, 20–40 and 40–60xa0cm surrounding the Pb–Zn mine. The particle size fractions were determined by the aggregate composition of macro-aggregates (0.25–2xa0mm), micro-aggregates (0.053–0.25xa0mm), silt (0.002–0.053xa0mm) and colloid (<u20090.002xa0mm).ResultsThere was a large proportion of the macro-aggregate (52.4%) and less of the colloid (1.8%). With a decrease in particle size, the pH, organic matter contents, cation exchange capacity, and free iron oxide increased in the soil aggregates. Although the total and available Cd and Pb contents were highest in the colloid, the macro-aggregate maximally contributed to the total Cd (48.18%), total Pb (53.48%) and available Pb (47.42%) content, and the colloid maximally contributed to the available Cd (47.21%) in soils. The Cd and Pb existed primarily as residual fractions, followed by Fe–Mn oxide fraction and the exchangeable fraction in soil aggregates. There were higher distribution factors for the residual and exchangeable fractions of both Cd and Pb in the colloid (DFu2009>u200933). Furthermore, there were close correlations between the Cd and Pb fractions and the pH and the phosphorus content and between the exchangeable Pb content and the content of organic matter, cation exchange capacity, and free iron oxide in soil aggregates.ConclusionCd and Pb existed mainly in the micro-aggregate and colloid and that their chemical fractions were closely related to the chemical properties in soil aggregates of the polluted farmland.

Characteristics of Heavy-Metal Tolerance and Growth in Two Ecotypes of Oxyria sinensis Hemsl. Grown on Huize Lead–Zinc Mining Area in Yunnan Province, China

A field survey of herbaceous plants growing on the Huice lead (Pb)–zinc (Zn) mining area in Yunnan, China was conducted to identify species accumulating concentrations of cadmium (Cd), Pb, and Zn. In total, 200 plant samples of 112 species from 34 families were collected. At the same time, 200 soil samples were collected. Based on Cd, Pb, and Zn tolerance and growth, wild Oxyria sinensis Hemsl. was chosen as a primary pioneer plant. Then, to confirm if Oxyria sinensis Hemsl. may be used as a pioneer plant, the tolerance to Cd, Pb, and Zn and growth of two ecotypes (mining-area ecotype and non-mining-area ecotype) Oxyria sinensis Hemsl. were studied further with pot experiments. In 10 samples of wild Oxyria sinensis Hemsl. in the Huice lead–zinc mine, concentrations of Cd, Pb, and Zn in the soil did not correlate with those in the root (P > 0.05) and shoot (P > 0.05), respectively. Correlations between Cd concentrations in root and shoot were not observed (P > 0.05), whereas those of Pb and Zn were observed (P < 0.05). Both the enrichment coefficient and translocation factor were <1 for Cd, Pb, and Zn for the wild Oxyria sinensis Hemsl. In the two ecotypes of Oxyria sinensis Hemsl., in pot experiments, the treatment concentrations of Cd, Pb, and Zn did not correlate (P > 0.05) with concentrations of Cd, Pb, and Zn in root and shoot. Significant correlations between the concentrations of Cd, Pb, and Zn in root (P < 0.01) and shoot (P < 0.05) were observed in the two ecotypes. Both enrichment coefficient and translocation factors were <1 for Cd, Pb, and Zn in the two ecotypes, respectively. Treatment concentrations of Cd, Pb, and Zn did not significantly correlate (P > 0.05) with plant height and crowns of the two ecotypes. Treatment concentrations of Pb and Zn did not correlate (P > 0.05) with the biomass of the two ecotypes, whereas that of Cd related significantly to biomass in the two ecotypes. Oxyria sinensis Hemsl. was suggested to utilize a tolerant strategy to heavy metals (i.e., exclusion). It was a pioneer plant and will be used in restoration of a vegetation cover in a Pb–Zn mine after further research in tolerant mechanisms and restoration ability are conducted.