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Cadmium (Cd)-contaminated soils are of concern because of their possible effects on ecosystems and human health. Millet (Setaria italica (L.) Beauv.) is moderately tolerant to salinity and poor soil fertility as well as pristine soils contaminated with trace elements. It has been hypothesized that low-molecular-weight organic acids (LMWOA) exuded into the rhizosphere may play important roles in Cd uptake by millet. Thus the objectives of this study were to assess the LMWOA exudations of millet in Cd-contaminated soils and to evaluate the capacity of millet to remove Cd for phytoremediation. Millet was grown for 3 weeks in soils containing between 0 and 1,000 mg Cd kg−1. These soils and plant tissues were analyzed for Cd content after harvest. The Cd accumulated in millet tissues was significantly increased with increasing Cd-amended rate. The total LMWOA concentrations in root exudates were significantly correlated with the amount of Cd accumulated in millet shoots and roots. High levels of Cd amendment stimulated secretion of LMWOA, a process capable of reducing Cd toxicity via the formation of Cd-organic complexes (Cd-LMWOA), thereby detoxifying the contaminated soil.

Contents and properties of heavy elements in iron-manganese cutans and the corresponding matrix soils of three subtropical Chinese soils (Fragiudalf, Ferrudalf, and Hapludult) were investigated to discern the effect of soil-forming factors on the enrichment of heavy elements in the iron-manganese cutans with respect to the matrices. Results showed that the contents of clay, organic matter (OM), bases, and heavy metal elements were higher in the cutans than in the matrices. Cutans in the Fragiudalf had a neutral pH and higher content of OM and bases than those in the other soils. The cutans in the Ferrudalf were acidic, with increased contents of Fe and Mn oxides. The cutans in the Hapludult were more acidic and clayey than the cutans in the Fragiudalf and the Ferrudalf. Moreover, the contents of free Fe oxides and ratios of extractable noncrystalline Fe oxide/free Fe oxide (Feo/Fed) in the cutans of the Hapludult were higher than those in the other cutans. Compared with the corresponding matrices, the contents of heavy-metal elements in cutans of Hapludult increased more than those in other iron-manganese cutans. The varimax orthogonal factor rotation of factor analysis was chosen to make the statistical test a good fit to show the elemental distribution between the cutans and their corresponding matrices. The results revealed that Mn oxides played a leading role in the enrichment of most heavy metals for the cutans in the Fragiudalf. In the Ferrudalf, Fe oxides strengthen the migration process of the metals to the cutans. For the cutans in the Hapludult, the influence of Mn oxides on the enrichment of heavy metals decreased, and the impact of clay and Fe oxides increased with respect to the cutans in other soils. The factors that affected the heavy metals were the least for the cutans of the Ferrudalf compared with those in the cutans of the Fragiudalf and the Hapludult. The transport of heavy metals from the matrix soils to iron-manganese cutans in the three soils was mainly influenced by the different soil-forming environments and soil compositions. Statistical analysis indicated that the soil-forming factors that affected the enrichment of heavy metals in the cutans were more prominent in the Ferrudalf than in the Fragiudalf and the Hapludult.

Forest fires can disturb the evolution of plant communities and influence both soil organic matter (SOM) and soil physicochemical properties. The historic vegetation changes and the influences on soil properties and OM induced by fires are still not well known for central Taiwan. This study investig

Clay mineralogy and whole-soil major element chemistry of an early Quaternary red soil and two late Miocene paleosols between basalt lavas on Penghu Islands (Pescadores), Taiwan, were studied to compare properties of soils from the different periods. The early Quaternary red soil consists of a kaolinite and smectite clay assemblage. The late Miocene paleosols are rich in kaolin minerals. The amounts of Si, Fe, and Al in the three profiles are the mineralogical differences. The depth distributions for clay and free Fe oxide contents suggest that the early Quaternary red soil formed in at least two stages. The early Quaternary red soil was classified as fine, mixed, hyperthermic, Typic Rodustalf. The late Miocene paleosols were classified as fine, kaolinite, hyperthermic, Typic Rhodic Paleustalf. The late Miocene paleosols contain more clay, lower SiO 2 /Al 2 O 3 and SiO 2 /(Al 2 O 3 + Fe 2 O 3 ) molar ratios, averages of 2.5 and 1.7, respectively, and higher chemical indexes of weathering than the early Quaternary paleosol. The SiO 2 /Al 2 O 3 and SiO 2 /(Al 2 O 3 + Fe 2 O 3 ) molar ratios and Mn 2+ and Mg 2+ distributions showed zigzag patterns, suggesting that changes in sea level influenced the early Quaternary profile during the soil formation.

Cesium is an emission element from nuclear energy generation easily transferred to food chain. More evidence has been found that Brassica crops take up pollutants from soils. The objective of this study was to investigate the correlation between soil bioavailability of cesium and low-molecular-weigh

The nature of minerals in the B horizons of alpine forest soils in subtropical and tropical areas remains to be identified. The objective of this study was to investigate the distribution of Fe-oxides and hydroxy-interlayered vermiculite (HIV) in typical alpine forest soils of Taiwan. Five pedons at roughly 2000 m elevation of Taiwan were selected as example for this study. High gradient magnetic separation (HGMS), conventional X-ray diffraction (XRD), differential X-ray diffraction (DXRD), and transmission electron microscopy (TEM) were employed to characterize the clay minerals. The content of crystalline Fe-oxides increased sharply from E to B horizons. Only Al-substituted lepidocrocite and goethite were identified by differential X-ray diffraction (DXRD) analysis in magnetic clay fractions of the B (or placic) horizons; no substantial hematite peaks appeared in the XRD patterns of any pedons. These observations are quite different from those of Spodosols or Spodosol-like soils developed in the temperate and frigid zones of North America. Hydroxy-interlayered vermiculite (HIV) was characterized by collapse of the 1.42-nm peak in the XRD diagrams toward 1.0 nm when the K-saturated clay samples were heated to 350°C. In the surface horizons, only vermiculite could be identified in the coarse clay fractions. The distribution patterns of acid ammonium oxalate extractable Fe and Al in these pedons indicate that Al and Fe were leached from the A horizons and accumulated in the B horizons when forming Al-substituted lepidocrocite, goethite, and HIV. This is attributed to the combined effect of organic acids, Al, and Fe in the pedogenic environments. The present findings are of fundamental significance in understanding the formation of Spodosol-like soils in alpine forest soils in the subtropics and tropics.