Soil organic matter (SOM) is of primary importance for maintaining inherently low SOC contents (typically below 1%, Hunt soil productivity, and agricultural management practices may signifiet al., 1982). Consequently, small changes in the SOM cantly influence SOM chemical properties. However, how SOM chemical characteristics change with agricultural practices is poorly under-content are significant to the agricultural production of stood. Therefore, in this study, we evaluated the impacts of tillage the region. An evaluation of tillage and crop residue (conventional vs. conservation) management on the structural and management practices to rebuild SOC levels has been compositional characteristics of SOM using cross-polarization magicconducted by Hunt et al. (1996). These researchers monangle-spinning (CPMAS) and total sideband suppression (TOSS) itored changes in SOC levels in numerous small tillage solid-state 13 C nuclear magnetic resonance (NMR) and diffuse reflecplots and found that after 9 yr of CnT, the SOC content tance Fourier transform infrared (DRIFT) spectroscopy. We characin the top few centimeters was significantly higher than terized both physically and chemically isolated SOM fractions from a the soil under CT management. Campbell et al. (1999) Norfolk soil (fine-loamy, siliceous, thermic Typic Kandiudults) under reported that over an 11-to 12-yr period, increases in long-term tillage management (20 yr). The solid-state 13 C NMR results C storage in the 0-to 15-cm soil depth, because of indicated that humic acid (HA) from conventional tillage (CT, 0-5 cm) was less aliphatic and more aromatic than HA from conservation adoption of no-tillage, were small (0-3 Mg ha Ϫ1). Most tillage (CnT). The aliphatic C content decreased with increasing depth of the differences were observed in the 0-to 7.5-cm soil (0-15 cm) for both CT and CnT treatments. The reverse trend was depth, with little change in the 7.5 to 15 cm. However, true for aromatic C content. Based on reactive/recalcitrant (O/R) the short and long-term influences of disturbance on C peak ratio comparisons, HA was more reactive in the top soil (0-5 mineralization are complex and may vary depending cm) under CnT than CT. Both soil organic C (SOC) and light fraction on types of soil and plant residues (Hu et al., 1995; (LF) material were higher in the 0-to 5-cm soil of CnT than CT Franzleubbers and Arshad, 1996; Alvarez et al., 1998). treatment. Our results show that long-term tillage management can The strong influence of soil management on the amount significantly change the characteristics of both physical and chemical and quality of SOM was also reported by others (Janzen fractions of SOM.

Human tooth enamel provides a nearly permanent and chronological record of an individual's nutritional status and anthropogenic trace metal exposure during development; it might thus provide an excellent bio archive. We investigated the micro-spatial distribution of trace metals (Cu, Fe, Mg, Sr, Pb, and Zn) in 196 x 339 microm2 raster pattern areas (6.6 x 10(4) microm2) in a deciduous tooth using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Ablated areas include prenatal and postnatal enamel, the neonatal line, the dentine-enamel junction (DEJ), dentine, and the dentine-pulp junction. Topographic variations in the surface elemental distribution of lead, zinc, strontium, and iron intensities in a deciduous tooth revealed heterogeneous distribution within and among regions. 43Ca normalized elemental intensities showed the following order: Sr>Mg>>Zn>Pb>Fe>Cu. Elevated zinc and lead levels were present in the dental pulp region and at the neonatal line. This study demonstrates the ability of LA-ICP-MS to provide unique elemental distribution information in micro spatial areas of dental hard tissues. Elemental distribution plots could be useful in decoding nutrition and pollution information embedded in their bio apatite structure.

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Summary Traits that allow more efficient foraging for a deficient resource could increase the competitiveness of a species in resource‐poor habitats. Considering the metal‐nutrient mobilization ability of many allelochemicals, it is hypothesized that, along with the reported toxic effect on the neighbors, these compounds could be directly involved in resource acquisition by the allelopathic plant. Using nutrient manipulation treatments in hydroponic culture, this hypothesis was tested using Centaurea diffusa, an invasive species that produces the putative phytotoxin 8‐hydroxyquinoline (8HQ). The exudation of 8HQ by C. diffusa was very limited and transient. It was further shown that: C. diffusa utilizes 8HQ for its own acquisition of iron, a nutrient deficient in many of its alkaline, invaded habitats; there possibly exists a unique mechanism for the uptake of the 8HQ‐complexed iron (Fe) in C. diffusa, which is novel to the nongraminaceous species; although phytotoxic at very low concentrations, the toxic effect of 8HQ showed a conditional response in the presence of metals, and was significantly reduced when 8HQ was complexed with copper (Cu) and Fe. This study, in addition to elucidating one of the possible adaptive mechanisms conferring competitive advantage to C. diffusa, also outlines measures to negate the phytotoxicity of its putative allelochemical. The results indicate that the exudation of 8HQ by C. diffusa could be primarily for nutrient acquisition.

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Microspatial analyses of the trace element composition of dental enamel are made possible using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Fine spatial resolution, multielement capabilities, and minimal sample destruction make this technique particularly well-suited for documenting the distribution of elements in sequentially calcifying layers of enamel. Because deciduous enamel forms from week 13 in utero up to 9 months postnatally (thereafter essentially becoming inert), the application of LA-ICP-MS allows for the retrospective measurement of prenatal and early postnatal trace-element uptake during a critical period of child development. In this study, we compared intra- and intertooth intensities of 25Mg, 57Fe, 66Zn, 68Zn, 88Sr, 138Ba, and 208Pb via LA-ICP-MS of 38 exfoliated deciduous incisors and canines donated by 36 participants in the Solís Valley Mexico Nutrition Collaborative Research Support Program (NCRSP). Pre- and postnatal comparisons within teeth showed significant increases (P < 0.001) and greater variation in the abundance of all isotopes in postnatal enamel, with the exception of a decrease in 25Mg (P < 0.001) and constant values for 88Sr (P = 0.681). Conversely, comparisons by tooth type and mouth quadrant revealed few significant differences between teeth of the same individual. We argue that more variation in the trace element composition of teeth occurs across developmental areas within a tooth than among different teeth of the same person. This study further demonstrates that sequentially calcifying areas of enamel have different chemical concentrations. The results support the use of microspatial analyses of enamel for understanding changes in nutrition, pollution, and residence.

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