ABSTRACT
Complexation of dissolved organic matter (DOM) plays a crucial role in regulating the fate and risk of agrochemicals. Here, taking a toxic herbicide MCPA (4-chloro-2- methylphenoxyacetic acid) as the target, the effect of land conversion on complexation behavior of DOM to agrochemicals was investigated in paddy soil. Furthermore, the mechanisms were explored in a new perspective of DOM chemodiversity. Soil DOMs were selected from four long-term cropping systems, including paddy field (PF), vegetable field (VF), rice-vegetable rotation (RV) and abandoned land (AL). The results showed that the DOMs in PF and AL were rich in hydrophilic substances (e.g., carbohydrates or protein-like molecules) with low aromaticity. However, after converting PF to VF and RV, abundant aromatic macromolecules and aliphatic alkanes were observed in DOM. Due to those changes in DOM chemodiversity, the binding site and capability of DOM were highest in VF and RV, and were positively correlated with DOM aromaticity, MW, humus and polar groups (e.g., amino). This was because the complexation of "DOM-MCPA" was static binding via ligand exchange and H-bonding among polar groups and hydrophobic interaction among aromatic skeletons. The EEM-PARAFAC confirmed that microbial humic-like substances dominated the complexation of DOM rather than terrestrial humic-like and tryptophan-like matters. The 2D-COS analysis further revealed that the complexation of DOM preferentially occurred in amino, polysaccharide C-O and aliphatic C-H for PF and AL, but in aromatic C=C, amide C=N for RV and VF. In summary, these findings provide molecular insight into the effect of land conversion on DOM complexation activity, which highlight the importance of DOM chemodiversity. These results will contribute to the risk assessments of agrochemicals in paddy soil.
Subject(s)
2-Methyl-4-chlorophenoxyacetic Acid , Soil , Agrochemicals , Dissolved Organic Matter , Humic Substances/analysis , Soil/chemistry , Spectrometry, Fluorescence/methodsABSTRACT
With the aim of improving the ionic and electronic conductivities of Li2ZnTi3O8 for high performance lithium ion battery applications, Li2Zn0.9M0.1Ti3O8 (M = Li+, Cu2+, Al3+, Ti4+, Nb5+, Mo6+) compounds are successfully fabricated using facile high temperature calcination at 800 °C. Physical characterization and lithium ion reversible storage demonstrate that Zn-site substitution by multivalent metal ions is beneficial for improving the migration rate of ions and electrons of Li2ZnTi3O8. X-ray diffraction analysis and scanning electron microscopy reveal that the crystal structure and microscopic morphology of bare Li2ZnTi3O8 do not change by introducing a small amount of foreign metal ions. As a result, Li2Zn0.9Nb0.1Ti3O8 retains a reversible capacity as high as 198 mA h g-1 at the end of the 500th cycle among all samples. Even when cycled at high temperatures, Li2Zn0.9Nb0.1Ti3O8 still maintains excellent reversible discharge capacities of 210 mA h g-1 and 196 mA h g-1 at 1000 mA g-1 for the 100th cycle at 50 °C and 60 °C, respectively. All the conclusions indicate that Li2Zn0.9Nb0.1Ti3O8 is a high-performance anode material for large-scale energy storage devices.
ABSTRACT
This study aimed at understanding the differences in traits of functional twigs and leaves of a typical alpine shrub species, Rhododendron przewalskii, at Kaka Mountain in the headwater region of Minjiang River. Leaf and twig traits were compared for shrubs at different growth stages (flower bud stage and flowering stage) and altitude (3600 m and 3800 m). The effects of spatial heterogeneity on their correlations and trade-offs were evaluated at leaf and twig levels, respectively. Our results showed that twig length was significantly longer at low altitude than high altitude for the shubs at the same growth stage. The number and mass of flowers at flowering stage were significantly higher at high altitude than those at low altitude. At the same altitude, twig mass, number of leaves, total leaf mass, total leaf area and total petiole mass were all significantly greater at the flower bud stage than those at the flowering stage, while the individual leaf mass and individual petiole mass at flower bud stage were significantly smaller than those at flowering stage. Compared with the flower bud stage, the proportion of leaf mass decreased by 13% at the flowering stage, while biomass proportion of twig significantly increased. At the flower bud stage, twig mass had a higher contribution to total twig mass. In contrast, the contribution of total leaf mass to total twig mass was higher at flowering stage. More biomass of leaf was allocated to individual leaf mass at flower bud stage. More biomass of leaf was allocated to individual petiole mass and individual leaf mass at flowering stage at low altitude and high altitude, respectively. At low altitude, allometric growth patterns presented between twig mass and total leaf area, total leaf mass. Similarly, individual petiole mass and individual leaf area had allometric growth. Our results indicated that the functional traits of twigs and leaves varied across both altitude and plant growth stage.
