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The recycling of polyolefins for multiple life cycles is becoming a legislative requirement in the South African plastics industry. This study shows that this cannot be a blanket requirement for all polyolefins. While HDPE displays good resistance to weathering, the decrease in molecular weight limits the maximum number of life cycles before which the resultant product has lost all integrity. Impact polypropylenes fare much worse during weathering and more than 50% of impact properties are lost within the first 12 months of exposure. The blending of virgin material into degraded material can recover some properties of HDPE but not in the case of impact polypropylenes. The same legislation can therefore not be applied to all plastics and specific targets should depend on polymer composition. [ABSTRACT FROM AUTHOR]

• SOC stock after logging and shifting cultivation recovered rapidly in rainforests. • SOC groups were largely labile O-alkyl C and aromaticity after forest disturbances. • Litter C, microbial diversity and soil nutrient related to SOC functional groups. • SOC has greater stability in terms of decomposition degree in old-growth rainforests. Recent evidence has demonstrated that tropical forest secondary succession has significant influences on soil organic C (SOC) storage. However, the changes in the SOC functional groups with forest restoration are still uncertain. In this study, the stock and functional groups of SOC in tropical forest recovery after two types of disturbance were measured, and the key influencing factors were analyzed. The SOC stocks were significantly higher in the young-secondary forests after shifting cultivation and in the clear cut forests than in the old-growth forests. However, the shifting cultivation and logging practices significantly increased the ratio of carbohydrate C to N-alkyl/methoxyl C (CC/MC), indicating that the decomposition degree of SOC in the old-growth forests was higher. The proportion of aromatic C in soil was higher in the young-secondary forests after shifting cultivation than in the old-growth forests. The proportion of aromatic C in litter and fine roots, the α-diversity of soil fungal and bacterial communities, and soil phosphorus were positively correlated with soil aromatic C between the shifting cultivation secondary and old-growth forests. The proportion of O-alkyl C in soil was higher in the logged forests than in the old-growth forests. The proportion of O-alkyl C in litter was positively correlated with O-alkyl C in soil between the logged and old-growth forests. Our results suggest that the labile O-alkyl C functional group recovers more rapidly after logging practices, and restoration after shifting cultivation increases the labile carbohydrate C functional group and aromaticity in tropical lowland rainforests. However, SOC has greater chemical stability in terms of the decomposition degree in tropical old-growth forests. [ABSTRACT FROM AUTHOR]

Plant-soil negative feedback ( NF) is recognized as an important factor affecting plant communities. The objectives of this work were to assess the effects of litter phytotoxicity and autotoxicity on root proliferation, and to test the hypothesis that DNA is a driver of litter autotoxicity and plant-soil NF., The inhibitory effect of decomposed litter was studied in different bioassays. Litter biochemical changes were evaluated with nuclear magnetic resonance ( NMR) spectroscopy. DNA accumulation in litter and soil was measured and DNA toxicity was assessed in laboratory experiments., Undecomposed litter caused nonspecific inhibition of root growth, while autotoxicity was produced by aged litter. The addition of activated carbon ( AC) removed phytotoxicity, but was ineffective against autotoxicity. Phytotoxicity was related to known labile allelopathic compounds. Restricted 13C NMR signals related to nucleic acids were the only ones negatively correlated with root growth on conspecific substrates. DNA accumulation was observed in both litter decomposition and soil history experiments. Extracted total DNA showed evident species-specific toxicity., Results indicate a general occurrence of litter autotoxicity related to the exposure to fragmented self- DNA. The evidence also suggests the involvement of accumulated extracellular DNA in plant-soil NF. Further studies are needed to further investigate this unexpected function of extracellular DNA at the ecosystem level and related cellular and molecular mechanisms. [ABSTRACT FROM AUTHOR]

Low-molecular-weight organic acids (LMWOAs) derived from root exudates and complexed with available metals in the rhizosphere soils of Taiwan red cypress (Chamaeyparis formosensis, FRS), peacock pine (Cryptomeria japonica, JRS), and moso bamboo (Phyllostachys pubescens, PRS) were identified by gas chromatograph (GC). The fresh plants (i.e., leaves, stems, roots, and litters) and soil samples of those three vegetations were examined for their organic functional groups. This study focused on (1) assessing methods for processing LMWOAs in the rhizosphere soils and fresh plants by GC analysis and (2) determining the relative proportions of organic carbon (C) functional groups in the three vegetations and fresh plant materials with 13C nuclear magnetic resonance (NMR) analysis. The proportion of LMWOAs contents followed the order of PRS>FRS>JRS>bulk soils. The recovery and spiking tests analyzed by GC showed good recovery (>83.6%) and reproducibility of LMWOAs. The proportion of organic functional groups in the rhizosphere and bulk soil quantified by 13C NMR analysis followed the general order alkyl-C>aromatic-C>O-alkyl-C>N-alkyl-C>phenolic-C>acetal-C>carboxyl-C. The carbohydrates, hemicellulose, lignin, and cellulose contents obtained by 13C NMR analysis suggested that Phyllostachys pubescen (PB) cannot easily be decomposed under the mountain forest soil environments. [ABSTRACT FROM AUTHOR]

Abstract: Acetobacter xylinum NQ-5 (ATCC 53582) and AY-201 (ATCC 23769) cultivated in the Hestrin–Schramm medium containing d-glucose with a natural 13C-abundance of 1.1% were investigated regarding their cell division rates and the bacterial movements. Comparative studies were carried out in the presence of d-glucose-U-13C6 with a uniform 13C-labeling of 99% as the sole carbon source. The bacterial growth rates in numbers were found to increase in the 13C-enriched media by about 13% for NQ-5 and 26% for AY-201, respectively. The movements of single cells caused by the inverse force of the secretion and deposition of cellulose nanofibers on nematic ordered cellulose (NOC) templates were investigated by real-time video analyzes using light microscopy. As a result, d-glucose-U-13C6 reduced the speed of motion for both strains, which was an opposite trend to the above growth rates in the cell division. The deposited cellulose fibers were proved to be in a cellulose crystalline form by CP/MAS 13C NMR and NIR FT Raman spectroscopic measurements, although the biosynthesized and thereafter-deposited cellulose has a strong interaction with the surface of NOC. [Copyright &y& Elsevier]

The pyrolysis of poly (ethylene terephthalate) (PET) in the presence of ZSM-5 zeolite and NiCl2 as a catalyst was studied at different temperatures under N2 atmosphere. Quantitative 13C nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FT-IR) were applied to characterize the waxy and solid residue. The carboxyl and aliphatic hydroxyl groups in the waxy residue have been greatly depleted after the use of zeolite during pyrolysis on the basis of the results of 13C NMR and FT-IR analysis. The proportion of aromatic hydroxyl groups increased by 21.82% when the mass ratio of zeolite to PET was set to 2.0/1.0. The results indicate that ZSM-5 is able to facilitate the decomposition of carboxyl, aliphatic groups, and ether bonds in the primary products produced from the pyrolysis of PET. In addition, the deoxygenation effects on the waxy products have been significantly enhanced with the addition of zeolite based on the results of NMR. [ABSTRACT FROM AUTHOR]