Soil aeration is a crucial factor that regulates crop residue decomposition, and the chemical composition of decomposing crop residues may change the forms and availability of soil nutrients, such as N and P. However, to date, differences in the chemical composition of crop straw residues after incorporation into soil and during its decomposition under anaerobic vs. aerobic conditions have not been well documented. The objective of the present study was to assess changes in the C-containing functional groups of wheat straw residue during its decomposition in anaerobic and aerobic environments. A 12-month incubation experiment was carried out to investigate the temporal variations of mass, carbon, and nitrogen loss, as well as changes in the chemical composition of wheat (Triticum aestivum L) straw residues under anaerobic and aerobic conditions by measuring C-containing functional groups using solid state nuclear magnetic resonance (NMR) spectroscopy. The residual mass, carbon content, and nitrogen content of the straw residue sharply declined during the initial 3 months, and then slowly decreased during the last incubation period from 3 to 12 months. The decomposition rate constant (k) for mass loss under aerobic conditions (0.022 d-1) was higher than that under anaerobic conditions (0.014 d-1). The residual mass percentage of cellulose and hemicellulose in the wheat straw gradually declined, whereas that of lignin gradually increased during the entire 12-month incubation period. The NMR spectra of C-containing functional groups in the decomposing straw under both aerobic and anaerobic conditions were similar at the beginning of the incubation as well as at 1 month, 6 months, and 12 months. The main alterations in C-containing functional groups during the decomposition of wheat straw were a decrease in the relative abundances of O-alkyl C and an increase in the relative abundances of alkyl C, aromatic C and COO/N-C = O functional groups. The NMR signals of alkyl C and aromatic C in decomposing wheat straw residues under anaerobic condition were higher than those under aerobic conditions. The higher mass percentages of lignin and the higher signals of aromatic C and alkyl C functional groups in decomposing wheat residues under anaerobic conditions than under aerobic conditions were due to the slower decomposition rates of aryl C and alkyl C in wheat straw residues under anaerobic conditions.
In order to study the linkages between the crop straw decomposition rate and the change in soil biological properties after the straw returned to the soil with different iron (Fe2+) contents, a 180-day incubation experiment was performed to examine the decomposition of maize straw (MS) under three Fe2+ levels, i.e., 0, 0.3, and 1 mg g−1. Enzyme activities regarding straw decomposition and microbial communities under 0 and 1 mg g−1 Fe addition were also detected. The results showed that Fe2+ addition significantly inhibited MS decomposition. This was evidenced by the higher contents of hemicellulose, cellulose, and lignin in Fe2+ treatments on day 180. High-Fe addition (1 mg g−1) decreased the activity of Laccase (Lac) by 71.82% compared with control on day 30. Furthermore, the principal coordinates analysis (PCoA) indicated that high-Fe mainly affected the bacterial community. In particular, it suppressed the relative abundance of Microbacteriaceae in phylum Actinomycota that, in turn, is a potential decomposer of crop straw by secreting lignocellulolytic enzymes. A high level of Fe2+ inhibited the decomposition of hemicellulose, cellulose, and lignin in MS by reducing the relative abundance of phylum Actinobacteria in bacteria and suppressing Lac activity. Our findings provide guidance for returning crop straws in soils with high-Fe content.
Determination of the bioavailability of the hydrophobic organic contaminant benzo[a]pyrene (B[a]P) is extremely important for assessing its environmental risk. The effect of addition manner of B[a]P on the bioavailability and toxicity of B[a]P in soil remains unclear. In this study, soil samples, spiked with B[a]P by one-time or multiple-time additions, were tested to investigate the available fraction of B[a]P in soils, the uptake of B[a]P by red wiggler worms ( Eisenia fetida ), as well as superoxide dismutase (SOD) and peroxidase (POD) activities in earthworm coelomocytes at different periods. Results showed that the available fraction of B[a]P in soils and the amount of B[a]P assimilated by earthworms declined sharply from 1 d to 28 d during the incubation period and then decreased slowly from 28 to 56 d in both the one-time and the multiple-time addition tests. The available fraction of B[a]P in soils and its uptake by earthworms were significantly lower in multiple-time addition samples than those in one-time addition samples, a finding which was consistent with the SOD and POD activities in earthworms during the whole 56-d incubation period. These variations in the characteristics of the two addition treatments may be due to the differences in the way the B[a]P aged in the soil. These results indicated that the addition method was an important factor influencing the bioavailability of organic contaminants in soils.
ObjectiveThe objective of the study was to explore the relationship between social support and fatigue as well as the mediating role of social functioning on that relationship.BackgroundPsychosocial factors such as social support and social functioning may influence patients’ fatigue symptoms. There is limited evidence on the relationship between social support, social functioning, and fatigue in liver transplant recipients.MethodsA total of 210 patients with liver transplants from two tertiary hospitals were enrolled in the current study. Questionnaires used include one for general demographic data, the Perceived Social Support Scale (PSSS), Social Disability Screening Schedule (SDSS), and Fatigue Symptom Inventory (FSI).ResultsA total of 126 (60%) recipients reported fatigue. Gender, residence, BMI, and liver function were the primary factors affecting fatigue. Social support was positively correlated with social functioning and was negatively correlated with fatigue. The effect of social support on fatigue was partially mediated by social functioning (35.74%).ConclusionThe fatigue of liver transplant recipients should be attended to. The higher the social support, the lower the fatigue of liver transplant recipients. Social support may also reduce fatigue through social functioning. The liver transplant team should help the liver transplant recipient establish a social support system, restore social functioning, and reduce fatigue symptoms.
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