Response of soil N2O production pathways to biochar amendment and its isotope discrimination methods.

Reducing nitrous oxide (N2O) emission from farmland is crucial for alleviating global warming since agriculture is an important contributor of atmospheric N2O. Returning biochar to agricultural fields is an important measure to mitigate soil N2O emissions. Accurately quantifying the effect of biochar on the process of N2O production and its driving factors is critical for achieving N2O emission mitigation. Recently, stable isotope techniques such as isotope labeling, natural abundance, and site preference (SP) value, have been widely used to distinguish N2O production pathways. However, the different isotope methods have certain limitations in distinguishing N2O production in biochar-amended soils where it is difficult to identify the relative contribution of individual pathways for N2O production. This paper systematically reviews the pathways of soil N2O production (nitrification, nitrifier denitrification, bacterial denitrification, fungal denitrification, coupled nitrification-denitrification, dissimilatory nitrate reduction to ammonium and abiotic processes) and their response mechanism to the addition of biochar, as well as the development history and advantages of isotopes in differentiating N2O production pathways in biochar-amended soils. Moreover, the limitations of current research methods and future research directions are proposed. These results will help resolve how biochar affects different processes that lead to soil N2O generation and provide a scientific basis for sustainable agricultural carbon sequestration and the fulfilment of carbon neutrality goals.

Response of microbial communities in the tobacco phyllosphere under the stress of validamycin.

Validamycin, is classified as an environmentally friendly fungicide. It has high efficacy with little associated pollution risk, and it has been used in China on tobacco for many years especially during leaf spot season. To understand changes in microbial communities and functional aspects of the tobacco phyllosphere after exposure to validamycin, the chemical was sprayed on tobacco leaves during brown spot epidemic periods caused by Alternaria alternata, and asymptomatic and symptomatic leaves of tobacco were sampled at different times (0 day before, 5, 10, and 15 days after application). The fungal and bacterial population diversity and structure were revealed using Illumina NovaSeq PE250 high-throughput sequencing technology, and Biolog-ECO technology which analyzes the metabolic differences between samples by using different carbon sources as the sole energy source. The results showed that the microbial community structure of both asymptomatic and symptomatic tobacco leaves changed after the application of valproate, with the microbial community structure of the asymptomatic tobacco leaves being more strongly affected than that of the symptomatic leaves, and the diversity of bacteria being greater than that of fungi. Phyllosphere fungal diversity in asymptomatic leaves increased significantly after application, and bacterial abundance and diversity in both asymptomatic and symptomatic leaves first increased and then decreased. Validamycin treatment effectively reduced the relative abundance of Alternaria, Cladosporium, Kosakonia, and Sphingomonas in leaves showing symptoms of tobacco brown spot, while the relative abundance of Thanatephorus, Pseudomonas, and Massilia increased significantly after application. Furthermore, the ability to metabolize a variety of carbon sources was significantly reduced in both types of leaves after validamycin application, and both types had a weaker ability to metabolize α-Ketobutyric Acid after application. This study reveals phyllosphere micro-ecological changes in symptomatic and asymptomatic tobacco leaves during different periods after validamycin application and the effects on the metabolic capacity of phyllosphere microorganisms. It can provide some basis for exploring the effect of validamycin on the control of tobacco brown spot.

[Microbiology and clinical analysis of six cases of hospital-acquired pneumonia caused by Acinetobacter baumannii].

OBJECTIVE: To study the microbiology, clinical features and treatment outcomes of hospital-acquired pneumonia (HAP) caused by Acinetobacter baumannii. METHODS: Six cases of HAP, caused by Acinetobacter baumannii producing PER-1 type extended-spectrum beta-lactamase verified by molecular biological methods, were studied in Bethune International Peace Hospital, from January to August 2005. Clinical data were collected and analyzed. Pulsed-field gel electrophoresis (PFGE) were used to analyze the homology of these strains. The genes of beta-lactamase (BLA), aminoglycoside-modifying enzymes (AME), resistant to disinfectant-sulfanilamide (qacEDelta1-sul1), and class 1 integrase (intl1) were analyzed using PCR and verified by DNA sequencing. RESULTS: Among these 6 strains of Acinetobacter baumannii, five were susceptible only to imipenem, and 4 were susceptible to meropenem. The PFGE types identified from these isolates were A1 (n=2) and A2-A5 (n=1, respectively). They all were positive for PER-1, TEM-1, and genes of qacEDelta1-sull and intl1. Three of them harbored genes of aac (3)-I and aac (6')-I. Two had aac (3)-I and ant (3'')-I. One had aac (3)-I. All the patients had severe underlying diseases, and had received mechanical ventilation. They all had received broad spectrum antibiotics within 15 days before Acinetobacter baumannii were identified. Although carbapenem and/or cefoperazone/sulbactam had been used, only 3 patients survived. CONCLUSION: The 6 PER-1 type extended-spectrum beta-lactamase-producing Acinetobacter baumannii isolates were closely related and had complex mechanisms of drug resistance. The prognosis of patients infected by them was poor.