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The objective of this study was to investigate how the relationships between bacterial communities and organic C (SOC) in topsoil (0–5 cm) are affected by tillage practices [conventional intensive tillage (CT) or no-tillage (NT)] and straw-returning methods [crop straw returning (S) or removal (NS)] under a rice-wheat rotation in central China. Soil bacterial communities were determined by high-throughput sequencing technology. After two cycles of annual rice-wheat rotation, compared with CT treatments, NT treatments generally had significantly more bacterial genera and monounsaturated fatty acids/saturated fatty acids (MUFA/STFA), but a decreased gram-positive bacteria/gram-negative bacteria ratio (G+/G−). S treatments had significantly more bacterial genera and MUFA/STFA, but had decreased G+/G− compared with NS treatments. Multivariate analysis revealed that Gemmatimonas, Rudaea, Spingomonas, Pseudomonas, Dyella, Burkholderia, Clostridium, Pseudolabrys, Arcicella and Bacillus were correlated with SOC, and cellulolytic bacteria (Burkholderia, Pseudomonas, Clostridium, Rudaea and Bacillus) and Gemmationas explained 55.3% and 12.4% of the variance in SOC, respectively. Structural equation modeling further indicated that tillage and residue managements affected SOC directly and indirectly through these cellulolytic bacteria and Gemmationas. Our results suggest that Burkholderia, Pseudomonas, Clostridium, Rudaea, Bacillus and Gemmationas help to regulate SOC sequestration in topsoil under tillage and residue systems.

Selenium nanoparticles (SeNPs) have attracted considerable attention globally due to their significant potential for alleviating abiotic stresses in plants. Accordingly, further research has been conducted to develop nanoparticles using chemical ways. However, our knowledge about the potential benefit or phytotoxicity of bioSeNPs in rapeseed is still unclear. Herein, we investigated the effect of bioSeNPs on growth and physiochemical attributes, and selenium detoxification pathways compared to sodium selenite (Se (IV)) during the early seedling stage under normal and salt stress conditions. Our findings showed that the range between optimal and toxic levels of bioSeNPs was wider than Se (IV), which increased the plant’s ability to reduce salinity-induced oxidative stress. BioSeNPs improved the phenotypic characteristics of rapeseed seedlings without the sign of toxicity, markedly elevated germination, growth, photosynthetic efficiency and osmolyte accumulation versus Se (IV) under normal and salt stress conditions. In addition to modulation of Na+ and K+ uptake, bioSeNPs minimized the ROS level and MDA content by activating the antioxidant enzymes engaged in ROS detoxification by regulating these enzyme-related genes expression patterns. Importantly, the main effect of bioSeNPs and Se (IV) on plant growth appeared to be correlated with the change in the expression levels of Se-related genes. Our qRT-PCR results revealed that the genes involved in Se detoxification in root tissue were upregulated upon Se (IV) treated seedlings compared to NPs, indicating that bioSeNPs have a slightly toxic effect under higher concentrations. Furthermore, bioSeNPs might improve lateral root production by increasing the expression level of LBD16. Taken together, transamination and selenation were more functional methods of Se detoxification and proposed different degradation pathways that synthesized malformed or deformed selenoproteins, which provided essential mechanisms to increase Se tolerance at higher concentrations in rapeseed seedlings. Current findings could add more knowledge regarding the mechanisms underlying bioSeNPs induced plant growth. Graphical Abstract

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A Gram-stain-positive, rod-shaped, facultatively anaerobic bacterium, designated strain ES3-24 T , was isolated from a selenium mineral soil. The isolate was endospore-forming, nitrate-reducing and motile by means of peritrichous flagella. The major menaquinone was menaquinone 7 (MK-7) and the predominant fatty acids (.5 %) were anteiso-C 15 : 0 , iso-C 16 : 0 , C 16 : 0 and anteiso-C 17 : 0 .The major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine and two unknown aminophospholipids. Strain ES3-24 T contained meso-diaminopimelic acid in the cell-wall peptidoglycan and the DNA G+C content was 49.6 mol%. According to phylogenetic analysis based on the 16S rRNA gene sequence, strain ES3-24 T was most closely related toPaenibacillus terrigena A35 T , with 16S rRNA gene sequence identity of 98.3 %, while the other members of the genus Paenibacillus had 16S rRNA gene sequence identities of less than 95.0 %. DNA-DNA relatedness between strain ES3-24 T and P. terrigena CCTCC AB206026 T was 39.3 %. In addition, strain ES3-24 T showed obvious differences from closely related species in major polar lipids, nitrate reduction and other physiological and biochemical characteristics. The data from our polyphasic taxonomic study reveal that strain ES3-24 T represents a novel species of the genus Paenibacillus, for which the name Paenibacillus selenitireducens sp. nov. is proposed.

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A novel Gram-stain-negative, strictly aerobic, non-motile, rod-shaped, capsule-forming bacterium, designated strain YLT33T, that formed orange-red colonies was isolated from mountain cliff soil from Enshi Grand Canyon, southwest China. Growth occurred at 4-35 °C (optimum 28 °C) and at pH 6.0-10.0 (optimum 7.0). It showed maximum (99.3 %) 16S rRNA gene sequence similarity and formed a monophyletic clade with Sphingoaurantiacus polygranulatusMC 3718T (=CCTCC 2014274T). The DNA G+C content was 68.5 mol% and strain YLT33T showed a 50.5 % DNA-DNA relatedness value to S. polygranulatusMC 3718T. The major fatty acids (>5 %) were C17 : 1ω6c (40.7 %), C15 : 0 (10.4 %), C15 : 1ω6c (9.4 %), summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH; 8.6 %), C17 : 1ω8c (7.1 %), C18 : 1ω7c (6.1 %), and C15 : 0 2-OH (5.7 %). Ubiquinone-10 was the sole respiratory quinone. The polar lipids of strain YLT33T contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, sphingoglycolipid, two unknown glycolipids and one unknown phospholipid. Carotenoids were present in cells. Homospermidine was the major polyamine. In addition, strain YLT33T showed obvious differences from the closely related strain S. polygranulatusMC 3718T with respect to major polar lipids, fatty acids and other morphological, physiological and biochemical characteristics. These results from polyphasic taxonomic studies reveal that strain YLT33T represents a novel species of the genus Sphingoaurantiacus, for which the name Sphingoaurantiacuscapsulatus sp. nov. is proposed. The type strain is YLT33T (=CCTCC AB 2015150T=KCTC 42644T).