Converting paddy fields to Lei bamboo (Phyllostachys praecox) stands affected soil nutrient concentrations, labile organic carbon pools, and organic carbon chemical compositions

Background and aims

Land-use change often markedly alters soil carbon (C) and nitrogen (N) pool sizes with implications for climate change and soil sustainability. The objective of this research was to study the effect of converting paddy fields to Lei bamboo (Phyllostachys praecox) stands on soil C and N and other nutrient pools as well as the chemical structure of soil organic C (SOC) in the soil profile.

Methods

Soils (Anthrosols) from four adjacent paddy field–bamboo forest pairs with a known land-use history were sampled from Lin’an County, Zhejiang Province. Soil water soluble organic C (WSOC), hot water soluble organic C (HWSOC), microbial biomass C (MBC), readily oxidizable C (ROC), water soluble organic N (WSON), and other soil chemical and physical properties were determined. Soil organic C functional group compositions were determined by ¹³C-nuclear magnetic resonance (NMR).

Results

Concentrations of soil available P, available K, and different N forms increased (P?<?0.05) by the land-use conversion. Higher concentrations of SOC and total N (TN) were observed in the subsoil (20–40 and 40–60 cm soil layers) but not in the topsoil (0–20 cm layer) in the bamboo stands than in the paddy fields. The storage of SOC and TN in the entire soil profile (0–60 cm) increased by 56.7 and 70.7 %, respectively, after the land-use change. The increases in the SOC stock of the three soil layers were 11.0, 14.3, and 9.5 Mg C ha^?1, respectively. The conversion decreased WSOC concentrations in the subsoil but increased the ROC concentration in the topsoil. Solid-state NMR spectroscopy of soil samples showed that the conversion increased (P?<?0.05) the O-alkyl C content while decreased the aromatic C content, alkyl C to O-alkyl C ratio (A/O-A), and aromaticity of SOC.

Conclusions

Conversion of paddy fields to bamboo stands increased soil nutrient availability, and SOC and TN stocks. Effects of land-use change on C pools and C chemistry of SOC varied among different soil layers in the profile. The impact of the land-use conversion on soil organic C pools was not restricted to the topsoil, but changes in the subsoil were equally large and should be accounted for.     

Human Parainfluenza Virus Type 2 V Protein Inhibits TRAF6-Mediated Ubiquitination of IRF7 To Prevent TLR7- and TLR9-Dependent Interferon Induction

Paramyxovirus V proteins block Toll-like receptor 7 (TLR7)- and TLR9-dependent signaling leading to alpha interferon production. Our recent study has provided evidence that interaction of the V proteins with IRF7 is important for the blockade. However, the detailed mechanisms still remain unclear. Here we reexamined the interaction of the human parainfluenza virus type 2 (HPIV2) V protein with signaling molecules involved in TLR7/9-dependent signaling. Immunoprecipitation experiments in HEK293T cells transfected with V protein and one of the signaling molecules revealed that the V protein interacted with not only IRF7 but also TRAF6, IKKα, and MyD88. Whereas overexpression of TRAF6 markedly enhanced the level of V protein associating with IRF7, IKKα, and MyD88 in HEK293T cells, the level of V protein associating with TRAF6 was little affected by overexpression of IRF7, IKKα, and MyD88. Moreover, knockdown or knockout of endogenous TRAF6 in HEK293T or mouse embryonic fibroblast cells resulted in dissociation of the V protein from IRF7, IKKα, and MyD88. These results demonstrate that binding of the V protein to IRF7, IKKα, and MyD88 is largely indirect and mediated by endogenous TRAF6. It was found that the V protein inhibited TRAF6-mediated lysine 63 (K63)-linked polyubiquitination of IRF7, which is prerequisite for IRF7 activation. Disruption of the tryptophan-rich motif of the V protein significantly affected its TRAF6-binding efficiency, which correlated well with the magnitude of inhibition of K63-linked polyubiquitination and the resultant activation of IRF7. Taken together, these results suggest that the HPIV2 V protein prevents TLR7/9-dependent interferon induction by inhibiting TRAF6-mediated K63-linked polyubiquitination of IRF7.     

Heterotrophic nitrification and aerobic denitrification by a novel Halomonas campisalis

A novel halophilic strain that could carry out heterotrophic nitrification and aerobic denitrification was isolated and named as Halomonas campisalis ha3. It removed inorganic nitrogen compounds (e.g. NO₃ ^?, NO₂ ^? and NH₄ ⁺) simultaneously, and grew well in the medium containing up to 20 % (w/v) NaCl. PCR revealed four genes in the genome of ha3 related to aerobic denitrification: napA, nirS, norB and nosZ. The optimal conditions for aerobic denitrification were pH 9.0, at 37 °C, with 4 % (w/v) NaCl and sodium succinate as carbon source. The nitrogen removal rate was 87.5 mg NO₃ ^?–N l^?1 h^?1. Therefore, this strain is a potential aerobic denitrifier for the treatment of saline wastewater.     

Rubia austrozhejiangensis sp. nov. (Rubiaceae) from Zhejiang,China

Rubia austrozhejiangensis Z. P. Lei, Y. Y. Zhou & R. W. Wang, a new species of Rubiaceae from China, is described and illustrated. The new species is similar to R. ovatifolia Z. Ying Zhang and R. argyi (H. Lév. & Vaniot) H. Hara ex Lauener, but differs from the former in having stems and branches cylindrical, not quadrate‐angled, long‐ovate to ovate‐lanceolate leaf blades, many‐flowered inflorescence, and smaller mericarps, 3–4 mm in diameter. In R. ovatifolia, stems and branches are quadrate‐angled, leaf blades ovate, ovate‐cordate to rounded cordate, and the inflorescences are sparsely flowered. Compared to R. argyi, the new species has cylindrical, not quadrate‐angled stems and branches, leaf blades that are long‐ovate to ovate‐lanceolate, 3–5‐veined, and slightly reflexed corolla lobes. In R. argyi, stems and branches are quadrate‐angled or winged, the corolla lobes are spreading, and the mericarps are 5–7 mm in diameter.     

Biomass accumulation and partitioning, photosynthesis, and photosynthetic induction in field-grown maize (Zea mays L.) under low- and high-nitrogen conditions

The objectives of this comparative study were to investigate the responses of biomass accumulation and partitioning to nitrogen supply and to examine the effect of low-nitrogen supply on the photosynthetic responses of maize leaves to steady-state and dynamic light. While the difference in leaf number and stem diameter was not statistically significant, there was a significant difference in plant height between the low-nitrogen and high-nitrogen maize plants. During grain-filling period, the ear leaf of the low-nitrogen maize plants possessed lower values of maximum photosynthetic rate, maximum stomatal conductance, maximum transpiration rate, apparent quantum yield, light compensate point, and carboxylation efficiency than did that of the high-nitrogen maize plants. Contrarily, lower values of intercellular CO₂ concentration and dark respiration rate were observed in the high-nitrogen maize plants. In addition, a slower response to simulated sunflecks was found in the ear leaf of the low-nitrogen maize plants; however, stomatal limitations did not operate in the ear leaf of the high-nitrogen or low-nitrogen maize plants during the photosynthetic induction. As compared to the high-nitrogen maize plants, the low-nitrogen maize plants accumulated much less plant biomass but allocated a greater proportion of biomass to belowground parts. In conclusion, our results suggested that steady-state photosynthetic capacity is restricted by both biochemical and stomatal limitation and the photosynthetic induction is constrained by biochemical limitation alone in low-nitrogen maize plants, and that maize crops respond to low-nitrogen supply in a manner by which more biomass was allocated preferentially to root tissues.     

Electrochemical Investigation of a Microbial Solar Cell Reveals a Nonphotosynthetic Biocathode Catalyst

Microbial solar cells (MSCs) are microbial fuel cells (MFCs) that generate their own oxidant and/or fuel through photosynthetic reactions. Here, we present electrochemical analyses and biofilm 16S rRNA gene profiling of biocathodes of sediment/seawater-based MSCs inoculated from the biocathode of a previously described sediment/seawater-based MSC. Electrochemical analyses indicate that for these second-generation MSC biocathodes, catalytic activity diminishes over time if illumination is provided during growth, whereas it remains relatively stable if growth occurs in the dark. For both illuminated and dark MSC biocathodes, cyclic voltammetry reveals a catalytic-current–potential dependency consistent with heterogeneous electron transfer mediated by an insoluble microbial redox cofactor, which was conserved following enrichment of the dark MSC biocathode using a three-electrode configuration. 16S rRNA gene profiling showed Gammaproteobacteria, most closely related to Marinobacter spp., predominated in the enriched biocathode. The enriched biocathode biofilm is easily cultured on graphite cathodes, forms a multimicrobe-thick biofilm (up to 8.2 μm), and does not lose catalytic activity after exchanges of the reactor medium. Moreover, the consortium can be grown on cathodes with only inorganic carbon provided as the carbon source, which may be exploited for proposed bioelectrochemical systems for electrosynthesis of organic carbon from carbon dioxide. These results support a scheme where two distinct communities of organisms develop within MSC biocathodes: one that is photosynthetically active and one that catalyzes reduction of O₂ by the cathode, where the former partially inhibits the latter. The relationship between the two communities must be further explored to fully realize the potential for MSC applications.     

Application of exogenous substances reduces tobacco-specific nitrosamines content by regulating biosynthesis of nicotine and nitrite in burley tobacco

Tobacco-specific nitrosamines (TSNAs) are carcinogenic chemicals found in tobacco plants. The increasing health consciousness of individuals had led to an increased interest in research on reducing TSNAs content. The aim of this study was to use a pot experiment in which exogenous substances were applied to burley tobacco to dissect the mechanism of TSNAs production. The results indicated that spraying the exogenous substances IAA, NAA, SA and combination thereof on burley tobacco after topping decreased TSNAs content by 2.69–29.4 % in upper leaves and 0.23–39.3 % in middle leaves without affecting total sugar, total nitrogen, potassium and chlorine contents. The application of exogenous substances could down-regulate expression of the NR gene and the activity of the NR enzyme, resulting in less accumulation of the TSNAs precursor nitrite. The exogenous substances significantly reduced nicotine accumulation, which was consistent with low enzyme activities and the down-regulated expressions of genes involved in nicotine biosynthesis, especially significant in the case of quinolinate phosphoribosyltransferase. These results suggested that the application of exogenous substances on burley tobacco after topping could reduce TSNAs content which may be attributed to the regulation of exogenous substances on nitrite and nicotine. This also implies one potential improvement to agronomic practices aimed at controlling the accumulation of TSNAs in burley tobacco.