Evaluating responses of nitrification and denitrification to the co-selective pressure of divalent zinc and tetracycline based on resistance genes changes.

The responses of nitrification and denitrification to the divalent zinc (Zn(II)) and tetracycline (TC) co-selective pressure were evaluated in a sequencing batch reactor (SBR). The removal rates of organics and nitrogen, nitrifying and denitrifying enzymatic activity, and microbial diversity and richness at the Zn(II) and TC co-selective pressure were higher than those at the alone Zn(II) selective pressure, while were lower than those at the individual TC selective pressure. The Zn(II) and TC co-selective pressure induced the TC resistance genes abundance increase and the Zn(II) resistance genes levels decrease, and enhanced bacterial enzymatic modification resistance to TC and bacterial outer membrane resistance to Zn(II). The network analysis showed that the genera Nitrospira and Nitrosomonas of nitrifiers and the genera Ferruginibacter, Dechloromonas, Acidovorax, Rhodobacter, Thauera, Cloacibacterium, Zoogloea and Flavobacterium of denitrifiers were the potential hosts of antibiotics resistance genes (ARGs) and/or heavy metals resistance genes (HMRGs).

[Effects of light intensity on the phenotypic plasticity of invasive species Ambrosia trifida].

Through artificial shading, this paper studied the phenotypic plasticity of invasive species Ambrosia trifida in its morphology, biomass allocation, and photosynthesis characteristics in response to different light intensities. As compared with the control, shading increased the stem height, crown width, leaf area, specific leaf area, and the proportion of leaf biomass in total biomass of A. trifida significantly, but decreased the total biomass, biomass per unit leaf area, and root to shoot ratio. Under natural light condition, the crown width and leaf area were smaller and the root to shoot ratio was larger, which benefited the decrease of water loss under high temperature and high light intensity and manifested the stronger phenotypic plasticity of A. trifida in its morphology and biomass allocation in response to different light intensities. Under shading, the mean daily net photosynthetic rate, transpiration rate, and stomatal conductance decreased, while the stomatal CO2 concentration increased. At noon when the light intensity was the highest, the photosynthetic rate, transpiration rate, and stomatal conductance under low shading reached the maximum. Under moderate shading and high shading, the chlorophyll content increased significantly, and the chlorophyll a/b had a significant decrease, which could improve the utilization of light energy by A. trifida under shading environment.