Effects of elevated CO(2) and Pb on the microbial community in the rhizosphere of Pinus densiflora

Climatic CO2 level-driven changes in the bioavailability, accumulation, and health risks of Cd and Pb in paddy soil-rice systems

Rising atmospheric carbon dioxide (CO₂) and soil heavy metal pollution, which affects safe rice production and soil ecosystem stability, have caused widespread concern. In this study, we evaluated the effects of elevated CO₂ on Cd and Pb accumulation in rice plants (Oryza sativa L.), Cd and Pb bioavailability, and soil bacterial communities in Cd-Pb co-contaminated paddy soils via rice pot experiments. We showed that elevated CO₂ accelerates the accumulation of Cd and Pb in rice grains by 48.4-75.4% and 20.5-39.1%, respectively. Elevated CO₂ levels decreased soil pH value by 0.2 units, which increased Cd and Pb bioavailability in soil but inhibited iron plaque formation on rice roots, ultimately promoting Cd and Pb uptake. 16S rRNA sequencing analysis revealed that elevated CO₂ increased the relative abundance of certain soil bacteria (e.g., Acidobacteria, Alphaproteobacteria, Holophagae, and Burkholderiaceae). A health risk assessment showed that elevated CO₂ markedly increased the total carcinogenic risk values for children, adult males, and adult females by 75.3% (P < 0.05), 65.6% (P < 0.05), and 71.1% (P < 0.05), respectively. These results demonstrate the serious performance of elevated CO₂ levels in accelerating the bioavailability and accumulation of Cd and Pb in paddy soil-rice ecosystems, with particular risks for future safe rice production.

Graphitic carbon nitride (g-C3N4) alleviates cadmium-induced phytotoxicity to rice (Oryza sativa L.)

In the present study, graphitic carbon nitride (g-C3N4) was synthesized in a tube furnace and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR). Different concentrations (0-200 mg/L) of g-C3N4 were prepared in nutrient solution amended with or without 20 mg/L CdCl2 for the greenhouse study. Rice seedlings were exposed to g-C3N4 and Cd for 20 days. Our results suggest that 200 mg/L g-C3N4 significantly increased the fresh weight and root and shoot length as compared with the control, and notably alleviated Cd-induced toxicity. The addition of 200 mg/L g-C3N4 significantly reduced the root and shoot Cd content by approximately 14% and 23%, respectively. In addition, 200 mg/L g-C3N4 significantly elevated the nitrogen content and decreased C/N ration in rice shoots; most importantly, it alleviated Cd-induced nitrogen reduction. Our findings demonstrated the potential of g-C3N4 in regulating plant growth and minimizing the Cd-induced phytotoxicity, and shed light on providing a new strategy to maintain heavy metal contamination in agriculture using a low-cost and environmental friendly NMs.

The isolation and functional identification on producing cellulase of Pseudomonas mendocina

The straw can be degraded efficiently into humus by powerful enzymes from microorganisms, resulting in the accelerated circulation of N,P,K and other effective elements in ecological system. We isolated a strain through screening the straw degradation strains from natural humic straw in the low temperature area in northeast of china, which can produce cellulase efficiently. The strain was identified as Pseudomonas mendocina by using morphological, physiological, biochemical test, and molecular biological test, with the functional clarification on producing cellulase for Pseudomonas mendocina for the first time. The enzyme force constant Km and the maximum reaction rate (Vmax) of the strain were 0.3261 g/L and 0.1525 mg/(min.L) through the enzyme activity detection, and the molecular weight of the enzyme produced by the strain were 42.4 k_D and 20.4 k_D based on SDS-PAGE. The effects of various ecological factors such as temperature, pH and nematodes on the enzyme produced by the strain in the micro ecosystem in plant roots were evaluated. The result showed that the optimum temperature was 28°C, and the best pH was 7.4∼7.8, the impact heavy metal was Pb²⁺ and the enzyme activity and biomass of Pseudomonas mendocina increased the movement and predation of nematodes.