Opposite effects of soil pH on bacteria and fungi β diversity in forests at a continental scale

Microbial Carbon Limitation Mediates Soil Organic Carbon Sequestration in Sugarcane-Watermelon Intercropping System

Intercropping is an effective approach for enhancing soil organic carbon (SOC) sequestration. However, the effects of intercropping on SOC dynamics and the underlying factors in rhizosphere and bulk soils are still unclear. In this study, we examined the impacts of sugarcane monoculture and sugarcane-watermelon intercropping on soil properties, soil respiration, SOC fractions, and microbial C limitation with continuous two years in 2023-2024 years in the Nala area of Guangxi Province. Our results revealed that intercropping significantly decreased CO2/SOC by 25% and microbial C limitation by 21% in the rhizosphere, with more pronounced reductions observed in bulk soil by 33% and 25%, respectively. This means that the intercropping reduced soil respiration and this effect can be offset by the rhizosphere effects. Additionally, the sugarcane-watermelon intercropping increased the contents of mineral-associated organic carbon (MAOC) by 15~18% and particulate organic carbon (POC) by 34~46%. The random forest analysis indicated that enzyme activities (explaining 20~38% of variation) and soil properties (explaining 22% of variation) were the primary drivers of reduced CO2 emissions. The PLS-PM showed that intercropping decreased microbial C limitation by influencing soil pH and soil water content (SWC), and then increased MAOC, which finally led to a decline in CO2 emissions. Overall, these findings highlight the decreasing CO2 emissions during the use of the intercropping system and the importance of microbial C limitation in the soil C cycle via soil respiration and SOC fractions.

Preliminary study on mercury pollution affecting soil bacteria near a mercury mining area

In order to further explore the effect of mercury contamination soil (nearly 20 years) near a mercury mining area (Tongren, Guizhou, China) on the diversity and structure of the soil bacterial communities, five groups of soil samples (SMO2, SMO20, SMO30, SMO500, and SMO650) were collected at distances of 2, 20, 30, 500, and 650 m, respectively, from the only sewage outlet of a mercury mining area (Guizhou, China). All soil samples were collected from the 0-20 cm topsoil layer. After processing them, the soil microbial DNA was extracted from each soil sample, and sequenced via high-throughput sequencing technology. The sequencing results indicated a significantly greater diversity of the soil bacterial community in SMO2, SMO20, and SMO650 (relative high mercury contents) than in SMO300 and SMO500 (relative low mercury contents). Alpha diversity analysis revealed that the soil bacterial community diversity in SMO2 and SMO20 significantly exceeded that in SMO30, SMO500, and SMO650. The soil bacterial community structure analysis revealed identical and distinct dominant bacterial communities within the soil sample groups at both phylum and class levels. According to the further analyzed relationships between the soil environmental factors and bacterial community abundance for each sample group, the pH, distance (mercury content), and electrical conductivity (EC) had greater impacts on the structure of the soil bacterial community than available N, P, K. The survival of high relative abundance bacterial community taxa in the microbial communities provides compelling evidence of the high adaptability of bacteria to long-term mercury contamination of the soil environment. The results of this study provide a scientific reference and impetus for further research on the mechanism(s) responsible for tolerance to high mercury stress in mercury-contaminated soil.