Parent material influences soil properties to shape bacterial community assembly processes, diversity, and enzyme-related functions.

Soil parent material is the second most influential factor in pedogenesis, influencing soil properties and microbial communities. Different assembly processes shape diverse functional microbial communities. The question remains unresolved regarding how these ecological assembly processes affect microbial communities and soil functionality within soils on different parent materials. We collected soil samples developed from typical parent materials, including basalt, granite, metamorphic rock, and marine sediments across soil profiles at depths of 0-20, 20-40, 40-80, and 80-100 cm, within rubber plantations on Hainan Island, China. We determined bacterial community characteristics, community assembly processes, and soil enzyme-related functions using 16S rRNA high-throughput sequencing and enzyme activity analyses. We found homogeneous selection, dispersal limitation, and drift processes were the dominant drivers of bacterial community assembly across soils on different parent materials. In soils on basalt, lower pH and higher moisture triggered a homogeneous selection-dominated assembly process, leading to a less diverse community but otherwise higher carbon and nitrogen cycling enzyme activities. As deterministic process decreased, bacterial community diversity increased with stochastic process. In soils on marine sediments, lower water, carbon, and nutrient content limited the dispersal of bacterial communities, resulting in higher community diversity and an increased capacity to utilize relative recalcitrant substrates by releasing more oxidases. The r-strategy Bacteroidetes and genera Sphingomonas, Bacillus, Vibrionimonas, Ochrobactrum positively correlated with enzyme-related function, whereas k-strategy Acidobacteria, Verrucomicrobia and genera Acidothermus, Burkholderia-Caballeronia-Paraburkholderia, HSB OF53-F07 showed negative correlations. Our study suggests that parent material could influence bacterial community assembly processes, diversity, and soil enzyme-related functions via soil properties.

[Enrichment Factors, Health Risk, and Source Identification of Heavy Metals in Agricultural Soils in Semi-arid Region of Hainan Island].

To understand the enrichment factors and pollution levels of heavy metals in agricultural soils in the semi-arid region of Hainan island, 1818 surface soil samples were collected in Gancheng Town and analyzed for their heavy metal contents and physicochemical composition. Correlation analysis was used to determine the heavy metal enrichment factors. The geo-accumulation index (Igeo), comprehensive ecological risk index (RI), and hazard index (HI), as well as carcinogenic risk (CR), were used to assess the degree of pollution and health risk. Positive matrix factorization (PMF) was used to determine the primary sources of pollution and priority sources. The average values of heavy metal contents in the topsoil were 22.7, 0.128, 33.4, 14.5, 0.032, 9.32, 32.5, and 43.3 mg·kg-1 for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively. With the exception of Zn, the concentrations of other heavy metals in the topsoil were higher than the soil background values of Hainan, showing different degrees of heavy metal accumulation effect. The Igeo revealed that the major pollutant element in soils was As, followed by Cd and Cu. The RI showed that the proportion of soil samples that were high-risk level or worse was 29.4% of the total number of samples, among which As was the major source of risk. The health risk assessment results indicated that As, Cr, and Ni exposure presented carcinogenic risk for children with high CR values. Based on PMF, four major sources of heavy metals were identified in the study area. Hg was derived mainly from industrial sources, and As was closely associated with agricultural activities. Ni, Cu, Cr, and Zn were related to soil parent materials. Pb and Cd were associated with agricultural activities and traffic emissions. The PMF models combined with correlation analysis were useful for estimating the source apportionment of heavy metals in soils.

[Accumulation and Health Risk of Heavy Metals in Cereals, Vegetables, and Fruits of Intensive Plantations in Hainan Province].

The accumulation of some harmful elements in plants from intensive production systems pose a serious threat to human health. In this study, seven heavy metals(Cu, Pb, Zn, Cr, Cd, As, and Hg) and their distribution characteristics in the crops, vegetables, and fruits were analyzed alongside single factor evaluation and Nemero index analysis. Combined with dietary recommended consumption data from the Chinese Nutrition Society, the dietary exposure of heavy metals were further analyzed, and a consequent safety risk assessment was conducted. A total of 673 crop, vegetable, and fruit samples were collected from typical intensive production systems in Hainan Province. The results showed that the content of Cu, As, and Hg in the 673 plant samples was below the value of the national food standard. The exceed rates of Pb, Zn, Cr, and Cd were 2.67%, 3.71%, 2.53%, and 3.71%, respectively. The heavy metal comprehensive pollution degree of six species of plants showed the trend of leafy vegetables > tuber crops > non-leafy vegetables > legume crops > fruits > cereals. In particular, Cr in leafy vegetables showed significantly higher hazard quotients(HQ) than that in other types, and exceeded 1, suggesting a high potential health risk via the ingestion of heavy metals through leafy vegetables. The relatively lower hazard index(HI) values of tuber crops, non-leafy vegetables, legume crops, fruits, and cereals suggest that these types of plants are more suitable for intensive production systems.